Rolling element bearings require an elastohydrodynamic film between the rotating members for proper lubrication. That s the theory. This technique is used in friction welding. This simple principle of separation, by a pure uncontaminated viscous lubricant, is the basis for dependable, predictable, bearing performance. The result is no contact, low heat and no wear.
Viscosity is also an important characteristic of a lubricant.
It is the measure of a liquid s resistance to flow. Generally, a lubricant is selected with the minimum viscosity necessary to provide adequate separation of the working elements of the bearing. Excess viscosity will result in friction and heat generation within the bearing. Almost all industrial lubricants are based on animal, vegetable or mineral oils. Mineral oils, usually petroleum based, are graded light, medium and heavy, according to their viscosity.