Long Life and High Reliability EP Steel Saves €38,400 Annually for Operator

The Sendzimir Mill is used for cold-rolling wide sheets of metal to close tolerances. It has small -diameter working rolls, each backed by a pair of supporting rolls, and each pair of these supported by a cluster of three rolls. It was in the operation of these rollers that the bearing wear and premature failures were occurring. The operating conditions meant that the inner raceways of the bearing rings were flaking, reducing the life of the roller support bearings considerably.

The failures were costing the mill operator €61,800 annually; this figure consisting of the cost of new bearings, €42,000; six maintenance stops per year, each of 3-hrs duration, at €1,000 per hour; the remainder: €1,800, being associated costs.

Clearly these costs were unsustainable in a highly competitive manufacturing environment, and so a solution was sought to the problem, by involving bearing manufacturer NSK. NSK became involved through its asset improvement programme, which has provided major cost savings and efficiency improvements for manufacturers in all market sectors.

Engineers from NSK were invited to view the Sendzimir Mill, and to propose solutions as to how the life problem could be solved. The engineers analysed the flaking and wear failures found in the inner rings and also the operating conditions and lubrication of the bearings. Following these analyses, they recommended assembling new bearings for the mill, with the bearing inners rings manufactured from NSK’s special EP steel.

Offering up to three times the life of conventional bearing materials, NSK’s Extra Long Life and High Reliability EP steel is the result of a new evaluation technique employed by NSK (NSK – ISD2) into steel manufacturing technology.

EP steel offers significant improvements in purity and reduction of non-metallic inclusions relative to conventional bearing steels, and also has fewer large sized particles than Vacuum Arc Remelted (VAR) steel or conventionally refined steels.

NSK’s recommendations were accepted by the mill operator, and replacement bearings were supplied with inner rings manufactured from EP steel. The value of this product improvement can be judged from the operating life that the bearings have provided since fitment. Previously, bearings were lasting an average of 2-months – 1,500 to 3,000 hours of operation. However, with the new bearings fitted the life was increased by more than 5,000 hours, saving the mill operator €38,400 annually in avoidable costs.