Material Selection for PSU Molds
PSU (Polysulfone) is a high-performance amorphous engineering plastic with excellent heat resistance, mechanical strength and biocompatibility, widely used in medical, food, electronics and automotive fields. Its molding temperature is 340-380°C, mold temperature 130-160°C, with high melt viscosity and poor fluidity; modified PSU added with glass fiber or flame retardant has stronger abrasiveness. PSU molds have strict requirements on material heat resistance, wear resistance, corrosion resistance and polishability, and wrong material selection will shorten mold life and affect product quality.
1. Core Requirements of PSU for Mold Materials
PSU is molded at high temperature for a long time, and the mold cavity is in a harsh environment of repeated cold and heat, high shear friction and slight corrosion, so the mold material must meet five core requirements. First, thermal stability, it can work continuously above 160°C without hardness reduction, deformation or thermal fatigue cracking. Second, wear resistance, high-viscosity PSU melt has strong scouring on the mold, and glass fiber reinforced PSU will aggravate wear, requiring sufficient hardness to resist scratches and pull marks. Third, corrosion resistance, PSU decomposes a small amount of acidic gas at high temperature, and ordinary steel is prone to rust and pitting, so anti-corrosion performance is essential for high-end products. Fourth, polishability, PSU is mostly used for high-appearance and transparent parts, requiring cavity roughness Ra ≤ 0.4μm, and medical parts need mirror effect of Ra ≤ 0.1μm. Fifth, dimensional stability, small heat treatment deformation, ensuring long-term precision of the mold.
2. Hierarchical Selection Scheme of PSU Mold Materials
Economical Type (Small Batch, Structural Parts)
Applicable to trial production or internal structural parts with output less than 50,000 molds, pure PSU without glass fiber. Recommended materials: P20 and 718H pre-hardened plastic mold steel. P20 hardness 28-32HRC, 718H hardness 33-38HRC, no quenching required, easy to process, low cost and short delivery cycle. The disadvantage is poor corrosion resistance and limited heat resistance, polishability up to Ra≈0.8μm, only suitable for non-appearance parts, not for transparent or glass fiber reinforced PSU products.
General Type (Medium Batch, Appearance Parts)
Applicable to products with 50,000-300,000 molds, general appearance and transparent PSU parts, low glass fiber content (≤10%). Recommended materials: NAK80 and 718HH pre-hardened mirror steel, hardness 37-43HRC, uniform structure, excellent polishability up to Ra 0.1-0.4μm, good wear resistance and heat resistance, no complex heat treatment, high cost performance. Note that long-term high-temperature production may have slight rust, requiring daily maintenance.
High Corrosion Resistance Type (Large Batch, High-End Parts)
Applicable to medical, food-grade, glass fiber reinforced (10%-30%) PSU products with output more than 300,000 molds, the preferred material for high-end PSU molds. Recommended material: S136/S136H stainless steel, containing more than 13% chromium, with excellent rust and corrosion resistance, no pitting under long-term high-temperature decomposition gas. S136H pre-hardened hardness 32-36HRC, quenched S136 hardness 48-52HRC, mirror polishability up to Ra ≤ 0.1μm, strong dimensional stability, long service life, fully adapted to high-performance PSU molding requirements.
High Life Wear-Resistant Type (Ultra-high Batch, High Glass Fiber)
Applicable to PSU products with glass fiber content exceeding 30%, ultra-large batch (more than 500,000 molds) and continuous 24-hour production. Recommended materials: H13 (1.2344), 8407 hot work mold steel, after quenching and tempering, hardness 48-52HRC, excellent high-temperature strength, thermal fatigue resistance and wear resistance, can withstand long-term scouring of high glass fiber materials. Nitriding treatment can be added on the surface, surface hardness up to HV800-1000, further extending service life, suitable for ultra-long life precision molds.
3. Supporting Process and Use Suggestions
After material selection, supporting processes are crucial to ensure performance. S136, H13 and other materials must undergo standard quenching and tempering to stabilize hardness and size; pre-hardened steels such as P20 and NAK80 cannot be quenched twice to avoid cracking. For glass fiber reinforced PSU molds, surface nitriding or chrome plating is recommended to improve wear resistance and release performance. During production, keep the mold clean, and do a good job in rust prevention during shutdown. Match reasonable mold design: short and thick runners, sufficient cold slag wells and balanced temperature control system to reduce melt impact.
Summary
PSU mold material selection needs to focus on heat resistance, wear resistance, corrosion resistance and polishability, and flexibly configure according to production batch and product grade. Small batch structural parts can choose P20 and 718H to control cost; medium batch appearance parts are suitable for NAK80; large batch, medical, food-grade and glass fiber reinforced PSU molds give priority to S136 series; ultra-high batch and high glass fiber working conditions choose H13 type hot work steel. Scientific material selection with standardized processing and maintenance can not only ensure the appearance and precision of PSU products, but also improve mold life and reduce comprehensive production costs, supporting stable and efficient high-performance plastic production.
