FAG Spindle Bearings for Higher Performance and Productivity

FAG Spindle Bearings for Higher Performance and Productivity Schaeffler Group Industrial is displaying newly developed solutions for spindle bearings and optimized existing products at EMO 2007. High-speed cylindrical roller bearings permit the combination of high speeds and high spindle load carrying capacity while allowing simple adjacent structures. In this way, they ensure more efficient spindles that offer enhanced productivity. The thermally robust tandem set also contributes to higher load carrying capacity and stability of the bearing support in high-speed machining applications. On the other hand, the optimization of Floating Displacement Lager (FD-Universal) and the greasing of sealed spindle bearings results in time and cost savings as well as enhanced safety. Non-locating bearings With most spindle bearing applications, the use of non-locating bearings is a vital necessity in order to compensate for thermal expansion. The use of cylindrical roller bearings and Floating Displacement bearings (FD bearings) makes it possible to carry out this necessary length compensation within the bearing. Cylindrical roller bearings boast high load carrying capacity with medium speed capacity while FD bearings offer maximum speed capacity with lower load capacity which is sufficient for a wide range of applications. With the development of a high-speed cylindrical roller bearing, FAG has now closed a gap in its product range. High-speed cylindrical roller bearings Thanks to consistent friction minimizing measures, Schaeffler Group Industrial was able to develop a high-speed cylindrical roller bearing with steel rollers that can achieve speed levels that are as much as 80 percent higher than those of conventional cylindrical roller bearings and even surpasses the speeds achieved with hybrid bearings and brass cage. Nevertheless, its load carrying capacity is only slightly lower. The bearing boasts optimized contact geometry and an outer lip riding PEEK cage of considerably less friction than rolling element riding machined brass cages. Due to lower operating temperatures resulting from lower friction, the stress on the lubricant in the rolling contact zone is lower too. This results in longer grease life. Optimization of the existing cylindrical roller bearing range Simultaneously with the development of high-speed cylindrical roller bearings, the existing cylindrical roller bearing range was also refined further. During the process, the maximum achievable speed was increased by approx. 10 percent for standard cylindrical roller bearings with brass cage and by a further 40 percent for bearings with outer lip riding PEEK cage, or by 55 percent compared to the former standard cylindrical roller bearing with brass cage. For hybrid cylindrical roller bearings, the switch over from rolling element riding brass cages to outer lip riding PEEK cages has resulted in a 30-percent speed increase. When using half the number of rollers, hybrid cylindrical roller bearings can almost reach the speed level of Floating Displacement bearings. Floating Displacement bearings The Floating Displacement bearing is the ideal non-locating bearing for maximum speeds if the bearing is not subjected to heavy external loads. Compared to high-speed hybrid cylindrical roller bearings, it offers a much more cost-efficient solution. Another advantage is that it is less sensitive to changes in radial clearance during operation. In the newly developed universal Floating Displacement bearing (FD-Universal), the manufacturing radial clearance of the bearing is now adjusted depending on the bore diameter. As long as a specified tolerance is adhered to for the shaft diameter, the radial clearance will be within the desired, safe zone after assembly. In this way, mounting and stock keeping become much easier. Furthermore it is also possible to mount several Floating Displacement bearings next to each other in order to increase the load carrying capacity. Thermally robust tandem set In main spindles with high radial load carrying capacity, there are often several bearings combined to form tandem or triple sets on the locating bearing end. As all bearings in one set show the same protrusion, they also have the same preload and carry the same loads. During operation, however, differences in temperature due to heat input from the drive rotor will arise, which cause changes in preload. In particular the inner ring is usually warmer than the outer ring, which leads to higher preload in the bearing closer to the motor because the outer bearing is unloaded due to the axial expansion of the shaft. At EMO 2005, FAG presented application-specific optimized (universal) tandem sets for such applications. In these solutions, which are especially optimized for one particular application, the bearing closer to the motor has a defined radial clearance on the outer ring. Due to this characteristic, the outer ring of this higher loaded bearing can yield radially. In the newly developed, thermally robust tandem set, the higher loaded bearing which is closer to the motor also deflects more readily than the outer, less loaded bearing. This, however, is achieved through a well-aimed adjustment of the bearing rigidity. While the universal tandem set carries equal proportions of load at the outer and inner rings at identical temperatures, differences in preload arise under these conditions with the thermally stable tandem set. In the scope of temperature differences between the inner and outer rings typical of motor spindles, however, the preload differences in a thermally stable tandem set are lower than in the universal tandem set. The more even load carrying of both bearings reduces the stress level in the rolling contact zone of the inner bearing. At the same time, the dynamic and static rigidity of the spindle is improved. This results in higher operational reliability, improved spindle performance and, where applicable, better workpiece quality. Optimized grease distribution in sealed bearings When starting up a grease-lubricated spindle, a grease distribution run ensures the optimal distribution of grease in the bearing. The duration of the grease distribution run can be significantly reduced through skilful predistribution of grease. Schaeffler Group Industrial has developed new greasing methods that enable the positioning of grease selectively, close to the points where it is supposed to be after grease distribution. This reduces the grease distribution run period and thus costs too. In addition, the grease distribution run becomes more reliable especially when only low centrifugal forces occur with comparably low maximum speeds, so that it takes longer for the grease to abut the outer ring