Best cheap crucible

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dpeterson3
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Best cheap crucible

Post by dpeterson3 » Sun Jan 17, 2010 10:36 pm

Hello all. I heated my Gingery-style furnace today. I finally got my casting sand to the point where it would make a good mold (I am still very much a newbie to casting). I have been using soup can crucibles, and this is the second time I have burnt through one. I know cans are too thin, so what should I use. I don't know where to get large diameter steel pipe, and I can't weld, so I am not sure what to do. M y dad suggested a glass canning jar, but I thought it would shatter.

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Re: Best cheap crucible

Post by Harold_V » Mon Jan 18, 2010 12:25 am

dpeterson3 wrote:Hello all. I heated my Gingery-style furnace today. I finally got my casting sand to the point where it would make a good mold (I am still very much a newbie to casting). I have been using soup can crucibles, and this is the second time I have burnt through one. I know cans are too thin, so what should I use. I don't know where to get large diameter steel pipe, and I can't weld, so I am not sure what to do. M y dad suggested a glass canning jar, but I thought it would shatter.
Have you considered buying a proper crucible? (silicon carbide, or graphite/clay).
When you melt in metallic objects, unless they are protected by a refractory wash, the molten metal dissolves some of the vessel you use, which isn't doing the alloy any favors.

The solvent power of molten metals is staggering. Try to avoid using anything metallic.

As far as using glass goes, by the time it approaches red heat, even if it hasn't shattered, it would be akin to using a paper cup. Glass doesn't remain hard and brittle with temperature, it becomes soft, eventually melting, just like metals do.

Harold

dpeterson3
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Post by dpeterson3 » Mon Jan 18, 2010 10:36 am

I was only toying with the idea of using glass for aluminum. It won't get hot enough to melt with aluminum. It would be scared of it melting if I were trying to melt iron.
Have you considered buying a proper crucible? (silicon carbide, or graphite/clay).
I am a freshman in college. I don't have a good way of ordering one nor do I have the money. I have considered making a refractory crucible. I am a bit afraid of cracking a non-metalic crucible. I tried to make one out of a flowerpot and cracked it within 2 minutes of heating. Metalic crucibles seem to be a lot more forgiving of thermocycles.

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Post by Harold_V » Mon Jan 18, 2010 2:31 pm

dpeterson3 wrote:I was only toying with the idea of using glass for aluminum. It won't get hot enough to melt with aluminum. It would be scared of it melting if I were trying to melt iron.
You missed the point. Glass becomes soft and pliable when heated, behaving much like rubber. You wouldn't be able to handle the container when the aluminum was molten, assuming it didn't crack due to thermal shock.
Harold wrote:Have you considered buying a proper crucible? (silicon carbide, or graphite/clay).
dpeterson3 wrote:]I am a freshman in college. I don't have a good way of ordering one nor do I have the money. I have considered making a refractory crucible. I am a bit afraid of cracking a non-metalic crucible. I tried to make one out of a flowerpot and cracked it within 2 minutes of heating. Metalic crucibles seem to be a lot more forgiving of thermocycles.
I agree, a metallic vessel is more forgiving, but I'm not convinced crucibles are as unstable as you assume. I think if you'd explore a crucible, you'll find they are quite tough.

Graphite/clay crucibles are very unforgiving of moisture. They readily crack if they are heated without tempering. That is a process of slowly heating the crucible to drive out moisture. Once that's done, they are quite stable. Silicon carbide does not require the tempering process.

In the past, when I refined precious metals, I ran both silicon carbide and graphite/clay crucibles. Fluxing was the devil---it cuts short, drastically, the life of a crucible, but in all my years of melting, I never had a crucible break. It wasn't uncommon to have as much as 200 troy ounces in a heat, which is a respectable load.

If you must stick with metallic vessels, invest in a wash, to limit, or eliminate, the absorption of iron in your heats.

If money is tight (I fully understand. I was not born to wealthy parents), you may enjoy success using a short pipe nipple, fitted with a cap. The cap should not be gray iron, but ductile or malleable iron will work fine, as neither is subject to thermal shock the way gray iron is.

Luck.

Harold

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Fender
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Post by Fender » Mon Jan 18, 2010 10:48 pm

I agree with Harold; buy a proper crucible for your furnace. You can buy a small crucible (but still bigger than a soup can) for about $25. Google "Budget Casting Supply" and look for a clay graphite type A crucible that is the right size for your work. Follow the directions on tempering it before use.
I have three clay graphite crucibles that I've been using off and on for over thirty years, and have never broken one. Each is dedicated to different metals: one for aluminum, another for brass or bronze, and a third for iron. I've probably melted aluminum at least 25 times in those years, and I'm still using the same crucible.
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Post by steamin10 » Wed Jan 20, 2010 4:14 am

Glass can be worked in a furnace, just like the glass blowers. It will soften and glow and is fun to play with.

It will shatter if it is not above about 600 degrees and pushed in the fire. That is about the tempering temperature for glass things blown and made by hand. (down to 450). Things just made have to be tempered to remove the stress. Glass shards finely broken are commonly used on brass to keep down the casting of fumes from the zinc burning off. It is hooked out as a sticky mass just before pouring, or making additions as a prelude to pouring.

I have destroyed dramatically, three clay crucibles, of about a gallon size. One I tried to grip the edge with tongs and raise it from the furnace, WRONG! Only part full it flexed and tore right down the side, spilling into the furnace. Had to pull the base block and the congealing Aluminum out of the bottom. The next day reset the base block on sand& furnace clay and dried it up. Second simply dropped on the floor, cold, it shattered like a clay flower pot. Third I was in a hurry to fire, and did not give time to remove the moisture from long idle time. It popped and crackled and shed the outer skin of itself, in the too hot furnace.

Always use picking tongs to lift the crucible out, and set it in a pouring shank. Make sure your shank has a cross rod, or holding hooks on the pouring side to keep it in the loop, of the shank.. Always wear a head cover and safty glasses at the minimum, in case you get some steam pops. Never leave a skull in the vessel, pig out, as the expansion upon heating can damage the bottom and sides. A vessel full of cold metal is a complete loss, ask me how I know..

I once poured a mold set out the night before, and had a sizable pop when I poured the first cup of aluminum in. I ruined the timing of the pour, so we shook it out to remake the mold in a hurry and try to repour.

We killed a mouse that was trying to build a nest in the flask only overnight. Yechh!
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
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Post by Harold_V » Wed Jan 20, 2010 4:54 am

steamin10 wrote:A vessel full of cold metal is a complete loss, ask me how I know..
Heh!

Many years ago, I ended up buying a large assortment of flasks and other foundry related things, from one of the high schools that was closing the industrial arts programs. These were items that had escaped the auction that I had attended, where I met the instructor. I expect the deal was for his benefit, but it was outstanding for me. Twenty metal flasks, along with a pyrometer (non-ferrous) and countless other items, all for just $300 cash.

Amongst my "treasures" was included a #16 crucible, full to the top, with aluminum.

I still have it.

I realize that heating the aluminum will crack the crucible. I keep hoping to come up with a way to remove the aluminum. Fat chance, when it's a bilge crucible.

Yep----don't put 'em away with a charge inside. If you must, make sure it's very small, and the crucible is tilted such that it fills only a small portion of the bottom and up the side, so it can expand without breaking the crucible.

Harold

edit: deleted unintended portion of quote.
Last edited by Harold_V on Fri Jan 22, 2010 12:09 am, edited 1 time in total.

dpeterson3
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Post by dpeterson3 » Thu Jan 21, 2010 5:51 pm

You guys keep saying clay, so let me ask you this. I tried to use a flowerpot with a refractory bottom plug as a crucible. I cracked it while heating. I blamed it on being a cheap flowerpot, but now I am not sure. The ceramic engineers here seem to think it should have worked and they are the ones who design these things. How should I heat it. I think my problem may have been heating too fast. I don't have a very good way to regulate the air flow to my furnace and I am burning charcoal so limiting fuel isn't easy either. How do you properly heat a crucible before melting so you don't crack it?

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Post by Qst42know » Thu Jan 21, 2010 6:45 pm

Flower pots are only partially vitrified (fused) and of a low temp porous clay. Forget the flower pot as it won't work. Not all clays are created equal and there are many entirely different formulations and types. Trust the crucible clay chemists to know which ones are suited for the job.

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Fender
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Clay crucibles

Post by Fender » Thu Jan 21, 2010 10:02 pm

Technically they are clay-graphite crucibles, not clay. I don't know the exact composition, but since they are grey/black I assume there is more graphite than clay.
Steamin10 is right, you have to lift the crucible out of the furnace from the outside of the crucible (see attached photo)
Attachments
Crucible.jpg
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Post by Harold_V » Fri Jan 22, 2010 12:15 am

Everything I've ever read about bilge crucibles indicates they should be lifted just as the lifting tong shows. To pick them up by other methods, or from the lip is asking for failure.
For those that don't have any experience, when a crucible is at operating temperature, it is somewhat soft and pliable. You need not worry about it cracking when up to heat so long as it is held correctly.

I agree fully with the comment that a flower pot is not suited for use as a crucible. Even if it was to function as one, the risk of severe burns should it fail while being handled with a molten charge makes it a poor choice.

Harold

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Post by steamin10 » Sat Jan 23, 2010 11:00 pm

Ya, the first heat you handle is real freaky, with all the new stuff you are not sure of. The heat, the vessel glowing and moving around in the tongs. Making that first pour rapidly, and running like hell when the concrete floor spalls out into the air. pop-pop-POP! FUN. Females that come to watch are rather noisy and vocal about the proceedings, and must be shielded or ignored, and best not around. They do anti-terror (theirs) haranges about safty, and other silly stuff. Use heavy plywood, or dry sand on the floor to pour on. 3/4 plywood will smoke and take scourch marks, but not support anything beyond a matchstick fire. Sand is a pain and must be stored in its poundage, very dry.

Flower pots and other objects like that, do not work and are a waste of time and rescource. Buy a crucible, and tend it, it will last. I used a cast iron dutch oven, and thought I was slick. Forget that too. Iron has too many negative effects on aluminum, and slip/ ciramic coatings are not easy to maintain well either.

Buy or borrow CW Ammen's books on casting and learn some tried and true basics. They are well applied to the backyard guy, or small commercial foundry.
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
It is not getting caught in the rain, its learning to dance in it. People saying good morning, should have to prove it.

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