Top Things to Consider When Assessing Ejector Pins for Breakage

Ejector pins are a critical component to the injection molding process. An ejector pin is driven into the rear of a mold cavity to force the finished piece out and is also often referred to as a knockout pin. Having pins you can count on can make the difference between manufacturing a product efficiently or creating future unwanted costs.

If you’re experiencing ejector pin breakage here are some things to consider when assessing your pins:

  1. What is the application? Are the pins supporting or ejecting?
  2. Is the mold design balanced (symmetrical)?
  3. How much of the working pin length is being used for ejection stroke vs. overall ejection stroke designed for the mold?
  4. How much of the ejector pin ‘working’ area is supported?
  5. Is guided ejection being employed within the ejector assembly?
  6. Is the ejector plate assembly experiencing deflection?
  7. Is the ejector pin experiencing deflection during injection or ejection?
  8. How is the ejector assembly returned? Springs, early ejector returns, return pins, press pull-backs, homemade method?
  9. What is the clearance around the ‘fit’ area of the ejector pin?
  10. Is the bore finish approximately 0.4 micron?
  11. Were the bores for the ejector pin jig bored or CNC to assure proper alignment and concentricity?
  12. Is the ejector pin a vented location?
  13. What is the polymer being molded? Is it ‘sticky’?
  14. Is the ejector pin being used in an area such as a ‘gate pad’ where packing pressures may be high and long in duration, creating deflection of the pin?
  15. Did just one pin break or a series of pins? Are they within the same quadrant of the mold if applicable?
  16. Consider a longer supported ‘working’ pin length and consider a longer shoulder
  17. Always test the pin hardness on a flat surface area of the pin and test with the appropriate hardness testing load on a scale, such as 60 kg. Do not use a heavy 150 kg load on the scale as it will provide an inaccurate reading.
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Edited by Leafly Mould Provides Injection Mold, Plastic Mold, Injection Molding, Die Casting Mold, Stamping Mold