Whether it is the surface shrinkage of the injection molded part or the internal shrinkage hole, it is a problem of shrinkage, which is often caused by insufficient filling of the molten material when the thick part is cooled. Once such defects are generated, no matter how to increase the pressure, increase the water inlet, and prolong the injection time, the shrinkage of the injection molded parts cannot be solved. What should I do?

From the past practical experience, among the raw materials commonly used in injection molded parts, due to the rapid cooling rate, the shrinkage of the PC material is difficult to solve, and the shrinkage and shrinkage of the PP material is also difficult to handle. Therefore, when encountering the serious shrinkage problem of thick parts, some unconventional injection molding techniques are needed.

In the production, first of all, to ensure that the injection molded parts are not deformed, the method of minimizing the cooling time is adopted to allow the injection molded parts to be prematurely released at high temperatures. Because the temperature of the outer layer of the injection molded part is still high, the skin is not too hard, and the temperature difference between the inside and the outside of the workpiece is relatively large, which is beneficial to the overall shrinkage, thereby reducing the concentrated shrinkage inside the injection molded part.

Since the shrinkage amount of the injection molded part as a whole is constant, the more the overall shrinkage is, the smaller the concentrated shrinkage amount is, and the degree of internal shrinkage and surface shrinkage is thus reduced. Secondly, after the injection molded parts are prematurely released, they should be properly cooled to maintain a certain hardness on the surface of the injection molded parts, so that it is not easy to produce shrinkage.

However, if the problem of shrinkage of the injection molded part is serious, moderate cooling will not be eliminated. It is necessary to adopt a method of freezing water to make the surface of the molded part harden quickly to prevent shrinkage, but internal shrinkage holes may still exist. On the basis of this, the method of extending the glue injection time instead of the cooling time is adopted, and the surface shrinkage and even the internal shrinkage cavity improvement will be better.