LUBRICANTS

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LUBRICANT

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A LUBRICANT (sometimes referred to as "lube") is a substance (often a liquid) introduced between two moving surfaces to reduce the friction between them, improving efficiency and reducing wear. -have the function of dissolving foreign particles. Petroleum-based lubricants like Vaseline tend to dissolve petroleum products such as rubber and plastic; water-based lubricants will dissolve polar chemicals; silicone-based lubricants can breakdown silicone toys.

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-it protects the internal combustion engines in motor vehicles and powered equipment. -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, silicone, fluorocarbons and many others are sometimes used as base oils.

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-Lubricants are comprised of a base fluid, usually of petroleum origin, combined with added chemicals that enhance performance. Base fluids are collected from two main sources. Refined crude oil or a mixture of chemical compounds that perform the same task.

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PURPOSE or FUNCTION OF A LUBRICANT 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

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KEEP MOVING PARTS APART Lubricants are typically used to separate moving parts in a system. This has the benefit of reducing friction and surface fatigue together with reduced heat generation, operating noise and vibrations. Lubricants achieve this by several ways. The most common is by forming a physical barrier i.e. a thin layer of lubricant separates the moving parts. This is termed hydrodynamic lubrication. In cases of high surface pressures or temperatures the fluid film is much thinner and some of the forces are transmitted between the surfaces through the lubricant. This is termed elasto-hydrodynamic lubrication.

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Reduce friction Typically the lubricant-to-surface friction is much less than surface-to-surface friction in a system without any lubrication. Thus use of a lubricant reduces the overall system friction. Reduced friction has the benefit of reducing heat generation and reduced formation of wear particles as well as improved efficiency. Lubricants may contain additives known as friction modifiers that chemically bind to metal surfaces to reduce surface friction even when there is insufficient bulk lubricant present for hydrodynamic lubrication, e.g. protecting the valve train in a car engine at startup.

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Transfer heat Both gas and liquid lubricants can transfer heat. However, liquid lubricants are much more effective on account of their high specific heat capacity. This circulating flow also determines the amount of heat that is carried away in any given unit of time. High flow systems can carry away a lot of heat and have the additional benefit of reducing the thermal stress on the lubricant. Thus lower cost liquid lubricants may be used. The primary drawback is that high flows typically require larger sumps and bigger cooling units. A secondary drawback is that a high flow system that relies on the flow rate to protect the lubricant from thermal stress is susceptible to catastrophic failure during sudden system shut downs. An automotive oil-cooled turbocharger is a typical example. Turbochargers get red hot during operation and the oil that is cooling them only survives as its residence time in the system is very short i.e. high flow rate.

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Carry away contaminants and debris Lubricant circulation systems have the benefit of carrying away internally generated debris and external contaminants that get introduced into the system to a filter where they can be removed. Lubricants for machines that regularly generate debris or contaminants such as automotive engines typically contain detergent and dispersant additives to assist in debris and contaminant transport to the filter and removal. Over time the filter will get clogged and require cleaning or replacement, hence the recommendation to change a car's oil filter at the same time as changing the oil. In closed systems such as gear boxes the filter may be supplemented by a magnet to attract any iron fines that get created. Poor filtration significantly reduces the life of the machine (engine) as well as making the system inefficient.

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Transmit power Pascal's law is at the heart of hydrostatic power transmission. Hydraulic fluids comprise a large portion of all lubricants produced in the world. Protect against wear Lubricants prevent wear by keeping the moving parts apart. Lubricants may also contain anti-wear or extreme pressure additives to boost their performance against wear and fatigue

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-Prevent corrosion Good quality lubricants are typically formulated with additives that form chemical bonds with surfaces to prevent corrosion and rust. -Seal for gasses Lubricants will occupy the clearance between moving parts through the capillary force, thus sealing the clearance. This effect can be used to seal pistons and shafts.

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Types of lubricants - Liquid including emulsions and suspensions - Solid - Greases - Adhesive

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Liquid lubricants Lanolin (wool grease, natural water repellant) Water Mineral oils Vegetable (natural oil) Synthetic oils Others Note: although generally lubricants are based on one type of base oil or another, it is quite possible to use mixtures of the base oils to meet performance requirements.

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Lanolin - A natural water repellent, lanolin is derived from sheep wool grease, and is an alternative to the more common petro-chemical based lubricants. This lubricants are also corrosion inhibitors, protecting against rust, salt and acids. Water - Water can be used on its own, or as a major component in combination with one of the other base oils. Commonly used in engineering processes, such as milling and lathe turning.

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Mineral oil This term is used to encompass lubricating base oil derived from crude oil. The American Petroleum Institute (API) designates several types of lubricant base oil identified as: Group I - Saturates <90% and/or sulphur >0.03%, and Society of Automotive Engineers (SAE) viscosity index (VI) = >80 to <120 - Manufactured by solvent extraction, solvent or catalytic dewaxing, and hydro-finishing processes. Common Group I base oil are 150SN (solvent neutral), 500SN, and 150BS (brightstok)

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Group II – Saturates >90% and sulfur <0.03%, and SAE viscosity index >80 to <120 - Manufactured by hydrocracking and solvent or catalytic dewaxing processes. Group II base oil has superior anti-oxidation properties since virtually all hydrocarbon molecules are saturated. It has water-white color.

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Group III – Saturates > 90%, sulfur <0.03%, and SAE viscosity index >120 - Manufactured by special processes such as isohydromerization. Can be manufactured from base oil or slax wax from dewaxing process. Group IV – Polyalphaolefins (PAO)

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Group V – All others not included above Such as naphthenics, PAG, esters, and etc. In North America, Groups III, IV and V are now described as synthetic lubricants, with group III frequently described as synthesised hydrocarbons, or SHCs. In Europe, only Groups IV and V may be classed as synthetics. The lubricant industry commonly extends this group terminology to include:

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Group I+ with a Viscosity Index of 103 - 108 Group II+ with a Viscosity Index of 113 - 119 Group III+ with a Viscosity Index of >= 140 Can also be classified into three categories depending on the prevailing compositions: - Paraffinic - Naphthenic - Aromatic

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Vegetable (natural) oils These are primarily triglyceride esters derived from plants and animals. For lubricant base oil use the vegetable derived materials are preferred. Common ones include high oleic canola oil, castor oil, palm oil, sunflower seed oil and rapeseed oil from vegetable, and Tall oil from animal sources. Many vegetable oils are often hydrolyzed to yield the acids which are subsequently combined selectively to form specialist synthetic esters.

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Synthetic oils Polyalpha-olefin (PAO) Synthetic esters Polyalkylene glycols (PAG) Phosphate esters Alkylated naphthalenes (AN) Silicate esters Ionic fluids

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Solid lubricants Teflon or PTFE Teflon or PTFE is typically used as a coating layer on, for example, cooking utensils to provide a non-stick surface. Mineral Graphite, hexagonal Boron nitride. Molybdenum disulfide and Tungsten disulfide are examples of materials that can be used as solid lubricants, often to very high temperature. The use of such materials are still restricted by their poor resistance to oxidation (e.g., molybdenum disulfide can only be used up to 350C in air, but 1100C in reducing environments).

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Mineral Graphite, hexagonal boron nitride, and molybdenum disulfide are examples of materials that can be used as solid lubricants often to very high temperatures. The use of such materials is still restricted by their poor resistance to oxidation. For example, molybdenum disulfide can only be used up to 350 C in air, but 1,100 C in reducing environments.

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Additives A large number of additives are used to impart performance characteristics to the lubricants. The main families of additives are: Antioxidants Detergents Anti-wear Metal deactivators Corrosion inhibitors, Rust inhibitors Friction modifiers Extreme Pressure Anti-foaming agents Viscosity index improvers Demulsifying/Emulsifying

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Application methods Spraying/dipping/brushing: Dispersion of solid lubricant as an additive in oil, water or grease is most common used. For parts that are inaccessible for lubrication after assembly a dry film lubricant can be sprayed. After the solvent evaporates, the coating cures at room temperature to form a solid lubricant. Pastes are grease like lubricants containing a high percentage of solid lubricants used for assembly and lubrication of highly loaded, slow moving parts. Black pastes generally contain MoS2. For high temperatures above 500°C pastes are composed on the basis of metal powders to protect metal parts from oxidation necessary to facilitate disassembly of threaded connections and other assemblies.

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FREE POWDER Dry-powder thumbling is an effective application method. The bonding can be improved by priory phosphating the substrate. Use of free powders has its limitations, since adhesion of the solid particles to the substrate is usually insufficient to provide any service life in continuous applications. However, to improve running-in conditions or in metal forming processes a short duration of the improved slide conditions may suffice.

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AF-coatings Anti-friction coatings are "lubricating paints" consisting of fine particles of lubricating pigments, such as molydisulfide, PTFE or graphite, blended with a binder. After application and proper curing, these lubricants bond to the metal surface and form a dark gray solid film. Many dry film lubricants also contain special rust inhibitors which offer exceptional corrosion protection. Most long wearing films are of the bonded type but are still restricted to applications where sliding distances are not too long. AF-coatings are applied where fretting and galling is a problem (such as splines, universal joints and keyed bearings), where operating pressures exceed the load-bearing capacities of ordinary oils and greases, where smooth running in is desired (piston, camshaft), where clean operation is desired (AF-coatings will not collect dirt and debris like greases and oils), where parts may be stored for long periods of time.  

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COMPOSITES   Self lubricating composites: Solid lubricants as PTFE, graphite, MoS2 and some other anti friction and anti wear additives are often compounded in polymers and all kind of sintered materials. MoS2 for example is compounded in materials for sleeve bearings, elastomere O-rings, carbon brushes etc. Solid lubricants are compounded in plastics to form a "Self lubricating" or "Internally lubricated" thermoplastic composite. PTFE particles for example compounded in the plastic form a PTFE film over the mating surface resulting in a reduction of friction and wear. MoS2 compounded in Nylon reduces wear, friction and stick-slip. Furthermore it acts as a nucleating agent effecting in a very fine crystalline structure. The primary use of graphite lubricated thermoplastics is in applications operating in aqueous environments.

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