PPO (polyphenylene oxide) and its modified materials (including PPO+PS, PPO+PA, glass fiber reinforced PPO+GF) are high-performance engineering plastics with high melting temperature, high melt viscosity and strong abrasiveness, especially glass fiber reinforced grades, which have extremely strong abrasive wear on the mold surface. Therefore, the material selection of PPO molds is completely different from that of ordinary plastic molds, and must focus on high temperature resistance, wear resistance, corrosion resistance, dimensional stability and polishing performance. Correct mold material selection directly determines the service life of the mold, the appearance quality of the product and the stability of long-term production, and can effectively reduce the frequency of mold maintenance and later production costs.
Mold Base MaterialsThe mold base is a non-forming part, mainly used for supporting and positioning, and does not directly contact with high-temperature melt, so it can be selected according to the standard of conventional engineering plastic molds. The mainstream materials are 45# steel and S50C medium carbon steel, which have high cost performance and sufficient strength. The mold base must be tempered to ensure overall rigidity and stability, and the hardness is controlled at HB180-220, so as to avoid slight deformation under long-term high-temperature production conditions, resulting in product flash and mold misalignment. This kind of material is suitable for all PPO mold bases, moving and fixed templates, support plates, ejector pin plates and other non-forming structural parts, without additional surface hardening treatment, which can control the overall production cost of the mold.
Cavity and Core MaterialsThe cavity and core are the core forming parts of the mold, directly contacting with high-temperature PPO melt for a long time, bearing high temperature, high pressure, wear and corrosion, so the material selection is the most critical. It needs to be classified and selected according to whether PPO contains glass fiber, product output and appearance requirements. For non-glass fiber or low-glass fiber PPO, mainly used for appearance parts and medium and low output products, NAK80 and 718H pre-hardened mold steel are preferred. NAK80 has a hardness of HRC38-42, good polishing performance, can achieve mirror effect, and has certain corrosion resistance; 718H has good toughness and easy processing, suitable for products with general appearance requirements. For glass fiber reinforced PPO+GF, which has strong abrasiveness, H13 and SKD61 hot work mold steels must be selected, which have excellent high temperature resistance and wear resistance. After heat treatment, the hardness reaches HRC48-52, which can resist the abrasive wear of glass fiber for a long time. For high-precision, long-life and high-cleanliness PPO products, S136/S136H stainless steel and 8407 high-performance hot work steel are selected, which have superior corrosion resistance and polishing performance, and are suitable for long-term high-volume production.
Inserts, Slides and Wear PartsPPO melt has high viscosity, and the mold is mostly designed with inserts, slides and slides. These parts are concentrated in force, frequent in wear and high in disassembly frequency, so materials with good wear resistance and toughness need to be selected. Conventional inserts, slides and slides are made of H13 or SKD61, with a heat treatment hardness of HRC50-54.
Small cores, deep rib inserts and ejector pins are prone to fracture and wear, and SKH51 high-speed steel or ASP23 powder steel is selected, which has high hardness and good toughness. For parts requiring anti-rust and mirror effect, S136 stainless steel is used to avoid rust affecting product appearance during long-term production.
Gate Bushing and Exhaust Block MaterialsThe gate bushing and main runner are in contact with high-speed flowing PPO melt for a long time, with serious wear and high-temperature erosion, so they are made of SKD61 or H13 with good high-temperature resistance and wear resistance. The exhaust block and exhaust insert are prone to material residue and corrosion, and H13 after quenching treatment is selected, with a hardness of more than HRC50, to prevent carbon deposition and corrosion and ensure smooth exhaust. In addition, for glass fiber reinforced PPO molds, the cavity and core surfaces are recommended to be nitrided to further improve surface hardness and wear resistance and extend mold life.
