What are the functions of lube oil in machinery?
The main functions of lube oil are that they are able to:
- Under all loads, temperatures and speeds, keep surfaces separate, thus minimising friction and wear.
- Remove the heat produced by friction and act as a cooling fluid.
- Protect surfaces from the attack of aggressive products formed during operation
- in order to remove residue and debris that may form during operation show cleaning capability and dirt holding capacity
- In some cases act as noise damper and sealant also.
- In order to guarantee constant behaviour over the forecast useful life, it should always remain adequately stable
Describe the properties of lube oil?
- Viscosity:- it determines the resistance of oil internal cohesive forces and promotes setting up of certain conditions for the friction between the moving surfaces
- Coking capacity or carbon residue:- is the tendency to form carbon residue while burning at elevated temperatures. high carbon residue causes gumming of piston rings preventing their movement in the grooves
- Sediments:- are the particles formed due to wear and carbon. Their maximum allowable content is 1.5%. they cause clogged oil filters and purification problems
- Corrosiveness:- is the tendency of the oil to oxidize due to the presence of oxygen in high-temperature gaseous surroundings.
- Base number:- is the capacity of the oil to neutralize the sulfuric compounds which are formed, especially in modern engines burning sulfur-rich residual fuel.
- Neutralization value:- is the measurement of the acidity or alkalinity of the oil.
- Total acid number(TAN):- is the measure of the combined organic acid due to oxidation of the oil, and the inorganic acids due to contamination by the acidic products of combustion.
- Strong acid number (SAN):- is the measure of the inorganic acids which are formed due to contamination by the acidic products.
- Total base number (TBN):- the measure of alkalinity of alkaline oil.
- Flash point:- is the measure of the tendency of the oil vapours to ignite.
- Pour point:- is the lowest temperature at which an oil ceases to flow or can be poured.
- Dynamic coefficient of friction :- is the ration of the tangential force required to overcome friction.
- Oiliness :- is the tendency of the oil to adhere or wet the moving surfaces.
- Anti-oxidation :- is the tendency to resist oxidation.
- Cracking stability :- is the property of the oil tobe stable and resist cracking at high temperatures. cracking is the breakdown of molecules into smaller sizes at high temperatures.
- Detergency and Dispersancy :- is the tendency to colloidally suspend, disperse and wash away any harmful combustion product in the oil.
- De-emulsivity :- is the property of the oil to separate from water in a non-miscible emulsion.
- Foaming :- is the undesirable phenomenon of the oil mixing with air resulting in cavitation and overheating.
- Cloud point :- is the temperature at which a cloud forms, due to wax crystal formation at low temperatures.
Describe the procedure for collecting sample of lube oil for shore testing/on-board testing?
Standard samples are sent ashore for testing at regular intervals e.g. every three months. These are the steps taken care of while taking samples for lube oil for sampling:
- The sample point should be marked (generally with yellow color) and taken at the same point every time.
- The sample is to be taken when engine is running at normal speed, so that oil is circulated.
- It is taken at the closest supply point into the engine/system.
- Before collecting the sample. drain the sampling line.
- The sample is taken at a very slow rate i.c. decanted over 5 minutes.
- The sample container label should have the following details:
- Ship’s name.
- Date of sample taken
- Description of machinery and oil
- Running hour of machinery
- Running hours oil
- Sample point location.
Describe the procedure for on board lube oil testing?
For testing lube oil onboard a special kit is provided. It contains all requeired tools and chemicals to performs such tests.
- TBN test :- is ascertained by measuring the “resultant pressure rise” of a test mixture. the chemical is that of the alkaline lube oil additive (calcium) with the reagent T.10 ml oil sample and 10 ml reagent N are mixed and placed in a testing unit cup. 10 ml reactive agent T is added and testing cup unit sealed and properly mixed. The resultant pressure rise is compared with a chart according to the type of oil used.
- Water Content Test :- The water content is ascertained by measuring the ‘resultant pressure rise’ of a test mixture. 5 ml oil sample and 15 ml petroleum reagent A (a paraffin or toluene) are mixed in the test unit cup. A standard amount in a sealed sachet of reagent B (calcium carbide) is added and the mixture sealed and shaken thoroughly. The chemical reaction takes place between water in the oil and the reagent calcium carbide to form acetylene gas which gives a resultant pressure rise.
- Water Crackle Test:- is done by heating 10 drops of oil in an aluminium foil container over a flame. A crackling sound confirms the presence of water in lube oil.
- Viscosity Test :- Viscosity is usually measured using a flow stick comparator method. The relative flow rate is measured between a new oil and the used oil.
- Alkalinity Test :- A ‘pH’ paper indicator can be used to check the reserve alkalinity in the oil sample.
- Flash Point:- This test be done by “pensky-Martens” apparatus is available onboard. the flash point will change if there is a fuel oil leak into a lube oil.
- Spot Test:- It shows the amount of insoluble particles in the oil. A standard oil sample is taken and mixed thoroughly. A spot of oil is dropped on a special test ‘blotter’ paper and allowed to dry. After a few hours, the spot is compared with the standard spot reference.
- Sea water content:- It tests the chlorine content or the oil sample. 5 ml oil sample and 5 ml distilled water are mixed and the water separates. 3 to 5 drops of mercuric thio-cyanate and an iron salt are added to 1 ml of the water from the earlier mixture. Chlorine ions react to form a reddish orange mixture of chloro-mercurate and ferric thio-cyanatc. This color is compared to a scale chart calibrated from 0 to 300 ppm.
What test are done on lube oil sample in shore testing ?
Shore testing involves the following tests:
- Spectro-Analysis:- This test determines the contamination by metal and additives. The following metals can be found by this test:
Fine Lead. Copper, Aluminum from bushes or bearings. Vanadium from heavy fuel oil contamination. Sodium from sea water salt, HFO contamination. Chrome from piston rings. Iron from lubricated moving parts of the engine like piston crown, liner, camshaft etc.
Spectro-Analysis is done by Plasma Atomic Emission procedure for particles of 10 micron (or less)in size. The quantity of these particles can be determined by a particle quantifier which gauges the quantity in terms of ‘PR index’. Separation of the particles is done by a rotary particle depositor.
- Flash Point Test:– It is done by using the Pensky Martens standard apparatus.The test sample is slowly heated in a closed apparatus at a constant race and an external flame is introduced at different temperature intervals through an open shutter. For new lube oils, flash point should be at least 220 deg.C.
- Base Number :- Oil sample (Anhydrous chloro benzene + Glacial acid) is tritrated with ( per-chlorine acid + glacial acid). Accurate tit-ration is done by using an electrical potential bridge arrangement which gives a current reading proportional to the tit-rating rate.
- Kinemafic viscosity :- It is done by measuring the time required for a specific quantity of oil at a certain temperature to flow under a fixed gravitational head in a capillary. This time measurement is directly proportional to the kinematic viscosity.
- Density :- It is measured by means of a glass hydrometer with its temperature controlled. Ir is an important parameter when choosing the correct size gravity disc in a centrifuge.
- Water Content :- It can be measured by the distillation method. Oil is heated under reflex with a water-im-miscible solvent. The condensed water is separated from the solvent in a trap.
- Micro Biological Test :- This test is only carried out if the lube oil is suspected of microbial degradation. A nutritive gel is applied over a glass slide and immersed i,, the oil sample. It is allowed to incubate for 12 hours. Bacteria manifests itself by red spots on the slide which is then compared with reference guide
- Insoluble Content :- It is a measurement of the Pentane or Toluene in-solubles.
- For Pentane in-solubles : A mixture of the oil sample and pentane is centrifuged. It is decanted and the precipitate washed with pentane twice. The dried weight gives the pentane in-solubles i.e. in-solubles due to wear, carbon or dirt particles.
- For Toluene in-solubles : A mixture of the oil sample and pentane is centrifuged. It is decanted and the precipitate washed off with pentane twice.It is then washed once with a toluene alcohol solution, and again with toluene. The dried weight gives the toluene in-solubles i.e. din and inorganic particles.
Please do read about problems faced by marine engineers regarding storage of heavy fuel oil and its properties.
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