Friction modifiers question

[FrankN4]

OK I still think "I got it."

Please,,please correct my assumptions here where needed.

I have this great engine. I choose brand X because it has 1200 of ZDDP(more may cause harm to the engine, less won't help AS MUCH) The ZDDP will coat, adhere to, plate my crankshaft journal and rod bearings. If I operate the engine in a way that caused an oil starvation, the ZDDP on the journal and the ZDDP on the rod bearing will protect my journal and bearings(to a point)but in the process of doing so the ZDDP against ZDDP has a higher coeficient of friction as it is sheared away.

Now, I keep all the ZDDP and add the best friction modifier in the world(whatever that is) I now get a coat of the FM on top of the coat of ZDDP. However, the FM is no where near as firmly attatched, it comes off easily, with little friction. Now comes my oil starvation. The FM against FM shears off rather easily so very little relative friction, but, it doesn't protect nearly as much or for nearly as long. Now we may be back down to the ZDDP.

Somehow, I also have the idea that the FM is constantly and almost immidiately replaced when oil flow comes back to whatever normal is, and the process can start over. In this way we have the fluid oil flowing over FM and the fluid oil flow is much easier(poor word choice?)because of the FM, requires less work from the oil poump, reduces engine self consuming loads, and gas mileage goes up :^)

Please grade and crituque my paper as you have time. It is OK to call me ignorant, but only if you really belive so.

Thanks, Frank

 

[Tempest]

Most looks good except:
Quote:
In this way we have the fluid oil flowing over FM and the fluid oil flow is much easier(poor word choice?)because of the FM,

The FM aids in light contact between metal surfaces, it does not help oil flow as such. They typically provide some level of AW, but not in the same category as ZDDP or similar, which come into play with more forceful contact.

 

[bruce381]

FM's work in Boundry/hydrodynamic range where AW work in a boundry range.

 

[Tempest]

Originally Posted By: bruce381
FM's work in Boundry/hydrodynamic range where AW work in a boundry range.


Then I am missing something. How do they come into play in the hydrodynamic regime? There has to be contact or near contact for the FM affect does there not?

 

[Gary Allan]

I'm the idiot here, but I thought that FM modified the stress in the normal laminar shearing. Effectively make it easier to shear/pump/etc outside of its viscosity confines. This is my first exposure to boundary properties of FM. Again, I really focused on filtration too much when I was in composition class. I was dipping my paddle.

 

[bruce381]

Better to say mixed film or very thin hydrodynamic for FM's they work at low prerssures I guess what I'm trying to say AW work within the boundry regime and FM's sorta betrean. I'm not saying this right.

EP Full metal to metal
AW Full metal to boundry
FM's Boundry to hydrodynamic

even hydrodynamic has/can have thin film areas where the polar FM additves can add slip and reduce friction kinda like
a borderline boundry area.
bruce

 

[Tempest]

Quote:
even hydrodynamic has/can have thin film areas where the polar FM additves can add slip and reduce friction kinda like
a borderline boundry area.


So the stacked esters or moly will begin to move along with the wedge before there is actuall metal contact?

 

[Gary Allan]

Is this a mucous layer? (yes, I'm half joking)

 

[4wheels]

Originally Posted By: JAG
ZDDP could be called a friction increaser. It modifies friction but in the positive direction. Friction coefficient and anti-wear effects are independent of each other.


Hmm, interesting, I thought ZDDP reduced friction. But after re-reading how ZDDP works more as a "plastic" I guess that makes sense. Learn something every day...

If the OP wanted a Friction Modified oil, and the Amsoil HDD fulfilled his specs in every other category (more or less), would it be a safe option to add a can of Lubro-Moly MOS2 additive and get his FM'd oil that way?

 

[JAG]

I am ashamed to admit that I used Lubro-Moly MOS2 additive. It was in a weaker than recommended dosage because I knew it was an iffy idea. All those solids that have a tendency to settle out and build up on things (like piston ring lands, piston rings, oil pans, valves, piston tops, etc.) scares me and it's use in IC engines is generally frowned upon by formulators. Most formulators greatly prefer organo-moly additives, like MODTC, over MOS2. Those types are in solution.

Anything you add to HDD to try to friction modify it is going to modify the oil in a complex way (even if it's undetectable to the user). It won't be a 2+1=3 way. Anything from no effect, to good effect, to bad effect can happen regarding many performance parameters. It may hurt one thing, help another, hurt another, etc... If you want to experiment go ahead but be informed about the potential effects.

Many people have had fuel economy benefits from adding maintenance doses of Auto-RX to their oil. It could maybe be considered a friction modifier....the liquid type - esters.

 

[MolaKule]

I can see that a simple explnation won't suffice.

If one looks at the "Stribeck" curve you will see a chart with the vertical axis as the Coefficient of Friction, and the horizontal as (ViscosityXSpeed)/Pressures value.

Boundary lubrication would be the severe wear portion without an AW or EP additve and represents a high COF; the next lower friction area would be EHL or elastohydrodynamic Lubrication or the Mixed Lubrication regime with lower friction; then further to the right (with even lower friction) one would see hydrodynamic lubrication. I.E., one sees greater loads from left to right with S curve going from the high friction regimes to low friction regime.

http://en.wikipedia.org/wiki/Lubrication

and do an INternet search on Stribeck or Stribeck Curve to see the actual graph, such as:

http://www.me.utexas.edu/~bryant/courses/me383s/DownloadFiles/LectureNotes/BoundaryLubrication.pdf

http://www.tribology-abc.com/abc/stribeck.htm

I like this one best:


http://www.sae.org/events/pfs/presentations/2005spikes.pdf

 

[4wheels]

Thanks MolaKule... excellent source of info as always.

 

[Tempest]

Quote:
"What is a friction modifier? How do these modifiers help in industrial gear oil?"

Friction modifiers and mild antiwear agents are polar molecules added to lubricants for the purpose of minimizing light surface contacts (sliding and rolling) that may occur in a given machine design. These are also called boundary lubrication additives. Esters and natural and synthetic fatty acids, and some solid materials such as graphite and molybdenum disulfide, are used for these purposes.

These molecules have a polar end (head) and an oil-soluble end (tail). Once placed into service, the polar end of the molecule finds a metal surface and attaches itself. If one could 'see' the orientation of the molecules on the surface, it would appear something like the fibers of a carpet, with each molecule stacked vertically beside the others.

As long at the frictional contact is light, these molecules provide a cushioning effect when one of the coated surfaces connects with another coated surface. If the contact is heavy, then the molecules are brushed off, eliminating any potential benefit of the additive.

When the machine designer anticipates more than light surface contact (from shock loading for instance) then the designer would select a stronger type of friction modifier characterized as an antiwear additive. Zinc dialkyldithiophosphate is a common antiwear agent. This type of additive literally reacts with the metal surface when the reaction energy (temperature) is high enough. The reaction layer provides sacrificial surface protection.

As the loading and metallic contact increase, the strength of additive and the strength of the reaction process increases. This leads to the use of sulphur-phosphorus based EP chemicals. The EP additives form organo-metallic salts on the loaded surfaces that serve as sacrificial films to protect against aggressive surface damage.

Mike Johnson, Noria Corporation


http://www.lube-tips.com/focus/2005_02_02.htm

Quote:
Considerable research work has been carried out to measure the effectiveness of friction modifiers, both in base oil and in fully formulated engine oils. Most of this work has studied the behavior of friction modifiers on rubbing ferrous surfaces.

http://www.informaworld.com/smpp/content~content=a782907702~db=all~jumptype=rss

I'm still not getting how these work in the hydrodynamic regime?

 

[MolaKule]

Quote:
I'm still not getting how these work in the hydrodynamic regime?


Think of the Stribeck curve as going from right to left in terms of more friction and more potential contact (in the case of no FM, AW, or EP additives).

I tend to think of friction modifiers "engaging" at the vertical line between hydrodynamic and mixed lubrication somewhere between stribeck numbers 10 to 5.

http://www.me.utexas.edu/~bryant/courses/me383s/DownloadFiles/LectureNotes/BoundaryLubrication.pdf

 

[FrankN4]

OK Assume that I have two identical oils here before me. Both are 5w30. Both have 40C cSt of 65....100C cSt of 11.5....VI of 180+....HTHS of 3.2....TBN of 12....800 ZDDP. The only difference is that one has NO FRICTION MODIFIERS and the other has ALL THE FRICTION MIDIFIERS IT CAN HANDLE. I am going to change the oil and filter at no more than half of the recommened OCI.(if it says 7500 I will change at 3000) I am starting with a new engine, just home from the dealer. What would be the difference in engine wear between the two oils? I expect the engine to be running great at 200,000 miles.

 

[Tempest]

Quote:
I tend to think of friction modifiers "engaging" at the vertical line between hydrodynamic and mixed lubrication somewhere between stribeck numbers 10 to 5.


Ok, I'll go with that. I assume that FMs stick up "higher" or build up on AW pads so that they are engaged before AW?

Quote:
I expect the engine to be running great at 200,000 miles.

Just about any oil will get you there. FM aren't so much involved in AW. From the link that I posted above:
Quote:
As long at the frictional contact is light, these molecules provide a cushioning effect when one of the coated surfaces connects with another coated surface. If the contact is heavy, then the molecules are brushed off, eliminating any potential benefit of the additive.

 

[Gary Allan]

Quote:
What would be the difference in engine wear between the two oils?


Probably "none" that can be perceived, if any. Your service will probably dictate the effects on the engine and those will probably still fall in a buffer zone that can drift from outstanding to common. Depending on your service, you should be able to double your OCI and get the same result. Just my opinion.

You could add a block warmer (even if you're in Texas) to totally eliminate any fuel enrichment related insults.

 

[FrankN4]

Tempest and Molakule, thank you again so very much.

I think that I may be having trouble seeing a distinction between friction and wear. I always thought that friction equaled wear, more friction=more wear. I think maybe that we are talking about the "wear"/"friction" of FM against FM or AW/EP against AW/EP rather than the wear of journal against bearing.

The oil that GM recommends for my truck is 5w30 and has a cSt 40C of 64.8. It has a cSt 100C of 11.3. If I use the graph provided by widman, this oil would still have a cSt of 10.00 at an oil temp of 223F. Crossing the mountains with all my campin equipment would raise the oil temperature. At 224F, it would drop below the cSt of 10(30 grade) that GM says my engine needs.

As the oil film gets thinner, the asperities of the rod journal and the rod bearing are getting closer together. When they get extremely close, yet not touching, the whiskers of the FM on the bearing will shear against the whiskers of the FM on the journal?(question) If they get close enough to touch, we are down to the ZDDP(or whatever) But, would the asperities not shear each other from the journal material or bearing material? Would not the ZDDP film have to be thicker than the standoff of the asperities, or, actually be plated on the asperities so that the ZDDP plated on the tips of the asperities would shear before the asperities actually touched. If things got so bad that the asperities were actually butting up against each other, shearing each other,unless for a very short time, does that mean the game is pretty much over==blown engine?

I can see how FM would have very little to do with actual journal/bearing wear. I am still somewhat fuzzy about how FM actually helps fuel economy. Seems like you would have to use an oil that was lets say "borderline" viscosity wise. Is that it? Is that the beauty of FM? It lets my engine "survive" with a 5w30 that pumps easier(CAFE?) than a 0W-40/5W-40 which is really probably the "best"(yeah, I know, best has to meet a lot of qualifications)

I gotta go dig some post holes, the old fashioned way. Maybe that will relax my brain.

Thanks all.

 

[Gary Allan]

Quote:
At 224F, it would drop below the cSt of 10(30 grade) that GM says my engine needs.


Where does GM state this? Do they say, anywhere, if you tow, knowing that oil temps will most likely exceed 100C/212F, that you need to graduate to a 40 grade (Dr. Haas - ah-ha)?? Not anywhere I've ever seen.

That is, just because the 30 grade that they spec is between 9.30-12.49 Cst @ 100C/212F, how do you know that your engine is at risk at 8 Cst or even 5Cst? How do you know that these conditions are not buffered into the spec? If I read my manuals correctly (always suspect) the only recommendation is to shorten the OCI.

Just out of curiosity, do you think that 212F is some terminal oil temp designed/spec'd into engines? It's a good marker for normal ..but..most fail that aren't forced cooled (with an oil:coolant exchanger) if they're at high output (for some 70mph is high enough output). Without forced cooling or auxiliary cooling, I think you're around or above 224F just towing anything at any speed.

 

[Tempest]

Quote:
Would not the ZDDP film have to be thicker than the standoff of the asperities, or, actually be plated on the asperities so that the ZDDP plated on the tips of the asperities would shear before the asperities actually touched.

That is a question with ZDDP and other AW. EP additives actually reshape the surface of the metal to be "rolled out" and smoother, along with leaving a film in place. Not sure if the flattening or polishing occurs with ZDDP.
Quote:
If things got so bad that the asperities were actually butting up against each other, shearing each other,unless for a very short time, does that mean the game is pretty much over==blown engine?

Asperity contact and shearing is wear. It just doesn't happen all that much and additives help in that fight.
Quote:
Is that the beauty of FM?

ZDDP actually increases friction, even though it protects from wear. The idea of friction modifiers is to keep the parts off the ZDDP to keep things "slick" through very gentle "near misses" of surfaces. I'm not sure if or why they would have an effect on pumping.