Black Streaking

Suggested Corrective Actions

Machine

  • Check for cracked machine cylinder.
  • Clean overhead area around hopper.
  • Move mold to machine with smaller cylinder.
  • Properly seat nozzle against bushing.
  • Purge or clean dirty cylinder or nozzle.
  • Reduce screw RPMs to reduce frictional heat
  • Turn on feed throat water.

Material

  • Correct over drying to improve flow and fill.
  • Dry material if moisture or volatiles are entrapped at weld lines.
  • Material may be setting up too fast.

Mold

  • Change mold slide grease to higher temperature grade.
  • Check for grease or oil in mold.
  • Reduce lube level of knockout pins.
  • Reduce temperature of hot runner block.