Effect of Different Grinding Time on the Performance of Gypsum Mould

Abstract

In order to improve the performance of gypsum mould, dry grinding process was applied to the pretreatment of gypsum powder and the effect of the ball-milling time on the performance of gypsum powders was mainly studied in our work. X-Ray powder diffraction (XRD) and scanning electron microscope (SEM) were employed to characterize the phase compositions and microstructures of gypsum mould. The results show that the initial and final setting time of gypsum slurry reduces with the increasing of ball-milling time. But the initial and final setting time changed slightly when the ball-milling time was extended to 1 hour or more. Furthermore, the water absorption of gypsum moulds made by the pre-grinded gypsum powders was increased by 42.0 percent in the case of 2 hours’ grinding time, yet the flexual strength of the mould was slightly decreased by 12.5 percent. The main phase of gypsum powder was unchanged, but decrystallization degree increased after dry grinding process. Meanwhile, the crystal orientation and particle aggregation of the gypsum powders were destroyed, and the particle length of that was shortened. As a result, the gypsum moulds obtained by the as-treated gypsum powders have high porosity and water absorption.