Inlet roughness tribodevices: dynamic coefficients and leakage

The new class of bearings recently described by the author has some interesting properties. These bearings generate pressure by an effective wedge or inlet step formed by the local roughness instead of the standard inlet geometries. This means that the micro- rather than macro-geometry in the inlet zone ensures that the flow into the bearing meets less resistance than it does out of the bearing. The first paper presented a simple model, consisting of flat pads of infinite width sliding over a smooth counterface. The roughnesses were in the form of transverse or longitudinal grooves. Load capacity, friction and coefficient of friction were calculated. In the present paper the model is studied further and the normal stiffness and damping coefficients as well as the flow are calculated and compared with values for similar smooth standard shapes. It is seen that the coefficients of the new class of devices may be considerably higher and the flow lower than for similar conventional bearings when the film thicknesses are small. It is concluded that they should find useful applications in many practical devices when a certain film is needed for lubrication purposes, but when leakage should be kept a minimum. Piston rings, high precision bearings and possibly hard disks may be envisaged.