Influence of Operational Condition of Oil Seals on Their Frictional Properties

Abstract

It has been shown that the frictional properties of oil seals are expressed by an equation, f = Φ(μUb/Pr)1/3, where in μ, b and Pr are the absolute viscosity of oil, the contact width of seal lip edge, and the total contact load of a sealing lip, respectively, under the stable condition. The proportional constant in this equation, Φ, is a function of the frictional properties, independent of a viscosity of oil and a sliding velocity. The quantity Φ is related to the oil-film shape at the rubbing portion between the sealing lip of oil seals and shaft surface. The shape of the oil film is influenced by the sliding velocity of the rubbing surface because of the viscoelasticity of the rubber material forming the sealing lip. The value of Φ depends on the velocity, decreasing with increasing velocity. Furthermore, Φ depends on the surface roughness of the shaft and sealing lip material. In the present paper, it is found that the value of Φ at stable operating conditions varies (according to the frictional torque. The friction torque depends on the condition at the starting of the shaft rotation, such as oil temperature and viscosity. The value of the shearing stress at the edge of the sealing lip calculated from the frictional torque has an upper limit.