Pusher Pins

A pusher pin is a spring-loaded ejector pin that returns to its retracted position automatically after the ejection stroke, without requiring the ejector plate return mechanism. The key differences: (1) Built-in compression spring inside the pin body provides 5–30N return force (adjustable by spring selection). (2) The pin extends during ejection (pushed by ejector plate) and retracts when the ejector plate returns — same as a standard pin. (3) The spring ensures the pin is fully retracted before mold close, preventing damage if the ejector return system fails or is delayed. Pusher pins are typically 20–30% more expensive than standard pins due to the spring mechanism.

Standard pusher pins are available with spring return forces of 5N, 10N, 15N, 20N, and 30N, selectable by spring type. The required return force depends on: (1) pin weight — heavier pins need more spring force to overcome gravity in horizontal molding machines, (2) friction — pins with tight bore clearance need more force to overcome static friction, and (3) mold orientation — vertical machines may need higher spring force to ensure reliable return. The spring is designed for a minimum of 1 million cycles at rated force. Over-specifying spring force is not recommended because it increases the ejection plate force requirement and can cause premature spring fatigue.

Yes — pusher pins are rated for 1 million+ cycles with standard springs, and 2 million+ cycles with fatigue-rated springs (available as an option). The spring is the life-limiting component, not the pin body. For molds running above 500,000 cycles per year, MISUMI recommends: (1) using fatigue-rated springs (10–15% cost premium), (2) scheduling spring inspection every 500,000 cycles (check for permanent set — if the spring free length has decreased by more than 5%, replace), and (3) keeping spare spring sets on hand (replacement takes 5 minutes per pin). The pin body itself (M2 or H13 steel) has the same wear life as a standard ejector pin.