Bearing selection should begin with the machine load case, not with a catalog picture. The correct bearing must support the loads, run at the required speed, survive the intended life, and fit the shaft and housing correctly.
1. Identify the Load
Separate radial load from axial load and determine whether the load is steady, variable, shock-like, or rotating relative to the bearing ring. Gears, pulleys, belts, and couplings can create combined loads that are easy to overlook.
2. Check Speed
Bearing speed capability depends on bearing type, load, lubrication, cage design, cooling, and operating conditions. A catalog speed figure should not be treated as a universal guarantee for every application.
3. Understand Dynamic Load Rating
The basic dynamic load rating is used in bearing-life calculations. For many rolling bearings, the basic rating life is expressed with a relationship of the form L10 = (C/P)p, where C is dynamic load rating, P is equivalent dynamic bearing load, and p depends on bearing type.
4. Check Equivalent Load
When both radial and axial loads are present, the equivalent dynamic load may involve factors that depend on the bearing type and load ratio. Use the bearing manufacturer’s current catalog equations rather than assuming one simplified formula works for every bearing.
5. Consider Fit
Ring creep can occur when a loaded ring is not adequately located. The appropriate shaft and housing fit depends on which ring rotates relative to the load, load magnitude, temperature, and the need for assembly or service removal.
6. Lubrication and Environment
| Condition | Design consideration |
|---|---|
| Dust | Sealing and contamination control |
| High temperature | Lubricant and material temperature limits |
| Water exposure | Corrosion resistance and sealing |
| High speed | Lubrication, cage and heat generation |
Practical Selection Sequence
- Define radial and axial loads.
- Determine operating speed and temperature.
- Choose a bearing family suited to the load direction.
- Calculate equivalent load and required life.
- Check shaft and housing dimensions.
- Specify fits, seals, lubrication, and mounting method.
- Verify the selected bearing using the manufacturer’s catalog.
Conclusion
Bearing selection is a system calculation. Load, speed, life, fit, lubrication, contamination, and installation all interact. Use manufacturer data for the final selection, especially for high-speed or safety-critical machinery.