Aetiology of defects in large ceramic moldings

This study is an attempt to identify the causes of defects that appear in l arge ceramic injection molded bodies after sintering. It asks the question: are such defects established at the injection molding stage or are they ca used by the debinding process or by sintering? Moldings with ascending thic kness were prepared using a mold cavity with replaceable tool faceplates. C ontrol over pressure during solidification was compared by using convention al molding and a novel molding technique that uses an insulated sprue. The organic vehicle is polyoxymethylene, which can be displaced by catalytic de gradation in the solid state. This is a shrinking unreacted core process wi th a clearly defined reaction boundary in which there is no provision for p article movement in the liquid state. This study tracks the development of defects at each stage and concludes that the defects apparent after sinteri ng have their origin in injection molding, even though they do not mature u ntil a later stage.