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Home » Plastic molding » injection molding troubleshooting sink mark defect

injection molding troubleshooting sink mark defect

January 14, 2019 by mechanicaleng blog Leave a Comment

Sink marks appear when thermal shrinkage of plastics material is not compensated. A sink mark usually appear at rib, boss position, or thickness of product is changed. This post I will explain about cause and sink mark troubleshooting.

plastics injection molding sink marks
plastics injection molding sink marks

I. Sink mark causes.

+ Thickness of product is not equal, samples usually have sink marks at transfer thickness.

+ Temperature of cylinder, or mold temperature is high.

+ Cooling time and holding pressure time is low, samples is not cold.

+ Holding pressure, injection pressure is low, samples can not fill in the mold.

+ When setup injection machine, plastics materials is smaller than we need.

+ Gate and runner are small so molten plastics can not fill in the mold under high pressure.

II. Injection molding sink mark troubleshooting

+ Check cushion amount of remaining materials. If it is too small, we need to increase materials, cushion about 3 mm. Check screw tip (non-return value), or barrel (cylinder).

+ Increase holding pressure, holding pressure time, and cooling time.

+ Reduce mold temperature, material temperature, and injection speed.

+ Check size of runner, gate. We can increase dimension of runner and gate to prevent molten plastics cooling early.

+ Make more air vent for this mold.

+ Decrease thickness of product at sink marks area, make rib if it is necessary.

 

 

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Filed Under: Plastic molding Tagged With: injection molding troubleshooting, molding defect

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