143:. They offer lubrication at temperatures higher than liquid and oil-based lubricants operate. Dry lubricants are often used in applications such as locks or dry lubricated bearings. Such materials can operate up to 350 °C (662 °F) in oxidizing environments and even higher in reducing / non-oxidizing environments (molybdenum disulfide up to 1100 °C, 2012 °F). The low-friction characteristics of most dry lubricants are attributed to a layered structure on the molecular level with weak bonding between layers. Such layers are able to slide relative to each other with minimal applied force, thus giving them their low friction properties.
25:
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Many dry film lubricants 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
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Anti-friction (AF) 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 "slippery" or dry lubricants bond to the metal surface and form a dark gray solid film.
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Graphite is best suited for lubrication in air. Water vapor is a necessary component for graphite lubrication. The adsorption of water reduces the bonding energy between the hexagonal planes of the graphite to a lower level than the adhesion energy between a substrate and the graphite. Because water
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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), and where parts may be stored
402:
Dispersion of solid lubricant as an additive in oil, water, or grease is most commonly 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
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Dry-powder tumbling is an effective application method. The bonding can be improved by prior phosphating of 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.
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is a ceramic powder lubricant. The most interesting lubricant feature is its high temperature resistance of 1200 °C service temperature in an oxidizing atmosphere. Furthermore, boron nitride has a high thermal conductivity. (Cubic boron nitride is very hard and used as an abrasive and cutting
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of many solids is attributable to a lamellar structure. The lamellae orient parallel to the surface in the direction of motion and slide easily over each other resulting in low friction and preventing contact between sliding components even under high loads. Large particles perform best on rough
454:, carbon brushes, etc. Solid lubricants are compounded in plastics to form a "self-lubricating" or "internally lubricated" thermoplastic composite. For example, PTFE particles compounded in the plastic form a PTFE film over the mating surface, resulting in a reduction of friction and wear. MoS
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of PTFE, stable unflocculated dispersions of PTFE in oil or water can be produced. Contrary to the other solid lubricants discussed, PTFE does not have a layered structure. The macro molecules of PTFE slip easily along each other, similar to lamellar structures. PTFE shows one of the smallest
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Reciprocating motion. A typical application is a sliding or reciprocating motion that requires lubrication to minimize wear, as, for example, in gear and chain lubrication. Liquid lubricants will squeeze out while solid lubricants do not escape, preventing fretting, corrosion, and
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at 400 °C is restricted by oxidation. Particle size and film thickness are important parameters that should be matched to the surface roughness of the substrate. Large particles may result in excessive wear by abrasion caused by impurities in the
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However, a layered crystal structure alone is not necessarily sufficient for lubrication. In fact, there are some solids with non-lamellar structures that function well as dry lubricants in some applications. These include certain soft metals
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Natural graphite is derived from mining. The quality of natural graphite varies as a result of the ore quality and its post-mining processing. The end product is graphite with a content of carbon (high grade graphite 96−98% carbon), sulfur,
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act as lubricants at high temperature and in oxidizing atmosphere environments, where liquid lubricants typically will not survive. A typical application involves fasteners that are easily tightened and unscrewed after a long stay at high
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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.
656:
Singh, H.; Mutyala, K. C.; Mohseni, H.; Scharf, T. W.; Evans, R. D.; Doll, G. L. (July 2015). "Tribological
Performance and Coating Characteristics of Sputter-Deposited Ti-Doped MoS2 in Rolling and Sliding Contact".
407:. 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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surfaces at low speed, finer particles on smoother surfaces and at higher speeds. These materials may be added in the form of dry powder to liquid lubricants to modify or enhance their properties.
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is structurally composed of planes of polycyclic carbon atoms that are hexagonal in orientation. The distance of carbon atoms between planes is longer and, therefore, the bonding is weaker.
205:, since a liquid lubricant allows particles to get stuck in the lock worsening the problem. It is often used to lubricate the internal moving parts of firearms in sandy environments.
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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 MoS
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product and is characterized by its high purity of carbon (99.5−99.9%). Primary grade synthetic graphite can approach the good lubricity of quality natural graphite.
694:"An investigation of material and tribological properties of Sb2O3/Au-doped MoS2 solid lubricant films under sliding and rolling contact in different environments"
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For applications where only a minor lubricity is needed and a more thermally insulating coating is required, then amorphous graphite would be chosen (80% carbon).
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Ceramics. Another application is for cases where chemically active lubricant additives have not been found for a particular surface, such as polymers and ceramics.
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formed at several hundred degrees
Celsius in metallic sliding systems. However, practical use is still many years away due to their physically unstable nature.
303:. In an oxidative atmosphere, graphite is effective at high temperatures up to 450 °C continuously and can withstand much higher temperature peaks.
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lubrication performance often exceeds that of graphite and is effective in vacuum as well, whereas graphite is not. The temperature limitation of MoS
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Extreme contact pressures. The lamellar structure orients parallel to the sliding surface, resulting in high bearing-load combined with a low
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vapor is a requirement for lubrication, graphite is not effective in vacuum. Because it is electrically conductive, graphite can promote
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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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and some other anti-friction and anti-wear additives are often compounded in polymers and all kind of sintered materials. MoS
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coefficients of static and dynamic friction, down to 0.04. Operating temperatures are limited to about 260 °C.
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is mined from some sulfide-rich deposits and refined to achieve a purity suitable for lubricants. Like graphite, MoS
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Other components that are useful solid lubricants include boron nitride, polytetrafluorethylene (PTFE), talc,
228:. Similar usage as molybdenum disulfide, but due to the high cost only found in some dry lubricated bearings.
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Solid lubricants are useful for conditions when conventional lubricants are inadequate, such as:
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between two surfaces sliding against each other without the need for a liquid oil medium.
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Graphite and molybdenum disulfide are the predominant materials used as dry lubricants.
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has a hexagonal crystal structure with the intrinsic property of easy shear. MoS
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Self-lubricating composites: Solid lubricants such as PTFE, graphite, MoS
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are materials that, despite being in the solid phase, are able to reduce
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557:"Space tribology – An overview of application of tribology in space..."
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Graphite is characterized by two main groups: natural and synthetic.
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Singh, H.; Mutyala, K.C.; Evans, R.D.; Doll, G.L. (December 2015).
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201:, machine-shop works, etc. It is also very common for lubricating
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Limited interest has been shown in low friction properties of
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638:, NASA Technical Memorandum TM-103803, 1991. Available at
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Thorsten
Bartels et al. "Lubricants and Lubrication" in
222:. Used in space vehicles. Also called "white graphite."
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49:. Unsourced material may be challenged and removed.
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185:The four most commonly used solid lubricants are:
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481:Ullmann's Encyclopedia of Industrial Chemistry
216:and space vehicles. Does lubricate in vacuum.
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500:Scharf, T. W.; Prasad, S. V. (2013-01-01).
252:, cerium fluoride, and tungsten disulfide.
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310:Synthetic graphite is a high temperature
109:Learn how and when to remove this message
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47:adding citations to reliable sources
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16:Solid substance used as a lubricant
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271:High temperature. Graphite and MoS
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167:, some solid oxides, rare-earth
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698:Surface and Coatings Technology
640:hdl.handle.net/2060/19910013083
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236:Structure-function relationship
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671:10.1080/10402004.2015.1015758
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506:Journal of Materials Science
502:"Solid lubricants: a review"
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589:SKF dry lubricated bearings
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526:10.1007/s10853-012-7038-2
398:Spraying/dipping/brushing
208:Molybdenum disulfide (MoS
489:10.1002/14356007.a15_423
370:Hexagonal boron nitride
220:Hexagonal boron nitride
659:Tribology Transactions
585:"SKF DryLube bearings"
555:harshvs (2016-10-28).
420:Anti-friction coatings
382:Polytetrafluorethylene
377:Polytetrafluorethylene
165:polytetrafluroethylene
611:"Coating Terminology"
334:Molybdenum disulfide
197:actions, open gear,
141:molybdenum disulfide
43:improve this article
634:Sliney, Harnold E,
518:2013JMatS..48..511S
393:Application methods
483:, 2005, Weinheim.
434:for long periods.
301:galvanic corrosion
226:Tungsten disulfide
189:Graphite. Used in
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704:: 281–289.
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731:Lubricants
725:Categories
595:2 December
570:2016-12-02
467:References
438:Composites
69:newspapers
736:Tribology
679:136631684
542:135902634
534:1573-4803
242:lubricity
214:CV joints
169:fluorides
99:July 2010
560:tribonet
312:sintered
293:Graphite
288:Graphite
265:galling.
137:graphite
130:friction
514:Bibcode
452:O-rings
427:splines
173:diamond
83:scholar
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157:silver
149:indium
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675:S2CID
591:. SKF
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460:nylon
203:locks
195:piano
90:JSTOR
76:books
615:DECC
597:2011
530:ISSN
240:The
153:lead
139:and
62:news
706:doi
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357:MoS
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318:SiO
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161:tin
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