Ejector Marks
Depressions, raised spots, gloss differences or punch-through at ejector areas. Process, geometric, mechanical and thermal causes are separated.
Ejector marks are local marks left at the points where the ejector pins press during ejection. They appear as a glossy, matte or slightly sunken circle. A certain amount of marking is unavoidable; the problem is when the mark is on a visible surface or becomes deep enough for the material to be strained.
How to Recognize It
- Depressions/raised spots at ejector positions; a corresponding gloss difference on the visible surface.
- In severe cases the ejectors punch through the part.
Physical Causes
- Process: early ejection or high ejection forces.
- Geometry: the ejector is not flush (axial clearance) or is the wrong length.
- Mechanical: the ejector cross-section is small, the mold/ejection system is poorly dimensioned.
- Thermal: a temperature difference between the ejector and the mold wall (a shrinkage difference around an overheated ejector).
Solution Steps at the Machine
Apply the steps in order and one at a time: after each change, wait a few cycles and assess the result. If there is no improvement, undo the change and move on to the next step.
- If there is a gloss difference, avoid pressure peaks: optimize the switchover, reduce the holding pressure/time.
- If ejection is early, increase the cooling time.
- If the ejection forces are high, apply the shrinkage management in the Ejection Deformation guide.
- Try lowering the mold wall temperature.
Mold, Design and Material Solutions
- Refit the ejector; check the countersink and contact surfaces.
- For a protruding mark, a longer ejector; for punch-through, ejectors with a larger cross-section/more ejectors.
- Provide an even mold temperature distribution.
Which defect is it confused with?
A wrong diagnosis leads to turning the right parameter in the wrong direction. This defect can be confused with the ones below; the right-hand column gives the practical way to tell them apart.
| Confused with | How to tell them apart |
|---|
| Ejection Scratches | Scratches run along the side faces of the part, in the ejection direction. An ejector mark is local, at the point where the pin presses. |
| Stress Whitening | Whitening shows that the material has been damaged. An ejector mark is often only a surface mark; if the two are seen together at the same point, the ejector force is excessive. |
Frequently asked questions
What should be done if the mark is getting deeper?
It means the part is being ejected before it has cooled sufficiently. Lengthen the cooling time somewhat or enlarge the ejector contact area. The permanent solution is to increase the number of ejectors and spread the force.
Why are the marks more pronounced in some cavities?
In multi-cavity molds there can be temperature and filling differences between cavities. In a cavity that stays hotter, the part comes out softer and the mark deepens. The cooling imbalance should be checked.
Prepared by:Uğur Çamlıca· Teknik Part · Source: manufacturer documentation and field practice