Screw slipping / poor feeding

The screw rotates but material cannot be conveyed forward effectively, and extrusion output drops significantly. When this defect appears in extrusion molded products, it is usually closely related to process links such as die design, screw plastication state, cooling and sizing system, or haul-off stability. Persistence of the defect will lead to out-of-tolerance product dimensions, unqualified appearance, or decreased mechanical properties, increasing scrap rate and rework costs. Timely diagnosis and troubleshooting from both extrusion process parameters and equipment status are basic requirements for ensuring stable continuous production.

1. Equipment factors: Feed section temperature too high causes material to slip on the screw surface. 2. Operational factors: Hopper bridging causes material interruption. 3. Equipment factors: Screw wear causes conveying efficiency decline. 4. Material/formulation factors: Back pressure too high hinders material advance. 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: Reduce feed section temperature (use a cold water jacket if necessary). 2. Mold/tooling improvement and maintenance: Eliminate hopper bridging. 3. Equipment inspection and system maintenance: Check and replace the worn screw. 4. Material/formulation optimization: Reduce back pressure (replace or clean the screen). 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 slipping / poor feeding 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.