Film skewing / deviation

During conveying, stretching, and winding after calendering, the film web deviates from the center line, gradually shifting to one side; in severe cases the film edge touches equipment edges or falls off guide rollers. Deviation not only causes uneven winding end faces (telescoping), but also makes film surface tension distribution asymmetric, aggravating thickness unevenness and wrinkles. Continued worsening of deviation will force the production line to slow down or stop for adjustment.

1. Mold/tooling factors: Parallelism deviation of rolls. 2. Mold/tooling factors: Unequal gaps at both ends of calender rolls. 3. Comprehensive factors: Uneven transverse thickness of calendered film. 4. Process parameter factors: Uneven winding tension. 5. Roll gap adjustment factors: Crown and cross-angle compensation of calender rolls is the core means of controlling the transverse thickness distribution of the film. Crown design is based on roll deflection calculations; if it does not match the actual process load, it will cause abnormal transverse distribution of film thickness — thicker in the middle and thinner at both ends, or an inverse bow-shaped distribution.

1. Process parameter optimization and adjustment: Calibrate parallelism of all conveying rolls. 2. Mold/tooling improvement and maintenance: Adjust inter-roll gaps to be uniform. 3. Equipment inspection and system maintenance: Improve film transverse thickness uniformity. 4. Material/formulation optimization: Adjust the winding tension controller. 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 film skewing / deviation in calender molding. The core of the solution lies in precise adjustment of roll gap compensation, uniform control of roll temperature distribution, and assurance of feed system stability. It is recommended to start troubleshooting from roll system parameters and gradually go deeper into the equipment and formulation levels.