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The Shop => Metal Stuff => Topic started by: vtsteam on July 15, 2013, 08:01:58 PM

Title: Oil fired crucible furnace
Post by: vtsteam on July 15, 2013, 08:01:58 PM
This is an extension of the Sawed Off Cupola thread I started earlier, since that furnace is no longer being tried as a single charge charcoal cupola.

Its now an oil fired crucible furnace, so I thought it deserved a new thread.

Recent events:

Yesterday I had a missrun in pouring the mold  -- the pour was cold. The burner I made wasn't able to feed fuel at a high enough rate to get the iron fluid, though it did melt. Three hours of heating finally resulted in the fuel running out and  forced pour. The result -- no casting, only a sprue.

Today I took the burner off of the furnace and checked it out. The same burner more or less had successfully melted my first iron a couple weeks ago, but that one leaked oil. The burner was a Kwikie burner design. This atomizing burner was set too far back in the pipe housing in a 4" thick refractory lining (by design), so the spray impinged on the pipe walls and dripped out.

I re-built it with a longer and larger diameter spray tube extension that brought the nozzle 2" closer to the furnace barrel. Otherwise the design was unchanged. But new delivery problems arose -- traced at first to a bad silver braze joint. With that repaired I tried yesterday's melt. That was the missrun.

Today, after taking it out I couldn't see anything wrong with the burner. So I figured that the nozzle was just screwed in too close to the jet orifice to allow enough fuel to pass. I opened it a quarter turn and re-installed in the furnace. The difference was dramatic! It was back to being a jet engine!

So with that worked out at 3:30, I thought I'd give it another try before dinner. I broke up some cast iron, loaded the crucible and fueled the burner with an container of old diesel fuel -- about 3 gallons worth that I found in the shed.

The burn went great! I molded up a flask while the furnace was heating, with a very healthy roar. I had to stop the burn a couple times to add iron, as I couldn't fit it all in at once. I needed about 7 pounds for this casting.

Finally the metal seemed readyafter dipping a rod in and having it come out pretty clean -- a little thin shiny slag and that was it.

When I went to lift the crucible, it stuck to the wall and plinth, and I couldn't get the tongs around it. The crucible seemed fairly plastic -- temps must have been high! Finally I maneuvered it off of the wall, but carried the plinth out with it. When I set it down in  the sand to skim off the slag the plinth released, and I pushed it out of the way. it was then easy to lift it in  the shank and pour. Very fluid this time, I filled the mold, and still fluid the excess splashed a little out of the ingot mould while pouring.

Great pour! Man iron is exciting! A real high to get it to melt and fill a mold.

All in all, it took an hour and a half exactly from lighting the furnace until the pour was done. I'm sorry I didn't measure the fuel beforehand, but I think it took around a gallon or gallon and a half. Just a great day!  :ddb:

Pictures when I can get them up.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 15, 2013, 09:12:56 PM
Plinth comes free of crucible ...


(http://www.vtsteam.com/OilFurnace/OilFurnace4.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 15, 2013, 09:14:55 PM
The pour....

(http://www.vtsteam.com/OilFurnace/OilFurnace6a.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 15, 2013, 09:16:48 PM
All in, time to shut it down....



(http://www.vtsteam.com/OilFurnace/OilFurnace3.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 15, 2013, 09:18:07 PM
The shake out.....


(http://www.vtsteam.com/OilFurnace/OilFurnace2.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 15, 2013, 09:20:45 PM
First two pieces of iron....


(http://www.vtsteam.com/OilFurnace/OilFurnace1.jpg)
Title: Re: Oil fired crucible furnace
Post by: tekfab on July 15, 2013, 09:27:08 PM
I think i'm going to have a go at making a Kwikie burner, after all i've got 600 (yes 600) gallons of used oil to dispose off so expect many questions !

Mike Young
Title: Re: Oil fired crucible furnace
Post by: awemawson on July 16, 2013, 02:27:15 AM
Steve

I used to sprinkle something on the plinth brick to stop it sticking to the crucible but for the life of me I cannot remember what. Can't have been sand as that would fuse at those temperatures   
Title: Re: Oil fired crucible furnace
Post by: NeoTech on July 16, 2013, 04:12:23 AM
Would be awsome to see a cross cut or a surface cut out of that square block.
Title: Re: Oil fired crucible furnace
Post by: mattinker on July 16, 2013, 05:45:22 AM
A piece of card board or thick paper will leave carbon to separate the crucible from the plinth.

regards, Matthew
Title: Re: Oil fired crucible furnace
Post by: awemawson on July 16, 2013, 06:41:53 AM
Steve

I used to sprinkle something on the plinth brick to stop it sticking to the crucible but for the life of me I cannot remember what. Can't have been sand as that would fuse at those temperatures

Ha ha - I've remembered ! Not sprinkled but put - Morgan Crucible recommend placing a piece of cardboard between the plinth brick and the crucible to stop sticking and that's what I did. Gosh the old grey cells must be dying faster than I thought  :scratch:
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 16, 2013, 08:07:51 AM
Thank you lads!   :beer: Yes, two layers of corrugated cardboard had been placed under the crucible, as well as a dusting of plumbago on the plinth. The problem seems to come when spilling a bit of slag when adding metal during the melt. Very fluid in the highest heat of the furnace It works down the outside of the crucible and slides into the space between the two. The cardboard carbon blows away near the glue line allowing it to take effect. Luckily it is spotty so tilting the crucible when skimming pulls it free.

The whole thing feels stiff taffy like when ready to pour -- including the crucible this time. Plinth sagged slightly and the crucible glued itself to the furnace wall and had to be pulled free as gently as I could manage, so I could get the tongs around it. Crucible is slightly distorted in shape today therefore. All very exciting when ready to pour!
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 16, 2013, 06:04:50 PM
Would be awsome to see a cross cut or a surface cut out of that square block.

Here you are. The casting had a shrink cavity on the top face, and a couple of serious bubbles. These last two were hidden until the face was milled. The shrink cavity would probably not be a problem, since this piece was intended to be bored out fairly heavily, but the bubbles may have spoiled it. We'll see.

This casting was not as soft as the last one -- it made life a little difficult for the HSS mills, but was machinable. Plenty of graphite came out.


Clean face:


(http://www.vtsteam.com/OilFurnace/OilFurnace7.jpg)


Shrink cavity and bubbles ( upper face)


(http://www.vtsteam.com/OilFurnace/OilFurnace8.jpg)


How it is supposed to go -- both get bored out:


(http://www.vtsteam.com/OilFurnace/OilFurnace9.jpg)



Title: Re: Oil fired crucible furnace
Post by: NeoTech on July 17, 2013, 05:12:02 AM
That looks really nice and solid, no pours.. =)

I imagine you didnt do "crack" test wedges like ironman does in his vids?  Still very nice looking.

could that shrinkage been avoided if you had used some form of reservoir between the molding cavity and the sprue?
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 17, 2013, 08:33:45 AM
Thnks NeoTech.

I'm trying to figure out how to avoid the shrink depression and bubbles next time. Iron is a little different than aluminum, but similar.

As a problem for me, shrinkage is less bad -- I can often plan a casting or work around it.

Big bubbles like those (6-8mm deep) are a serious problem. While I had shrink depressions sometimes in aluminum, I didn't have anything like those bubbles. Small ones once in  awhile maybe, and sometimes very fine gas porosity if the melt was stirred too much and it was a humid day and older scrap, but nothing like like these big bubbles.

Possibilities:

1.) Maybe the sand was rammed too hard (I did vent it with a wire, but I could try less ramming pressure)

2.) Maybe the sand was too moist (hard for me to judge -- it's new sand, Bentonite instead of fire clay, and this is iron instead of aluminum, so it's very different than what I'm used to. I could try molding drier.

3.) Maybe air got in while pouring. I used two arc shaped gates (instead of my usual one) and they were pretty deep this time compared to last when I had the misrun. So they channeled the iron very fast. The sprue was 1.25" dia and dowel shaped, not tapered. When I poured I tried to pour fast, but it really drained fast so the sprue did not look choked during the pour. It probably should have.

I could make up a tapered metal sprue cutter -- like the real molders use, and/or reduce the size of the sprue, reduce the number of gates, or reduce the depth of the gates in order to keep the sprue more easily choked with iron during the pour.

4.) Shrinkage depression --- the cope was 3.5" deep, and the pattern was entirely in the drag, so there was 3.5" of head pressure. I could build up above that to increase head pressure.

Or I could add a riser to feed hot metal as the casting shrinks. Although with such a small casting and a 1.25" dia sprue, I thought the sprue would feed it.

One problem with a riser is that it takes even more metal in the melt, and I'm starting to approach the maximum comfortable capacity of my crucible already at 7 pounds. I had to add metal twice during the melt. A sprue or riser would add another pound and a half or so.

Anyway those are the ideas I've had so far.


Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 17, 2013, 07:44:59 PM
Checked out the crucible and furnace more closely this morning. The crucible really took a beating last time when it got stuck to the furnace wall, and is no longer usable. Here's a picture of the used one and a new one.

Besides the chips cracks and shape distortion, the walls had thinned quite a bit. I sure hope I'm not going to get only 3-4 melts out of a crucible or this is going to get expensive fast. I don't think the 3 hour marathon the other day did it any good. Also I really had the blast up at the last 20 minutes of the last pour -- maybe that was too much. Could also be to much air early on, or maybe even the soda ash flux. I could try a slightly more reducing flame.

Anyway, hope to get more pours out of the next one.


(http://www.vtsteam.com/OilFurnace/OilFurnace11.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 17, 2013, 07:48:28 PM
The furnace lining on the other hand is doing great. It is just somewhat more glazed than it was. Starting to look like pottery.


(http://www.vtsteam.com/OilFurnace/OilFurnace10.jpg)
Title: Re: Oil fired crucible furnace
Post by: NeoTech on July 18, 2013, 02:54:41 AM
Hmm, if the extra volume of metall is a problem, i would prob. just cast the piece a bit thicker so not that much extra added material was needed and then just cut it down to size and hopefully get the imperfections out that way. =)

Isnt there someting like a flux for cast iron? Wouldnt that solve the gas inclusions problems?
Title: Re: Oil fired crucible furnace
Post by: awemawson on July 18, 2013, 04:02:22 AM
You always get the crud and voids at the top of a shallowish casting unless you make gating to avoid it. I'd be tempted to make up the mould vertically with an extra sacrificial bit to machine off, and also increase the head of the pouring basin
Title: Re: Oil fired crucible furnace
Post by: MetalCaster on July 18, 2013, 05:14:04 PM
A couple of suggestions from the things I have learned in the past:

1. All crucibles are not created equal, some are rated for ferrous metal, and some are not.  Crucibles have a maximum temperature rating, and for cast iron work, you should be using a crucible that is documented for operation at around 3000F, ferrous-metal-rated (generally the clay type, but not all clay types).

2. According to the crucible literature I have seen, the burner should enter the furnace wall at the centerline where the crucible sits on the plinth, and the burner should not impinge on the crucible, but rather the burner flame should enter to one side of the crucible.  This entry point is also important to get the flame to swirl around the crucible and distribute the heat evenly without overheating any one spot on the crucible.

3. The crucible literature mentions that the crucibles should be carefully lifted from the lower part of the crucible, with full support around the crucible.

4. There is a book called "Basic Principles of Gating and Risering" by the American Foundrymen's Society, Inc. that is very helpful in designing sprue systems that do not aspirate air, and gate and runner systems that fill the mold evenly while skimming off slag, and risers where needed for shrinkage, as well as venting to relieve gassing from the cores and mould itself.  Venting is extemely critical if you are using water-based sand and core mixes.  Oil-based sands do not work very well with cast iron since the metal is so hot it tends to wash and errode the sand.  I have seen some use oil-based sand with cast iron with some success though.

I have heard reports of people using quality cast-iron-rated crucibles for 100 pours or morre.  There is no reason for a good quality crucible to fail prematurely unless you use it in excess of its temperature or metal-type rating.

The soft fire bricks that have a lot of air entrained in them will not hold up to cast iron temperatures.  The hard fire bricks apparently will hold up to cast iron temps as you demonstrate, but the hard bricks may need a little more insulation behind them since they will not insulate as well as air-entrained bricks.

Good luck.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 18, 2013, 07:02:36 PM
NeoTech, there is a machining allowance, but it wasn't enough. I would like to avoid taking off 6mm, however through better molding practices, if I can.

Andrew, I think you're right it would have been better to orient vertically, but I'd have needed a deeper drag. I do think more head on the pouring basin would have helped. I'm thinking maybe ramming softer might also relieve the gas, and reducing sand moisture, maybe. Also, there was no crud -- just a depression and bubbles, so feeding and gas/moisture relief were the problem.

However, look at Ironman's castings -- amazing stuff. Big wide plates, letter plates, muffler parts, etc, with super finish, 2 simple gates (like the ones I used/imitated) very low head -- copes are quite shallow, shallower than mine, simple small sprues, the plates oriented horizontally, and they come out finish quality, with no shrink depressions, no crud, no bubbles, crisp lettering. So it can be done. I'm just not doing it right.

MetalCaster, hello, welcome to the forum. Please introduce yourself, and tell us about your melting rig and projects. Do you cast in iron?

re. your suggestions/questions -- I used a 3000 degree rated clay/graphite crucible.

re. burner: the burner doesn't impinge directly on the crucible. The flame swirls around the furnace barrel all the way to the lid.

re tongs: the lifting tongs fit the crucible properly and it is lifted at the proper point in the bilge.  (Please see my earlier construction thread re. "Sawed off cupola" for all of these details.)

re. firebrick: The hard firebrick I used has very good insulating qualities since it is 4" thick. Thickness counts in insulation -- read about thickness in relation to R values in insiulation if interested. I believe this furnace probably does nearly as well as some of the 2" kaowool foundries, and I'm sure it would compete with castable refractory furnaces of lesser thickness for insulation value -- there's also packed sand/clay with airspace in this build. This furnace does not get hot to the touch on the outside for a very long time after a melt is underway, and retains heat after it is over overnight.

Soft firebrick is holding up perfectly in the lid -- it has a barrier of about an inch of sand/fireclay under.  Materials are not good or bad per se. -- the devil is in the details. Be careful of generalizations, like saying soft firebrick is unsuitable for use in an iron melting furnace, Specific cases,  application and actual experience can contradict a lot of the commonly repeated axioms on the internet.

re. mold venting: my moulds were vented, as I mentioned earlier.

re. core venting:  I wasn't using a core.

re. gating references:  I have a lot of foundry books illustrating a multitude of gating and risering schemes, methods, and theory but if you watch Ironman's youtube videos, you will see perfect flat simple castings in iron with the simplest double or single gates. We aren't casting a V-8 engine block here.

re. crucible misuse via overtemp, or wrong metal rating -- it's possible the final temp was too high, as I mentioned above. I think there are many other possible factors, too, though. Oxidizing or reducing atmosphere, corrosive flux, etc. And as mentioned also earlier, the reason for the crack and mishapen upper portion was that the crucible got glued to the furnace wall and had to be pried off. That might also have been partly because of overheating. My bigger concern is crucible thinning. If the crucible is not up to par, then okay, but if it's a result of a bad furnace atmosphere, or the sodium carbonate I used, or over temp, then those are things I can, and would like to correct.

Again welcome, and please introduce yourself. A fellow metal caster wold be a great addition!  :beer:





Title: Re: Oil fired crucible furnace
Post by: awemawson on July 19, 2013, 02:31:29 AM
Really you need silicon carbide crucibles for repeated use with iron
Title: Re: Oil fired crucible furnace
Post by: MetalCaster on July 19, 2013, 11:42:14 AM
According the rep, the Morgan silicon carbide crucibles are not ferrous-metal rated, and are not rated for iron temperatures either.

The Morgan clay-graphite unit is rated at nearly 3000 F and ferrous-metal rated.

Not sure about other curcible manufacturers.

VT-Thanks for the welcome, I am a lurker type, so will remain a wall flower.  Yes, I do cast iron.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 19, 2013, 01:29:32 PM
Metalcaster. no fair commenting on others work without sharing your own!

Tell us about your rig, what you've cast in iron with it, how long it has been in operation, what kind of crucibles you've tried and what the results were of different crucibles.

Pics would be good, we love pictures!
Title: Re: Oil fired crucible furnace
Post by: awemawson on July 19, 2013, 02:17:28 PM
According the rep, the Morgan silicon carbide crucibles are not ferrous-metal rated, and are not rated for iron temperatures either.

The Morgan clay-graphite unit is rated at nearly 3000 F and ferrous-metal rated.

Not sure about other curcible manufacturers.

VT-Thanks for the welcome, I am a lurker type, so will remain a wall flower.  Yes, I do cast iron.

Yes I'm obviously remembering it the wrong way round. Old age is a terrible thing :(

All my crucibles are Morgan ones, but they've been in storage for 6 years!
Title: Re: Oil fired crucible furnace
Post by: MetalCaster on July 19, 2013, 02:45:09 PM
You have seen my work, nothing new to show there.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 19, 2013, 03:12:21 PM
Doubly unfair!

Apologies.
Title: Re: Oil fired crucible furnace
Post by: MetalCaster on July 19, 2013, 04:34:08 PM
No apologies due or required.

Pat J here.
Title: Re: Oil fired crucible furnace
Post by: doubleboost on July 19, 2013, 04:53:04 PM
Steve

I used to sprinkle something on the plinth brick to stop it sticking to the crucible but for the life of me I cannot remember what. Can't have been sand as that would fuse at those temperatures

Beer mats work well
John
Title: Re: Oil fired crucible furnace
Post by: awemawson on July 19, 2013, 05:00:34 PM
Do they need a dousing in Newcastle Brown Ale first ? 

 :lol:
Title: Re: Oil fired crucible furnace
Post by: dsquire on July 19, 2013, 05:05:58 PM
You have seen my work, nothing new to show there.

MetalCaster

I have checked all of your previous posts and can find no pictures of your work. It would be nice to see your work as you sound like you have a lot of skill and experience.  :)


Perhaps you could go to http://madmodder.net/index.php/board,3.0.html and make an introductry post to help the members get to know you.  :D


Cheers  :beer:

Don
Title: Re: Oil fired crucible furnace
Post by: tekfab on July 19, 2013, 05:07:11 PM
I'm guessing he was here previously under a different guise ?

Mike
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 19, 2013, 05:15:13 PM
Steve

I used to sprinkle something on the plinth brick to stop it sticking to the crucible but for the life of me I cannot remember what. Can't have been sand as that would fuse at those temperatures

Beer mats work well
John

Damn, I should have saved up back when I remembered where they came from!
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 19, 2013, 07:39:47 PM
Today I increased the size of the exhaust port in the furnace lid to 4". Don't know if that will help or hinder melting. I think it will probably allow more air through, by reducing back pressure, which means I can open the fuel up all the way.

I couldn't do that before without the furnace smoking. The main reason I did it though, was to allow dropping additional metal more easily into the crucible, and also observing the melt.

I also tried out making some cores using Ironman's Portland cement and sand mix method. I used 1" PVC pipe as the core boxes. I slit them ahead of time. I used a very fine grade of sand I had on hand.

I was worried they would dry out before curing (in 3 days) so I put them inside a ziplock plastic bag, and also put a crumpled up wet paper towel in with them. Since humidity would then be 100% inside the bag, I didn't see any reason not put the whole thing out in the sun -- since that would speed up cure. Concrete blocks are rapid cured when cast by exposure to steam, so I though this might work in a similar way.

It's been very hot here the last week, but sunny at last. Temperatures have been up in the mid 90's F (34 C). So I'm sure the temperature was high in that bag today. Condensation showed the humidity was in there. I'll probably still go 3 days and then dry the cores as well after. But this was just an expeiment.
Title: Re: Oil fired crucible furnace
Post by: ironman on July 19, 2013, 08:21:15 PM
vtsteam

What you can do is before you add water to your sand is weigh the sand dry and then put in 4% water. For future mixes you may have to adjust the moisture level. For thick castings ram the sand more gently so it has more porosity.

 I see that you noticed I don't put in vents in the middle of the core. When molten iron touches the core/mold surface gases have to travel through the sand to reach the vent. If the sand has no porosity it will bubble through the metal. It will always take the path of lest resistance. Can you see why I don't bother with vents?

It is extremely rare for me to get blowholes in my castings so I must be doing something right. Have a look at my video " How to change steel to cast iron using a waste oil furnace" to see how I solved the shrinkage problem on the pulley casting. You will notice how shallow the copes are on my molds.

Just increasing the head pressure will not fix the shrinkage problem, making large enough risers so they will freeze last instead of the casting feeding the riser. 

When I saw the photo of how distorted your crucible was it would have been scary to lift out the crucible. Years ago I used to ask the foundry supplier is the crucible rated for iron? His answer was the crucible was rated for 1400C. Since then I never ask if the crucible is rated for iron and use them for iron. I have used a lot of crucibles over the years and never had one deform like yours.

 I have seen photos in other forums of crucibles with bad faults and are unusable after two melts. It is sad to say but I have come to the conclusion that the U.S.A. makes really bad crucibles. The ones I use are imported from Mexico, India, scotland and Brazil and never had a problem with them. I find some brands will last longer than others.

I have destroyed two crucibles through misuse, so making mistakes is part of the learning process. I never use flux with cast iron. Soda ash is the second worst flux to use in a crucible, the worst is borax. They will dissolve your crucible very quickly. If you insist on use fluxes your crucible, it will have a very short life.

vtsteam as a beginner there is no way your furnace will reach 1650C (3000F) I have a pyrometer that will measure to 1770C (3218) and in a typical iron melt the furnace is struggling to get over 1570C (2858F). I have never used a silicon carbide crucible for iron. I was hoping someone would buy one and see how much longer they last compared to a clay graphite crucible.

 Over the years many hobbicasters have visited my home foundry and everyone has said I do everything differently from what is written in books or the way they think it should be done. But when they leave I find out a few weeks later they have copied nearly every method I use. 

Metalcaster welcome to the forum. I'm sure everyone would like to know what sort of casting you have done.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 19, 2013, 10:08:41 PM
Thanks greatly Ironman!!

Crucible life:

I will definitely drop using the sodium carbonate. I also put a few charcoal pieces in, but I would guess you wouldn't think that hurt anything this last time.

Risers:

I did watch all of your casting videos last night looking for clues and tips about my shrinkage and bubbles problem, so I definitely noticed the two big risers on that pulley.

But I also noticed lots of castings where you had no risers, and much smaller sprues, and different shapes and sizes for gates than I used -- so I would like to try to get closer to what you do there first, to see what happens, before adding a riser. My sprue was 1.25" diameter. And I couldn't pour fast enough to fill it -- I think my 2 gates were too big in cross section, too.

Actually, I probably can't add a riser because of lack of crucible capacity. Although smaller sprue might help that quantity problem. Everything is interrelated.

Crucible distortion:

That happened in the last melt -- it didn't do that in the earlier ones. But I really cranked the furnace in the last 20 minutes this time -- and there was more flux.

Or maybe as you say, I should try a different make of crucible. Can you recommend a brand to look for? Is there any particular one you like?

I have one more new one, and I will try to see how it lasts without flux, a little gentler temp ramp up, etc. Maybe there will be a difference in lifespan. I will be very cautious about any leathery "feel".

I'm very happy copying what you do in preference to books where they differ, and grateful for your experience.



Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 19, 2013, 10:17:44 PM
One more thing I noticed in the video -- if a video can show such a thing -- I don't think you ram as hard. I'm guessing that would affect blow holes if your sand is more permeable because of lighter ramming.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 19, 2013, 11:18:54 PM
Sorry to make multiple posts, but I just also re-read your post and  you mentioned your shallow cope height. I definitely noticed that!

I have been thinking of making some of your style aluminum flasks. My eyeball estimate from the video is something like 1.75" flask height by 9" by 12". Is that right?

And about 3/8" thickness with small triangular corner gussets with tapped holes for screwing frames together, and positioning pins and holes mid frame(1/4" diameter?) Probably offset in position some so they can't be put together the wrong way.....
Title: Re: Oil fired crucible furnace
Post by: MetalCaster on July 19, 2013, 11:30:52 PM
Use one 1/4" and one 5/16" pin so you can't reverse the cope and drag.
The Alloy Avenue guy mentions that carriage bolts with the head sawn off make good pins, and I can vouch for that.

Ironman- You are familiar with my work too.  PatJ from you-know-where.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 20, 2013, 08:32:50 AM
Pat, this is what I'm talking about wanting to make:

Title: Re: Oil fired crucible furnace
Post by: MetalCaster on July 20, 2013, 12:39:26 PM
Ironman makes it look easy.
Not only has he mastered iron, he has mastered green sand.
My sand too often is to wet, or too dry (I use oil-based sand), or something else goes wrong with the sand, and just about time I get the mould done and all the gates and risers cut, it all falls out of the flask half.

Some put a groove or two in the walls of the flask, but if your sand is right, you probably can use a bare inner wall.

Here are a few made locally.
I would try and make the tabs on either end cast integral to the unit (I think in the photos below they are screwed on).
I will have to review Ironman's tabs to see if they are cast on.

And the pins seem abnormally large in the photos below, but the flasks I have which use 1/4" carriage bolts on one side are prone to getting out of alignment.
In the future I will use 5/16" and larger bolts for the pins (different size either side).

I only have wood flasks at this point, but hope to make some metal flasks one day.
Metal ones last a lot longer than the wood ones.

Edit:  Yep, ironman uses an integrally cast handle, as I suspected he would.
Title: Re: Oil fired crucible furnace
Post by: ironman on July 21, 2013, 04:21:59 AM
vtsteam

For many years I used Morgan crucibles made in Australia and they were terrible! I used to call them candle wax crucibles because they would melt every time they were used. A friend told me about Vesuvius crucibles, so I bought one and it lasted four times longer melting iron than the morgan crucible. I got really lucky there and when I saw the morgan rep I said I would never buy his crucibles ever again. That being said I still have to buy the crucible pedestals from morgan because Vesuvius don't have small pedestals.

When I started to melt iron I used soft fire bricks as a pedestal and the same thing happened, it leaned over and touched the furnace wall. I then used hard fire brick and they cracked because of the weight of the iron in the crucible. I gave up on fire bricks and got the pedestals from morgan. They last as long as the crucible.

The top of the crucible to the exhaust vent is the hotest part of my furnace, so that is where the most wear and tear happens. Over time my crucibles get shorter because of this.
 
You must have micrometers in your eyes, every dimention with the molding box is correct except for the height (50 mm).

It is very hard to put into words how to gate castings because each one is different. I have a lot of experience and know what to do. Reading books without experience can lead to errors, you just have to make mistakes to learn. Good judgement comes doing as well as reading.

Pat

My early boxes had screw in handles but thought that cast in handles were less trouble to make.

Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 21, 2013, 07:09:31 AM
Thank you again Ironman for your advice and experience.

Putting two and two together, if you use less ramming force than I have, and use a cope of 1/2 the depth I have, the gas permeability of your cope must be a fraction of what mine is. I think I can see why you don't get blow holes, and don't need to vent cores.

You are (I think) using finer sand -- probably finer than I could have used without getting a lot of gas entrapment. Years in the past with aluminum, I tried very fine sand -- 140 mesh, but had blow hole problems that way. So I just used that fine stuff for facing sand. That's the reason I asked about the mesh of your facing sand.

Also, if you are using smaller diameter sprues and copes of 1/2 the depth compared to those I have used, then the amount of material tied up in sprues is possibly 1/3 what I have.  This means, with a limited size crucible, that I would have more capacity to add a riser, possibly.

Speaking of crucible capacity, I have what were advertised as A-6 crucibles. I checked their capacity by weighing the amount of water they held on a gram scale, and it turns out they are A-4 crucibles of about .75 liter.  Their designation is A for shape and the 6 is the number of kilograms of brass it will hold. Thus an A-6 will hold 13.2 pounds of brass in our weight system.

The Morgan crucibles, on the other hand, designate the A as shape, again, but the 6 designates the number of pounds of aluminum it holds. Since brass is about 3 times as dense as aluminum, that would translate to about 18 pounds of brass -- 1.2 liter -- or a substantial difference.

After carefully measuring my furnace and tongs, it looked like I could fit a true A-6 rather than the smaller A-6's I have and get nearly 50% more capacity. Unfortunately I hadn't seen your reply yet last night, so I ordered a Morgan Salamander A-6.

Oh well!  I guess when all of these crucibles give up the ghost, (which may not be very long in the future) I'll finally get the right size and right brand.

A question about crucible treatment, Ironman:

Do you replace the crucible in the furnace after a pour to let it cool down slowly, or do you leave it in air to cool?

Title: Re: Oil fired crucible furnace
Post by: MetalCaster on July 21, 2013, 11:16:54 AM
I have not had any problems with the Morgans, but there are different grades even within one manufacturer such as Morgan.

The rep told me that for non-ferrous work, the Morgan "Hi-Melt" was the most long-lasting, and this is a silicon carbide crucible.
The "Hi-melt" is rated 1000-1400 C (1830-2550 F).

For ferrous work, he recommended the "Salamander Super" which is rated 850-1600 C (1562-2912 F), and these are clay-graphite.
The brochure mentions that they can also be used for non-ferrous work.

Note in the photo below that both are labeled "Slamander", which is very misleading given the fact that one is only rated for 2550 F and non-ferrous work.

I think you would get good service from either of these two units if used with the respectively rated metals.

I have also heard reports of crucibles cracking if not placed back into the furnace to cool slowly.
I put mine back in the furnace just to keep them clean, dry and protected until they are cool and can be stored sealed in a plastic bag.

Morgan mentions many things that will damage a crucible such as heating them too fast when they are cold, causing uneven thermal expansion and cracking, improper loading, lifting and supporting from the wrong position, not keeping them dry, etc.
I think the silicon carbide units have to be fired at least once to seal the glaze before they are used to melt metal.
Morgan also mentions not letting the flames impinge directly onto the curcible.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 21, 2013, 01:03:31 PM
Thanks Pat, I had already looked at Morgan manufacturer's literature before ordering the crucible, a Super.

I would like to hear what Ironman does in his own shop, re. crucible care, since that is genuine long time practical experience that I trust.
Title: Re: Oil fired crucible furnace
Post by: MetalCaster on July 21, 2013, 01:22:08 PM
Ironman has 20 years experience with pouring iron using both crucibles and cupolets (if I understood him correctly), and more importantly a lot of experience with making green sand.
Both are really critical since no matter how good you are at melting and pouring iron, if your mould fails, then you have nothing.

Edit:
Someone corrected me on the word "cupola", and said that the small units that are top-fed are "cupolets", not "cupolas".

Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 21, 2013, 08:17:25 PM
I made several changes and cast iron today.

First change was the enlarged exhaust hole in the furnace lid.
Second change was reducing the size of the sprue from 1.25" to 1" in order to keep it choked with metal.
Third change was to add some of my 140 mesh sand to the 60 mesh greensand I have used recently. About 15% was added.
Fourth change was to ram somewhat lighter
Fifth change was to use no sodium carbonate as flux
Sixth change was to preheat the new crucible to red heat at moderate burner throttle before adding metal.
Seventh change was to alter the pattern to include a semicircular groove to form a greensand core. This piece willl later be bored out, and the cored channel will make this easier. It also reduces the the mass of metal poured..

First Try:

I'd like to say everything worked out, but unfortunately I poured short. The much larger amount of slag of a very pasty consistency fooled me into thinking there was more metal in the crucible than there was -- and that it was hotter than it was when i dipped in a poker and it came out clean. Also the gates were a little shallow, so basically I ended up with a nice bar ingot of about 3/4" thick, but not a part.

Second Try:

I could tell the pour was short, so I didn't wait very long to unmold. I decided to use the residual heat in the furnace to attempt another melt. So I quickly broke up more scrap, and fired up the furnace. While it was heating I rammed up a new mold. I decided that I'd try a riser in this one as an additional change, but make sure the crucible was full of metal, not just 1/3 slag. I figured my smaller sprue, and the new core groove would give me enough additional metal in a full crucible to afford an 1.25" riser. Also I'd put in slightly deeper gates, and be absolutely sure the metal under the slag was fluid.

I pulled the crucible out when I thought it was ready, and scraped the very thick sluggish slag out of the way where I would pour -- I couldn't scoop it all off easily, as I had when I used Sodium Carbonate -- that stuff really liquifies the slag.

I poured and watched the riser fill to the brim, and had enough metal left over to pour an ingot as well. Good!

In a couple minutes the riser started to shrink down -- which I took as a good sign! Both the sprue and riser dropped quite a bit. Here's a pic:



(http://www.vtsteam.com/OilFurnace/OilFurnace12.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 21, 2013, 08:43:42 PM
The part came out well!  The surface wasn't smooth I still don't have seacoal for a facing sand, but the added 140 mesh sand seems to have made for a finer surface grain than before. The lighter ramming doesn't seem to have caused any irregularity or coarse patterns, and the corners look good.


Bottom of the part:


(http://www.vtsteam.com/OilFurnace/OilFurnace13.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 21, 2013, 08:57:24 PM
The top surface shows a big improvement over the last pour of this part. There are only 3 small shallow blow holes -- these will be easily removed with the machining allowance, and when the part is bored -- unless there are some hidden holes. I have a feeling that's all there are.

I believe the reduction in ramming pressure and smaller sprue (which I kept choked while pouring) helped trap less gas, and relieve it where present, creating fewer and smaller pockets. If I go to a shallower cope, it's possible venting and permeability will improve even further.

The greatest improvement was the elimination of the shrink depression. This was probably due to the addition of the riser. The greensand core that formed the channel might have helped as well by reducing the thickness in the center of the casting. Less thickess, less retained  heat at the center. Since the channel also makes machining easier, it was definitely worthwhile adding it to the pattern.

I'm very happy with the results and  feel I'm on the right track. Plus I have a good part!

Here's the top  (dark areas are dampness from a rinse):


(http://www.vtsteam.com/OilFurnace/OilFurnace14.jpg)




Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 21, 2013, 09:08:18 PM
And as a follow-up for furnace operation, the furnace consumed 2.5 gallons of diesel fuel total over the two melting sessions during a 4 hour period.

Actual time to melt for the first pour was 1 hour 5 minutes from lighting, and after a 45 minute cool down, the furnace ran for an additional hour to achieve the second melt -- which had more metal.

The crucible looked in good condition, though I couldn't remove a fair amount of pasty slag this time because without flux it was tough stuff  to try to scrape out. I put the crucible back in the hot furnace to cool slowly, so I'll get a better look at it tomorrow. I think it is retaining wall thickness better than the first one had. It felt solid, not leathery during the pours.
Title: Re: Oil fired crucible furnace
Post by: MetalCaster on July 21, 2013, 09:46:04 PM
That looks like a good pour.  I am not sure about the small blowholes though, what type of sand are you using (water or oil-based?).

And the amount of slag you are getting sounds a little excessive.
I get very little slag and only need a light skim, but I start with clean iron.

Looks like you are on a roll.

And very conservative fuel usage too.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 22, 2013, 05:50:44 PM
Re-cast the part again today to try a few more changes:

First change, built a new cope 2" deep in place of the older one 3.5" deep.
Second change, increased the size of the riser from 1.25" dia to 1.5" dia
Third change, increased the size of the well under the 1" sprue to 1.5 dia
Fourth change, made the path of the gates more square than curved
Fifth change, dusted the mold cavity with plumbago

Total furnace melt time from lighting to pour 1:15
Diesel fuel used: 1.25 gal

Results were a general further improvement over the last pour. Finish was greatly improved, though corners were more rounded (result of blacking). There were still a couple of minor holes, though they looked like they would be removed when the surfaces were machined, and the channel bored to 1" dia.

The main problem that came up was again my mis-estimate of the amount of slag/vs metal in the pot, and a nearly short pour as a result. I did not fill the sprue and riser completely, though they filled sufficiently to make a good casting.

I really need to slag out the crucible while in the furnace, rather than out, so I can get a better visual take on the amount of metal in the pot -- and can add more if needed. The slag is very puffy so it takes up a lot of space. The slag used to appear much smaller when I used a flux which liquified it. Now it's got the appearance of cottage cheese. Last pour I scraped it in the furnace and added more metal -- there was plenty for the pour. This time I didn't scrape it beforehand and assumed I had enough metal.

I had no trouble with the shallower cope, and I think it is going to be an improvement. I think the riser and gating were good, except that the gates could have been bigger -- the pour went unusually slowly. Possibly because of the lower head pressure of the thinner cope. I think a completed pour with more metal might have made a very good part.


(http://www.vtsteam.com/OilFurnace/OilFurnace15.jpg)
Title: Re: Oil fired crucible furnace
Post by: MetalCaster on July 22, 2013, 06:04:58 PM
Nice work.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 22, 2013, 08:22:29 PM
Thank you, Pat.

In answer to your earlier questions:

The greensand is traditional silica sand and bentonite, per ironman's formula.

The iron is from broken up cast iron radiators. The pieces are thin, and so probably would make more slag than thicker iron.
Title: Re: Oil fired crucible furnace
Post by: awemawson on July 23, 2013, 03:40:53 AM
Cast Iron radiators of the finned 'school' or 'hospital' type are usually a high phosphorous iron and as such should be very fluid when pouring but rather hard to machine. From what you've said earlier your castings machine nicely which is at variance with this - just an observation.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 23, 2013, 08:34:54 AM
Yes Andrew they do machine well -- better in fact than I had thought (and mentioned) earlier.

I believed that they were rough on a HSS end mill and said so at one point, but I think that was just trapped silica sand particles and scale on the surface, not the underlying metal itself. I did use a hand grinder to try to remove the outer skin before milling, but didn't get everything.

After milling I drilled  the same piece through, the drill cut beautifully -- very clean sharp holes, and those nice little uniform bits of swarf mixed with graphite, and a good rate of penetration.

I have no carbide tooling other than a bunch of odd shaped inserts I bought at the Bernardston engine show. I really need to make some kind of milling holder for them -- some kind of fly cutter -- so I can clean off castings without wrecking my HSS mills.

I also don't have an HSS milling cutter sharpener fixture -- just a bench grinder.  I do have a big box of used end mills someone gave me -- hundreds of them, so I would like to be able to sharpen them. I also have a boxed new green wheel.

Takes time to get from A to B like this.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 23, 2013, 04:29:49 PM
Can't melt today because of rain. Here are some informational pix from the melts so far.

First set is of three broken ingots, left after pours. I'm not sure which pour goes with which ingot. But they are definitely 3 different pours (or attempts to pour).

(http://www.vtsteam.com/OilFurnace/Ingot1.jpg)



(http://www.vtsteam.com/OilFurnace/Ingot2.jpg)



(http://www.vtsteam.com/OilFurnace/Ingot3.jpg)

Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 23, 2013, 04:42:14 PM
The next two are the two crucibles used. The one on the left was retired after 3 melts/attempts. It was used with a flux of soda ash (sodium carbonate).

The one on the right was used without flux. Also 3 melts. You can see the difference in the slag in each -- especially at the bottom. This crucible is coated with rough slag, but is still usable. The wall thickness is greater and it has retained its shape. In the side view the ceramic looks much better. The slag on the exterior also looks different.

(http://www.vtsteam.com/OilFurnace/Crucible7.jpg)


(http://www.vtsteam.com/OilFurnace/Crucible8.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 23, 2013, 04:49:15 PM
Finally, some not very exciting pictures of slag scraped off of the second (unfluxed) crucible. Texture and appearance is like very sticky cottage cheese when molten. It is very tenacious and difficult to scrape, even hot.

(http://www.vtsteam.com/OilFurnace/Crucible9.jpg)
Title: Re: Oil fired crucible furnace
Post by: MetalCaster on July 23, 2013, 05:12:24 PM
The residual slag is suppose to be scraped out of the crucible immediately after a pour, but I have found that to be easier said than done.

That slag is tough stuff.
I don't have anywhere near the slag you do, perhaps 1/20 of that or less.
Title: Re: Oil fired crucible furnace
Post by: Mayhem on July 24, 2013, 03:25:23 AM
It looks like you are making real progress Steve.  I am following with interest, as I know very little about this and hope to get into it (if I can get my burner working).
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 24, 2013, 07:56:38 AM
Thanks Mayhem, it's all new to me as well -- thought I was reasonable at casting when it was aluminum, but iron is definitely teaching me patience, here.

I think the shrinkage issue may be solved, the main things I need to work on are bubbles and slag removal. I'm going to push my limits on what I think of as usable sand in terms of dryness and light ramming to try to get permeability up. I do also vent the sand with wire. Those are the little holes you see in the picture of the cope sand, back a ways in this thread. Cope depth has been decreased to 2"

For slag reduction and removal, I'm going to try a little crushed oyster shell as a flux this next pour, added later in the melt. I hope this will cause less crucible erosion than I had with the soda ash.

Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 24, 2013, 04:32:27 PM
Here's a pic of the radiator scrap I've been using:

(http://www.vtsteam.com/OilFurnace/Crucible10.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 24, 2013, 04:34:20 PM
Here's a closer shot of it -- some pieces are relatively clean looking on the inside, and some are quite rough, with what look like sand inclusions from a core:


(http://www.vtsteam.com/OilFurnace/Crucible11.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 24, 2013, 04:37:05 PM
Here's a tool I made today to help me scrape slag out of the crucible while it is in the furnace. It was made from a piece of L shaped angle iron left over from the pallet i used to make the furnace base, and a 2 foot length of 1/2" re-bar:


(http://www.vtsteam.com/OilFurnace/Crucible13.jpg)
Title: Re: Oil fired crucible furnace
Post by: MetalCaster on July 24, 2013, 04:43:04 PM
That does look a bit crusty on the one piece.

I only use clean metal to avoid slag problems.
I bought some ground corn cob, and will either be wire brushing my metal, or sand blasting it with corn cob.

I tried using some baking soda and salt with an aluminum pour, but then tried it again without either, and still had good results, but again starting with clean metal.

I have seen others around here use radiators, but I have not had trouble (yet) with just regular gray cast iron as far as being fuid enough to pour.

Those high-temp pyrometers are quite expensive, so I only use one with brass/bronze/aluminum.
For cast iron, it is just sort of a look/feel/time guess unfortunately, but it does get fluid enough to pour.
I can't dilly-dally around though after pulling the crucible out of the furnace, it has to be poured straight away or it will get cold in a hurry.
Title: Re: Oil fired crucible furnace
Post by: MetalCaster on July 24, 2013, 04:44:02 PM
I need to make one of those scapers.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 24, 2013, 04:53:50 PM
Today's second pour. The first pour was a mess -- a piece of slag on the outside of the crucible prevented it from seating all the way down in the pouring shank, I didn't notice. About half way through the pour the crucible slipped out of the shank and emptied the remainder on top of the sand -- hence the burn marks in this cope. One more short pour   :doh:

After uttering a few sentiments that would have made doubleboost blush, I re-grouped, dumped the flask in a wheelbarrow, re-loaded the crucible, started the second melt, and rammed up a new mold.

This time instead of the radiator scrap, I used one of my earlier castings, a sprue and an ingot -- figuring these were all clean metal, and much more massive than the other stuff. I hoped for a lot less slag and a good pour. It melted pretty quickly in the hot furnace, and I dumped in about an ounce of crushed oyster shell. This did seem to liquify the slag better. I had a fuller pot of metal, it seemed, too.

When it seemed hot enough I pulled it out scraped the slag -- much less and better behaved, checked the fit in the shank carefully. and poured.

Unfortunately I thought I saw a small bit of slag go in part way through the pour -- I hoped it would be trapped in the well or gates. If I'd had a partner, he (or she) could have held back the slag with a rake. There always seems to be a little bit clinging to some part of the crucible.

Here's what the second pour looked like -- nice and neat. Not like the first!!

(http://www.vtsteam.com/OilFurnace/Crucible14.jpg)

Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 24, 2013, 04:58:45 PM
I had enough at the end to pour an ingot -- a bit of slag dropped in when I tipped the crucible all the way here, too.

While waiting for the mold to cool, I broke the ingot in half to look at the grain. Looks good, and uniform gray, except for the bit of slag.


(http://www.vtsteam.com/OilFurnace/Crucible15.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 24, 2013, 05:02:10 PM
Breaking out, the bottom of the casting looked good -- graphite blacking was helping some -- also corners were relatively sharp. This time sprue and riser were well filled -- though short, since the cope is only 2" deep.


(http://www.vtsteam.com/OilFurnace/Crucible16.jpg)
Title: Re: Oil fired crucible furnace
Post by: MetalCaster on July 24, 2013, 05:04:02 PM
That looks like good clean metal.

I made a crucible retainer for my smaller crucibles, but it was not a positive engagement, and so the crucible shifted when I went past 90 degrees, and sloshed metal everywhere.  The sliding/locking retainers seem to work best, and they make positive contact with the crucible.

We need to get you a web cam so we can watch the action.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 24, 2013, 05:21:59 PM
Hopes were up but after cleaning the sand off, no good.   :wack:

Same old story with a new set of words. Slag inclusions.



(http://www.vtsteam.com/OilFurnace/Crucible18.jpg)



Pretty sure these aren't the same as the blow holes I got earlier -- not sure if they show well in the photo here, but in real life they are rougher irregular holes and look like inclusions inside.

So, I'm not sure if I was successful in totally getting rid of blow holes, or partially successful, but I did manage to get a different problem this time.

Well, slag has been a problem, one way or another all along. It seemed to be no problem when I used sodium carbonate -- but of course, crucible lifespan was a problem.

I might go back to soda ash, but this time added just before the pour -- as the oyster shell was.

Maybe that will give me truly liquid slag that I can skim off completely. It was like green syrup before, not this slushy stuff.

Using "clean metal" seemed to help some, as did shell flux, but it's just not enough here.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 24, 2013, 05:32:22 PM
Definitely discouraging.

I guess the shrink depression problem is past, and the surface finish has improved. And maybe even the blow holes are gone -- not sure about that one. But slag is a ..............  :(
Title: Re: Oil fired crucible furnace
Post by: tekfab on July 24, 2013, 05:36:18 PM
Just out of curiosity have you thought about casting it the other way up ?

Mike
Title: Re: Oil fired crucible furnace
Post by: MetalCaster on July 24, 2013, 05:47:08 PM
As ironman said, it can take years to get the methods and materials figure out.
I am suspecting your sand mix, since your risers and such appear be be breaking with a clean interior.

Ironman had a lot of trouble with sand when he started.
Do you have any sodium silicate and CO2 you can try?
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 24, 2013, 06:19:11 PM
Sorry Pat, not interested in anything but traditional greensand. If it takes years to master, so be it.

Sand type doesn't cause slag inclusions. Pouring slag does.

Gating can catch it. But better not to pour it in the first place.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 24, 2013, 06:33:16 PM
Just out of curiosity have you thought about casting it the other way up ?

Mike

Mike, both surfaces need to be machined to mating surfaces, so it would just transfer the problem.

It could be cast vertically as awemawson once mentioned, and the upper end trimmed -- allowing a generous machining allowance and assuming slag inclusions weren't the problem.

But a new pattern would have to be made and draft would have to taper along the length which would be pretty wasteful of material. I guess one face could be parallel to the true datum, and that one would have to be the channeled face.

I guess it's do-able as a last resort. But the other mating piece is a more complicated shape, and has lettering, so it must be cast horizontally. I do have one of those already cast -- the first piece I ever did in iron -- beginner's luck on that one.

But also, I need to learn what is wrong here, and how to handle it. So even though it's frustrating to spend so much time on this simple piece, I want to learn how to cast it and have it work.
Title: Re: Oil fired crucible furnace
Post by: awemawson on July 25, 2013, 03:34:04 AM
Steve
 I expect that like me, the journey is as important as the end result. Most of my workshop activity involves finding new skills and learning new things. The end product in my case is really a byproduct!
Andrew
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 25, 2013, 09:26:48 AM
That's right Andrew, if I move on now then I'll never understand molding iron in greensand.

I know it CAN be done, the evidence is all around us in a couple centuries worth of superb iron castings. Not to mention ironman's videos.

The radiators I broke up are fairly amazing in themselves. Making one of those would have been a heck of a lot more demanding than this simple little rectangular block of iron I'm trying to figure out. Some of these tube style radiators are 5/8" ID cross section and 1/8" skin thickness, with ribs, and a central parting line. Must have been some real interesting cores there -- and I think I've even found some chaplets in the scrap.

Just getting those cores out is ship-in-a-bottle-stuff.  They must have had the mix just perfect for them to fall apart easily, yet strong enough to hold those intricate long narrow shapes, perfectly positioned. No way did they get scrapers inside after the pour. :scratch:

Now that was iron casting.  :bow:
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 25, 2013, 07:41:16 PM
Today's casting:

Decided to try a different cast iron stock -- I have a rail or old automotive frame section that is cast iron -- can't tell which. It was found in an old abandoned auto junkyard long since bulldozed over. Looks like a narrow train rail, but definitely cast iron. I broke off 7 pounds of it -- it's about 1/2" thick stock when broken up. Nice solid chunks compared to the radiator stock. I made it up to 8 pounds with one of the short pour castings I had from earlier attempts. Figured that would add a little phosphorus to the melt, and it was clean.

I also retired the second crucible -- it is just completly crudded up with slag inside, and the upper walls are getting thin. I think I got 5 melts out of that one. Both were purchased 7 years ago and were stored ever since, awaiting construction of an iron melting furnace.

I just received a 3rd crucible from the same source. Same size but looks a little different. Wondering if it would be any better. So I put the new metal in the new crucible. Decided not to use flux this time since I figured there would be much less slag.

Molding sand seemed a little damper than it was last pour -- that time it was on the borderline of unworkably dry. But  I don't think I had blow holes-- just slag inclusions.

Anyway, rammed it up, melted the metal -- that went really well this time. Nice full pot, not much slag, and it was removable. Did a careful job of that. The metal was nice and hot. I poured the mold perfectly, though there might have been the slightest pause at one point where the sprue wasn't choked.

I thought this would really be a good one because everything went so well. But no there was a really big blow hole -- biggest of any of the pours by far. Maybe it was the very slight pause in pouring. I'm thinking the sand isn't permeable enough, though.

So trying to think what could be the matter with the sand. It is brand new U.S. Silica F60 (foundry grade 60 mesh) sand, bonded with ceramics grade bentonite @ 7%.  Water was originally added at 4%, but after molding it has been adjusted by feel.

Previously for aluminum I used 100 mesh sandblasting sand with fire clay @ 15%. I used that sand for 11 years, and was very used to the feel of it when properly tempered.

I am not used to the feel of the new iron sand -- it's quite different. I tend to judge the moisture content by how well mold edges hold up when cutting gates and lifting the pattern. Last pour before this one when the sand was very dry, the edges tended to crumble when cutting gates. It was what I would call borderline unworkable. But it did seem that permeability was adequate finally and the blowholes weren't a problem (slag was).

What has occurred to me this evening is that maybe I don't have enough bentonite in the mix. Maybe I had a little more clay in the mix the corners wouldn't crumble with even less water -- in other words, more green strength with less moisture and I hope, more permeability as a result (also less steam released). It's possible that I am compensating for too little clay binder by adding more water than is necessary.

This is all probably because I don't have any prior experience with bentonite. I don't know its proper feel. Also there are more than one type of bentonite -- so an exact recipe like ironman's might not fit my particular sand and greensand mix. I might need 8% instead of 7%.

So that is what I might try next. A little more clay, and a further reduction in moisture if possible.




Title: Re: Oil fired crucible furnace
Post by: awemawson on July 26, 2013, 04:15:14 AM
Steve,

I used to use a 'Speedy Moisture Meter' to test my sand - not every time but reasonably regularly, as I didn't cast often enough to do it by judgement. They turn up on eBay fairly regularly.
Title: Re: Oil fired crucible furnace
Post by: tom osselton on July 26, 2013, 04:38:31 AM
Found this at http://www.foundry101.com/archive.htm

Sand mixture for iron and steel casting is LESS than 5% bentonite and 70 grit. Sea coal is also added to prevent burn ln.

I just looked at your pic "the shake out" on page 1. I see the sprue with the two gates connecting the block but I don't see a riser might be reducing the venting.

Tom
Title: Re: Oil fired crucible furnace
Post by: RussellT on July 26, 2013, 08:01:34 AM
Your comments on the skill of casting radiators reminded me of window frames.

A friend was involved with the restoration of an old (19thC) industrial building and the original window frames were cast iron with small panes of glass.  Some of them were damaged and so they wanted some new ones cast.  Unfortunately they struggled to find anyone who could cast them!

I'm impressed with your determination on iron casting, I'm sure your hard work will pay off with good castings soon.

Russell
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 26, 2013, 12:19:30 PM
Steve,

I used to use a 'Speedy Moisture Meter' to test my sand - not every time but reasonably regularly, as I didn't cast often enough to do it by judgement. They turn up on eBay fairly regularly.

Andrew thank you for that suggestion.

I'm thinking that weighing a sample of greensand on my gram scale before putting in an oven to dry at low temp and then re-weighing would work, too. I might do that just to get an idea where I am with sand that I think "feels" right. Might be some surprises there.....

Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 26, 2013, 12:33:33 PM
Found this at http://www.foundry101.com/archive.htm

Sand mixture for iron and steel casting is LESS than 5% bentonite and 70 grit. Sea coal is also added to prevent burn ln.

I just looked at your pic "the shake out" on page 1. I see the sprue with the two gates connecting the block but I don't see a riser might be reducing the venting.

Tom

Tom thanks for the reference. I'd seen that before, and I notice they don't actually cast iron.

They also have two references on their site like the one you quote -- one says "UNDER 4%" and the other says "UNDER 5%". My take on that site is that they are very nice people and do a good job of popularizing hobby aluminum casting craft with copies of pre-existing objects as patterns, but they aren't really a good technical resource.

I've seen references to a range of bentonite by both technical commercial sources  as well as people who have decades of experience in iron casting., like Ironman, Stewart Marshall, and others. 7 or 8% is well within that range. Bentonite is also not just a single chemical substance. there is western and southern bentonite, with different properties, calcium bentonite and sodium bentonite. These can also be blended.

Right now I'm trying to figure out what kind I have. It is labeled "Whittaker" and "Bentonite 149". I've found just a few references connected with those -- one shows more sodium than calcium, so I'm currently guessing it is sodium bentonite.

Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 26, 2013, 12:46:47 PM
Russell, thanks so much! I sometimes wonder if it isn't boring or irritating to people for me to keep going onand on  with examples of bad castings. I sometimes think I ought to wait until I can post things that work out, and save all the long list of mistakes and problem pours. But hell, John Doubleboost shows us what really goes on when you try new things, and I enjoy, and learn from that part of his videos.

So I figured just keep posting this crap as it happens, until you get a good casting, Steve. Or just finally give up! Which I have to admit sometimes crosses my mind. Particularly when I open one up that I'm sure went well, and see a bigger hole than I had before, or a bunch of slag! Seems like when that happens, the next day, I'm up for it again, and think, "Wait, maybe if i just do this .......this time for sure...."

Anyway thank you Russell -- you all make it worthwhile.

 :nrocks:
Title: Re: Oil fired crucible furnace
Post by: andyf on July 26, 2013, 01:28:11 PM
Russell, thanks so much! I sometimes wonder if it isn't boring or irritating to people for me to keep going on and on  with examples of bad castings. I sometimes think I ought to wait until I can post things that work out, and save all the long list of mistakes and problem pours.

Though I'll never start casting iron myself, it's still very interesting watching you climb the learning curve (or cliff). Anyhow, if you only posted perfect pours, no-one would really know what you did to get rid of the earlier imperfections.

Andy
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 26, 2013, 08:23:53 PM
Thank you Andy! I'm glad it's still interesting to people.

It rained today, but I did take the opportunity to take a 50 gram sample of my sand and dry it in a 200F oven for a half hour and re-weigh it. Seems I lost 2 grams, so that works out to 4% moisture content.

The sample was on what I would think of as the dry side, by feel to start with. So this gives me a rough reference to what 4% water is like.

Probably I should repeat that with 200 grams to get a more accurate read -- might do that tomorrow. Then I could gradually add measured amounts of water to the dried sand to get 3 through 6 percent moisture samples. This will help me a lot because I'm not used to the feel of bentonite tempered greensand.

I can say that for several of the early pours and a few of the later ones the moisture content was higher than 4%. So that was probably part of the problem with blow holes.

Title: Re: Oil fired crucible furnace
Post by: awemawson on July 27, 2013, 02:25:52 AM
4% is what I aimed for for both aluminium and cast iron and it seemed to be ok
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 27, 2013, 11:16:02 AM
Thanks Andrew -- ironman also shows 4% in his mix.

Unfortunately my test yesterday seems off. I was thinking, my digital scale only reads to 1 gram, and with a 50 gram sample +- 1 gram is the same as +- 2%. So it could have meant I had anywhere from 2% moisture to 6% moisture. Not necessarily 4%.

So I repeated it this morning, this time with a 200 gram sample. And I got 195 grams after drying. Which is 2.5% +- 0.5%.

So yes, the sand is a little on the dry side  for me by feel, and by actuality.

But that shouldn't hurt permeability I would think, and as long as the mold holds together, I would think it's a positive.
Title: Re: Oil fired crucible furnace
Post by: MetalCaster on July 27, 2013, 11:21:06 AM
VT-

I have been on a similar journey for the last few years with the iron thing.

I have had a lot of conversations with Ironman, and the general concensus between us is that there is a lot of misleading information on the internet about things in general and casting iron and other metals in particular.

I has been difficuilt for me to sort through what I am told with what I discover for myself, and what I assume to be educated guesses.

My approach has been to break down the problem into managable parts, and solve one problem at a time.

I had a lot of recommendations to use coke for fuel, and build a cupola, but after searching for weeks for coke, and living one state away from the motherload of coke mines, I found that the normal joe cannot buy coke in small quntities.

I looked at propane, propane and oxygen, charcoal, kerosene, etc.
I finally settled in on diesel as fuel since it burns cleanly, is readily available from a large number of sources, and is much cheaper than kerosene around here.

I had to figure out how to make an efficient burner, and ended up with a hybrid combination of several designs that were out there on the net.
The hybrid burner works very well.

I did a lot of research on crucibles to find one that would last for a long time.
A crucible should last between 50-100 melts minimum.

I researched alloys, melting temperatures, machinability, availability, costs, etc.

I looked at types of sand, water-based, oil-based, binders, resin-based, sodium silicate, etc.

And I did some castings, all with Petrobond so far.

So what do I do when things go south?
Break down the problem and isolate the problem to a single source, then solve that problem and reintroduce other variables slowly, one at at time.

My suggestsion for using sodium silicate-based moulds is to eliminate many/most of the variables, to find out if the problem is with the sand, or the metal you are using.
If you use a sodium silicate mould, and still have blowholes, then it is not the sand, it is the metal.

I start with clean metal of a known composition, again to eliminate variables and start with a known entitiy (clean gray Class 40 cast iron that is easily machined).

Your crucibles are apparently not rated for cast iron temps, or you are directing your burner straight onto your crucible or something.  You got a big problem there.
There are guys on Alloy Avenue who do cast iron every day on a commercial basis and get over 100 pours per crucible.  There is no reason why you can't buy the same crucible they have.  That is an easy problem to solve.

You could start with some clean cast iron of known composition, then see if you still have gassing, inclusions, etc.

I have seen too many people use one or more additives without even checking to see if they could pour successfully without an additive.
Again don't intorduce multiple variables into the problem at the same time, expecially if you don't even need them.

Your sprue and riser are very short, but if you are getting a decent mould fill, then sufficient pressure is being developed.
The idea behind the sprue/runner/gating/risering is to prevent air aspiration, trap lose sand, skim slag, create even pressure at every gate, control solidification, and preventing shrinkage.
An even and consistent pressure is desirable to fill the mould, and I have found that vents on the top of the mould are necessary to get rid of trapped air, and would almost certainly be critical with water-based sand to vent steam.  I have also seen many commercial guys vent the core through the center and all the way out the mould.

So while I don't have a lot of casting experience, I have done a large amount of research, and specifically I have paid close attention to the guys who are doing a lot of cast iron work. 
I would recommend a more systematic approach.
No doubt you can do as good or better iron work than anyone out there, but I personally don't like to take a more tortuous path than I already face.
I see nothing to be gained by rediscovering the mistakes that many others have already made, unless like someone already stated "the journey is more important to you than the destination".
Title: Re: Oil fired crucible furnace
Post by: tekfab on July 27, 2013, 11:29:15 AM
Good Post MC   :thumbup:

Mike
Title: Re: Oil fired crucible furnace
Post by: NeoTech on July 27, 2013, 01:08:38 PM
Well if you don't have the means to buy the things you need.. The trial and error process is the logic step to take. I enjoyed this thread because of the trial and error process of repeating tests and casts.

I dont personally agree with learning from others is always the best thing. Sometimes playing with fire and get burned is the best lesson for figuring something out and getting the experience from it as needed. (dont put the damn hand in the fire). And is especially true when you dont have the means to follow some step by step commercial procedure outlined in a book.

But i do as well tend to go my own way and do whatever i think will work after sorting out the basics - experience isnt learned its experienced..

Oh well, less pie throwing and more trials an tribulation. Somewhere on the road taken the answer will show it self.. =)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 27, 2013, 02:32:50 PM
Pat, I think I have seen the same information repeated enough to have it memorized by now. That's not my way. I look forward to reading your own casting project threads.  I do see great value to be gained by rediscovering the mistakes that many others have already made, and as Andrew already stated "the journey is more important than the destination". 

Change of subject. Here are photos of my F60 silica sand without any binder.

(http://www.vtsteam.com/OilFurnace/Sand1.jpg)



(http://www.vtsteam.com/OilFurnace/Sand2.jpg)

Title: Re: Oil fired crucible furnace
Post by: tekfab on July 27, 2013, 02:53:55 PM
That's quite possibly the nicest F60 silica sand that i've ever seen.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 27, 2013, 03:04:54 PM
That sand would I believe be called sub-angular in grain shape. I've made up some new greensand today with 4% bentonite, and 4% water. The idea being to try it, and possibly gradually increase the bentonite content by 1 % steps over a few castings.

I won't be able to try that until tomorrow in order to let it rest. But I will cast today using my other sand at 2.5 % moisture content, as measured today, and with the new thicker iron I used last pour. the crucible will be one of the poor ones, but it has only one pour under its belt, and is clean inside. I should get another 3 melts out of it before switching to the new Salamander Super A-6, which needs a pouring shank and tongs made to fit.

I will not use flux today.
Title: Re: Oil fired crucible furnace
Post by: tekfab on July 27, 2013, 03:22:39 PM
The picture is not crystal clear but to me it looks like you have a sub-angular/sub-rounded mix but as i said i'm only going by what i can see in the pcture.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 27, 2013, 05:17:43 PM
Sounds good to me.
Title: Re: Oil fired crucible furnace
Post by: Rob.Wilson on July 27, 2013, 05:23:48 PM
Looks like silica gel to me Steve  :palm:


Rob
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 27, 2013, 05:25:58 PM
So thats it!!!!

Rob, you've solved it.  :lol: :lol: :lol: :lol: :lol: :lol: :lol:
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 27, 2013, 05:38:46 PM
Metal is poured. Just waiting for it to cool. Seemed to go pretty well. Mostly skimmed it in the furnace. I did give it a quick skim just before pouring while it was outside the furnace. Greensand was dry.  Riser filled, Well vented. Used thick Iron stock for the melt.  Total time from lighting furnace to pour was 1 hour 20 min. That included shutting down at 1 hour to add metal to the pot, and one time to scrape slag. Also of course making up the mold.

Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 27, 2013, 09:31:56 PM
Bit of a delay for dinner and family movie time.

So, shake out showed familiar problems. But not just similar problems, almost identical patterns of problems to a prior pour. And THAT was interesting. Take a look:

This pour:

(http://www.vtsteam.com/OilFurnace/OilFurnace16.jpg)


And the earlier pour:

(http://www.vtsteam.com/OilFurnace/Crucible17a.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 27, 2013, 09:41:48 PM
So I'm not too upset about this one. Because it is a clue. So what is it trying to say?

Well, what am I looking at? Two sets of flaws in almost the same patterns.

The flaws appear almost entirely in  the central channel. And they don't appear in the middle of that channel, but in 2 groups either side of the center.

Now if these were gas or steam bubbles, we would expect them to be beside the channel, not in the channel itself, because they would tend to go to the highest point in  the casting. In fact it would be pretty hard to get them to stay under a ridge of sand, which is what the channel is as a mold surface.

So why are they there and why are they in the pattern they have?

Well lets try to draw them as groups on top of the photo.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 27, 2013, 09:50:51 PM
(http://www.vtsteam.com/OilFurnace/OilFurnace16b.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 27, 2013, 09:58:34 PM
These holes are in the flow lines going from sprue to the riser.

Why are they where they are?

The central channel sand ridge is slowing and trapping them before the freeze. These holes are slag covered bubbles. There is no way that increased sand permeability or vents are going to get rid of them. They are solids. They are lighter than the iron, so they don't appear on the bottom of the casting -- they are near the top, but the channel blocks them.

Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 27, 2013, 10:13:27 PM
So where do they come from?

Well one likely possibility is of course the metal scrap. And thin radiator metal has a lot of surface area, with rust and maybe even some sand inclusions from coring inside. So it could generate a lot of slag -- being thin it also could oxidize badly in the furnace atmosphere. .

But now we get to an interesting distinction between the two different pours with the same patterns. The first one was poured with thin radiator scrap, but the second one was poured with only five chunky pieces of thick cast iron with very little rust. That metal melted quickly and was skimmed three times -- twice in the furnace and once outside just before the pour. So you would expect clean metal.

But something I noticed this time is another clue. There was a lot of slag the first two skimmings. And it was the old pasty frothy thick kind I'd had with the thin radiator metal. But that was odd, because the prior melt, with the very same kind of metal, in the very same crucible poured with no slag.

So what's the difference?

Well one thing was different.

The crucible was new last time.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 27, 2013, 10:23:22 PM
Suppose the crucible itself was generating the slag. A particularly sticky frothy hard to remove cottage cheesy slag.

That might make sense because a crucible is supposedly made of refractory materials. If they melt, or even more interestingly chemically react with molten iron, you'd expect it to be a pretty nasty type of slag -- almost a solid, not fluid at all, since it is close to its solid temperature. It's not like glass or something else with a lower melting point. And a chemical reaction between the iron and the cruciblecould produce a frothy gassy quality. It would also mean that there was an afiinity between the iron and the slag. They might be hard to separate from eachother. Mingle.

If you think about it, where did the crucible substance go, as these got thinner and thinner each melt? Was it really that they sloughed off on the outside where the heat was greatest. Where the flame was?

Or were they dissolving into the iron melt?

Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 27, 2013, 10:36:41 PM
Let's take a look at an earlier photo of two of the crucibles:



(http://www.vtsteam.com/OilFurnace/Crucible7.jpg)

Title: Re: Oil fired crucible furnace
Post by: dsquire on July 27, 2013, 10:43:34 PM
Steve

I'm wondering if there is any way to measure the crucibles to determine if they are getting thinner on the inside or the outside?

I know I'm not saying much but I am following every post. Keep up the good work.  :D :D

Cheers  :beer:

Don

Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 27, 2013, 10:48:37 PM
The one on the left is the first one I tried, the one that got leathery on the last pour and distorted. On the right is the second crucible I tried. I's had one pour, which I believe had no flux. They both show some surface pitting, and a spill of slag down the sides. But no sign of the refractory actually fusing or melting. No sags or hot spots. You can tell by the way that neither had the flame directly playing on them -- no local discoloration. The flame swirls around the crucibles in the furnace, as it should.

The main difference between the two crucibles, is that the one on the left was fluxed with sodium carbonate - soda ash - and on its last pour it received a fair handful of that. The soda ash was quite effective at dissolving the slag in the melt, despite the fact that it received only thin radiator metal. In fact that flux was so effective that in truly liquified the slag into a syrup consistency -- the only time this has ever happened in all of the melts I've done.

So it is a powerful flux, capable of liquifying the really difficult slag I've had. It also coincidentally affected the whole crucible, made it soft.

But was that a coincidence. Or were both the slag and the crucible the same substance?
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 27, 2013, 11:05:13 PM
Don, I think that for sure there is thinning on the inside, and especially visible at the top where hot metal and gas and slag all come together. I'm sure there is some erosion on the outside. But I just have a feeling that the significant part of it is occurring on the inside.

Now here's a couple statements to contemplate. One from BCS:

"These "A" shape crucibles are formed from what appears to be clay, fire clay grog and a smattering of silicon carbide particles. "

Yet these crucibles are identified as "Clay Graphite" crucibles. Why silicon carbide?

I should hasten to add I did not buy my crucibles (6years ago) from BCS. But I suspect they may be from the same source manufacturer.

And the second statement I have to find a source for, but I've seen it fairly commonly in a few references -- that silicon carbide is attacked by molten iron.

Title: Re: Oil fired crucible furnace
Post by: awemawson on July 28, 2013, 03:01:51 AM
Steve,

Are you venting your moulds as well as giving them a riser and poring basin?

I used to insert a 'needle' made from 1.5mm gas welding rod on about a 1" matrix all over the pattern area. The trick is to push it in so it ALMOST touches the pattern. In fact if you do touch the pattern you just get little pips on the casting to file off.

This greatly helps with escaping gasses giving a free passage to atmosphere avoiding the metal.

Andrew
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 28, 2013, 11:16:57 AM
Hi Andrew. Yes I have been venting all of them, and especially took pains on this last one. It got 30 vents with wire, Fifteen each side. And I even pushed them through to contact the pattern. The vents on the drag side left pips, those on the cope side did not. The cope is only 2" thick these days, so perhaps there was insufficient hydrostatic pressure to push it up the vents. It did rise up the riser however.

I don't believe these slag bubbles will dissipate through a vent however. They are hollow solids, not just gas pockets. That is why they collect at the bottom of the groove in the cope side of the casting, instead of dissipating, or rising to the higher edges and corners of the casting.

I cannot imagine permeability is the problem:

The cope is 2" thick, the sand is 60 mesh of good quality, the mold was vented 30 times, the moisture content was a measured 2.5% +- .05%, and the clay is quality bentonite (probably sodium type).

The only thing I can do at this point to increase permeability would be to reduce bentonite percentage -- which I have already initiated by mixing up new sand at 4% bentonite last night. I've given it overnight to age, but my impressions were that it was way under-bonded, and maybe unworkable even at 4% moisture -- at least yesterday -- we'll see how it feels today.

I really do not believe sand is the problem. But am trying to be open by trying this option. I think it is a slag problem, and that is where the solution is going to lie.
Title: Re: Oil fired crucible furnace
Post by: awemawson on July 28, 2013, 11:25:11 AM
Personally I think you need to work on keeping the slag away from the mould! Can you form a pouring basin system that has a longish horizontal run before plunging into the mould with a skimmer bridging it to leave the slag behind. Or even decant the iron into a previously heated pourer.

I appreciate that you are working single handed - were you not your helper would need to hold the slag back as you pour. Can you devise some system a bit like a tea pot where the fluid leaves the pot from below the surface?
Title: Re: Oil fired crucible furnace
Post by: NeoTech on July 28, 2013, 11:43:00 AM
with no idea about pouring melted iron.. but, have you tried those small nifty "mesh" thingys you see some people put in therem oulds.. like a small stainless mesh or something that sits in the inlet of the mould cavity supposedly to sort out the slag.. i imagine you conjour up one from fine mesh stainless.. Like those used in .. ehm ehm whats the word.. sand shaky sorting stuff thingymajigs.. you know.. ;)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 28, 2013, 11:55:42 AM
Thanks Neotech -- yes I've seen filters and read about them. And also gating is used to trap slag and sand impurities between the sprue and the casting.

But first I would like to concentrate on eliminating slag from the pour if possible. And to do that I have to find out where it is coming from. Ironman has written that there are 4 sources he's seen for new iron casters. Over oxidizing furnace atmosphere, too slow a furnace melt, badly oxidized thin metal, spending too much time skimming outside of the furnace before pouring.

I'd like to add to those the possibility that the crucible is contributing material to the melt, and this might be a particularly difficult type of slag, if it is indeed happening.
Title: Re: Oil fired crucible furnace
Post by: tom osselton on July 28, 2013, 07:55:39 PM
 I found this take a look at the more information on casting flux it generates a pdf file.
Lol didn't put the link!! Mindfart or what!
http://www.vesuvius.com/en/end-markets/iron-steel/casting/ingot-casting/
Tom
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 30, 2013, 10:33:27 AM
Andrew and Tom -- sorry i didn't answer your last two posts, for some reason I didn't see them in "new posts".

Thanks guys. All helpful ideas and good practice for dealing with slag. But first, I want to get to the source problem -- if it's over oxidation in my heating and pouring practice, or if it's bad crucible materials entering the melt, I want to know that as a fact, rather than just surmising about causes. And when actually identified, I want to solve those source problems first. Then liquify and trap slag if needed.

Next step for me is making the tongs and shank to fit the new Morgan crucible. Also milling the existing castings to see whether the small flaws are more than skin deep. If the flaws mill out, I can use them. If not I'll re-melt them. They are basically thick clean ingots at this stage.
Title: Re: Oil fired crucible furnace
Post by: awemawson on July 30, 2013, 11:18:13 AM
Steve,

When I set up my 100kW induction furnace at my last place (**), I had to replace the permanently fixed crucibles in the two 'furnace bodies' (*) that I had. They were a special size, and I ended up having a batch made in Poland and shipped to the UK - they were pricey but not exorbitant. Researching crucible materials at the time I came to the conclusion that Alumina was the way to go as it was good for all the metals I was melting (Aluminium, Bronze, Brass, and Iron)

Morgan Crucible started life in Battersea on the south bank of the River Thames just across the river from where I lived in Chelsea at the time. When I was leaving school I was offered an apprenticeship there but declined it !

(*) Two furnace  'bodies' - one is a 'total inversion' model where the mould is strapped on top of the body, which is then inverted and the metal pours straight in. The other also tips but has a spout and allows direct filling of a mould. Both look rather like building site cement mixers with large 'steering wheel' handles for tipping!

(**) Still got it but haven't re-commissioned it since I moved here although I have run in a 3 phase 415 volt 160 amp per phase supply so I can run it direct rather than use the generator as I previously did.

Title: Re: Oil fired crucible furnace
Post by: NeoTech on July 30, 2013, 11:20:09 AM
Induction furnace... Oki.. you need to start a build thread on of those.. (been trying my hands at induction... i just blew out the fuse box ) ;)
Title: Re: Oil fired crucible furnace
Post by: awemawson on July 30, 2013, 11:24:01 AM
I was thinking the same as I typed that. When the Traub lathe is finally tucked up and put to bed, maybe that'll be my next project - it's time I got round to it. I even put up a fireproof extension to house it then filled it with other stuff   :bang:
Title: Re: Oil fired crucible furnace
Post by: Mayhem on July 30, 2013, 11:39:14 AM
What NeoTech said (with pictures, lots of pictures).
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 30, 2013, 01:17:25 PM
Yes I'd like to see that, too.

Just as an explanation of what I've done so far and why, I'm going to quote here from C.W. Ammen's "The Complete Handbook of Sand Casting" 1979:

"Melting cast iron in a crucible is actually so simple, it's a wonder more people don't do it.

"The usual practice incorporates clay and graphite crucibles. The iron, free from contaminants (anything other than iron) is broken into small pieces, the size of walnuts or a little larger. The crucible is charged (filled) with alternate layers of charcoal and iron, to which is added about two handfuls of soda ash. The soda ash can be placed either below or on top of the charge. After you have gone this far with this process, cover the crucible with an old crucible bottom and place a circular piece of corrugated cardboard between the base and support block to prevent the crucible from sticking. Start the furnace with the flame set to slightly oxidizing.. Gray iron melts at about 2327 degrees Fahrenheit. Although this figure may look large compared to that for the melting point of brass, you will find that the layers of charcoal promote rapid melting that can be done in not much more than the time it takes for brass. With a little practice you can produce high grade iron castings. (Old cast-iron steam radiators can be easily broken up to produce an excellent source of very fluid iron.)"

My first casting, and the most successful so far, followed this procedure exactly - including making a clay cover for the recommended "clay/graphite" crucible and incorporating charcoal, and soda ash, as well as the radiator source metal. Unfortunately the soda ash seemed to soften the crucible after only a couple of melts.

I own and have read probably 10 books on casting, including the extensive online US naval casting manual. Almost all provide alternate and even opposing views on all aspects of casting, including casting flaws, sand recipes, etc.

It's clear to me that the truest line above is "With a little practice you can produce high grade iron castings."

A little practice....that's what's more commonly called experience. There are no absolute recipes for success. Only a process towards it, experience, where you learn and discover the special requirements of your own equipment and materials and your own capabilities.

Title: Re: Oil fired crucible furnace
Post by: tom osselton on July 31, 2013, 08:03:46 AM
 I know I haven't cast anything but I have a theory :  The pics that you posted both look similar, as for your pic of the flow of the metal I think it is the position of the riser. I believe that the metal travels along the path you say but when they meet some goes into the riser (at a right angle) and some of it will go towards the center, the left side will circle clockwise and the right counterclockwise putting the defects basicaly in the same spot on both castings. You might want to try it with one gate and riser moving the riser to a corner so the flow is funneled into it. If you still want to use two gates you could have a main at the farthest point and another not as thick so it feeds at a slower rate. Like you said there are a lot of casting books but I can't  remember any that talked about the placement of sprue's or risers or the hydrodynamics that take place. I'd be interested to get Ironman's thought on this.

Tom
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 31, 2013, 11:51:34 AM
Tom, my own understanding:

The main function of the riser is to feed metal to prevent shrink depressions or cavities. I haven't had a shrinkage problem since I started using one. But the riser does not reduce blow holes or slag inclusions.

Blow holes can be reduced by better sand permeability, lower sand moisture content, and venting.

Slag inclusions can be reduced by slagging the melt and gating. The ideal there is to prevent slag from entering the mold in the first place. Though once it is in a mold, gating can help trap it.

Excess or difficult slag in the melt can prevent complete slagging before the pour. Difficult slag can come from the metal used, excessively oxidizing furnace atmosphere, slow melting, and, in my opinion, the crucible materials.

Slag can be made easier to remove by fluxing the melt. But flux can deteriorate crucibles.

So, all of the above need to be juggled in relation to the materials and furnace you have, to give you the quality of casting you expect.

Not every casting purpose requires a perfectly cast part. I've seen casting flaws in commercial products, and in other individuals' work. A machining allowance is, in a sense, a way of dealing with the surface flaws and draft which are a necessary result of sand casting.

But in trying to learn how to cast iron, I want to try to achieve a no flaw casting, so I at least know the subject better. Or as well as I can.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 31, 2013, 03:05:30 PM
Today I decided to "use up" my last small crucible before going to the new A6 Salamander Super.

Instead of trying to pour the same pattern again, I decided to just make ingots. And to do that I would use my old broken up radiator material, rather than cleaner thicker iron.

And I decided to use flux, since i didn't care about the crucible. I would do two melts, one with oyster shell, in the form of the ground up powder they feed chickens. it is supposed to be calcium carbonate -- as is limestone or agricultural lime.

And for the second melt, I would go back to good old sodium carbonate (soda ash).

This would at least do something useful with the old crucible and convert the radiator scrap into clean metal, plus give me a comparison with the two fluxes.

Well actually, there was no cmparison. The oyster shell did little to liquify the slag -- it was still really bad -- black cottage cheese taking up half the melt, and sticking tightly to the crucible. In fact after the crucible cooled I could see a few places where it insulated itself in a chunk and hadn't even melted. I don't actually know what that stuff is made of -- could have concrete floor sweepings in it -- who knows. It's just grit for the hens.

But since it didn't all melt, and thinking I might not have enough furnace heat, I decided to increase the air pressure to the burner nozzle. This had been at 45 psi lately, and I upped it to 60 psi.

That really did seem to make a difference -- probably atomized the fuel better, because I noticed that I actually ended up using less throttle, even thought there was more heat and flame height. And the flame burned cleaner -- quite visibly better.

So, second trial with the sodium carbonate went MUCH better -- a faster melt by about 20% but the slag was totally different. I was a bit cautious with the soda ash flux because it's supposed to be much more destructive to crucibles -- I used about an ounce. I'd used 2 ounces of calcium carbonate earlier.

But what a difference -- the slag was easily scooped off in one piece to leave a pool of clean shiny metal in the pot. While I won't say it liquified the slag, it did compact it into a single "chewey" crust that I could scoop off with a spoon. It was also much lighter in weight (less contained iron).

All in all, just what I would have liked in a pour.

So, it looks like the radiator iron can be used, but it definitely needs a flux to slag well. And it probably should be poured into ingots before use to clean it up.

Next pour will be with the new crucible....
Title: Re: Oil fired crucible furnace
Post by: vtsteam on July 31, 2013, 04:32:40 PM
(http://www.vtsteam.com/OilFurnace/IronIngots.jpg)
Title: Re: Oil fired crucible furnace
Post by: tom osselton on July 31, 2013, 10:57:08 PM
Looks good!
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 01, 2013, 08:22:48 AM
snip..... Like you said there are a lot of casting books but I can't  remember any that talked about the placement of sprue's or risers or the hydrodynamics that take place.

Tom, I forgot to answer this part of your earlier question -- most foundry books do talk about risers -- Terry Aspin's are very good casting books in general. Fewer talk about sprue placement. However, there is a lot of hands on specific placements in any of the machine building books that Gingery wrote -- most have 20 castings or more to build and all show sprue and riser placements for each casting,with notes and instructions where needed. These are the most complete and accurate of this type of thing because it is very specific per pour, and is tested to work, rather than generalized theory.

For detailed general/theoretical/technical discussions of placement shapes and sizes of sprues, risers, and gates, the US Navy Foundry Manual (available online here: http://www.hnsa.org/doc/foundry/ ) and Steve Chastain's Metal Casting: A Sand Casting Manual for the Small Foundry Vol 2. both go into it.

As usual with foundry books, however, you will find disagreement and inconsistency, or just downright impractical information for a small home metal casting operations. Technical books provide suggestions, but practice must prove their usefulness in real life in specific cases with specific materials and specific furnaces.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 01, 2013, 01:04:25 PM
Here is a comparison of the slag scraped from the melt before pouring radiator metal when fluxed with, left, ground oyster shell (calcium carbonate), and right, soda ash (sodium carbonate).

Besides the roughness of the slag on the left, notice the white specks of unmelted shell. The right hand slag is glass-like and iridescent -- not metallic in color, and weighs less than the slag on the left. The slag on the left is only part of what was removed, while the slag on the right was the full amount, which scooped off in one swipe.


(http://www.vtsteam.com/OilFurnace/SlagComparison.jpg)
Title: Re: Oil fired crucible furnace
Post by: NeoTech on August 01, 2013, 03:04:28 PM
Seems like you have solved that little issue.. =)

FYI, you can break down a V8 motor block thats is already cracked by heating the cylinders and then take a sledgehammer to it... =)
In the winter around here anyway i imagine i could freeze crack the whole thing..  (started some experimentations of acuiring cast iron from engine blocks.)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 01, 2013, 04:08:03 PM
Neo, don't know yet. If it eats up a $75 crucible, then it isn't practical -- we'll see. First melt with the new crucible will be without flux and with thick metal to take it easy.

Watch out for flying metal when breaking up cast -- especially the hot stuff. I've had some fun encounters in the past. Face protection is a good idea. But yeah cold probably will make it easier -- you and I probably have similar winters. I have to work outdoors though, and I imagine some of that cast will get lost in the snow, only to reappear in the spring!

Today it rained so I did a little cold forging of the lift out tongs to fit them carefully to the new crucible. Then I rolled a steel strap and welded on some handles for a hand shank. This is the closing type rather than the ring shank I made last time. I've had two instances where the crucible slipped in the ring shank when pouring, and it's no fun!

If you think about the geometry of a tapered crucible you will realize that this is a possibility when a crucible is even tilted to horizontal. It may not slip out of the ring, but it can suddenly alter its position in the ring with a consequent redirection of the metal. Even the best fitting ring will soon be pretty approximate as a crucible ages and shows slag spills, etc.

Anyway, I saw a clamping ring type shank in Colin Peck's book, so I used that principle here, though with my usual favored re-bar, and a bent down end.

(http://www.vtsteam.com/OilFurnace/PouringShankNew.jpg)
Title: Re: Oil fired crucible furnace
Post by: ironman on August 02, 2013, 03:10:34 AM
Tom

A riser is always is put in the center/middle of a casting so it feeds better. when a thick section is in a corner and the rest of the casting is thinner then the riser has to be located there. Some castings may require many risers. Some cast irons don't need any risers because as the iron is freezing graphite comes out of the liquid and expands offsetting shrinkage.
Title: Re: Oil fired crucible furnace
Post by: tom osselton on August 02, 2013, 02:03:45 PM
Yes I know what you mean I was just pointing out what I saw in the pic how the two streams would meet and  would travel in a circular patern. It is all interesting and will give it a go soon with aluminum to start. I have a blower and beer keg I'm working on and went with the fiber insulation because that would be the best choice in our winters I think the others probably would crack upon heating, or I can use the kiln in the basement for some al.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 02, 2013, 03:21:38 PM
I couldn't put a riser on top in the center because of the cored channel down the middle. But the riser works as it is presently located because there have been no shrink depressions since I started using it -- about 5 castings ago.

On the other hand, maybe the riser could be used to trap slag inclusions if it were in the center on top. Maybe they would float up into it. Unfortunately the channel is there and a riser would defeat the whole purpose of coring it.

Thinking about this, it might be possible if I made a new pattern, with the channel on the bottom instead of the top. (Yes there is a top and a bottom because of the draft.) Then the flat surface would be on top, and the channel on the bottom. A riser could then be located on top.

That might work -- maybe I'll try it.

But it is side stepping the issue of "where is the slag coming from in the first place". I might want to solve that first.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 02, 2013, 03:54:00 PM
Cast this morning, with the new crucible, and just opened the mold. Not perfect, but a visible improvement. defects are fewer and smaller.

The crucible exterior looks shiny and new, the interior has some slag I couldn't scrape out, but i believe it probably has done well, too. It's too hot still to look at closely, and I'm letting it cool slowly in the furnace.

The slag was relatively compact and manageable -- not as nice as with flux added -- but much better than it had been with the old crucibles.

Total furnace run time was 1 hour 5 minutes. Actual melting time was 45 minutes, as metal wasn't added until 20 minutes after the furnace was lit.

Definite progress on all fronts. Photo of casting below:



(http://www.vtsteam.com/OilFurnace/OilFurnace17.jpg)
Title: Re: Oil fired crucible furnace
Post by: awemawson on August 02, 2013, 04:08:52 PM
Steve,

I used to bring the charge of iron and the furnace up to heat together, inverting an old crucible over the main one to allow more metal in the uncompacted state which would run into the lower crucible and avoid flames impacting and oxidising the melt thus forming more slag. Not sure that your furnace is tall enough for this approach though?

Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 02, 2013, 06:36:27 PM
Andrew, it isn't tall enough, although i did earlier make a top for the crucible out of fireclay and sand, and that actually worked. In fact it stayed perfectly intact through a couple of melts unlike those old crucibles! Had me thinking maybe I ought to make my own.

But the top wouldn't allow additional metal -- just what would fit.

This time I figured I'd follow Morgan's recommendations -- they say to bring it slowly to a red heat before adding metal, then give it full blast.

I've tried that method twice now. And the odd thing about it is, I get a faster melt that way than I do filling the crucible from the start. And use less fuel.  :scratch:

I'm thinking that my furnace has lots of thermal mass to heat up -- unlike one with fiber blanket types. The walls are 4" thick so it still insulates well. But it takes awhile to get up to temp. Not lots of heat necessarily . Just time. In fact lots of heat probably just blows up the stack until things warm up.

Same thing for the crucible. Takes time. But takes less time if nothing is in it. Then when everybody is hot enough and radiating red heat, add metal and pour on the coals.

I dunno. Somethings happening to make it faster.  I guess that's as good a theory as any!
Title: Re: Oil fired crucible furnace
Post by: NeoTech on August 03, 2013, 10:53:43 AM
been thinking of making crucibles as well.. my mom work as a professionaly pottery..maker.. *what the hell its called* Ceramics.. person..

Anyway, she has a machine to make clay.. And then i found this .. man.. And his crucible making endeavours. =)

Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 03, 2013, 11:10:51 AM
I've seen that one before Neotech. It seems like a lot of work considering he is just using it for aluminum. A steel crucible with sand and fireclay lining would work as well, and most, including me, just use iron or steel alone.

Now if that crucible could be used for iron, that would be different! I don't like his tall tubular shape much, and I don't have a pottery wheel to make a bilge style crucible, so I would want to coil form it. But maybe it would be possible. He does use graphite in the mix, which seems to indicate he was thinking about the higher temp metals. Just confusing that he eventually just pours aluminum with it.

Vince Gingery wrote a book on crucible making (also using a press) which I have. But I don't believe he uses graphite, and also he says that it isn't for melting iron.

I believe that the only reason I'd ever venture into ceramics to build a crucible would be for iron. Everything else can be melted in clay lined iron or steel, which are much simpler -- and safer.

An iron melting cupola furnace has a very great advantage in that it doesn't require a crucible. Just a clay lined ladle. It also has a great melt rate. The only problem for me is that (so far) it requires coke, which I can't get.

I may try charcoal again in a bit -- with new ideas.....
Title: Re: Oil fired crucible furnace
Post by: NeoTech on August 03, 2013, 11:20:21 AM
Pottery wheel is easy to make.. but learning to do pottery.. is not easy. ;)

But basicly a pottery wheel has a aluminium cast small disc mounted on a rod supported by a upper and lower bearing the lower wheel can be kick wheel or put a motor there.. The kickwheel is actually simpler to use and can be motorised by a long rope more or less..

I think that mix he uses there with borosilicate glass, and graphite is for alot higher temperatures then he is doing in the end of the video.. which feels more like a "look it works" kinda thing.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 03, 2013, 11:38:39 AM
I have a crucible making thread already, so let's move there....


Oooops, it's actually about ladles, but I'll continue there.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 05, 2013, 02:47:09 PM
I decided to make a new pattern, somewhat larger, that incorporated another part I needed. Also this allowed me to reverse the draft so I could place a riser on the non-channeled side.

I decided to go with my latest method of melting (specific to my particular furnace and furnace lining) of using a low throttle to ramp the furnace and crucible up to red heat before adding iron. I then added 4 pounds of metal -- I needed 12 lbs for this pour, and planned two more additions. This was my largest melt -- the last had been 9 pounds. I also gave it full blast, but just slightly leaner flame than I had been using. Still very slightly rich.

I didn't bother timing the initial heat, but timed from the first addition of metal. It melted the first 4 pounds in 20 minutes, the second 4 pounds in 17 minutes,  And the last in 15 minutes. I gave it 15 minutes of extra heat to make sure, and the poker test verified it was hot metal.

This is how my own furnace seems to work best.

I got a perfect pour. No flaws. Absolutely clean. I think I now understand my furnace, my metal, my sand, my particular pattern making requirements, and my own molding requirements. And I think I can extend that to future castings. It's been a long road for me, but each time it didn't work there was an improvement of some sort or a realization. I had to see what didn't work, and learn what worked best with what I specifically have. I think I know that now. Thanks to the many who were supportive, and I'm sure I will learn a lot more as I continue to cast IRON!

I'm psyched!!!!  :ddb: :ddb: :ddb: :ddb: :ddb: :ddb:  :nrocks:


(http://www.vtsteam.com/OilFurnace/OilFurnace18.jpg)
Title: Re: Oil fired crucible furnace
Post by: Pete W. on August 05, 2013, 02:56:11 PM
Hi there, VT,

Tenacity tells!   :clap:   :clap:   :clap:   :clap:   :clap:   :clap: 

You must be very pleased, and so you should be.  Well done.
Title: Re: Oil fired crucible furnace
Post by: awemawson on August 05, 2013, 03:09:46 PM
Excellent Steve. Get you teeth into the ankle of a  problem and hang on in there until it gives in  :thumbup: :thumbup: :thumbup: :thumbup:
Title: Re: Oil fired crucible furnace
Post by: NeoTech on August 05, 2013, 03:15:05 PM
That looks frickin awsome!  :headbang: :headbang: :headbang:
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 05, 2013, 04:02:18 PM
Thank you guys!!!!!!!!!!  :bow: :bow: :bow: :bow: :bow:

Just cleaned it with wire brush and ground off the flash:


(http://www.vtsteam.com/OilFurnace/OilFurnace19.jpg)
Title: Re: Oil fired crucible furnace
Post by: doubleboost on August 05, 2013, 04:07:17 PM
You should be well happy with that  :bow: :bow: :bow: :bow: :bow: :thumbup: :thumbup: :thumbup: :thumbup: :thumbup:
John
Title: Re: Oil fired crucible furnace
Post by: dsquire on August 05, 2013, 04:14:46 PM
Steve

Congratulations. Your hard work is starting to pay off. That definitely looks like a keeper to me.  :D :D

Cheers  :beer:

Don
Title: Re: Oil fired crucible furnace
Post by: tekfab on August 05, 2013, 04:41:09 PM
Now if you try casting the other part "upside down" you get a surprise.    :coffee:

Mike
Title: Re: Oil fired crucible furnace
Post by: awemawson on August 05, 2013, 04:45:20 PM
OK Steve, confess, which professional foundry did you get to do that  :clap:
Title: Re: Oil fired crucible furnace
Post by: RussellT on August 05, 2013, 05:14:20 PM
Great work.  Persistence pays off.

 :bow: :clap: :bow: :clap: :bow: :clap: :bow: :clap:

Russell
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 05, 2013, 09:28:31 PM
Wow, thank you all! That just feels great!   :bow: :bow: :bow: :bow:  :beer:

 :mmr:
Title: Re: Oil fired crucible furnace
Post by: ironman on August 06, 2013, 08:30:11 PM
That looks really great.

What did you do to make this one a success?
Title: Re: Oil fired crucible furnace
Post by: tom osselton on August 06, 2013, 09:05:24 PM
Well done definetly a keeper!!  :beer:
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 06, 2013, 09:20:28 PM
Tom, Ironman, thank you.  :bow:

Ironman, to answer your question:

1.) I made a new pattern, reversing the draft, so I could place a riser on the non-channeled side. I could not put a riser on the old pattern because it would mess up the channel. Previously the riser was beside the pattern -- the only place it could be with the pattern draft the way it was oriented.

By altering the draft orientation and placing the riser on top of the pattern, any buoyant slag could go up the riser rather than get trapped in the channel section of the casting. Also the channel section now faced downwards, so it would naturally be protected.

While these changes would help deal with any slag in the mold, I have been on a concerted effort to eliminate slag coming into it in the first place. So:

2.) I altered my melt method to add iron later in the furnace cycle -- after the crucible and furnace walls had reached a red heat. My furnace has more mass than a blanket insulation furnace, so it has a longer warm up period. There is no reason to put iron in during this period and allow it to oxidize. I started with an empty crucible.

And to save fuel, there is no reason to run the warm-up at full throttle. 1/4 throttle works fine to bring the furnace walls and crucible to red heat. Time is more important than burner temperature for this. Once it is at red heat, metal can be added, and the furnace run at full throttle.  At this point the furnace will melt at an average rate of 1 pound per 5 minutes.  Gradually accelerating to 1 pound per 3 minutes.

3.) I gave it a longer post melt heating period to try to get the pouring temperature as high as I had patience for. That was about 15 minutes after all the iron was melted. I wanted any slag to come to the top and amalgamate, and for the casting to be fluid enough to give any slag time to come up the riser.

4.) I altered the mix ratio of the flame -- I had been running slightly richer on previous melts -- I went almost neutral -- ie. a couple almost imperceptible whisps of black smoke from the lid edges (not the glory hole). I believe this created hotter furnace temps.

5.) I increased the pressure of the burner to 60 PSI. This burner is an atomizing burner. There are two air sources, the blower (a vacuum cleaner) and the atomizing air nozzle fed by a compressor. That last one is what was increased to 60 PSI. This fed more fuel at a smaller droplet size. The flame was naturally bigger.

6.) The new better quality larger capacity crucible did not add slag to the melt, and its larger size (with more metal) retained heat better when bringing to the pour.

In other words, a lot of variables were adjusted. Apparently for the positive.



Title: Re: Oil fired crucible furnace
Post by: Meldonmech on August 07, 2013, 04:20:18 AM
Hi VT,
           Well you got there in the end, and what a nice result.

                                           Well done   David
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 07, 2013, 07:36:59 AM
Thanks so much David!  :beer: :beer: :beer:

I'm going to cast some new flasks in aluminum today, iron is tough on wood ones.  :dremel:

Well, I'll need a new wooden flask to cast the aluminum ones, so I guess I'll be making that, too!  :)
Title: Re: Oil fired crucible furnace
Post by: Mayhem on August 07, 2013, 07:45:49 AM
Excellent job there Steve - I'm glad you stuck with it and took us along for the ride.
Title: Re: Oil fired crucible furnace
Post by: tekfab on August 07, 2013, 08:33:48 AM
Well done Steve, for my own reference what crucible have you ended up using ? I'm about to build my own furnace and i may as well utilise your experience. I'll be starting of with Aluminium but would like to progress to iron so what would you recommend.

Mike
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 07, 2013, 09:20:09 AM
Thanks tekfab!  :beer:

I'm hardly in a position to recommend crucibles since my experience before was poor, and my current crucible has only been used for 3 iron melts. So I can't say long term if it will hold up for me, under my conditions of use.

But it looks good so far and is far better than the "3000 degree" (advertised) clay-graphite crucibles I started with, so I have hope for it.

Personally, I would try to get the same brand crucible that Ironman uses, which is Vesuvius. And I believe more specifically it is the "Diamond" hard variety -- though not sure about that exact term.

The crucible I have now is an A6 MorganMM Salamander Super and the label said A&0130H0165&-SUX4-3GN-IL, and made in INDIA. It was close to $75 delivered.

But whether that is good or bad, I don't know yet. Let's get 20 more castings under our belt and see how it does!

But for casting aluminum, I would never use an expensive crucible. I would just continue to use a cast iron plumbers pot, or a made up one from steel, lined with a little fireclay and sand mix.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 07, 2013, 10:05:00 AM
Mayhem, thanks, man!  :beer: I may be building a forge like you did soon. How is your lathe doing?
Title: Re: Oil fired crucible furnace
Post by: awemawson on August 07, 2013, 12:04:58 PM
I've always been concerned with iron dissolving into molten aluminium when using a steel or iron crucible. So I always used a clay/graphite one. Even small quantities of iron in aluminium make significant alterations to it's mechanical properties. Though I am aware very many home casters do use steel.


http://www.aomevents.com/conferences/afi/papers/Taylor.pdf
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 07, 2013, 01:31:40 PM
Andrew, good to mention.  The cheapskate high quality alternative to both schools of thought is a clay lining in a homemade steel pot.

I suppose the ingots could be poured in a greensand mold instead of a steel one -- but the last seems almost universal on the casting forums.
Title: Re: Oil fired crucible furnace
Post by: awemawson on August 07, 2013, 02:05:16 PM
I suppose it really depends on what you are doing with the castings. If they are only ornamental, or so generously proportioned that strength isn't an issue it could be said that it doesn't matter. But if you want to be able to heat treat the casting and get particular machining qualities especially, then iron anywhere near it is a no no. As that article says, once the iron is in the aluminium effectively it's staying there for good!

I always avoided use  of steel crucible, and used a dip wash coat on the various tools I used such as stirrers and skimmers. Problem is that the over metal that is poured to ingot may be used for something more fussy than the current one, but you've already contaminated your stock
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 07, 2013, 03:04:55 PM
I'm really don't see myself doing that kind of thing with aluminum castings, Andrew, but if other people are, please don't follow my example!   :) 

I work with old pistons, bell housings, marine engine castings, old sprues and an occasional extrusions combined as melting stock, so heat treating this bastad mix probably wouldn't turn it into a silk purse! Those steel clips in the pistons don't guarantee iron-free aluminum either -- they were cast in place, so I'm sunk by GM and Ford from the start!

Spent the day making handle loose pieces for the pattern for the new flasks. And then making an even bigger wooden flask to make the flasks in. Kinda like a fish eating a smaller fish, eating a smaller fish, etc.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 12, 2013, 11:12:51 PM
Back to iron....I should update this thread. . .

I ended up building steel flasks rather than aluminum, though I did make an aluminum flask casting pattern in case I get a lot more aluminum some day. The construction of the simple steel flasks is located in a separate thread by that name. I also cast a new iron piece for my steam conversion in the new flasks and it went very well. I'm definitely liking the new gear. I also poured a second melt -- just some ingots made from scrap radiator material to clean the metal for future pours. I figured once the furnace was hot from the first pour, it made sense to do a little more melting.

So far the new crucible has held up very well. I haven't used any flux with it however. The last pour of ingots from radiator scrap does appear to have left some of the old pasty slag in the crucible -- I'm thinking of adding a little flux, cautiously, toward the end of the next pour to see whether I can liquify the pasty stuff, clean up the metal better and leave a cleaner crucible.
Title: Re: Oil fired crucible furnace
Post by: Meldonmech on August 13, 2013, 12:15:05 AM
Hi VT,
           That is a an amazing result, and justifies all your hard work and determination

                                         Well Done    Cheers David
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 13, 2013, 09:11:22 AM
Thanks David!  :beer:
Title: Re: Oil fired crucible furnace
Post by: DMIOM on August 14, 2013, 04:52:37 AM
Steve,

I've just seen the photo below of your new carbide mill cleaning up one of your castings. Not only is the mill working well but very impressed how clean & homogeneous the casting looks.

Dave  :clap: :thumbup: :clap: :thumbup: :clap: :thumbup: :clap:

Does a nice job, too. This was what it did to a back yard casting.


(http://www.vtsteam.com/OilFurnace/Flymill2.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 14, 2013, 07:26:19 PM
A pretty sight -- an evening pour beginning to cool.


(http://www.vtsteam.com/OilFurnace/OilFurnace20.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 14, 2013, 07:32:16 PM
Thank you Dave! :bow: :beer:

When I think about it, it is kind of amazing to take some old rusty radiators and some waste oil and have it turn into something that looks like that.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 15, 2013, 04:17:00 PM
This is yesterday's casting. I decided to try pure (rusty) radiator scrap -- not refined ingots, sprues, prior castings or thicker iron. I did the opposite of what I've been doing recently, and added the metal to the crucible before bringing to a red heat, added charcoal to cover, and added a tablespoon of sodium carbonate (fingers crossed the crucible wouldn't get messed up).

Then I continuously added more Iron as the stuff in the crucible melted. Finally just before the pour, I added about a tablespoon more of the sodium carbonate, stirred and waited another ten minutes. Finally lifted the crucible set it in the shank, scraped the slag off quickly and poured.

Looks as good as the last one -- the little spot is just where a vent wire hit the pattern, but not a structural flaw. This face will be machined and the bore widened.

(http://www.vtsteam.com/OilFurnace/OilFurnace21.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 15, 2013, 04:20:35 PM
Here is the top of the casting. No shrink depression or slag inclusions. Just goes to show you don't need pristine metal to get a pristine casting.


(http://www.vtsteam.com/OilFurnace/OilFurnace22.jpg)
Title: Re: Oil fired crucible furnace
Post by: NeoTech on August 15, 2013, 04:31:13 PM
Sweet looking casting.. You seem to have boiled out all the impurities of the process...  =)
Title: Re: Oil fired crucible furnace
Post by: awemawson on August 15, 2013, 04:41:08 PM
Well done Steve, it looks as though you've cracked this process and are getting consistent results. It must be very satisfying
Title: Re: Oil fired crucible furnace
Post by: tom osselton on August 15, 2013, 08:08:22 PM
I'm glad to see it all coming together,  can't wait to try but the basics first (alum / brass).
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 15, 2013, 10:17:21 PM
Thanks Neo, Andrew, Tom!!

Just realized I forgot to black the top of the mold, and that's why the sand cast looks rougher above. Did the bottom though. So much to remember each time.

Tom how close are you to your first melt?

It's really memorable when you do. Pretty amazing when you put the crucible back in the furnace with everything shut down and quiet, the mold filled, and you take off mask and gloves, and realize, "I just poured metal!"

Then the looooooong wait until it cools. One hour seems like ten.
Title: Re: Oil fired crucible furnace
Post by: tom osselton on August 16, 2013, 03:19:51 AM
I am day's away I had to pick up some more of the fiber blanket so now just have to give it a zircon coating on the inside then it will be ready. With the blower I am going to shim it 1/8 inch to center it better in the housing I have tryed the blower with a dimmer switch so that controls the blast good lastly I will makeshift a mount to hold it in position till a final frame is made.
Tom

Note to self pick up sand  :D
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 16, 2013, 09:09:07 AM
Tom, would you consider documenting your build in a thread with photos? I and I'm sure others would enjoy seeing it.
Title: Re: Oil fired crucible furnace
Post by: Mayhem on August 16, 2013, 10:40:04 AM
Steve - well done!

Tom - I'd like to see a write up and pics.
Title: Re: Oil fired crucible furnace
Post by: tom osselton on August 16, 2013, 12:01:01 PM
Well I can probably do something like that mind you it is basicaly the same as Ironmans small furnace build  http://madmodder.net/index.php/topic,7802.0.html  so far only one screwup   :palm:  I had the lid marked in two place 2" apart and my son cut the wrong one with the plasma not his fault though I should have said that one.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 16, 2013, 07:16:32 PM
I'd like to see it, too! And I bet Ironman would be happy to see your new furnace to his design as well.

Title: Re: Oil fired crucible furnace
Post by: ironman on August 16, 2013, 08:18:02 PM
Yes I would like to see it.

Was your zircon paint expensive? Here in Australia it is.
Title: Re: Oil fired crucible furnace
Post by: awemawson on August 19, 2013, 05:03:02 PM
Steve, I came across these two .pdf files while looking for pictures of my induction furnace - I think that they will interest you perhaps:


Ironman - yes the Zircon was pricey but I didn't use much
Title: Re: Oil fired crucible furnace
Post by: tom osselton on August 19, 2013, 06:51:31 PM
Ironman
The zircon is itc 100 that I used it is definetly pricy $100.00 for one pint. It looks different than the paint you used it was quite watery and seemed like it left a sandy substance in the bottom of the tin not too much though. I brushed it into the base joint. I was thinking maybe it reached it's saturation point. The fiberwool was $12.00  and change per foot. It is done though just sitting on the floor I have not made a frame yet to lift the lid but that's what sticks are for!  I fired it up this afternoon and it ran great even though I had to use a smaller pipe 1"  inside dia easy change when I find some so no worries I am a happy camper  :ddb:  So thanks for posting your video (s) I always learn something.  :D
Ps

 :worthless:
Coming soon
Title: Re: Oil fired crucible furnace
Post by: tom osselton on August 21, 2013, 11:27:56 AM
Here it is if you haven't seen it in the project''s thread.

http://madmodder.net/index.php/topic,8920.0.html
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 25, 2013, 03:52:14 PM
I've been away on holiday with the family, so apologies for late responses. Thanks Andrew -- those look interesting -- looking forward to giving them a read.  :dremel:

Tom great to see your furnace construction -- looking forward to following your thread!  :clap:

I was thinking of casting today -- first day back -- but decided to do something instead that I've wanted to do for awhile. Basically set up the wood lathe and make some loose pieces for riser pattern, sprue plug, sprue basin pattern, and a runner pattern.

These will save me a lot of time in cutting these in the sand and then cleaning and tamping the loose sand. These are somewhat similar to the permanent pouring system patterns sometimes seen on match plates. The difference is, these will all be loose pieces -- intended for single piece castings without a mounting plate.

The sprue plug is tapered -- I'd previously achieved that by rapping the top of a straight sprue dowel to form the taper before removing the dowel. The bottom of the plug has a brass pin to fit in a hole in the the sprue basin pattern. That will help keep it in position during ramming.

The riser pattern replaces a piece of 1-1/2" OD pipe I had used on the last few castings -- the new pattern has a rounded bottom and is not hollow as the pipe was. The rounded bottom should reduce loose sand after pulling the riser as well as reduce surface area to keep the metal in the riser hot longer.

The sprue basin has a hole to mate with the sprue. I won't have to dig out a basin any more, and again, loose sand will be less of a problem -- I won't have to smooth it down, and the basin will be pre-formed.

The runner has a taper at the end to serve as a slag trap. Again -- a nice pre-formed channel with less cleanup required.

I can see making a few more of these kinds of mold parts to put them together like "TinkerToys" to fit various situations.


(http://www.vtsteam.com/OilFurnace/LoosePieces.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 25, 2013, 03:54:03 PM
This is more or less how they might look assembled with a pattern for a pour:


(http://www.vtsteam.com/OilFurnace/LoosePieces2.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on August 26, 2013, 08:03:04 AM
Finished.


(http://www.vtsteam.com/OilFurnace/LoosePieces3.jpg)
Title: Re: Oil fired crucible furnace
Post by: ironman on September 17, 2013, 09:20:23 PM
Photos of crucibles
Title: Re: Oil fired crucible furnace
Post by: dsquire on September 17, 2013, 10:01:20 PM
ironman

I have edited your post to remove the duplicate photo's for you.  :D

Cheers  :beer:

Don


Title: Re: Oil fired crucible furnace
Post by: ironman on September 19, 2013, 12:20:50 AM
Thank you for that.
Title: Re: Oil fired crucible furnace
Post by: stvy on September 26, 2013, 01:58:26 PM
Steve,

Just wanted to thank you for this thread. I have been following it since it started and because you shared your failures on the way to your final well earned success I feel inspired to one day try some casting at home. Its a while off for me, too much DIY at home yet. But one day.....

Thanks,
Steve
Title: Re: Oil fired crucible furnace
Post by: vtsteam on September 26, 2013, 04:24:20 PM
Well thank you Steve in return!  :beer: I hope you will share your progress with a furnace of your own when the time comes, too. It's great to see people master this stuff. I think it is always going to be a little different for everybody, because materials, burners, fuels, shapes, and sizes are always going to be different. Each will present a unique set of problems and requirements, and it will probably take a while to figure out how to get the best out of each one.

I hope to cast at least one more iron part I need before the snows hit, and I'll put that here.

I'm not sure of my ability to cast during the winter in Vermont. Maybe I can create an outside snow free space nearby, along with re-organizing my workshop. I also do wonder what the cold will do to my ability to reach iron melting temps. It will probably require pre-heating of the blast. I have done aluminum before in winter with a simple charcoal furnace, so I'm sure that at least is possible.

An interesting point -- heated blast opens possibility to experiment with the furnace as a cupola one more time using anthracite coal as a fuel. From what I've read about historical blast furnace practice, anthracite would require a heated blast to be successful. I have some anthracite coal, and it is readily available here, so very tempting to try.

Anyway, this thread may not be at an end yet. :dremel: Thanks again for your thanks!   :nrocks:
Title: Re: Oil fired crucible furnace
Post by: mattinker on September 26, 2013, 04:30:21 PM
I'm not sure of my ability to cast during the winter in Vermont. Maybe I can create an outside snow free space nearby, along with re-organizing my workshop. I also do wonder what the cold will do to my ability to reach iron melting temps. It will probably require pre-heating of the blast. I have done aluminum before in winter with a simple charcoal furnace, so I'm sure that at least is possible.

I doubt that the 40°C difference in temperature is going to make a lot of difference in comparison with the temperature needed to melt and pour cast iron!

Good luck! Regards, Matthew
Title: Re: Oil fired crucible furnace
Post by: unc1esteve on November 02, 2013, 11:45:37 PM
Vtsteam,
I have read your casting posts several times.
Any more progress?
I use to carve profiles of my grandchildren in wood
and have them cast in brass, 9" x 9" x 3/4".
I want to do several more of these but the foundry
I dealt with has long closed.
I would like to cast my own carvings.
Just getting started.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on November 03, 2013, 05:41:13 PM
Hi unclesteve. I haven't cast since I last wrote here -- I started on a major moving and cleanup of my "shop". It's now in fairly good shape. I have moved my furnace down the hill to be near the shop, and have kinda been entertaining the idea of trapping heat from it to heat the shop. Not too attached to that idea, but still holding it as a possibility.

Meanwhile have been cutting trees and splitting wood to prepare for winter. Also been building a small foam RC airplane in the evenings.

I'm sure you can build a furnace to melt brass, and would be happy to help if I can. Brass melts at a lower temperature than iron, so a furnace and fuel requirements are easier. I've melted brass with store bought charcoal briquets in a regular Gingery charcoal furnace. Of course you can use any other fuel as well.

Brass does present its own problems -- overheating burns the zinc in it -- and there are some casting differences -- but these are all pretty well covered in the available info. Temperature control is important.

But I think it is very do-able, if you are interested.
Title: Re: Oil fired crucible furnace
Post by: unc1esteve on November 04, 2013, 04:34:03 PM
Vtsteam,
Have you seen this burner?
Comments.

     


Title: Re: Oil fired crucible furnace
Post by: unc1esteve on November 04, 2013, 07:00:34 PM
I just made this burner.
I used 2" outer tube.
I used 1/4"  pipe for the oil feed with a
cap drilled similar to a shower head.
Tested it with water, works great but
I have no experience with oil burners.
I will continue on tomorrow, right now it is
time for a beer.  Anyone else like
Budweiser & Clamato?
Title: Re: Oil fired crucible furnace
Post by: AdeV on November 04, 2013, 08:25:23 PM
Are there any nice'n'simple plans for a high-output oil burner out there anywhere? I see lots of these things on Youtube & the like, but rarely a set of plans or easy to follow instructions...

I've acquired a barrel full of old motor engine oil, I was planning to centrifuge it and use it as fuel for the old Lister CS engine, but with winter approaching & not having started on the centrifuge yet, I wondered if I couldn't make an oil-burning stove to help keep me warm while I slave over a cold Jag engine...

Fortunately, my dockside location means I'm not in a smoke-free zone, and I could (in theory at least) put the burner unit outside & use a heat-exchanger to extract the heat without having to vent the fumes.

(PS: Sorry for the thread hijack, just seemed that anyone who was interested in oil burners are probably tagging along here.... pls feel free to reply via PM rather than pollute this thread - ESPECIALLY if you are warning me about fumes, the legality of burning old motor oil, etc.)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on November 04, 2013, 10:40:55 PM
Vtsteam,
Have you seen this burner?
Comments.

Hi unc1esteve,

1.) I believe what he melted was pot metal, which you can do over even a wood fire -- considerably lower melting point than even aluminum. The door handles he melted were, I believe brass plated over the pot metal. They are cheap and widely available.

2.) oil is overkill for that purpose -- though it can be done. But charcoal briquets would have worked as well and been less dangerous than his particular setup.

3.) The oil delivery pipe was huge, and plastic, and the gate valve oversized and difficult to control. 1/4" copper pipe with a needle valve would have been more appropriate.

4.) No shutoff valve at the oil reservoir. His control valve is his shutoff valve. A fire in this area would prevent interrupting the flow, which is gravity feed instead of siphon.

5.) Oil reservoir located too close to burner.

6.) Furnace looks to be cement -- inadequate for brass melting temps. Okay maybe for pot metal.

7.) water and waste motor oil have very different viscosity, so something that atomizes water may not do well with that kind of oil -- also dependent on temperature. Diesel fuel is more like water in viscosity, if a burner does not work well for waste oil.

The style of burner is standard blown oil pipe. Ironman was one of the earliest users I'm aware of to develop this for small furnaces like ours. Lionel of backyard metalcasting /alloyavenue was a much later popularizer. WC Amen in his book shows earlier incarnations. Steve Chastain gives good engineering info on flares for oil burning, etc, but I think Ironman's is by far the simplest and best developed of these. His pressurizes the oil line, I believe.

The type of burner I use (Kwiky) is also requires a source of pressure, not just a blower. The difference is that the oil is atomized by a air jet -- like a spray gun -- before being mixed with the blower air. I have never tried any other burner so I can't fairly compare mine with any other. It does work, though, and melts iron.

I would like to see the above list of problems corrected by anyone contemplating an oil burner. I don't think it is hard to accomplish a safer system than the one shown, at minimal expense. The most expensive part for doing brass work will probably be the furnace itself, not the burner. Inexpensive hi temp refractories are a challenge to find nowadays.  I happened to have firebrick on hand, but also needed fireclay, and good refractory sand. A lot of our local sand has shale and other sedimentary rock in it so isn't very refractory.


Title: Re: Oil fired crucible furnace
Post by: vtsteam on November 04, 2013, 10:59:57 PM
Are there any nice'n'simple plans for a high-output oil burner out there anywhere? I see lots of these things on Youtube & the like, but rarely a set of plans or easy to follow instructions...

Adev, here's an oldie that I've always like the looks of:

http://www.motherearthnews.com/renewable-energy/free-heat-zmaz70sozgoe.aspx
Title: Re: Oil fired crucible furnace
Post by: vtsteam on November 04, 2013, 11:19:26 PM
unc1steve -- a few more thoughts about that video:

He wasn't prepared with an ingot mold to pour the remainder of his metal into after the mold pour.

His crucible was very tall for its diameter, and so therefore difficult to pour from.

He was pouring what looked like a lost foam pattern in loose sand, not a conventional removable pattern (like your wooden plaque) in a greensand filled flask. That's quite a different process.

He seemed like a person who had not done any reading outside of some internet or youtube dabbling. I strongly suggest that anyone contemplating casting read David Gingery's furnace book(s) and or Terry Aspin's books. Reading both will give a good background in all aspects of molding and casting in an easy to read format. They are all inexpensive paperbacks.
Title: Re: Oil fired crucible furnace
Post by: unc1esteve on November 05, 2013, 11:40:19 AM

When I first saw the video I thought it
was a joke.  This guy could have easily
set himself on fire when the 'furnace'
flamed over.  His clothing looked like
the flammable synthetic type.
What I am interested in is the simplicity
of the burner.  Will continue on today.
Need to set up outside.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on November 19, 2020, 04:29:33 PM
I'm going to be firing this baby up for the first time in 7 years tomorrow.  :zap:
Title: Re: Oil fired crucible furnace
Post by: tom osselton on November 19, 2020, 07:17:01 PM
Should be fun our season is over I’m afraid.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on December 12, 2020, 10:47:57 PM
Both my furnaces could use re-lining after living unused for a couple years outdoors. I did fire the plaster-lined propane furnace and did a few brass and zinc castings with it last month (mentioned in my lathe thread) But brass is too difficult to cast now in December -- last two tries were cold shorts. Cause was mainly low outdoor temperatures leading to low furnace temperature (also due to a somewhat deteriorated lining) and low greensand temperatures. Well, that plus a poured part with thin sections. Zinc and aluminum are still fine to melt in it though.

I didn't get around to firing the oil fired iron furnace after all,  and ended up moving the foundries around and organizing my lean-to casting space. If I'm to cast brass in winter I'll need to do it in the oil furnace with it's much higher output burner, and thicker insulation. But also I want to cast iron again. So it also needs re-lining.

 This time I've decided to bite the bullet and re-line with ceramic insulating blanket and reflective coating ala Ironman. The spare money is available, and I am finally able to buy the esoteric hard coating (which was unavailable before -- at least to non-commercial buyers like me). This should (I hope) heat up faster, and be better insulation against the winter cold. We'll see. The blanket insulation arrived today, but the coating is delayed -- supposedly arriving later in the week.

The iron will be for castings for an engine I want to build. Really looking forward to seeing how this new lining works out! :dremel:
Title: Re: Oil fired crucible furnace
Post by: vtsteam on December 13, 2020, 05:21:02 PM
It was fairly warm out today for this time of year, so I made a start on the new lining for the oil fired iron furnace.  After scraping away the cap, of sand and fire clay mix, The top layer of fire bricks were revealed. They looked in very good condition.

(http://www.sredmond.com/vtsteam/OilFurnace/NewLining1.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on December 13, 2020, 05:26:36 PM
Removing the firebricks. The sand and clay mix was quite crumbly. The fire bricks were somewhat weakened by the iron melts, and had hairline cracks, but were all substantially intact, and would have probably lasted for many more years, from the looks of it. There was no surface degradation or disintegration at all.

(http://www.sredmond.com/vtsteam/OilFurnace/NewLining2.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on December 13, 2020, 05:28:43 PM
The firebricks actually had a vitrified surface buildup, rather than erosion. The white flecked area is the additional material, and the outer black shiny area is a glaze.

(http://www.sredmond.com/vtsteam/OilFurnace/NewLining3.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on December 13, 2020, 05:32:21 PM
I saved both the firebricks and the sand clay material to serve as a backing to the new mineral wool furnace insulation I will be adding. Here used firebricks have been used to build up the bottom of the furnace.

(http://www.sredmond.com/vtsteam/OilFurnace/NewLining4.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on December 13, 2020, 05:34:07 PM
Then some of the sifted crumbly sand and clay mortar has been used as infill.

(http://www.sredmond.com/vtsteam/OilFurnace/NewLining5.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on December 13, 2020, 05:44:54 PM
I sifted the rest of the old mortar and added a bucket of sand, and a bucket of fireclay. Mixed it up in a wheelbarrow with a hoe, gradually adding water until it was a nice stiff rammable mix.

Next, I took a quart of the mix and added more water to make a mud. This was smeared lightly all over the inside of the furnace shell to wet it and make the stiffer mortar stick better to the metal.

Then I pressed handfulls of the stiffer mortar/refractory into the furnace by hand, then pounding it into place with a piece of brick to get it to pack in place really well. I had just enough to apply an inch thick coating throughout the furnace shell by evening. I covered it over to finish tomorrow. Next will be molding into the bottom an Ironman style plinth, and then firing the shell to dry it out and prepare it for adding the mineral blanket insulation.

Here's what it looked like at the end of the day:

(http://www.sredmond.com/vtsteam/OilFurnace/NewLining6.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on December 14, 2020, 01:33:27 PM
Plinth added:

(http://www.sredmond.com/vtsteam/OilFurnace/NewLining7.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on December 14, 2020, 01:40:18 PM
And then I loaded the furnace up with split kindling to dry out and initial fire the refractory. It started to snow, though the temperature was just above freezing. Just a light snow. As I recall when it, the same thing happened when I went to fire the lining the first time I built this furnace -- as a cupola.  :loco:

(http://www.sredmond.com/vtsteam/OilFurnace/NewLining8.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on December 14, 2020, 01:43:43 PM
Baking under way. The kindling has burnt down into a 6" layer of hot embers, and I'm adding larger split wood to build that up higher:

(http://www.sredmond.com/vtsteam/OilFurnace/NewLining9.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on December 14, 2020, 02:28:25 PM
An hour later, I have about a 10" bed of glowing embers so far:

(http://www.sredmond.com/vtsteam/OilFurnace/NewLining10.jpg)

Title: Re: Oil fired crucible furnace
Post by: vtsteam on December 14, 2020, 02:33:18 PM
I decided this was enough baking for today and put a disk of 1/8" steel on top as a cover.

(http://www.sredmond.com/vtsteam/OilFurnace/NewLining11.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on December 14, 2020, 02:38:24 PM
Then blocked the tuyere opening, and sprinkled sand around the edge of the cover to seal it. This will convert all of the remaining brands in the furnace to charcoal, which I will have a use for when I start melting iron. The furnace should continue to bake for some time after.

Kind of curious experiment to see if powdered charcoal can substitute for plumbago in mold facings, and also whether (per Ironman video with plumbago and coke) it will convert steel to cast iron in a crucible.

(http://www.sredmond.com/vtsteam/OilFurnace/NewLining12.jpg)
Title: Re: Oil fired crucible furnace
Post by: vtsteam on December 14, 2020, 11:19:48 PM
hmmmm, just recalled that powdered charcoal probably won't work as a gas producing facing the way plumbago does, because it actually needs the impurities of coal to produce the momentary gassing that gives it the characteristic smooth finish. Charcoal is too pure carbon. I think I recall that from some conversation here -- somewhere -- maybe with ironman.....

But charcoal still might work in a steel conversion to cast iron experiment where pure carbon is wanted. And for plumbago substitution, I wonder if store bought charcoal briquets, powdered are impure enough to make the gas layer. Well, the only way to find out is to experiment!  :zap: :zap: :zap:


Title: Re: Oil fired crucible furnace
Post by: awemawson on December 15, 2020, 02:30:44 AM
I understand that finely powdered bituminous coal was added to the greensand in iron foundries to create this gas boundary layer to achieve a smooth casting.
Title: Re: Oil fired crucible furnace
Post by: vtsteam on December 15, 2020, 09:19:01 AM
Yes, Andrew, "seacoal".

I actually have some coal that I could powder, but it's anthracite, the common coal here. I don't think it will do the same thing as bituminous coal. It will not work in a cupola either, Or I should say, it has been used historically only when it was discovered that it absolutely required a heated blast to work, unlike coke. At one time I wanted to experiment to see if a hot blast would work with anthracite on my "sawed off" cupola (now the re-configured oil furnace) but never did. Charcoal was tried, but found to be not energy dense enough on the very small scale of my short and narrow cupola.
Title: Re: Oil fired crucible furnace
Post by: awemawson on December 15, 2020, 10:21:57 AM
I thought that 'Seacoal' was just washed up coal found on the beach originating where eroding cliffs have an exposed coal  seam. So in North East England it is found in significant quantities and used to be 'gleaned' to fuel cottage hearths.

So presumably if this is the case 'seacoal' can be any sort of coal, bituminous or not  :scratch:

(Another source of seacoal was from the myriad of colliers that plied up and down the East coast of England for centuries with coal from the Newcastle coal fields to London - any that went overboad due to accident or sinking could be washed up on the beach.)

 (Hence the expression 'taking coals to Newcastle' ie a pointless action)


 

Title: Re: Oil fired crucible furnace
Post by: vtsteam on December 15, 2020, 11:36:20 AM
Well, Andrew here's a lengthy reference from from American Foundryman, (January- February 1951), which we can take with a grain of seacoal, as usual re. foundry opinions and beliefs. Personally I wouldn't be surprised if seacoal got it's name from the floaties you mention, being an obvious relationship. Unless of course we really do have good old  "Dud" Dudley to thank for invention of the name :)
Quote
SEACOAL
History
The use of "coal dust" in molding sand originated in England. It was later introduced to the North American foundrymen as "sea­coal." One particular English or Welsh coal seam appeared to be the most satisfactory for foundry purposes and became the standard with which other coals were compared. Some authors believe that since the coal seam was near the Welsh coast and the mines were deep under the ground, extending under the sea, the term "seacoal" emphasized both its origin and its sea transportation to the U.S.A. However, the author has pursued the term "seacoal" for many years and believes that it originated from Lord Dudley's nomenclature in his patent applications in 1620. Lord Dudley applied for a patent in behalf of his son, "Dud" Dudley, for "melting oron ewre (ore) and of making the same into caste workes or barrs with "SEA-COLES" or "pit-coles" in furnaces with bellowes. " These "sea-coles" were described as being low in ash, sulphur and impurities for making the metal. The foundryman thought the same coal should be used in making sand molds. After a long and tiring search by the author, an old English file produced this answer after many years of investigation.

Characteristics
Seacoal (coal dust) is a highly volatile bituminous coal, ground to various degrees of fineness by pulverizing mills which is then graded by screening or by air classification methods. It is mixed and mulled with molding sand in various proportions. When it, or the products of its destructive distillation come into direct contact with molten iron, seacoal seems to improve the casting finish. Where molds are cast which contain seacoal, the sand peels more freely from the castings and the cleaning of the castings are more easily accomplished. Seacoal is one of the least expensive materials used in molding sand to give these results. Seacoal has been termed a "facing" in the foundry as a result of this property.

Effect
The effect of seacoal is so well known that it is accepted as a requirement in the pr3oduction of gray iron, ductile (nodular or S.G.) iron and malleable castings. The many advantages it offers have perpetuated its foundry use.

Factors
Several principal factors must be considered in the selection of seacoal (coal dust). The Volatile Combustible Matter, Fixed Carbon, Ash Content, Sulphur, and Moisture Content of the coal source measures its quality. Cost and reliability of the producer are the most important factors when purchasing the coal. Other factors to be considered in the selection of a specific grade of seacoal are: 1) The grain fineness of the base sand, coupled with its sand grain distribution. 2) Type and amount of bonding material used. 3) Permeability of the molding sand desired. 4) Weight of the casting to be produced. 5) Desired surface finish of the casting. 6) System of gating the pattern. 7) Metal pouring temperature and length of pouring time. 8) Density of the rammed sand mass around the casting. 9) Length of time the molds stand after pouring. 10) Type and temperature of the metal poured.

There are many additional variables to be considered, as seacoal affects most of the properties of the molding sand. Investigators claim that seacoal principally acts as a reducing agent, thus it prevents sand from adhering, or burning-on to the casting. Others dispute this claim.

Functions of Seacoal as a Sand Additive
Coal and coke in the molding sand burn, thus consuming the oxygen in the mold cavity to provide a reducing atmosphere as the mold is initially poured. Heat is absorbed by the mold from the molten metal. The temperature is increased to the "coking" temperature range of the seacoal present. During "coking," uncondensable reducing gases are produced, such as, hydrogen, methane, ethane, tars, light oils, and others which are distilled-off. The tar fraction plus the light oils burn and then contribute a carbon film or "sooting" action on the mold as a "bonus" factor, acting as an inhibiting agent. The volatile matter in seacoal consumes some of the oxygen immediately in the mold cavity as the metal ignites the seacoal upon entering the mold. This sooting prevents cutting action of the flowing metal against the molding sand and inhibits fusion of the silica sand grains. The gas content from the seacoal tends to form a cushion at the surface of the mold-metal interface, and the metal lies more evenly and quietly. Metal penetration is re­duced by the formation of the gas cushion which is aided by the coal's coking action. The gas pressure fills all the mold's voids between the sand grains giving the desired smooth casting surface but still permitting the venting of noxious gases. A certain amount of mold gas pressure is desired to help prevent metal penetration.

Sizing of The Seacoal
It is believed that seacoal should approximate the same size as the base sand grain in order to not alter the permeability of the mold­ing sand, but this is only an opinion. Seacoal on losing its volatile matter becomes coke, a fixed carbon. Some coals on coking swell to nearly three times their original volume, which may be detrimental to the surface of the castings. The coking theory has not been fully defined or proven, but the author believes it is a functioning part of the seacoal in helping to overcome apparent metal shrinkage. Some foundrymen claim that fines (those less than the U.S. No. 200 Standard Sieve) should be removed from commercial seacoal. It is the author's opinion that to narrow the range of particle sizes might exhibit a lag in the formation of the seacoal's gas cushion which it generates on heating. The reducing atmosphere which seacoal de­velops should form instantaneously, and removal of the fines may act as a disadvantage in certain cases. To cite an example, one cubic foot of coal in the solid state burns rather slowly when thrown into a flame; whereas, if it is ground to fine particle sizes, the coal would instantan­eously ignite, if subjected to the flame combustion. Time is a factor to be considered. Foundries find it detrimental to remove too many fines from foundry sands, as metal penetration and rough casting sur­faces can result. Since sand surfaces in the drag side of the casting is subjected to metal weight, the metal tends to force easier into the interstices of the sand grains, as the sand voids increase in size. Wash­ing and cutting of the metal may also result around the gates from too-open sands as they are more brittle. Open sands are also difficult to patch, or work. A carbon film is highly desirable in most cases to improve the finish of the castings.

Amounts Added
Too much seacoal increases the temper water demand due to increased surface area of the mixture. This causes rougher castings. Excess seacoal creates an evolution of gas which may cause blows, or porosity in the castings. Molding sand which is too rich in seacoal may promote defects called, "Map of Ireland," "Fins" or "Veining." Seacoal in moderate amounts is very beneficial, but as with the case of any other raw material used in the foundry, too much is detrimental. Seacoal depreciates hot compression strength at 1250°F. and 2000°F. (1010° C. and 1093° C.) rather effectively.

Grades
Seacoal is sold by grade designations namely: A, B, C, D, D-½. A and B grades are coarser and are used for molding heavier castings, C to D-½ grades are recommended for lighter to medium castings and for giving more detailed surface finish. Foundry facing suppliers have attempted to standardize on the best three commercial grades, namely: B, C, or D grades. "Dustless" seacoal (treated) and standard non-treated grades are available through most foundry supply houses. "Dustless" seacoal is a ground coal which has received a secondary treatment of oil or waxes to minimize dust when it is handled in the foundry.

Analyses and Screen Tests of Seacoal

Seacoal Analysis

The analyses and screen tests (Table No. 25) are approximate. They may vary at least 5% on each sieve depending upon the sup­pliers choice of sieves, and arrangement of sieving with the customer.

The Properties of Seacoal

 Properties of Seacoal

Summarizing
SEACOAL AFFECTS THE FOLLOWING PROPERTIES:
Green Compression Strength-Increases (generally, as long as the temper water doesn't increase).
Dry Compression Strength-Increases, as temper water increases. (6% by weight of seacoal increases dry compression strength approximately 35%, as temper water is also increased to give workability-moldability.)
Hot Compression Strength-Decreases, as seacoal furnishes a reducing mold cavity atmosphere.
Permeability-Generally decreases, due to the high "fines" content of the commercial grades of seacoal.
Flowability-Decreases, as the water demand increases in the molding mixture.
Temper Water Required-Increases by 10% of the weight of seacoal contained in the mixture. (Most of this water is held on the seacoal's surface, instead of being absorbed as in bonding agents. However, seacoal which is coked or formed into an ash sometimes acts as a sponge and absorbs an excessive amount of temper water. This build-up must be avoided by new clean sand additions, otherwise the molding sand becomes ashy and brittle.)
Mold Hardness-Increases, if the same effort or work force is applied. (Even though the mold hardness increases, the metal tends to lie more quietly in the mold when seacoal is present, than when it is not. Avoid high mold hardness on thin section castings which freeze rapidly.)
Deformation-Increases up to 6.5% by weight seacoal. The increase is dependent upon the seacoal's grain size. Temper water is gen­erally increased. If the water does not increase slightly, the mold­ing sands become brittle and break easily. Both wood flour and seacoal (coal dust) tend to make a smoother, softer and more moldable molding sand when used in regular amounts up to 4% to 5% seacoal, or 1% wood flour additions. Excessive amounts of seacoal and wood flour result in molding sands becoming low in resilience, they become brittle, they are difficult to handle and are poor in general practice.
Refractoriness and Sintering-Increases, which is possibly due to the carbon or carbon film developed during pouring of the metal.
Volume Changes in Molding Sand-Less expansion and contraction characteristics of the mold is beneficiated by the use of seacoal. Many of the common defects which are directly associated to the expansion and contraction of sand mixtures seem to disappear when seacoal is present. Seacoal is related to the clay content, moisture content, sand grain distribution and particle grain size. The beneficial limits of seacoal when added to the molding sand tend to vary under different working conditions.
Mold-Wall Movement-Effect of: ( 1) It is found that variations in mold materials influence metal solidification. Seacoal minimizes mold-wall movement. (2) As carbonaceous materials such as seacoal and wood flour are gradually increased in a molding mixture, within a definite limit, the piping of an iron riser of the casting decreases. (3) In comparison to western bentonite or fire clay, southern bentonite appears to lessen mold wall movement, but seacoal addi­tions improve all three bond mixtures. (4) In experiments, wood flour decreases the piping tendency of the metal, which is further aided by seacoal additions. (5) As the temper water of the molding sand mixtures increases, the piping tendency of the metal increases, but seacoal additions help to overcome excessive additions of temper water. (6) It appears that a dense, hard rammed mold results in less movement of the mold-metal interface and less seacoal is required. (7) Oil bonded core sands produce sound castings, but so does seacoal when added to green sand mixtures. Metal exudes slightly from the riser instead of piping when there is a lack of mold-wall movement. Sufficiently rammed molds in green sand act similarly. (8) Mixtures of molding sands and bonding agents are very complex. It is illogical to make definite comparisons between different mixtures. Each base mixture should be considered on an individual basis, but 5% by weight of seacoal in gray iron, ductile (nodular or S. G.) iron and/ or malleable iron castings helps to hold castings closer to pattern size and to have lesser mold-wall movement."

Title: Re: Oil fired crucible furnace
Post by: vtsteam on December 15, 2020, 11:46:19 AM
Phew!

And now for something completely different. The morning-after photo:

(http://www.sredmond.com/vtsteam/OilFurnace/NewLining13.jpg)