Rolling bearings

Rolling bearings are one of the most prevalent and important components in machine manufacturing. Rolling bearings are bearings that facilitate the movement of components by means of a rolling motion and significantly reduce friction. In contrast to plain bearings, the friction loss is at least ten times lower. Rolling bearings are particularly suitable for high speeds with reduced noise and heat generation. Rolling bearings are therefore used in particular for the location of axles and shafts that are to implement rotating movements. Lubricants can further optimize the processes here.

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.

BearingPictureAdvantages 
Ball bearings   
Einreihiges Rillenkugellager mit der Artikelnummer 16007-A-C3 von Schaeffler
  • distinct variety of types and designs
  • flexible lubrication
 
Axial-Schrägkugellager BSD 3572 CGA
  • Absorption of diagonally acting loads
  • Installation in pairs possible
 
Spannlager mit Exzenterring
  • Widened inner ring simplifies mounting on the shaft
 
 
  • 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   
Vollrolliges-Zylinderrollenlager_SL045011-PP
  • can absorb high radial loads and speeds due to the linear contact
 
axial-kegelrollenlager
  • Absorption of combined radial and axial loads
 
Pendelrollenlager von SKF - Art.Nr. 22208 E
  • Compensation of misalignments possible
  • Extremely loadable
  • Absorption of very high radial and relatively high axial forces
 
Nadellager in massiver Ausführung von Schaeffler mit der Artikelnummer RNA4906-XL
  • 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.

der Aufbau eines Kugellagers mit Dichtscheiben an beiden Seiten

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 can have different shapes and are also the eponym for the different types of rolling bearings.

Ball = Ball bearing (deep groove ball bearings, angular contact ball bearings, self-aligning ball bearings, radial insert ball bearings)
Needle = needle roller bearings
Cylinder = cylindrical roller bearings
Barrel = Barrel or spherical roller bearing
Taper = Tapered roller bearing

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

der Aufbau von Wälzlagern anhand eines Kugellagers dargestellt

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.

Lubrication of rolling bearings

The lubrication of rolling bearings is an important topic and is essential for the reliable working of rolling bearings. Statistically, around 80% of all rolling bearing failures are due to lubrication. It is therefore important to pay particular attention to correct lubrication. Lubrication fulfills the following tasks:

Creating a load-bearing lubricant film between the rolling element and the inner or outer ring.
Protecting the rolling bearing from corrosion
Damping the running noise
Protecting the rolling bearing from contamination (grease lubrication)
To dissipate heat (oil lubrication)

waelzlager wird geschmiert

Greases, oils or solid lubricants (special cases) can be used to lubricate rolling bearings. The choice of lubricant to be used depends largely on the level of stress, speed and operating temperature of the bearing.

 

Grease lubrication

Grease lubrication requires low maintenance and usually provides sufficient protection against contamination, which makes it possible to seal bearings easily and cheaply.

Calcium, sodium, aluminum and lithium soap greases are usually used to lubricate rolling bearings. The type of grease to be used depends on the operating temperature, behavior against moisture, sealing behavior and consistency. Calcium and lithium greases are mostly used to lubricate highly loaded bearings. Lithium soap grease with silicone oil has better temperature properties but lower load capacity.

The natural aging and contamination of the grease requires renewal at certain intervals (lubrication interval). If the lubrication period is longer than the service life of the rolling bearing, permanent lubrication is used. Permanent lubrication means that the bearing receives a single grease filling (e.g. in the case of deep groove ball bearings with cover or sealing washers).

Oil lubrication

Oil lubrication is used when high speeds or medium speeds at higher loads or the operating temperature no longer permit grease lubrication or when the oil is used for heat dissipation or where adjacent components are already oil-lubricated.

The type of oil to be selected depends on the requirements of the components without any disadvantages for the rolling bearings. Mineral-based oils which meet the minimum requirements according to DIN 51501 are suitable for lubricating the rolling bearings; however, oils with better aging resistance according to DIN 51517 are preferable.

We offer the following types of products

Deep groove ball bearings

Deep groove ball bearings are available in a distinct variety of types and designs. Predestined for high and very high speeds. Deep groove ball bearings can support radial-axial combined loads in both directions.

Angular contact ball bearings

Angular contact ball bearings are available in many designs and versions. Forces are transmitted from one raceway to the other at a specific pressure angle. Predestined for simultaneously acting radial and axial loads.

Self-aligning ball bearings

Self-aligning ball bearings are insensitive to static and dynamic angular errors. They have the lowest friction of all rolling bearing types, which makes them run somewhat quieter and cooler even at higher speeds.

Radial insert ball bearings

Insert ball bearings are ready-to-fit units with the outer ring curved outwards. Static pendulum function between outer ring and housing can compensate for misalignments. Suitable for heavily contaminated environments.

Cylindrical roller bearings

Cylindrical roller bearings are available in many different designs. Due to the line contact between the rolling element and the bearing ring, these bearings can support high radial loads and high speeds.

Needle bearings

Needle roller bearings contain thin cylindrical rolling elements. The very small diameter of the rolling elements compared to their length enables a compact solution that provides high rigidity and load carrying capacity.

Spherical roller bearings

Spherical roller bearings are extremely resilient and can support very high radial as well as relatively high axial forces. The universality of the spherical roller bearing makes it one of the most widely used bearing types.

Tapered roller bearing

Tapered roller bearings are special (line contact) roller bearings in which the rolling elements have the shape of a truncated cone – they enable very high forces to be transmitted in the radial and axial directions.

waelzlager zubehoer

Rolling bearings accessories

PACH Systems offers you various adapter sleeves, withdrawal sleeves and shaft nuts for mounting the rolling bearings on shafts or in housings.