Molds & Tooling
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Insufficient flatness of PU
Problem Phenomenon
Flatness of PU flat products >0.5mm/100mm, warpage
Cause Analysis
PU shrinkage large and different in each direction; mold cooling uneven; residual stress release causing continuous warpage
Solution
1) Uniform mold temperature to reduce temperature difference; 2) Increase holding pressure to reduce shrinkage difference; 3) Annealing to release residual stress
Key Takeaway
Insufficient flatness is caused by shrinkage difference and stress; uniform cooling and annealing are key
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