Selecting bearings with 'whole life' costs in mind
Despite their high initial cost, top quality, long-life bearings - like
high-efficiency electric motors - will save you a lot of money in the
long run. Trevor Morris says you shouldn't select your bearings until you
have understood the 'whole life' cost implications of your choice
Bearings are a key component in most machines, their reliability and
operating life having a significant impact on operating costs. And as the
pace of bearing technology accelerates, bearings can play a wider role in
reducing the 'whole life' costs of machines - not through cheaper
components, but by applying the latest materials, sealing and lubrication
technology to improve machine design and reduce maintenance costs.
Take as an example the UK pump market, worth an annual £980m, with
centrifugal pumps accounting for around 80% of this total. Each of these
pumps is equipped with between four and five bearings - two or three in
the pump and at least two in the motor. The typical life specified for
these bearings is three years, but when properly installed, lubricated
and maintained this can be as high as 12 or even 15 years. In practice,
however, average bearing lives can be as low as one year, accounting for
60-70% of all process pump failures. Even when making a generous
allowance for both incorrect assembly and poor maintenance, undoubtedly
some of these failures are due to the process industry's historical
insistence that bearings should cost very little.
In this author's view, 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 that enable whole life cost reductions to be achieved despite a
higher initial purchase price.
A key objective of whole life cost reduction is increasing a bearing's
service life. Incurred wear adversely affects service life, but this can
be reduced, as can the tendency towards mixed friction during start/stop
operations, using bearings that combine the best in materials, surface
engineering, sealing and lubrication technology. With the resulting
reduced probability of failure, unscheduled stoppages are far less common
so costly downtime is avoided. Additionally, the costs of lubricant
procurement and disposal go down; there are less mounting and dismounting
requirements and there is a marked fall-off in the demand for replacement
bearings. This all adds up to one thing: within a relatively short time
the higher grade bearing will pay for itself in spite of its higher
purchase price.
Trevor Morris is with Barden UK, which supplies the FAG/Barden X-Life
Ultra bearing range - premium products that are claimed to achieve a
service life that is up to three times that of conventional bearings.
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