A self-aligning bearing is a mechanical gear designed to support the shaft and accommodate the misalignment between the shaft and the housing. The rolling elements of the self-aligning bearing, mostly balls or rollers, allow the machine to rotate smoothly. There are four typical types of self-aligning bearings: self-aligning ball bearings, spherical roller bearings, toroidal roller bearings, and self-aligning thrust bearings. Self-aligning bearings are widely used in mining, heavy machinery, power machinery, agricultural industry, just to name a few.
There are four essential components of a self-aligning bearing: the outer ring, the inner ring, the rolling element, and the cage. Sometimes there are shields or seals. A self-aligning ball bearing consists of an outer ring raceway and double rows of balls that are secured and separated by cages on the inner ring. The cages, also known as the separator or the retainer, are used to evenly space the rolling elements. The inner ring is also called the inner race, or the cone on tapered bearings. Similar to the inner ring, the outer ring is also called outer race, or cup on tapered bearings.
The rolling elements are sandwiched between the inner ring and the outer ring. Typically, the balls or rollers form the rolling element of a self-aligning bearing. The rolling elements can be cylindrical, barrel, tapered, or needle-shaped. The rolling elements are lubricated. Some self-aligning bearings are installed with a metal shield that protects the bearing to some degree from foreign particle ingress that can potentially contaminate the lubricant inside the bearing.
In the case when the internals of the bearing, the rolling elements, and the cases, are completely separated from the outside environment, a seal is used instead of a shield. this type of bearings is sealed for life. Seals are usually manufactured from rubber or Teflon, they can completely seal the internal parts of the bearing to prevent foreign particle ingress and moisture ingress.
Typical lubricants for the bearings are grease and oil. The grease contains oil and a thickening agent to make the lubricant better adhere to the bearing's internal surfaces. The thickening agent can be either soap-based or non-soap-based.
When installing the self-aligning bearing, the bearing should be screwed on the sleeve with the lock nut but the lock washer. Tighten the lock nut with a lock nut spanner until the self-aligning bearing and the sleeve grip the shaft. Replace the lock nut with the lock washer after the positioning and fitting of the bearing are assured. Finally, screw the nut back on the sleeve and bend one of the lock washer tabs into a matching slot in the nut.
Self-aligning bearings can take heavy loads and automatically accommodate misalignment. Incorporating with a raceway at a high speed, self-aligning bearings are not only sensitive to angular misalignment but generate less friction and heat. The bearings are also known as the anti-friction bearings as a result. The feature of low heat generation of the self-aligning bearings extends both bearing life and maintenance intervals. They are widely applied in fans for they can reduce noise and vibration.
As above-mentioned, there are four different types of self-aligning bearings: the self-aligning ball bearings, spherical roller bearings, toroidal roller bearings, and self-aligning thrust bearings. Here are another two commonly used bearing types.
There are two types of self-aligning ball bearings, the ones with a parallel bore or tapered bore. Commonly, the rolling elements are double rows of balls in a self-aligning ball bearing. Self-aligning ball bearings are commonly applied for mixing, blending, and stirring machinery, and also be used in intermediate shaft positions and fan applications where the ability for self-alignment is important and the loads are relatively light.
A spherical roller bearing has a roller forming the rolling element, generally cylindrical in shape. With the spherical internal shape of the rings and rollers, it suits applications where there are heavy loads and misalignment at moderate speed, such as material handling and wind turbine applications.
The main difference between self-aligning bearings and other types of bearings is the ability to automatically correct the misalignment between the shaft and the housing. It is recommended to use the self-aligning bearing when the shaft alignment and housing are difficult or when the shaft may bend during operation.
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