The Peckish Synapse

customboss · December 17, 2024

https://www.machinerylubrication.com/Read/30835/lubricant-film-strength

Film strength is one of the most critical lubricant properties for protecting a machine’s internal components from wear and degradation. It is heavily influenced by the lubricant’s base stock and additives. This article will discuss the importance of a lubricant’s film strength and what impacts its effectiveness.

Film Thickness

When you think of lubrication, what comes to mind? It might be the base oil creating a film thickness to separate two metal surfaces. After all, the primary intent is to avoid metal-on-metal surface contact. For the base oil to provide separation in this situation, there must be a balance of three contributing factors: the relative velocities, the base oil viscosity and the amount of load.

These three factors are also influenced by other elements such as temperature and contamination. When the film thickness is the result of a balance between these factors, it is called hydrodynamic lubrication.

In applications with rolling contact (and thus negligible relative sliding motion), film thickness between the metal surfaces can still occur, even with greater localized pressure points. In fact, these pressure points play an important role.

The base oil’s pressure-viscosity relationship allows the oil’s viscosity to increase temporarily due to the higher pressures. This is called elastohydrodynamic lubrication. A full film separation remains, albeit a very thin one.

In practice, it is best to keep machine surfaces separated, with the film thickness providing the best opportunity for reduced friction and wear. But what happens if these film thickness conditions are not met, such as when there is insufficient relative velocity, inadequate viscosity or too much load?

Most machine designs and operating parameters will require instances when insufficient velocity exists, such as starts and stops or changes in directional motion. There may also be concerns when the temperature increases too much, causing the viscosity to decrease, or excessive contamination contributes to abrasive contact in the film gap.

When the hydrodynamic or elastohydrodynamic lubrication prerequisites are not met, the base oil will require support during what is called boundary contact conditions. This support involves wear and friction-control additives.

The base oil and additives are carefully blended together to produce the specific lubricant product (either oil or grease), which is formulated to mitigate the anticipated boundary conditions. The lubricant then possesses film strength and boundary lubrication properties.

Boundary lubrication

Film Strength

Film strength can be described as the lubricant’s ability to lessen the effects of friction and control wear by means other than the film thickness. As mentioned, the viscosity is the primary contributor to film thickness during hydrodynamic and elastohydrodynamic lubrication.

When the base oil viscosity is insufficient to overcome metal-to-metal surface contact, the base oil and additive chemistry work together to create a surface protection mechanism. During these boundary conditions, boundary lubrication is also influenced by the chemical and physical properties of the mechanical surfaces and any contributing environmental factors.

Even when loads and temperatures are higher and relative surface velocities are lower, the film strength is improved.

Unlubricated Surface Interactions

If you were to observe contacting mechanical surfaces on a molecular level, you would see that they can be relatively rough, even if they are machined to be very smooth and appear that way to the unaided eye. This could be compared to how the earth looks like a perfect sphere from the perspective of an astronaut in space but is brimming with mountains and valleys of all heights and depths when viewed by someone standing on the earth’s surface.

This is relevant because when two unlubricated metal surfaces come in contact, the actual contact area will be substantially less than the apparent contact area. The surfaces will only come in contact where these “microscopic mountains” called asperities are the tallest and reach to the other surface, preventing lower asperities from making contact.

These asperity surfaces can then elastically deform based on the corresponding shear strength of the metals. Thus, the real contact area will increase proportionally with an increase in load because the initial contact points will elastically deform first and more contact points will connect.

Friction

Friction, the resistance to sliding motion of interacting surfaces, is subject to several influencing parameters or processes. Most people consider the roughness of the surface as the primary contributing parameter for friction.

However, when considering that the real contact area may be less than 1 percent that of the apparent contact area, the actual roughness becomes much less relevant. The significant process contributing to friction is a result of the adhesive bonds occurring at the atomic level of asperity contact.

Wear Generation

In conditions where there is inadequate lubricant film thickness between the metal surfaces, the asperity contact points can lead to cold welding, which is the prerequisite for adhesive wear. The adhesion at these asperity points undergoes a work-hardening process, which strengthens the material.

Thus, the shear point happens at layers below the asperity contact point where the metal has not been strengthened. As the metal shears, the asperity tip is then either transferred to the other surface or broken off as an abrasive particle.

Adhesion is often seen as the initial form of mechanical wear, but as abrasive particles present themselves (either from wear or from an external source), abrasive wear can become more destructive. This form of abrasion is called three-body abrasion, whereas two-body abrasion is caused by cutting or gouging of sharp surface contact points.

During rolling contact, surface fatigue can occur. Fatigue mechanisms stem from cracks propagated at the surfaces or up from layers under the surface that contain inclusions or other impurities. The high stresses from rolling conditions at these surfaces will lead to fatigue wear.

Mitigating Surface Interactions

Friction and wear-control additives are formulated in small quantities within the base oil and have polar properties that foster metal surface attraction. These attractions are then further encouraged to chemically react with the surface as a result of the interacting conditions, which are inversely associated to the conditions leading to sufficient film thickness: higher pressure and higher temperature.

When machine surfaces interact with higher pressures and temperatures, the additives mitigate the typical effects of metal-to-metal contact (wear) by creating initial molecular layers on the machine surface that are more ductile. These friction-control layers directly reduce the shear strength during contact and become sacrificial.

The initial layers can mitigate friction by allowing the lubricant’s weaker molecular bonds to release with less force compared to that of the strong bonds that result from the metal-to-metal asperity boundary conditions. The formation of low-shear-strength films is also influenced by the base stock type and the metallurgy of the mechanical surfaces.

There are three types of lubricant additives that help reduce this friction and control wear formation: friction modifiers, anti-wear additives and extreme-pressure additives.

Friction Modifiers (Lubricity or Oiliness Agents)

Polar compounds, such as a fatty acid added to the base oil, decrease friction at low sliding speeds by forming a soap film. They typically are used in components that are sensitive to fuel economy to reduce friction and stick-slip at low speeds, such as in an engine or transmission.

They act like anti-wear additives but are more effective with lighter loads and do not require high temperatures. The resulting low-shear-strength soap breaks down at higher temperatures. However, when the surface metal is more reactive to the fatty acid, creating a metal soap, the breakdown temperature is higher.

Anti-wear Additives

These polar compounds are typically sulfur- or phosphorus-based, such as a zinc dialkyldithiophosphate (ZDDP) type of additive. They are designed to chemically react with the metal surface only at boundary conditions.

However, anti-wear additives are more effective at higher temperatures, where they become more activated and create a barrier film. ZDDP-type additives have been widely used for wear protection and are also beneficial as antioxidants in the oil.

Extreme-pressure Additives (Anti-scuff Additives)

Friction modifiers and even anti-wear additives become less useful and break down when surface temperatures get too high. Extreme-pressure additives, which are also sulfur- and phosphorus-based, are the best choice when high surface temperatures are expected.

These additives form a low-shear-strength, soap-like film with metal surface reactions and can withstand fairly high temperatures. While the reaction is beneficial for the film to be developed, it is important to take caution when the reaction has the potential to result in chemical corrosion of more reactive metals.

Physics and Chemistry

The physical molecular interactions of asperities at the actual contact pressure points are the main concern when unlubricated or poorly lubricated machine surfaces come into sliding contact. At this molecular scale of the machine surfaces, boundary conditions are subject to numerous principles of physics and chemistry.

The role of oxidation, corrosion, chemisorption and other chemical reactions at the machine surfaces must be carefully balanced when additive compounds are selected for film strength protection.

These friction and wear-control additive films on the metal surfaces reduce the shear strength at the contact points. The low-shear-strength films are sacrificial during physical interactions and protect the surface from the effects of adhesive, abrasive and fatigue wear.

These submicron films have a gradation of liquid to solid properties as they get closer to the metal surface. While the base oil is preferred to protect the machine surfaces with hydrodynamic and elastohydrodynamic lubrication, boundary conditions will exist.

Therefore, to protect against boundary conditions, a properly formulated lubricant with friction and wear-control additives should be used to provide a film strength that is proportional to the exhibiting mechanical interactions within reasonable limitations.

BENNETT FITCH

References

Fitch, E.C. (1992). “Proactive Maintenance for Mechanical Systems.”

Fitch, J.C., Scott, R., & Leugner, L. (2012). “The Practical Handbook of Machinery Lubrication - Fourth Edition.”

Fein, R.S. (1991). “Lubrication Engineering.” Journal of the Society of Tribologists and Lubrication Engineers.

Fein, R.S. (1997). “Boundary Lubrication Relations.” Tribology Data Handbook.

Rabinowicz, E. (2014). “Friction.” Access Science.

Mortier, R.M., Fox, M.F., & Orszulik, S.T. (2010). “Chemistry and Technology of Lubricants - 3rd Edition.”

Rigney, D.A. (1980). “Fundamentals of Friction and Wear of Materials.” ASM

Grumpy Bear · December 18, 2024

That is a lot of fancy words to describe the importance of viscosity. Surrounded by a lot of irrelevance.

customboss · December 18, 2024

5 hours ago, customboss said:

. After all, the primary intent is to avoid metal-on-metal surface contact. For the base oil to provide separation in this situation, there must be a balance of three contributing factors: the relative velocities, the base oil viscosity and the amount of load.

Grumpy Bear · December 18, 2024

6 hours ago, customboss said:

. After all, the primary intent is to avoid metal-on-metal surface contact. For the base oil to provide separation in this situation, there must be a balance of three contributing factors: the relative velocities, the base oil viscosity and the amount of load.

Hersey Number!

Now we are getting somewhere. Didn't take seven paragraphs either. :crackup:

To the portion in bold.

Hersey is based on that parameter. YES! However in practice, it is the word in bold red, viscosity, period. Loose the words "the base oil". Tis the point of VM's and in that point; the basis of my arguments. Those, VM's, used in practice, not the lab or what is possible, are by and large unreliable and need hedging when wear is the primary concern.

@jwhjr is waiting for a reply (below) :crackup:

17 hours ago, jwhjr said:

Can't wait to hear a 7 paragraph reply to this on why you're wrong.

To this me thinks:

18 hours ago, customboss said:

Grumpy a well formulated SAE 20 is VERY RESISTANT TO VISCOSITY BREAKTHROUGH regardless of temperature.

I didn't reply mulling over the 'meaning' of "breakthrough'. The opening quote to this post informs me that you are aware that "breakthrough" (allowing metal on metal contact) isn't solely dependent on viscosity and as I know you know this, it infers you mean something other and as such there is nothing to correct. My assumption may be incorrect as you reference SAE20, a straight weight. You may have meant this generically meaning any *W20 :dunno: . Point is, I'm unclear of your point.

***************************************

I'm going to ignore for the moment the arguments for one SAE Grade over another and focus on stability and what is meant by "Stay in Grade". I'm going to use this multigrade Box Store oil blended by Warren Oil as the example;

Start with the specifications for an SAE *W30 oil. 100C viscosity boundaries are 9.3 cSt to <12.5 cSt and a minimum HTHS viscosity of 2.9 cP.

Note the three tests I've highlighted in YELLOW for the 100 C viscosity. That top yellow line is the line the oil must meet in the bottle as unused oil. That is the qualifier. But this is not what your motor sees over the course of the oils useful life. The VM's shear, 10.91-9.4 and that value is reflected in the lowest yellow line. In this case the PSSI value is 9.4 cSt and just above the SAE virgin minimum. Thus this oil is considered to be a "Stay In Grade" oil. This oil lost 1.51 cSt of viscosity, 13.84%. But it stayed in grade. Is that the entire story? Not even close...

Look at the second yellow line. The 100 C High Shear test has a value of 6.9 cP. Different units. Tricky, right. The Engineering Tool Box list the specific gravity of 5W30 at 100C nominally as .860 which gives us an approximation of the cSt value at 8.02 cSt. That is inside the upper limit of a *W16. A similar loss on a percentage basis is taken in the HTHS value which is not published but we did get a look at it's effects in the HPL video Lake Speed Jr did when they tested HPL No-VII oils. For OCP polymers this loss is ridiculous and those oils are not advertised as "Stay In Grade". Yet still sold as *W30's.

This is the 'feature' of VM's used to get that 0.5 to 1.5% fuel efficiency improvement AT THE SACRIFICE OF WEAR.

A straight weight mineral SAE30, Valvoline Daily Protection specifically, has a 100 C viscosity of 10.3 cSt and even after shearing the DI package via KRL testing is still above 10 cSt and as a Newtonian fluid which is not shear sensitive is STILL 10.3 cSt under ANY shear.

So how do you HEDGE that loss? C'mon man, you know the answer to that.

When I've wanted a shear stable 5W30 I use Red Line which has a tested ASTM D6278 TEST LOSS OF ZERO. A 30 weight that stays a 30 weight regardless of the shear rate to the end of a reasonable service life and well above the HTHS limits set for the grade. Meeting those of a 5W40.

If I want a W16 in my motor I'll use Costco's 5W30. If I want a W30, it's Red Line.

AMSOIL will pass stay in grade shear stability test but as a GF6 Engergy Conserving oil the 100 C HTHS test is going to be out IMHO and until I see labs saying otherwise I'd hedge up 5W40 if a 30 is what I was after.

But hey, believe as you wish and do as you like. Ya just ain't putting stuff that won't satisfy Hersey in my motor.

customboss · December 19, 2024

11 hours ago, Grumpy Bear said:

Point is, I'm unclear of your point.

The science based point is that load and relative velocity are as important as base oil viscosity. But don’t ignore WHY viscosity is what it is. Do not use a crappy Kirkland Warren 5w30 as a proof. The molecular structure of the lubricants chemistry,…. especially the base oil matters. Your constant harping about viscosity ignores the fact it’s a measure of resistance to flow. Not always higher is better argument.

Most modern engines have low loads and higher flows of lubricant than in past thus a lower viscosity fluid is by design called for.

Grumpy Bear · December 19, 2024

19 hours ago, customboss said:

The science based point is that load and relative velocity are as important as base oil viscosity. But don’t ignore WHY viscosity is what it is. Do not use a crappy Kirkland Warren 5w30 as a proof. The molecular structure of the lubricants chemistry,…. especially the base oil matters. Your constant harping about viscosity ignores the fact it’s a measure of resistance to flow. Not always higher is better argument.

Most modern engines have low loads and higher flows of lubricant than in past thus a lower viscosity fluid is by design called for.

Funny you should call Kirkland CRAPY oil. GM licensed it as a DEXOS1GEN3 and the API as SM/SN/SN+/SP and ILSAC as a GF-6A certified oil.

Kirkland. Amazon Basics, MAG1, SuperTech....all junk? All carry all of these licenses.

How did they get these approvals? Who's test did they pass?

19 hours ago, customboss said:

Your constant harping about viscosity ignores the fact it’s a measure of resistance to flow. Not always higher is better argument.

Let's correct you thinking. I know what viscosity is. I don't ignore it and you know better than to say so. That's getting childish friend.

No it is not always better once there is ENOUGH and this is where we really disagree.

Edited December 19, 2024 by Grumpy Bear

Grumpy Bear · December 19, 2024

19 hours ago, customboss said:

The science based point is that load and relative velocity are as important as base oil viscosity.

This is a smoke and mirrors statement. Hersey Number indeed considers all three points. Your wording however is absent ALL the facts. Not just the base oil viscosity, (as you state), but ALL VISCOSITY contributions, no matter how that number is obtained. In the case of a multigrade that depends on VM's, ALL of it is considered. Cheap VM's FAILURE to HOLD the viscosity is the issue and as such it fails the physics.

19 hours ago, customboss said:

Most modern engines have low loads and higher flows of lubricant than in past thus a lower viscosity fluid is by design called for.

Load is controlled by the right foot and total mass. Smaller motors asked to EXCEED the previous generation does NOT provide a lower power cylinder load (BMEP). Most of the time it is the SAME load at a lower velocity (rpm and piston FPM) which increases the value of the viscosity required. Pay. 2.7 liter motors making 454 torque and power in heavier trucks. Give it a rest.

15 minutes ago, Grumpy Bear said:

Your constant harping about viscosity ignores the fact it’s a measure of resistance to flow.

Let's circle back to this in bold. It's worth the harping. When an oil is specified the first and primary consideration is VISCOSITY then after that cleanliness and so on and so forth. Each new iteration comes with a "Backward Compatible" statement. Is it really?

SAE 30 mineral oil does not have the same nor even close to the same OPERATING VISCOSITY of a GF-6A *W30. Not even in the same galaxy. I just PROVED (Costco report) that todays LICENSED 5W30 has the operating viscosity of a *W16. A proof you cannot deny but only call crappy and yet licensed. :idiot:

In my writing I EXPLAIN that to get the viscosity your motor NEEDS with TODAYS oils you MUST increase either the licensing specification (top of the HTHS for the license) or play the hedge of using a more vicious GRADE to get to the minimum requirement IN OPERATION.

ANY oil with the DEXOS1GEN3 license SHOULD MEET THE SAME MINIMUM SPECS. Ego any oil that is in a bottle with that license is enough. And now you are calling it all CRAPPY. That sir is not useful.

diyer2 · December 20, 2024

jwhjr · December 20, 2024

57 minutes ago, diyer2 said:

It's like you're inside my mind

Donstar · December 20, 2024

10 minutes ago, diyer2 said:

What is your passion? Most of us have an interest that not everyone shares. I appreciate and respect the research and the resulting synopsis of others. My wife and I will often find ourselves talking about a topic that is of no interest to the other. Sometimes it's a case of polite listening. Yesterday, I listened to a detailed explanation of how and why my wife chose to get her hair done that morning. I in turn explained the whys and how we need to maintain our new battery backup. Stifling or mocking each other's enthusiasm will ultimately bring hurt to ourselves. Karma?

KARNUT · December 20, 2024

21 minutes ago, Donstar said:

What is your passion? Most of us have an interest that not everyone shares. I appreciate and respect the research and the resulting synopsis of others. My wife and I will often find ourselves talking about a topic that is of no interest to the other. Sometimes it's a case of polite listening. Yesterday, I listened to a detailed explanation of how and why my wife chose to get her hair done that morning. I in turn explained the whys and how we need to maintain our new battery backup. Stifling or mocking each other's enthusiasm will ultimately bring hurt to ourselves. Karma?

This is true even if it is tiresome sometimes. Can’t say I haven’t gained knowledge even if it gets a-bit in the weeds sometimes. Eventually sometimes during the day with conversations with my wife I start talking about cars. She’ll start complaining about the stove and the one burner that doesn’t work right. I’ve been telling her for at least two years to replace it. Here one eventually gets insulted. Honestly I don’t know who’s right. Doesn’t really matter except I did learn not to trust the manufacturer. Yup I was still naive enough to believe them. Probably saved me a transmission rebuild in the odyssey. That’s money, so that’s something.

customboss · December 20, 2024

Ok, given my answers. You can’t separate viscosity from load from relative velocity. Even in the Mitsubishi 3 cylinder 1.2L engine. Running a 5w40 grade oil is needlessly causing viscous drag cutting your optimum mpg grumpy. If the spec for US is 0w20 or 5w30 run Redline in this grades.
The design load , velocity , vis does NOT change with your full throttle foot or less. The engineers made sure it could handle the design RPM and load range for all approved viscosities. In the third world where this engine was made to operate, the oil quality is suspect at best and most mechanics and folks in those markets can only source higher viscosity, conventional lubricants, and they believe higher viscosity is equals better quality, which is false. Now, if all you can get is a is a thicker oil in Thailand that is higher quality versus a crappy poor quality less viscous oil then you go with the higher viscosity oil for safety. In our market grumpy, you have access to very high-quality oils. There is no need to run a 5W-40 red line full synthetic in this particular engine. Hershey number or not.

You even state that red line 0W 20 full synthetic is super stable high temp high sheer so why would you run a higher viscosity oil if it’s so stable at the high pressure area?

txab · December 20, 2024

For some reason this thread makes me want.......

OnTheReel · December 21, 2024

ESP x3 and GT variants faired surprisingly well post-KRL. That Porsche C40 approval is the real deal.

Grumpy Bear · December 27, 2024

Remember how Castrol changed the legal meaning of SYNTHETIC?

Marketing has changed the meaning of FILM STENGTH and of LUBRICITY. I am not buying any of the three new definitions. Ya all want to start calling red the new blue then have at. But for me, words mean what the words mean.

FILM STENGTH is FILM THICKNESS period.

Here's a little tick used in marketing. cSt viscosity is in consideration of density but Hersey values are in absolute cP. As Esters of the same cSt have different densities than mineral oils their cP is higher which at the same load and veloicity creates a thicker film.

Viscosity is the internal resistance. How it reacts to ITSELF. Lubricity is how it act with the surfaces it lubricates. I've shown this several times in finding fluids that are the same viscosity and vastly different lubricity. Things like oyster snot and fried okra. Chick fat. Whale oil was once used to add lubricity. Esters do this like whale oil does it. A non solid, non metallic polar bond that facilitates planar shear at the boundary between the ester and the PAO or Mineral oil.

Moly, Graphene and ZDDP ZDDT are SOLID LUBRICANTS or artificial Boundary layers. Mini ball bearings or glass hard surface deposits. The Stribeck curve and the HERSEY numbers are generated on viscosity alone. The Y axis on asperity height.

HINT: WEAR IS UNAVOIDABLE.

But kids there are enough published studies that show an SAE 20's wear is about 30% higher than a SAE30. Insisting it isn't so is irrational.

You can't stop it. But you can slow it down a bunch. VISCOCITY is the FIRST Tool in that box. The chemicals are there for those times the film thickness gets below the asperity height. If it could be done with chemicals alone oil would be a thing of the past. We would just use solid coatings.

Nothing built today will last very long on oils without BOTH viscosity and the AW/EP chemistries added to them but you cannot substitute one for the other and get as good a result and using them together.

Don't be absurd. Load and speed are the very definition of cylinder pressure and rpm. :wtf:

Mitsubishi Mirage.com 2.5 MILLION MILES of fuel logs. You will find in the "view detailed logs' section that those using 0W20 are getting 10 mpg less average economy that Raven is on 5W40. 20%. Those using 5W30 fall in between. Put on your Sherlock deer stocker the argue the data. The average is 2 mpg below the EPA values while Raven is 8 mpg over. Don't kid yourself there are tons of 'hyper-milers' on that site. It's sort of what the vehicle is about isn't it.

You bored with what I write? Then don't read it. No one is putting a gun to your head.

But you whiners that are hijacking a thread? Go start your own.