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Understanding Bearing Loads

Bearing loads are an important factor to consider when selecting and using bearings. The term ‘load’ refers to the forces that act on a bearing while it is in operation. These forces can come from a variety of sources, including the weight of the equipment being supported, the forces generated by the motion of the equipment, and external forces such as wind or earthquakes. By understanding bearing loads, engineers and maintenance personnel can select the most appropriate bearing for a particular application and optimize its performance.

Types of Bearing Loads

Understanding Bearing Loads

There are two main types of bearing loads: radial loads and axial loads. Radial loads act perpendicular to the axis of rotation and are the primary load in many applications. For example, the weight of a shaft and the forces produced by its rotation can create radial loads. Axial loads, on the other hand, act parallel to the axis of rotation and are common in applications such as gearboxes and thrust bearings.

  1. Static load: A static load is a constant, unchanging load that a bearing experiences while it is in operation. Examples include the weight of a machine component or the force needed to maintain a part in position.
  2. Dynamic load: A dynamic load is a load that varies over time as a bearing is in operation. The magnitude, direction, and frequency of dynamic loads can be affected by various factors such as the speed of rotation or vibrations in the system.
  3. Shock load: A shock load is a sudden or abrupt impact that a bearing experiences due to events such as collisions or drops. Shock loads can cause damage to bearings, so it is important to choose a bearing that can withstand or dissipate shock loads effectively.
  4. Overload: An overload occurs when a bearing experiences a load that exceeds its design limits. This can be due to a sudden and unexpected increase in load or a long-term overload. Overloading can cause damage to bearings, such as fatigue or cracking.

Bearing Loads Capacity

Bearing load capacity is a measure of the maximum load a bearing can handle without failure. It is important to select a bearing with a load capacity that exceeds the maximum expected load for the application to avoid premature failure. It is also important to consider the type and direction of the load when selecting bearings, as different bearings are designed to handle different types and directions of loads.

  1. Dynamic Load Rating: The dynamic load rating is a measure of a bearing’s load capacity under dynamic loading conditions. It represents the load that a bearing can handle for a specific number of revolutions before failing due to fatigue.
  2. Static Load Rating: The static load rating is a measure of a bearing’s load capacity under static loading conditions. It represents the load that a bearing can handle without failing due to deformations or other damage.
  3. Equivalent Dynamic Load: The equivalent dynamic load is a calculated load used to determine the dynamic load rating required for a bearing under non-uniform load conditions. It takes into account both the magnitude and direction of the load to calculate a load that is equivalent to a uniform radial load.

Bearing Life and Fatigue

Bearing life is a measure of the expected lifespan of a bearing under a given set of operating conditions. Fatigue is a potential failure mode for bearings that can occur due to repeated loading and unloading. By understanding the factors that affect bearing life and fatigue, engineers can optimize bearing selection and maintenance strategies.

  1. Bearing Life Calculation: Bearing life can be calculated using various formulas and standards, such as ISO 281 and ANSI/ABMA 9. Different factors such as load, speed, lubrication, and temperature can affect bearing life, and these factors should be considered when performing bearing life calculations.
  2. Fatigue Life: Fatigue life is a measure of the number of cycles a bearing can endure before developing cracks or other damage due to fatigue. It is affected by several factors, including bearing material, load, speed, lubrication, and temperature.
  3. Maintenance: Regular maintenance, such as lubrication and inspection, can help extend bearing life and prevent premature failure due to fatigue or other factors.


Bearing loads are an important consideration when selecting and using bearings in various applications. Understanding the types and direction of loads, the load capacity of bearings, and the factors that affect bearing life and fatigue can help engineers and maintenance personnel optimize bearing performance and prevent premature failure.

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