Plain and linear bearings are typically used in applications where rotational stability is not an issue and where smooth and flat surfaces are desirable. A plain bearing is a rotating bearing which allows angular rotation about a center point in both right and left (or right and left) handed designs (often within a given angular range). A linear roller bearing is one such type of bearing. They are often used as counterweights or spindles to counterbalance larger elements, such as a crane, wheel axle, or other axle carriers.
Spherical bearings are usually of one of two types. A spindle like bearing can have one or more rolling elements that are secured by grooves or by castellated channels. The roller assembly is secured by a cam mechanism. The second type of spherical bearing has fixed rolling elements and is designed to provide smooth transmission of shaft energy between the rollers and the housing. These types of bearings are also often used as spindles or counterweights.
An alternating loads circular plain bearing has the same basic design as the spindle bearing, with the exception of a stationary lift device. This design makes it ideal for use in applications that need a relatively low level of transmission of mechanical forces throughout the bore. This type of bearing can handle most common bolt patterns including: axial, electronic and alternating loads. The elliptical mp bearing offers good reliability in the higher level of load capacity, while the linear mp offers better value in the lower level of load capacity.
The best way to determine the appropriate type of bearing for your application is to assess your working conditions and then match the mechanical properties of the various Plain and Rotary Bearings available. If you work at higher load levels, you may want to consider a stronger and heavier radial bearing. Conversely, if your work is lower or the cost of materials is lower you may opt for a less heavy, but still sturdy, spherical bearing. Spherical plain bearings offer many benefits over other bearing designs. They:
There is very little difference between the performance of two different types of plain bearings; however, the distribution of stress can be different between them. A highly stressed, heavily loaded component will tend to benefit from an axial or spherical bearing. On the other hand a poorly loaded component can abuse either design by developing excessive friction.
Spherical bearings tend to exhibit less friction than either axial or circular designs. The main reason for this is that there is no metal ring that experiences heat during operation. When heat causes metals to develop an electric charge, friction is formed. The contact between the moving rod end of a spindle and a spherical bearing results in reduced friction. Additionally, axial and circular designs tend to work well with the existing lubrication levels and existing structures, whereas spherical bearings need to be re-lubricated periodically.
Spherical bearings have a greater supply of rolling elements that can be varied in size. This feature results in a higher rate of axial rotation than with other designs. Additionally, with high speed rolling elements, the wear rate is less than with bearings with a lower rate of rolling elements. The use of larger and smaller spherical bearings has a significant effect on the life span of a bearing.
It is important to select a bearing with sufficient stiffness for the application. Rolling speeds are primarily affected by stiffness, so it is important to choose a bearing with adequate stiffness for the application and associated conditions. For example, axial and circular designs should have a stiffness factor of ten to one when comparing between axial and spherical plain bearings. It is also important to ensure that the diameter of the rollers is compatible with the diameter of the spindle. Poorly matched rolls can lead to catastrophic failure of bearing components.
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