Processing Machinery
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Poor thermal stability of general-purpose polyethylene raw material causing degradation during processing
Fenómeno do problema
The product color turns yellow or darkens, black spots or burnt spots appear on the surface, and the mechanical properties decrease.
Material degradation is a manifestation of molecular chain breakage, and in severe cases a large amount of low molecular substances are produced, affecting product quality.
Análise das causas
（1）The barrel temperature is set too high, exceeding the thermal stability temperature of the material
（2）The material stays in the barrel for too long, and the heat history accumulates and degrades
（3）The screw speed is too fast, and shear overheating causes degradation
（4）The antioxidant content of the raw material is insufficient or has been consumed
（5）The regrind is used many times, and the antioxidant is exhausted
Solução
（1）Control the barrel temperature at a reasonable value within the range of 160-260°C to avoid overheating
（2）Reduce the residence time of the material in the barrel and avoid long-time high-temperature retention
（3）Reduce the screw speed to 50-100rpm to reduce shear heat generation
（4）Select grades with good thermal stability, and add antioxidants if necessary
（5）Control the regrind ratio to not exceed 20%, and the regrind should not exceed 2 times
Conclusão principal
Thermal degradation is caused by high temperature, long residence time, or excessive shear, and needs to be solved from temperature control, speed, and regrind management.
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