With the RS (robust and fast) spindle bearing series and TR (thermally robust) cylindrical roller bearing series from FAG, Schaeffler delivers a combination of high load carrying capacity and large power reserves for increasing speed. At the same time, the optimized friction behavior of the internal design also reduces the frictional energy of the bearing support. This becomes especially apparent when the spindle turns at high speed for a long time. The option of lubricating the bearing support with grease even at high speeds increases the operational reliability of the spindle and reduces the costs due to the omission of the compressed air used to supply the bearings with lubricant.
RS bearings for the working side of the spindle: Robust and fast
On the working side of a spindle, axial and radial forces from the cutting process have to be supported and the tool precisely guided. Spindles that turn at high speed generally employ high-precision angular contact ball bearings for this purpose. FAG’s new RS-series bearings feature an internal design with optimized friction behavior and are equipped with large rolling elements with a contact angle of 20 degrees. These bearings have a high load carrying capacity and are suitable for very high speeds. This allows the frictional torque of the bearing support to be significantly reduced on the working side. The large-ball bearings in the RS series allow the frictional torque to be reduced to the same level as that of the small-ball bearings (HS, HC) with both oil air lubrication and grease lubrication. The large-ball bearings have a significantly higher load carrying capacity than their small-ball counterparts.
The higher speeds of which RS bearings are capable is another way in which their use can help reduce operating costs and energy consumption, as this makes it possible in many cases to forego the use of oil air lubrication with spindles that turn at high speed. At a speed of 20,000 rpm and under identical operating conditions, the frictional torque with grease lubrication is around 14% lower than that which occurs with oil air lubrication. In addition to the lower power consumption, the operating costs are also reduced because the use of compressed air to supply the bearing with lubricant is omitted. A further advantage is the increased operational reliability of the spindle, as a failure of the lubricant supply is not possible and there is no risk of contamination from the air entering the bearing.
TR bearings for the non-locating bearing side of the spindle: Thermally robust
On the non-locating bearing side, the use of a cylindrical roller bearing offers significant advantages compared to other solutions such as angular contact ball bearings that are adjusted by means of springs. It allows a simple adjacent construction to be used and also ensures a reliable non-locating bearing function, as this takes place directly and without constraining forces in the bearing and does not have to be implemented using the housing fit. It also provides high radial rigidity. On the other hand, cylindrical roller bearings generally have a higher level of friction than comparable angular contact ball bearings, which manifests itself in the form of a lower limiting speed.
The friction in the rolling contact is principally affected by the preload. In cylindrical roller bearings, this is dependent on the speed and the temperature difference between the inner and outer ring. Centrifugal forces and the higher temperature of the inner ring cause it to expand to a greater extent than the outer ring during operation. This means that the radial preload of a cylindrical roller bearing increases significantly during operation compared to the setting made during installation.
FAG cylindrical roller bearings in the TR version have a flexible outer ring that significantly reduces the preload increase during operation. This means that the bearing is insensitive to fluctuating temperature differences and displays significantly lower frictional energy. The internal design, which features optimized friction behavior and a PEEK cage that is guided on one side of the outer ring, produces an optimized distribution of the lubricant and is suitable for high speeds.
The use of ceramic rollers as opposed to steel rollers also reduces the weight of the rolling elements and thus also the friction due to the lower centrifugal forces. What is more, the ceramic material’s lower coefficient of thermal expansion also means that the rise in the radial preload in operation is reduced, which leads to a further reduction of bearing friction. Because ceramic material does not tend to adhere to steel, the pairing of steel rings and ceramic rolling elements in hybrid bearings is tribologically more favorable than that of bearings with steel rolling elements. This leads to lower temperatures in the rolling contact and to reduced strain on the lubricant, and thus makes these bearings more suitable for high speeds while extending the operating life of the grease.
The use of flexible outer rings to reduce the preload that occurs during operation is also worthwhile in hybrid cylindrical roller bearings. Halving the number of rollers is another measure that can be taken to reduce friction in cylindrical roller bearings. This reduces the bearing’s load carrying capacity, but this still remains fully sufficient for the function it performs on the non-locating bearing side. The radial rigidity is also reduced; at the same time, however, the friction is reduced to 53% compared to hybrid cylindrical roller bearings with the full number of rollers.
Contact:
Martin Adelhardt
Schaeffler AG
Vice President Communications
Schaeffler Industrial
Georg-Schäfer-Strasse 30
97421 Schweinfurt
Germany
Tel. +49 9721 91-3400
Fax +49 9721 91-3375
Email: [email protected]
Johanna Katzenberger
Schaeffler Technologies AG & Co. KG
Communications
Schaeffler Industrial
Georg-Schäfer-Strasse 30
97421 Schweinfurt
Germany
Tel. +49 9721 91-3873
Fax +49 9721 91-3375
Email: [email protected]
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