1. Heat resistance With the advent of high-speed molding machinery, the production speed of plastic products has been accelerated. Because the molding temperature is generally between 160 and 350 °C, some fluidity is not good, and the forming speed is fast, which will cause the mold surface temperature to exceed 400 °C in an extremely short time. When the working temperature of the mold is high, the hardness and strength of the mold will be reduced, resulting in early wear of the mold or plastic deformation and failure. In order to ensure the precision and deformation of the mold when used, the mold steel should have high heat resistance. To reduce the temperature rise, the die steel should have good thermal conductivity and a low thermal expansion coefficient.
2. With sufficient temperature at the working temperature The working conditions of the mold are mostly very bad, and some often bear a large load, resulting in brittle fracture. Extrusion pressure is relatively high, generally 10 ~ 35MPa. Therefore, in order to prevent the mold parts from being suddenly broken during work, the mold must have high strength and toughness.
3. Wear resistance As the use of plastic products expands, inorganic materials such as glass fibers are often added in plastics to enhance plasticity. Due to the addition of additives, the fluidity of plastics is greatly reduced, resulting in wear of the mold. The mold is required to have good wear resistance.
4. Corrosion resistance Adding flame retardant and polyvinyl chloride to the abs resin may release corrosive gases during the molding process. Sometimes the mold is rusted and damaged at the air flow passage opening, so the mold steel is required to have good corrosion resistance.
5. Good cutting performance With the large-scale plastic products, complex shapes and precision, it is required that the steel used for the mold has good cutting performance, and the work hardening is small during the cutting process. In order to avoid the deformation of the mold and affect the accuracy, it is hoped that the processing residual stress can be controlled to the minimum.
6. The surface of the mirror polishing mold cavity is smooth, and the molding surface is required to be polished into a mirror surface with a surface roughness of less than Ra 0.4 μm in order to ensure the appearance of the plastic extrusion and facilitate demoulding.
7. Dimensional Accuracy The mold insert has high machining accuracy and high precision. The dimensional accuracy of the cavity is generally 3 to 5. The joint surface of the patchwork cavity requires close contact so that the molten material does not enter the gap and cause leakage.