Аңдатпа
During the manufacturing of sand-resin shell molds, the resin undergoes a solid-liquid-solid phase transformation under heating. In order to increase the shell strength and reduce the binder (pulverbakelite) content, variable static pressure corresponding to the resin phase transition was applied in addition to thermal exposure. The base pressure was 0.25 MPa and was applied immediately after the mixture was poured onto a pattern plate heated to 230°C. After 10 s, the pressure was increased to 0.35 MPa and then reduced to 0.2 MPa after another 10 s. Experimental results showed that castings produced in shell molds formed under variable pressure are characterized by minimal and uniform internal stress distribution. In addition, such castings demonstrate high surface quality (Rz = 70-80 μm) and absence of internal defects.