Injection Molding
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Sink Marks of PE Injection Molded Products (Thick-Wall Type)
Fenómeno del problema
Thick-wall PE parts have severe surface sink that conventional holding pressure can hardly eliminate.
Análisis de la causa
Excessive wall thickness makes the volumetric shrinkage exceed the range that conventional holding pressure can compensate; PE's inherent high-shrinkage characteristic is further amplified at thick walls, and once the gate freezes, holding pressure can no longer be transmitted to the thick-wall core, shrinkage compensation is interrupted, and sink marks follow.
Solución
①Core out thick walls to reduce material, reducing shrinkage at the source; ②Place the gate near the thick wall and enlarge it to delay freeze-off; ③Increase holding pressure; ④Strengthen cooling in thick-wall areas; ⑤Conduct a gate freeze-off study to determine the effective holding window.
Conclusión clave
For PE thick-wall sink marks, 'structural material reduction first': solid thick blocks are a breeding ground for sink marks, and material reduction is more effective than piling on holding pressure; large thick blocks should be avoided at the design stage of thick-wall PE parts.
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