Lube-Tech
pointless as a prescreening test. For this reason, most ‘simple’ laboratory bench tests are irrelevant as they typically apply too high loads or contact pressures.
(a) (b)
Fig 7. SEM micrographs from (a) disk and (b) vane after MultiSpecimen testing at 1.2 GPa (800 lbf) for 1 h. (Red area of Figure 6)
PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
No.114 page 5 (a)
(b)
Fig 9. (a) Comparison of weight loss and (b) ranking of five different hydraulic fluids, obtained from Conestoga Vickers (ISO 20763) and Falex MultiSpecimen tests (20 hrs, 150 lbf)
Fig 8. Failure map for test conditions of MultiSpecimen vane pump tests
Correlation with Conestoga Vickers Vane pump test
After confirming that the test methods produces repeatable data and that it generates the same wear phenomena as in the Conestoga Vickers Vane pump test, a correlation study was performed on 5 modern performance fluids, with ISO 20763 test results ranging between 10 and 70 mg. Figure 9 (average of minimum 2 tests) shows an excellent ranking correlation, indicating that this technique can be effectively used for the comparison and ranking of hydraulic fluids. The test results do not yet match quantitatively with those of the ISO Vane pump test but are extremely useful to pre-screen and complement the pump test. Thanks to the proven correlation, lubricant manufacturers can now evaluate variations of a product on smaller volumes and in shorter test time.
42 LUBE MAGAZINE NO.143 FEBRUARY 2018
A further ranking of the examined hydraulic fluids can be achieved by comparing their frictional behaviour and in particular of the evolution of the tribosystems torque as a function of testing time (see Figure 4b). What is interesting is that the hydraulic fluids with the lowest weight loss (Figure 9) also brought about a lower torque in the tribosystem (Figure 4b). Only exception was hydraulic fluid E, which despite having the lowest ‘steady state’ torque, resulted in an average ranking in terms of weight loss. However, we should notice the high torque recorded during run-in might be linked to a higher initial wearing off of the surface of the vanes and disk. This is another clear indication that these prescreening tests should be performed at longer testing times (based on this work we advise for at least 20 hrs of testing). In addition, a fluctuation of the torque around an average value was observed for hydraulic fluid C during these tests. We believe that this fluctuation could be attributed to several phenomena. First during these tests wear particles (debris) are formed at the contacting interface and especially in this case where a higher weight loss was recorded for the tribosystem (Figure 9). Indeed, in the ‘world of Tribology’ it is widely known that in the
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