Author Topic: Oil fired crucible furnace  (Read 67208 times)

Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #75 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.
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #76 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.
I love it when a Plan B comes together!
Steve
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Offline awemawson

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Re: Oil fired crucible furnace
« Reply #77 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
Andrew Mawson
East Sussex

Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #78 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:
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #79 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.




I love it when a Plan B comes together!
Steve
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Offline awemawson

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Re: Oil fired crucible furnace
« Reply #80 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.
Andrew Mawson
East Sussex

Offline tom osselton

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Re: Oil fired crucible furnace
« Reply #81 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
« Last Edit: July 26, 2013, 05:06:46 AM by tom osselton »

Offline RussellT

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Re: Oil fired crucible furnace
« Reply #82 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
Common sense is unfortunately not as common as its name suggests.

Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #83 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.....

I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #84 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.

I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #85 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:
I love it when a Plan B comes together!
Steve
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Offline andyf

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Re: Oil fired crucible furnace
« Reply #86 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
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #87 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.

I love it when a Plan B comes together!
Steve
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Offline awemawson

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Re: Oil fired crucible furnace
« Reply #88 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
Andrew Mawson
East Sussex

Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #89 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.
I love it when a Plan B comes together!
Steve
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MetalCaster

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Re: Oil fired crucible furnace
« Reply #90 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".
« Last Edit: July 27, 2013, 11:46:08 AM by MetalCaster »

Offline tekfab

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Re: Oil fired crucible furnace
« Reply #91 on: July 27, 2013, 11:29:15 AM »
Good Post MC   :thumbup:

Mike

Offline NeoTech

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Re: Oil fired crucible furnace
« Reply #92 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.. =)
Machinery: Optimum D320x920, Optimum BF20L, Aciera F3. -- I have not failed. I've just found 10,000 ways that won't work. http://www.roughedge.se/blogg/

Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #93 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.







« Last Edit: January 14, 2018, 11:16:24 AM by vtsteam »
I love it when a Plan B comes together!
Steve
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Offline tekfab

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Re: Oil fired crucible furnace
« Reply #94 on: July 27, 2013, 02:53:55 PM »
That's quite possibly the nicest F60 silica sand that i've ever seen.

Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #95 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.
I love it when a Plan B comes together!
Steve
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Offline tekfab

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Re: Oil fired crucible furnace
« Reply #96 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.

Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #97 on: July 27, 2013, 05:17:43 PM »
Sounds good to me.
I love it when a Plan B comes together!
Steve
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Rob.Wilson

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Re: Oil fired crucible furnace
« Reply #98 on: July 27, 2013, 05:23:48 PM »
Looks like silica gel to me Steve  :palm:


Rob

Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #99 on: July 27, 2013, 05:25:58 PM »
So thats it!!!!

Rob, you've solved it.  :lol: :lol: :lol: :lol: :lol: :lol: :lol:
I love it when a Plan B comes together!
Steve
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