Whole life cost, not price, selects the bearing

Any decision in favour of a specific bearing solution should only be taken after examining the whole life cost and not merely the bearing purchase price, says Trevor Morris of Barden UK.

Any decision in favour of a specific bearing solution should only be taken after examining the whole life cost and not merely on the basis of the bearing purchase price, says Trevor Morris of Barden UK.

In today's highly pressurised production environments the mantra for engineers is that the total cost is critical.

In view of this, the general task of the production engineer is to minimise process costs while at the same time safeguarding product quality.

Bearings are a key component in most manufacturing and processing applications, their reliability and operating life having a significant effect in ensuring that operating costs are minimised.

Moreover, as the pace of bearing technology accelerates, opportunities for technology transfer mean that bearings can play a wider role in reducing the whole life costs of machines.

This is achieved not by supplying cheaper components, but by applying the latest materials, sealing and lubrication technology to improve the machine design and reduce its maintenance costs.

The example of the UK process industry ably supports the above argument.

Currently the UK market for pumps is worth about GBP 980m a year, centrifugal pumps accounting for 80% of this total, each being equipped with between 4 and 5 bearings - 2 or 3 in the pump and at least two in the motor.

The typical 1L10 life specified for these bearings is three years, but when properly installed, lubricated and maintained this should rise to 12 or even 15 years.

In practice, however, average-bearing lives can be as low as just one year, accounting for 60% to 70% of all process pump failures.

Even making a generous allowance for both incorrect assembly and poor maintenance, then undoubtedly some of these failures are due to the process industry's historical insistence that bearings should cost very little.

What is becoming increasingly obvious, however, is that the decision in favour of a specific bearing solution should always be taken after analysing the overall cost / benefit issue and not merely on the basis of purchase price.

Buttressing this argument is the fact that today's high technology bearings offer improved features which enable whole life cost reductions to be achieved, providing benefits to both pump manufacturers and users - despite an overall higher bearing price.

Increased bearing service life - in the overall drive to reduce whole life costs of machines a key objective has to be increasing the bearing service life.

Incurred wear is one decisive factor adversely affecting service life - and hence the efficiency of the machine.

However, wear can be reduced, and also the tendency towards mixed friction during start/stop operation, by the use of FAG/ Barden's X-Life Ultra bearings.

A synergy of materials, surface engineering, sealing and lubrication technology, these bearings achieve a service life, which is up to three times that of conventional bearings.

X-life bearings prove their economic benefits in reduced life cycle costs of complete systems.

Due to the reduced probability of failure, unexpected bearing failures are far less common, leading to reduced machinery downtime, while service life is extended.

Additionally, the costs for lubricant procurement and disposal go down; mounting and dismounting requirements decrease and the demand for replacement bearings is reduced.

What all this means to the user is that within a relatively short time the high-grade X-Life bearings will pay for themselves in spite of their higher purchase costs.

The potential for reduced costs with X-Life bearings can be demonstrated using the example of a 37kW milling spindle of a machining centre with a HSK63 interface.

The bearing arrangement for the spindle consists of two sealed HCB7014C bearings in tandem arrangement at the tool end and another identical bearing at the spindle rear end.

The cost for a new bearing arrangement for the spindle, including spindle exchange and production loss, is GBP 3,800, the bearing cost itself being approximately GBP 450.

With three-shift operation in series production and due to the start-stop procedures during operation, the end of the lubricant service is reached after one year's operation and a bearing exchange becomes necessary.

Yearly maintenance costs are thus GBP 3,800.

In case of a replacement by X- Life Ultra bearings (XCS7014C), the average time until new bearings are required is increased to three years due to the reduced tendency towards mixed friction during start-stop operations while the machining quality remains the same.

With bearing costs, which are 75% higher, yearly maintenance costs of GBP 1350 arise, which corresponds to savings of 64%.

Moreover, even if the distance traveled by the X-Life Ultra bearings is only 50% higher, the saving still amounts to 27%.

What the above example underlines is that, if advanced bearing technology is employed correctly, then cost reductions may be achieved in spite of a higher bearing price, which, in turn, offers advantages both for both the machine user and machine manufacturer.

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