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The durability and performance of your bearings are directly influenced by their load-carrying capacity. A bearing’s load-carrying capacity is determined by the maximum load it can withstand, under both static and dynamic conditions.

Understanding the static and dynamic loads on your bearings allows you to optimize their service life, ensure bearing safety by preventing deformation, select the right bearing for the right machine, reduce costs, improve the efficiency of your equipment, and more. The load capacity of bearings is calculated based on the weight of the equipment and the payload, while taking into account operating conditions and the safety factor. In this article, we explain everything you need to know about these different loads so you can choose the bearing best suited to your needs.

What is the static load of a bearing?

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The static load of a bearing corresponds to the maximum load it can withstand when stationary, at room temperature, or when rotating at very low speeds, without undergoing permanent deformation.

It is crucial to consider the safety factor when calculating static load capacity to ensure that actual operating conditions—which often differ from standard specifications—are properly accounted for.

To prevent such permanent deformation, a maximum radial load is defined, which corresponds to the permissible stress in the stationary bearing. In other words, this stress is tolerated by the bearing without affecting its service life. This maximum allowable load (_C0 value) is therefore referred to as the static load capacity of the bearing base.

When selecting a bearing, you must therefore consider its dimensions when it is stationary or undergoing slight movements while supporting continuous or intermittent loads.

The basic static load capacity of a bearing (_C0)

ISO Standard 76 establishes the criteria for maximum permissible deformations and defines the static load as the force that causes the highest pressure at the contact point between the rolling element and the raceway. A bearing’s load capacity is determined according to specific standards, taking into account operating conditions and technical specifications to ensure the safety and performance of transportation equipment. These contact pressure values are:

• 4,200 MPa* for ball bearings and thrust ball bearings.

• 4,600 MPa* for self-aligning ball bearings.

• 4,000 MPa* for roller bearings and thrust roller bearings.

These contact pressure values cause a permanent deformation of the rolling element and raceway of approximately 0.0001 times the diameter of the rolling element. They are considered purely radial for radial bearings; axial and centered for thrust bearings.

To make the best use of a bearing’s static load capacity, it is generally necessary to use shafts and housings made of robust and durable materials. The total load must not exceed the basic static load rating. A static overload will result in:

• permanent deformation of the rolling elements,

• a loss of performance due to poor load distribution,

• a reduction in the service life of the materials,

• mechanical malfunction (inaccuracy, instability, loss of productivity),

• safety risks for users (elevators, aviation, industry, etc.).

*The symbol MPa stands for megapascal. It is a unit of pressure or stress equal to 1 million pascals (^10⁶ Pa). We use it to determine the contact pressure exerted on the contact surfaces between rolling elements. 

Application of Static Load

Static load is applied to support heavy loads with minimal movement or without rotation. It is crucial to understand the importance of static load capacity in the transport of heavy equipment, as it determines the safety and efficiency of moving goods.

It is therefore found:

• in heavy machinery such as machine tools, where press bearings are subjected to high loads;

• static equipment such as pivot/support systems and hydraulic presses;

• in the aviation sector, particularly for landing gear;

• the automotive industry, for suspension pivots or gearboxes;

• wind turbines contain blade or nacelle bearings that are subjected to heavy loads but experience no movement.

What is the dynamic load of a bearing?

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The basic dynamic load rating determines a bearing’s rated service life. It represents the maximum load a bearing can withstand at room temperature when the surfaces are in motion. To ensure a precise dynamic load capacity, it is essential that transportation equipment move in a straight line on flat surfaces, taking into account uniform load distribution and standard operating conditions. The dynamic load is therefore primarily based on oscillating or rotating movements under load, but also on vibrations and other operations under high-frequency alternating loads.

The basic dynamic load of a bearing is calculated according to ISO 281, which is used to determine the nominal service life of bearings.

It is crucial to calculate the bearing’s service life in order to:

• estimate the bearing’s service life,

• optimize maintenance by minimizing replacement intervals and associated costs,

• select the bearing best suited for its application,

• significantlyreduce risks and failures,

• improve the overall performance of various pieces of equipment.

If you have any questions about dynamic load, please don’t hesitate to contact us for assistance and expert advice.

If we compare the static and dynamic load capacities of ball bearings and roller bearings, we see that their load capacities differ—whether in terms of static or dynamic capacity. In both cases, a roller bearing of the same size as a ball bearing will have a higher load capacity due to its linear contact surface. Their design distributes loads more effectively ; therefore, roller bearings will always have higher static and dynamic load capacities.

Let’s take the example of the SKF 6206-2RS ball bearing and the SKFNU206-ECP roller bearing ; we can see that they have the same dimensions. However, if we look at their static load capacity, we see that the ball bearing has a capacity of 11.2 kN, compared to 32 kN for the roller bearing. The same applies to the dynamic load capacity: 20.3 kN for the ball bearing versus 56 kN for the roller bearing. 

Your choice will depend entirely on your specific needs. However, to help you make the best decision, please feel free to contact our customer service team. 

Newtons and Kilonewtons: What’s the Difference?

Some basics

The Newton (N) is the unit of measurement used in the International System of Units (SI). 1 Newton corresponds to the force required to accelerate a mass of 1 kg at a rate of 1 meter per second squared (1 m/s²).

The kilonewton (kN), on the other hand, is used for larger forces, such as those encountered in mechanics.

1 kN is equal to 1,000 Newtons. 

1 N is equal to 0.001 kilonewtons.

The Kilonewton in the Calculation of Static and Dynamic Loads

Kilonewtons play an important role in the durability and reliability of components, helping to prevent permanent deformation, fatigue, or component failure. They are used to assess the impact of the force exerted on a component. Bearings are rated in terms of static and dynamic load capacity, which allows their performance to be determined based on the weight of the transport equipment and operating conditions.

Static load in kilonewtons: The constant force applied to a component can be expressed in kilonewtons. For example, a bearing with a diameter of 100 mm can withstand a static load of 10 kN without suffering irreversible deformation. This load is essential for sizing components and ensuring their stability and safety.

Dynamic load in kilonewtons: Here, the force is exerted on the components and varies depending on movement. For example, a rotating drive shaft can generate force variations that, during different movements, can reach 15 kN or more. These fluctuations in force during operation must therefore be taken into account to ensure that the components can withstand these cyclic loads.

Bearing Service Life

The basic rated life of a bearing

The basic rated life of a bearing is a reliable estimate of a bearing’s performance. It is governed by ISO 281 and is used to calculate the life achieved by 90% of bearings operating under dynamic loads.

The basic rated life of a bearing depends on several factors: modern bearings, quality, lower loads, favorable/unfavorable operating conditions, etc.

Below are the operating hours of bearings by application. 

Image source: SNR