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Each Moment is Important to Us! Accounting for Moment Loads with Thin-Section Bearings

Each Moment is Important to Us! Accounting for Moment Loads with Thin-Section Bearings

Date Published: Sep 07, 2015

Radial, Axial and Moment Loads

 

There are three main loads to consider when selecting a bearing in any engineering application: radial, axial (or thrust) and moment loads.

 

Figure 1: Three main loads to consider when deciding a bearing type

 

A radial load is any force applied perpendicular to the center axis of an object, an axial load acts parallel to the center axis of an object while the moment load is applied along the rotational axis, as shown in Figure 1. You can think of the moment load as any force that can cause an object to rotate. Normal radial single ball bearings aren’t designed for these moment loads so Carter Manufacturing Limited stocks a Silverthin™ product line specifically to satisfy these engineering constraints.

Moreover, imagine tightening a bolt with a wrench, as shown in Figure 2. The closer your hand is to the bolt, the more difficult it is to turn the bolt. Conversely, the further your hand is from the point of rotation, the easier it is to turn the bolt. This is because the moment force is defined by the product of the distance from the center of the bolt, d and the perpendicular applied force F, thus a bigger distance yields a bigger moment (while keeping the force constant).

 

Bearing Selection Considerations

 

Figure 2: The moment force is shown by the product of the distance, d, and the perpendicular force, F.

 

When engineers are choosing a bearing for their specific application, it is common to combine a series of bearings working together in order to handle the variety of loads within the system. Typically, bearing loads are thought of only in terms of radial or axial but with only a single bearing, any radial load applied at any distance from the center of the bearing ball path will create a moment load. Silverthin™ Thin-Section Bearings offer a bearing with a unique raceway geometry specifically to handle this moment load.

 

Silverthin™ X-Type versus Radial Bearings

 

These “X-Type” bearings distribute the load at four points of contact, as shown in Figure 3. When compared to the conventional radial ball bearing raceway with only two points of contact, pictured in Figure 4, it is clear to see the difference in load distribution. An “X-Type” bearing can handle all three types of applied loads. This is particularly effective when only one bearing is used in the system, as shown in Figure 5.

 

Figure 3: Cross-sectional view of “X-Type” raceway 

Figure 4: Cross-sectional view of radial raceway   

 

X-Type Bearing Application

 

A simple example is a robotic arm that extends from a static base in order to pick up and rotate a load, shown in Figure 6. A thin section or slewing ring bearing at the base of the structure would experience this moment load. Therefore it is necessary to install a bearing capable of handling the moment forces.

 

Figure 5: “X-Type” Thin-Section Bearing used in a one bearing system to handle moment load

 

Figure 6: Visual representations of ” X-Type” Thin-Section Bearing applications

 

Bearings should be engineered to withstand the full life requirement of the application and it is vitally important to consider all potential loads when designing and selecting the correct bearing.

Carter Manufacturing Limited has a Sales and Design Engineering team capable of assisting you with all of your thin-section bearing needs. Please contact us or call us at 01865-821720.

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