Plaster mold casting of A356
Plaster mold casting of A356
(OP)
Hi
I have made a casting of A356 in a Plaster mold.
We have a lot of Hydrogen voids, 2,5 % voids.
We have used degasing tablets.
the heat have been meltet more than 8 hours.
Do anu one know why we get these voids. is it beacus the mlt is more tahn 8 hours old or is the watre in the Plast mold which evaporates
I have made a casting of A356 in a Plaster mold.
We have a lot of Hydrogen voids, 2,5 % voids.
We have used degasing tablets.
the heat have been meltet more than 8 hours.
Do anu one know why we get these voids. is it beacus the mlt is more tahn 8 hours old or is the watre in the Plast mold which evaporates





RE: Plaster mold casting of A356
RE: Plaster mold casting of A356
Can there come so much hyrdogen in the heat so the degassing tablets can get the hydrogen out of the heat???
How long is a desired melting and pouring cycle??
RE: Plaster mold casting of A356
RE: Plaster mold casting of A356
RE: Plaster mold casting of A356
I can send you a microsope pic of the the part
RE: Plaster mold casting of A356
Re "watre in the Plast mold which evaporates."
It is absolutely imperative to bake the moisture out of plaster molds to avoid defects & possible explosions. Plaster of Paris (gypsum) must be baked above 320 oF (160 oC) to remove all moisture, check the product bulletin if using a special casting plaster. Gypsum is ~impermeable to gases -- was a more permeable plasters used? Venting?
8 hours holding a melt???? Why not 8 minutes?
A356 doesn't have a lot of Mg (0.3-0.4%) or Zn (0.05% max), so maybe only lose some Mg.