Mold Venting Design: Solving Gas Traps and Burn Marks

[eric_liu]

Proper venting is often overlooked but accounts for many molding defects.

Types of Vents:

• Parting line vents: shallow grooves 0.02-0.05mm deep
• Ejector pin vents: clearance 0.02-0.04mm
• Insert vents at gas trap locations
• Vacuum venting: active cavity evacuation

Vent Depth by Material:

• Amorphous (ABS, PC): 0.03-0.04mm
• Semi-crystalline (PE, PP): 0.02-0.03mm
• High-flow (LCP): 0.02mm max
• Rubber: 0.02-0.05mm

Land Length: 3-10mm before opening to atmosphere

Diagnosing Issues:

1. Burn marks at last fill area → insufficient venting
2. Short shots with no other defects → trapped gas
3. Glossy marks at weld line → gas trapped at melt front

Advanced Solutions:

• Porous steel inserts (25-30% porosity)
• Stepped vent grooves
• Automated vent cleaning for high-production molds

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