Rolling bearings are essential components in mechanical engineering. They can be categorized in various ways, generally based on rolling element shape, load-bearing direction, and structural form. One of the most common classifications is based on rolling element shape, primarily including ball bearings and roller bearings. Ball bearings, with spherical rolling elements, offer advantages such as low friction and high rotational speed, making them suitable for high-speed applications such as electric motors and machine tool spindles. However, because the spheres make point contact with the inner and outer rings, their load-bearing capacity is relatively low, making them less commonly used in equipment subject to heavy loads.
Roller bearings are further subdivided based on the shape of their rollers. Common types include cylindrical roller bearings, tapered roller bearings, spherical roller bearings, and needle roller bearings. Cylindrical roller bearings have cylindrical rolling elements that form line contact with the inner and outer rings. They have a much higher load-bearing capacity than ball bearings and are suitable for applications with heavy radial loads, such as rolling mills and heavy machinery like cranes. Tapered roller bearings have conical rollers that can withstand not only radial loads but also heavy axial loads. They are widely used in applications requiring bidirectional loads, such as automotive rear axles and machine tool spindle boxes.
Rolling bearings can be categorized by the direction of the load they can withstand: radial bearings, thrust bearings, and radial-thrust bearings. Radial bearings primarily support radial loads, with a nominal contact angle between 0° and 45°. Deep groove ball bearings are typical examples of radial bearings, capable of stably withstanding radial forces even at high speeds. Thrust bearings, on the other hand, are designed to withstand axial loads, with a nominal contact angle between 45° and 90°. Common thrust ball bearings are commonly used in components that must withstand axial forces, such as crane hooks and machine tool worktables.
Bearings can be further categorized by their structural form into caged bearings and full-complement rolling element bearings. Caged bearings evenly space the rolling elements, preventing friction and collision between them. This helps increase the bearing’s speed and service life. Most general-purpose bearings use this structure. Full-complement rolling element bearings, on the other hand, lack a cage; the rolling elements completely fill the space between the inner and outer rings. This significantly increases their load capacity, but at a relatively low speed, making them suitable for heavy-load, low-speed operating environments.
Rolling bearings can also be categorized by accuracy level and sealing type. Accuracy levels range from low to high, including Grade 0, Grade 6, Grade 5, Grade 4, and Grade 2. High-precision bearings are primarily used in precision machine tools, instrumentation, and other equipment requiring high rotational accuracy. Sealing types include open, contact, and non-contact seals. Sealed bearings effectively prevent lubricant loss and contaminant ingress, making them suitable for harsh environments with high dust and humidity. Each rolling bearing categorized by type has its own unique characteristics, and selection should be considered based on specific operating conditions.
