Effect of Water/Plaster Ratio on Preparing Molds for Slip Casting of Sanitaryware; Rheology of the Initial Plaster Slurry, Microstructure and Mold Properties

Abstract

ABSTRACTIn the common industrial range of water/plaster ratio to make plaster molds for slip casting of sanitaryware (from 66 to 82 parts of water/100 parts of plaster by weight), rheology of the initial plaster slurry, and microstructure and final properties of the mold and cast body were evaluated. Working time or time suitable for pouring plaster slurry to make the molds with lowest probability of defects (before an abrupt increase in viscosity due to the formation of gypsum crystals), such as pin holes and incomplete filling of cavities because of poor flow behavior, was determined through viscosity curves as a function of time. At the highest water/plaster ratio, the optimum working time for making the plaster molds was found. As the water/plaster ratio was increased, morphology of the gypsum crystals was modified towards large needles, promoting an increase in the mold porosity (up to 11%) that enhanced the main property of the plaster mold, i.e. casting rate (up to 8%), without changing the properties of the cast body and with a slight reduction in compressive strength of the mold (1.5%).