Maintenance Technology May 2017 - 24

RELIABILITY STRATEGIES

Fig. 2. Pay Attention to Load Issues
100%
90%
80%
70%

Bearing Life

60%
50%
40%
30%
20%
10%

1x

2x

3x

Load
Constant Speed
The life of a bearing is inversely proportional to the cube of the load.

are unsure these types of situations are
occurring," Tranter cautioned, "then
they almost certainly are." He pointed
to several areas where seemingly
minor issues could be causing serious
problems:
■ Shaft alignment. When two shafts
are "collinear" (no angle or offset

between their centerlines) it reduces
stress on the bearings, couplings,
shafts, and the rest of the machine
components. Research has revealed
that just 5/60th of a degree of angular
misalignment can cut bearing life in
half (see Fig. 1).
If you use laser alignment with

Where Does Condition Monitoring Fit?
Condition monitoring plays several crucial
roles in the battle against self-inflicted reliability problems. For example, providing
an early warning of impending problems
minimizes the impact of premature
failure, and detecting and eliminating the
root causes ensures that we achieve the
greatest life and value from our precious
assets.
Many plant personnel, however,
believe that if they have a condition-

24 |

MAINTENANCE TECHNOLOGY

appropriate tolerances, and you
remove soft foot, then this will not
be a source of poor reliability. By
the way, just because your vibration
analyst does not detect misalignment does not mean that your
machines are precision aligned.
■ Balancing. When you balance to
ISO 1940 grade G 1.0, the cyclical
forces on the bearings, shaft, and
structure are minimized and you
gain reliability. If you do not have a
balancing standard, then unbalance
will be a root cause of failure. If you
wait until the unbalance generates
"high" vibration, then you will have
reduced the life of the equipment
and supporting structure. That's
because the life of a bearing is
inversely proportional to the cube
of the load (see Fig. 2). Tranter
noted that, while this calculation
sounds very complicated, it basically
means that if you double the load, a
bearing's life will be reduced to an
eighth (23).
■ Lubrication. When you correctly
lubricate bearings and gears,
whether with grease or oil, and that
lubricant is free of contaminants,
you will achieve maximum life.
But if bearings are not adequately
greased, their life will be reduced. If
the oil is contaminated, the viscosity
is incorrect, or additives are
depleted, then the life of gears and
bearings will be greatly reduced.

Jason Tranter, Mobius Institute

monitoring program in place, equipment
reliability will be optimized. That,
unfortunately, is not true.
Most detected faults are avoidable.
While it is important to get an early
warning, it is much more important to
avoid the problem in the first place. Condition monitoring can help by detecting the
root causes of failure, including misalignment, unbalance, lubrication issues,
and looseness, among others. If those

problems are cost-effectively nipped in the
bud, then we avoid future failures.
Another way condition monitoring
plays a role in plants is in acceptance
testing. As part of the purchase agreement, condition-monitoring specialists
can perform tests to ensure the new or
overhauled equipment is "fit for purpose."
You may be surprised at how many
problems you actually bring into your
plant.

MAY 2017



Table of Contents for the Digital Edition of Maintenance Technology May 2017

Maintenance Technology May 2017 - Cover1
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Maintenance Technology May 2017 - 1
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