Re: Follow-up Question


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Posted by ruth on July 14, 19100 at 10:29:17:

In Reply to: Follow-up Question posted by David Conway on July 14, 19100 at 09:27:28:

Sorry, i (and my kiln programmer) are obviously a bit too metric!

Its very dangerous to have moisture in the mould as when the metal is poured in the water escapes anyway it can and can blow the molten metal back out at you, quickly. You must also make sure you warm any tools that will actually go into the crucible when the metal is molten (eg ladle for removing dross) as they can chill the pot or worse if water on them (condensation etc)gets into the metal it can explode. It is probably worth stressing the importance of wearing the right protective clothes and a visor as if this, or anything similar, does happen you want the most protection you can get. We recently dropped a pot when getting it out of the pit furnace and i was very relieved to be covered in flame retardent fabric from head to toe!

One mould failure that we have had when casting with students is moulds collapsing when they come out of the kiln. The plaster and grog has to be an even thickness of about 2inches as otherwise the thin parts can just collapse in the heat - by removing the water you remove the plaster's strength so have to treat them with care. NB the moulds are often crazed on the surface or can appear cracked when you look down the pouring funnel. This is not normally a problem though. Wrapping in plaster and scrim as they come out of the kiln gives them added support to enable them to cope with the weight of the metal. Flashing on the cast from cracks in the plaster can be taken off easily with a chisel.


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