SKF轴承知识培训PPT.ppt

Bearing Basics 1 - * Bearing Axial Internal Clearance For certain bearing types, radial clearance is sometimes presented in catalogs as Axial Clearance, also called End Play. Special Clearances are sometimes available (e.g., C2H) Sometimes Nomenclature is combined: C783 = C78 (ABEC 5) + C3 P62 = ISO P6 + C3 Bearing Basics 1 - * Effects of Temperature Expansion rates vary with the material, for example, aluminum expands faster than steel. Bearing components under load act like springs. When a bearing is mounted with a press fit on the shaft, the shaft will compress slightly, and the inner ring of the bearing will expand slightly, reducing clearance in the bearing. Once the application begins running, friction heat may further reduce clearance. Whatever is leftover is considered the operational clearance in the bearing. In some cases, all the clearance is removed and the rings and rolling elements are in full contact with one another. This condition is known as Preload. Bearing Basics 1 - * Bearing Basics 1 - * Preload vs. Clearance Preload is sometimes desirable, as in heavily loaded pumps. The designer will generally err on the side of safety, choosing an initial bearing clearance that leaves a slight operational clearance. Relative bearing life decreases very rapidly if the bearing is preloaded. Excess clearance reduces overall bearing life at a much lower rate. Bearing Basics 1 - * Bearing Basics 1 - * Bearing Basics 1 - * Bearing Selection Criteria Why was a particular bearing chosen to do the job? Sometimes the wrong bearing is selected! Speed rating is measured at about 75° C Couplings can handle more misalignment than the bearings, but the resultant forces have to go somewhere. See Page 23 of the 4000 US General Catalog. This general page assists designers in choosing the correct bearing type for an application. Power Density is roughly the amount of load that can be carried by a bearing in a given space. Generally, designers prefer greater power density