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MDA Technologies 2/2014

MDA Technologies 2/2014

Machine elements

Machine elements High-speed axial bearings for high performance and accuracy For high requirements with regard to rigidity and load carrying capacity, the bearing supports of main spindles are often designed as a combination of double-row cylindrical roller bearings and thrust bearings. In addition to high rigidity, thrust and radial bearings are separated in this bearing variation, which has the advantage that the kinematics in the bearing are not affected by the load since the bearings do not have to support any tilting moments. This situation has led to a new development – highspeed FAG axial bearings of series BAX. The use of high-speed FAG axial bearings of series BAX now enables speed parameters to be realized on main spindles with a combination of axial bearings without radial retention and cylindrical roller bearings that were previously only achievable with spindle bearings. This bearing combination offers the separation of the axial and radial loads in the bearing support. Since no tilting moments must be supported, the kinematic characteristics under combined load are not impaired. This makes the bearing support particularly robust. The user benefits from the high machining accuracy due to the high rigidity. The high load carrying capacity and good speed capacity enable good machining performance and high productivity. The new series BAX is interchangeable with double-row angular contact thrust ball bearings in terms of their dimensions, and it combines high axial load carrying capacity and rigidity with the suitability for high speeds of main spindle bearings. In combination with state-of-the-art, high-speed cylindrical roller bearings, high-speed spindles with high axial and radial rigidity and load carrying capacity can be implemented. These spindles are accurate, robust and permit a high cutting capacity. Interchangeable Whenever high rigidity and load carrying capacity are important for spindles, two-row angular contact thrust ball bearings are frequently combined with two-row cylindrical roller bearings. The dimensions of BAX bearings are compatible with type 2344 double-direction angular contact thrust ball bearings. Figure 1 shows that they can be replaced with only minor changes to the add-on parts and without changing the shaft and the housing. BAX bearings are in a loose radial location, identical to double-direction angular contact thrust ball bearings, and in this way only support axial loads. High speeds To fulfill high rigidity and load carrying capacity requirements on the operating side, the main spindle bearing support frequently comprises the combination of double row cylindrical roller bearings and axial bearings. This type of bearing support also has the advantage that axial and radial bearings are separated and the kinematics in the bearing are not disrupted by the loads. Low speeds were the disadvantage of this solution. The double row axial angular contact ball bearings available until now were only suitable for moderate speeds due to their contact angle of 60°. However, the contact angle of BAX bearings is 30° and they are also available with a contact angle of 40° for higher axial rigidity. BAX bearings are also equipped with a phenolic fabric cage for low friction. This means that speeds can be increased by 20% with oil-air lubrication and by 30% with grease lubrication (figure 2). Further increases in speed are possible by changing to single row cylindrical roller bearings and BAX bearings in hybrid design, i.e. with ceramic rolling elements. Speed parameters of up to 1.35 million mm/min. can be achieved with a contact angle of 30° and oil-air lubrication. High rigidity A comparison of basic rigidities also shows that BAX bearings have an advantage. Bearing support variants with double row cylindrical roller bearings and double row axial angular contact ball bearings have a radial 20 MDA Technologies 2/2014

Machine elements 01 BAX bearings are an alternative to double direction axial angular contact ball bearings rigidity around 2.5 times as high as that with four conventional spindle bearings. In axial rigidity, the advantage is around 60%. The combination of cylindrical roller bearings and high-speed axial BAX bearings with a contact angle of 40° also achieves this high level of radial rigidity. The axial rigidity is at the level of the bearing support variant with four spindle bearings. In terms of maximum speed, however, the combination with BAX bearings is higher than that with double row axial angular contact ball bearings (figure 3). BAX bearings of design 2344 are dimensionally compatible with double direction axial angular contact ball bearings. Substitution is possible with only slight changes to adjacent components and without changes to the shaft and housing. Accuracy class P4S results in superior smooth running. The possible bore diameters are between 50 and 200 mm. Adjustable 02 BAX bearing: Comparison of speeds BAX bearings are equipped with a cage made from compression molded material. This results in low cage friction and permits high speeds. The P4S accuracy class leads to superior smoothness of operation. The possible bore diameters range from 50 to 200 m. For greater axial rigidity, both a 30º and a 40º pressure angle are available. BAX bearings are generally offered as ready-to-install sets in DB arrangement (DB = Duplex Backto-Back) and in preload categories L (=light) and M (=medium). In addition to the steel balls design, the bearings are also offered with ceramic balls to achieve specific speed parameters. With a pressure angle of 30° and oil-air lubrication, speed parameters of up to 1.35 million mm/min can be achieved. www.schaeffler.com 03 BAX bearing: Comparison of rigidity About Company name: Schaeffler Technologies Brands: INA, LuK und FAG Headquarters: : Herzogenaurach, Germany Turnover: € 11,1 bn (2012) Employees: over 76 000 worldwide Products: Rolling bearing and plain bearing solutions, linear and direct drive technology, as well as high-precision products for the automotive industry MDA Technologies 2/2014 21

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