Maintworld Issue3 2016

CONDITION MONITORING
Graph 1: The lubrication technician follows a pre-defined path through a group of bearings.
Friction? Ultrasound can hear friction.
So by simply placing an airborne flexible
sensor close to a gap in a coupling guard,
the technician can hear and record the
periodic friction associated with coupling
misalignment.
One highly topical example of a crossover
application is bearing lubrication.
Industry around the world is realising
that there is a problem here. Major bearing
manufacturers tell us that between
50 and 80 percent of all premature
bearing failures are cause by lubrication
issues.
If the manufacturers are correct,
what is the point of taking vibration
readings that are not focussed on finding
lubrication issues? Few, definitely not
all, vibration practitioners have additional
training in lubrication. Those that
do recognise that the higher frequency
measurements associated with ultrasound
provide greater sensitivity to the
frictional condition.
A bearing that needs grease will
warm up, so why not use an IR camera?
This is partially true, but if the environment
that the bearing is operating in
is already hot, it is unlikely that underlubrication
is going to cause a further
elevation in the temperature. Furthermore,
lubrication physics tells us that
under-lubrication and over-lubrication
will both increase friction and therefore
temperature. This will make the use of
an IR camera difficult.
Finally, there may be other defects
TO CORRECTLY DEPLOY A
MONITORING TOOL, FIRST
KNOW WHAT TO LOOK FOR
AND THEN CHOOSE HOW
TO FIND IT.
present – consider a fan bearing next
to a misaligned pulley. Our IR training
tells us that the misalignment will warm
up the pulley. Thermodynamics tells us
that the heat from the warm pulley will
conduct down the shaft and warm up the
pulley bearing. Oh! I have a hot bearing,
I must grease it. Is it possible to lubricate
away pulley misalignment?
FMEA is suggesting that the course of
action is to design out this problem. The
problem springs from the reality that all
bearings do not consume grease at the
same rate, which means that their need
for replenishment is different. Accepting
this reality means that greasing large
groups of bearings in the same way on a
time basis is not logical.
One of the key approaches which is being
used around the world for this major
problem is on-condition lubrication using
ultrasound. In Graph 1 we can see a lubrication
history using ultrasound:
This is a route-based approach. The
lubrication technician follows a pre-defined
path through a group of bearings.
For each bearing there is a history of
readings. If the current reading exceeds
an alarm condition, the technician
1. stores the “before” reading,
2. makes a comment to flag that the
bearing was greased,
3. performs an ultrasonic lubrication
4. records a second “after” reading
The result is a history for every bearing
in the database. When it was greased and
what condition it was left in.
Using ultrasound during the lubrication
process means that the difference
between a bearing that needed grease
(reduction in ultrasound) is clearly different
from a bearing that was already
over-greased (increase in ultrasound).
Using ultrasound for lubrication in
this way has produced some incredible
successes. One mining Company
reported a staggering reduction in
grease consumption from 22 drums
(15Kg each) per month to just 1 drum
per month with a significant increase in
machine reliability. A water treatment
plant reported at the end of 2015 that
since the implementation of their ultrasound
programme, they had not had
an unexpected motor bearing failure in
three years.
Summary
There are many condition monitoring
tools at your disposal. Ensure that you
perform a thorough FMEA in order to
uncover those defects that are most
likely to hurt you and develop your condition
monitoring strategies to deal with
those problems in the most convenient
way for your engineering talents.
FMEAs frequently fail because the
output is corrupted to
1. What tools do we have?
2. What modes will we list then?
Instead of reaching the conclusions of:
1. What needs to be measured?
2. Do we have the tools to find these
modes?
Your future success depends upon
choosing the right tools.
FIGURE 1 and 2: Major bearing manufacturers tell us that between 50 and 80 percent of all premature bearing failures are
caused by lubrication issues.
18 maintworld 3/2016