Abstract
In the recent past, automotive manufacturers worldwide started to demand sheet metals with very high surface quality, particularly those used in exposed panels. In order to meet this requirement the majority of strip producers started to use thermal spray coatings of one kind of another on essentially all the rolls in annealing, galvanizing, and other processing sections. In fact, no sheet for an exposed application can be produced without the use of roll coatings. Bridle and accumulator rolls in both entrance and exit ends of a galvanizing line are usually coated with tungsten or chromium carbide and/or oxide ceramic. These coatings prevent surface damage on the roll and provide proper friction/grip. In some cases, a properly textured coating provides the desired characteristics or profile on the strip surface. Coatings for furnace and hot tension bridle rolls prevent pickup due to slippage, iron fines, or an accidental change in the furnace atmosphere. The coating on pot and stabilizer rolls in a galvanizing pot prevents not only dross adhesion but also provides high enough friction to eliminate hydroplaning. Deflector or tower rolls are also coated with carbide or ceramic to minimize zinc pickup. The coating on rolls, in general, allows smooth operation of the line and produces an improved strip surface. At the same time, it allows an extension in service life, thus reducing frequency of maintenance shutdown. This paper attempts to review the present state of the art and predict future development.
