Author Topic: Oil fired crucible furnace  (Read 66914 times)

Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #125 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....
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 #126 on: July 31, 2013, 04:32:40 PM »
« Last Edit: January 14, 2018, 11:28:16 AM by vtsteam »
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Offline tom osselton

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Re: Oil fired crucible furnace
« Reply #127 on: July 31, 2013, 10:57:08 PM »
Looks good!

Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #128 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.
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Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #129 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.


« Last Edit: January 14, 2018, 11:29:35 AM by vtsteam »
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Offline NeoTech

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Re: Oil fired crucible furnace
« Reply #130 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.)
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Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #131 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.

« Last Edit: January 14, 2018, 11:30:33 AM by vtsteam »
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Offline ironman

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Re: Oil fired crucible furnace
« Reply #132 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.

Offline tom osselton

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Re: Oil fired crucible furnace
« Reply #133 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.

Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #134 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.
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 #135 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:



« Last Edit: January 14, 2018, 11:31:49 AM by vtsteam »
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Offline awemawson

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Re: Oil fired crucible furnace
« Reply #136 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?

Andrew Mawson
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Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #137 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!
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Offline NeoTech

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Re: Oil fired crucible furnace
« Reply #138 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. =)

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Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #139 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.....
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Steve
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Offline NeoTech

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Re: Oil fired crucible furnace
« Reply #140 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.
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Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #141 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.
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Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #142 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:



« Last Edit: January 14, 2018, 11:33:57 AM by vtsteam »
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Offline Pete W.

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Re: Oil fired crucible furnace
« Reply #143 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.
Best regards,

Pete W.

If you can keep your head when all about you are losing theirs, you haven't seen the latest design change-note!

Offline awemawson

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Re: Oil fired crucible furnace
« Reply #144 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:
Andrew Mawson
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Offline NeoTech

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Re: Oil fired crucible furnace
« Reply #145 on: August 05, 2013, 03:15:05 PM »
That looks frickin awsome!  :headbang: :headbang: :headbang:
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Offline vtsteam

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Re: Oil fired crucible furnace
« Reply #146 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:


« Last Edit: January 14, 2018, 11:34:44 AM by vtsteam »
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Offline doubleboost

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Re: Oil fired crucible furnace
« Reply #147 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

Offline dsquire

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Re: Oil fired crucible furnace
« Reply #148 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
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Offline tekfab

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Re: Oil fired crucible furnace
« Reply #149 on: August 05, 2013, 04:41:09 PM »
Now if you try casting the other part "upside down" you get a surprise.    :coffee:

Mike