The main performance requirements of plastic molds In the plastic film molding process, the quality of the mold to ensure product quality is self-evident. Different types of plastic products and different 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 rate of plastic products has accelerated. Because the molding temperature is generally between 160 ~ 350 ℃, some fluidity is not good, and the molding speed is fast, which will make the mold surface temperature of the mold part exceed 400 ℃ in a very short time. When the working temperature of the mold is high, the hardness and strength of the mold will be reduced, leading to wear of the mold in the early stage or plastic deformation and failure. In order to ensure the precision and slight 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 excellent thermal conductivity and a low coefficient of thermal expansion.
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, which results in brittle fracture. Extrusion pressure is large, generally 10 ~ 35MPa. Therefore, in order to prevent the mold parts from being suddenly brittle during operation, the mold must have high strength and toughness.
3. Abrasion resistance With the expansion of the use of plastic products, plastic materials often need to add inorganic materials such as glass fiber to enhance plasticity, because the addition of the material will greatly reduce the fluidity of the plastic, resulting in mold wear, Therefore, the mold is required to have excellent wear resistance.
4. Corrosion resistance Adding flame retardants and polyvinyl chloride to the ABS resin, corrosive gas may be emitted during the molding process, and sometimes the mold is rusted and damaged at the air runner opening, so the mold steel is required to have excellent corrosion resistance.
5. Outstanding cutting performance With the large-scale, complicated and precise shape of plastic products, mold cutting steel is required to have excellent cutting performance and small work hardening during the cutting process. In order to prevent the mold from affecting the accuracy, it is expected that the machining residual stress can be controlled to a small limit.
6. Mirror surface polishing processability The inside and outside of the mold cavity are smooth. The molding surface needs to be polished to a mirror surface, and the surface roughness is lower than Ra0.4μm to ensure the appearance of the plastic pressed part and facilitate demolding.
7. Dimensional accuracy The mold insert has high machining accuracy and high cooperation accuracy. The cavity scale accuracy is generally 3 to 5 grades. The joint surface of the mosaic cavity needs to be tight to prevent molten material from entering the gap and causing leakage.
8. Photocorrosion performance of many patterns. In order to beautify, many plastic products have added patterns to their appearance. In the leather industry, large-scale corrugated embossing plates are used, which require mold steel to have good pattern photocorrosivity.
Therefore, the mold steel should meet the use properties such as strength, hardness, wear resistance, heat resistance, corrosion resistance, etc .; at the same time, it should have excellent polishing properties, dimensional stability, easy nitriding and small heat treatment deformation and other process properties; outstanding thermal conductivity And small linear expansion coefficient and other physical properties. Plastic molds should choose different quality and price levels of mold steel according to the specific requirements of the parts.