Key Design Points of PPS Automotive Impeller Injection Molds
PPS (Polyphenylene Sulfide) is a high‑performance engineering plastic with excellent heat resistance, dimensional stability, chemical resistance, and mechanical strength. It is widely used in automotive impellers, including water pump impellers, fan impellers, and blower wheels. Automotive impellers require high rotational balance, thin blades, precise geometry, and stable performance under high temperatures. Therefore, PPS impeller molds have extremely high requirements for structure, gating, venting, cooling, and ejection.
1. Structural Design and Rotational Balance
Automotive impellers are rotating symmetric parts, so concentricity and balance are critical. Molds are usually single‑cavity to ensure consistency. The core, cavity, and gate center must be highly aligned to avoid eccentricity. Blade geometry must be precisely machined to ensure uniform thickness and smooth surfaces.
Insert positioning is important for impellers with metal inserts. Poor positioning causes imbalance and noise during operation. Locating rings and precision fitting are used to ensure insert stability during injection.
2. Gating System Design
PPS has high melting temperature and relatively low flowability, especially when filled with glass fiber. Gating design directly affects filling and weld line strength. Hot runner systems are widely used to reduce pressure loss and improve surface quality.Center gates, fan gates, or multi‑point gates are suitable for impellers. The gate should be located at the hub to ensure uniform flow toward the blades. Gate size must be sufficient to avoid premature freezing and ensure effective packing.
3. Blade Cavity Machining and Venting
Blades are thin, deep, and curved, making them prone to short shots and burning. High‑speed machining and EDM are required for precise blade forming. Surface roughness must be controlled below Ra 0.8 μm to reduce flow resistance.
Venting is critical. Gas traps in blade tips cause burning and poor filling. Vent grooves, vent inserts, and split vents are arranged at blade ends and weld line areas. Vent depth is maintained at 0.02–0.03 mm to avoid flash.
4. Cooling System Design
PPS requires high mold temperature, typically 120–150°C. Uniform cooling prevents warpage and shrinkage. Cooling channels are designed around the cavity and inside the core. Baffles or spiral cooling channels are used in the central core to improve heat exchange efficiency. Stable mold temperature ensures consistent dimensional accuracy.
5. Ejection System Design
PPS is rigid and brittle, so improper ejection causes cracking or chipping. A combination of ejector sleeves, ejector pins, and ejector plates is used. Ejection forces must be evenly distributed on the hub and non‑functional areas. Draft angles of 1.0°–1.5° are recommended for glass fiber reinforced grades.
6. Mold Steel Selection
PPS and glass fiber are highly abrasive. Steels such as S136, STAVAX, or H13 are used with hardness above HRC 48. These materials offer excellent wear resistance, corrosion resistance, and polishability, ensuring long mold life and stable surface quality.
7. Process Compatibility
PPS requires high injection temperature and pressure. Molds must be designed to withstand high pressure without deformation. Process parameters such as filling speed, packing pressure, and cooling time must be matched with mold structure. Proper parameters reduce internal stress and improve impeller strength and balance.
8. Summary
PPS automotive impeller molds demand high precision, good venting, balanced flow, uniform cooling, and reliable ejection. Reasonable design ensures high rotational balance, dimensional stability, and surface quality. By integrating material characteristics, structural requirements, and production process, the mold can achieve stable mass production of high‑performance PPS impellers.
