On the frictional characteristics of ball bearings coated with solid lubricants

The problem of a ball bearing in normal contact between two transversely is otropic coated substrates is investigated using the finite element method ( FEM). A three-dimensional finite element model is developed that accurately determines the steady friction force in low-speed bearing systems containi ng soft layered solid lubricant films. Extensive numerical results, which a re verified using Hertzian contact theory and laboratory experiments, are o btained at 540 operating conditions by varying coating material, coating th ickness, normal load, ball material, and ball radius. Friction force result s generated from the FEM are normalized by introducing the dimensionless tr ansversely isotropic coating parameter, xi. A numerical expression for the normalized friction force in coated ball bearings is determined by curvefit ting the results of the 540 simulations performed. The relevance of such an expression, as related to the durability of low-speed bearings, is subsequ ently ascertained and discussed.