Material Drying
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PE '2079851475616104457 Parison Bubbles and Melt Fracture
Fenómeno do problema
Bubbles are visible in the parison or the surface is rough like sharkskin, and weak points or surface roughness appear in the container wall after '2079851475616104457.
Análise das causas
Bubbles come from raw material moisture, feed zone cooling leakage, and screw and barrel wear entraining air; regrind containing fine powder also carries air; melt fracture occurs when the exit shear stress exceeds the critical value, more obvious with low mold temperature, fast extrusion and high regrind ratio.
Solução
①Pre-dry the raw material (especially regrind) and control the ratio; ②check whether the feed zone cooling water leaks and whether the screw is worn; ③increase the back pressure to help venting; ④for melt fracture: increase the die temperature, reduce the speed, and add PPA if necessary; ⑤check the die head heater bands.
Conclusão principal
For the parison, 'check moisture and wear for bubbles, check shear and temperature for roughness': the two types of problems have completely different mechanisms, but both cause weak points in the container wall and must be eliminated at the parison stage.
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