Grease (lubricant) 2439173 224810601 2008-07-10T14:52:40Z JAnDbot 1725149 robot Adding: cs, de, es, ru, uk Modifying: fr {{otheruses|Grease}} Although the word '''grease''' originally described the [[Rendering (food processing)|rendered]] fat of animals, the term is now applied more broadly to mean a [[lubricant]] of higher initial [[viscosity]] than [[oil]], consisting originally of a [[calcium]], [[sodium]] or [[lithium]] [[soap]] jelly [[emulsion|emulsified]] with [[mineral oil]]. ==Properties== A ''true'' grease consists of an oil and/or other fluid lubricant that is mixed with another thickener substance, a ''soap'', to form a solid. Greases are a type of ''shear-thinning'' or [[Power-law fluids|pseudo-plastic]] [[fluid]], which means that the viscosity of the fluid is reduced under [[Shear stress|shear]]. After sufficient force to shear the grease has been applied, the [[viscosity]] drops and approaches that of the base lubricant, such as the mineral oil. This sudden drop in shear force means that grease is considered a [[plastic fluid]], and the reduction of shear force with time makes it [[thixotropic]]. It is often applied using a [[Grease gun (tool)|grease gun]], which applies the grease to the part being lubricated under pressure, forcing the solid grease into the spaces in the part. Soaps are the most common emulsifying agent used, and the type of soap depends on the conditions in which the grease is to be used. Different soaps provide differing levels of temperature resistance (relating to both viscosity and volatility), water resistance, and chemical reactivity. Powdered solids may also be used, such as [[clay]], which was used to emulsify early greases and is still used in some inexpensive, low performance greases. The amount of grease in a sample can be determined in a [[laboratory]] by extraction with a [[solvent]] followed by e.g. gravimetric determination<ref>Use of ozone depleting substances in laboratories. TemaNord 2003:516. http://www.norden.org/pub/ebook/2003-516.pdf</ref>. ==Uses== Greases are used where a mechanism can only be lubricated infrequently and where a lubricating oil would not stay in position. They also act as valuable sealants to prevent ingress of water and dust. Grease-lubricated bearings have greater [[friction]]al characteristics due to their high viscosity. Under shear, the viscosity drops to give the effect of an oil-lubricated bearing of approximately the same viscosity as the base oil used in the grease. Lithium-based greases are the most commonly used; sodium and lithium based greases have higher melting point (dropping point) than calcium-based greases but are not resistant to the action of [[water]]. [[Lithium-based grease]] has a dropping point at 190 °C to 220 °C (350 °F to 400 °F). However the maximum usable temperature for Lithium-based grease is 120 °C. Grease used for axles are composed of a compound of fatty oils to which [[tar]], [[graphite]], or [[mica]] is added to increase the durability of the grease and give it a better surface. ==Additives== [[Teflon]] is added to some greases to improve their lubricating properties. Gear greases consist of [[rosin]] oil, thickened with [[calcium oxide|lime]] and mixed with mineral oil, with some percentage of water. Special-purpose greases contain [[glycerol]] and [[sorbitan ester]]s. They are used, for example, in low-temperature conditions. Some greases are labeled "EP", which indicates "extreme pressure". Under high pressure or shock loading, normal grease can be compressed to the extent that the greased parts come into physical contact, causing friction and wear. EP grease contains solid lubricants, usually graphite and/or [[molybdenum disulfide]], to provide protection under heavy loadings. The solid lubricants bond to the surface of the metal, and prevent metal-to-metal contact and the resulting friction and wear when the lubricant film gets too thin. ==Other greases== Other types of lubricating material that are soft solids or high viscosity liquids at room temperature are often called grease, though they may not exhibit the shear-thinning properties typical of the oil/soap grease. [[Petroleum jelly|Petroleum jellies]], such as [[Vaseline]], are also sometimes called greases, and are commonly used for lubricating food-handling equipment. ===Silicone grease=== {{main|Silicone grease}} [[Silicone grease]] is an amorphous fumed, silica-thickened, polysiloxane-based compound, which can be used to provide lubrication and corrosion resistance. Since it is not oil-based, it is often used where oil-based lubricants would attack [[rubber]] seals. Silicone greases also maintain stability under high temperatures, and are often used, in pure form or mixed with [[zinc oxide]], to join [[heat sink]]s to [[computer]] [[central processing unit|CPU]]s. ===Fluoroether-based grease=== [[Fluoropolymer]]s containing C-O-C (ether) bonds for flexibility are soft, often used as greases in demanding environments due to its inertness. Fomblin by Solvay Solexis and [[Krytox]] by [[duPont]] are prominent examples. ===Laboratory grease=== [[image:Laboratory grease 1.jpg|right|thumb|[[Grease (lubricant)|Grease]] is used to lubricate glass stopcocks and joints. Some laboratories fill them into [[syringe]]s for easy application. Two typical examples: Left - [[Krytox]], a fluoroether-based grease; Right - a silicone-based high vacuum grease by [[Dow Corning]].]] {{see also|Laboratory glassware}} Apiezon, silicone-based, and fluoroether-based greases are all used commonly in laboratories for lubricating [[stopcock]]s and ground glass joints. The grease helps to prevent joints from "freezing", as well as ensuring high vacuum systems are properly sealed. Apiezon or similar hydrocarbon based greases are the cheapest, and most suitable for high vacuum applications. However, they dissolve in many organic [[solvent]]s. This quality makes clean-up with [[pentane]] or [[hexanes]] trivial, but also easily leads to contamination of reaction mixtures. Silicone-based greases are cheaper than fluoroether-based greases. They are relatively inert and generally do not affect reactions, though reaction mixtures often get contaminated (detected through NMR near δ 0). Silicone-based greases are not easily removed with solvent, but they are removed efficiently by soaking in a base bath. Fluoroether-based greases are inert to many substances including solvents, [[acid]]s, [[Base (chemistry)|base]]s, and [[oxidizer]]s. They are, however, expensive, and are not easily cleaned away. ===Water soluble grease analogs=== In some cases, the lubrication and high viscosity of a grease are desired in situations where non-toxic, non-oil based materials are required. [[Carboxymethyl cellulose]], or CMC, is one popular material used to create a water based analog of greases. CMC serves to both thicken the solution and add a lubricating effect, and often silicone based lubricants are added for additional lubrication. The most familiar example of this type of lubricant, used as a [[surgical lubricant|surgical]] and [[personal lubricant]], is [[K-Y Jelly]]. ==See also== *[[Dropping point]] ==References== *{{Grocers}} ==External links== *[http://www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-2-1424/c-5.pdf U.S. Army Corps of Engineers] grease definition and application guide (PDF file) [[Category:Lubricants]] [[bg:Грес]] [[cs:Kolomaz]] [[de:Schmierstoff]] [[es:Lubricante]] [[fr:Graisse (mécanique)]] [[id:Gemuk (pelumas)]] [[it:Grasso (lubrificante)]] [[ja:グリース]] [[pl:Smar]] [[pt:Graxa]] [[ru:Смазочные материалы]] [[tr:Gres]] [[uk:Мастило]]