Injection Molding
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COC Bubbles and Vacuum Bubbles
Problem Phenomenon
Bubbles or vacuum bubbles are visible inside COC transparent products, optical inspection judges them unqualified, and they mostly occur in thick-walled areas and at the roots of ribs.
Cause Analysis
The melt entrains air or shrinkage vacuum in thick-walled areas forms cells; excessive injection speed entrains air; insufficient holding pressure causes the core of thick walls to shrink and form vacuum bubbles; poor venting causes gas retention.
Solution
①Optimize the injection speed curve to avoid air entrapment; ②strengthen holding pressure feeding to eliminate vacuum bubbles; ③improve venting design; ④thin down or hollow out the structure of thick-walled areas; ⑤seal the hopper to prevent moisture absorption (although hygroscopicity is low, standardized management is still required).
Key Takeaway
COC bubbles need to be treated according to the two causes of air entrapment and vacuum; bubble inspection of transparent parts should use optical methods; low hygroscopicity does not mean they can be stored open.
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