Haul-off slipping

Fluctuation of haul-off machine speed causes periodic changes in product dimensions — pipe outer diameter fluctuating larger and smaller, profile wall thickness fluctuating thicker and thinner, with dimensional fluctuation amplitude exceeding the tolerance range. Haul-off slipping manifests as momentary pauses or accelerations of the product at the haul-off rollers, causing periodic marks on the surface. Unstable haul-off is one of the key threats to the continuous stable operation of an extrusion line.

1. Mold/tooling factors: Rubber on haul-off roller surface worn smooth. 2. Process parameter factors: Insufficient haul-off roller clamping pressure. 3. Comprehensive factors: Water/oil/release agent on product surface causes low friction coefficient. 4. Mold/tooling factors: Haul-off roller rubber layer aged and hardened. 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: Recondition or replace haul-off roller rubber layer to increase friction coefficient. 2. Mold/tooling improvement and maintenance: Increase clamping pressure (note that the product must not be flattened). 3. Equipment inspection and system maintenance: Remove residual water/oil from product surface. 4. Material/formulation optimization: Adjust haul-off roller rubber hardness. 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 haul-off slipping 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.