In injection molding production, the cooling time of plastic injection molded parts accounts for about 80% of the whole production cycle. Poor cooling will lead to product warping and deformation or surface defects, all of which will affect the dimensional stability of the product. Therefore, the reasonable arrangement of injection molding, pressure-holding and cooling time can improve product quality and productivity.
Cooling time generally refers to the period of time from when the plastic melt fills the cavity of the injection mold to when the mold is opened and the part is removed. When the part is fully cured and has a certain strength and rigidity, it is the right time to open the mold. Even when using the same plastic, the cooling time varies with the wall thickness, the temperature of the molten plastic, the demolding temperature of the molded part and the temperature of the injection mold.
1. The time required for the temperature of the central layer at the thickest part of the workpiece wall thickness to cool down to just below the heat deflection temperature of that plastic.
2. The time required for the average temperature in the section of the workpiece to cool to the specified mold exit temperature of the product.
3. The time required for the temperature of the central layer of the thickest wall of a crystalline plastic to cool below its melting point, or to reach a specified percentage of crystallization.