A New Method of Measuring Green and Fired Permeability of Investment Casting Shells

摘要

Foundries have long known the importance of having a shell that has sufficient permeability to allow air to penetrate the shell during the pouring of metal rather than remain trapped in the metal or at the metal/mold interface. More recently, the issue of shell permeability in the green state is being considered as an important factor in the ability of a shell to dewax without cracking. The traditional method of producing a shell sample for measuring fired permeability is to insert and seal a hollow rod into a ping pong ball and then invest the ball and a few inches of the tube. After final dry, the invested ball and rod are placed into a furnace and the ball is burned out. Permeability can then be measured after cooling.