塑胶产品龟裂（Plastic products cracking）.docVIP

塑胶产品龟裂（Plastic products cracking） 1. cracks Cracking is a common defect in plastic products, and the main cause is plastic deformation due to stress. The stress and deformation are mainly caused by residual stress, external stress and external environment. Crazing caused by residual stresses The residual stress is mainly due to the following three cases, namely, excessive filling, demoulding and metal insert. As the cracks produced in the case of excess filling, the solution is mainly in the following aspects: (1) due to the minimum pressure loss of the sprue gate, if the crack is mainly produced near the sprue gate, the multi-point distribution gate, side gate and handle gate shall be considered. (2) under the premise of ensuring that the resin is not decomposed and not deteriorated, the proper increase of resin temperature can reduce melt viscosity, improve flowability, and also reduce injection pressure to reduce stress. (3) under normal circumstances, when the mold temperature is low, it is easy to produce stress, and the temperature should be increased appropriately. But when the injection rate is higher, even if the mold temperature is lower, it can also reduce the stress generated. (4) the injection and holding time are too long, and the stress will be generated. It will be shortened appropriately or Th times to keep pressure. The switching effect will be better. (5) non crystalline resins, such as AS resin, ABS resin, PMMA resin and other crystalline resins, such as polyethylene, POM and other easy to produce residual stresses, should be noted. When the mold is released, because of the small slope of the stripping, the mould glue and the punch are rough, the force is too large to produce stress, and sometimes even whitening or cracking occurs around the ejector rod. If you carefully observe the location of the crack, you can determine the cause. In the injection molding at the same time embedded in the metal parts, the most likely to stress, and easy to prod