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