Plastic caps are favored by more and more manufacturers and people because of their plasticity, low density, high specific strength, high degree of bonding, high chemical stability and diverse appearance. The selection of plastic mould steel has a great influence on the quality of the mould. Therefore, the principle of plastic closure mould generally has the following four points:

1. Fatigue fracture performance
During the process of plastic bottle cap mould manufacturing, under the long-term effect of cyclic stress, it may cause fatigue fracture. Its form has small energy multiple impact fatigue fracture, tensile fatigue fracture and bending fatigue fracture.
The fatigue fracture properties of the mould mainly depend on its hardness, strength, toughness and the content of inclusions in the material.

2. Better high temperature performance
When the mould under a high working temperature, the hardness and strength will be lowered, resulting in early wear of the mould or plastic deformation and failure. So the mould steel should have high tempering stability to ensure high hardness and strength to hold the high temperature.

3. Resistance to cold and heat
Some plastic cap moulds are repeatedly heated and cooled during the working process, causing the cavity surface to be tensile, and with the press-induced the surface get cracking and spalling which increase the friction, impeding plastic deformation, and reducing the dimension accuracy, resulting in mould failure. Hot and cold fatigue is one of the main forms of mould failure. Therefore, for plastic bottle cap mould must have high resistance to cold and heat.

4. Corrosion resistance
Some plastic moulds will release HCI, HF and other strong aggressive gases when working due to heating which corrupt the mould surface, increase its surface roughness and aggravate wear and tear.

If want to product high-quality plastic cap mould, we must pay attention to the above points in order to ensure to get a high standard of cap mould with high requirements.