Activating
pro-active maintenance
Ashok
Kumar Gupta presents techniques to enable the users of hydraulic machines
and systems, to achieve effective hydraulic power, productivity and
profits
Pro-active
maintenance is the means to cure the root cause of system failure and
increase its life and efficiency. Maintenance in fact amounts to ‘life
extension’ for the machine. Contamination control in a hydraulic or
lubrication oil system by proper filtration equipment is a tool of pro-active
maintenance, which extends the life of the machine and prevents system
failure.
Solid
contamination is not the only spoliation that reduces the life of a
hydraulic system. The other factors responsible for degradation of the
system are high temperature, air entering into the system, vibration
in the system, shock and pressure surges.
In
fact the human body offers many parallels to hydraulic and lubrication
oil system of the plant and machines. Hydraulic machines are fluid dependent
(fluid being oil in a hydraulic machine). Higher contamination level
in the hydraulic system can be described as an incipient system failure,
meaning that while the machine is not currently experiencing low performance
or component degradation, the conditions that lead to failure and shortening
life are present and untenable. Just as the cholesterol level in human
body can be dangerous, high contamination level in a hydraulic system
is also very dangerous and correctable.
From
observation of advances in human medicine we can gain an excellent insight
to effective strategies in the maintenance of a hydraulic system.
A
hydraulic system is one of the most reliable and repeatable forms of
power and motion control. All that is required for getting the best
of the system is a ‘Systematic Contamination Control’. Seventy five
percent of the times, when the problems are encountered, they are related
to inadequate contamination control practices. The philosophy of pro-active
maintenance, therefore, is to adopt systematic contamination control.
Contamination:
the whys and hows
In
a Hydraulic system, there are usually four primary sources of contamination:
1.
Contamination that is built-in during manufacturing and assembly process
2.
Contamination that is ingested from outside the system during operation
from reservoir vent ports, power unit openings, maintenance events and
cylinder rod seals
3.
Contaminated through new oil in a system. Although hydraulic and lubrication
fluids are refined and blended under relatively clean conditions, the
fluid travels through many hoses and pipes before it is stored in drums
or in a bulk tank at the user’s facility. At this point, the fluid is
no longer clean as the numerous fluid lines it has travelled through
contribute metal and rubber particles, and the drums add flakes of metal
or scale. Storage tanks are a real problem because water condenses in
them causing rust particles. Contamination from the atmosphere can also
find its way into the tank unless satisfactory air breathers are fitted.
If
the fluid is stored under reasonable conditions, the principal contaminants
– on delivery – to the machine will be metal, silica and fibres. Sample
fluids from reputable suppliers have shown typical cleanliness levels
of 18/16/14 and can be even dirtier. Supertech SystemGuard with high
efficiency filters should be used to remove the contamination from new
fluids before filling it into the hydraulic or lubrication system.
4.
Internally generated contamination during operation due to the following
types of wears:
- v
Abrasive wear: Hard particles bridging two moving surfaces, scraping
one or both
- v
Aeration wear: Air bubbles in the fluid implode surface material
- v
Adhesive wear: Loss of oil film allows metal to metal contact between
moving surfaces
- v
Cavitations wear: Restricted inlet flow to pump causes fluid voids
that implode causing shocks that breakaway critical surface material
- v
Corrosive wear: Water contamination in the oil causes rust that degrades
the surface
- v
Erosive wear: Fine particles in a high speed stream of fluid eat away
a metering edge or critical surface
- v
Fatigue wear: Particles bridging a clearance cause a surface stress
riser or micro-crack that expands into a spall due to repeated stressing
of the damaged area
Costs
involved
The
burgeoning cost of maintenance is generally a serious business problem
and in many companies it often exceeds their annual net profit. Now
pro-active maintenance has received worldwide attention as the single-most
important means of achieving savings unsurpassed by conventional maintenance
techniques.
The
approach replaces the maintenance philosophy of failure reactive with
failure pro-active by avoiding the underlying conditions that lead to
machine faults and degradation. Unlike predictive or preventive maintenance,
pro-active maintenance commissions corrective actions aimed at failure
root causes, not just symptoms. Its central theme is to extend the life
of mechanical machinery as opposed to:
- Making
repairs when often nothing is broken
- Accommodating
failure as routine and normal
-
Crises failure maintenance against scheduled maintenance
Analysis
of causes for system failure
While
the root causes of failure are many, or at least presumed to be many,
it is generally accepted that 10 per cent of the causes of failure are
responsible for 90 per cent of the occurrences. Most often, the symptoms
of failure are......
....CONTD
