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Basics of Lubricants

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Basics of Lubricants

 

 

 

Viscosity also called dynamic viscosity is a measure of a fluid's resistance to flow. The SI unit is kilogram per meter per second (kg/m-s) while C.G.S unit is gram per centimeter per second (g/cm-s) or poise. The most common unit is centipoise (cP).

 The viscosity of a lubricant decreases as temperature increases and the viscosity of a lubricant increases as temperature decreases .The viscosity of a lubricant is closely related to its ability to reduce friction. Generally, the thinnest lubricant is ideal which still forces the two moving surfaces apart. If the lubricant is too thick, it will require a lot of energy to move the surfaces. If it is too thin, the surfaces will rub and friction will increase.

Kinematic viscosity is the ratio of the dynamic viscosity of a fluid to its density. It is a measure of a fluid’s resistance under the influence of gravity to flow. The SI unit is square meter per second(m2/s) while C.G.S unit is square centimeter per second (cm2/s )or stoke. The most common unit is centistokes (cSt) i.e square millimeter per second.(mm2/s).

viscosity index (V.I) Viscosity Index is the variation characteristics of viscosity with temperature. If the variation of temperature does not affect the viscosity of oil. it means oil has high Viscosity Index. It is a dimensionless quantity. It is determined by measuring the kinematic viscosities of the oil at 40 oC and 100 oC and using the tables or formulas included in ASTM D 2270.

 

 

 

flash point of a flammable liquid is the lowest temperature at which vapors of a given oil give a momentary flash when a tiny flame is brought near it under a specified test condition. The unit is oC.(degree Celsius).

fire point, is defined as the temperature at which the vapor continues to burn after being ignited.

The pour point of a liquid is the lowest temperature at which the oil ceases to flow under prescribed conditions. The unit is oC.(degree Celsius).

Most petroleum based oils have waxes and paraffin that solidify at cold temperatures. Oils with more waxes and paraffin will have a higher pour point while highly refined oils and synthetic oils will have significantly lower pour points.

 

Total Base Number  (TBN) is a measure of the reserve alkalinity of a motor oil and how well the oil can neutralize harmful acidic by-products of combustion. It can also be defined as the quantity of acid, expressed in terms of the equivalent number of milligrams (mg) of Potassium Hydroxide that is required to titrate the strong base constituents present in 1 gm. of oil sample. The minimum value of engine oil TBN should be 3.If TBN is less than 3 then oil should be changed.

  

Density of material is its mass per unit volume. The S.I unit is kilogram per cubic meter (kg/m3) while C.G.S unit is gram per cubic centimeter (g/cm3) also called gram per milliliter (g/ml).

 

Ash content is the percent by weight of residue left after combustion of an oil sample.Sulphated ash is a direct measure of the amount of oil additive that contain metal. These additives prevent deposit and wear. They generally contain metals such as calcium, magnesium and zinc.

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The Copper Corrosion Test assesses the relative degree of corrosivity of petroleum products ,including lubricants due to active sulfur compounds. A polished copper strip is immersed in a 30 ml of sample at elevated temperature. After the the test period, the strip is examined for evidence of corrosion. Results are rated by comparing the stains on a copper strip to a color-match scale from 1-4.

 

Additives are chemical compounds that improve the lubricant performance of base oil (or "base stock").

. Additives provides the anti oxidant,anti wear,anti rust,anti foaming ,detergency and dispersant .e.t.c .property to the lubricant

API Classification System :API stands for the American Petroleum Institute. This body has specified the performance standards that oils used in road vehicles should meet. For oils to use in passenger car engines, the letters API are followed by a set of two letters such as SM, etc. Service Levels for passenger car oils or ‘S’ indicates for Spark Ignition Engine. These specified performance levels have evolved through the years, from API SA to SN,
Similarly, the API designates the performance of diesel engine oils with a letter sequence such as API CF-4.’C’ indicates for commercial or compression ignition engine.  Automotive gear oils they use API GL-4.API GL-5 e.t.c
The highest API for commercial engine oils (diesel oils) today is API CJ-4.

Item

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SJ

SL

SM

Oxidation stability

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Anti-sludge performance

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Wear resistance of variable valve train system

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Rust prevention performance

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Low volatility performance

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Shear stability

Deposit control at high temperature

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Compatibility with oil seal

Compatibility with exhaust catalyst

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Anti-foaming performance

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Cold startability

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Filterability

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☆marks in total

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28

33

 

Society of Automotive Engineers (SAE) SAE Stands for the Society of Automotive Engineers, based in the U.S.A.The SAE grade specifies the most important parameters for engine oil mainly its viscosity. The SAE viscosity classification defines mainly viscosity limits at high and low temperature for any grade of lubricants. The SAE grade guide us to the right viscosity for different outside temperatures. Grades marked ‘w’ stand for winter are at a temperature below 00C.

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International Standards Organization is an organization which is worldwide in scope, sets standards and classifications for lubricants. An example is the ISO viscosity grade system.

Monograde (single grade) is a term used to describe an oil when its viscosity falls within the limits specified for a single SAE number.

Multigrade These are oils designed to give better viscosities at both high and low temperatures. Multi-Grade oils are made by adding viscosity index improver. The viscosity of all oils falls as they get hot - and multi-grade oils are formulated to minimize this effect. Multi-grade oils are defined by a viscosity rating at a low temperature, as well as one at 100 C.

 

 
 
 
 
 
   

 

 

 

 

 

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