In the process of injection production, the cooling time of plastic injection molding parts is about 80% of the whole injection production cycle. Bad cooling often results in warpage or surface defects, which affects the stability of the product size. Therefore, the reasonable arrangement of injection, pressure and cooling time can improve the quality and productivity of the product.
The cooling time of the part usually refers to the time when the plastic melt is filled from the cavity filled with the injection mold to the parts that can be removed. The time standard of opening and drawing parts can be opened. The parts are fully cured, with certain strength and rigidity. Even when molded with the same plastic, its cooling time is also different from the thickness of wall, the temperature of molten plastics, the ejection temperature of molded parts, and the temperature of injection moulds. So we do not have one hundred percent correct calculation of the cooling time, and we have to do the calculation only on the basis of the proper assumption.
At present, we usually use the following three standards as a reference for the cooling time:
(1) the center temperature of the thickest part of the plastic injection molding parts, which is cooled to all the time required under the thermal deformation temperature of the plastic.
(2) the central temperature of the thickest part of the wall of the crystallized plastic molding part is cooled to all the time below the melting point, or the time required to achieve the prescribed crystallization percentage.
(3) the average temperature within the section of plastic injection molding parts and the time required to cool to the prescribed temperature of the product.