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Casting Aluminum help please.
FLOPGUY:
--- Quote from: dmbasher on July 19, 2011, 05:29:14 PM ---I believe that industry melts out the foam before casting. Use anti - gassing tablets so you dont get a casting looking like Swiss cheese. At least use a thick steel pot or better, a proper crucible and make sure you have more than enough molten metal to do the job.Good luck.
--- End quote ---
Do you think I should get a cast iron pot?
I did a couple of sample casts at first making much thicker things, but the handle I am making is thinner.
I don't quite understand the ant-gassing tablets. How does that work?
PatJ:
I have noticed that some foam is pretty high density, and is much thicker than the typical "styrofoam" material.
A thick foam may not vaporize completely, expecially with AL which melts at a somewhat low temperature than some of the other metals.
The internet lists the melting point of AL at 1220 degrees F, but this may vary with the exact type of alloy.
I think the total output in BTU's of the burner is also important, as well as having a furnace that can direct most of that heat into the crucible. The temperature of the burner is not relevant if you can only heat up a 1" diameter spot on your crucible.
Casting seems to involve several arts including chemistry, metalurgy, non-linear shrinkage, pour rate, gating, solidification, slag removal, etc.
Gassing also seems to be a problem with some metals, but not necessarily all metals.
Having the correct porosity of moulding and core sand seems to be critical, as well has having the correctly sized and placed vent holes. Gates have to be located in the correct position or you will get solidification of the small sections before the large sections are filled.
The more I read, the more I see just how much of an art it is, and an expensive art at that.
Edit: Some metals absorb gas when they are melted, and release this gas when they solidify. If these metals are not degassed prior to pouring, then bubbles form in the casting when the metal solidifies.
I have been studying the book "The Complete Handbook of Sand Casting" by C.W. Ammen.
If you are going to achieve any level of consistency in your pours, you will need to read and understand all of the terms and proceedures in this book, or a book like it.
Even those who have mastered the art of casting have a certain amount of casting failures.
FLOPGUY:
--- Quote from: Big-on-Steam on July 19, 2011, 06:05:58 PM ---I have noticed that some foam is pretty high density, and is much thicker than the typical "styrofoam" material.
A thick foam may not vaporize completely, expecially with AL which melts at a somewhat low temperature than some of the other metals.
The internet lists the melting point of AL at 1220 degrees F, but this may vary with the exact type of alloy.
I think the total output in BTU's of the burner is also important, as well as having a furnace that can direct most of that heat into the crucible. The temperature of the burner is not relevant if you can only heat up a 1" diameter spot on your crucible.
Casting seems to involve several arts including chemistry, metalurgy, non-linear shrinkage, pour rate, gating, solidification, slag removal, etc.
Gassing also seems to be a problem with some metals, but not necessarily all metals.
Having the correct porosity of moulding and core sand seems to be critical, as well has having the correctly sized and placed vent holes. Gates have to be located in the correct position or you will get solidification of the small sections before the large sections are filled.
The more I read, the more I see just how much of an art it is, and an expensive art at that.
--- End quote ---
I am not making a very big handle and I am not melting more than a pound of Alum.
I am using fairly dense styrofoam.
My furnace, I found that I needed to leave an opening to get the torch at it maximum. It consumed the air up in the furnace.
Swarfing:
For my burner i use a 25mm tube through the side (10" long), an 0.8mm welding tip soldered to a piece of tube supported in front of the tube, i adjust this in and out for best heat and adjust gas for best roar, then drop back a bit. No fancy setup at all.
Stainless steel canisters last longer than normal steel ones (4 uses then bin). buy a proper crucible for the long haul.
stick some wire into your foam when filling your mould sticking out the top, pull these out once compacted and it will help with the gassing. Works for me and very little failure.
Remember if you get very little shrink back when it is cooling then the gas is still in the casting (some grades of aluminium shrinks less than others). Just adding table salt can help (small amount then stir in)
bry1975:
I always thought casting aluminum/aluminium was a very dirty job some years ago I had the job of collecting cast ally drain pipes and other parts like roof finials the place was like a BLACK hole interesting people tho.
Bry
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