The Schaeffler Group has developed a new bearing concept, the tube roller bearing, that prevents slippage in applications with low radial loads, such as wind turbine gearboxes. By replacing a standard roller set on a conventional cylindrical roller bearing with tube rollers with a slightly larger diameter, the FAG tube roller bearing prevents bearing slippage, which, if undetected, could result in bearing damage and possible bearing failure.
Currently the new bearings are undergoing field and endurance tests with Schaeffler customers in various industrial applications, including hot rolling mills, wind turbine gearboxes and paper mills.
In conventional cylindrical roller bearings, under low-load conditions, the rolling elements do not roll correctly but start to slip and the roller set and cage rotate, in some cases at lower than nominal speed. This can lead to damage. Under high loads, the rolling elements run correctly again and the cage rotates at its nominal speed.
On display at The Schaeffler Group's stand at the 2007 Hanover Fair, the new tube roller concept was demonstrated to visitors using a standard cylindrical roller bearing with brass housing. The roller set consisted of 12 rolling elements, nine of which were standard solid rolling elements, with the other three replaced with the new tube rollers, equally spaced around the bearing raceway. These tube rollers have a slightly larger diameter (around one micron) than the standard rollers and are also bored through the centre, which reduces stiffness during operation and prevents peak loads.
Preload and support
The larger diameter of the three tube rollers produces a slight preload in the bearing. Under very low load conditions, the tube rollers therefore support the load and drive the cage. Slippage of the roller set and any resulting damage is therefore avoided.
If the bearing is subjected to higher radial loads, the three tube rollers undergo elastic deflection and the forces are spread onto the rolling elements in the load zone.
The tube roller bearing is a design concept that is claimed to be unique to the Schaeffler Group. Compared with axially preloaded bearings, the new bearing also enables simplified designs, as well as easier assembly and installation. The bearings are also interchangeable with standard cylindrical roller bearings.