The analysis of fretting fatigue failure in backup roll and its prevention

In the present research, a fretting fatigue failure in a backup roll (BUR) was examined. Fretting fatigue properties of the roll material were experimentally obtained and the prevention of the fretting fatigue failure was proposed. BUR is one of the most important components in a steel making rolling mill for the control of plate thickness and flatness. The BUR was initially supported by oil film bearings. Recently, oil film bearings have been rapidly replaced by roller bearings for the purpose of high-precision rolling. After the replacements, fretting fatigue failures of BUR have begun to occur. Rotating bending fatigue tests were performed with a 40 mm diameter shrink-fit axle to evaluate the fretting fatigue strength of the BUR material and to examine the improvement of the fretting fatigue strength of the holding part of the BUR. The effects of roller machining and overhanging of the contact edge on the fretting fatigue strength were investigated. Based on the results of this study, roller machining was applied to the holding part of the BUR. Furthermore, the diameter of the holding part of the BUR was increased. No failure occurred due to fretting in the BUR for more than four years since these countermeasures were applied.