Which Material Should You Choose for Ejector Block Pins?
Key Takeaway: Use S45C (HRC 28–32) for standard molds — it's softer than the mold plate by design, acting as a sacrificial wear component. Use SUJ2 (HRC 58–62) for high-cycle molds (1M+ cycles) where S45C pins wear too quickly.
Material Comparison
| Property | S45C (1045 Steel) | SUJ2 (52100 Bearing Steel) |
|---|---|---|
| Hardness | HRC 28–32 | HRC 58–62 |
| Wear life | 300,000–500,000 cycles | 1,000,000+ cycles |
| Cost | $ | $$ |
| Mold plate damage risk | None (softer than plate) | Low risk (similar hardness) |
| Best for | Standard molds, <500K cycles | High-cycle molds, 24/7 production |
Why Block Pins Are Softer Than Ejector Pins
Block pins contact the mold plate face at every cycle. If the block pin is harder than the mold plate, it will indent and damage the plate surface over time — a much more expensive repair than replacing a worn block pin. S45C is intentionally soft so the pin wears instead of the plate. It's a sacrificial component by design.