Increasing service life and annual savings

At a factory in Spain producing automotive brake systems for the global marketplace, some 117 ball screws facilitate linear motion and tool table/changer positioning in a large number of CNC machining centres.

However, because of stringent requirements and tough environmental conditions, the ball screws have an average service life of only six months. As a consequence, unscheduled down-times were causing considerable additional costs to be incurred.

The supplier asked NSK for its expert advice to help to reduce the down-time frequency. In these situations, NSK offers support to customers in the framework of its AIP programme. A team of company specialists duly investigated the raceways and lubrication conditions in three faulty linear drives in order to determine failure causes.

The result: a combination of high loads, penetrating cutting fluids and high ambient temperatures which were responsible for the short lifespan.

To counter these issues, NSK recommended using ball screws that have been specially developed for high speeds and loads. This product range features a customer specific nut that is tailored exactly to the application and provides greater axial stiffness, not just of the ball screw, but the entire powertrain, thus increasing machine precision.

Moreover, as preload is spread over several balls, service life is increased considerably. As recommended by NSK, the ball screws were equipped with the company’s proprietary X1 high performance seals. These seals prevent any cutting fluid from penetrating the linear system and stop the ball screw lubricant from contaminating the machining centre's cutting fluid or coolant. The X1 seal also has excellent grease-retention capabilities.

Optimal lubrication of the ball screw in tough operating conditions is assured by using the K1 lubrication unit, which enables the lubricant's useful life to be considerably prolonged, again contributing to lower maintenance costs.

On a trial basis, two of the new NSK ball screws were fitted to the machining centres in Spain. The results were highly successful: ball screw lifespan increased by a factor of six.

Furthermore, since installation, there have been no more failures. The automotive supplier can now benefit from lower spare part costs and, above all, from significantly less production down-time.