Common Faults, Causes, and Solutions in PE/PP Sheet Production Lines
I. Uneven Sheet Thickness
Causes:
* Inconsistent temperature on both sides of the T-die head; lateral deviation in die lip clearance;
* Uneven heating and cooling of the three-roll calendering rollers;
* Roller surface deformation;
* Unequal pressure on both sides of the roller hydraulic pressure;
* Unstable material output from the extruder;
* Bridging of the feed material;
* Uneven mixing of raw materials;
* Fluctuating ratio of new material to recycled material;
* Inconsistent traction speed.
Solutions:
* Segmented fine-tuning of die head heating; fine-tuning of die lip adjusting bolts;
* Unifying the cooling water temperature of the three rollers;
* Overhauling the hydraulic pressure regulating system to ensure roller surface parallelism;
* Adding a mixing hopper to evenly mix new and recycled materials and stabilize extrusion speed;
* Overhauling the variable frequency traction synchronization system.
II. Bubbles, Blisters, and Holes on the Sheet Surface
Causes:
* High moisture content in raw materials (damp recycled or crushed materials);
* Excessively high extrusion temperature, causing localized material decomposition and gas generation;
* Clogged vents in the barrel, preventing the escape of moisture and small volatile molecules;
* Recycled materials mixed with PVC and other impurities decompose under heat.
Solutions:
* Pre-dry and dehumidify raw materials; air-dry damp recycled materials;
* Reduce the temperature in all zones of the machine; PP should not exceed 230℃, and PE should not exceed 210℃;
* Clean the vents regularly;
* Strictly control the sorting of impurities, prohibiting the mixing of other plastics.
III. Pitting, Crystal Points, and Fish-Eye Bumps on the Sheet Surface
causes:
* Unplasticized recycled particles, cross-linked materials, and impurities are present in the raw materials;
* Low screw plasticizing temperature, resulting in incomplete material melting;
* Damaged filter screen, allowing impurities to enter the die head.
Solutions:
* Replace with high-quality raw materials; sieve recycled materials to remove impurities;
* Appropriately increase the temperature of the intermediate barrel;
* Replace the filter screen on time.
