Processing Machinery
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Heat-resistant polyethylene extruded products show degradation discoloration
Fenómeno del problema
The extrudate turns yellow or darker in color, the surface is rough, and there may be an odor.
Degradation discoloration indicates that the material has undergone thermal-oxidative degradation, mechanical properties are severely reduced, and the product cannot be used.
Análisis de la causa
(1) Barrel temperature too high, material thermally degrades in the barrel
(2) Screw rotation speed too fast, shear overheating causes degradation
(3) Material residence time in the barrel too long, heat history accumulates
(4) Screw and barrel worn, producing metal-catalyzed degradation
(5) Insufficient or expired antioxidant in raw material
Solución
(1) Reduce barrel temperature to a reasonable value within 190-230°C
(2) Reduce screw rotation speed to reduce shear heat generation
(3) Check the screw and die head flow channel, eliminate dead corners to prevent stagnation
(4) Regularly check screw and barrel wear, replace in time
(5) Add appropriate amount of antioxidant (0.1-0.5%) or select a grade with good thermal stability
Conclusión clave
Degradation discoloration is caused by overheating or excessive shear, and needs to be prevented from the three aspects of temperature control, rotation speed and material selection.
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