Motor fixed end bearing
Fixed end bearings use radial bearings capable of carrying 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, matched tapered roller bearings, NUP type cylindrical roller bearings or with HJ angle rings NJ type cylindrical roller bearings.
For the selection of the fixed end of the motor bearing support (referred to as the fixed end of the motor), the following factors should be considered:
(1) The precision control requirements of the dragged equipment;
(2) The nature of the load driven 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 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 using deep groove ball bearings, the structure of the motor bearing support system is very simple, and the maintenance is also convenient. Deep groove ball bearings are mainly used to bear radial loads, but when the radial clearance of the bearing is increased, it has the characteristics of angular contact ball bearings and can bear combined radial and axial loads; it is not suitable to use thrust balls at high speeds. Bearings can also be used to withstand pure axial loads. Compared with other types of bearings with the same specifications and dimensions as deep groove ball bearings, this type of bearing has the advantages of small friction coefficient and high limit speed, and the disadvantage is that it is not resistant to impact and is not suitable for bearing heavy loads.
After the deep groove ball bearing is mounted on the shaft, within the axial clearance range of the bearing, the radial fit of the shaft or the housing in two directions can be limited. In the radial direction, the bearing and the shaft adopt an interference fit, and the bearing and the end cover bearing chamber or shell adopt a small interference fit. The ultimate goal of selecting this kind of fit is to ensure that the working clearance of the bearing is zero or slightly during the operation of the motor. Negative, so the running performance of the bearing is better. In the axial direction, the axial fit of the locating bearing and the associated components should be determined in combination with the specific conditions of the floating end bearing system. The inner ring of the bearing is limited by the bearing limit step (shoulder) on the shaft and the bearing retaining ring, and the outer ring of the bearing is controlled by the tolerance of the bearing and the bearing chamber, the height of the inner and outer cover of the bearing and the length of the bearing chamber.
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 the motor load requirements are high, and the axial matching size requirements with the load equipment are not very high In this case, the floating end will be selected at the drive end.
When the motor bearing support system is a double fulcrum and double bearing structure, when the radial load requirement is large, the drive end is also used as the floating end, especially for low-voltage high-power and high-voltage motors, the cylindrical roller bearing on the floating end can meet the radial heavy load requirements.
The roller and raceway of cylindrical roller bearing are in line contact or trimmed line contact, and the radial bearing capacity is large, which is more suitable for bearing heavy load and impact load. This series of bearings has a small friction coefficient and is suitable for operating conditions with high speed and limit speed close to deep groove ball bearings. N-type and NU-type cylindrical roller bearings, which are commonly used in motors, can move axially between the inner and outer rings of the bearing, which can adapt to changes in the relative position of the shaft and the shell caused by thermal expansion or installation errors, and can be used as free end support. However, the bearing has high processing requirements for the shaft or bearing chamber hole, and the relative deflection of the inner and outer ring axes after the bearing is installed should be strictly controlled to avoid contact stress concentration.
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 selection.
(1) When the floating end adopts a bearing with separable inner and outer rings, for a motor with a two-bearing structure, the fixed end is selected at the non-driving end; the outer ring of the fixed end and the floating end bearing and the inner and outer covers of the bearing adopt no axial clearance. Cooperate.
(2) When the floating end adopts an inseparable bearing, that is, the two ends of the small and medium-sized motors are relatively common ball bearing structures. In view of the influence on the installation accuracy of the dragging equipment, the driving end is used as the fixed end, and the floating end bearing is used. The ring should be limited, and there is an axial gap between the outer ring and the inner and outer cover of the bearing; at the same time, in order to ensure the axial matching displacement requirements during the operation of the motor, the radial cooperation between the bearing outer ring and the bearing chamber is not easy to be too tight.
The actual bearing configuration should match the operating conditions of the motor, including specific parameters such as clearance, heat resistance, and accuracy in the selection of motor bearings, as well as the radial matching relationship between the bearing and the bearing chamber.