Aluminum/brass mold and casting

[m31desantis]

So, I want to turn my forge into a low temp metal foundry as well.... 

 

Anyone got good ideas on how to make crucibles, or where to buy them?

 

or what material i could sculpt to make a good mold for casting?

[ThomasPowers]

Crucibles depend on what you plan to melt and how much of it.

 

I like petrobond as the mold making material.  Easy to work with.

[Nobody Special]

I used to use cut down fire extinguishers (the thin ones) for low temp stuff.

 

Fair warning, steel will oxidize, eventually leading to failure, getting occaisional rust flakes in your stuff, and you should always be uber cautious about cutting into the  walls of anything that's been pressurized or held chemicals.

 

I think you would have a much greater fail rate in a forge rather than a furnace because temp control would be harder, and there would be a more oxidizing flame on the steel. I heard they used to use thick walled cast iron for brass? Dunno.

 

Ceramic like fused silica is definitely a good way to go. I've had really bad luck with homemade ceramic or refractory ones, and you absolutely DON'T want one to break at a crucial moment. Burns from aluminum at 1400 degrees makes for bad owies.

 

What kind of forge are you using? If propane, probably great for this, if coal, you might be better off making a "coffee can" furnace.

 

Also, hi from Marietta. :D

[Robert Yates]

Silicon Carbide (SiC) Crucibles are high quality melting crucibles. They can be used at temperatures up to 1600C (3000^oF)and are suitable for melting and refining precious metals, base metals, and other products.

 

Yes, do preheat crucibles. This will drive off any moisture that may have been pulled out of the atmosphere during manufacturing, storage, and cooling from the previous firing. And for high value fires (like refining), it is good insurance.

Coating the inside of the crucible on the other hand probably does not help. If you want to coat the inside of the crucible with borax, go ahead as it probably will not hurt anything. But, the borax is a low melting temperature component so the coating will not form much of a barrier after you start heating things up. And, it will "cost" you one of the fires.

Some people do some refining in assay crucibles. The fire clay used in assay crucibles is not rated for nearly as high of temperatures as graphite or silicon carbide, and this is not really recommended. But, if you have had success doing this, make sure and preheat the crucible before use (as mentioned above).

Preheating can be done by placing the crucible on top of the furnace, or on a hot plate, or by putting them in the furnace and raising the temperature slowly. 

 

They are expensive but well worth it .

 

Sam

[Nobody Special]

Never had good luck in casting with borax. But I was using it mostly for flux. Got better results with silica sand, a little charcoal (shortly before casting), or my personal favorite, crushed oyster shell from the feed store (used to give chickens calcium).

[ThomasPowers]

For casting which metals?  I've had great luck using borax as a flux for casting fine silver and pure copper; don't use it for bronze or brass and I don't cast Al...

[Joe111]

Depends on how much material you want to melt. If you are just doing aluminum, Which is probably all you can do in a forge. Then weld a cap to a piece of pipe and some lifting lugs and you are ready to go. Im sure you arent making millspec items so the small amount of iron absorbtion wont be a problem.

Or if you want to buy one there are many options such as here:  http://backyardmetalcasting.com/. The problem is that no only do you need to buy the crucible but the lifting tongs and pouring shank also.