Figure 1: Cylindrical Roller Bearing
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Manufacturers design bearings to 'bear' or carry a load while restricting motion and reducing friction between moving parts. Cylindrical roller bearings are one type of bearing designed for high-load, circular needs. Ribs guide these cylindrical rolling elements on the inner or outer rings designed to move freely in the axial direction, making this bearing ideal for applications with thermal expansion on the shaft, like an electric motor.
A better understanding of cylindrical roller bearings, their functions, and their advantages and disadvantages helps select the correct bearing for each application.
A cylindrical roller bearing is a contact-type bearing that is different from other bearings. They use cylinder-shaped rolling parts instead of balls like you'd find in ball bearings. Because cylindrical rollers are in linear contact with the raceways, they have a greater circular load capacity than ball bearings.
Though the rollers are cylindrically-shaped, they are not true cylinders. The rollers are crowned or end-relieved to reduce stress, resulting in low friction. Low friction makes them an ideal choice for high-speed situations. Cylindrical roller bearings are typically lubricated with oil to reduce heat caused by high speeds.
Cylindrical roller bearings are radial-type roller bearings. This class of roller bearing includes tapered, spherical, and needle roller bearings. All cylindrical roller bearings have four essential components: an inner ring, an outer ring, rollers, and a cage. The bearing rings and rollers carry the load, and the cage (Figure 2) keeps the rollers in place.
Cylindrical roller bearings vary from clearance and lubrication options, depending on the manufacturer. They can be made with a cage or as a full complemented part. Some have no ribs on either ring, allowing axial movement of the rings, which can be used as free-end bearings.
Pressed steel or machined brass are the most common materials to form cylindrical roller bearing cages. Still, some use molded polyamide, which makes smoother and quieter running bearings. When necessary, hardened high carbon steel or carburized low carbon steel enhances bending fatigue and handles heavy shock loads.
Figure 2: Double-row cylindrical roller bearing cage and rollers
Though single row cylindrical roller bearings are the most common type, cylindrical rollers also come in multi-row options.
Figure 3: Double-row cylindrical roller bearing
With cylindrical roller bearings, the outer load is continuously re-distributed among the rollers. Fewer than half of the total number of rollers carry the application's load as the inner ring rotates. The weight distribution is superior to the load-bearing capacity of ball bearings. It contributes to the service life of the bearing.
There are several criteria to consider when selecting cylindrical roller bearings. For example, one must consider dimensions, the operational speed and load specifications, unique installation features, and materials' choice. DIN Standards 635-1 outline specific dimensions and symbols for single-row spherical roller bearings, while DIN 635-2 standards refer to double-row configurations.
One must consider three dimensions when selecting bearings for a specific application, including:
Axial load support in one direction (single-row) or two directions (double-row), and loading parameters, need to be considered when selecting the correct bearing, including:
An application may also require some unique features. In some instances, bearings are flanged for mounting or locating purposes. A spherical outside diameter has a greater load capacity and allows a bearing to be more tolerant of misalignment but requires more radial space.
Some applications require thoroughly hardened high carbon bearing quality steel, which is more durable than typical alloy or low carbon steel bearings. Further, material processing can add carbon and alloys to low carbon grades of steel. This process produces a fatigue-resistant case and a rigid, malleable core, improving the bending fatigue to accommodate heavy shock loads.
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Their greater radial load capacity and their ability to accommodate faster speeds, as well as other benefits, make cylindrical roller bearings an ideal solution for a variety of industries, including:
Yes. The design of the rollers and surface allows cylindrical roller bearings to manage heavy loading with low levels of friction.
Improper mounting and sealing, lubricant failure, and the presence of debris and contaminants are the most common reasons for bearing failure. In addition, excessive loading can lead to overheating and failure.
Cylindrical roller bearings, like all bearings, are subjected to rust, pitting, scratches, and chips. Bearings treated with a surface coating helps to extend the life of the bearing by preventing these instances.
Zinc-nickel plating, zinc, and phosphate coatings help protect against rust, pitting, scratching, and chipping.
The length/diameter ratio of needle-bearing rollers is greater than four. In contrast, the length of the rollers in a cylindrical roller bearing is shorter with a larger diameter.
The main difference between roller bearings and ball bearings is the type of rolling element used. Roller bearings use cylindrical rollers, while ball bearings use balls. Because of this, roller bearings can carry heavier loads and are better suited for applications where there is heavy radial or thrust loading.
Additionally, roller bearings typically have a higher load-carrying capacity and a lower speed rating than ball bearings. On the other hand, ball bearings are better suited for applications where there is high speed and low to moderate loading.
One of the most notable differences between roller bearings and ball bearings is that roller bearings are typically more expensive than ball bearings. However, they offer several advantages, including higher load-carrying capacity and increased accuracy.
Bearing size is an important aspect of roller bearings and several factors determine the size of a roller bearing. These factors include the diameter of the shaft it will be mounted on, the bore diameter of the bearing, the outside diameter, and the width of the bearing.
The bore diameter is the inner diameter of the roller bearing and is typically measured in millimetres (mm). The width of the bearing is the distance between the outer races of the bearing and is also measured in millimetres.
To determine the proper size of a roller bearing where the shaft is the rotating element and the outer ring has a transition fit, the diameter of the shaft it will be mounted on must be known. The diameter of the shaft must be larger than the bore diameter of the bearing, as the bearing must fit snugly over the shaft. A tight fit is needed to prevent the bearing from rotating on the shaft, which could cause damage to the bearing and reduce its lifespan.
On the other hand, if the outer ring is rotating, then the housing must have a smaller diameter than the outer ring, and the shaft will have a transition fit.
In addition to the bore diameter and width, the load capacity of the bearing must also be considered when selecting the right size. The load capacity of a roller bearing is determined by the type of bearing, its size, and its material. For example, larger bearings can typically manage higher loads than smaller bearings.
It's also important to consider operating conditions, such as speed and temperature, as these can affect the size and load capacity of the bearing. In high-speed applications, for example, bearings with a low friction coefficient and high load capacity may be needed.
To ensure the proper functioning and longevity of a roller bearing, it is crucial to select the proper size based on the specific application requirements. It is also essential to select the correct lubrication for the conditions.
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