New rotary table bearings offer increased machining accuracies

Schaeffler's new YRTC and ZKXDF series are available with inside diameters from 580mm up to 1030mm and offer a variety of technical advantages such as reduced friction, increased rigidity and operating speeds, as well as more compact designs. The demand for larger rotary table bearings with reduced friction and increased speed capability is growing. To meet this demand, Schaeffler's new YRTC range of rotary table bearings is available with IDs from 580mm up to 1030mm. The design of the bearings is based on a combination of Schaeffler's YRT and RTC series of rotary table bearings. This provides the basis for extremely dynamic rotary axes for rapid positioning and for form milling using multi-axis simultaneous machining. Operation at continuous speeds, for example, in intermittent turning, is also possible within the operating limits. Compared to traditional combination thrust and radial cylindrical roller bearings, power dissipation is also significantly reduced. As a result of this marked reduction in friction, a significantly increased proportion of the drive torque supplied by the machine tool drive is freed up for axis acceleration – which increases machine productivity. The amount of heat introduced to the machine tool also reduces with less friction, resulting in a reduction in temperature-induced changes in the geometry of the machine, which therefore increases machining accuracy. By using YRTC bearings with reduced friction, the control properties of the rotary axis improve, resulting in more precise geometry transitions when machining shapes and contours. Unique Ball Roller design Schaeffler has also developed a completely new design of rotary table bearing based on the company's innovative Ball Roller design concept. This innovation is based on a double row angular contact, thrust ball roller bearing in an 'O' arrangement that uses new assembly methods and a unique rolling element. For the Ball Rollers, all parts of a conventional ball that are not under load are removed. This means that around 15 per cent of the ball diameter is cut away from both sides. The result is a ball that is flattened on both sides and which is approximately 30 per cent narrower (and therefore lighter) than a conventional fully spherical alternative. Ball roller elements offer all the axial load handling capabilities of fully spherical balls, but allow overall bearing width and mass to be decreased by 15 to 20 per cent, as well as reducing friction. This not only saves valuable design space, but means that the 'slim' shape of the ball roller, in combination with new assembly methods, enables the number of rolling elements to be increased. This in turn enables the filling capacity of the bearing to be increased by up to 90%. Using more rolling elements in the same design space results in higher load ratings and longer service life, providing opportunities to downsize products and assemblies. The new ZKXDF rotary table bearings are currently being field tested by manufacturers of machining centres. These new bearings enable the design of more compact, higher performance rotary table supports in the high speed range, with bore diameters available from 580mm up to 1030mm.