(1) Function of a lubricant ? *****
01) Separate entirely the working surfaces, thus reducing static and dynamic friction to a minimum and preventing wear.
02) Remove heat, generated either within the bearing or from an out side source.
03) Protect against corrosion
04) Flush away contaminants.
05) Dampen noise.
06) In some case; act as a sealant.
(2) Types of Lubrication
Hydrodynamic
- Full fluid film lubrication.
Boundary
- Thin film lubrication
Hydrostatic
- Thick film lubrication
Elasto-hydrodynamic
- Thin film or square film lubrication.
(3) Properties of crankcase lube oil ?
(a) Viscosity (Suitable)
(b) Viscosity index (Hight)
(c) Pour Point (low)
(d) Flash point (high)
(e) Oxidation stability
(f) Carbon residues (low)
(g) Total acid number (TAN) + Total basic number (TBN)
(h) Detergency (i) Dispersancy
(4) What is viscosity
1.A measure of its internal resistance to flow.
2.Viscosity of oil changes with temperature, falling when temperature rises and vice versa.
3.Crankcase L.O – 130 to 240 seconds, Redwood No-1 at 60°C.
4.For cylinder oil, viscosity is 12.5 – 22 Cst
(5) What is viscosity index ? (VI)
(1) The rate of change of viscosity of an oil in relation to change of temperature.
(2) Low viscosity index has greater change of viscosity with change in temperature than the oil of high VI.
Good crankcase oil = VI scale is 75 to 85.
For cylinder Oil, VI is 85
(3) Highest VI of mineral oils is about 115 and with special additives, this may be raised to about 160
(4) Hydraulic oils, used in remote control hydraulic circuits must have very high VI; otherwise erratic response to the controls can be troublesome (Telemotor hydraulic system oil has VI of
110)
(6) What is a pour point ?
(1) It’s the lowest temperature at which an oil will barely flow.
(2) Pour point indicates that oil is suitable for cold weather or not.
(3) Pour point of engine crankcase should be -18 °C
(7) What is the flash point ? ***
It is the lowest temperature at which the oil will give off a sufficient inflammable vapour to produce a flash when a small flame is brought into the surface of the oil.
Close flash point for crankcase LO is around 220 °C.
Why flash point is important ?
FO:
It is important, fuel oil flash point is to be fairly high because of they were low, there would be a possibility of fire in storage.
LO:
Engine crankcase oil flash point should be as high as possible to prevent crankcase
explosion.
(For safe storage) to limit the oil storage tank heating temperature at least 14 °C lower than its F.P prevent fire.
Average Closed Flash Points
Petrol = -20 °C
70cSt Fuel Oil = 71 °C
Paraffin = 40 °C
Lube Oil= 220 °C
Diesel Oil= 65 °C
(8) What is TAN and TBN ?
It is the neutralization value of used engine lube oil.
The ability of an oil to react with a base reagent which indicates the acidity expressed as TAN.
The ability of an oil to react with acidic reagent which indicate the alkalinity expressed as TBN.
The results are expressed intern of milligrams of potassium hydroxide (KOH) required to neutralise one gram of sample oil for both TAN and TBN.
TBN for an oil used for :
Crosshead type diesel engine crankcase is -
8mg KOH/gram of oil.
For trunk type engine using heavy oil is -
30mg KOH/gram of oil.
(9) What type of engine are using high TBN and why ?
At trunk type engine using heavy fuel oil if blow pass occur incomplete combustion products reach directly into the crankcase and may cause the contamination with acid easily. Thus in this type of
engine to neutralize the acid contamination must be used high TBN oil.
(10) What are detergency / dispersancy ?
It is a chemical compound called detergent which has property of preventing the deposition of carbonaceous deposit and wash away with the lube oil.
Dispersant additive addition is made to divide the larger size deposits into tiny particles to be carried in a colloidal suspension evenly throughout the bulk of oil.
(11) Explain the L O sampling procedure to send for LO test ?
The sample should be drawn with oil circulation with the system such as a test cock on the discharge side of the LO oil pump.
Before taking the sample oil sufficient amount of oil should be drain out to clear the line.
The sample is filled into the chemically cleaned container after it is rinsed with the sample oil and immediately closed.
The container should be attached -
1) engine type
2) engine running hours
3) LO running hours
4)fuel used
5) draw off point and
6) date.
Sampling Procedure
Draw samples from a connection that comes directly out of the main oil supply line to the engine. Always sample for the same point. Sample only when the oil is up to its operating temperature with the engine running.
Depending upon the draw off point, sufficient amount of oil should be drained out of the line prior to drawing the sample. The sample should be filled into a chemically cleaned container after it is
rinsed with sample oil and immediately closed. The container should be attached with a label as follows:
Records for Sample
(1)Date of sample drawn
(2)Point of sample drawn
(3)Type of oil
(4)Type of machinery use
(5)Temperature of sample drawn
(6)The period of time since the last renewal of oils.
Avoid
Sampling form places where the oil may be stagnant or have little or no flow, such as:
-Sumps
-Auxiliary smaller pipelines
-Purifier suction or discharge lines.
-Drain cocks of filters, coolers etc.
-Sampling while engine is stopped
(12) Essential factor effecting the establishment of hydrodynamic lubrication ?
*****
01) Viscosity of oil
02) Load acting on the bearing
03) Surface smoothness of moving parts
04) Speed of rotating
05) Continuous LO supply
06) Bearing clearance, bearing length and pin diameter.
07) There must be convergence between fixed end and moving surface
(13) Where do locate ME LO sump and its fitting ?
It is located under the engine in the ship double bottom and surrounded by cofferdams.
It consist of :
1) level gauge
2) man holes
3) air vent pipe
4) sounding pipes
5) heating steam coils
6) suction pipe and
7) valves for LO p/p and purifier.
(14) Why magnetic fitter is fitted on LO system ? Where fitted ?
1.To prevent pump damage due to ferrous metal particles.
2.Screw p/p used in LO oil system is working in very fine clearance thus to prevent entering the small ferrous particles into the p/p.
3.Magnetic fitter is fitted prior to the main circulation LO p/p.
(15) Contaminants in the lube oil ?
a) Contamination of fresh Water (JW leaking)
b) Contamination of SW
(Cooler leakage)
c) Contamination of fuel
(Poor Atomisation, Unburned Fuel)
c) Oxidation products
(High Exhaust Temperature, Burned Cyl Oil, Carbon from
incomplete combustion)
d) Products of fuel combustion
e) Foreign mineral matters
(Scale formation, Wear and tear)
f) Bio logical contamination.
(16) Water contamination in lube oil ?
Causes :
1) condensation of water vapour within the crankcase
2) Leakage from the cooling water system for cylinder or piston
3) Leakage from the sump tank heating steam coils.
Effects
- Reduce cooling efficiency.
- Increase the acid formation in trunk type piston engine.
- Can cause corrosion on m/c parts.
- Microbial degradation, [Reduce centrifuging efficiency; promote local pitting and
corrosion]
- Reduce load carrying capacity
- Reduce L.O properties, and TBN of oil
- Form sludge due to emulsification
Remedies
- Proper purification with minimum throughput
- Batch purification if heavy contamination
Maximum Allowable % of water in LO
For crosshead engine, < 0.2 % is satisfactory
If water content exceed 0.5 ~ 1.0 %, immediate action should be taken
If > 1%, engine can be damaged
For trunk type engine, < 0.1% is satisfactory
If > 0.5 %, immediate action should be taken and
It is maximum permissible content
(17) Fuel dilution in lube oil ?
Causes :
1.Poor atomization of a fuel injector and back leak through the fuel injector p/p plunger and barrel.
Effects:
1.Fuel dilution usually diesel oil.
2.Lower viscosity and low fresh point
3.Lower viscosity LO reduces this properties ( e.g load carrying capacity )
4.Lower fresh point will case crankcase explosion.
How to move contaminants
Filtering - Removed large oil insoluble matter
Gravity separation - Heavy matters, sludge and water
Adding special additives - Reduce acids, sludge, finer oil insoluble matter
Centrifuging- Sludge, foreign matter and water
Water washing - Only for straight mineral oil or oil without additives, can
remove acids.
What will you do if LO is contaminated with FW or SW ?
(1)Batch Purification must be done
(2)Renovating Tank heating and regular draining
(3)For SW contamination, Water Washing is required
(4)Sump to be opened and thoroughly wipe out.
(18) How do you make batch purification ?
1.Firstly take the immobilization permit from the port authority.
2.The entire oil charge should be pumped by the purifier or by main circulation p/p into
renovating tank.
3.It should be allowed to settle for at least for 24 hours with heating about 60°C (60°C).
4.Water and sludge should be drained out periodically.
5.Cleaned the interior of the sump tank and carefully examined.
6.The oil should be passed through the purifier at its optimum efficiency and than pump back into the sump tank.
7.When sump tank empty, its interior should be cleaned and exaimed.
(19) When periodic batch purification make ?
1.If the oil is suspected from containing strong acids,
2.High insoluble contents due to poor combustion or water due to leak cooling system.
3.It is also made at least once a year when cleaned and examined for sump tank.
(20) 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.
(21) What is solid lubrication ?
Grease lubrication
(22) At what point will feed to the piston ?
1.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.
2.It is a limited lubrication.
23) What will be happen temp: is lower than pour point ?
The oil can not freely flow thus effect the pumping system (lubrication system)
(24) Why viscosity is important ?
FO:
Low viscosity is required for fuel in order to obtain good atomization at fuel valve.
LO:
LO must be chosen which has a suitable viscosity for the working temperature for
efficient lubrication.
(25) How to maintain L.O on board ? ******
(1) L.O onboard test is carried out regularly.
(2) Regular cleaned L.O line filter.
(3) L.O purifier should be run during ship is in sea
(4) Maintain L.O purifier performance
(5) Periodic batch purification must be carried out & cleaned L.O sump tank once a year
(6) Maintain L.O temperature within receptacle limit
(7) Maintain good L.O cooler efficiency
(8) Keep good fuel combustion system
(26) Why cooler is installed after filter ?
It is more effective to filter the hot oil, as pressure drop through the filter is less and filter is more complete.
(27) Action of L.O temperature abnormally high (What will you do as 2/E, if M/E L.O
temperature abnormally high) ********
(01) Inform bridge & reduce engine speed Ö Quick response
(02) Check engine overload or not (Exhaust temp:, fuel rack,..)
(03) Check L.O sump & L.O cooler & L.O purifier temperature (set value)
(04) Check L.O sump tank heating valve.
(05) Shut L.O cooler by-pass totally after stopping (or) too high temperature not fall
(06) Clean L.O cooler
(07) Check sump tank heating coil leakage
(08) Make L.O onboard test (esp Viscosity)
(09) Check L.O piping system leakage or blockage
(10) Make (inspection & check bearing clearance & loosing attachment
(11) Check ampere (or) load when turn the turning gear
(28) Action when increase L.O level
(01) Check piston cooling system (water)
(02) Check L.O purifier (gravity disc is correct or not) [L.O purifier water outlet sight galss]
(03) Check filling valve from storage tank
(04) Check L.O cooler/although oil pressure is greater than S.W pressure.
(29) Action when decrease L.O level
(1) Check rate of decreasing if slowly decrease, fill up L.O and find the leakage without stopping engine
(2) If rapidly decrease, inform to bridge and stop the engine. Find the leakage and repair. Possible leakage points:
(2a) Bed plate crack (check engine room bilge)
(2b) Piston cooling L.O system (check scavenge space & under piston space {entablature})
(2c) L.O cooler & L.O purifier
(2d) All pipes and connection
(3) Check L.O return valve from crankcase to sump tank close or not
(4) Check oil scraper rings & stuffing box
(30) Action when decrease L.O pressure :
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
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) Lubrication for Journal Bearing, Bottom End Bearing, Tilting Pad Thrust Bearing
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
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.
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.
If LO is contaminated with SW
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
Renovating 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 Renovating 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 oil1% water washed)
Difference in Cylinder oil and System oil
1.Cylinder oil is detergent / dispersant oil
2.System oil is straight mineral oil
L.O on board test
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
1) If there is no cracking, the oil is dry
2) If there is slightly cracking, the oil having a trace of water
3) 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.
If the change of colour is Red, it is acid
If blue/green, it is alkaline.
If yellow/green, it is neutral.
Foreign Particles Test
This can be done by either Spectrochemical analysis or Ferrographic analysis or Ferrographic analysis, each giving particle size less than 10 uM to 100 uM range depending on the tests applied.
The most powerful technique is Inductively coupled plasma atomic emission spectrometry (ICP OR PES), which uses a direct spray technique to determine the wear and contaminant elements present in the oil.
This technique will in the main only detect the particles below 10 uM size.
In ferrographic test, the sample is thinned first with some solvents and allowed to pass slowly down a slide surrounded by powerful magnetic field.
Then it is examined by special microscope with red and green filters under lights. The shape of the particles is used to identify the source of the wear debris.
The advance ferrography method was added to the PFA (Progressive Fast Analysis)
programme where all samples pass through the combination of two machines, a particle quantifier (PQ) and a rotary particle depositor (RPD).
These test measures the induced magnetic moment of debris as deposited on a substrate or contained within a specific volume of liquid.
These machines provide accurate test by rotating the metal particles and then separating into three different sizes, Theses three bands of particles are examined by very powerful microscope to
determine the type of materials and shape.
If more detailed examination is necessary, the debris may be subjected to a scanning electron microscope.