Shrinkage deformation

After cooling and sizing, the product shows dimensional shrinkage or twisted deformation exceeding design values. 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. Cooling/environmental factors: Cooling rate too fast causes internal stress freezing. 2. Process parameter factors: Improper die draw ratio setting. 3. Cooling/environmental factors: Crystallization shrinkage of crystalline polymers during cooling. 4. Comprehensive factors: Molecular orientation not fully relaxed.

1. Process parameter optimization and adjustment: Appropriately reduce cooling rate. 2. Mold/tooling improvement and maintenance: Optimize die draw ratio so die dimensions match product dimensions. 3. Equipment inspection and system maintenance: Increase sizing section temperature to give molecular chains relaxation time. 4. Material/formulation optimization: For materials with large shrinkage, reserve compensation allowance in die design. 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 shrinkage deformation 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.