Processing Machinery
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PVC Sink Mark Holding Pressure
Problem Phenomenon
Sink marks in thick-wall areas were obvious; increasing holding pressure improved them but lengthened the cycle
Cause Analysis
Insufficient shrinkage compensation in PVC thick-wall areas forms sink marks; poor heat conduction makes thick walls solidify slowly, requiring long holding pressure; thinning the wall thickness design is more fundamental than process compensation; during on-site troubleshooting, verify item by item according to this mechanism to avoid blindly adjusting the machine based only on experience
Solution
①Increase holding pressure and time; ②thin the structure of thick-wall areas or core out material; ③place the gate near thick-wall areas; after adjustment, continuously sample to verify the effect, and resume mass production after confirming stability
Key Takeaway
Holding pressure is effective for PVC sink marks but treats the symptom; structural thinning is the root cure—use both in combination; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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