One of the major production plants of a large Spanish Automotive Group is benefiting from savings of €2.500 per annum on the operation of a drilling unit on one of its main assembly lines. The savings have been provided by NSK as part of its cost saving, Asset Improvement Programme, which takes a holistic approach to bearing problems experienced in production environments.
The problem with the drilling unit was that its rear bearings repeatedly failed after 3 to 4 months of operation. The result of these failures was unplanned production stoppages and costly downtime, while the bearings were removed and replaced. With downtime costs running at €500/hour for the car plant, three breakdowns per year at around 2.5 hours in duration were costing the company €3.750 – and this on a single drilling rig.
NSK engineers visited the car plant to investigate the problem. They found that the sealed rear bearings were failing due to rotating at a higher speed than that specified (10,000rpm). NSK suggested fitting the bearings with non contact seals in order to achieve maximum speed with minimised friction.
In their report the engineers pointed up the nature of the problem. ‘While the seals are providing their protective function, the ball bearing is rotating at high speed. So if operating life is to be maximised, the type of seal employed must be chosen, not only with the operating conditions in mind, but also with the frictional effect the device will have upon the bearing starting and running torques. In essence, the speed at which the bearings operate is constrained by the friction that exists between the seals and the bearing inner ring.’
The engineer’s report highlighted the challenge of recent years: to develop a new generation of seals which combine high levels of sealing with speed capabilities similar to those of shields. NSK’s V type seal was developed for this very purpose. In contrast to conventional seals, V types are non-contact units which are held in the outer ring of a bearing by the elasticity of the rubber seal material.
With this design, friction is not a problem. Consequently, bearings employing the seals can be used at the same high speeds as bearings equipped with shields.
Following the change to non-contact seals, no bearing replacements have been required on the drilling unit for over a year. Now, only annual planned maintenance is carried out on the drilling unit: a 2.5 hour process costing €1.250 (2.5hrs x €500). The car manufacturer is therefore saving €2,500 per year in maintenance costs, and is also benefiting from long, trouble-free production runs.