Increasing the Lifetime of Mill Rolls by Applying Polymer Materials on Their Bodies

A key reason for breakdowns of backup rolls of hot and cold rolling mills is abrasive wear of their bodies. To increase the lifetime of the rolls, it is suggested to apply a wear-resistant single-layer coating from polymer antifriction materials (for example, fluoropolymer) or a double-layer coating (for example, copper–polymer) on the ground bodies. The coatings are applied by cladding with a flexible tool (a rotary wire brush). The surface layer of rolls is hardened, forming the required surface roughness, reducing an alignment period during their operation. The technical effect lies in the decrease in the friction coefficient to boundary friction (f = 0.01–0.05) and hardening of a surface layer of rolls. The authors developed a roll treatment method introduced on hot rolling mill 2500 at PJSC Magnitogorsk Iron and Steel Works. A brief description of the method is as follows: having ground backup rolls and achieved the required shape, an operator installs a wire brush instead of a grinding wheel on a roll grinding machine. A bar feeding device is installed on the shell. A single-layer coating (fluoropolymer grade F4К20) is applied in two passes of the tool (the rotary wire brush) along the surface of a rotating roll. The roll is removed from the machine after the treatment, assembled according to the operating procedure and installed into a stand. Then, after seven days of the operation, the roll is removed from the stand, and the surface wear is measured along the radius. The analysis of the industrial experiments showed that the wear rate of the rolls treated with rotary wire brushes and covered with a fluoropolymer coating was by 1.7–1.9 times lower than the wear rate of the rolls operating with no cladding. This method contributed to increasing a period between changes of backup rolls in finishing stands by twice, reducing a downtime period, increasing rolling mill performance, and reducing the roll consumption.