A bearing is a type of mechanical component regularly found within mechanical assemblies, and such elements serve to reduce the friction between moving parts while constraining relative motion. Journal bearings and rolling-element bearings are two common types regularly used in various applications, and they both present different styles of construction and functionality to benefit specific needs. To best understand how journal and rolling-element bearings function, we will discuss each and their differences.
A journal bearing, more commonly known as a plain or sleeve bearing, is considered the most simplistic type as they are simply a bearing surface devoid of any rolling elements. The journal is considered the section of the shaft that is in contact with the bearing, and it slides over the bearing surface during standard operations. Journal bearings take advantage of a pressure wedge of fluid that is created between the shaft and bearing, and the journal is typically given wear-resistant properties for its protection. For the construction of the bearing pad, soft materials such as bronze, copper-lead, carbon, or babbitt metals may be used.
Due to a lack of rolling elements, a properly lubricated journal bearing theoretically can continue operations indefinitely without fail. Despite this, wear will occur when the supportive oil film begins to thin or becomes removed, such as when the shaft is in a resting state. Because of this, many bearing liners are produced from soft materials that provide lower frictional coefficients, and pump parts may also be implemented for the means of pressurizing the bearing until the protective hydrodynamic wedge is produced again.
Rolling-element bearings, or rolling bearings, are those in which the load of an assembly is placed onto rolling elements situated between races for more optimal distribution. Such bearings may come in one of two types, those of which are ball bearings and roller bearings. Ball bearings are one of the most common types, and they utilize balls placed between inner and outer races for the means of distributing loads. As the races have a groove that permits a loose assembly for the balls, they tend to contact each race across a narrow area.
Roller bearings may come in a few common forms, those being cylindrical roller, spherical roller, gear, tapered roller, and needle roller bearings. Unlike ball bearings, roller bearings tend to have rolling elements that are cylindrical, semi-cylindrical, or tapered, though all are still contained within races. Roller bearings are beneficial for their ability to provide line contact, permitting a greater load capacity and shock resistance as compared to other bearing types.
In contrast to journal bearings, rolling-element bearings tend to have shorter lives due to the presence of multiple moving parts. As they become fatigued, spalled, or generally damaged, a rolling-element bearing may require replacement or repair before it fails. With all bearings, however, proper lubrication is always needed to deter the forces of friction for the means of efficiency and extending component service lives.