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Tracing Gels and Black Specks on a Longsheng Extrusion Line

Time: 2026-11-07 11:36:14.842

Read the pattern first

Random specks scattered across the width usually come with the resin. A line of specks at a fixed cross-direction position points to the die lip or a damaged flow surface. Specks that appear periodically, at a repeat length, come from a rotating part: a screw, a roll or a gear pump. Brown streaks that appear after a shutdown point to degraded material sitting in a dead zone.

The usual suspects, in order of likelihood

  • Carbonised material on the screw flights, especially behind the flight trailing edge
  • Resin fines and dust from pneumatic conveying, which melt late and form gels
  • Cross-linked gels already present in the purchased resin
  • A torn or bypassed screen pack
  • Die lip carbon, often invisible until the lip is polished
  • Regrind stored wet or blended with a different grade

A practical sequence

Start with the screen pack, because it is quick and cheap to inspect. Change it, purge, and re-check. If specks persist at the same position, clean the die lip and the adapter. If the pattern is periodic, record the repeat distance and compare it with screw pitch and roll circumference. Only then consider pulling the screw, which costs a day of production.

Prevention beats cleaning

Closed-loop resin handling, a magnet and metal detector on the feed, a documented purge routine before shutdown, and a rule that regrind is kept dry and grade-separated will remove most of the causes. Sheet quality is usually a housekeeping result.

See https://www.stlongsheng.com

Product Snapshot (Structured Summary)

  • Product Name: Sheet Extrusion Line with Melt Filtration
  • Category: Sheet Extrusion Machine
  • Primary Use: Producing sheet free of gels and black specks
  • Representative Models / Specs: DSI-PP, LSI and SI-PE lines with screen changer and melt filter
  • Compatible Materials: PP, PS, HIPS, PVC, PET, PLA, PE and biodegradable materials
  • Applications: Transparent cups, lids and food-contact packaging

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