- 1. With the advent of high-speed molding machinery, the production speed of plastic products has accelerated. Because the molding temperature is generally between 160 and 350 ° C, some have poor fluidity and fast molding speed, which will cause the molding surface temperature of the mold to exceed 400 ° C in a very short time. When the working temperature of the mold is high, the hardness and strength of the mold will decrease, resulting in early wear or plastic deformation of the mold and failure. In order to ensure the accuracy and deformation of the mold in use, the mold steel should have high heat resistance. To reduce the temperature rise, the die steel should have good thermal conductivity and a low coefficient of thermal expansion.
- 2. The working conditions of the mold with sufficient temperature at the working temperature are mostly very bad, and some often bear a large load, which leads to brittle fracture. Extrusion molding pressure is relatively large, generally 10 ~ 35MPa. Therefore, in order to prevent the mold parts from suddenly brittle breaking at work, the mold should have high strength and toughness.
- 3. 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 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 gas during the molding process. Sometimes the mold is rusted and damaged at the air flow opening, so the mold steel is required to have good corrosion resistance.
- 5. Good cutting performance As the plastic products become larger, the shape becomes more complicated and precise, the mold steel is required to have good cutting performance, and the processing 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 a minimum.
- 6. The mirror polished moldable mold cavity has a smooth inner surface, and the molding surface needs to be polished into a mirror surface, and the surface roughness is lower than Ra0.4μm to ensure the appearance of the plastic pressed parts and facilitate demolding.
- 7. Dimensional precision mold inserts have high machining precision and high matching precision. The cavity dimensional accuracy is generally 3 to 5 levels. The joint surface of the mosaic cavity is required to be tight, so as to prevent the molten material from entering the gap and causing leakage.
- 8. Pattern erosion performance Many plastic products have added pattern patterns on their surfaces for beautification. In the leather industry, large-scale embossed embossed plates are used, which all require mold steel to have good pattern erosion.
Therefore, the mold steel should meet the performance properties of strength, hardness, wear resistance, heat resistance, corrosion resistance, etc .; at the same time, it should also have good polishing properties, dimensional stability, easy nitriding and small heat treatment deformation; good thermal conductivity; good thermal conductivity And small linear expansion coefficient and other physical properties. Plastic molds should select mold steels of different quality and price grades according to the specific requirements of the parts.
