After experiencing ongoing problems with the bearings on a vital milling machine at a steel plant, the management team turned to NSK for a solution. Now the company has achieved high savings per year.
The steel mill produces rails for lift equipment that require the machining of two flat areas at the ends, which assist the fitting of the rails during assembly. While the time required to mill these rough surfaces is short, the stiffness of the machine’s spindle is critical due to the length of the rails. However, using the milling machine’s original bearings, the steel plant noticed that spindle stiffness reduced after just three months, making it necessary to change the spindle assembly, including motors.
Faced with a recurring and expensive situation, NSK was asked to find a solution. Expert NSK engineers visited the plant and analysed the spindle design as part of its AIP Added Value Programme. Calculations were made based on the use of tooling expected to deliver high cutting capacity and withstand high loads. Engineers also inspected the failed bearings and checked the wear bands of the raceways.
Following their analysis, NSK’s engineers recommended that the spindle be redesigned with a four row bearing set, instead of three, thus increasing the radial load capacity and radial stiffness. The contact angle was also changed from 15° to 25°, to increase the bending stiffness of the shaft. NSK’s high precision angular contact ball bearings (ACBB) were selected from its range of standard products.
The NSK high precision ACBB series is manufactured to conform to ISO standards. A choice of three contact angles, two cage designs and two types of ball material is available to suit application requirements.
After the steel mill had implemented the change, the bearings continued working in the milling machine for more than a year, with no failures experienced in the motor or transmission. Indeed, a full report was produced by NSK to verify the improved characteristics, detailing the enhanced bending stiffness of the shaft and extended operating life from three months to over a year.
When comparing the costs from before and after the adoption of NSK bearings, the savings are clear to see. Today, the steel mill no longer has to endure four production stops a year, while the costs for the replacement spindle assemblies and motors have also been eliminated. Taking these factors into account, it has been calculated that the plant is saving 35,600 euro per year.