GPPS (General Purpose Polystyrene) is a widely used transparent thermoplastic, with low melt viscosity, good flowability, moderate molding temperature (180-220°C) and no corrosiveness. It is mainly used for transparent covers, stationery and decorative parts, which have high requirements for surface finish and transparency. Mold material selection directly affects product quality, service life and cost. GPPS molds do not need high corrosion resistance, but focus on polishing performance, wear resistance and dimensional stability, selected based on production volume and product appearance requirements.

1. Basic Requirements for Mold Materials

Mold steel must have excellent polishing performance to achieve mirror or high-gloss finish, ensuring transparent products without fog or pinholes. It should have proper hardness and wear resistance to resist melt scouring, and good dimensional stability to avoid deformation after heat treatment and long-term use. Good machinability helps shorten processing cycle and reduce cost.

2. Materials for Small and Medium Batch Molds

For products with annual output below 500,000 shots and ordinary appearance, pre-hardened plastic mold steel (28-32HRC) is preferred. It does not need quenching, with small deformation, low cost and short processing cycle, meeting basic polishing requirements (Ra0.8-Ra0.4), suitable for small and medium-sized economic molds.

3. Materials for Medium and Large Batch High-mirror Molds

For products with 500,000-2,000,000 shots and high transparency requirements, mirror mold steel is selected. It has high purity and uniform structure, with hardness 48-52HRC after heat treatment, capable of reaching ultra-high mirror finish (below Ra0.2), ensuring product transparency and long service life.

4. Materials for Large Batch Long-life Precision Molds

For products over 2,000,000 shots and high precision requirements, high-performance mirror steel is chosen, with hardness 50-54HRC, higher wear resistance and stability, suitable for millions of shots continuous production, reducing maintenance frequency.

5. Material Matching for Mold Components

Cavities and cores adopt the above selected steels; runners and gates use materials with the same hardness. Guide pillars, ejector pins use wear-resistant bearing steel; templates use high-quality carbon steel for strength and cost control.

6. Selection Summary

Select materials based on actual demand: pre-hardened steel for small batches and cost saving, standard mirror steel for medium-large batches and high appearance, high-performance mirror steel for large batches and long life. Focus on polishing and wear resistance to ensure qualified GPPS products and stable mold operation.