In order to study the variation of average film thickness of end faces in contacting mechanical seal in running-in period

the change of surface topography was studied by fractal parameters characterization.Based on the fractal model of mechanical seals

an average film thickness prediction model of end faces in contacting mechanical seal was established by solving the volumes of surface voids of end faces.Running-in tests of two mechanical seals of B104a-70 type were carried out with water as test medium.Test temperature was 20℃

test pressure was 0.5 MPa

rotating speed was 2900 r·min-1

and spring pressures were 0.15 MPa and 0.3 MPa respectively.The results indicated that the end face of the soft ring tended to be smoothed rapidly and average film thickness decreased rapidly in running-in period.The average film thicknesses of two tested mechanical seals were both about 0.295 μm in the normal wearing stage.Surface topography had significant influence on average film thickness

while spring pressure had little influence on average film thickness.Studying the changes of surface topography and average film thickness has important significance both in the prediction of operating characteristics and in the design of end faces of contacting mechanical seals.