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:
- What is the application? Are the pins supporting or ejecting?
- Is the mold design balanced (symmetrical)?
- How much of the working pin length is being used for ejection stroke vs. overall ejection stroke designed for the mold?
- How much of the ejector pin ‘working’ area is supported?
- Is guided ejection being employed within the ejector assembly?
- Is the ejector plate assembly experiencing deflection?
- Is the ejector pin experiencing deflection during injection or ejection?
- How is the ejector assembly returned? Springs, early ejector returns, return pins, press pull-backs, homemade method?
- What is the clearance around the ‘fit’ area of the ejector pin?
- Is the bore finish approximately 0.4 micron?
- Were the bores for the ejector pin jig bored or CNC to assure proper alignment and concentricity?
- Is the ejector pin a vented location?
- What is the polymer being molded? Is it ‘sticky’?
- 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?
- Did just one pin break or a series of pins? Are they within the same quadrant of the mold if applicable?
- Consider a longer supported ‘working’ pin length and consider a longer shoulder
- 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.
Edited by Leafly Mould Provides Injection Mold, Plastic Mold, Injection Molding, Die Casting Mold, Stamping Mold