Molds & Tooling
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Whitening of PP weld lines
Problem Phenomenon
The weld line of PP products is obviously whitened, inconsistent with the surrounding color and gloss, especially conspicuous on dark-colored parts.
Cause Analysis
The converging front temperature is low, and the entrained gas, cold material, and impurities are enriched at the weld line, making the reflection characteristics there different from the matrix; the white line is more obvious when venting is poor.
Solution
①Increase the melt temperature and mold temperature so that the fronts converge fully; ②open vents at the confluence; ③set an overflow well to lead the cold front out of the cavity; ④adjust the gate position to move the weld line to a non-appearance surface; ⑤appropriately increase the injection speed.
Key Takeaway
PP weld line whitening = 'cold front + enrichment of gas and impurities': the three axes of raising temperature, venting, and setting overflow wells will obviously reduce the white line; plan the gate in advance for appearance parts to hide the weld line.
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