Shifting Stribeck Curve to the Left: What to Use?

[CrawfishTails]

I've been trying to figure out what is out there that can boost the ability of an oil to form a tougher elastic oil film, i.e, super-lubricity (SL) to shift the Stribeck Curve to the left.

Requirements: Any additive doing this must be synergistic, NOT surface-competitive, with ZDDP at the higher temperatures that ZDDP works.
Also, the additive must work at lower temperatures than ZDDP to augment it, not interfere with it.

 

[Shannow]

IMO, that's the bast place for the Myagi defence "best defence is no be there".

Yes, OEMs and oil companies are heading to the left for improvements in economy (while maintaining adequate life)...

To get to the left, you merely have to drop viscosity...if you are operating at "10" on the striebeck curve on a 3HTHS oil, then dropping to 2.7 will sit you at "9", moving you to the left.

As to additives to protect there...I think that's beyond the backyard chemist.

 

[CrawfishTails]

A couple of the places I've looked, in case you want to read all about it:
https://www.stle.org/assets/document/Tech_Beat_September_2009.pdf
http://www.crodalubricants.com/download....b5-bc32bb756ffe

I've found references and mentions of Polymer Esters (HyperLube and Lubregard Biotech active ingredients) capable of performing super-lubricity (SL) polar films in a non-surface-competitive way with normal ZDDP engine oils.

Does moly boost the oil film in the same way?

 

[CrawfishTails]

Shannow, I'm talking about moving the curve itself to the left.

 

[CrawfishTails]

For example, if we put plain basestock oil alone into our sumps and run, there is a Stribeck curve the cams, rings, bearings experience. Then, if we add in the anti-wear and SL superlubricity additives, the Stribeck curve is shifted. That kind of effect.

 

[CrawfishTails]

Assuming a fully formulated good engine oil can be improved upon, is there some evidence out there that its not just polymer esters that can do it? Ceratec might be too surface competitive, a moly-boron approach. Anyway, some evidence out there would be cool to have.

 

[Jetronic]

I think you're into solids if you want to reduce the friction in the boundary lubrication regime.

Nano-particles is being researched quite extensively, but that area is where MoS2, Graphite, tungstendisulfide etc excel (for now).

In the mixed regime, esters are likely the most effective.

 

[badtlc]

Sounds like Royal Purple's Synerlec.

 

[turtlevette]

Originally Posted By: CrawfishTails
Shannow, I'm talking about moving the curve itself to the left.


I've proposed the same thing to him many times. For example a 20wt that has the film strength of a 40wt because of special composition. He doesn't believe in that and thinks viscosity is the only indicator of film strength, whether its water, liquid metal, mineral oil, synthetic oil or whatever. He thinks viscosity is the only thing that matters, which I believe is outdated thinking.

I disagree but don't have the background to prove it. There is guy testing oils (540 rat blog) with a one arm bandit and he claims there is no correlation between viscosity and film strength. The thing is, you can't tell with those devices whether you're testing film strength or boundary additives. Probably both.

I'll read up on the links you provided, but intuitively I agree with you.

 

[Shannow]

Originally Posted By: turtlevette
I've proposed the same thing to him many times. For example a 20wt that has the film strength of a 40wt because of special composition. He doesn't believe in that and thinks viscosity is the only indicator of film strength, whether its water, liquid metal, mineral oil, synthetic oil or whatever. He thinks viscosity is the only thing that matters, which I believe is outdated thinking.

I disagree but don't have the background to prove it. There is guy testing oils (540 rat blog) with a one arm bandit and he claims there is no correlation between viscosity and film strength. The thing is, you can't tell with those devices whether you're testing film strength or boundary additives. Probably both.

I'll read up on the links you provided, but intuitively I agree with you.


Naw...your proposal was that a 20 weight could be made with a greater minimum oil film thickness than a thicker oil, not "film strength"...so don't put words in my mouth.

Laws (not suggestions) of physics are that MOFT is dependent on viscosity, all else being equal, a drop in viscosity always equals a drop in MOFT.

If you've mistaken MOFT for "film strength", and the 4 balls, 1 armed bandit/Rat tests, that's neither my fault, nor my issue...so again, don't tell me what I'm saying.

 

[Clevy]

Originally Posted By: turtlevette
Originally Posted By: CrawfishTails
Shannow, I'm talking about moving the curve itself to the left.


I've proposed the same thing to him many times. For example a 20wt that has the film strength of a 40wt because of special composition. He doesn't believe in that and thinks viscosity is the only indicator of film strength, whether its water, liquid metal, mineral oil, synthetic oil or whatever. He thinks viscosity is the only thing that matters, which I believe is outdated thinking.

I disagree but don't have the background to prove it. There is guy testing oils (540 rat blog) with a one arm bandit and he claims there is no correlation between viscosity and film strength. The thing is, you can't tell with those devices whether you're testing film strength or boundary additives. Probably both.

I'll read up on the links you provided, but intuitively I agree with you.





540 Rats testing is pointless and in no way representative of anything whatsoever. His methods are absurd.and pert plus shampoo can hang with some of his oils tested load carrying ability.
Why do people even reference that nonsense. Anyone with even a modest understanding of an engine realizes in seconds the testing method is absurd thus the results irrelevant.

 

[Shannow]

Originally Posted By: CrawfishTails
For example, if we put plain basestock oil alone into our sumps and run, there is a Stribeck curve the cams, rings, bearings experience. Then, if we add in the anti-wear and SL superlubricity additives, the Stribeck curve is shifted. That kind of effect.


The bottom line of the Stribeck curve (the X axis) is the dimensionless viscosityXspeed/load...the sloped area to the right is hydrodynamic, and represents both higher MOFT, and higher drag.

To shift more to the right, more MOFT, you increase viscosity, increase surface speed, or reduce load...pretty simple.

The area at the lowest point is where mixed lubrication is occuring, where the oil drag is low, and actual asperity contact is just happening...the rapid rise to the left is because there's more and more.

Viscosity moves you along the X axis, not additives.

Additives determine how high and sharp the increase to the left is, once the hydrodynamic "wedge" is no longer there...friction modifiers flatten it out, and can drop friction slightly lower than the low point on a traditional stribeck curve.

It's why manufacturers are these days allowing more boundary/mixed lubrication...it saves fuel...it doesn't make engines last longer, less friction is not necessarily less wear.

 

[Clevy]

Originally Posted By: Shannow
Originally Posted By: CrawfishTails
For example, if we put plain basestock oil alone into our sumps and run, there is a Stribeck curve the cams, rings, bearings experience. Then, if we add in the anti-wear and SL superlubricity additives, the Stribeck curve is shifted. That kind of effect.


The bottom line of the Stribeck curve (the X axis) is the dimensionless viscosityXspeed/load...the sloped area to the right is hydrodynamic, and represents both higher MOFT, and higher drag.

To shift more to the right, more MOFT, you increase viscosity, increase surface speed, or reduce load...pretty simple.

The area at the lowest point is where mixed lubrication is occuring, where the oil drag is low, and actual asperity contact is just happening...the rapid rise to the left is because there's more and more.

Viscosity moves you along the X axis, not additives.

Additives determine how high and sharp the increase to the left is, once the hydrodynamic "wedge" is no longer there...friction modifiers flatten it out, and can drop friction slightly lower than the low point on a traditional stribeck curve.

It's why manufacturers are these days allowing more boundary/mixed lubrication...it saves fuel...it doesn't make engines last longer, less friction is not necessarily less wear.




That's pretty interesting. Less friction doesn't always equate to less wear. I always thought that if friction was reduced then wear would be too however I've since learned that it's not always the case and it's possible for wear to increase with no changes in the co-efficient of friction.
That in itself is kind of mind blowing because common sense tells me they are connected when in reality one doesn't always affect the other.

 

[demarpaint]

That's an eye opener.

 

[Quest]

Thanks for the insightful analysis on this subject matter.

Learned something new every day.

Q.

 

[CrawfishTails]

Originally Posted By: Quest
Thanks for the insightful analysis on this subject matter.

Learned something new every day.

Q.


Shannow and all others on here can educate us. I'm really looking to "beef up" that last bit of oil film near Boundary Lubrication (BL) conditions for lower wear rates. (Note a running engine routinely enters minimal-to-zero oil film thickness (OFT) such as cam lobes, chains, piston rings on the top of the stroke, crank bearings and piston pins, especially at cold startup or low engine speeds or high loads.)

In particular, I guess the Croda polymer esters (hopefully similar to HyperLube's polymer esters!!!) slime on a tough low-temperature polar polymer ester stick film:

 

[CrawfishTails]

The pictures above are what I'm hoping the Hyperlube people have put together, using the correct polar intensity. Note its synergistic with ZDDP layers, and at different temperatures/pressures.

I'm considering just using moly additives Liquimoly MOS2 alone, hard to decide. Similar effects I guess. I may have gone overboard, but I'm currently running a half dose of Ceratec nano-tech particles with moly-boron, with half dose Hyperlube polymer esters. I might be getting carried away. Hope I'm not upsetting any delicate chemical balances in decent motor oil with that. Synergistic one hopes.

 

[Shannow]

CrawfishTails,
I get where you are at now.

Thus you might find this interesting (was looking at it in relation to a bunch of other threads)...right at the bottom...

http://www.machinerylubrication.com/Read/496/active-sulfur-ep-gear-oil

Quote:
Sequential Four-Ball Test
Scientists at Penn State University developed the sequential four-ball test (SQFBT), a variant of the established ASTM four-ball friction and wear tests.4 This three-step procedure begins with an initial 30-minute run on the test fluid. After this period, the initial wear scar is measured. The fluid is then tested for an additional 30 minutes and the change in scar size recorded. The difference is a measure of the lubricant’s antiscuffing performance in the absence of the initial “run-in” wear scar that normally occurs. In the last step, additive-free white oil replaces the test lubricant for a final 30-minute run after which the scar is again measured. This stage evaluates the ability of additive deposited on the steel surfaces to protect the metal from wear or scarring. An effective AW or EP lubricant should provide lasting protection by depositing additive onto the metal surface.

This test appears to offer some advantages over the traditional ASTM friction and wear tests in that it evaluates the lasting performance of gear oil antiwear and EP components. Additional development is needed to determine if the test correlates with other indicators of useful lubricant life.

However, the four-ball wear tests should not be relied on too heavily when determining EP additive content and useful life. In one study using a ball-on-disc apparatus at slow sliding speeds, investigators found that products of oil oxidation, likely carboxylic acids, contributed to lower levels of scuffing. These acids, however, may increase corrosion, accelerate additive attrition and form sludge and deposits.

 

[aa1986]

Ionic liquids appear to alter the Stribeck curve - although it's not a shift to the left.

Now are IL's considered additives or base oil substitutes? From what I've read, you only need a small proportion of IL to improve the friction and wear characteristics of PAO so in that respect it seems to be an additive?

 

[turtlevette]

Originally Posted By: Shannow
[If you've mistaken MOFT for "film strength",


I don't get the distinction. But I do get you're attempting to back out of a poor position. It's all documented. I stand by my paraphrasing of your position.

Being old school, you probably don't even believe in super lubricants.