Lubrication of Machinery - OIL LUBRICATION PDF Print E-mail
Written by Norrie   
Saturday, 27 March 2010 13:47
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Lubrication of Machinery
GREASE LUBRICATION
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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.

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' 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 level 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 reservoir …

'MUST NOT BE ALLOWED TO FALL BELOW THE DISTRIBUTION MECHANISM'



Figure: 2


Figure: 3

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 )

D. PRESSURE LUBRICATION

Large, powerful, high speed machines need great quantities of oil to perform 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.

( See Figure : 5 )

FORCED FEED LUBRICATION

Figure : 4

PRESSURE LUBRICATION

Figure : 5

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.

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