Types of lubricants in modern industry Semira Hajrlahovic Mehic, M.Sc. Inspector Counsellor Chemicals Office of the Republic of Slovenia

Overview Friction What is lubrication Regimes of lubrications Types of lubrications Lubricants Formulation of lubricants Classification of lubricants General capabilities expected from lubricant Parameters important for lubricants

Friction When on surface moves over the another surface, Resistance to relative motion of the surfaces arises

Friction May be defined as the opposing force set up between the surface of contact, when one body moves over the surface of another body

Friction When we look at the solid surface it appears smooth to naked eye but this smooth surface shows irregularities of projections and cavities when viewed under high power microscope

Control of Friction

What is lubrication Lubrication is the process, or technique employed to reduce wear of one or both surfaces in close proximity, moving relative to each other by interposing a substance called lubricant between the surfaces to carry or to help carry the load (pressure generated) between the opposing surfaces

The regimes of lubrication Mode of lubrication is called regime of lubrication: as the load increases on the contacting surfaces three distinct situations can be observed Fluid film lubrication : regime in which through viscous forces the load is fully supported by the lubricant within the space or gap between the parts in motion relative to one another object Hydrostatic lubrication when an external pressure is applied to the lubricant in the bearing, to maintain the fluid lubricant film where it would otherwise be squeezed out Hydrodynamic lubrication where the motion of the contacting surfaces, and the exact design of the bearing is used to pump lubricant around the bearing to maintain the lubricating film

Types of lubrication Considering the nature of motion between moving or sliding surfaces, there are different types of mechanisms by which the lubrication is done Hydrodynamic lubrication or thick film lubrication Hydrostatic lubrication Boundary lubrication or thin film lubrication Extreme pressure lubrication

Hydrodynamic lubrication or thick film lubrication Exists when the moving surfaces are separated by the pressure of a continuous unbroken film/layer of lubrication In this type of lubrication, the load is taken completely by the oil film Hydrodynamic lubrication depends on: relative speed between the surfaces, oil viscosity, load, and clearance between the moving surfaces Application of hydrodynamic lubrication: Delicate instruments Light machines ( watches, clocks, guns, sewing machines) Scientific instruments

Hydrodynamic lubrication or thick film lubrication

Hydrostatic lubrication Essentially is a form of hydrodynamic lubrication in which the metal surfaces are separated by a complete film of oil, but instead of being self-generated, the separating pressure is supplied by an external oil pump Hydrostatic lubrication depends on: the inlet pressure of lube oil and clearance between the metal surfaces whereas in hydrodynamic lubrication it depends on the relative speed between the surfaces, oil viscosity, load on the surfaces, and clearance between the moving surfaces

Hydrostatic lubrication Examples: The cross head pin bearing in two stroke engines employs In the cross head bearing, the load is very high and the motion is not continuous as the bearing oscillation is fairly short Under such conditions, hydrostatic lubrication offers the advantage as hydrodynamic lubrication cannot be achieved The oil is supplied under pressure at the bottom of bearing. The lube oil pump pressure is related to the load, bearing clearance, and thickness of the oil film required

Boundary lubrication or thin film lubrication Exists when the operating condition are such that it is not possible to establish a full fluid condition particularly at low speeds between the moving/sliding surfaces The oil film thickness may be reduced to such a degree that metal to metal contact occurs between the moving surfaces The oil film thickness is so small that oiliness becomes predominant for boundary lubrication

Boundary lubrication or thin film lubrication Boundary lubrication happens when: A shaft starts moving from rest The speed is very low The load is very high Viscosity of the lubricant is too low

Extreme pressure lubrication When the moving or sliding surfaces are under very high pressure and speed, a high local temperature is attained Under such condition, liquid lubricant fails to stick to the moving parts and may decompose and even vaporize To meet this extreme pressure condition, special additives are added to the minerals oils Additives are organic compounds like : chlorine (chlorinated esters), sulphur (sulphurized oils), phosphorus (tricresyl phosphate)

What is lubricant? A lubricant : is a substance/mixture introduced to reduce friction between surfaces in mutual contact property of reducing friction = known as lubricity Ultimately reduces the heat generated when the surfaces move Generally composed of a majority of base oil plus a variety of additives to impart desirable characteristics

Applications of lubricants Industrial Hydraulic, Air compressor, Gas Compressor, Gear Bearing and circulating system Refrigerator compressor Other motors (2 stroke engine oil) Aviation, marine, biomedical applications

Lubricants Automotive Industry-Engine oil, Automatic transmission fluid, Gearbox fluid, Break fluids

Functions of lubricants Keep moving parts apart Reduce friction Transfer heat Carry away contaminants & debris Transmit power Protect against wear Prevent corrosion Seal for gasses Stop the risk of smoke and fire of objects

Formulation of lubricants Typically lubricants contain 90% base oil (most often petroleum fractions, called mineral oils) and less than 10% additives Vegetable oils or synthetic liquids such as hydrogenated polyolefins, esters, silicones, fluorocarbons and many others are sometimes used as base oils Non-liquid lubricants include grease, powders (dry graphite, PTFE, molybdenum disulfide, tungsten disulfide, etc.) Dry lubricants such as graphite, molybdenum disulfide and tungsten disulfide also offer lubrication at temperatures (up to 350 °C)

Classification of lubricants By the origin animal (e.g., sperm oil, goose grease), vegetable (e.g., soybean oil, linseed oil), or mineral (e.g., petroleum, molybdenum sulfide) From ancient times until the late 19th cent. lubricants were obtained from vegetable oils or animal fats and oils

Classification of lubricants Today most derive from mineral oils, such as petroleum and shale oil, which can be distilled and condensed without decomposition Synthetic lubricants, such as silicones, are of great value in applications involving extreme temperatures polyglycols, silicones, organic amines, imines In certain types of high-speed machinery films of gas under pressure have been successfully used as lubricants

Classification of lubricants Solid lubricants wax, talc, molibdenum disulphide Semi solid lubricants grease and vaseline Liquid Lubricants mineral oils, vegetable oils, animal oils

Solid lubricants Posse lamellar structure preventing direct contact between the sliding surfaces even at high loads graphite and molybdenum disulfide particles boron nitride, tungsten disulfide and polytetrafluorethylene (PTFE), talc

Solid lubricants Mainly used as additives to oils and greases Used in form of dry powder or as constituents of coatings Added or alloyed into the surface when the component is being manufactured

Semi-fluid lubricants (greases) Produced by emulsifying oils or fats with metallic soap and water at 400-600°F (204- 316°C) Typical mineral oil base grease is vaseline Grease properties are determined by : a type of oil (mineral, synthetic, vegetable, animal fat), type of soap (lithium, sodium, calcium, salts of long-chained fatty acids) and additives (extra pressure, corrosion protection, anti-oxidation)

Semi-fluid lubricants (greases) Used in variety applications where fluid oil is not applicable and Where thick lubrication film is required: lubrication of roller bearings in railway car wheels rolling mill bearings, steam turbines, spindles, jet engine bearings and other various machinery bearings

Fluid lubricants (oils) Mineral fluid lubricants are based on mineral oils Mineral oils (petroleum oils) are products of refining crude oil Types of mineral oil: Paraffinic; produced either by hydrocracking or solvent extraction process Naphtenic; produced from crude oil distillates Aromatic ; products of refining process in manufacture of paraffinic oils

Self-lubricating composites Self-lubricating composites have been available for a long time Used rather extensively by industry to combat friction and wear in a variety of sliding, rolling, and rotating bearing applications Generally prepared by dispersing appropriate amounts of a self-lubricating solid (as fillers, preferably in powder form) with a polymer, metal, or ceramic matrix Examples :Ti, TiN, TiC, Pb, PbO, ZnO, Sb2O3

General capabilities expected from an engine lubricant Dispersivity or capacity to keep the cold parts of an engine clean Detergency or capacity to keep hot parts of an engine clean Thermal strength or capacity to withstand temperature changes Anti-oxidant or capacity to resist the action of oxygen

General capabilities expected from an engine lubricant Anti-wear or capacity to contain wear Anti-scuffing or capacity to preserve oil film even in the presence of high pressures Alkalinity reserve/capacity to neutralize acids formed during combustion Demulsibility or capacity to separate contaminants

General capabilities expected from an engine lubricant Resistance to hydrolysis or capacity to withstand the action of water which can affect additives Pumpability, centrifuge ability and filterability or capacity to separate insoluble elements Anti-rust, anti-corrosive and anti-foam just some of the other properties which protect the metalic object from wear down

Parameters important for lubricants Viscosity Iodine number Aniline point Emulsion number Points: drop, cloud, pour and neutralization Saponification number

Viscosity It’s a measure of a fluid’s resistance to flow Determines performance under operating conditions A low viscosity oil is thin and flows easily , a high viscosity oil is thick and flows slowly Too low viscosity of the liquid →lubricant film cannot be maintained between the moving surfaces Too high viscosity of the liquid → excessive friction Selected lubricant must be proper viscous Usually expressed in centipoise or centistoke

Viscosity Index The rate at which viscosity of a lubricant changes with temperature Silicones, polyglycol ethers, Diesters or triesters have high viscosity index Higher V.I., lesser is the variation of viscosity with change in temperature thus, a good lubricating oil should possess high V.I.

Iodine number Each oil has its specific Iodine Number Iodine Number determines the extent of contamination of oil Low Iodine Number is desirable in oils

Aniline Point The temperature at which separation of Aniline and oil takes place Aniline Point is a measure of aromatic content of the lubricant Low Aniline Point →oil have high aromatic % Higher Aniline point means low % of hydroca-robons (desirable)

Emulsion number Emulsification is the property to get mixed with water easily A good lubricating oil should: form such an emulsion with water which breaks easily (property is called demulsification) have lower demulsification number Quicker the oil separates out from the emulsion formed, better is the lubricating oil

„Points“:drop, cloud, pour and neutralization point I All paraffinic mineral oil base stocks contain small amounts of waxy materials Drop point is the temperature at which grease passes from the semi-solid to the liquid state So, it determines the upper temp. limit for the applicability of grease

„Points“: drop, cloud, pour and neutralization point II When the temperature of the oil is decreased, some of the waxy components come out of solution as tiny crystals, and the solution begins to appear hazy to the naked eye The temperature at which this occurs is called the cloud point Pour point: The lowest temperature at which the oil is fluid Both indicates suitability of lubricant in cold conditions (and thus must be low for oils)

Points“ :drop, cloud, pour and neutralization point III Determines acidity or alkalinity of oil As neutralization point of oil increases, age of oil decreases

Saponification number It’s the mg of KOH required to saponify 1 g of oil Mineral oils do not react with KOH and are not saponifiable Vegetable and animal oils have very high saponification values Significance: each oil has its specific saponification number deviation from it indicates the extent of adulteration helps us to ascertain whether the oil reference is mineral or vegetable oil

How to go on? Many types of lubricant available To choose/develop wright lubricant: Know and understand the logic of process Type of friction, operational conditions Properties/characteristic of lubricants

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