Elastohydrodynamic Lubrication - EHL or EHD

EHL is a foundational concept in tribology that describes the lubrication of gears, cams and bearings. In this short explainer video, we looking at what distinguishes elasto-hydrodynamic lubrication from the standard hydrodynamic lubrication, and how to select an "optimum" lubricant specific film thickness.
Here at Lubrication Expert we take a first-principles approach to lubricants and greases; helping industry understand lubrication technology and pushing the limits of what is possible.
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[@LubricationExplained]

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[@angelmarco3289]

Thank you very much for that video. It was fantastic, very well done and very insightful

[@mytech6779]

I have heard of cases where going way out to the extreme right on zn/p can result in a return to the mixed/boundary condition and increased wear. The specific example was a railroad company that had major increase in car bearing failures during cold winters, the problem diagnosis was that the actual viscosity of the base oil in the grease at the initial startup temperature was unable to flow into the bearing elements as fast as it was being displaced.(It was above the pour point.) The solution was a grease with a base oil that was less viscous at low temperatures and as extra measure reducing the texture/thickener content by one ngli grade so a larger percent of the base oil would be released at the low operating temperature. In addition to being a passive/non-pressure fed lubricant, this condition is also dependent on the width of rolling elements, the spacing and speed of elements, and the height of the liquid oil bath (speed of actual flow for a given viscosity), in other words the conditions of time and distance for the oil to flow in replenishing the film on the race.

[@LubricationExplained]

Yeah so I guess in that case we're talking more about oil starvation, and its definitely a concern in really cold climates. Also see it a lot where two different greases are mixed and the thickener hardens - it then can't flow and the bearing ends up dry.

[@chrisleon27]

Hello from China ,lubrication is a quite interesting subject ,

[@rizazo1212]

This is great! Thanks LE

[@LubricationExplained]

Glad you found it useful!

[@yousefalshehri9411]

So informative thanks

[@LubricationExplained]

Glad it was helpful!

[@albertwild4650]

Excellent explanation

[@LubricationExplained]

Glad it was helpful!

[@joshmanning2525]

what is surface roughness measured in ?

[@ssartaj90]

Sir, when we texture the bearing surface, the texture grooves would act as reservoir which aid effective lubrication in starting and stoping conditions. So by doing so we are altering the surface topography i.e. the value of denominator of lambda. Will that make any affect on the value of ideal lambda???

[@LubricationExplained]

Great question! Surface finishes contribute to the denominator for sure and are very common - cross-hatching on engine cylinder liners is another example of this. Rather than adjusting the ideal lambda value, generally the impact is to require a slightly larger film thickness (i.e. increase the numerator) .

[@ssartaj90]

@@LubricationExplained Thankyou

[@mytech6779]

@@LubricationExplained As far as I am aware the crosshatch texture on cylinders is mainly a method to allow the rings to quickly wear during the initial operation and make a better ring-seal following this break in period. A bit like lapping two surfaces against each other so they match very close but the surface texture substitutes for abrasive. While the initial roughness is increased they substantially smooth during break in.

[@Jello1963]

You said you would want a lambda > 2 in stop-start operations. What do you mean? When the bearing starts to rotate after been stopped for a while, lambda would be zero, wouldn't it?

[@mytech6779]

It means a lamda greater than 2 for the designed constant speed condition. Yes lamda will be 0 at a stop, but by increasing target lamda you reduce the time and speed required to build a film during the acceleration phase, and minimize the speed during deceleration where the film drops below lamda of 2; this greatly and non-linearly reduces the distance that a bearing surface travels with an insufficient lamda. (The distance needed to stop a car from a speed of 100 is about 4 times that needed to stop from 50, similar for acceleration. For a bearing without solid EP lubricant additives this would result in a 4x difference in wear.)

[@chrisleon27]

Besides ,I can't visit ur website ,it's unaccessible

[@bobbobo211]

"And this one is the sticking point" when describing the difficulties with obtaining pressure-viscosity, really tickled me. kzbin.info/www/bejne/omKWZYiEi7msrs0si=0ggfSn7WE9pIL6zv&t=625

[@zewenzhou3574]

The saliva voice

[@LubricationExplained]

🤣

[@imampatrick]

dude you literally didn't say anything about the difference between ehl - hl. I mean what was the point of naming your video EHL if you are not going to explain it? I have no idea what is the difference between ehd bearing and hd bearing right now.