Slewing bearings/slewing rings are large-scales bearings with special structures which can support combined load including axial load, radial load and tilting moment simultaneously. Those types of bearings have the features of compact structure, convenient guiding rotation, easy installation and easy to maintenance. Generally, slewing bearings have their own mounting holes, oil hole and sealing apparatus, in order to meet different requirements of various of main machines under different working conditions. Slewing bearings are widely used in large size slewing equipment including hoisting & transport machinery, digging machinery, constructional engineering machinery, port machinery, wind power generation, armamentarium, radar, missile launcher.