Ejector Marks / Push Marks
Causes, Solutions & Prevention in Injection Molding
Ejector marks occur when the part is too hot or soft during ejection causing pins to sink in or create localized stress.
Below you will find general information about this defect. To get a pinpoint solution tailored to your specific machine, material, and process parameters using the world’s most comprehensive injection molding troubleshooting database — sign up and access AI-powered troubleshooting, 7 engineering calculators, and detailed project tracking.
🔍Symptoms & Visual Identification
⚠️Root Causes by Category
⚙️ Process
- Cooling time too short part too hot at ejection
- Mold temperature too high
- Ejection speed too high
- Holding pressure too high part grips cavity harder
🔲 Mold
- Ejector pins too small diameter high contact stress sink into part
- No air valve suction holds part
- Insufficient draft angles
- Ejector plate not balanced one side pushes first
🧪 Material
- Low heat deflection temperature HDT material soft at mold temperature
- Deep ribs holding part in core side
📋 General
- Insufficient ejector pins for part area
- No stripper plate where needed
✅Solutions & Corrective Actions
⚙️ Process
- Increase cooling time until part is firm
- Reduce mold temperature
- Reduce ejection speed
- Reduce holding pressure check that part still meets dimensional spec
🔲 Mold
- Use larger diameter pins or blade plate ejectors
- Add air valve to break suction
- Increase draft angles minimum 0.5 degree prefer 1-2
- Balance ejector plate equal force across whole part
📋 General
- Add more ejector pins to distribute load
- Consider stripper plate for parts with ribs or cores
- Polish mold in ejection direction
🛠Step-by-Step Troubleshooting
Check Process Parameters
Increase cooling time until part is firm
Inspect the Mold
Use larger diameter pins or blade plate ejectors
Verify Material Condition
Low heat deflection temperature HDT material soft at mold temperature
❓Frequently Asked Questions
What causes ejector marks / push marks in injection molding?
Ejector Marks / Push Marks is caused by several factors including: Cooling time too short part too hot at ejection; Mold temperature too high; Ejector pins too small diameter high contact stress sink into part; No air valve suction holds part; Low heat deflection temperature HDT material soft at mold temperature; Deep ribs holding part in core side.
How do you fix ejector marks / push marks in injection molding?
Start by checking key parameters: Cooling time, Ejection speed, Draft angle, Ejector pin area (mm²). Increase cooling time until part is firm
Which plastics are most affected by ejector marks / push marks?
Common materials include: PP, ABS, PA6, POM, PE. Pay special attention to drying, shrinkage and mold temperature for each grade.
How do I prevent ejector marks / push marks in future production runs?
Prevention relies on three pillars: (1) process optimisation — verify Cooling time, Ejection speed; (2) mold maintenance — check gates, vents and cooling channels; (3) material control — ensure correct drying and virgin/regrind ratio.
What is the difference between ejector marks / push marks and similar defects?
White stress marks raised areas depressions or sink marks surrounding ejector pin locations. Part may deform at ejector positions. This distinguishes it from related surface defects during visual inspection.
📐Related Calculators
Run these engineering calculators to verify your process parameters and prevent this defect.
🔗Related Defects
About MBPlastiPro
Built by injection molding engineers, for injection molding engineers. MBPlastiPro combines decades of hands-on production floor experience with AI technology to help you solve defects faster, optimize processes, and deliver better parts.