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Definition What is a Rolling Bearing?

From konstruktionspraxis | Translated by AI 7 min Reading Time

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Wuxi InfiMotion Technology Co., Ltd.

Rolling bearings enable rotational movements and thus load transfers with minimal friction through the rolling motion of rolling elements. How is a rolling bearing composed and how does it generally function? An overview of a multifaceted technology.

Rolling bearings can be divided into ball bearings and roller bearings. Spherical roller bearings, like in the picture here, can take high loads in both directions. They are self-aligning and can compensate for misalignments and shaft deflections without significantly increasing friction losses or temperature.(Image: SKF)
Rolling bearings can be divided into ball bearings and roller bearings. Spherical roller bearings, like in the picture here, can take high loads in both directions. They are self-aligning and can compensate for misalignments and shaft deflections without significantly increasing friction losses or temperature.
(Image: SKF)

The term "rolling bearing" serves in this context as a collective term or umbrella term for all bearings in which rolling elements perform a rolling motion and transfer the load between two opposing surfaces.

What Components Make Up a Rolling Bearing?

A rolling bearing essentially consists of an inner ring, an outer ring, a cage, and so-called rolling elements. The rolling elements move on a bearing raceway as essential components of a rolling bearing and are enclosed by a cage.

In principle, a distinction can be made regarding design and assembly between:

  • Self-retaining rolling bearings, which are manufactured and assembled as a complete unit. They require no additional adjustment or preload.

  • Non-self-retaining rolling bearings, which consist of separate components. These must be installed and adjusted separately during assembly to achieve correct bearing clearance. Such bearings require preloading to avoid clearance and increase stiffness.

Where Are Rolling Bearings Used?

As machine elements, rolling bearings create a movable connection between two components, such as a shaft and housing, allowing load transfers with minimal friction compared to plain bearings. They are capable of accommodating radial, axial, and combined forces. They are used, for example, in

  • Machine tools

  • Robots (for example in precision and reduction gears)

  • in conveyor technology

  • in pumps

  • compressors

  • vehicles (such as wheel bearings and gearboxes)

  • ship propellers

  • aircraft engines

  • helicopters

  • wind turbines

  • as well as in everyday products like electric toothbrushes.

Since rolling bearings are generally standardized in their dimensions, they can be maintained and replaced with comparatively little effort.

How does a Rolling Bearing Work?

As mentioned earlier, a rolling bearing consists of the components inner ring, outer ring, a cage, and rolling elements. The inner ring is usually mounted on a shaft or axle, and the outer ring is mounted in the housing. The inside of the outer ring and the outside of the inner ring form the bearing raceway, where the rolling elements are located. The rolling elements rotate around their own axis and move on the raceway surface. As a central component, the cage ensures that the rolling elements are guided in the bearing at a constant distance from each other, allowing the inner and outer rings to move with minimal friction. To keep friction low and the bearing from wearing, the raceways on the inside of the outer ring and the outside of the inner ring must be lubricated.

What are the Main Types of Rolling Bearings?

Fundamentally, rolling bearings can be divided into

  • ball bearings and

  • roller bearings

which enable either point or line contact.

—ball bearings

Ball bearings have spherical rolling elements that create a point contact with the bearing raceways. The rolling elements thus touch only a very small area of the bearing raceways. Ball bearings include:

  • Deep Groove Ball Bearings—Deep groove ball bearings are somewhat of a classic among rolling bearings, as they are very versatile. The ball bearings have deep raceways (grooves) in which the rolling elements move. Deep groove ball bearings are suitable for accommodating both moderate radial and axial forces and are preferably used in small and medium-sized electric motors.

  • Angular Contact Ball Bearings—Angular contact ball bearings are characterized by inner and outer raceways offset from each other, allowing the rolling elements to move at a certain angle to each other. This enables the bearings to accommodate both axial and radial forces. The larger the contact angle, the higher the axial load capacity. Angular contact ball bearings are available in single-row and double-row designs. Single-row angular contact ball bearings can only accommodate axial forces in one direction, whereas double-row angular contact ball bearings can accommodate axial forces in both directions. By applying a preload, angular contact ball bearings can be adapted to an application to prevent bearing play and increase bearing stiffness.

  • Spherical Ball Bearings—Spherical ball bearings are double-row bearings consisting of an inner ring with two ball raceways and an outer ring. The raceway of the outer ring has a spherical shape and matches the curvature angle of the bearing. Spherical ball bearings are preferably used where a shaft and housing are not perfectly aligned with each other. The angle of the spherical ball bearing can be adjusted, allowing for compensation of shaft deflections, misalignments, or angular errors.

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—roller bearings

Roller bearings have conical, cylindrical, or barrel-shaped rolling elements that provide line contact with the raceways of the inner and outer rings.

Typical roller bearings include, for example:

  • Cylindrical Roller Bearings—Cylindrical roller bearings can endure high radial loads and are suitable for high speeds despite the line contact of the rolling elements. The rolling elements or rollers are guided within one of the bearing rings between fixed flanges (edges on the inner and outer ring of the bearing for guiding the rolling elements and transmitting axial loads) and are connected to the respective ring as a unit by the cage. Thus, one of the bearing rings can be removed to mount the rings separately.

  • Tapered Roller Bearings—Tapered roller bearings are line-guided roller bearings with conically arranged rolling elements. The inner and outer rings as well as the rolling elements are arranged so that their apexes meet at a common point. This arrangement results in an axial force where the rolling elements theoretically roll without sliding friction. Preferred applications for these bearings include heavily loaded industrial gearboxes, shipbuilding, as well as agricultural and construction machinery.

  • Spherical Roller Bearings—Spherical roller bearings have spherically ground raceways, allowing the rows of rolling elements to swivel around the axis of rotation. The barrel-shaped rolling elements can swivel with their axis inclined to the axis of rotation of the bearing (thus they are angularly movable), enabling spherical roller bearings to compensate for shaft deflections, alignment errors, and misalignments. Furthermore, they can accommodate very high axial and radial forces, making them ideal for use in very large machines, such as wind turbines (main rotor bearings) or ship propellers.

  • Needle bearings—Needle bearings are particularly compact designs of rolling bearings, whose rolling elements are relatively long in relation to the diameter of the cylindrical rollers. The rolling elements are therefore also referred to as needles or needle rollers. Needle bearings are particularly suitable for applications with limited space, where high radial forces may sometimes need to be accommodated.

What are the Advantages And Disadvantages of Ball And Roller Bearings?

Ball Bearings are particularly suitable for applications with high speeds. Due to their design with spherical rolling elements and thus a point contact with the raceways, they enable an extremely low-friction operation. Among the most commonly used ball bearings are deep groove ball bearings, as they can accommodate both radial and axial forces. Other widely used ball bearing variants include angular contact ball bearings and spherical ball bearings. Overall, ball bearings are the preferred choice in a wide range of machines and devices when a precise and reliable support of rotating parts is required.

Roller Bearings can accommodate higher radial and axial loads than ball bearings due to the line contact between rolling elements and raceways. They are therefore more suitable for applications where very high loads impact the bearings. Moreover, compared to ball bearings, roller bearings are less sensitive to shocks, vibrations, and oscillations. Certain types of roller bearings, such as cylindrical roller bearings, can also compensate for shaft expansions, which ball bearings cannot do. However, the robust design and the ability to handle high load capacities in roller bearings come at the cost of increased friction of the rolling elements on the raceways of the inner and outer rings, making them more suitable for applications with lower speeds. Due to their more complex design, roller bearings are also more difficult to mount and dismount compared to ball bearings and have lower guiding accuracy.

What Factors are Relevant When Selecting Rolling Bearings?

As is often the case, the selection of a rolling bearing depends on the specific requirements of an application and requires a careful consideration of the advantages and disadvantages of the various bearing types. The following factors are relevant when selecting a rolling bearing in this context:

  • space constraints

  • load

  • misalignment

  • accuracy

  • speed

  • quiet operation

  • stiffness

  • axial displacement

  • installation and removal

  • sealing

Who Invented it?

Sources do not consistently agree on who invented the rolling bearing. As early as around 2,500 BC, the Egyptians transported heavy loads on sliding skids over long distances. Later, elongated wooden rollers were placed between the transport surface for the loads and the skids. One could say that this was the first roller bearing.

Leonardo da Vinci is credited with inventing the first ball bearing. The rolling elements were made of wood and were subject to increased wear depending on the load.

The first patent for a ball bearing was granted in 1794 to the Welsh inventor Philip Vaughan. In his patent specification, he described how iron balls should be placed between a wheel and the axle of a cart to allow the cart wheels to rotate freely with reduced friction.

The Parisian bicycle mechanic Jules Suiray is associated with the first radial ball bearing, which he developed in 1869. The English racing cyclist James Moore won the first Paris-Rouen race with a bicycle that used these radial bearings.

Another inventor in the field of ball and ball bearing technology is Friedrich Fischer, who founded the "First Automatic Cast Steel Ball Factory Friedrich Fischer AG," later known as FAG Kugelfischer, in 1896.

Suppliers of Rolling Bearings

  • AWT

  • Blis ball screw drives

  • C&U Europe Holding

  • Findling Wälzlager

  • Franke

  • Frika

  • Fröhlich & Dörken

  • GMN Paul Müller Industrie

  • Hecht Kugellager

  • HQW Precision

  • HWG Horst Weidner

  • IBC Wälzlager

  • Interprecise Donath

  • IST Europe

  • Karl Diederichs

  • KIS Antriebstechnik

  • Kugel- und Rollenlagerwerk Leipzig

  • NTN Wälzlager

  • Norelem Normelemente

  • Rodriguez

  • Schaeffler

  • SKF

  • Timken

  • Tyrolit

  • Zanuso Kugellager

The list is an excerpt without a claim to completeness.

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