Processing Machinery
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Coexisting dents and vacuum bubbles in POM products
Problem Phenomenon
Sink marks on the surface of thick-walled products and internal vacuum bubbles appear at the same time, and simply increasing holding pressure cannot cure the problem at the root.
Cause Analysis
Excessive wall thickness difference causes the feeding channel at the center of the thick zone to freeze prematurely; holding pressure can compact the surface layer but cannot reach the center of the thick zone, forming a hollow interior with a dented exterior.；During on-site troubleshooting, verify item by item according to this mechanism, and avoid blindly adjusting the machine based only on experience
Solution
①Core out the thick zone and design for uniform wall thickness; ②optimize the gate position to be close to the thick zone; ③extend holding pressure in combination with low-speed feeding; ④evaluate gas-assisted molding.；After adjustment, take continuous samples to verify the effect, and resume mass production only after confirming stability
Key Takeaway
The combination of sink mark plus vacuum bubble strongly indicates a structural wall thickness problem; design modification is fundamental, and process adjustment can only partially alleviate it.；After confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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