Machinery operates under a wide range of conditions, and to meet specific application requirements, different types of bearings are essential. Bearings are categorized based on the shape of their rolling elements—ball bearings and roller bearings—and by the direction of the load they support—radial or thrust bearings.
When selecting a rolling bearing, several factors must be considered:
1. **Load Characteristics**: Ball bearings are ideal for light loads, while roller bearings are better suited for heavy or impact loads. For pure axial loads, thrust bearings are typically used. When radial loads dominate, deep groove ball bearings or short cylindrical roller bearings are common choices. If there's a small axial component, options like deep groove ball bearings, angular contact ball bearings, tapered roller bearings, or self-aligning ball bearings may be suitable. For high axial loads, angular contact ball bearings with large contact angles or combinations of radial and thrust bearings are recommended.
2. **Speed Capability**: Different bearings have varying speed limits. Bearings that minimize friction and heat generation are preferred for high-speed applications. It’s important to ensure the bearing is designed to operate below its maximum limit speed.
3. **Stiffness**: Under load, the contact points between the bearing rings and rolling elements experience elastic deformation. This deformation affects the bearing’s stiffness. Preloading can improve rigidity, and careful design of the bearing arrangement can also enhance performance.
4. **Self-Alignment and Installation Errors**: Bearings often face misalignment due to manufacturing or installation issues. Self-aligning bearings can compensate for such errors, making them ideal for applications where alignment might be challenging.
5. **Installation and Removal**: Some bearings, like tapered roller bearings and needle bearings, are separable, making them easier to install and remove. This feature is particularly useful in maintenance scenarios.
6. **Availability**: Even if a bearing is listed in a catalog, it may not be readily available. Conversely, some non-listed bearings may be produced in large quantities. Always verify the availability before finalizing the selection.
**Rolling Bearing Code System**
The bearing code is a combination of letters and numbers that identifies the bearing’s structure, size, tolerance, and performance characteristics. According to GB/T 272-93, the code consists of three parts: the prefix, the basic code, and the suffix.
- **Basic Code**: The foundation of the code, indicating the bearing type, size series, and inner diameter.
- **Type Code**: A number or letter specifying the bearing type (e.g., 6 for deep groove ball bearings).
- **Size Series Code**: Two digits representing width (for radial bearings) or height (for thrust bearings), followed by the diameter series.
- **Inner Diameter Code**: A number indicating the nominal inner diameter (e.g., 08 = 40 mm).
- **Prefix and Suffix**: These provide additional details about special features, such as seals (e.g., 2Z for double-sided dust covers) or tolerance classes (e.g., P6 for grade 6 precision).
Example:
- **6208-2Z/P6**: 6 = deep groove ball bearing; 2 = size series; 08 = inner diameter of 40 mm; 2Z = sealed on both sides; P6 = precision class 6.
- **23224**: 2 = spherical roller bearing; 32 = size series; 24 = inner diameter of 120 mm.
Understanding the bearing code system helps engineers make informed decisions and ensures proper selection for each application.
