The tribological properties of lubricating oil containing micro/nanoscale WS 2 (90 nm, 2 mm) and ionic liquid [C 7 H 11 F 3 N 2 O 3 S] are evaluated using a four-ball friction tester. Results show that the addition of micro/nano-scale WS 2 can improve the tribological properties of the base oil; moreover, adding the ionic liquid as a solvent may lead to a better mixing of the micro/nano-scale WS 2 and base oil and promote the dispersion of WS 2 in the sample oil. The base oil with 90 nm nano-WS 2 and ionic liquid presents the best anti-friction and anti-wear properties at 1 wt.% content. The surface analysis of wear scars reveals that ploughing is the main cause of wear in the three bottom balls. Furthermore, the wear furrows of nano-WS 2 as lubricating additive are uniform and symmetrical and can homogenously appear on the friction area. This work proves that the micro/nano-scale WS 2 plays an important role in improving the performance of tribological properties of lubricating oil.

The microscale/nanoscale lamellar-structure WS 2 particles with sizes of 2 µm and 500 nm were synthesized by solid-phase reaction method and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The synergies between microscale/nanoscale WS 2 particles and ZDDP as lubricating oil additives was evaluated by means of UMT-2 tribometer at room temperature. The wear scars were examined with SEM and electron-probe micro-analyzer (EPMA). The results show that the anti-wear properties were improved and the friction coefficient was greatly decreased with the simultaneous addition of WS 2 particles and ZDDP, and the largest reduction of friction coefficient was 47.2% compared with that in base oil. Moreover, the presence of ZDDP additive in the lubricant further enhances the friction-reduction and anti-wear effect of microscale/nanoscale WS 2 . This confirms that there is a synergistic effect between WS 2 particles and ZDDP.

Abstract. The dynamic force equilibrium equations of the cup of crowned tapered roller bearing under the combined loads condition are established in this paper, considering the centrifugal forces of each roller, the forces of the rib/roller end contact and the contact forces between crowned tapered roller and raceway. The equations are solved based on the Newton iteration method to analysis the dynamic load distribution of crowned tapered roller bearings. The load distribution and contact deformation of tapered roller bearing with three kinds of crowned rollers, such as rollers with straight profile, circular crowned profile and logarithmic crowned profile, are analyzed according to the Palmgren's formula and the numerical method based on influence coefficient method respectively. The results show that the Almgren's formula can be applied to calculation of the dynamic load distribution approximatively, while the numerical method must be used in contact deformation calculation for the crowned tapered roller bearing.

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