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Injection Mold Materials have Great Impact on Mold Service Life

The durability of injection molds is extremely dependent on the materials used, so care must be taken in the selection of mold materials. In general, mold materials should have the following properties:

1. High corrosion resistance
Many plastic additives, such as flame retardants, and even the chemical action of the melt itself can corrode the mold cavity. When the filler and reinforcing material containing abrasives are mixed in the plastic raw material, the damage of mold is more likely to be aggravated. For this, you'd better use corrosion-resistant steel, or to perform surface plating treatment on the mold, chrome plating or nickel plating.

2. Good thermal conductivity
Good mold temperature control has a great influence on the quality of plastic parts during injection molding, especially when processing semi-crystalline thermoplastics. Generally, the thermal conductivity of copper alloys is better than that of alloy steels, but their modulus of elasticity, hardness and durability are lower. Insufficient thermal conductivity of the steel can be compensated by cooling system.

3. High wear resistance
In order to increase the rigidity and mechanical properties of plastic parts, glass fiber and inorganic fillers are widely used in plastic formulations. After adding these additives, they are injected into the mold cavity at high speed together with the melt, and the friction in the mold cavity is extremely high. If the mold material is not wear-resistant, it is easy to cause excessive wear of the cavity. Therefore, the material for making such a mold should have high wear resistance.

4. Good polishing performance
Inner wall of mold cavity has high requirements, the roughness of it requires being very small to meet the requirement of good gloss on the surface of plastic part. For this, mold cavity is generally required to be polished, and the brighter the surface, the better. Therefore, the mold material is required to be easy to polish, the material selected can’t have these defects such as impurities and pores.

5. Good dimensional stability
When plastic molding, the temperature of mold cavity is required to reach 300 °C or higher. Such large temperature difference will easily cause that the cavity structure generates microscopic changes, which lead to the change of mold size and the un-stability of the size of plastic part. So, the heat treated steel can be used. In order to improve the hardness and wear resistance, injection mold is generally subjected to heat treatment. We’d better use the pre-hardened steel which has smallest influence on mold size and can be machined by cutting. This steel doesn’t require heat treatment after machining.
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