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#729029 - 10/18/02 02:47 AM Friction Reducers and AW Additives
MolaKule Offline


Registered: 06/05/02
Posts: 14527
Loc: Midwest
Oil Soluble Friction Reducers (FM's) and Anti-Wear Additives (AW's)
(with an emphasis on Friction Modifiers)
by MoleKule*

Oil soluble friction modifiers - once called friction reducers - have been used many years by the lubricant industry. Many products made use of friction reducers:
- Automatic Transmission Fluids (ATF's or those designed for smooth clutch engagement)
- Limited Slip Gear Oils for limited slip differentials and transaxles
- Multipurpose tractor fluids for wet brakes
- engine oils

There are also many other, lesser-known products, also containing friction modifiers in the form of animal fats, vegetable oils, sulpherized olefin coplymers, and esters.

Such products made use of friction modifiers as a way to meet performance requirements calling for smooth transitions from static to dynamic conditions and vice versa, as well as for reduced squawk, chatter, noise, frictional heat and start-up torque.

In the seventies, some gear oil additives were found to reduce frictional heat and gear operating temperatures under extreme load conditions while eliminating chatter in limited slip differentials. It was thought these same additives might be used in engine oils to accomplish the same function.

The ability to reduce friction and sometimes wear, over and above that provided by the base lubricant's viscosity, has been called "oiliness" or "lubricity." However, both of the latter terms are now considered obsolete. Early experimenters found that the ability of animal or vegetable fats and acids strengthened the tenacity of the oil films when incorporated in lubricating oils. These experimenters later found that the esters of vegetable or animal esters could be synthesized and produced from alcohols and acids of basic chemical compounds; what we call today as "Group V" lubricants. Their effectiveness was often rated in terms of "film strength," an expression that still remains in use.

Much confusion has abounded in the relationship between Anti-Wear (AW) or Extreme Pressure properties, and Friction Modifiers (FM). Both friction modifiers and Anti-Wear compounds both operate in the Boundary lubrication regime. AW additives are among the type of compounds that provide good boundary lubrication. Such materials as ZDDP, sulfurized fats and esters, organometallic compounds (such as Molybdenum dithiophosphates, Molybdenum dithiocarbamates, Antimony dithiocarbamates) have shown their ability to build and maintain strong boundary lubrication films under severe load conditions and heat. However, with the exception of second-generation gear oils, the older first-generation AW additives had little FM capabilities.

The critical difference between AW/EP additive films and FM films is in their mechanical properties. AW/EP films are semiplastic deposits which are hard to shear off. Thus, under shearing conditions, their coefficient of friction is moderately to high. The exceptions are the organometallic compounds listed above. Friction modification films consist of orderly, close-packed arrays of multimolecular "whiskers," loosely adhering to each other. The outer layers are sheared-off easily, allowing for low coefficient of friction. The phenomena can be described as a deck of plastic coated playing cards lying on the table and sliding off the top card easily.

Conversely, AW/EP films work by protecting the mating metal surfaces from asperities physically gouging the opposite surface. When a hydrodynamic film of oil is ruptured, this layer of AW/EP material protects the mating surfaces from catastrophic failure.

For some sense of scale, here are some further analogies:
1. The Coefficient of Friction (CF) of unlubricated surfaces is 0.5 and higher. In physical simulation, the process resembles the resistance of dragging an irregular rock over irregular rocky ground.
2. The CF for of friction of W/EP films is about 0.1 to 0.2. In simulation, it would resemble dragging a more or less flat stone over a flat rock.
3. The CF for a friction-modified film is about 0.01 to 0.02, compared to ice skating.
4. The CF of fully fluid films in hydrodynamic lubrication is about 0.001 to 0.006 or less. It can be compared to hydroplaning.

The preferred film is of course the hydrodynamic film. This is to followed by the friction-modified mode of operation, followed by an AW/EP regime. When high speeds or low loads are present, it is easy to maintain the hydrodynamic regime. When the speed falls, however, or the load rises above a critical point, the hydrodynamic regime breaks down and then it would be very desirable to be able to glide smoothly into a friction modification mode of operation. If no friction modification has been provided, the system defaults to a AW/EP regime. So friction modification and AW/EP is a logical method to widen the range of effectiveness of the lubricating film. Friction Modification depends much on the mechanism of contact (geometry) and molecular construction of the FM.

FM's may be produced from a number of chemicals:
- long-chain carboxylic acids and their derivatives including salts,
- long-chain phosphoric or phosphonic acids and their derivatives
- long-chain amides, imides, and derivative
- specially prepared esters and esters of base oils.

Some of the acids used to make the salts or esters may be phenylstearic, stearic, oleic, heptanoic, benzoic, and sebacic.

The configuration of the molecule (molecular structure) of FM's determines how many molecules are adsorbed on the surface. The slimmer molecules make stronger films because they allow closer packing. The base oil chain length also affects the strength of the adsorbed molecule. Different FM's are required for different base oils, and the interaction of FM's with other additives have to be investigated as well. The "concentration" of FM's is important as well. But only so much concentration will prove effective. A concentration above a certain point may show no improvement, so cost/concentration/effectiveness has to be evaluated during tests.

Fuel economy formulations involving FM's have to be selected on the following basis:
- FM properties
- dosage or treatment levels
- chemistry (chlorine, phosphorous, nitrogen, boron, ester type, etc)
- toxicity
- safety in handling
- oil solubility
- effect on metals, seals, and other engine materials
- possibility of synergism or antagonism
- acidity or alkalinity
- compatibility with other additives
- raw material availability and costs
- ease and cost of manufacturing
- patent coverage.

FM's can be employed in different forms in an additive package for a specific formulation. It can be added by itself without any other function, or may be part of molecule in a detergent (such as a sulfonate) or as part of a Viscosity Improver or antioxidant.

Example of an FM/Detergent additive may be a long-chain calcium, magnesium, or sodium sulfonate, preferably one long chain of the benzene ring.

Since FM's are surface-active materials, and as such, compete with other useful additives, care must be taken in their selection and concentration in any fully formulated lubricant.

*Adapted from a paper by Papay, of the Ethyl Corporation, St. Louis, Missouri.

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#729030 - 10/19/02 09:23 AM Re: Friction Reducers and AW Additives
Jay Offline


Registered: 07/16/02
Posts: 1600
Loc: Arroyo Grande, CA
Good post, MolaKule. I think I know much more about friction modifiers now. According to your article they only come into play when hydrodynamic lubrication fails which makes me wonder just how often this happens.

Mobil 1 says their 0w-30 oil is their "gas mileage" oil. They make improved gas mileage claims for it that they don't make for their 5w-30 oil even though the two have almost identical viscosities. I thought this must be due to more FM's added to the 0w-30. Hydrodynamic lubrication must fail nearly continuously for any gas mileage benefit to be realized from FM's then.

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#729031 - 10/19/02 02:38 PM Re: Friction Reducers and AW Additives
Patman Offline



Registered: 05/27/02
Posts: 19281
Loc: Oakville, Ontario
quote:
Originally posted by Jay:
Good post, MolaKule. I think I know much more about friction modifiers now. According to your article they only come into play when hydrodynamic lubrication fails which makes me wonder just how often this happens.


I think it happens a lot more than we think. On a cold engine when the oil is thicker, and harder to pump, I think these come into play a lot. Plus for anyone that drives their car very hard, I imagine that in the upper rpms the oil gets sheared back quite a bit, perhaps not completely, but enough to necessitate the AW additives. Which is why someone who drives their car hard will see a bigger improvement in engine wear when they switch from an oil with a poor antiwear package compared to one with a great antiwear package. Someone who drives at light throttle everywhere may not see all that big of a difference in their oil analysis results between the two oils.

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#729032 - 10/20/02 06:52 PM Re: Friction Reducers and AW Additives
MolaKule Offline


Registered: 06/05/02
Posts: 14527
Loc: Midwest
Jay,

I think a lot depends on which component in the engine you're discussing. For journal bearings, my theory is that the lubrication regime is 95% or better hydrodynamic. For cams and followers that are highly loaded with stiff springs, I suspect more boundary lubrication than hydrodynamic, say 60/40; for piston rings on cylinder walls, I would say maybe 40/60.

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#729033 - 10/24/02 03:32 AM Re: Friction Reducers and AW Additives
Jay Offline


Registered: 07/16/02
Posts: 1600
Loc: Arroyo Grande, CA
Another question about friction modifiers: What is it about a friction modifier that would allegedly cause a motorcycle wet clutch to slip that an anti-wear additive wouldn't? For example, Mobil will say, "Don't use Delvac 1 in motorcycles because it has friction modifiers." Well, a motorcycle-specific oil has to have a robust AW package for the transmission. Why wouldn't this cause the clutch to slip?

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#729034 - 10/24/02 07:37 AM Re: Friction Reducers and AW Additives
MolaKule Offline


Registered: 06/05/02
Posts: 14527
Loc: Midwest
Well, Amsoil says the same thing, which is why they formulated Motorcycle specific oils. They increased the AW additives and removed the friction modifying chemicals.

The friction modifier would interfere with the engagement and contact of the two clutch surfaces, and would attempt to keep the two surfaces from touching each other. The AW additives simply adhere to metal surfaces, not the composite surfaces of the clutch, whereas the FM's would adere to all surfaces.

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#729035 - 10/24/02 10:43 AM Re: Friction Reducers and AW Additives
Jay Offline


Registered: 07/16/02
Posts: 1600
Loc: Arroyo Grande, CA
Mystery solved, thanks!

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#729036 - 10/24/02 10:55 PM Re: Friction Reducers and AW Additives
TooSlick Offline


Registered: 08/02/02
Posts: 5785
Loc: Dixie
Jay,

It is actually much more simple than that ....

The Mobil 1, 0w-30 flows better while the engine is warming up. It does also not thicken up as much if your equilibrium oil temps are less than 210F - ie, the standard test temp for viscosity. So in cold weather, it will provide a fuel efficiency benefit even on long trips, compared to the 5w-30 or 10w-30.

This is true of all 0w-30 synthetics, in comparison to 5w-30/10w-30 grades ....

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#729037 - 10/25/02 07:16 AM Re: Friction Reducers and AW Additives
Jay Offline


Registered: 07/16/02
Posts: 1600
Loc: Arroyo Grande, CA
I have a couple of viscosity vs temp. charts from Mobil 1, ASTM Standard Chart 0341, that cover the range -40*C to 230*C. Already plotted on one of the charts is all of M1's 30-weights and their 15w-50. The viscosity of 0w-30 and 5w-30 is so close that the lines practically overlay from -40 all the way to 100*C and beyond. (The 10w-30 is significantly thicker at lower temps, though.) So I don't see how Mobil1 can claim better gas mileage from the 0w-30.

I'm talking about kinematic viscosity. When you say, "0w-30 flows better when the engine is warming up", are you talking about kinematic viscosity or dynamic viscosity? There are big holes in my understanding of dynamic viscosity.

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#729038 - 08/10/04 09:58 AM Re: Friction Reducers and AW Additives
MolaKule Offline


Registered: 06/05/02
Posts: 14527
Loc: Midwest
Basically, there are two classes of friction modifiers:
A. Metallo-0rganic compounds (such as Moly MoDTC)
b. Organic

Organic friction modifiers are very useful for items like roller followers.

The chemistry is one of two types:
1. Long chain fatty amides or
2. "Partial" esters of glycerol mono-oleates.

The mode of action is as for most friction reducers, and that is adsorbed layers of molecules are formed that are easily sheared-off, with the result of reduced friction. The lubrication regimes for friction modifiers are: 1.) Boundary Lubrication, 2.) Mixed Lubrication, and 3.) Elasto-Hydrodynamic lubrication.


I think we will see both types (metallo-organic and pure organic) friction reducers used especially in the XW20 oils.

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#729039 - 08/09/04 10:05 PM Re: Friction Reducers and AW Additives
MolaKule Offline


Registered: 06/05/02
Posts: 14527
Loc: Midwest
quote:
So I don't see how Mobil1 can claim better gas mileage from the 0w-30.

I'm talking about kinematic viscosity. When you say, "0w-30 flows better when the engine is warming up", are you talking about kinematic viscosity or dynamic viscosity? There are big holes in my understanding of dynamic viscosity.

I was speaking of kinematic viscosity. Discussions of dynamic viscosity are usually relegated to ATF fluids.

Due to the fact that the 0W30 has more VII's, the friction is slightly less, since it is known that certain VII's also reduce friction somewhat.

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#729040 - 08/10/04 09:34 AM Re: Friction Reducers and AW Additives
Gerret Offline


Registered: 07/29/04
Posts: 46
Loc: Texas, USA
Thanks MoleKule (and Papay).

This post answers some questions that I had regarding the differences between motorcycle and car motor oils. I noticed that the Lubedev.com guy (who deserves a whole subsection on the BITOG forum for his, um, unorthodox theories) advocates using motorcycle oil in cars. I disagreed, but I didn't have a clear reason why until after reading your post.

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#729041 - 08/10/04 12:37 PM Re: Friction Reducers and AW Additives
faa777 Offline


Registered: 06/27/04
Posts: 3
Loc: Jebel Ali
MolaKule,

Thanx for the detailed information.

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#729042 - 09/26/05 06:46 AM Re: Friction Reducers and AW Additives
MolaKule Offline


Registered: 06/05/02
Posts: 14527
Loc: Midwest
quote:
Reducing friction isn't just for fuel economy, but reducing wear. I'd guess that some oils, maybe Redline for instance, would have higher viscosity oils that are as fuel efficient as another brand's lower viscosity oils. This would mean RL's Cf is lower. So in theory you could have a GF-4 oil that met the fuel efficient spec but could still protect very well bc it would still be a higher viscosity. Any thoughts?
You can't destroy the laws of physics. Thicker fluids mean higher energy losses, but also means thicker hydrodynamic films. And this is where the short term research is going; add a thicker fluid with a very good VI and shear characteristic to a thinner PAO, and use the appropriate protection and performance additives.

Now once more, I think you and others have confused Anti-Wear (AW) additives with friction reducers (FM's). Now FM's can mean friction reduction across the board, or friction that changes, depending on the relative speed between surfaces.

Friction reducers work by depositing sacrifical whiskers that are lopped off, much like a mower does to grass, keeping the metal separated mostly during the hydrodynamic or mixed lubrication regime. Friction reducers can also reduce the shearing action of the fluid, thus leading to better MPG and less energy dissipated in the oil.

Anti-Wear additives lay down a film that becomes plastic under pressure, preventing the surfaces from actually touching during the boundary lubrication regime, I.E., when there is barely an oil film or when the contact pressure is so high, the oil film is squeezed out (film strength exceeded by the localized pressure).

An Extreme Pressure (EP) additive not only forms a film, but chemically reacts with the first few micrometers of metal surface to form a sacrificial film such that the sacrificial film is allowed to SHEAR, rather than having the metal surfaces gouge, gall or shear against each other.

FM's and AW additives are used in engines oils and hydraulic fluids.

EP, AW, and FM additives are used in MT and differential gear lubes, with the EP additives being the predominant additive.

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#729043 - 09/26/05 07:05 AM Re: Friction Reducers and AW Additives
bruce381 Offline


Registered: 06/23/05
Posts: 3324
Loc: Millbrae, CA
quote:
Originally posted by MolaKule:
Basically, there are two classes of friction modifiers:
A. Metallo-0rganic compounds (such as Moly MoDTC)
b. Organic

Organic friction modifiers are very useful for items like roller followers.

The chemistry is one of two types:
1. Long chain fatty amides or
2. "Partial" esters of glycerol mono-oleates.

The mode of action is as for most friction reducers, and that is adsorbed layers of molecules are formed that are easily sheared-off, with the result of reduced friction. The lubrication regimes for friction modifiers are: 1.) Boundary Lubrication, 2.) Mixed Lubrication, and 3.) Elasto-Hydrodynamic lubrication.


I think we will see both types (metallo-organic and pure organic) friction reducers used especially in the XW20 oils.

Question here in Elasto Hydro Duynamic lubricaton regimes since the fluid is at that moment a solid how can a FM do anything? They (FM's) only work in boundry conditions and/or mixed not in hydro dynamic or elasto hydro dynamic. Please explain this?
bruce

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