Filler component for investment casting slurries

A method of making an investment casting slurry comprising:

• mixing a filler component and a binder, wherein a major portion of more than 50 weight % of the filler component comprises finely divided particles selected from the group consisting of silica, aluminum, silicate, alumina and zircon;
• and a minor portion of less than 50 weight % of the filler component comprises finely divided kaolin particles having a plate shaped, needle shaped or tubularshaped structure, in a concentration sufficient to reduce drainage time of a slurry containing said filler component after application to an investment casting pattern, when compared with a slurry without said minor portion wherein:
• the filler component and the binder component lack organic fibers;
• a major filler component which defines between 0.99 and 85 weight percent of the filler component has, on average, a generally similar extent in their three dimensions;
• a minor filler component which defines between 0.1 to 15 weight percent of the filler component particles has, on average, at least one dimension of the particle which is at least about four times greater than at least one other dimension of the particle;
• the filler component when formed into a slurry has a viscosity of 8 to 30 seconds using a Gardco/ISO Mini Dip Viscosity Cup with a 6 mm orifice.