Pre-Moisturized β-hemihydrate for 3D Printed Molds

The premise that small quantities of dihydrate pre-mixed with hemihydrate could help develop nucleation and accelerate the hydration process is tested and experimentally proved to be applicable in three-dimensional (3D) printing while processing a plaster-silica sand composite treated with different levels of pre-moisture. Mechanisms and mechanics of bonding and influences of varying process parameters could be established based on photomicrographic and mechanical testing results using printed samples. The maximum volume errors resulting from the gypsum crystal growth are noted to be around 15% and 10% in the green and baked states, respectively, much lower than those reported with the traditional plaster processing routes, due to the relatively lower moisture levels employed in 3D printing. Green and baked compressive strengths showed mixed variations due to interactions between pre-moisture and plaster levels. The maximum compressive strength achieved after baking is within the range of strengths essential for casting nonferrous metals such as aluminum as per the ASTM standards.