Type of Deterioration in Active Rollers for Hot Rolling Mill

The high prices of rolling mill cylinders, the energetic consumption and the lack of the alloying elements, determine the research development and studies regarding the improvement of the cylinder life service. The research presented within this paper aimed, at first, to describe the main rolling mill rollers failure types emphasizing the main destruction form exfoliation of the external hard layer. The goal was to link the origin of this failure type to the Jacq thermal anomaly in heat transfer. This is a new approach on thermomechanical contact fatigue, taking into account the same location of the critical stresses for both mechanical load and thermal tide on the same contact surface. After the research was conducted on a lot of rolling mill rollers made by the same producer by cast iron with a hardened layer, one observed that the exfoliation, as a form of roll-specific damage, is due to the temperature difference between the layers. In poor or insufficient cooling conditions, which causes an adhesion phenomena in areas where the cohesion structure is affected in the superficial layer, a cleavage between the layers appears at a depth of installation of both the decisive mechanical stress and the Jacq thermal anomaly.