There are many factors affecting the cooling of injection molds, such as the shape of the plastic part and the design of the parting surface, the type of cooling medium, temperature, flow rate, geometric parameters and spatial arrangement of the cooling pipe, mold material, melt temperature, and the top of the plastic part. Temperature and mold temperature, thermal cycle interaction between plastic parts and molds, etc.
(1) Low mold temperature can reduce the molding shrinkage of plastic parts.
(2) The mold temperature is uniform, the cooling time is short, and the injection speed is fast, which can reduce the warpage deformation of the plastic parts.
(3) For the crystalline polymer, increasing the mold temperature can stabilize the size of the plastic part and avoid post-crystallization, but it will lead to defects in the molding cycle and the brittleness of the plastic part.
(4) As the crystallinity of the crystalline polymer increases, the stress crack resistance of the plastic is lowered, so that it is advantageous to lower the mold temperature. However, for high-viscosity amorphous polymers, since the endurance cracking resistance is directly related to the internal stress of the plastic part, it is advantageous to increase the mold temperature and the filling speed and reduce the feeding time.
(5) Increasing the mold temperature can improve the surface quality of the plastic parts. Determination of mold temperature During the injection molding process, the mold temperature directly affects the filling of plastics, the shaping of plastic parts, the molding cycle and the quality of plastic parts. The temperature of the mold depends on the crystallinity of the plastic, the size and structure of the part, the performance requirements, and other process conditions such as melt temperature, injection speed, injection pressure, and molding cycle. For an amorphous polymer, the melt solidifies as the temperature decreases after being injected into the cavity, but no phase transition occurs. The mold temperature mainly affects the viscosity of the melt, that is, the filling rate. Therefore, for amorphous plastics having a low melt viscosity and medium density such as polystyrene, cellulose acetate, etc., a lower mold temperature can be used to shorten the cooling time.
