Poor vacuum sizing / pipe ovality

The pipe cross-section is elliptical rather than perfectly circular, with ovality out of tolerance; poor vacuum sizing effect manifests as unstable pipe outer diameter dimensions or unqualified roundness. Poor vacuum sizing directly affects the fitting seal between pipes and pipe fittings; elliptical pipes show uneven gaps during socket connection, greatly increasing leakage risk. This defect is closely related to vacuum system sealing, sizing sleeve design, and cooling water temperature.

1. Cooling/environmental factors: Insufficient vacuum. 2. Mold/tooling factors: Sizing sleeve water ring or vacuum holes blocked. 3. Equipment factors: Vacuum pump power insufficient or pipeline air leakage. 4. Mold/tooling factors: Improper sizing sleeve dimension design. 5. Cooling/environmental factors: Cooling water temperature too high.

1. Process parameter optimization and adjustment: Check vacuum system sealing and clear blockages. 2. Mold/tooling improvement and maintenance: Ensure the vacuum pump reaches design power. 3. Equipment inspection and system maintenance: Design appropriate sizing sleeve dimensions according to process requirements. 4. Material/formulation optimization: Reduce cooling water temperature to the range required by the process. 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 poor vacuum sizing / pipe ovality 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.