The nodes of hot-dip galvanizing lines operate in an aggressive environment - zinc-aluminum melt with a temperature of 460oC. At elevated temperatures, Zn from the melt reacts with Fe from the steel and adheres to the rollers, leading to pressures on the strip. Due to the agglomeration of Zn and its subsequent deposition on the sliding nodes, the wear of the seats also occurs.
HVOF-coatings of Plakart based on WC / Co and MoB / CoCr increase the resistance of the rollers to the effects of melt, wear and sticking.
The estimated effect: coatings provide resistance to the rollers to several months without repolishing, and also prevent the formation of rolling marks.
Fujimi performed coating tests on the continuous galvanizing line of Nucor Crawfordsville, USA. The samples were made of steel 316L, after the coating was polished. After grinding, the coating thickness was 100 µm. The samples were immersed in a molten Zn bath for 30, 60 and 90 days. After immersion, no visible changes were found on the samples, only a thin layer of Zn was glued to the surface. The layer is easily removed by hand. SEM showed a slight diffusion of Zn in the coating.
The use of protective coatings can increase the life of the rollers and reduce the costs associated with the withdrawal of the nodes of galvanizing lines during their dismantling, as well as losses from damage to the product.