Successful case

How to deal with the common injection defects

Date: 2019-11-15 Author: Grandshine Views: 907


1) Short shot

Phenomenon: Plastic material does not completely fill the cavity (Cavity)

Reasons and treatment methods: 1, the metering setting is insufficient; 2, the injection pressure is too low; 3, the mold temperature or the tube temperature is not insufficient; 4, the back pressure is too low or no back pressure causes the screw to idling; 6, release too much spray; 7 flow distance is too short or plastic flow is poor; 8, sprue or runner is too small.

2) Flash

Phenomenon: Plastic material overflows the cavity


Reason and treatment:


1, too many metering settings; 2, the injection pressure is too large; 3, the clamping force is insufficient; 4, the mold temperature is too high or the temperature of the tube is too high; 5, the plastic fluidity is too good; 6, the plastic crystallization rate is too Slow; 7,the parting line of the mold is not tight enough

3) Black spots

 Phenomenon: black spots on the surface of the molded parts

Reason and treatment:

1. When the plastic is poured into the barrel, the paper bag scraps or sutures and dust are poured into the barrel; 2, the barrel, the screw, the material tube and the nozzle is not cleaned when refueling 4, Plastic factory out processing improperly, mixed with sundries; 5, the mold surface is not clean; 5, the color master selection error (cracking)

  4) Brown Marks

Phenomenon: Black or yellow stripes appear on the surface of the molded article.

Reason and treatment:

1, the mold or plastic temperature is too high; 2, the plastic stays in the material tube for a long time; 3, the injection pressure is too high, shear heat; 4, the mold venting position is incorrect or too small; 5, the screw speed is too fast and the back pressure is too high; 6, the additive in the plastic is improper formulated, and the heat stability is poor;

  5) Sink marks

Phenomenon: the surface of the finished product is sink, especially the sharp portion of the thickness (because the central cooling of the thick meat is slow)


Reason and treatment:

1, the injection pressure is too low, the holding time is too short; 2, the injection speed is too fast; 3, the mold and plastic temperature is too high; 4, the finished meat thickness is poorly designed; 5, the runner and the inlet gate is too small; 6, the parts of the mold are unevenly cooled; 7, the plastic shrinkage rate is too large, the crystallization speed is too slow

6) Bubble (Void)

There are two reasons of gaps in the finished product:

1 occurs in the thickness part of the product, which is formed by the central cooling contraction.

2, the decomposition of air, moisture or plastic volatilization.

Reason and treatment:


1, the injection pressure is too low, the holding time is too short; 2, the back pressure is too low; 3, the plastic temperature is too high, staying too long; 4, the finished meat thickness is poorly designed; 5, the mold flow path, the inlet gate too Small; 6, plastic drying is insufficient; 7, spraying agent too much.

The above is from baiduwenku

 Grandshine has more than 10 years experience in mold design, mold development and plastic injection molding

www.grashine.com