1. Heat resistance
With the emergence of high-speed molding machinery, plastic products production goes faster. Since the molding temperature is generally between 160 ~ 350 ℃, some poor mobility, fast forming speed, forming part of the mold will very soon overtake the surface temperature of 400 ℃. When mold temperature gets higher, mold hardness and strength will decrease, leading to early failure and die wear or plastic deformation. To ensure the precision molds and small deformation, tool steel should have a higher heat resistance when in use. To reduce the temperature, mold steel should have good thermal conductivity and low thermal expansion coefficient.
2. Have sufficient temperature at operating temperature
Mold working conditions are mostly very poor, some often bear a greater load, leading to brittle fracture. Larger extrusion molding pressure is generally 10 ~ 35MPa. Therefore, to prevent mold parts at work suddenly brittle fracture, the molds should have a high strength and toughness.
3. Wear resistance
With the expansion of the use of plastic products, the plastic is often required to add an inorganic material such as glass fiber reinforced. Since the additive is added, so that the plastic flow is greatly reduced, leading to wear of the mold. So the mold with good wear resistance required.
4. Corrosion resistance
Add flame-resistant agents such as polyvinyl chloride in to ABS resins, may evolve corrosive gases during the molding process, the mold sometimes corrosion in an air stream at the crossing and damaged, so the mould requires to have good corrosion resistance.
5. Good cutting performance
With the plastic products of large-scale, complex shapes and precision required, the mold steel should have good cutting performance during cutting work hardening. To prevent mold deformation and affect the accuracy, we hope machining residual stress can be controlled to a minimum.
6. The mirror polishing properties
Cavity surface is smooth, polished mirror-forming surface required, the surface roughness of less than Ra0.4μm, in order to ensure the appearance of plastic moldings and facilitate molding release.
7. Dimensional accuracy
Mold inserts with high precision and high accuracy, precision cavity size is generally three to five. Fight insert cavity engaging surface adhesion required, in order to avoid molten material into the gap, caused by leakage of material.
8. Patterns of light corrosion
Many plastic products beautify its surface patterns through engraving. The application of large sticks embossing plate, which require mold steel has good pattern light corrosion resistance.
Therefore, the plastic mold steel should meet the strength, hardness, wear, heat, corrosion and other performance; should also have good polishing resistance, dimensional stability, ease of nitrogen and heat distortion and other process performance; good thermal conductivity and a small linear expansion coefficient and other physical properties. Plastic mold should choose different grades of quality and price according to the specific requirements of the molded parts.