Introduce the cylindrical bearing
Of course. Here is a detailed introduction to cylindrical bearings.
Quick Summary
A cylindrical bearing (full name: Cylindrical Roller Bearing) is a type of rolling-element bearing designed primarily to support very high radial loads at moderate to high speeds. As the name implies, its rolling elements are cylindrical rollers, which have a higher load-carrying capacity than balls of the same size.
Their key design feature is that the rollers have line contact with the raceways (as opposed to point contact in ball bearings), which distributes the load over a larger area.
Core Design and Characteristics
Rollers: The cylindrical rollers are guided by ribs on either the inner or outer ring. This ensures precise rolling motion and prevents skewing.
Separability: Most cylindrical roller bearings are separable, meaning the inner ring with rollers and cage (the inner assembly) can be mounted separately from the outer ring. This simplifies installation, maintenance, and inspection.
High Rigidity: Due to the line contact and often multiple rollers, they offer high rigidity against radial forces, minimizing deformation under load.
Low Friction: Well-designed cylindrical bearings exhibit very low friction, making them suitable for high-speed applications.
Common Types and Design Variations
Cylindrical bearings are classified into different series based on their internal design, specifically the number and configuration of the guiding ribs. The most common types are:
N Type (NF): No ribs on the outer ring, one or two ribs on the inner ring. This allows the outer ring to float axially, making it ideal for applications where shaft expansion (thermal growth) needs to be accommodated. The shaft is axially located relative to the housing.
Example: NJ, NUP, NH types all build upon this concept for different axial locating needs.
NU Type: No ribs on the inner ring, one or two ribs on the outer ring. This allows the inner ring to float axially. The housing is axially located relative to the shaft. It is the most common type for supporting pure radial loads.
NJ Type: Has two fixed ribs on the outer ring and a single rib on the inner ring. This can handle light axial loads in one direction.
NUP Type: Similar to NJ but includes a loose guide ring or thrust collar that enables the bearing to handle limited axial loads in both directions. It can be used for axial location of the shaft in both directions.
The following table summarizes the main types and their capabilities:
| Bearing Type | Rib Configuration | Axial Displacement | Axial Load Capacity | Typical Use Case |
|---|---|---|---|---|
| NU | No inner ring ribs | Inner ring can float | None | Pure radial load; free axial expansion |
| NJ | Two ribs on outer ring | Limited | One direction | Radial load + light one-way thrust |
| NUP | Includes a thrust collar | Fixed | Both directions | Radial load + light two-way thrust; axial location |
| N | No outer ring ribs | Outer ring can float | None | Pure radial load; housing-located |
Key Advantages
Very High Radial Load Capacity: The primary advantage. They can support heavier radial loads than same-sized deep groove ball bearings or spherical roller bearings in some cases.
High-Speed Performance: Excellent suitability for high-speed applications due to low friction and the ability to be manufactured with precision cages.
Accommodates Shaft Expansion: The separable design and specific types (like NU and N) allow for free axial displacement of the shaft or housing, crucial in machinery like gearboxes and electric motors that heat up during operation.
High Rigidity: Maintains precise shaft positioning under heavy loads.
Easy Maintenance: The separable nature allows for easy inspection and mounting/dismounting.
Limitations
Generally not for pure axial loads: They are not thrust bearings. While some types (NJ, NUP) can handle limited axial loads, they are not designed for applications dominated by axial forces.
Misalignment sensitivity: They are not self-aligning. They require the shaft and housing to be well-aligned within very tight tolerances. Misalignment can cause stress concentrations and premature failure.
Typical Applications
Cylindrical roller bearings are ubiquitous in industrial machinery wherever high radial loads are present.
Electric Motors and Generators: The most common application. NU types support the rotor shaft and allow for thermal expansion.
Gearboxes and Transmission Systems: Support gears and handle high radial forces.
Machine Tool Spindles: Where high precision, rigidity, and speed are required.
Vibrating Screens: Often used in pairs to handle heavy loads and allow for shaft expansion.
Pumps and Compressors
Railway Axle Boxes
Comparison with Other Bearing Types
vs. Deep Groove Ball Bearings: Cylindrical bearings have a much higher radial capacity but cannot handle significant axial loads like deep groove ball bearings can.
vs. Tapered Roller Bearings: Both handle high radial loads. Tapered rollers are designed to handle combined (radial and axial) loads simultaneously, while cylindrical bearings are primarily radial.
vs. Spherical Roller Bearings: Spherical bearings can handle very high radial loads and misalignment, but they typically have lower speed limits and higher friction than cylindrical bearings.
In summary, the cylindrical roller bearing is the go-to choice for engineers when the primary requirement is to support very high radial loads efficiently and at high speeds, especially when shaft expansion needs to be managed. Its separability is a key feature for ease of installation and maintenance.
WhatsApp
Email
0086 18554001053