Injection molding burning streaks/silver streaks

- Mar 30, 2018 -

Appearance

Silvery or dark surface streaks and in exceptional cases black discolorations.

Cause

1. Damage to the plastic melt due to excessively high temperatures or overlong residence times resulting from gaseous decomposition products.

2. High shear heating due to small gate cross sections or by sharp changes of direction in the mold.

Correction

1. Reduction of the injection molding speed.

2. Avoidance of undersized gates and sharp changes in direction in the mold.

3. Check the controller of the hot runner system and the barrel heater.

4. Reduction of melt temperature, screw speed (rpm), residence time (if necessary use a smaller plasticizing unit) and back pressure.