It's crucial to understand the application bearing loads that will be placed on the bearing, when estimating a bearing's lifespan and performance. Load ratings are a guide to the load that a bearing can withstand in an application and are used in life calculations
What is a Bearing Load?
A bearing load is defined as the force that's transferred from one bearing ring, through some or all the rolling elements, to the other bearing ring. Application loads generally transfer to the shaft and then to the bearing's inner ring, then, to the outer ring.
A bearing supports many different load combinations but most types of application loads can be boiled down to these four main groups:
- Radial Loads
- Axial Loads
- Preloads
- Centrifugal Loads
Radial Loads
Radial load is the force applied perpendicular to the axis of a mechanical component or bearing. It works perpendicular to the axis, aiming to compress or deform the component radially. The force experienced by a wheel rolling on a surface is an example of radial load.
When in operation, the shaft assembly pushes radially on the inner ring of the bearing transferring a load through the rolling elements to the outer ring.
Radial loads don't transfer force in an equal and uniform way onto the rolling elements.
Axial Loads
Axial load, also known as thrust load, is a force applied parallel to the axis of a mechanical component or bearing. It tends to move components along the axis, either towards or away from the source of the force. The pushing or pulling a component in a straight line is the simplest example of an axial load.
Preloads
Bearing Preload is an axial or thrust load applied to a bearing that removes excess play. There are many ways to apply preload, as well as many benefits and potential problems with preload. This article will provide an overview of bearing preloading in common radial and angular contact ball bearing applications.
The purpose of preload in a bearing system is to eliminate clearance that is designed into standard ball bearings. Almost all radial ball bearings are made with a clearance or space between their components to allow for free movement. This space, if not taken up by a preload can allow the rolling elements to slide rather than roll, or even allow for races to misalign.
The best preload for a system should be individually determined based on a bearings size and the system's required stiffness, starting torque, running torque, life, and loading parameters. Excessive preload can cause increased heat, fatigue, and torque. Insufficient preload can allow resonant vibration causing fretting of the raceways.
- Left image: A bearing with no play, or an interference fit has all rolling elements loaded, wears and heats up excessively.
- Center image: A bearing with standard play in the free state has low rigidity, and rolling elements can slide or skid instead of rotating.
- Right image: A standard bearing with proper preload applied will provide system rigidity, reduced vibration, and optimal bearing life.
Centrifugal Loads
Centrifugal loads come from the rotational speed (RPMs) of an application. High-speed applications can produce a powerful centrifugal load which can sometimes be the reason for the max speed of an application.
Centrifugal force is the apparent force that is felt by an object moving in a curved path that acts outwardly away from the center of rotation.
Bearing Load Ratings
It is essential to consult with your supplier or look up the load ratings in manufacturers catalogs to determine the most suitable bearing. Accurate calculations of these forces are essential in choosing the right bearing type and ensuring its efficiency and life.
radial load rating
Dynamic Load Capacity is defined as the constant stationary radial load in which a rolling bearing can theoretically last with a basic rating life of one million revolutions.
Static radial load rating
Static Load Capacity: Shown in manufacturers catalogs as the maximum load a bearing can withstand without any permanent deformation while stationary. Exceeding the manufacturers catalog specifications may lead to material fatigue and eventual bearing failure. This specification is typically designated as the symbol C0 and is measured in units of force, such as Newtons (N).
A basic fatigue life rating known as L10 is a bearing's basic fatigue life rating and is calculated using the number of rotations in which 90% of all bearings in a specific group achieve or exceed a calculated time without failure (probability of failure: 10%). More information please refer to Bearing life L10