Uneven winding edges (telescoping)

During winding, various defects occur: too loose tension causes loose roll slipping, too tight tension causes film surface stretching deformation, uneven roll edges in plum-blossom shape, core wrinkling, etc. Poor winding directly affects product storage stability and subsequent processing — loose rolls have film layers sliding during storage producing wrinkles, tight rolls increase film surface internal stress causing shrinkage deformation. Winding tension control is the last key process of the calendering production line.

1. Comprehensive factors: Film deviation. 2. Comprehensive factors: Winding shaft not perpendicular to film width direction. 3. Comprehensive factors: Uneven film thickness causes roll diameter to be too large at corresponding positions. 4. 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. 5. Feed uniformity factors: The temperature uniformity of the calender feed and the shape stability of the material bank directly affect the uniformity of feeding into the roll nip. A material bank that is too narrow, skewed, or unevenly rolling all cause transverse thickness abnormalities in the product; the temperature and flow rate of the banbury or extrusion feed must be kept stable.

1. Process parameter optimization and adjustment: Install a deviation correction device and set control parameters. 2. Mold/tooling improvement and maintenance: Correct winding shaft centering. 3. Equipment inspection and system maintenance: Improve film thickness uniformity. 4. Systematic troubleshooting method: Troubleshooting of calendering problems follows the sequence "roll gap → roll temperature → feed → tension → cooling". First check and precisely adjust the roll gap crown and cross angle, then confirm the uniformity of each roll's temperature distribution, next check the feed bank shape and rolling behavior, further adjust the winding tension control parameters, and finally optimize the cooling roll temperature and contact method. Change only one variable at a time to confirm the effect. 5. 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 uneven winding edges (telescoping) 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.