Guide to Injection Moulding of Ceramics and Hardmetals: Special Consideration of Fine Powder

Abstract

The small particle size of ceramic and hardmetal powders significantly increases the risk of particle agglomeration with an associated increase in viscosity of plastisols used in powder injection moulding. The agglomeration is counteracted by adding surface active compounds to the powder containing plastisol. A model is presented for the functioning of such additives in injection moulding or fine (ceramic, hardmetal) powder. The idea is to create a thin, dense adsorbed layer which reduces the attractive van der Waals forces without adding considerably to particle size, thus decreasing viscosity without creating perfect stability. In this manner, the pseudoplasticity necessary for the injection moulding is retained. The approach outlined shows that the adsorbates working as dispersants should be short molecules such as stearic acid, stearyl alcohol, and octadecyl silanes, all built around a C18 chain. PM/0786