Extrusion & Post
13 مشاهدة
Sharkskin appears on the surface of cross-linked polyethylene extruded products
ظاهرة المشكلة
Periodic rough streaks resembling sharkskin appear on the extrudate surface, rough to the touch.
Sharkskin affects product appearance quality and, in severe cases, affects mechanical properties; it is common in film and pipe extrusion.
تحليل الأسباب
(1) Extrusion speed too fast, melt undergoes stick-slip alternating flow at the die exit
(2) Die temperature too low, melt adhesion to die wall large
(3) Cross-linked polyethylene melt elasticity large, stress release uneven when exiting the die
(4) Die inner wall finish insufficient or worn
(5) Melt temperature too low, high viscosity prone to melt fracture
الحل
(1) Appropriately increase die temperature to the higher value within 170-220°C
(2) Reduce extrusion speed so that the melt exit speed is lower than the critical speed
(3) Polish die inner wall to Ra≤0.2μm, chrome plating treatment if necessary
(4) Increase sizing section length at the die exit to stabilize melt flow
(5) Appropriately improve the matching of screw rotation speed and haul-off speed
الخلاصة الأساسية
Sharkskin is the result of stick-slip flow of the melt at the die exit, and is improved by increasing the die temperature and reducing the extrusion speed.
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