Material Drying
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Bubbles in EVA injection molded thick walls
Problem Phenomenon
Dense bubbles 0.1-0.5mm appear inside EVA injection molded thick wall products, concentrated at wall thickness center
Cause Analysis
Holding pressure insufficient <40MPa or holding pressure time short with thick wall center not compacted; raw material contains moisture; injection speed too fast entrapping air; poor mold venting
Solution
1) Increase holding pressure to 60-80MPa; 2) Extend holding pressure time to fully compact thick walls; 3) Fully dry raw material to moisture <0.02%; 4) Add vent grooves or vent pins to mold; 5) Progressively decelerate injection to avoid air entrapment
Key Takeaway
Thick wall bubbles are caused by insufficient holding pressure, moisture and poor venting combined
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