There are many factors that affect the cooling of injection molds, such as the shape of the plastic part and the design of the parting surface, the type, temperature, flow rate of the cooling medium, the geometric parameters and spatial arrangement of the cooling pipe, the mold material, the melt temperature, the ejection temperature required by the plastic parts and the mold temperature the thermal cycle interaction between the plastic parts and the mold,etc.
1. Low mold temperature can reduce the molding shrinkage of plastic parts.
2. Uniform mold temperature, short cooling time and fast injection speed can reduce the warpage of plastic parts.
3. For crystalline polymers, increasing the mold temperature can make the size of the plastic part stable and avoid post-crystallization, but it will lead to the defects of prolonged molding cycle and brittle plastic parts.
4. As the crystallinity of the crystalline polymer increases, the stress crack resistance of the plastic decreases, so it is advantageous to lower the mold temperature. However, for high-viscosity amorphous polymers, since their resistance to cracking is directly related to the internal stress of the plastic part, it is advantageous to increase the mold temperature and filling speed and reduce the feeding time.
5. Increasing the mold temperature can improve the surface quality of the plastic parts. The mold temperature is set during the injection molding process, and the mold temperature directly affects the filling of the plastic, the shaping of the plastic part, the molding cycle and the quality of the plastic part.
6. The mold temperature depends on the crystallinity of the plastic, the size and structure of the plastic part, performance requirements and other process conditions such as melt temperature, injection speed, injection pressure and molding cycle.
For amorphous polymers, the melt solidifies as the temperature decreases after being injected into the mold 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 with low and medium melt viscosity, such as polystyrene-PS, a lower mold temperature can shorten the cooling time.