PC, or polycarbonate, offers outstanding toughness, high transparency, heat resistance, and mechanical strength, making it irreplaceable in automotive, home appliance, electronic, optical, and industrial components. However, PC melt releases trace corrosive gases during high-temperature processing, and transparent PC parts require extremely high mold finish and precision. Therefore, mold steel selection directly affects service life, product stability, and surface quality. The material must meet requirements for corrosion resistance, polishability, wear resistance, and fatigue resistance. This article explains systematic material selection principles for PC molds to balance performance, lifespan, and cost.
Core Principles of Material SelectionThe selection of mold steel for PC focuses on four core properties: corrosion resistance, high mirror finish, wear resistance, and fatigue resistance. Different production volumes and quality standards correspond to different steel types. For standard PC products with medium batch size, pre-hardened steels such as P20 and 718H are widely used. They offer HRC 30–36 hardness, excellent machinability, and do not require quenching, greatly shortening mold production cycles. For high-transparency products like lenses, lamp covers, and optical components, mirror steels such as S136 and STAVAX are preferred. These steels have high purity, superior corrosion resistance, and can be polished to mirror effect, preventing rust, pitting, and corrosion caused by PC melt. For high-volume, long-life molds, through-hardened steels including H13 and SKD61 are ideal. After heat treatment, their hardness reaches HRC 48–52, providing excellent wear and impact resistance for millions of cycles.
Matching Material Performance to Product RequirementsTransparent PC parts have extremely high requirements for surface finish and clarity. Therefore, mold steels must provide excellent polishability and corrosion resistance. Mirror steels prevent micro-pits and maintain long-term gloss. Structural PC parts used in automotive and industrial fields bear high stress and frequent friction, requiring steels with high strength and toughness. Cooling systems, venting, and ejection structures must also match material characteristics to ensure uniform cooling, reduce internal stress, and avoid deformation. For example, molds using S136 steel are often equipped with balanced cooling and precise venting to maintain optical clarity. Steels for structural parts are matched with reinforced ejection and guiding systems to ensure stability under high pressure.
Cost and Service Life BalanceIn actual production, cost-effectiveness is a key factor. Pre-hardened steels like P20 and 718H have low cost and short cycles, suitable for 100,000 to 500,000 shots. Mirror steels and through-hardened steels have higher costs but far longer lifespans and better stability, making them suitable for high-end and high-volume projects. Manufacturers should choose based on product positioning, order quantity, quality requirements, and budget. Correct material selection reduces early failure, maintenance costs, and downtime, significantly improving overall economic benefits.
Influence of Steel Quality on PC Product DefectsPoor-quality steel easily causes rust, pitting, and deformation, leading to defects such as flow marks, dull surface, stress marks, and bubbles in PC products. High-quality steels with stable composition and uniform hardness ensure consistent molding. In contrast, inferior steels wear quickly and require frequent repairs, reducing production efficiency. For transparent PC, any tiny defect on the mold surface is amplified on the product. Therefore, only reliable mold steels can ensure long-term stable production of high-quality PC components.
