Methods used to reinforce self-lubricating polymers generally also cause a significant increase in coefficient of friction, so that a trade-off must be made between coefficient of friction and wear resistance. Polytetrafluoroethylene (PTFE) composites filled with alumina nanoparticles and graphite were prepared by compression molding. Friction and wear experiments were carried out in a reciprocating sliding tribotester at a reciprocating frequency of 1.0 Hz, contact pressure of 5.0 MPa and relative humidity of (75 3)%. The nanocomposites slid against a 45 carbon steel track. Results showed that PTFE + 15 wt% alumina + 5 wt% graphite composite (D) exhibited a coefficient of steady-state friction lower than PTFE + 15 wt% alumina composite (B), while wear resistance of composite D is higher than composite B, and by about 200 times higher than unfilled PTFE. This behavior originates from the effective lubrication of graphite that possesses an extremely low coefficient of friction under the high humidity condition.
Shaft clinching forming assembly has become a mainstream clamping technology of wheel bearings. The radial deformation of inner rings is the main negative impact in the shaft clinching forming process. The elastoplastic finite element method was used to study the shaft clinching forming process of wheel bearings, and the accuracy of the numerical simulation was verified by experiment. The ratio of the inner ring outside diameter variation to the clamping force ( RIC) was taken as an optimization objective. Response surface methodology was used to optimize the loading path of punches in the shaft clinching forming process. Three factors were selected, including the central angle between two successively appeared outermost points of the plum blossom shape loading trajectory ( θ), the rotation speed of the punch ( ω), and the tilted angle of punches ( α). The results show that the central angle θ is the most sensitive factor, and the interaction effects of the central angle θ and the speed of autorotation ω on the ratio RIC are the most significant. Finally, the minimum ratio RIC and a corresponding loading path are obtained. The research results can be applied to other rotary forging processes.
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