SKF轴承选型原则要点.ppt

* * DGBB: The permissible angular misalignment lies between 2 and 10 minutes of arc. SABB: The permissible angular misalignment for open bearings lies between 2.5 - 3 degrees. * A new extended table for the selection of the etac is introduced in the new catalogue. The new table make the selection of a proper eta_c value a lot easier !! * The advantages of back-to-back are: ? The shaft is normally turned / ground which makes it easy to achieve a shoulder which gives a flat, perpendicular support to the bearing inner ring side face. With a standard locking nut a good clamping force can be applied at a minimum of bearing deformation or distortion. ? ? The temperature increase is often lower in back-to-back arrangement compared with face-to-face. The reason for this is that the geometry of the raceway acts as a “pump wheel” throwing excessive grease out from the bearing while bearings arranged in face-to-face will “pump” the grease in between the two bearings thus causing higher internal friction and as a consequence from this higher temperature. Temperature differences of some 20 % have been reported from the market. ? ? Bearings in back-to-back offers high stiffness for bearings exposed to moment loading even if this fact almost never is utilized in pump bearing arrangements. ? An advantage with face-to-face arrangement is: ? ? Bearings arranged in face-to-face are less sensitive to misalignments between shaft and housing. * Types of Rotation ? It is very important to establish the type of rotation, i.e. which ring rotates and which is stationary, as this defines what type of fit is required for each ring. To prevent creep, which can be very damaging to the bearing and the shaft or housing, the rotating ring requires an interference fit, the stationary one a transition or “loose” fit. For vibration applications and out of balance loads, the stationary ring can also require an interference fit. This type of application is referred to as “direction of rotation