ROLLING BEARING SELECTION - A look at the bigger picture

When selecting rolling bearings for industrial plant, machines and equipment, it is important to analyse the total cost of ownership (TCO) and not just the purchase price of the bearings, says Dr Steve Lacey, technology centre manager at Schaeffler UK

load carrying capacity and stiffness, or minimise friction. In applications where design envelopes


olling bearings are critical components in rotating plant,

machines and equipment, including machine tools, automated handling systems, wind turbines, paper mills and steel processing plants. The decision in favour of a specific rolling bearing should always be taken after analysing the total cost of ownership (TCO) of the bearing, and not merely on the basis of purchase price alone. Buying cheaper bearings can prove more expensive in the long-term, and the purchase price often accounts for just 10 per cent of the overall costs. When it comes to buying rolling bearings, saving a couple of pounds here and there can lead to higher energy costs, higher maintenance overheads, unplanned machine downtime, loss of production and dissatisfied customers.

EARLY DESIGN INVOLVEMENT To industrial OEMs, the design of bearings can add value to their own products in many ways. By engaging with OEMs early in the design and development stages, bearing suppliers can customise fully optimised, integrated bearings and assemblies, which meet the specific requirements of an application. Bearing suppliers can add value by, for example, creating and customising internal bearing designs that maximise


are small, the bearing design can be optimised for ease of assembly and to reduce assembly times. For example, screw threads on assembly mating surfaces can be incorporated into the bearing design. It may also be possible to incorporate components from the surrounding shaft and housing into the bearing design. Features such as these can lead to cost savings over the whole life of the machine. Other features can include special sealing technology within the bearing to help save space; anti- rotation features to prevent slippage under the effects of rapid changes in speed and direction of rotation; surface coating to minimise friction; and optimising bearing operation under boundary lubrication conditions. The bearing supplier can

examine closely the overall costs of machines, plants and their components, from purchase, energy consumption and maintenance, all the way through to repairs, dismantling and disposal. Well-known cost drivers and hidden expenses can therefore be identified, optimised and eliminated. Schaeffler, for example, aims to continuously improve quality standards and, therefore, the running properties of rolling bearings, through optimised design and materials. It offers a well- aimed, comprehensive technical advisory service and training, in order to find the best suitable solution for each application. The company’s sales and field service engineers are supported by advanced software for bearing selection, calculation and simulation. Furthermore, factors such as efficient instructions and suitable tools for bearing mounting, all the way through to condition-based maintenance, lubrication, dismounting and reconditioning, are all taken into consideration. Local Schaeffler technology centres (STC) bring

When it comes to

engineering and service knowledge even closer to the customer to enable technical issues to be addressed quickly and effectively.

buying rolling bearings, saving a couple of pounds here and there can lead to higher energy costs,

maintenance overheads and unplanned downtime.”

PAPER INDUSTRY EXAMPLE In paper manufacturing, rolling bearings in CD-profile control rolls of calender machines are normally subjected to low loads. The loads are only higher when the gap between the rolls is open. For these applications, machine manufacturers traditionally choose spherical roller bearings with adequate load carrying capacity for the high-load phase. However, in the low-load phase this has led to slippage, resulting in premature bearing failure. By coating the rolling elements and optimising lubrication, these slippage effects can be reduced, but not completely eliminated. For this reason, Schaeffler developed the ASSR bearing (Anti-Slippage Spherical Rolling Bearing). The bearing comprises rings of standard spherical roller bearings, but barrel rollers alternate with balls in each of the two rows of rolling elements. In the low-load phase, the balls ensure slippage-free operation, while the barrel rollers take up the loads

in the high load phase. While the original bearings typically

achieved a service life of about one year, the new ASSR bearings are expected to last for up to 10 years. This means fewer rolling bearings are required over the life of the machine, a reduction in maintenance requirements and savings of six-digits over the entire machine lifecycle. All this was achieved by taking only one single machine position into consideration. Further optimisation, and therefore additional significant savings, can be achieved by supplementary measures, such as online condition monitoring and vibration diagnosis, temperature monitoring or dynamic/static balancing.

Schaeffler UK


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