Patent ID: 7503379

Claim:
A method of improving the removal of an investment casting shell surrounding a metallic article, said shell being made from the deposit of layers of refractory slurry and stucco onto a pattern, and containing, after firing, an amount of an alkali metal oxide or an alkaline earth metal oxide sufficient to reduce the strength of the shell, which comprises the steps of: firing the shell, pouring the molten, metallic part into the shell, and then hydrating the shell, whereby the strength of the shell is further reduced to facilitate its removal from the metallic part, wherein said alkali metal oxide or alkaline earth metal oxide has a first average grain size, and is present in at least one layer of said stucco, said stucco also containing a finely divided refractory material having a second average grain size that is no more than 50% greater or less than the first avenge grain size.