Plastic injection molding dark streaks solution

Plastic injection molding dark mark appearance

• Streaks ranging in color from dark to black.

Dark streaks caused by deposits of thermally damaged material from the hot runner

Plastic injection molding dark mark cause

• Processing using a screw which is too deeply flighted in the feed section (air intake)


• “Dead spots” in the plasticizing unit or hot runner system


• Defective nonreturn valve


• Screw decompression is too great or too fast


• See diesel effect

Plastic injection molding dark mark correction

• Raise temperature in feed section so that melting is earlier; use more suitable screw


• Check plasticizing unit and hot runner for zones of impeded flow and if necessary correct them


• Replace defective nonreturn valve


• Shorten the path for screw decompression or decompress a reduced rate


• Improve mold vent operation or design

 

Plastic injection molding dark streaks solution