The main performance requirements of plastic molds In plastic film molding processing, the quality of the mold guarantees the quality of the product is self-evident. Different types of plastic products, different product molding processes, have different requirements on the material, performance and shape of the mold.
1. Heat resistance With the advent of high-speed molding machinery, the production speed of plastic products is accelerating. Since the molding temperature is generally between 160 and 350 ° C, some fluidity is not good, and the forming speed is fast, so that the molding surface temperature of the mold part exceeds 400 ° C in a very short time. When the working temperature of the mold is high, the hardness and strength of the mold are lowered, resulting in early wear of the mold or plastic deformation and failure. In order to ensure the accuracy and deformation of the mold during use, the mold steel should have high heat resistance. In order to reduce the temperature rise, the mold steel should have good thermal conductivity and a low coefficient of thermal expansion.
2. Working conditions with sufficient temperature at the working temperature are mostly very harsh, and some often withstand large loads, resulting in brittle fracture. The extrusion molding pressure is relatively large, generally 10~35MPa. Therefore, in order to prevent the mold parts from being suddenly brittle during operation, the mold has high strength and toughness.
3. Abrasion resistance With the expansion of the use of plastic products, inorganic materials such as glass fibers are often added to plastics to enhance plasticity. Due to the addition of additives, the fluidity of plastics is greatly reduced, resulting in wear of the molds. The mold is required to have good wear resistance.
4. Corrosion resistance Adding a flame retardant and polyvinyl chloride to the ABS resin may cause corrosion gas during the molding process, and sometimes the mold is rusted and damaged at the air flow passage, so the mold steel is required to have good corrosion resistance.
5. Good cutting performance With the enlargement and precision of plastic products, it is required that the steel for molds has good cutting performance and work hardening during cutting. In order to avoid the deformation of the mold and affect the accuracy, it is hoped that the residual stress can be controlled to a minimum.
6. The surface of the mirror polishing process cavity is smooth, the molding surface needs to be polished into a mirror surface, and the surface roughness is lower than Ra 0.4μm to ensure the appearance of the plastic pressed part and facilitate demolding.
7. Dimensional accuracy The mold insert has high precision and high precision, and the cavity size accuracy is generally 3~5. The joint surface of the mosaic cavity is required to be tight to prevent the molten material from entering the gap and causing leakage.
8. Pattern pattern photo-etching performance Many plastic products have been added with a pattern on the surface for the beautification. In the leather industry, the application of large-scale embossed embossed sheets requires mold steel to have good pattern photo-etching properties.
Therefore, the mold steel should meet the performance of strength, hardness, wear resistance, heat resistance, corrosion resistance, etc.; also should have good polishing properties, dimensional stability, easy nitriding and heat treatment deformation and other process performance; good thermal conductivity And physical properties such as small linear expansion coefficient. Plastic molds should be selected according to the specific requirements of the parts of the mold steel of different quality and price grade.