Film Strength ??

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Seems like I read somewhere a few years back that. A oils film strength is determined by how well the bonds between the molecules hold together under extreme heat and pressure. Or something to that effect. Does this sound right? And Is boundary lubrication the same as film strength? Would a ATF have a higher film strength than motor oil? And where would gear oil fit in on film strength? Sorry if these are stupid ?s just curious. Thanks
 
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quote:
Originally posted by Hirev: Seems like I read somewhere a few years back that. A oils film strength is determined by how well the bonds between the molecules hold together under extreme heat and pressure. Or something to that effect. Does this sound right? Sounds likely And Is boundary lubrication the same as film strength? No. Boundary lubrication is what you need when the film is broken. Would a ATF have a higher film strength than motor oil? And where would gear oil fit in on film strength? Very high boundry lubrication due to extreme pressure additives...not sure about film strength. Sorry if these are stupid ?s just curious. Thanks
Ken
 
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The Silkolene web site gives some interesting info on this. From memory (which sucks), PAO's are hopless when it comes to film strengh. Esters are pretty good and dinos are better than PAO's. I'm sure an internet expert will chime in soon enough (kind of like me). [ July 13, 2003, 09:03 PM: Message edited by: satterfi ]
 
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quote:
Originally posted by satterfi: The Silkolene web site gives some interesting info on this. From memory (which sucks), PAO's are hopless when it comes to film strengh. Esters are pretty good and dinos are better than PAO's. I'm sure an internet expert will chime in soon enough (kind of like me).
Very interesting site satterfi , thank you.
 

Hirev

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quote:
Originally posted by satterfi: The Silkolene web site gives some interesting info on this. From memory (which sucks), PAO's are hopless when it comes to film strengh. Esters are pretty good and dinos are better than PAO's. I'm sure an internet expert will chime in soon enough (kind of like me).
Wow! Thanks for the tip. [bowdown]
 
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I always thought film strength was based on interfacial tension,the purer the basestock the higher the IFT in which case the PAO would be higher than group three,three higher than two etc.With ester basestock having polarity to boot giving it the ability to adhere to metel well.Interesting side note,on PCS Instruments site I read an abstract on oil films on metel surfaces where a ester/pao blend was used.The hydrodynamic film thickness was determined by the overall blend viscosity but when EHL was achieved it took on the characteristics of the more polar ester.
 

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RB is correct. In general, the order of increasing film strength is: 1. mineral oil 2. PAO's 3. esters 4. advanced lubrication fluids from exotic materials.
 
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I bothered to look up what Silkolene had to say and it is a bit different than what I said. Here's the quote: "Synthetic Hydrocarbons or PAO's (Poly Alpha Olefins) These are, in effect, very precisely made equivalents to the most desirable mineral oil molecules. As with esters, they work very well at low temperatures, and equally well when the heat is on, if protected by anti-oxidants. The difference is, they are inert, and not polar. In fact, on their own they are hopeless 'boundary' lubricants, with less load carrying ability than mineral oil. They depend entirely on the correct chemical enhancements." You can read more here: http://www.silkoleneoil.com/techtips.htm under "Synthetics: The Myth"
 
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satterfi, I'm more than a wee bit confused as to why an inert compound would need an anti-oxidant. BTW [Off Topic!] you don't post on Shooters Online do you ??
 
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Wow, if PAO's have worse film strength than mineral oils, shouldn't we all move up a grade when using synth's???? (Personally I thought it was the other way around) Why would they have worse film strength? What doesn this say about shear strength??
 

Patman

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Originally posted by Dr. T: Wow, if PAO's have worse film strength than mineral oils, shouldn't we all move up a grade when using synth's???? (Personally I thought it was the other way around) Why would they have worse film strength? What doesn this say about shear strength??
Read what Bob said though:
quote:
That is true on a molecular film strength but not necessarily hydrodynamic film strength.
 
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I guess film strength and boundary lubricant are different. I'm not sure why [I dont know] If your read what Silkolene said, it has something to do with load carrying ability. [Off Topic!] I don't know of Shooters Online.
 
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Boundary lubrication occurrs when the fluid film thickness doesn't or can't keep the opposing sufaces apart and asperities are contacting one another,creating heat and wear,thats when AW/EP and antiscuff add's come into play and protect the surfaces from welding together,fluid film thickness is largly determined by the lubricants viscosity,temps,speed and load.The molecular attraction between molecules that create surface tension would also come into play to a certain extent IMO but I don't think it's really noticable when it comes UOA's.I do believe though that the higher the viscosity index,the higher the ability of the base stock to maintain the fluid film,but this may be because of the ability to use a thicker basestock and less VII's in a formula because of reduced thickening at lower temperatures. The Silkolene website goes on to say that PAO's are solvent,or added for solvency ,which I'm sure is not true,thats why they add ester,and lower grade basestock to get the addives to blend in.
 
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