World Library  
Flag as Inappropriate
Email this Article

EP additive

Article Id: WHEBN0027567903
Reproduction Date:

Title: EP additive  
Author: World Heritage Encyclopedia
Language: English
Subject: Lubricant, Motor oil, EP, Gear oil, AW additive, List of gasoline additives, Tricresyl phosphate
Collection:
Publisher: World Heritage Encyclopedia
Publication
Date:
 

EP additive

Extreme pressure additives, or EP additives, are additives for lubricants with a role to decrease wear of the parts of the gears exposed to very high pressures. They are also added to cutting fluids for machining of metals.

EP additives are usually used in applications such as gearboxes, while AW additives(antiwear) are used with lighter load applications such as hydraulic and automotive engines.

EP gear oils perform well over a range of temperatures, speeds and gear sizes to help prevent damage to the gears during starting and stopping of the engine. Unlike AW additives, EP additives are rarely used in motor oils. The sulfur or chlorine compounds contained in them can react with water and combustion byproducts, forming acids that facilitate corrosion of the engine parts and bearings.[1]

EP additives typically contain organic sulfur, phosphorus or chlorine compounds, including sulfur-phosphorus and sulfur-phosphorus-boron compounds, which chemically react with the metal surface under high pressure conditions. Under such conditions, small irregularities on the sliding surfaces cause localized flashes of high temperature (300-1000 °C), without significant increase of the average surface temperature. The chemical reaction between the additives and the surface is confined to this area.

The early EP additives were based on lead salts of fatty acids ("lead soaps"), "active sulfur" compounds (e.g. thiols and elementary sulfur), and chlorinated compounds. During the 1950s the use of lead soaps was eliminated and replaced by zinc and phosphorus compounds such as Zinc dithiophosphate.[2]

Some of the EP additives are:

[1]

The activity of halogenated hydrocarbons increases with decreasing stability of the carbon-halogen bond. At local contact temperatures ranging between 305-330 °C, the additive thermally decomposes and the reactive halogen atoms form a surface layer of iron halogenides on the part surface. Eventual failure of the contact point comes when the contact temperature exceeds the melting point of the iron halide layer. Under such conditions, small particles of carbon are generated as well. Some compounds used in lubricant additives are chloroalkanes, trichloromethyl phosphine acids, organic esters of a-acetoxy-b,b,b-trichloroethyl phosphonic acid, trichloromethyl esters of phosphoric acid, trichloromethyl derivates of sulfur, trichloroacetoxy compounds, esters or amine salts of chlorendic acid, 1,2,3,4,7,7-hexachloro-5-dimethylbicyclo[2.2.1]-2-heptene, etc.

Oil-soluble organophosphates, with or without zinc, have excellent high-pressure and antiwear properties, and provide corrosion protection especially in presence of chlorinated hydrocarbons. ZDDP starts decomposing at 130-170 °C, while the activation temperature of TCP typically exceeds 200 °C. Their reaction products form a chemically bonded lubricating film on the surfaces.

Polysulfides serve as carriers of inactive and active sulfur.

Molybdenum compounds decompose under high pressure to form an in-situ deposited layer of molybdenum disulfide. Molybdenum dithiocarbamates are used as additives for greases.

Sulfur containing EP additives can cause corrosion problems in gears with parts made of bronze, brass and other copper alloys when high temperature environment is encountered.

References

See also

This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.