Molds & Tooling
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EVA internal shrinkage voids
Problem Phenomenon
Shrinkage voids of 0.5-2mm diameter in the center of thick-walled EVA products
Cause Analysis
After cooling of thick-wall areas the interior shrinks but the surface has solidified and cannot be fed; holding time insufficient with the gate freezing 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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