What is the best bearing for combined loads?

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4.1.3 Combined loads

Combined loads consist of radial and axial loads acting simultaneously. The axial load capacity of a bearing is influenced by the angle of contact; a larger angle permits greater axial load capacity. Increasing the axial clearance in single row ball bearings enhances their load-bearing capabilities. Single and double-row angular contact ball bearings, as well as tapered roller bearings, are optimal choices for accommodating combined loads (fig. 4.3a). Additionally, double-row spherical roller bearings, thrust ball angular contact bearings, and to some extent, spherical roller thrust bearings can support combined loads. When the axial component of the load is relatively small, self-aligning ball bearings, along with NJ, NUP or NJ roller contact bearings, and NU bearings with HJ attachment rings (fig. 4.3b), can be employed for combined load applications.

 
Fig. 4.3a
Fig. 4.3b
Single-row angular-contact ball bearings, tapered roller bearings, NJ roller-contact bearings, and NU+HJ and axial spherical roller bearings are limited to transferring unidirectional axial loads. A change in the arrangement of the acting load necessitates the use of an additional bearing. For effectively capturing such combined loads, combined single-row angular contact ball bearings or single-row tapered roller bearings are preferred (fig.

As a complement to thrust bearings, ball bearings or four-point ball bearings may be utilized to bear axial forces (fig. 4.4).

 
Fig. 4.4

Fig. 4.4

When selecting a bearing, several key factors come into play. The first is the load the bearing can sustain.
There are two principal types of loads:
' axial load: aligns parallel to the axis of rotation
' radial load: aligns perpendicular to the axis

Link to Hangzhou Journal Bearing

Each bearing type is specifically crafted to handle either axial or radial loads; some can manage both, referred to as a combined load. To support such a load, a tapered roller bearing is often recommended. For high radial loads, a cylindrical roller bearing is ideal. Conversely, for lighter loads, a ball bearing might suffice, as they tend to be more cost-effective.

Rotation speed is another crucial aspect to consider. Certain bearings are capable of enduring higher speeds, particularly when they feature cages, like those found in cylindrical roller bearings and needle bearings, enabling greater speed compared to cage-less designs. Nonetheless, opting for higher speeds may compromise load capacity. Moreover, the potential for misalignment should not be overlooked, as some bearings, such as double-row ball bearings, may not be suitable under such conditions.

Consequently, attention should be paid to the bearing’s construction: insert and spherical bearings facilitate support for misalignment issues. We suggest opting for bearings with automatic alignment capabilities that correct alignment defects resulting from shaft bending or installation errors. Operating conditions play a significant role in the selection of an ideal bearing; it’s essential to assess the environment wherein the bearing will be utilized. Your bearing may be subjected to various contaminations, which could contribute to noise disturbances, impact, or vibration.

Your bearing must not only withstand impact but also operate without becoming a nuisance. Another vital consideration is the bearing life; factors like speed and frequency of use can have significant effects.

Choosing an appropriate sealing system is crucial for ensuring the long-lasting and efficient operation of a bearing. It’s vital to protect the bearing from impurities and external elements such as dust, moisture, corrosive fluids, or even leftover lubricants. This decision hinges on the lubricant type, ambient conditions (and therefore, contamination level), fluid pressure, and rotational speed. For instance, if fluid pressure is high (approximately 2-3 bars), mechanical seals are typically the best option. Otherwise, the choice will align with the lubricant type—be it grease or oil. Common solutions for grease lubrication include deflectors or washers, and narrow machined passages; while oil lubrication often incorporates groove systems for oil recovery.

Use conditions can also impact your choice, especially regarding bearing assembly. The required rigidity and precision of your application must be factored in. In particular cases, you might opt for applying a preload during the bearing assembly to enhance rigidity, which also positively affects bearing life and system noise levels.

To choose the proper preload, whether radial or axial, it's necessary to be informed about the rigidity of all components, either through experimentation or software. Additionally, the select material for your bearing is a crucial criterion. Bearings come in various materials—metal, plastic, or ceramic—chosen based on the intended application. We advocate for selecting the most compression-resistant bearing; however, remember that material selection does influence the bearing’s cost.

For more information, please visit Industrial Combined Journal Bearings.