Poor cooling and setting

After passing the cooling rolls, the product is not fully set; the surface still feels sticky or deforms easily, hardness is insufficient, and dimensions are unstable. Products with poor cooling and setting continue to deform during winding and storage, with large and unstable shrinkage. In rigid PVC sheets and transparent films, insufficient cooling also causes low crystallinity, affecting light transmittance and mechanical properties.

1. Mold/tooling factors: Cooling roll temperature too high or cooling medium flow insufficient. 2. Process parameter factors: Calendering speed too fast causes insufficient cooling time. 3. Equipment factors: Product thickness too large, exceeding equipment cooling capacity. 4. Mold/tooling factors: Scale on cooling roll surface affects heat exchange. 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: Reduce cooling medium temperature and increase flow. 2. Mold/tooling improvement and maintenance: Reduce calendering speed if necessary. 3. Equipment inspection and system maintenance: Regularly clean scale from cooling rolls. 4. Material/formulation optimization: For thick products, switch online to larger diameter cooling rolls or add cooling sections. 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 poor cooling and setting 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.