With the development and continuous production of high-performance plastics, the types of plastic products are increasing and their applications are expanding. The products are becoming more refined, larger, and more complex.
1) Wear and corrosion of cavity surface
The plastic melt flows in the mold cavity under a certain pressure, and the solidified plastic parts are pulled out of the mold, which will cause friction and wear on the molding surface of the mold. The fundamental cause of plastic mold wear failure is the friction between the mold and materials.
However, the specific form and process of wear are related to many factors, such as the pressure, temperature, material deformation speed, and lubrication condition of the die in the working process. When the materials and heat treatment used in the plastic mold are unreasonable, the surface hardness of the cavity of the plastic mold is low and the wear resistance is poor, which is shown as follows:
The dimension of the cavity surface is out of tolerance due to wear and deformation; The roughness value becomes higher due to galling, and the surface quality deteriorates. Especially when solid materials are used to enter the mold cavity, it will aggravate the wear of the cavity surface. In addition, when plastic processing contains chlorine, fluorine, and other components, which are decomposed into corrosive gases HC1 and HF by heating, the surface of the plastic mold cavity is corroded and worn, leading to failure.
If there is wear damage at the same time, the coating or other protective layer on the cavity surface will be damaged, which will promote the corrosion process. The cross action of the two kinds of damages accelerates the corrosion wear failure.
2) Plastic deformation failure
The plastic deformation failure can be caused by the pressure and heat on the surface of the plastic mold cavity, especially when the small mold is working on the large tonnage equipment, it is more likely to produce overload plastic deformation. The strength and toughness of the materials used in the plastic mould are insufficient, and the deformation resistance is low; Another reason for plastic deformation failure is that the hardening layer on the surface of the mold cavity is too thin, the deformation resistance is insufficient, or the working temperature is higher than the tempering temperature, so that the transformation softening occurs, which makes the mold early failure.
3) Fracture
The main reason for fracture is the structural stress and thermal stress caused by structure and temperature difference, or insufficient tempering, which transforms the residual austenite into martensite at the service temperature, causing local volume expansion, and the organizational stress generated in the mold.

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