Statistical Analysis about Crack and Spalling on Work Roll for Hot Strip Mill Finishing Rear Stands

Abstract

Concerning cracks and spallings of high alloy grain cast iron roll for hot strip mill finishing rear stands, we have been trying to clarify their originating processes by the field data of rolls. From the analysis of reports about types of failure, roll operating and maintenance conditions for 80 pieces of damaged rolls, the followings became clear ralating to the mechanism of crack and spalling.
When a crack is introduced on a roll body by cobble, quick roll change will result in a small damage. However, when the cracked roll is used continuously for rolling, we will get a heavy damage such as a large spalling, which is over 100 mm in width and over 50 mm in root depth. Sometimes, a breaking short on a roll body took place by the propagation of crack by cobble.
It is important to find out the crack quickly after cobble to avoid the heavy damage of the roll. The roll material with higher resistance to thermal shock and load caused by cobble has to be manufactured. Introducing an eddy current testing method to find out a small crack, gives rise to effective decrease in roll damage.