Rolling bearings

The structure of rolling bearings

Rolling bearings are normally of the same design, but differ mainly in the arrangement and shape of the rolling elements used. Almost all rolling bearings consist of an inner and outer ring, between which the rolling elements are located that roll in the raceways. A cage is usually used to ensure uniform distribution and guidance of the rolling elements. The rolling elements of the bearings (balls or rollers/needles) are also used for differentiation, so that a distinction is made between ball and roller bearings.

The key difference: point or line contact

The key difference between the two designs lies in the contact between the rolling elements and the raceway surface. Whereas in the case of ball bearings the contact between balls and raceway surface is point-shaped from a geometrical point of view, the rolling elements of roller bearings contact the raceway surface in a linear manner. Both types of contact have their advantages and disadvantages. Point contact favors the operation of ball bearings at high speeds, although they cannot support as high loads as roller bearings. Roller bearings, on the other hand, have a larger contact area, which means they can support heavier loads and have greater rigidity.  Conversely, the frictional torque of roller bearings is greater than that of ball bearings, which means that they are used in particular in applications with comparatively low speeds (e.g. in gearboxes).  

More detailed information on the individual ball bearing and roller bearing types can be found under the respective sub-pages. The following table provides a rough overview.

Bearing	Picture	Advantages
Ball bearings
Deep groove ball bearings		distinct variety of types and designs flexible lubrication
Angular contact ball bearings		Absorption of diagonally acting loads Installation in pairs possible
Radial insert ball bearings		Widened inner ring simplifies mounting on the shaft
Self-aligning ball bearings		Inner ring, cage and balls can be swiveled a few angular degrees from the center position (thus compensating for static and dynamic angular errors)
Roller bearings
Cylindrical roller bearings		can absorb high radial loads and speeds due to the linear contact
Taper roller bearings		Absorption of combined radial and axial loads
Spherical roller bearings		Compensation of misalignments possible Extremely loadable Absorption of very high radial and relatively high axial forces
Needle bearings		high load capacity Optimal for bearing cases where only limited installation space is available

Various factors are important when selecting the right rolling element and bearing. The right choice depends, for example, on the speed, load and type of load (axial or radial).

Materials of rolling bearings

The inner and outer rings, as well as the rolling elements, are generally made of high-purity chrome-alloyed special steel. This material not only offers the required hardness and purity, but also fulfills the important requirements of high load carrying capacity and long service life. In addition to chrome-alloyed special steel, special materials such as ceramics and plastics are also used. Although plastics cannot withstand extremely high temperatures, they are significantly lighter than steel. The cages of the rolling bearings are mainly made of steel, brass and plastic. However, special designs are also possible here.

For special operating conditions and fields of application, rolling bearings are also available in special designs, ranging from stainless steel to hybrid bearings in which, for example, the bearing rings are made of steel and the rolling elements are made of ceramic. Hybrid bearings can be used, for example, in spindle bearings for machine tools.

Cover plates / Sealing washers

Rolling bearings without cover plates or sealing washers are not protected against dirt or foreign bodies from the outside. As a rule, these types are used in closed installation situations, e.g. in closed gearboxes. As an alternative to the open design, rolling bearings are also offered by many manufacturers with sealing washers or cover washers on both sides or on one side. Sealing washers or cover washers retain the grease required for lubrication in the bearing.