A comparative study on the tribological behaviour of hexagonal boron nitride (h-BN) as lubricating micro-particles-An additive in porous sliding bearings for a car clutch

The present paper is based on experimental studies of self-lubricated porous sliding bearings with hexagonal boron nitride (h-BN) as an additive. The friction coefficients of powder matrix lubricated by (h-BN + oil) were measured at varying loads of 1.05-2.0 MPa and sliding speeds of 1.35 and 2.5 m/s. The results are discussed in the form of performance characteristics such as the coefficient of friction, bearing temperature, and load-carrying capacity. The micro-particles of the h-BN additive were between 1 and 2 μm in diameter. The effect of the PV (pressure-velocity) parameter on the transition time to seizure for porous bush composites impregnated by the lubricant has been studied. It was found that the addition of the micro-particles to the oil decreased the friction coefficient about twice as compared to self-lubricated bearings lubricated only by oil. The main effect of (h-BN micro-particles + oil) in comparison to Mobil DTE-BB lubricant appears to be that the impregnation of h-BN micro-particles persists for a long period of time and the micro-particles are gradually released, being supplied to the contact surfaces. For a manufacturing application, the porous bearings were assembled in a car clutch.