Method of Protecting Rolling Element Bearings Against Oil-Out Conditions and Bearings Made Thereby

A method of enhancing the operating life of roller bearings (B) subject to oil-out conditions, the roller bearings comprising inner and outer races (IR, OR) and rolling elements (RE) positioned between the inner and outer races, the roller elements having a side surface (RS), a first end face and a second end face (SS);

• the method comprising determining the thickness of a metal carbide/amorphous hydrocarbon coating which will enable the bearing to operate for a predetermined period of time after an oil-out condition starts;
• and applying a metal carbide/amorphous hydrocarbon coating layer (16) over at least one of the first end face and the second end face of the rolling element;
• said coating being applied to have a thickness of said determined thickness;
• wherein the tungsten carbide coating layer comprises crystalline tungsten carbide contained in an amorphous carbon or amorphous hydrocarbon matrix.

A roller bearing assembly (B) comprising an inner race (IR), an outer race (OR), and a plurality of roller elements (RE) positioned between the inner and outer races;

• the roller elements comprising a side surface (RS), a first end face and a second end face (SS);
• the roller elements having a coating (10) applied only to one or both of the first end face and the second end face of the roller element;
• the coating comprising an outer layer (16) comprised of crystalline tungsten carbide contained in an amorphous carbon or amorphous hydrocarbon matrix, the metal carbide crystals having a size of less than about 10 nm and comprising less than 50% of the coating;
• the coating having a thickness which will enable the bearing to operate for a predetermined period of time after an oil-out condition starts.