With the rapid development of manufacturing industry, plastic mould is an indispensable tool in plastic forming and processing. The proportion of plastic mould in total mould output increases year by year. With the development and continuous production of high-performance plastics, the types of plastic products are increasing, their uses are expanding, and the products are becoming more and more precise. Large-scale and complex development. With the development of high-speed moulding production, the working conditions of moulds become more and more complex.
1) Abrasion and Corrosion of Cavity Surface
Plastic melt flows in the cavity with a certain pressure, and solidified plastic parts come out of the mould, which cause friction and wear on the surface of the mould. The fundamental cause of plastic die wear failure is friction between die and material. However, the specific form of wear and the wear process 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 material and heat treatment used in plastic mould are unreasonable, the surface hardness of the cavity surface of plastic mould is low and the wear resistance is poor, which is manifested as: the dimension of the cavity surface is over-tolerant due to wear and deformation; the roughness value is increased due to drawing, and the surface quality is deteriorated. Especially when solid material is used to enter the plastic model cavity, it will aggravate the wear of the cavity surface. In addition, when plastics are processed, chlorine and fluorine are decomposed into corrosive gases HC1 and HF by heating, resulting in corrosive wear and tear on the cavity surface of plastic mould, leading to failure. If wear is accompanied by wear damage, the coating or other protective layer on the surface of the cavity will be damaged, which will promote the corrosion process. The interaction of two kinds of damage accelerates corrosion-wear failure.
2) Plastic Deformation Failure
Plastic deformation failure can be caused by pressure and heat on the surface of plastic model cavity, especially when small dies work on large tonnage equipment, it is easier to produce overload plastic deformation. Another reason for plastic deformation failure is that the hardened layer on the surface of the die cavity is too thin, the deformation resistance is insufficient or the working temperature is higher than the tempering temperature, which causes the phase transformation softening and causes the early failure of the die.