Screen clogging / frequent screen changes

The pressure differential before and after the screen rises rapidly, extrusion pressure keeps climbing, and screen change frequency is far higher than normal (e.g., from once every 8 hours to once every 2 hours). Screen clogging causes extrusion output to drop, back pressure to rise, and melt temperature to increase, forming a vicious cycle of triple instability of pressure-temperature-output. Frequent screen changes not only increase downtime and material waste, but also make initial product quality unstable after each screen change.

1. Material/formulation factors: High impurity content in raw material (gels, carbonized material, dust, etc.). 2. Comprehensive factors: Screen mesh count selected too high. 3. Material/formulation factors: Poor pigment or filler dispersion produces large particles. 4. Die design factors: The geometry of the die flow channel, the land length, and the outlet dimensions directly affect melt flow stability and product dimensional accuracy. Unreasonable flow channel design (presence of dead corners, excessively large convergence angle) is an important root cause of melt fracture, material buildup, and flow marks, and must be addressed starting from optimization of the die structure. 5. Cooling and sizing factors: The cooling rate and uniformity of extruded products determine crystallinity, internal stress level, and dimensional stability. Uneven cooling causes pipe ovality, profile deformation, and internal stress concentration; the cooling water circuit layout and water temperature control must be optimized.

1. Process parameter optimization and adjustment: Strengthen incoming raw material inspection and use clean raw materials. 2. Mold/tooling improvement and maintenance: Select screens with appropriate mesh count according to product requirements (higher is not always better). 3. Equipment inspection and system maintenance: Optimize the pigment/filler masterbatch system to ensure good dispersion. 4. Material/formulation optimization: Use an automatic screen changer to reduce downtime. 6. Preventive management: Establish standardized process parameter cards and quality control limits for each mold/product, and regularly conduct process capability index (CPK) evaluations. For recurring problems, use fishbone diagrams or 5Why analysis to trace the root cause, and solidify countermeasures as PFMEA control points. Establish a regular equipment maintenance system and implement life management for key tooling such as dies/spinnerets/calender rolls/coating heads.

The essence of frequent screen clogging is insufficient raw material cleanliness or improper screen mesh count selection. The solution approach is "clean source + reasonable screen selection + automatic screen change": strengthen incoming raw material inspection and use clean materials, select reasonable mesh count according to product requirements rather than blindly pursuing high mesh count, and use automatic screen changers to reduce downtime losses.