Functions and Properties of Lubricating Oil On Ships
Functions and Properties of Lubricating Oil On Ships
Functions and Properties of Lubricating Oil On Ships
Ships
What are the functions of a lubricant?
1. Separate entirely the contact surfaces, thereby reducing static and dynamic friction to least
possible value to prevent wear and tear.
2. Remove heat generated within the bearing.
3. Protection of the working surfaces against corrosion.
4. Removal of contaminants.
5. Dampen noise produced.
6. Act as a sealant.
What is viscosity?
It is a measure of internal resistance to flow between liquid layers.
Viscosity of lube oil reduces when temperature rises and vice versa.
For engine crankcase lube oil, viscosity is 130 to 240 Redwood No-1 seconds 60°C.
For cylinder oil, viscosity is 12.5 – 22 Cst
What is Total Acid Number or TAN and Total Base Number or TBN?
The ability of an oil to react with a base reagent which indicates the acidity is expressed as
TAN.
The ability of an oil to react with acidic reagent which indicate the alkalinity is expressed as
TBN.
The results are expressed in milligrams of potassium hydroxide (KOH) required to neutralise
one gram of sample oil for both TAN and TBN.
TBN for an oil used for cross head type diesel engine crankcase is 8mg KOH/gram of oil.
TBN for an oil used for trunk type engine using heavy oil is 30mg KOH/gram of oil.
What is grease ?
1. It is a semisolid lubricant consisting of high viscosity mineral oil and metallic soap with filler.
2. Metallic soaps are compound of Ca, Na, Al.
3. Filler are lead, zinc, graphite and molybdenum.
What is solid lubrication ?
Grease lubrication is known as solid lubrication
At what point cylinder oil is injected ?
The cylinder oil is feed to the piston at the time when the top two piston rings pass
the lubrication holes in the cylinder during the piston stoke.
It is a limited lubrication.
What will be happen temperature is lower than pour point ?
The oil can not freely flow thus effect the pumping system (lubrication system)
What will you do as 2/E, when decrease in sump lubricating oil level by marine
engineer?
Check rate of decreasing if slowly decrease, fill up L.O and find the leakage without
stopping engine.
If rapidly decrease, inform to bridge and stop the engine. Find the leakage and repair.
Possible leakage points are:
* Bed plate crack (check engine room bilge)
* Piston cooling L.O system (check scavenge space & under piston space {entablature})
* Check L.O return valve from crankcase to sump tank close or not
What will you do as 2/E, when decrease in lubricating oil pressure observed?
1. Start stand by pump
2. Change & clean L.O filter
3. After engine stopping, check bearing clearance and L.O pipe connection
4. Check L.O pump discharge & suction pressure
5. Check L.O temperature
What is meant by hydrodynamic lubrication (full fluid film)?
1. Moving surfaces are separated completely by the pressure of a continuous unbroken film or
a layer of lubricant, generated by the movement of the two surfaces relative to each other.
2. Essential requirement is formation of a wedge of lubricants between surfaces.
3. Thickness of film 0.025 – 0.10 mm.
4. Happens in lubrication for Journal Bearing, Bottom End Bearing, Tilting Pad Thrust Bearing
What is meant by boundary lubrication?
1. It exists when a full-fluid film lubrication is not possible.
2. The sliding surfaces are separated by only a thin film of lubricant.
3. High friction between the surfaces and some degree of metal to metal contact occurs
4. Lubricant oil film decreases, until asperities of mating surfaces touch
What is meant by hydrostatic lubrication?
1. A form of thick film lubrication, but instead of being self- generated, it is supplied from
an external source by oil under pressure from a pump.
2. Lubrication for Crosshead Bearings, with attached pump.
What is meant by elasto-hydrodynamic lubrication?
1. Applies to line contact or nominal point between rolling or sliding surfaces, such as
rolling contact bearings and meshing gear teeth.
2. Thin film or squeeze film lubrication limits metal to metal contact.
3. Elastic deformation of the metals occurs, and there is effect of high pressure on the lubricant.
What will you do as 2/E, if lube oil is contaminated with sea water?
1. When sump oil is contaminated with SW, find sources of leakage (may be from LO cooler
during ME stopped) stoppage and rectified.
2. In port or while ME is stopped, transfer contaminated oil through purifier or transfer pump
into settling tank, settled for at least 24 hours at about 60 C°, and water and sludge drained
out periodically.
3. Oil passed through purifier at 78° C with optimum efficiency, and pump back to settling tank.
4. When sump tank is empty, interior cleaned and examined.
5. Purified oil sent to laboratory and tested
6. During this time, new oil should be used
7. Oil should be reused, if lab results recommended that it is fit for further use. (Straight mineral
oil 3% water washed. Additive oil 1% water washed).
What are the difference in Cylinder oil and System oil?
Cylinder oil is detergent / dispersant oil
System oil is straight mineral oil
What are the lube oil tests carried out on board Ships ?
Viscosity Determination
The simplest method is three tube rolling ball viscometer
Assuming the oil in the engine to be SAE 30 grade, one tube is filled with minimum
safety viscosity (about SAE 20) and another one filled with maximum safety viscosity (about
SAE 40). The last tube is to be filled with test sample.
All tubes are placed in a bucket of warm water until the oils are at the same temperature.
The three tubes then mounted on a tilted board and inverted. An internal hollow ball in each
tube then rises to the surface.
If the time taken in the test sample is between that of the lower and upper limit oils, the oil is
fit for further use. If not, it must be replaced.
Insoluble Content
A drop of sample oil is released from a given height onto a special filter paper.
Compare the result with the known varying insoluble content. The upper limit for straight mineral
oil is 1% to 1.5 % and for detergent dispersant oil is 5%.
Water and other Contaminants
A known amount of sample oil in the test tube is heated and must be shaken the while doing so
If there is no cracking, the oil is dry
If there is slightly cracking, the oil having a trace of water
If there is a heavily crackling, the oil is heavily diluted with water
Acidity / Alkalinity Determination
Acidity is tested by extracting the acids from the sample by means of shaking with a known amount of distilled
water. The acidic extract is then placed on a watch glass with an indicator solution of known strength. The
mixture is then drawn up into a glass tube and its colour compared with a series of colour standards, each
representing a known PH value, from which the sample can be determined quite accurately.
Another method is :
A drop of indicator solution is placed on to blotting paper and this is followed by a drop of sample oil placed at
the centre of the drop of previous absorbed indicator.