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.
