Injection Molding
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Sink marks in PU '2079851475616104452
Problem Phenomenon
Sink marks of 0.2-0.5mm surface depressions in thick-walled areas of PU injection molded products
Cause Analysis
Holding pressure insufficient or holding time short; gate freezes too early so holding pressure cannot be transmitted; large wall thickness difference, after thin wall freezes, thick wall cannot be fed
Solution
1) Increase holding pressure to 70-90MPa; 2) Extend holding until gate freezing +2s; 3) Product design reduces wall thickness differences with gradual transition; 4) Add supplementary gates in thick-walled areas
Key Takeaway
Sinking is caused by insufficient holding pressure and wall thickness differences; high holding pressure and multiple gates are the core countermeasures
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