Uneven pipe wall thickness

The circumferential wall thickness difference of the pipe exceeds the allowable tolerance range, local areas are too thin or too thick, and the wall thickness unevenness exceeds 5%~10%. Wall thickness deviation directly causes the pipe's pressure-bearing capacity to decline——the thinnest point becomes a stress concentration point and ruptures first in the hydrostatic test. This defect can be found by online detection with an ultrasonic thickness gauge, and is usually directly related to die concentricity deviation or poor sizing sleeve alignment.

1. Mold/tooling factors: improper adjustment or offset of the concentricity between the die and the mandrel. 2. Mold/tooling factors: poor alignment between the sizing sleeve and the die. 3. Mold/tooling factors: uneven cooling in the vacuum sizing tank. 4. Comprehensive factors: traction force fluctuation causing pipe deflection.

1. Process parameter optimization and adjustment: re-calibrate the die-mandrel concentricity, use a wall thickness measuring instrument for online monitoring. 2. Mold/tooling improvement and maintenance: adjust the center alignment between the sizing sleeve and the die. 3. Equipment inspection and system maintenance: check whether the vacuum tank water ring or spray is blocked. 4. Material/formulation optimization: stabilize the traction speed, eliminate traction slippage. 6. Preventive management: Establish standardized process parameter cards and quality control limits for each set of 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 the 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.

The essence of uneven pipe wall thickness is that the die-mandrel geometric deviation and poor alignment of the sizing system cause the melt to be distributed unevenly in the circumferential direction. The core solution idea is 'precise calibration + online monitoring': calibrate the die concentricity and sizing sleeve alignment, and cooperate with online wall thickness measurement feedback for real-time fine adjustment.