During injection molding production, ejector whitening (also known as ejector pin whitening mark) is a common surface defect. It appears as whitish marks at positions where ejector pins contact the product. This not only impairs appearance but can also lead to cracking at ejector pin positions or product damage, seriously reducing qualification rate.
Based on practical production experience, the core causes and actionable on-site solutions for ejector whitening are summarized below. The content balances professionalism and operability, suitable for technicians and operators, and can also be used for customer communication and production reports.
Ejector whitening is mainly caused by abnormal stress during ejection, excessive demolding resistance, or unreasonable holding pressure parameters that result in internal stress concentration, which releases at the ejector pin contact area and causes surface whitening.
The troubleshooting logic follows:
First adjust process parameters → Then modify the mold → Finally solve special working conditions.

I. Unreasonable Process Parameters (Priority Check, Fast Solution)
Parameter deviation is the most common cause. Adjusting injection parameters first can quickly restore production without mold modification.
A. Excessively high holding pressure
Over-packing causes high internal stress. The ejector pin area bears excessive force during ejection, resulting in whitening.
Solution: Gradually reduce holding pressure by 5%–10% each time, run 3–5 shots for verification until whitening disappears.
B. Excessively long holding time
Prolonged holding traps internal pressure and tightens adhesion between product and mold, increasing ejection resistance.
Solution: Shorten holding time by 0.2–0.5 s each time, adjust according to product thickness and material, avoid sink marks.
C. Late holding pressure switchover
Late switchover causes over-filling, high internal pressure and abnormal ejection force.
Solution: Advance switchover position by 1–2 mm, switch to holding at 95%–98% cavity filling to reduce stress.
D.Excessively fast ejection speed
High-speed ejection creates sudden impact, especially for brittle materials (PS, ABS), causing uneven stress and whitening.
Solution: Reduce ejection speed, use step ejection (slow first, then fast) to minimize impact and ensure smooth ejection.

II. Mold Structure Issues (Checked When Parameter Adjustment Fails)
If whitening remains after parameter adjustment, optimize the mold to fundamentally reduce demolding resistance.
A. Insufficient demolding draft angle
Small draft causes tight adhesion after cooling, high ejection resistance and stress concentration.
Solution: Increase draft angle via mold modification:
ABS: 0.5°–1°
PP: 1°–2°
B. Lack of chamfers or rounded corners
Sharp corners at ejector pins or cavity edges cause stress concentration and increase friction.
Solution: Add chamfers or radii at ejector pin positions and sharp corners to reduce scratching and resistance.

III. Special Working Conditions (Targeted Solutions for Hidden Issues)
Some whitening is caused by vacuum suction during ejection, a hidden factor requiring structural optimization.
Vacuum suction on ejection side
A closed space forms between core and product, creating vacuum adhesion and forcing the ejector pins to overwork.
Solution:Install air valves in the core to break vacuum with compressed air before ejection;
Optimize ejection sequence with pre-ejection vacuum breaking.

IV. On-Site Handling Notes

A. Troubleshooting order: Adjust parameters first → Check mold → Solve vacuum issues, to avoid unnecessary mold modification.
B. Trial verification: After each adjustment, run 3–5 shots and check for whitening, sink marks, short shots or deformation.
Material adaptation: Use gentler adjustments for brittle materials to avoid damage.
Summary
C.The core principles to solve ejector whitening are:
Reduce ejection resistance, release internal stress, break vacuum suction.
D. By following the workflow:
Parameter adjustment → Mold modification → Special treatment
you can efficiently eliminate ejector whitening, improve qualification rate and reduce production loss for most injection-molded products.