In the process of SMC molding, several key factors should be considered, including molding temperature, molding pressure and molding time.
The pressure is usually expressed in (MPA), that is, the ratio of the total force exerted by FRP hydraulic pressure to the pressure and the ratio of the projected area balanced to the pressure. In the process of molding, the role of pressure is to increase the density of materials, promote the flow of molding materials and the pressure source generated by the volatilization of low molecular materials in the molding aids. When processing products with complex shape, thin wall, large depth or area, the mold cavity can be filled only by overcoming large flow resistance, so high molding pressure is required.
The spreading high temperature may accelerate the cross-linking reaction, thus rapidly increasing the viscosity of the covering. Therefore, higher molding pressure is required to match, and higher pressure will increase the product density, promote rapid flow and mold filling, overcome swelling and prevent air holes. However, excessive pressure will reduce the service life of the die, increase the power consumption of the hydraulic press, and increase the residual stress in the product. Therefore, when processing thermosetting plastic molded products, prepressing, preheating and appropriately increasing the molding temperature are often used to avoid using high molding pressure. If the preheating temperature is not properly increased or the preheating time is prolonged, the fluidity of partially cured materials will be reduced during the preheating process. Instead of reducing the pressure, higher pressure will be used to ensure that materials fill the mold cavity.
