Introducing Our Film Thickness Feature.

Newly patented: lubrication analysis with flucon’s E-Lub Tester.

May we introduce? Our E-Lub Tester is the world’s first fully automated dielectric tribometer – and now also equipped with a patented lubricant film thickness feature.

The E-Lub Tester enables precise measurement of the impedance of a moving rolling bearing filled with a lubricant sample under variable operating conditions. Speed, axial load, and lubricant temperature can be varied individually or in combination to determine the resulting lubrication condition.

The heart of the tribometer is an in-house developed impedance meter used for precise electrical impedance spectroscopy (EIS) from 100 Hz to 10 MHz.

Unique measuring principle: new data from a proven machine element

The metal test bearing, a conventional 51208 axial deep groove ball bearing, is filled with a lubricant that acts as a dielectric at the latest when movement begins.

With suitable contacting of the drive shaft, the test bearing can be analyzed as a circuit of complex resistances between the rotating and the stationary shell, as shown below.

With 15 steel balls, this results in 2x 15, and thus a total of 30, lubricating films in the form of R-C elements connected in parallel or in series:

Depending on the set operating conditions, easily reproducible values ​​are obtained for the total ohmic resistance R and the total capacitance C of the bearing with the oil or grease inside.

Full lubrication is generally characterized by high resistance and low capacitance values, although the electrical conductivity and relative permittivity of the lubricant also play a very important role. When the speed decreases or the load or temperature increases, the lubrication gap height decreases. As a result, R also decreases, while the capacitance increases.

Exact determination of lubrication condition and film thickness – thanks to a patented method

Anyone who wants to analyze the lubrication condition more precisely based on impedance cannot avoid the electrical lubricant properties mentioned above, as the specific electrical conductivity significantly influences the R value and the relative permittivity significantly influences the C value.

Our team has developed a unique method based on dielectric measurements on numerous oil and grease samples in our in-house high-pressure fluid laboratory that enables the precise determination of the minimum lubricant film thickness for any operating point, even without knowledge of the pressure-viscosity coefficient.

A traffic light-styled lubrication indicator (see above) displays the current tribological operating condition and determines whether boundary lubrication (solid contact), mixed lubrication (partial or sporadic solid contact), or full lubrication (complete solid separation by a lubricant layer) is present.

In addition, the minimum lubricant film thickness h_min is determined based on the surfaces involved.

Validation of h_min using high-pressure measurements

These resulting minimum lubrication gap heights could be correlated for all investigated lubricants with reliable values ​​determined for point contact in the present bearing geometry according to Hamrock and Dowson’s approximation.

For this purpose, high-pressure viscosity measurements up to 1.4 GPa (14,000 bar) were carried out in the HP fluid laboratory (see above) and the pressure-viscosity coefficients (α_p) were determined.

E-Lub Tester: available now as a tribometry adapter for Falex Four-Ball

Our E-Lub Tester is now also available as an adapter for the Falex Four-Ball. The Four-Ball offers the advantage of complete automation thanks to an interface for speed and load adjustment.

This is particularly useful for extensive map measurements, which no longer require manual intervention.

Another E-Lub Tester feature: Determining the dielectric strength of EV lubricants

With the help of a specially developed signal generator, the E-Lub Tester also allows you to measure the dielectric strength (electrical breakdown tendency) at any desired operating point. This test allows lubricants to be effectively qualified for sustainable operation in electric vehicle drives and wind turbines.