Injection Molding
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PVC Injection Product Uneven Discoloration
Problem Phenomenon
Local darkening and yellowing, inconsistent between batches.
Cause Analysis
Local shear heat or hot runner temperature deviation; retained material in runner mixed in; PVC extremely sensitive to local overheating; during on-site troubleshooting, verify item by item according to this mechanism, avoid blindly adjusting the machine based solely on experience.
Solution
①Hot runner temperature homogenization; ②Clean retention areas; ③Reduce shear; ④Stabilize melt temperature curve, avoid quality drift caused by temperature fluctuation; ⑤Clean retained carbonized material in barrel, nozzle and hot runner dead corners.
Key Takeaway
PVC local discoloration = 'local overheating': hot runner temperature difference and retention are the two sources; PVC is heat-sensitive, any local overheating shows color — temperature control uniformity is fundamental.
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