Molding Process
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HDPE Shrinkage 1.5-4%
Problem Phenomenon
Product dimensional deviation is large, sink marks are obvious in thick-wall areas, and shrinkage differences at different wall thicknesses are significant
Cause Analysis
HDPE high crystallinity makes its shrinkage of 1.5-4% rank at the forefront of general-purpose plastics; crystallization shrinkage superimposed with thermal shrinkage makes thick-wall areas crystallize more fully and shrink more; wall thickness differences cause uneven shrinkage and warpage
Solution
①Allow mold shrinkage allowance of 1.5-4% and correct through mold trials; ②uniform wall thickness design within ±10%; ③strengthen holding pressure to compensate shrinkage in thick-wall areas; after adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability
Key Takeaway
HDPE's high shrinkage is its crystallization nature; mold shrinkage allowance plus wall thickness uniformity plus holding pressure compensation are the three key measures for dimensional control; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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