Screw wear

The screw flight height gradually decreases and the clearance with the barrel increases, causing plastication quality and conveying capacity to continuously decline. Manifestations of screw wear include: extrusion output gradually decreasing, increased product surface roughness (poor plastication), and difficulty in melt temperature control (increased clearance causes unstable shear). The clearance in the compression and metering sections of a severely worn screw can increase to 2~3 times that of a new screw, making the extrusion process completely out of control.

1. Material/formulation factors: Filler abrasion. 2. Comprehensive factors: Long-term operation under high temperature and high shear. 3. Equipment factors: Unfiltered hard particles entering the screw. 4. Equipment factors: Mechanical friction between screw and barrel. 5. 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.

1. Process parameter optimization and adjustment: Select wear-resistant screws (bimetallic screws, cemented carbide spray coating). 2. Mold/tooling improvement and maintenance: Control processing temperature not to exceed material recommended values. 3. Equipment inspection and system maintenance: Strengthen raw material pretreatment to remove hard impurities. 4. Material/formulation optimization: Regularly check the screw-barrel clearance. 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.

This problem is a typical manifestation of screw wear in extrusion molding. The core of the solution lies in eliminating the root cause of the defect through systematic optimization of process parameters (temperature, speed, pressure) and precision correction of the die/sizing system. It is recommended to start with parameter adjustment and gradually go deeper into the equipment and tooling levels.