Molds & Tooling
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Internal shrinkage voids of PU
Problem Phenomenon
Shrinkage voids of 0.5-2mm diameter in the center of PU thick-walled products
Cause Analysis
After cooling of thick-walled area, interior shrinks but surface already solidified, cannot be fed; holding time insufficient, gate freezes too early
Solution
1) Extend holding time until the gate is completely frozen; 2) Increase gate size to delay freezing; 3) Product design to reduce wall thickness differences
Key Takeaway
Shrinkage voids are caused by thick-wall shrinkage and insufficient holding; extending holding is key
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