A rolling bearing is a machine element that guides moving components such as shafts, axles or rotary tables and transmits the forces that occur into the surrounding structure. Rolling elements, i.e. balls or rollers, roll between two raceways. Because they roll instead of slide, friction remains low, even when starting from standstill. This is what fundamentally distinguishes the rolling bearing from the plain bearing, in which two surfaces slide on each other.
This page gives an overview of the types of rolling bearings, the criteria for selection and the designs that Franke develops and manufactures.
Design of a rolling bearing
A classic rolling bearing consists of an inner ring, an outer ring, rolling elements and a cage. The raceways on which the rolling elements roll are machined into the rings. The cage keeps the rolling elements at a distance and prevents them from rubbing against each other. Depending on the design, seals are added that keep the lubricant in the rolling bearing and keep dirt out.
In the Franke wire race bearing, the solid rings are eliminated: the rolling elements run on hardened steel wires that are inserted into the surrounding structure. The bearing arrangement thus becomes part of the design.
Types of rolling bearings
Rolling bearings can be classified according to three characteristics: the shape of the rolling elements, the main load direction and the design. In practice, these groups overlap. An angular contact ball bearing, for example, is a ball bearing that carries radial and axial forces at the same time.
By rolling element: ball bearings and roller bearings
Ball bearings use balls as rolling elements. The point contact with the raceway ensures low friction and allows high rotational speeds. Ball bearings are the most widely used type of rolling bearing.
Roller bearings use rollers. The line contact distributes the load over a larger area, so roller bearings of the same size carry higher loads. Depending on the roller shape, a distinction is made between cylindrical roller bearings, tapered roller bearings, barrel roller bearings and needle roller bearings.
By load direction: radial, axial and angular contact bearings
Radial bearings mainly carry forces perpendicular to the axis of rotation; a typical example is the radial ball bearing. Axial bearings are designed for forces in the direction of the axis of rotation. In between are rolling bearings with a contact angle such as the angular contact ball bearing, which carries combined loads.
For bearing arrangements that must carry radial forces, axial forces in both directions and tilting moments at the same time, the four point contact ball bearing with one row of balls or rolling bearings with crossed rollers are suitable. In many applications, both designs replace a combination of two rolling bearings.
By design: slim bearings, large diameter bearings and wire race bearings
Slim bearings have a very small cross section in relation to their diameter and are suitable for confined installation spaces and large hollow shafts. Large diameter bearings and slewing rings are ready to install units with a large diameter, often with mounting holes and gearing. The wire race bearing is a design of its own in which the raceways consist of wire.
Types of rolling bearings compared
| Rolling bearing type | Rolling elements | Main load direction | Typical strength |
|---|---|---|---|
| Deep groove ball bearing | balls | radial, low axial forces in both directions | high rotational speeds, low friction |
| Angular contact ball bearing | balls | combined, axial in one direction | high axial loads at high rotational speeds |
| Four point contact ball bearing | balls | radial, axial in both directions, tilting moments | compact bearing arrangement with one row of balls |
| Cylindrical roller bearing | cylindrical rollers | radial | high radial loads |
| Tapered roller bearing | tapered rollers | combined | high combined loads |
| Needle roller bearing | needle rollers | radial | very low radial section height |
| Rolling bearing with crossed rollers | cylindrical rollers, arranged crosswise | radial, axial in both directions, tilting moments | high stiffness |
| Axial bearing | balls or rollers | axial | pure axial loads |
Selecting the right rolling bearing
Which rolling bearing suits an application depends on several factors that influence each other:
- Load: magnitude and direction of the forces, tilting moments, shocks and vibrations.
- Rotational speed and dynamics: high rotational speeds favour balls, high loads at moderate speeds favour rollers.
- Accuracy and stiffness: running accuracy, bearing clearance or preload and the permissible deformation under load. More on this under bearing tolerances.
- Installation space and weight: available cross section, diameter and weight requirements, for example in robotics or aviation.
- Environment: temperature, contamination, moisture, vacuum or magnetic fields. Here, material, seal and lubrication are decisive.
- Maintenance and lifetime: lubrication intervals, accessibility and the required service life.
Standard rolling bearing or customised rolling bearing?
For many applications, a standardised rolling bearing from the catalogue is sufficient. However, as soon as installation space is tight, the diameter becomes large, weight matters or special materials are required, catalogue products reach their limits. The design is then built around the rolling bearing instead of the other way round.
A customised rolling bearing, on the other hand, is adapted to the application: diameter, cross section, material of the surrounding structure, rolling elements and torque resistance. Franke develops and manufactures such rolling bearings in its individual programme.
Rolling bearings from Franke: designs and product lines
The basis of all Franke rolling bearings is the wire race bearing principle. The raceway rings made of hardened spring steel absorb shocks and vibrations and compensate for slight deformations of the surrounding structure, for example due to temperature changes. The rolling bearing runs without bearing clearance, and the torque resistance is adjustable. Because the surrounding structure can be designed freely, the weight and installation space of the overall product can be reduced considerably.
Wire race bearings for installation
- Type LEL: ball bearing with ground raceways for maximum smooth running and precision, diameter 70 to 150 mm
- Type LER: economical ball bearing with profiled raceways for medium rotational speeds and accuracies, diameter 40 to 150 mm
- Type LEW: roller bearing with crosswise arranged rollers for high stiffness and moment loads, diameter 150 to 400 mm
- Type LSA: slim bearing with thin wall thickness for confined installation spaces, inner diameter 3 to 15 inches
Ready to install slewing rings
- Type LVA and Type LVB: steel version for radial, axial and combined loads, LVB with higher load rating, diameter 100 to 1,800 mm
- Type LVC: double row angular contact ball bearing made of steel for high axial loads, diameter 100 to 1,800 mm
- Type LVD: steel version with external gearing for motorised drive, diameter 100 to 1,800 mm
- Type LVE: aluminium version with toothed belt gearing, lightweight design, diameter 100 to 1,800 mm
- Type LVG: double row angular contact roller bearing made of aluminium with high moment load capacity, diameter 200 to 400 mm
- Type LVW: roller bearing made of anodised aluminium with crosswise arranged rollers, diameter 200 to 500 mm
Rotary tables and direct drives
- Type LTA and Type LTB: rotary tables with worm gear
- Type LTD: backlash free direct drive with torque motor without gearbox, for maximum dynamics and positioning accuracy
All products at a glance: product overview rolling bearings
Applications of rolling bearings
Franke rolling bearings are used in mechanical engineering, robotics and handling, automation technology and semiconductor manufacturing, measurement and testing technology, apparatus and device engineering, packaging machines, intralogistics, vehicle construction, power generation, safety technology and textile machines, among others. In medical technology, Franke direct drives run in computer tomographs from well known manufacturers. Examples and requirements of the individual industries are shown in the overview applications for rolling bearings.
Frequently asked questions about rolling bearings
What types of rolling bearings are there?
Rolling bearings are classified by the shape of the rolling elements into ball bearings and roller bearings, by load direction into radial, axial and angular contact bearings and by design into slim bearings, large diameter bearings and wire race bearings, for example. The best known types include deep groove ball bearings, angular contact ball bearings, four point contact ball bearings, cylindrical roller bearings, tapered roller bearings and needle roller bearings.
What is the difference between a radial bearing and an axial bearing?
A radial bearing mainly carries forces that act perpendicular to the axis of rotation, for example the weight of a shaft. An axial bearing is designed for forces in the direction of the axis of rotation. Angular contact ball bearings and four point contact ball bearings carry both force directions.
What is a wire race bearing?
In a wire race bearing, the rolling elements do not run on solid rings but on hardened steel wires that are inserted into the surrounding structure. The bearing arrangement thus becomes part of the design, which saves installation space and weight. The principle was developed by Erich Franke.
How do I choose the right rolling bearing?
The decisive factors are the magnitude and direction of the load, rotational speed, required accuracy and stiffness, available installation space, weight and ambient conditions such as temperature or contamination. For special requirements, it is worth seeking advice from a manufacturer such as Franke.
When is a customised rolling bearing worthwhile?
Whenever a standard rolling bearing does not meet the requirements for installation space, weight, diameter or material. A customised rolling bearing is adapted to the design instead of adapting the design to the rolling bearing.
Further terms in the Franke glossary: Ball bearing | Roller bearing | Wire race bearing | Individual bearings
More about Franke rolling bearings: Product overview rolling bearings | The Franke principle | Individual programme