In order to improve the performance of plaster molds for investment casting, a diverse content ofglass fiber and polypropylene (PP) fiber was incorporated into the slurry for the preparation of a fiber-reinforcedmold. The green and fired bending strengths, thermal expansion properties, permeability, and thermal shockresistance of the mold were examined, and the scanning electron microscope (SEM) with energy dispersivespectrometer (EDS) was applied for the observation of fracture morphology. With appropriate content, theintroduction of glass fiber was proved to increase the green bending strength and fired bending strength, restrainthe thermal expansion and improve the thermal shock resistance of the mold, while the polypropylene fiber addedwas able to raise the green bending strength and the permeability, reduce the thermal expansion and heightenthe thermal shock resistance as well, though the fired bending strength would be weakened slightly. Evenlydistributed fibers were capable of enhancing the mechanical properties of the matrix, but agglomerations andbundles of fibers resulting from excessive addition had a negative impact. Meanwhile, it was also manifestedthat micropores left by ablative polypropylene fibers could improve the permeability and reduce the thermalexpansion of the mold, and the fired bending strength would be decreased slightly by the deterioration ofcontinuous structure. Three different ratios of hybrid fiber were employed in plaster molds, which can meet alteredrequirement of castings. The samples modified with hybrid fiber possessed lower thermal deformation, higher airpermeability, and better resistance of thermal shock, while the mechanical strength was equal to the fiber freesample or slightly increased.
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