Can Cylindrical Roller Bearings Handle Axial Loads?

Cylindrical roller bearings play a vital role in a vast array of mechanical systems across industries like automotive, manufacturing, and heavy machinery. Known for their high radial load capacity and robust design, these bearings are engineered to support rotating shafts with minimal friction. However, a common question among engineers and machinery operators alike is: Can cylindrical roller bearings handle axial loads? This article aims to provide an in-depth exploration of the axial load-handling capabilities of cylindrical roller bearings, complete with technical insights, practical considerations, and clear examples.

Understanding Cylindrical Roller Bearings: Structure and Function

Cylindrical roller bearings are defined by their unique construction—a series of cylindrical rollers that are arranged parallel to the bearing axis. This design distinguishes them from ball bearings, which use spherical rolling elements. The linear contact between the rollers and raceways allows for a larger contact area, enhancing load distribution and enabling the bearing to handle higher radial loads efficiently.

Unlike tapered or spherical roller bearings, cylindrical roller bearings are not inherently designed for axial loads. Their primary function lies in supporting radial loads, particularly in applications that involve high-speed rotation and high radial force. These bearings are typically divided into several types—such as NU, N, NJ, and NUP types—each differing in their ability to accommodate axial displacement or axial load.

For example:

This table illustrates that only certain configurations like NJ and NUP can manage some degree of axial load. But to what extent? Let's delve deeper.

Can Cylindrical Roller Bearings Handle Axial Loads?

The short answer is yes, but with limitations. While standard cylindrical roller bearings are not primarily designed to handle axial loads, certain types—like NJ and NUP—can accommodate axial forces to a limited extent.

Axial Load Handling in NJ-Type Bearings

NJ-type bearings feature a shoulder on one side of the inner ring and a separate thrust collar. This configuration allows the bearing to support axial loads in one direction. The amount of axial load they can tolerate, however, is significantly lower than that of bearings designed specifically for axial forces, such as thrust ball bearings or tapered roller bearings.

These bearings are commonly used in applications like gearboxes and compressors, where moderate axial forces occur as a secondary effect of radial forces or thermal expansion. However, it's critical to ensure that the axial loads do not exceed the manufacturer’s specifications, as this can cause premature wear or bearing failure.

Axial Load Handling in NUP-Type Bearings

NUP-type cylindrical roller bearings offer slightly better axial load-handling performance. They include two fixed shoulders on the inner ring and one fixed plus one loose flange on the outer ring, allowing them to support axial loads in both directions. This makes them suitable for applications with small bidirectional axial loads—such as electric motors and railway axle boxes.

However, even in NUP-type bearings, axial load capacity is generally just a fraction of the radial capacity. For instance, a NUP bearing rated for 100 kN radial load may only manage 10–15 kN of axial load. Designers must, therefore, carefully calculate expected loads and select the correct bearing type accordingly.

Engineering Considerations When Using Cylindrical Roller Bearings for Axial Loads

When deciding whether to use cylindrical roller bearings in applications involving axial loads, several engineering factors must be taken into account:

• Load Ratio Analysis: Engineers must assess the ratio between radial and axial loads. If axial loads exceed 20–25% of the radial load, a different bearing type may be more appropriate.

• Housing and Shaft Alignment: Misalignment can exacerbate stress on the rollers, especially under axial forces. Proper alignment ensures even load distribution.

• Speed and Lubrication: Higher speeds can lead to increased friction and heat generation, especially when axial forces are present. Adequate lubrication is essential to prevent metal-to-metal contact.

• Mounting Configuration: The correct mounting of NJ and NUP types is crucial for proper axial load handling. Improper assembly can cause slippage or flange deformation.

Example Calculation for Axial Load Suitability

Let’s consider a NJ type bearing with a radial capacity of 120 kN and an axial limit of 12 kN. If the application involves a radial load of 90 kN and an axial load of 10 kN, the ratio is:

Axial/Radial Load Ratio = 10 / 90 = 0.111 or 11.1%

Since 11.1% is within the safe limit (typically below 15–20%), this bearing could be deemed suitable—provided other conditions like lubrication and alignment are properly addressed.

Alternatives for Better Axial Load Support

If the axial loads in your system are significant, it may be wiser to consider alternative bearing types that offer dedicated axial support. Here are a few:

This table highlights why cylindrical roller bearings are often chosen for radial-dominant load applications. For true axial support, tapered or angular contact bearings are often better suited.

Conclusion

Cylindrical roller bearings, while exceptional for radial loads, have limited capabilities when it comes to axial forces. Types like NJ and NUP provide some flexibility, but their axial load ratings are inherently lower. For engineers and designers, it's essential to understand these limits and choose the appropriate bearing type based on actual application needs.

By carefully analyzing load requirements, consulting technical documentation, and considering the design limitations, you can safely use cylindrical roller bearings in applications involving light to moderate axial forces. However, when axial loads dominate, switching to specialized bearing types is not just recommended—it’s necessary for long-term reliability and efficiency.