Michita Hokao

Bearing torque characteristics of lithium soap greases with some synthetic base oils

This article describes the influence of rheological properties on the bearing torque characteristics of the lithium soap greases with five types of base oils. The greases used had different yield stress depending on the base oils even with the same thickener concentration. Measurement of bearing torque was conducted for a deep-groove radial ball bearing by using a bearing test apparatus. The bearings filled with greases initially exhibited high torque but showed gradual decrease in the torque with prolonged rotation, where the greases with higher yield stress showed larger normalized torque decrease. Observation of bearing after the rotation revealed a tendency that the greases with larger normalized torque decrease had been pushed aside in the raceway by channeling. This implied that the greases with higher yield stress tended to show channeling. On the other hand, the greases with lower yield stress circulated within the bearing by churning and showed smaller normalized torque decrease. These behaviors were explained in terms of the yield stress of the greases and the shear stress to entrain the greases into the contacts. Observation of grease structure was made with atomic force microscopy showed that the greases whose thickener network structure was distributed more densely had higher yield stress.

Lubricating Characteristics of Fluorine Grease Containing Silica Nanoparticles

Electrical motor bearings for use in automotive control units are sometimes exposed to high-temperature operating conditions. Therefore, these bearings are sometimes packed with fluorine grease in order to meet the demand for long service life performance. In recent years, there is growing demand for lower initial torque in these same bearings without sacrificing service life performance. This paper describes the effects of fluorine grease containing silica nanoparticles on initial bearing torque of electrical motor bearings. Silica nanoparticles are effective in helping to reduce amounts of initial bearing torque and help stabilize bearing torque due to improved channeling characteristics.Copyright