Spherical roller bearings offer higher reliability in heavy duty applications
09 October 2018
Schaeffler is seeing an increase in demand for its robust, high performance range of spherical roller bearings, which are suitable for harsh operating environments.
Ideal for 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 1,030mm, is suitable for various applications, including continuous casting machines used in steel processing, paper mills, vibrating screens and wind turbine rotor shafts.
Spherical roller bearings are double-row, self-contained units that comprise 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 in the method “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 solutions 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 used in steel processing. 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 such as steel processing. 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.
The distinct advantages of using Schaeffler’s spherical roller bearings means that these bearings are ideally suited to paper production applications. Where needed, the conversion of a standard spherical roller bearing to X-life quality, Schaeffler customers benefit from a 15 percent increase in basic dynamic load ratings, and up to 60 percent longer service life compared to 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 solutions 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 strain on the grease.
Due to their robust design and high load carrying capacity, spherical roller bearings in Schaeffler’s premium quality X-life rating offer optimum solutions for vibrating screens. The low friction characteristics of the X-life bearings not only withstands 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 member of the X-life spherical roller bearing family are those working as the main shaft bearing in wind energy 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 allows 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 has resulted in improved load distribution, lower contact pressures and a significant reduction in the axial displacement.
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