Influence of Work Hardening on the Surface of Backup Rolls for a 4-High Rolling Mill Fractured during Rolling Campaign

Abstract

Backup rolls are the main tool in a four-high rolling mill; the rolling forces applied in load cells promote the fatigue of the material due to mechanical contact between backup rolls and work rolls. This work investigated the causes of recurrent failures in backup rolls, with cracking always initiated on the surface of the roll body and finishing in the main radius between neck and roll body. Aiming to find the causes of failure, visual inspection and morphology of the fracture were performed, complemented with mechanical tests of hardness on the stress concentration area, in addition to validating the results by applying the finite element method, using ANSYS Mechanical Static Structural Software. It was concluded that the fatigue crack initiated on the surface of BUR due to work hardening continued growing up over the fatigued material, creating beach marks, and finally, a fracture occurred in the main radius of BUR due to stress concentration. The work hardening is the main cause of spalling on BURs and other mechanical components exposed to mechanical contact.

Analysis of Edge Drop on Strip Due to Bending and Elastic Deformation of Back up Rolls in a Four-High Cold Mill

“…The mesh had a total of 980,438 nodes and 544,956 elements. The contact region mesh (BUR-WR-Strip) was considered with a bonded system, and no sliding or separation between face and edges is implement without penetration [22]. A 3D-FEM was employed to simulate the rolling process, using the ANSYS Mechanical Static Structural Software (ANSYS 2023R2) considering the dimensions of mechanical components of the process.…”

“…The mesh had a total of 980,438 nodes and 544,956 elements. The contact region mesh (BUR-WR-Strip) was considered with a bonded system, and no sliding or separation between face and edges is implement without penetration [22]. Results obtained with theoretical analysis and simulation with FEM will be validated with results obtained from a compact X-ray thickness gauge installed in the last stand of a four-high cold mill.…”