Grease is a semisolid lubricant. Greases generally consist of emulsified soaps with minerals or vegetable oils. The characteristic feature of greases is that they have a high initial viscosity, which in the shear application, drops to give the effect of oil lubricated bearings roughly the same viscosity as the base oil used in fat. This change in viscosity is called shear thinning. Greases are sometimes used to describe lubricants that are only soft solids or high viscosity liquids, but these materials do not show the shear thinning properties that are characteristic of the classic grease. For example, petroleum jellies such as Vaseline are generally not classified as obese.
The grease is only applied to a mechanism that is rarely lubricated and where the lubricating oil will not remain in its position. They also act as sealants to prevent ingress of water and compressed materials. The lubricating bearings have greater friction characteristics due to their high viscosity.
Video Grease (lubricant)
Properti
Oil true consists of oil and/or other lubricants mixed with thickener, usually soap, to form solid or semipadate. Fat is a kind of shear-thinning or pseudo-plastic liquid, which means that the viscosity of the liquid is reduced below the shear. Once enough strength to shift the grease has been applied, the viscosity drops and approaches the base lubricant, such as mineral oil. This sudden drop of shear force means that the fat is considered a plastic liquid, and the reduction of shear forces with time makes it thixotropic. This is often applied by using a grease gun, which applies the lubricant to the part that is lubricated under pressure, forcing the solid lubricant into the chamber in that section.
Thickeners
Soap is the most commonly used emulsifier agent, and the selection of soap types is determined by the application. Soaps include calcium stearate, sodium stearate, lithium stearate, and mixtures of these components. Fatty acid derivatives in addition to stearate are also used, especially 12-hydroxistearat lithium. The nature of soap affects temperature resistance (related to viscosity), water resistance, and chemical stability of the resulting fats.
Solid powdered dust
Solid powder can also be used as a thickener, especially as clay, which is used in some low-cost, low-performing greases. Fat-based fatty oils have also been prepared with other thickeners, such as tar, graphite, or mica, which also increase fat resistance.
Technical assessment and grease analysis
Lite-based grease is the most commonly used; Sodium and lithium based greases have a higher melting point (drop point) than calcium-based grease but are not resistant to water action. Lite-based grease has a falling point at 190 to 220 Â ° C (350 to 400 Â ° F). However the maximum temperature that can be used for lithium based grease is 120 Â ° C.
The amount of fat in the sample can be determined in the laboratory by extraction with the solvent followed by eg. gravimetric determination.
Additive
Wheel greases consist of rosin oil, condensed with lime and stirred with mineral oil, with some percentage of water. Specific greases contain glycerol and sorbitan esters. They are used, for example, in low temperature conditions. Some greases are labeled "EP", which shows "extreme pressure". Under high pressure or shock loading, normal lubricants can be compressed until the oily part becomes physical contact, causing friction and wear.
The EP lubricant contains a solid lubricant, usually graphite and/or molybdenum disulfide, to provide protection under heavy loads. The solid lubricant binds to the metal surface, and prevents metal-to-metal contact and the friction and wear produced when the lubricant film is too thin.
Solid additives such as copper or ceramic powder are added to some greases for static high pressure and/or high temperature applications, or where corrosion can prevent dis-assembling of components later in life in their service. This compound works as a release agent. All solid additives can not be used in bearings because of the strict tolerance of only normal fat or oil permitted. Solid additives will cause reinforced wear.
Maps Grease (lubricant)
History
Oil from the early Egyptian or Roman era is estimated to be prepared by combining lime with olive oil. Saponification oranges are some triglycerides made up of oils to provide calcium grease. In the mid-19th century, soap was deliberately added as a thickener to oil. For centuries, all materials have been used as fat. For example, black slugs Arion ater are used as axis-lubricant to lubricate wooden trees or carts in Sweden.
Classification and standards
Together developed by ASTM International, the National Lubricating Grease Institute (NLGI) and SAE International, the standard ASTM D4950 "standard classification and specification for automotive service grease" was first published on in 1989 by ASTM International. It categorizes greases suitable for the lubrication of casing components and wheel bearings of vehicles, based on performance requirements, using codes adopted from "chassis system and bearing bearing service system"
The given performance categories may include different consistency greases.
The size of the consistency of grease is generally expressed by the NLGI consistency number.
The standard elements of the standard ATSM D4950 and the NLGI consistency classification are reproduced and described in the SAE J310 standard "automotive grease standards" published by SAE International.
Standard ISO 6743-9 "lubricants, industrial oils and related products (class L) - classification - part 9: X family (fat)" , first released in 1987 by the International Organization for Standardization, specifies the classification of greases used for lubrication of equipment, machinery components, vehicles, etc. This provides a multi-part code for each fat based on its operational properties (including temperature range, water effects, loads, etc.) and NLGI consistency numbers.
More grease
Silicone fats
Silicone fat is a thickened amorphous silica, a polysiloxane-based compound, which can be used to provide lubrication and corrosion resistance. Because it is not oil-based, it is often used where an oil-based lubricant will attack a rubber seal. Silicon grease also maintains stability under high temperatures. They are often used, in pure form or mixed with zinc oxide, to join the heat sink to the computer's CPU.
Fluorase-based lubricant
Fluoropolymers contain C-O-C (ether) bonds for mild flexibility, and are often used as fat in demanding environments because of their inertia. Fomblin by Solvay Solexis and Krytox by duPont is a prominent example.
Laboratory grease
Apiezon, silicon-based, and fluoroether-based greases are all commonly used in laboratories for stopcock lubricants and ground glass joints. The grease helps prevent the connection from "freezing", as well as ensuring the high vacuum system is properly sealed. Apiezon or a similar hydrocarbon-based grease is the cheapest, and is best suited for high vacuum applications. However, they dissolve in many organic solvents. This quality makes cleaning with pentane or hexane trivial, but also easily leads to contamination of the reaction mixture.
Silicone-based greases are less expensive than fluoroether-based greases. They are relatively inert and generally do not affect the reaction, although the reaction mixture is often contaminated (detected via NMR near? 0). Silicone-based greases are not easily removed with solvents, but they are disposed of efficiently by soaking in a basic bath.
Fluoroneter-based fat greases are inert to many substances including solvents, acids, bases, and oxidation. They are, however, expensive, and not easy to clean.
Food grade lubricant
Class-grade grease is a fat that comes in contact with food. Basic lubricants of the food grade class are generally low sulfur petrochemical, less easily oxidized and emulsified. Another common poly used? olefin base oil also the United States Department of Agriculture (USDA) has three terms of food quality: H1, H2 and H3. H1 lubricant is a food grade lubricant used in food processing environments where there is the possibility of incidental food contact. H2 Lubricants are industrial lubricants used in equipment and machine parts on site without the possibility of contact. H3 lubricants are food grade lubricants, usually edible oils, used to prevent rust on hooks, trolleys, and similar equipment.
Water-soluble grease enzyme
In some cases, lubrication and high viscosity of fat is desirable in situations where non-toxic, non-oil materials are required. Carboxymethyl cellulose, or CMC, is one of the popular ingredients used to make fatty, water-based greases. CMC serves to thicken the solution and add lubrication effects, and often silicone-based lubricants are added for additional lubrication. The most common example of this type of lubricant, used as a surgical and personal lubricant, is K-Y Jelly.
Cork fat
Cork grease is a lubricant used to lubricate cork, for example in a wind instrument. It is usually applied using a small lip-balm/lip-stick such as an applicator.
See also
References
- This article combines text from publications now in the public domain: Ã, Ward, Artemas (1911). The Grocer's Encyclopedia . Ã,
External links
- US. Definition and application guide of Army Corps of Engineers (PDF file)
New location: Navigate to USACE Home & gt; [Publication] & gt; [Manual Engineer] & gt; [EM 1110-2-1424 Lubricants and Hydraulic Liquids]
- US. Definition and application guide of Army Corps of Engineers (PDF file)
- The Grocer's Encyclopedia online.
Source of the article : Wikipedia
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