Roll sticking / roll wrapping

The melt excessively adheres to a certain roll surface and cannot be smoothly stripped and transferred to the next roll, manifesting as the material film wrapping around the roll instead of transferring through normally. When roll sticking occurs, production is forced to stop and the wrapped material must be cleaned; in severe cases material accumulates and scorches on the roll surface. Roll sticking is one of the most destructive failures in calendering production, not only causing downtime losses but also possibly damaging roll surface finish.

1. Mold/tooling factors: Roll temperature too high causes melt-roll surface adhesion force too strong. 2. Mold/tooling factors: Improper stripping angle between rolls. 3. Mold/tooling factors: Poor matching between roll surface material and processed material. 4. Material/formulation factors: Insufficient lubricant/release agent in the formulation. 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: Appropriately reduce that roll's temperature. 2. Mold/tooling improvement and maintenance: Adjust inter-roll gap and stripping point position. 3. Equipment inspection and system maintenance: Check the condition of roll surface coating (chrome plating, Teflon coating). 4. Material/formulation optimization: Appropriately increase lubricant. 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.

The essence of roll sticking is that the adhesion force between melt and roll surface exceeds the separation force required for normal stripping. The solution approach is "cool down + adjust angle + add additives": reduce that roll's temperature to reduce adhesion force, adjust the stripping angle to increase the separation force direction component, and appropriately increase lubricant in the formulation to reduce interface adhesion.