Common Problems and Solutions of Injection Mold Trial (3)

  • Jul 04,2022

Air trap


--> Characteristics of injection molded part defects

Can easily be seen in "air traps" in transparent injection molded parts but can also occur in opaque plastics, it relates to the thickness, and usually caused by the plastic shrinking away from the center of the injection molded part.

 

--> Possible cause of the problem

1) The mold is not fully filled.

2) Abnormal operation of stop valve.

3) Plastic not completely dry.

4) Pre-molding or injection speed is too fast.

5) Some special materials should be produced by special equipment.

 

--> Solution

1) Increase shot volume.

2) Increase injection pressure.

3) Increase screw forward time.

4) Decrease melted temperature.

5) Decrease or increase injection speed.

6) Check whether the non-return valve is cracked or not functioning.

7) Drying conditions should be improved according to the properties of the plastic to allow the plastic to dry completely.

8) Appropriately reduce the screw speed and increase the back pressure, or reduce the injection speed.

 

 

Injection gate is stuck


--> Characteristics of injection molded part defects

The nozzle is held by the nozzle sleeve.

 

--> Possible cause of the problem

1) The nozzle sleeve is not aligned with the nozzle.

2) Too much plastic in nozzle sleeve.

3) Nozzle temperature is too low.

4) Plastic is not fully solidified in the sprue, especially the larger diameter sprue.

5) The arc surface of the nozzle sleeve and the arc surface of the nozzle do not match properly.

6) Not enough draft angle of the runner.

 

--> Solution

1) Realign nozzle and nozzle sleeve.

2) Decrease injection pressure.

3) Decrease screw forward time.

4) Increase the nozzle temperature or use a separate temperature controller to heat the nozzle.

5) Increases the time for cooling, but it's better to use a nozzle sleeve with a smaller nozzle instead of the original nozzle sleeve.

6) Correct the mating surface of the nozzle sleeve and the nozzle.

7) Properly expand the draft angle of the runner.

 

 

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