How Load-Carrying Capacity Affects Bearing Service Life
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Bearings, much like humans, are subject to stress. Choosing the right bearing means ensuring it can handle the pressure without "getting stressed out." In other words, it's crucial that the bearing's load capacity is sufficient for the forces it will encounter during operation.
If a bearing is subjected to a load that exceeds its capacity, it can lead to accelerated fatigue or even permanent deformation, significantly reducing its lifespan. When selecting a bearing, two main types of stress should be considered: static and dynamic.
Static stress refers to the condition of the bearing rather than the nature of the load. It occurs when a bearing—whether stationary or moving very slowly—is subjected to a load, whether constant or variable. If the load is too heavy, it can cause plastic deformation on the rolling surfaces, potentially flattening the rolling elements and leading to premature failure.
Dynamic stress, on the other hand, relates to the motion of the bearing. This type of stress arises when a load is applied to a rotating bearing. If the load is too high for the bearing’s capacity, it can cause early fatigue, resulting in cracks and flaking in weak areas of the bearing. This ultimately leads to failure due to material fatigue, which is essentially the end of the bearing's life.
There are several theories explaining what causes fatigue failure in bearings. The maximum shear stress theory suggests that the primary cause is the highest shear stress within the bearing. The distortion theory proposes that stress distribution over a zone, rather than at a single point, leads to fatigue. The third theory, alternating shear stress, claims that orthogonal stresses within the bearing are responsible for material fatigue.
While each theory has some support, the alternating shear stress theory is widely used in calculating the fatigue life of rolling bearings. The fatigue life, also known as rating life, is defined as the number of revolutions or hours a bearing can operate at a constant speed before 10% of a group of identical bearings show signs of material fatigue. Typically, the rating life decreases as the load increases.
At Emerson Bearing, our team of experts is here to help you select the right bearings for your application, ensuring they don’t get "stressed out." Whether you're looking for guidance on load capacity, stress analysis, or maintenance tips, we’re here to assist. Contact us today, or explore our **Catalog** and **Technical Toolbox** pages for more resources and insights into how we can support your needs.