Uneven bank rolling

The material bank between calender rolls rolls inconsistently in local areas, causing local feed shortage or excess, with corresponding product areas showing thickness abnormalities or surface defects. The material bank is the rotating material band formed by calender feed above the roll nip; its shape and rolling manner directly affect feed uniformity into the roll nip. When the bank rolls unevenly, one side is fully fed while the other side lacks material, causing obvious transverse differences in the product.

1. Comprehensive factors: Bank shape asymmetric left and right. 2. Operational factors: Feed position off center. 3. Mold/tooling factors: Axial roll temperature unevenness affects melt viscosity. 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.

1. Process parameter optimization and adjustment: Adjust feeding mechanism and method so the bank is uniformly distributed along the roll axis direction. 2. Mold/tooling improvement and maintenance: Balance roll temperature. 3. 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. 4. 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 bank rolling 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.