Performance improvement under boundary lubrication conditions using sliderbearings with silicon nitride/steel in high torque hydraulic motors

The influence of materials and surface topography on static and dynamic coe fficients of friction was experimentally investigated in a test apparatus u nder boundary and mixed lubrication conditions. Specimen materials were gre y iron and silicon nitride (Si3N4) of different surface topographies, slidi ng against chromium steel at a maximum Hertzian line contact pressure of 50 MPa. The lubricant was a standard mineral-based hydraulic fluid (ISO VG 68 ) held at +40 degrees or -28 degrees C. The static and dynamic coefficients of friction under boundary lubrication conditions were both significantly reduced by the change from grey iron to silicon nitride as sliding material against Cr-steel, while the lowest static friction with Si3N4 was found fo r an intermediate surface roughness.