Continued from page 17 The parameters for friction and wear tests are as follows:
used to quantify the amount of hydrogen that was blocked by the membrane.
Vacuum tests were also carried out to determine if the lubricant additive is able to prevent the generation of hydrogen.
FE8-25 Pitting Tests – An assessment was made of the influence of the lubricant additive to alleviate the formation of WEC in the FAG FE8 bearing test rig. The test conditions were drive speed 750 rpm; load 60 kN; and temperature 100°C. The test bearings were axial cylindrical roller bearings (F-562831), The rate of lubricant flow circulation was 0.125 l/min.
Figure 5: Illustration of hydrogen permeation
Results & Discussion The tribology measurements demonstrate that the lubricant additive has an advantageous impact on the friction and wear behaviour.
The friction test results were as follows:
Figure 4: FE8-25 test rig
Hydrogen Permeation Test – A series of permeation tests were carried out according to DIN EN ISO 17081 procedure, (method of measurement of hydrogen permeation and determination of hydrogen uptake and transport in metals by an electrochemical technique).
The objective was to determine the capability of the lubricant additive to block hydrogen. The permeation cell consisted of two electrochemical cells. The first cell, the charging cell, was filled with sulphuric acid (H2
SO4 The wear test results are as follows:
) and the second cell, the recombination cell, was filled with sodium hydroxide (NaOH). The charging cell and the recombination cell were separated by the permeation sample (steel membrane). In the charging cell hydrogen atoms are formed by electrolysis, while in the recombination cell a current is measured due to recombination of diffused hydrogen atoms to form hydrogen molecules. The permeation sample was conditioned by rubbing with a steel cylinder at contact pressure of 60 megapascals (MPa). When hydrogen was passed through a steel membrane, its recombination generated a current. The electrical current was measured as function of time. This was
18 LUBE MAGAZINE NO.161 FEBRUARY 2021
The FE8-25 pitting test results show that the low reference oil without the lubricant additive typically produces WEC within 30 to 45 hours. The test oil with the addition of the lubricant additive reached a running time of 422 hours with no formation of WEC. These results demonstrate that the addition of the lubricant additive produced a tenfold improvement in WEC lifetime performance.
Figure 6: Bearing condition after test Continued on page 20
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