Injection Molding Defects And Solutions -- Sink Marks

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Injection Molding Defects and Solutions -- Sink marks 2025-10-11

Sink Marks (Depressions)

Surface dents or depressions appear on molded parts. This defect occurs when the molten resin shrinks in volume during cooling and solidification but is not sufficiently compensated by additional material. It often appears on the backside of thick sections or behind ribs.

Causes (2.1)	Solutions (2.2)
2.1.1 Runner or gate too small, or insufficient number of gates.	2.2.1 Improve runner and gate size, or increase the number of gates.
2.1.2 Wall thickness too large or uneven (sink marks often occur behind thick sections).	2.2.2 Modify mold cooling system to ensure adequate cooling in thick areas.
2.1.3 Improper gate location, unfavorable for feeding or packing.	2.2.3 Adjust gate position and moderately increase mold temperature to facilitate packing.
2.1.4 Melt temperature and mold temperature too high, or cooling time too short.	2.2.4 Lower melt and mold temperatures, and increase cooling time.
2.1.5 Mold temperature too low, causing vacuum voids.	2.2.5 Raise mold temperature to ensure sufficient packing.
2.1.6 Low injection pressure or slow injection speed.	2.2.6 Increase injection pressure and injection speed.
2.1.7 Injection and holding time too short.	2.2.7 Extend injection and holding time.
2.1.8 Insufficient feeding or residual material (cushion).	2.2.8 Increase shot size and cushion to improve packing.
2.1.9 Poor melt flow or excessive flash.	2.2.9 Increase mold temperature to improve flow; raise clamping force to prevent flashing.
2.1.10 Low melt temperature leading to poor flowability.	2.2.10 Increase melt temperature to enhance flowability.
2.1.11 Low nozzle temperature or small nozzle diameter.	2.2.11 Raise nozzle temperature or use a larger nozzle.
2.1.12 Screw rotation speed too high.	2.2.12 Reduce screw rotation speed.
2.1.13 Injection speed too low or too high; back pressure too low.	2.2.13 Adjust injection speed (increase or decrease as appropriate) and raise back pressure.
2.1.14 Faulty heating band or thermocouple in the hot runner system.	2.2.14 Replace the defective component.
2.1.15 Hot runner nozzle too small or blocked.	2.2.15 Replace or clean the nozzle.

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Дефекты литья под давлением и их решение — Неполное заполнение

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