The working conditions for injection moulding of Chair Mould are different from those of cold stamping dies. Generally, the work must be carried out at 150-200 degrees Celsius. Besides being subjected to pressure, the chair mould must also be subjected to the temperature. The basic performance requirements of the steel used for the chair mould are summarized as follows according to the use conditions and processing methods of the moulding chair mould:
1. Excellent machinability: Most of the moulded chair mould require cutting and fitter repair in addition to EMD processing. In order to prolong the service life of cutting tools, enhance cutting performance and reduce surface roughness, the hardness of the steel used for chair mould must be appropriate.
2. Good thermal stability: The shape of the injection moulded parts of the chair mould is often complicated and difficult to process after quenching. Therefore, the parts with good thermal stability should be selected as far as possible. When the two-colour mould is processed after heat treatment, the linear expansion coefficient is small, the heat treatment deformation is small, the dimensional change rate caused by temperature difference is small, the metallographic structure and the mould size are stable, and the processing can be reduced or stopped, thus ensuring the dimensional accuracy and surface roughness requirements of the chair mould.
3. Good polishing performance: For high-quality two-colour injection-moulded plastic products, the roughness value of the cavity surface is required to be small. For example, the surface roughness value of the injection mould cavity is required to be less than Ra 0.1 ~ 0.25, while the optical surface is required to be Ra<0.01nm. the mould cavity must be polished to reduce the surface roughness value. The steel materials selected for this purpose require fewer impurities, fine and uniform structure, no fibre directionality, and no pitting or orange peel defects during polishing.
4. Sufficient surface hardness and wear resistance: The hardness of plastic mould is usually below 50-60HRC. The chair mould after heat treatment shall have sufficient surface hardness to ensure sufficient rigidity of the mould. During the work of the chair mould, due to the filling and flowing of plastic, it is required to bear large compressive stress and friction force, which requires the mould to maintain the stability of shape accuracy and dimensional accuracy and ensure the mould has sufficient service life. The wear resistance of the chair mould depends on the chemical composition of the steel and the heat treatment hardness, so enhancing the hardness of the mould is beneficial to enhancing its wear resistance.
