Black Spots, Brown streaks.

Black spots and brown streaks appear as dark spots or streaks in the molded part and are usually caused by thermal damage to the melt. Possible Solutions Check the material for contamination. Decrease the melt temperature. Decrease the overall cycle time. Purge and/or clean the screw and barrel. Decrease the screw speed. High screw speeds may cause the material to degrade. Material may have too much regrind content. Material may be overdried. Decrease drying time/temperature. Refer to drying instructions provided by the material supplier. Material may be prone to thermal degradation. It may be necessary to use a more thermally stable material. Dead spots may be occurring, ensure that the alignment between the machine nozzle and mold sprue is correct. Residence time may be too long, or the shot size may be too small for the machine. It may be necessary to move the mold to a machine with less injection capacity.