There are many factors influencing the cooling of injection mold, such as the design of the shape and parting surface of the plastic parts, the type of cooling medium, temperature, flow velocity, cooling pipe geometry parameters and space layout, mold material, melt temperature, the top out temperature and mold temperature, mold temperature, plastic parts and mold heat cycle interaction and so on.
( 1 ) the low mold temperature can reduce the molding shrinkage of the plastic parts.
( 2 ) the mold temperature is uniform, the cooling time is short, the injection speed can reduce the warpage of the plastic parts.
( 3 ) for crystalline polymer, the increase of mold temperature can stabilize the size of the plastic parts, avoid the crystallization phenomenon, but will lead to the elongation of the molding cycle and the defects of the plastic parts.
( 4 ) with the increase of crystallinity of crystalline polymer, the stress cracking resistance of plastic decreases, so it is advantageous to reduce the mold temperature. But for the high viscosity there is no polymer, because of its endurance cracking is directly related to the internal stress of the plastic parts, so it is beneficial to improve the mold temperature and mold filling speed and reduce the feeding time.
( 5 ) improving mold temperature can improve the surface quality of plastic parts. In the determination of mold temperature injection molding process, mold temperature directly affects the mold filling, molding, molding cycle and quality of plastic parts. The mold temperature depends on the crystallinity of the plastic, the size and structure of the plastic parts, performance requirements and other process conditions such as melt temperature, injection speed, injection pressure and molding cycle. For amorphous polymer, the melt is cured with the decrease of temperature after injection mold cavity, but the phase change does not occur, the mold temperature mainly affects the viscosity of the melt, that is the mold filling rate. Therefore, for low melt viscosity and medium there is no plastic such as polystyrene, cellulose acetate, using a lower mold temperature can shorten the cooling time.