Lambda Ratio

The lambda ratio was originally developed to quantify the quality of lubricant operating regimes relative to bearing performance; since the 1990s, the lambda ratio has been used to define optimal lubricant regimes for gears. The lambda ratio is a measure of the lubricant film thickness relative to the composite roughness of two mating/contacting surfaces. The larger the lambda ratio, the greater the separation between the mating surfaces. Full EHL (elastohydrodynamic lubrication), where the surfaces are completely separated by the lubricant film, is always the desired operating regime.

If a power transfer system operates in mixed or boundary lubrication regimes, the mating components will experience degrees of metal-to-metal contact, which will generate increased rates of surface wear. As wear in the system increases, debris is introduced into the lubricant. This debris serves to clog lubricant filters, break down the lubricant and further exacerbate wear in gears/bearings. As a result, lubricants tend to be specified conservatively to enhance the film thickness in operation. Derivatively, energy losses due to the higher lubricant viscosity are commonly accepted as a necessary compromise to overcome low lambda ratio environments.

Additionally, to combat some of these tradeoffs to wear and frictional losses, lubricants can make use of specialty additives.  While these additives have a function, they can also have negative effects. Additives increase the cost and complexity of a lubrication system, and as they are consumed/degrade, the risks that they were meant to mitigate are reintroduced.

Lambda ratio and lubricant performance can be improved without increasing lubricant viscosity or introducing lubricant additives by simply reducing component surface roughness. REM’s ISF® Process is a convenient method to make such an improvement as it significantly reduces surface roughness while generating an optimized non-directional microtexture. These changes to the surface increase the lambda ratio and eliminate the parasitic friction created by peak asperity interaction.

One critical factor to remember is very few dynamically loaded systems experience full EHL under normal operating conditions unless the components have been isotropically superfinished. This operating characteristic is why run-in wear occurs at the start of system operations, and it is also the reason why, over the lifetime of a component/system, you may witness continual wear and abrasion on the mating surfaces.

Where a system meets its design life, clever designers exploit the extra lambda ratio gain generated by REM’s ISF® Technology to lower the viscosity of the lubricant and simplify the additive package. The result is an increase in system efficiency, an increase in component life, and a reduction in lubrication costs through the increase of lubricant life and the reduced need for costly lubricant additives.

REM’s ISF Technologies can be applied to a very wide range of components types, sizes, and metals. These processing technologies are available via outsourced processing at a REM facility or as technology installations at a customer site. Contact us today to learn more or to start a project.