TRIBOLOGY
Development of tribometric tools for characterising the electrical response of lubricants – Initial results from a modified 4-Ball wear test
Tushar Khosla & Allen Cong, Rtec Instruments, Inc., Ashlie Martini & Alex Hartzler, University of California Merced School of Engineering, and Mathias Woydt, MATRILUB Materials l Tribology l Lubrication
Amperage and voltage are game changers in formulating lubricants for electrified tribosystems. The electrical response of tribofilms and hydrodynamic fluid films as a function of operating conditions can be quantified using tribometric tools designed specifically for this purpose. Such tools can then be used to identify cause-root-relationships and guide lubricant formulation concepts. Towards this goal, here we report the electrical properties of lubricants measured using a modified 4-ball wear test. To reduce the complexity and size of the test matrix, two methodologies for assessing the response of the tribosystem to amperage and determining the current carrying capacity of the lubricant are demonstrated.
Introduction The green technologies favored by policymakers are wind turbines (upstream) and electrified powertrains (downstream). Their key tribosystems are “slip-rolling contacts” or “highly concentrated contacts”. Tribofilms protect these tribosystems from adhesive failure (scuffing, seizure, galling) and determine the friction and wear behavior. The electrical properties of tribofilms can vary over orders of magnitude and depend on the temperature. These additional properties must be evaluated as part of the overall tribometric evaluation of a lubricant.
Lubricants and fluids must maintain good anti-wear
performance and long drain intervals as well as significantly reduce friction while being compatible with arcing and electrostatic fields. Parasitic currents generate different types of bearing currents, which can occur in inverter-fed electrical powertrains affecting the lifetime of bearings. These additional requirements of tribo-contacts overlap with the standard metrics used to evaluate the functional profile of a lubricant.
Voltage and amperage as DC and AC (frequency) create a huge test matrix in conjunction with a multitude of electrical properties, like electrical contact resistance (DC), impedance Z (AC), relative permittivity (εr dielectric dissipation factor (tan δ) and phase shift Θ
), LUBE MAGAZINE NO.190 DECEMBER 2025 9
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64
