Injection Molding
13 مشاهدة
Burnt marks/burn spots appearing in random copolymer polypropylene injection molded products (variant: strengthened measures)
ظاهرة المشكلة
Black or brown burnt spots appear locally on the product, usually at the flow end or positions with difficult venting.
The material at the burnt mark has thermally degraded, mechanical properties have severely declined, and the product is scrapped.
Especially, additional attention is needed on top of the original basis; this problem is more prominent and requires focused attention.
تحليل الأسباب
(1) Gas in the cavity is compressed and heated; the temperature exceeds the material's ignition point, causing local carbonization and burning
(2) Injection speed is too fast; gas in the cavity has no time to escape and is compressed to produce high temperature
(3) Poor mold venting; trapped air is compressed at the flow end
(4) Barrel temperature is too high; the material has partially degraded in the barrel
(5) Screw speed is too fast; shear overheating occurs in the screw
(6) On top of the original basis, additional attention is needed as process parameter fluctuations or equipment condition changes aggravate this problem
الحل
(1) Reduce injection speed, especially in the later filling stage, allowing time for gas to escape
(2) Improve mold venting, adding vent grooves, vent pins or vent inserts at burnt mark positions
(3) Appropriately lower barrel temperature to a reasonable value within the 190-260°C range
(4) Reduce screw speed and back pressure to prevent shear overheating
(5) Check gate position to avoid the melt forming enclosed air pockets
(6) And strengthen process monitoring; on top of the original basis, additional attention is needed to pay special attention to parameter stability
الخلاصة الأساسية
Burnt marks are the result of trapped air in the cavity being compressed and heated, causing material carbonization; the core solutions are improving venting and reducing injection speed.
In different production scenarios, targeted preventive measures need to be taken.
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