Spherical roller bearings: reliable in heavy-duty applications

Well suited to heavy-duty industrial applications, particularly where very high load-carrying capacities and reliability are key design criteria, or where there is a need to compensate for shaft misalignment, Schaeffler's range of X-life spherical roller bearings offer longer operating life, improved machine performance and higher reliability.

The X-life range, which includes eight bearing series with bore diameters from 20mm up to 1030mm, is suitable for various applications, including continuous casting machines used in steel production, paper mills, vibrating screens and wind turbine rotor shafts.

X-life explained

Spherical roller bearings are double-row, self-contained units comprising solid outer rings with a spherical raceway, solid inner rings and barrel rollers with cages. The inner rings have cylindrical or tapered bores.

Many bearing sizes within the spherical roller bearing range are available in X-life quality. As standard, these bearings have no central rib on the inner ring and are therefore able to use longer barrel rollers. Furthermore, the bearings benefit from improved kinematics and optimised surfaces. As a result, the basic dynamic load rating and basic rating life (under similar operating conditions) are improved significantly.

At Schaeffler, the systematic calculation of basic load ratings is compiled using the 'Method to investigate rolling bearing rating life'. This describes all calculation and test methods that are necessary in order to determine all the reference values that influence rating life. This procedure has been certified by Germanische Lloyd (GL-CER-002-2015).

For the customer, these benefits translate into higher machine availability, new design possibilities, more economical bearing systems due to downsizing and lower operating costs due to reduced energy consumption.

Continuous casting machines

X-life spherical roller bearings are used as locating and non-locating bearings on continuous casting machines in steel production. The compact design of the bearing, combined with improved basic load ratings and friction-optimised kinematics, provide improved performance and longer operating life in tough, aggressive operating environments. The sheet steel cages provide excellent resistance to wear and contamination. Schaeffler also provides sealed spherical roller bearings in X-life quality for many continuous caster sizes. The standard dimensions enable easy mounting and replacement of existing bearings.

Paper mills

The distinct advantages of Schaeffler's spherical roller bearings mean these bearings are well suited to paper production applications. Where needed, the conversion of a standard spherical roller bearing to X-life quality enables paper mills to benefit from a 15 per cent increase in basic dynamic load ratings, and up to 60 per cent longer service life compared with previous bearing designs.

Higher basic static load ratings lead to improvements in the static load safety factor of the bearings. Under similar operating conditions, this means that significantly longer bearing life can be achieved, even with a considerable increase in load.

In the latest bearing designs for paper mills, similar or higher performance can be achieved using smaller diameter bearings. By downsizing (smaller design envelope, reduced friction, lower lubricant requirement, higher speeds) more economical bearing systems can be achieved. As a result, the improved bearing kinematics lead to lower operating costs because both friction and bearing temperatures are minimised, which, in turn, place less demand on the grease.

Vibrating screens

Because of their robust design and high load-carrying capacity, Schaeffler's premium-quality X-life spherical roller bearings offer optimum options for vibrating screens. The low-friction characteristics of the X-life bearings not only withstand the very high alternating loads that occur in vibrating screens, but also help to reduce noise levels and operating temperatures, resulting in improved machine efficiency. Spherical roller bearings for vibrating screens have specific specifications to meet the special requirements of the application.

Wind turbine rotor bearings

The latest members of the X-life spherical roller bearing family are main shaft bearings in wind turbines. In a wind turbine, the design of the rotor shaft bearing is critical, as this bearing is directly exposed to the loads and forces induced by the wind. Alternating loads with extreme peaks and troughs, as well as fluctuating operating temperatures, represent further challenges to the bearing designer. In addition, high axial loads coming primarily from one direction are uncommon application conditions for a spherical roller bearing. In order to improve reliability, availability and therefore the cost-effectiveness of wind turbines, Schaeffler has optimised its spherical roller bearings for main rotor bearing supports. This bearing design is used exclusively on the shaft bearing support - the most common bearing support concept.

To optimise the bearing, both its micro- and macro-geometry were addressed. The result is conclusive: it was possible to reduce friction and pressures in the bearing, to improve the distribution of forces and to increase the axial rigidity. These optimised spherical roller bearings therefore have greater resistance to wear, which specifically occurs as a result of axial displacement. These bearings successfully completed a comprehensive range of tests as part of their validation for Schaeffler's X-life premium-quality seal of approval.

The asymmetrical design of spherical roller bearing represents a significant step forward. It substantially increases the axial load-carrying capacity and therefore the operating life of main bearings in wind turbines. It enables a larger contact angle to be used on the bearing row subject to axial loads and a smaller contact angle on the bearing row subject primarily to radial loads. This results in improved load distribution, lower contact pressures and a significant reduction in the axial displacement.

For more information about spherical roller bearings from Schaeffler, email Schaeffler UK's Communications and Marketing Department at [email protected] and request a copy of TPI 251 (please mention MachineBuilding.net.