Ejection Scratches — Causes and Solution

Ejection scratches form as the surface rubs against the mold wall while the part separates from the mold. They appear as parallel lines running in the ejection direction. At their root lies either an insufficient draft angle, the condition of the mold surface, or the part not yet having cooled sufficiently.

How to Recognize It

Scratches in the ejection direction on textured outer surfaces.
In thin-walled lower areas scratches can form even with the same angle (low shrinkage potential).
If there are scratches on the side faces, lateral mold deformation is suspected.

Physical Causes

The draft angle is insufficient for the depth of the texture; the part shrinks and locks into the texture.
A pressure peak in the area far from the gate (late switchover) overpacks the part.
Weak mold dimensioning perpendicular to the closing direction → lateral cavity expansion (parts with large side faces, unsupported cores).

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.

Check the switchover point (avoid peaks caused by a late switchover).
Reduce the holding pressure and time (staged profile); note: the degree of gloss may change.
Increase the cooling time.

Mold, Design and Material Solutions

Increase the draft angles or use a lower roughness.
Increase the wall thickness (higher shrinkage releases the texture).
For lateral scratches, the only remedy is often a more RIGID mold.

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 Deformation	With deformation the shape of the part is distorted and its dimensions change. With a scratch only the surface is damaged; the geometry is retained.
Ejector Marks	An ejector mark leaves a local mark at the points where the ejector pins press. Ejection scratches run along the side faces of the part, in the ejection direction.

Frequently asked questions

What should the draft angle be?

The general rule is at least 1° per face; on textured surfaces this value increases markedly depending on the texture depth. If the angle is insufficient, no process setting will eliminate the scratch completely.

Does lengthening the cycle help?

Lengthening the cooling time lets the part come out harder and reduces scratching, but because it lengthens the cycle it should be a last resort. First try lowering the ejection speed and checking the condition of the mold surface.

Prepared by:Uğur Çamlıca· Teknik Part · Source: manufacturer documentation and field practice

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