Uneven roll temperature

Calender roll surface temperature unevenly distributed along the axial direction. When this defect appears in calender molded products, it is usually closely related to process links such as roll gap adjustment, roll temperature distribution, feed uniformity, or winding tension control. Defects in calendered products often have transverse distribution characteristics, directly associated with roll surface condition and material bank behavior. Continuous occurrence will affect the film's appearance, thickness uniformity, and subsequent processing performance; troubleshooting must start from both roll system adjustment and the feed system.

1. Mold/tooling factors: Uneven flow distribution of heating medium (heat transfer oil, water) inside the roll body. 2. Mold/tooling factors: Scaling in roll internal heating channels causes poor local heat transfer. 3. Mold/tooling factors: Fast heat dissipation at roll ends causes low temperature at both ends. 4. Mold/tooling factors: Deviation between temperature control system measurement point and actual roll surface temperature. 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: Clean roll internal heating channels to remove scale or carbon deposits. 2. Mold/tooling improvement and maintenance: Optimize the heat transfer oil circulation system. 3. Equipment inspection and system maintenance: Add auxiliary heating compensation at both roll ends. 4. Material/formulation optimization: Use a surface infrared thermometer to calibrate temperature control deviation. 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 uneven roll temperature 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.