Selection and matching of fixed-end and floating-end bearings of motors

Selection and matching of fixed-end and floating-end bearings of motors
Fixed-end bearings use radial bearings capable of withstanding combined (radial and axial) loads. These include: deep groove ball bearings, double row or matched single row angular contact ball bearings, self-aligning ball bearings, spherical roller bearings, mating tapered roller bearings, cylindrical roller bearings of the NUP type, or cylindrical roller bearings of the NJ type with HJ angular rings.

For the selection of the motor bearing support fixed end (referred to as motor fixed end), the following factors should be considered:

(1) Precision control requirements of the towed equipment;

(2) The nature of the load to be dragged by the motor;

(3) The bearing or bearing combination must be able to withstand a certain axial force.

Combining the above three design elements, in small and medium-sized motors, deep groove ball bearings are more often used as the first choice for motor fixed end bearings.
Deep groove ball bearings are the most commonly used rolling bearings. When deep groove ball bearings are applied, the structure of the motor bearing support system is very simple and easy to maintain and repair. Deep groove ball bearings are mainly used to withstand radial loads, but when increasing the radial clearance of the bearing, with the characteristics of angular contact ball bearings, can withstand radial and axial joint loads; high speed and should not be used when the thrust ball bearings, but also can be used to withstand pure axial loads. With deep groove ball bearing specifications of the same size of other types of bearings, such bearings have the advantage of small coefficient of friction, high limiting speed, the disadvantage of impact resistance, not suitable for bearing heavy loads.
Deep groove ball bearings mounted on the shaft, in the bearing axial clearance range, can limit the shaft or shell radial fit in both directions. In the radial direction, the bearing and the shaft with the interference fit, bearing and the end cover bearing chamber or shell with a small interference fit, choose this kind of fit the ultimate goal is to ensure that in the process of motor operation, the working clearance of the bearing is zero or slightly negative, so that the bearing running performance is better. In the axial direction, positioning bearings and associated parts of the axial fit, it should be combined with the specific conditions of the floating end bearing system to determine. The inner ring of the bearing is limited by the bearing position limit step (shoulder) on the shaft and the bearing retaining ring, while the outer ring of the bearing is controlled by the fitting tolerance of the bearing and the bearing chamber, the height of the bearing inner and outer cover stops and the length of the bearing chamber.
Motor Floating End Bearings

Motor floating end is also called free end, is relative to the fixed end; in general, the floating end is selected in the non-driving end, but in the case of motor load requirements are high, and the axial fit dimension requirement with the load equipment is not very high, the floating end will be selected in the driving end.

Motor bearing support system for double pivot, double bearing structure, in the radial load requirements, also will be the driving end as the floating end, especially for low-voltage high-power and high-pressure motors, the floating end of the cylindrical roller bearings can meet the requirements of the larger radial load.
Cylindrical roller bearings with roller and raceway for line contact or repair under the line contact, radial bearing capacity, more suitable for bearing heavy loads and shock loads, the inner ring or outer ring can be separated, easy to install and dismantle. This series of bearings have small friction coefficient, suitable for high speed, limit speed close to the deep groove ball bearing operating conditions. N-type and NU-type cylindrical roller bearings commonly used in motors can move axially between the inner and outer rings of the bearings, and can adapt to changes in the relative position of the shaft and the shell caused by thermal expansion or mounting errors, and can be used as free-end bearings. However, the bearing on the shaft or bearing chamber hole processing requirements are higher, bearing installation after the inner and outer ring axis of the relative skew of the situation should be strictly controlled, so as not to cause contact stress concentration.

Relative to the fixed-end bearing, in order to meet the requirements of the axial displacement of the rotor part of the motor during operation, in accordance with the different bearing selection, the axial clearance requirements of the outer ring of the bearing and the inner and outer bearing cover are different.

(1) When the floating end adopts bearings with separable inner and outer rings, for two-bearing structure motors, the fixed end is selected at the non-driving end; axial clearance-free fits are adopted between the outer rings of the fixed-end and floating-end bearings and the inner and outer covers of the bearings.

(2) When the floating end of the non-separable bearings, that is, small and medium-sized motors are more common at both ends of the ball bearing structure, in view of the impact on the installation accuracy of the dragging equipment, the driving end of the fixed end of the driving end of the bearing should be limited, the floating end of the bearing inner ring and the bearing inner and outer cover of the axial clearance between the stops; at the same time, in order to ensure that the motor operation of the axial fit requirements, the radial bearing outer ring and the bearing chamber fit It is not easy to be too tight.

The actual bearing configuration should be matched with the operating conditions of the motor, including the motor bearing selection for clearance, heat resistance, precision and other specific parameters, as well as the radial fit of the bearing and the bearing chamber.

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