Burn Mark Prevention: Gas Release Pin Selection Guide
Key Takeaway: Burn marks (diesel marks) are caused by trapped air igniting from adiabatic compression. Fix sequence: (1) verify parting line vents first, (2) add gas release pins at end-of-fill points, (3) if marks persist, switch to multi-groove pins for higher venting capacity.
Burn Mark Root Cause Diagnosis
Before selecting gas release pins, confirm the burn mark cause — not all burn marks are venting issues:
| Symptom | Cause | Solution |
|---|---|---|
| Burn at rib/boss tip | Trapped air (most common) | Gas release pin at burn location |
| Burn at weld line | Two flow fronts trapping air | Relocate gate or add vent at weld line |
| Random burn spots | Material degradation (too hot) | Reduce barrel temperature, not a venting issue |
| Burn near gate | Shear degradation | Reduce injection speed, enlarge gate |
Gas Release Pin Placement Strategy
According to injection molding simulation best practices documented by Autodesk Moldflow:
- Primary placement: At the end-of-fill point in each problem rib (furthest from gate)
- Secondary placement: At weld line intersections where two flow fronts meet
- Spacing: One gas release pin per 50–80mm of rib length for continuous venting