Molds & Tooling
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PP Sink Mark High Shrinkage
Problem Phenomenon
【Problem Phenomenon】PP thick wall rib position sink marks are obvious, caused by high shrinkage
Cause Analysis
PP shrinkage rate is high at 1.0-2.5%, the outer layer of thick wall areas solidifies first and inner shrinkage pulls in the surface; insufficient holding pressure and early gate freezing aggravate it; during on-site troubleshooting, verify item by item according to this mechanism to avoid blindly adjusting the machine based only on experience
Solution
Increase holding pressure to 50-80% with delay; reduce material in thick areas; enlarge gates to ensure feeding; strong cooling of thick areas; after adjustment, take continuous samples to verify the effect, and resume mass production only after confirming stability
Key Takeaway
PP sink mark is the nature of high shrinkage, three moves of holding pressure, material reduction and strong cooling; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence; include this case in the defect archive as a troubleshooting reference for similar problems in the future
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