Greetings Doug, You said,
"They are not related." This may be true sometimes (1), but I think there is some kind of relationship between the two, but it may not be easy, or simple to explain. I found an excellent online reference on lubrication, friction and viscosity here: http://www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-2-1424/c-2.pdf I found this on page 6 of the reference: "Lubricants: Reduced wear and heat are achieved by inserting a lower viscosity (shear strength) material between wearing surfaces that have a relatively high coefficient of friction." The army took ten pages to cover the topic of lubrication, so it is a somewhat complex topic. This site also had some interesting data on biodiesel as a lubricity enhancer / additive: http://www.me.iastate.edu/biodiesel/Pages/bio23.html I was taught in my fluid mechanics class that "viscosity is the resistance (friction) to flow of fluid under an applied sheer force". I think that too low or too high a viscosity motor oil (all other parameters being equal) increases friction in the engine (less apparent lubricity of the fluid?). There is an optimal viscosity. From what I have read, friction (or the inverse? lubricity, or lack of friction?) is a complex property of the entire system, where the two surface materials on either side of the fluid, the fluid, any particles released from the two sliding surfaces, and the viscosity of the fluid all affect the sliding friction. Said another way, there is a relationship between friction and lubricity. A higher lubricity lubricant reduces the friction in a system. Viscosity is a measure of the resistance (a kind of friction. The army document above discusses different, other kinds of friction.) to flow of fluid between two sliding surfaces (an applied sheer force). The problem is the relationship is very complex. Film thickness also gets involved which involves viscosity. Lastly viscosity, and film thickness are affected by temperature which increases with heat (friction). (1) To make matters worse (in answering this question and getting to the heart of engineering definitions), there are dry film lubricant coatings (Teflon and Moly) that I am familiar with, that increase the lubricity of the sliding surface. They are dry films, not fluids and to my knowledge they do not have a viscosity. In this case I guess you would be right, viscosity would not be related to lubricity. Finally I found this on page 8-9. It was an eye open for me, as I had not run across it before. "Oiliness. Lubricants required to operate under boundary lubrication conditions must possess an added quality referred to as oiliness or lubricity to lower the coefficient of friction of the oil between the rubbing surfaces. Oiliness is an oil enhancement property provided through the use of chemical additives known as antiwear (AW) agents. AW agents have a polarizing property that enables them to behave in a manner similar to a magnet. Like a magnet, the opposite sides of the oil film have different polarities. When an AW oil adheres to the metal wear surfaces, the sides of the oil film not in contact with the metal surface have identical polarities and tend to repel each other and form a plane of slippage. Most oils intended for use in heavier machine applications contain AW agents." Best, Mike McGinness [EMAIL PROTECTED] wrote: > I understand that lubricity has to do with the ability of the oil to > maintain a lubricating film under pressure. > > Viscosity has to do with how readily the oil flows. > > They are not related. > > An early detailed study of the properties of lubricants was done by > Ricardo Engineering for the British Air Ministry in the 1920's. I'm sure > there has been a lot done since. > > Doug Woodard > St. Catharines, Ontario > > On Thu, 13 Apr 2006, Keith Addison wrote: > > [snip] > > > ...the difference between lubricity and viscosity isn't > > that clear, or at least not to me, especially when you add high > > temperatures. Anyone know better? > > _______________________________________________ > Biofuel mailing list > Biofuel@sustainablelists.org > http://sustainablelists.org/mailman/listinfo/biofuel_sustainablelists.org > > Biofuel at Journey to Forever: > http://journeytoforever.org/biofuel.html > > Search the combined Biofuel and Biofuels-biz list archives (50,000 messages): > http://www.mail-archive.com/biofuel@sustainablelists.org/ _______________________________________________ Biofuel mailing list Biofuel@sustainablelists.org http://sustainablelists.org/mailman/listinfo/biofuel_sustainablelists.org Biofuel at Journey to Forever: http://journeytoforever.org/biofuel.html Search the combined Biofuel and Biofuels-biz list archives (50,000 messages): http://www.mail-archive.com/biofuel@sustainablelists.org/
