Hydrodynamic bearing lubrication

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Sep 23, 2008
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Hmm, what I learned is don't rev the bejesus out of your motor and don't use a lot of throttle at low rpm. And some additives are good for reducing start up wear. I didn't find anything pointing out the benefits of thinner oil other than slight loses in friction. Good articles though even for us non-engineers. Ian
 
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Dec 2, 2002
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Washington St.
About thinner oil...other things equal, thinner oil has less film strength. If the film strength is inadequate the hydrodynamic wedge of oil breaks down, there is metal to metal contact, and the bearing wipes. The engine designer balances the oil viscosity at the temperature inside the bearings, the surface area of the bearing (more area spreads the load and reduces pressure), bearing diameter for higher peripheral surface speed, etc. The misdirected ramblings of the cosmetic plastic surgeon, Dr. Haas, never mentions this critical hydrodynamic lubrication. Hydrodynamic lubrication takes place even in oil bath bearings where there is no oil pump and no flow. The oil pump and flow is necessary in heavily loaded bearings so the flowing oil can carry heat away.
 
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 Originally Posted By: Ken2
The misdirected ramblings of the cosmetic plastic surgeon, Dr. Haas, never mentions this critical hydrodynamic lubrication.
That is incorrect. Reread the material. Also, feel free to present us with the pearls of YOUR wisdom with as much hard work, energy and thought as he did. Not to mention sheer volume. Nobody said you have to agree with Haas, or that you can't actively disagree with his conclusions, but, in good faith, he gave us a lot of facts to chew on and he doesn't deserve to be snidely badmouthed by hypercritical lightweights.
 
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Back side of the bearing shows a slowly reducing pressure, carrying almost all the way around the back side of the bearing. In reality, the rapidly increasing radial gap causes the back side pressure to drop rapidly (often to suction). The pressure profile shown would push the shaft across to the right, meaning that your eccentricity (e) would be in the opposite direction to where it actually lives.
 
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Understand I guess it depends at what shaft speed you take a look at maybe picture is for a simple view?
 
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 Originally Posted By: bruce381
maybe picture is for a simple view?
I think you are correct...but once on the internet, it becomes lore.
 
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So if the shaft speed gets high enough and the load is low enough the shaft starts circling round and round and things blow up. A correct pressure diagram would not leave the readers wondering why the shaft is moved to the left a bit.
 
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