So I have a client that is asking about if they should switch from one lubricant to another in a planetary gearbox they have.

The main advantage that this new lubricant has is that it has a much lower viscosity (about 1/2 as much) and it is more thermodynamically stable.

With all things being equal, I'm looking to try to get a rough order of accuracy estimate for the efficiency increase in switching to this new lubricant. I've been looking through some hydrodynamic lubrication theory, but haven't found anything that is really what I'm looking for.

Any known references or established theories related to this would be extremely helpful! :)

  • $\begingroup$ Tribology would be the word to start a search... at least that was what they called lubrication when we studied it along with the Moody chart... $\endgroup$ – Solar Mike Jun 7 '19 at 15:34
  • $\begingroup$ I'm sorry but the lower viscosity is a disadvantage! $\endgroup$ – Sam Farjamirad Jun 7 '19 at 16:47
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    $\begingroup$ @SamFarjamirad: It would be interesting to know why you think a lower viscosity would be a disadvantage. My thoughts are, that a lower viscosity lubricant in a gear box might result in a thinner coating of lubricant on the moving parts, which under high performance conditions could be detrimental. But, I could be wrong. $\endgroup$ – Fred Jun 7 '19 at 16:54
  • $\begingroup$ @Fred Bingo, that's the whole point of lubrication. In gears and bearings, it's impossible to achieve a full film lubrication thanks to contra-form contact surfaces, with other words the working point does't go any further than mixed-film friction on Stribeck curve, so if you reduce the viscosity even more, then you find yourself in boundary friction which is needless to say is no no no. $\endgroup$ – Sam Farjamirad Jun 7 '19 at 17:25

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