Slewing bearing is a kind of large bearing which can bear comprehensive load, and can bear large axial, radial load and overturning moment at the same time. Slewing ring usually has installation holes, internal or external gears, lubricating oil holes and sealing devices, so it can make the main engine design compact, easy to guide and maintain. It has four series: teeth-type, outer-type and inner-type four-point contact ball bearings, double-row angular contact ball bearings, cross-cylindrical roller bearings, cross-tapered roller bearings and three-row cylindrical roller composite bearings. Slewing rings are widely used in marine equipment, construction machinery, light industry machinery, metallurgical machinery, medical machinery, industrial machinery and other industries.