Longitudinal corrugation of pipes

Corrugated undulations appear on the longitudinal inner/outer walls of the pipe. 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. Mold/tooling factors: Improper distance between die and sizing sleeve. 2. Cooling/environmental factors: Unstable vacuum with periodic changes. 3. Process parameter factors: Extruder pressure fluctuation. 4. Process parameter factors: Periodic changes in the ratio of haul-off speed to extrusion speed. 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: Adjust the distance between die and sizing sleeve to an appropriate value. 2. Mold/tooling improvement and maintenance: Check the vacuum system to eliminate leakage and fluctuation. 3. Equipment inspection and system maintenance: Stabilize extrusion pressure. 4. Material/formulation optimization: Eliminate haul-off speed fluctuation. 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 longitudinal corrugation of pipes 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.