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Selection And Matching Of Motor Fixed End Bearing And Floating End Bearing

Selection And Matching Of Motor Fixed End Bearing And Floating End Bearing

2021-01-15

Motor fixed end bearing

Fixed-end bearings use radial bearings capable of bearing combined (radial and axial) loads.These bearings include: deep groove ball bearings, double row or paired single row angular contact ball bearings, self-aligning ball bearings, spherical roller bearings, combined tapered roller bearings, NUP type cylindrical roller bearings or NJ type cylindrical roller bearings with HJ Angle ring.

For the selection of motor bearing support fixed end (motor fixed end for short), the following factors should be considered:

(1) Accuracy control requirements of the dragged equipment;

(2) the load nature of motor drive;

(3) Bearings or bearing combinations must be able to withstand a certain axial force.

Combined with the above three aspects of design elements, deep groove ball bearings are more often used as the first choice for fixed end bearings of small and medium-sized motors.

Deep groove ball bearings are the most commonly used rolling bearings.When deep groove ball bearings are used, the structure of motor bearing support system is very simple and easy to maintain.Deep groove ball bearing is mainly used to bear radial load, but when the radial clearance of the bearing is increased, it has the characteristics of angular contact ball bearing and can bear radial and axial combined load.When the speed is high and the thrust ball bearing is not suitable, it can also be used to bear pure axial load.Compared with other types of bearings with the same specification and size as deep groove ball bearings, this kind of bearings have the advantages of small friction coefficient and high limit speed, and the disadvantages are not impact resistant and not suitable for bearing heavy loads.

When the deep groove ball bearing is mounted on the shaft, the radial fit in the two directions of the shaft or housing can be limited within the axial clearance range of the bearing.In the radial direction, interference fit is used between bearing and shaft, and small interference fit is used between bearing and end cover bearing chamber or shell. The ultimate goal of choosing such fit is to ensure that the working clearance of the bearing is zero or slightly negative during the operation of the motor, so that the running performance of the bearing is better.In the axial direction, the axial match between the positioning bearing and the associated parts should be determined in combination with the specific situation of the floating end bearing system.The bearing inner ring is limited by the bearing position limit step (shaft shoulder) and the bearing retaining ring on the shaft, and the bearing outer ring is controlled by the matching tolerance between the bearing and the bearing chamber, the height of the inner and outer cover of the bearing and the length of the bearing chamber.

Motor floating end bearing

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

When the motor bearing support system is double-fulcrum and double-bearing structure, when the radial load requirements are large, the driving end is also used as the floating end. Especially for low-voltage high-power and high-voltage motors, the cylindrical roller bearings at the floating end can meet the requirements of large radial load.

Cylindrical roller bearing roller and raceway for line contact or repair line contact, radial bearing capacity is large, more suitable for bearing heavy load and impact load, the inner or outer ring can be separated, easy to install and disassemble.This series of bearings have small friction coefficient and are suitable for high speed and extreme speed close to deep groove ball bearings.Type N and NU cylindrical roller bearings are commonly used in the motor. The inner and outer rings of the bearings can be moved axially. They can adapt to the change of the relative position between the shaft and the shell caused by thermal expansion or installation error, and can be used as free end support.However, the bearing has higher processing requirements for shaft or bearing chamber hole, and the relative deviation of inner and outer ring axis after bearing installation should be strictly controlled to avoid concentration of contact stress.

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

(1) When the floating end adopts a bearing with separable inner and outer rings, the fixed end is selected at the non-driving end for the two-bearing structure motor;There is no clearance between the outer ring of the fixed end and the floating end bearing and the inner and outer cover of the bearing.

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

The actual bearing configuration should be matched with the operating conditions of the motor, including specific parameters such as clearance, heat resistance, precision, and the radial matching relationship between the bearing and the bearing chamber in the selection of the motor bearing.


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