Material Drying
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Silver streaks on PP injection molded parts
Problem Phenomenon
Silvery-white streaks appear on the product surface along the flow direction, which diminish after drying.
Cause Analysis
Moisture adsorbed on the surface of PP pellets vaporizes in the melt; degradation gas or shear overheating can also produce similar silver streaks.; during on-site investigation, verify item by item according to this mechanism to avoid blindly adjusting the machine based only on experience
Solution
①Dry the pellets appropriately; ②control the melt temperature to prevent degradation; ③reduce the screw speed to reduce shear; ④check the moisture content and quality of the regrind.; after adjustment, continuously sample and verify the effect, and resume mass production after confirming stability
Key Takeaway
Investigate PP silver streaks along the three clues of moisture, degradation, and shear; verify by drying first, then check the temperature history.; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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