A STUDY ON LUBRICATION MECHANISM AND WEAR SCAR IN SLIDING CIRCULAR CONTACTS

The effects of test method, normal load and sliding speed on the lubri cating characteristics of a paraffinic base oil were experimentally in vestigated using a four-ball tester with a contact resistance instrume nt. Results show that at light load, elastohydrodynamic lubrication ca n only be found in the specific speed method, but a little wear scar s till existed in the standard test method because of the contact initia lly. The specific speed method has a higher contact resistance than th ose of the standard test method at light load, but this is not always true at high load. According to the measured data of friction coeffici ent, contact resistance, and wear scar, and the observation of the wea r surface, the lubrication mode can be clearly classified into four re gimes under the various normal loads and sliding speeds. The transitio n curve between boundary lubrication and initial seizure makes no sign ificant difference for both specific speed and standard test methods. This result shows that the initial seizure is significantly influenced by the load and sliding speed rather than by the test method. In the partial elastohydrodynamic lubrication (P-EHL) regime, the relationshi p between the wear scar diameter D and the contact resistance R(c) has been quantitatively and qualitatively obtained. The diameter of the w ear scar can be predicted by measuring the contact resistance R(c) usi ng this empirical equation. The transition curve between the P-EHL and elastohydrodynamic lubrication is in very good agreement with the pre diction using the minimum film thickness obtained by Hsu and Lee with the assumption of Lambda = 3.