CASTING CHARACTERISTICS OF CLAYS: I,IMPROVED METHODS FOR DETERMINATION*

Part I of this investigation covers the development of reliable laboratory tests to indicate the relative properties of different clays with the primary consideration of their casting behavior. Methods are given for the determination of casting rate, permeability, water retention, fluidity, thixotropy, organic content, shrinkage, and dry strength. By determining the effect of varying increments of electrolyte on the foregoing properties, it is possible to select clays which have desirable casting characteristics for commercial use. Samples of fast- and slow-casting kaolins and ball clays were used to indicate the utility of the methods employed; results are also given for two composite bodies. In developing the test procedures using the Büchner funnel (vacuum), the effect of the following factors was determined: mixing procedure, ratio of clay to flint, feldspar vs. flint as the nonplastic, electrolyte content, quantity of slip used, specific gravity of slip, slip temperature, aging, and vacuum pressure; The optimum procedure for testing clays was then evolved. Part II and Part III of this series of studies are in preparation for publication.