I'm trying to cast aluminum using plaster and i was wondering if any one know how much the plaster has to be baked and how to tell if the plaster is dried fully and ways to do it. thx
When okorder /... Aluminum melts at about 1200 F. Silver at about 1700 F. So this would work fine. You would need a Kiln to heat the investment up to these temps - in a pinch a ceramic kiln would work. If you don't get all the moisture out the mold could explode from steam pressure - be careful - read some books or visit some backyard casting sites. Aluminum is also cast using sand casting techniques.Good luck.
Plaster releases water at two points - in ordinary or accelerated drying it loses the water needed for setting and stops feeling cool and feels dry. If it is heated past 900F it loses chemically bound water and may fall apart. Aluminum melts at several hundred degrees higher than this and if the mold is intended to hold a mass of aluminum is is likely to destroy the mold. If the aluminum casting is fairly flat less of a problem. The common method for dealing with this is to add 50% silica flour (bad for lungs warning) to the dry plaster when making the mold. Then the mixed material mold can be used and preheated to take materials at least up to fused/molten glass, although the mold is commonly lost (not reusable) at these temps and just barely holds together.
