Hot Permeability of Coating Layer for Evaporative Pattern Casting Process

In the evaporative pattern casting process, casting defects occur depending on the properties of the foam pattern itself and the coating material. In particular, the permeability of the coat strongly affects product quality. However, there are some difficulties in improving casting defects caused by the permeability because there exists no appropriate evaluating method for hot permeability. We propose a new convenient method for the high precision measurement of coating permeability from room temperature to elevated temperature (hot permeability) using a suction type permeability tester. Remarkable difference in the hot permeability of the coat is found even if the room temperature permeability of coat is the same. Additionally the nature of hot permeability of the coat is classified into three types, they are decrement in permeability, constant, and increase from room temperature. Evaluation of castings based on the hot permeability data obtained by this method in the actual production site reveals a slight influence on the pouring rate. Measurement of the hot permeability of coating should therefore be useful for preventing casting defects