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Lubrication of Machinery
INTRODUCTION
In industry, mechanical equipment such as pumps, compressors, turbines, motors and any other
type of machine having moving parts, need 'LUBRICATION' - to minimise friction and wear, to carry
away heat from moving parts, to clean and to prevent rust .
LUBRICATION
Lubrication is the science of reduction of friction by using oils, greases or other special materials
between the moving parts and the stationary parts of machines.
We are all familiar with the problems which can arise with our car if we allow the oil level in the sump
to become too low or the oil too old and dirty.
Replacement of bearings, pistons and/or piston rings and cylinder liners ..etc, is very expensive and
time consuming, not to mention the inconvenience caused by the car being off the road for a while.
The selection of the correct lubrication to be used in any machine is also very important. In industry,
the science of lubrication is taken to a very high standard in order to protect the many hundreds of
different types and sizes of modern machinery.
As stated earlier, the purpose of lubrication is to reduce or minimise friction and wear; to cool and
carry away heat from moving parts in close alignment with stationary parts; to minimise oxidation of
metals (rust) and to clean the surfaces of the metal by carrying away very small solid deposits.
GREASE LUBRICATION
The simplest lubrication system is by using 'Greases'. These can be smeared over the moving parts
of equipment like valve stems and spindles.
Grease is usually applied by means of ' Grease Cups ' which are fitted to the casing which houses
the shaft or spindle to be lubricated.
The grease-filled cup is threaded and screwed on to the grease injection point. The cup is given a'turn' or two at specified intervals. As the cup is turned, grease is forced into the injector which feeds
it to the shaft.
The injection of grease can also be made by using a 'grease nipple' attached to the casing. In this
case, a 'grease gun' (hand operated pump), is connected to the nipple and a pump action is used to
force grease onto the shaft. In most cases, the grease injection point is placed in the casing opposite
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to a 'Lantern Ring' which in turn is placed in the packing in the shaft packing box. The lantern ring
distributes the lubricant around the shaft.
GREASE LUBRICATION
Figure: 1
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OIL LUBRICATION
A. MANUAL APPLICATION OF OIL
Again, lubrication using oil can be done in simple cases by smearing oil on the surfaces to be
lubricated. Oil can also be 'squirted' or injected onto the surfaces by a hand pumped oil can
Figure: 1A.
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OIL
Figure: 1A.
B. 'SPLASH' METHOD OF LUBRICATION
Many machine casings are fitted with an oil filled reservoir through which the shaft passes. The
machine shaft passes through the reservoir casing above the oil level. An oil 'Slinger-ring' is placed
around the shaft and has a much larger diameter than the shaft so that the ring hangs in the oil in
the reservoir.
As the shaft rotates, the ring also rotates and picks up oil. The force of rotation causes the oil to be
thrown off the ring and 'splashed' over the shaft (and bearings). The oil drips off the shaft and
bearings and back into the reservoir.
Other machines which have cam-shafts and crank-cases, have the oil contained in the crankcase.
As the camshaft rotates, a 'Scoop' device attached to the bottom of the connecting rod 'big-end'
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bearing, scoops up oil and its rotation, again, splashes oil over the moving parts.
Other similar methods are used where the webs of the big ends are partially immersed in the oil in
the crankcase which causes the splash effect.
The level of oil in the reservoir or crankcase is maintained by adding oil as required, either directly to
the reservoir (as in a car engine), or by way of an oil 'bottle' which feeds the reservoir. The oil l evel in
either case must be checked in the sight glass or in the bottle and topped up as required with the
correct grade of oil. (See Figures : 2 & 3)
The oil in the re servoir
'MUST NOT BE ALLOWED TO FALL BELOW THE DISTRIBUTION MECHANISM'
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Figure: 3
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C. FORCED FEED LUBRICATION
Reciprocating machines generally have a lube oil distributor which consists of an oil tank containing
a built-in pump. The unit has a system of distribution lines which deliver a small portion of oil at
intervals to each location in the machine which requires constant lubrication. The delivery of the oil '
pulses ' can be seen in the sight glass in each of the distribution lines. The pump is operated by an
electric motor or by a mechanical arm driven by the reciprocating motion of the engine.
( See Figure : 4 )
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D. PRESSURE LUBRICATION
Large, powerful, high speed machines need great quantities of oil to perf orm the functions of
lubrication, cooling and sealing, properly and efficiently. The oil supply in these cases, is provided by
pumping the oil around the bearings. In the supply system, the oil is pumped, cooled, filtered and
controlled at the desired pressure before being fed to the machine bearings. Oil temperature,
pressure, flow and level, are monitored constantly and the systems fitted with alarm instruments to
warn of impending problems, and trip systems to shut down the machine at pre -set, undesired
conditions.
The oil supply consists of a closed circulation system consisting of a reservoir, pumping, filtering,
cooling and controlling units throughout the circulation of the oil which then returns to the reservoir
from the machine bearings. Some lube oil units are operated independently of the machine being
supplied. Others have the main lube oil pump being driven by the shaft of the machine with auxiliary
A/C and emergency D/C pumps as standbys.
The turbine/compressor units are fitted with many safety devices for alarm and shut-down in the
event of undesirable lube / seal oil operating conditions arising.
These can consist of : - Low lube oil / seal oil pressure or level, High lube oil / seal oil temperature,
High bearing temperature .. etc. A typical example diagram of a pressure lubrication system as used
in a turbine/compressor unit is seen in the figure.
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( See Figure : 5 )
FORCED FEED LUBRICATION
Figure : 4
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PRESSURE LUBRICATION
Figure : 5
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When a turbine/compressor unit is shut down or trips, it takes a while for the system to come to rest
and more time for it to cool down. The auxiliary pump should automatically cut-in to provide lube oil
to the machines until they have completely stopped and cooled down. The D/C emergency pump is
provided for the same use in the event of total power failure.
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Lube oil is also necessary when machines having long rotor shafts are shut down. The rotor and
shaft will be hot for a long time and, as they cool down, they must be rotated slowly by a 'Turning
Gear' to prevent 'bowing' or bending of the shaft. The turning gear and machine bearings will still
need lubrication.
Last Updated on Saturday, 27 March 2010 13:52