Motor fixed end bearing
Fixed-end bearings use radial bearings that can withstand 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 HJ angular 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-sized motors, deep groove ball bearings are more often used as the first choice for fixed-end bearings of the motor.
Deep groove ball bearings are the most commonly used rolling bearings. When deep groove ball bearings are used, 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 load, but when the radial clearance of the bearing is increased, it has the characteristics of angular contact ball bearings, which can bear the combined radial and axial loads; it is not suitable to use thrust balls when the speed is higher. When bearing, it can also be used to bear pure axial load. Compared with other types of bearings with the same specifications and dimensions of deep groove ball bearings, this type of bearing has the advantages of small friction coefficient and high limit speed, but 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 installed on the shaft, within the axial clearance of the bearing, the radial fit between the shaft or the housing can be restricted. In the radial direction, the bearing and the shaft adopt an interference fit, and the bearing and the end cover bearing chamber or housing adopt a small interference fit. The ultimate goal of selecting this 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 between the locating bearing and the associated components should be determined in accordance with the specific conditions of the floating end bearing system. The inner ring of the bearing is limited by the bearing position limit step (shoulder) on the shaft and the bearing retainer ring. The outer ring of the bearing is controlled by the matching tolerance of the bearing and the bearing chamber, the height of the stop 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-drive 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 as the drive end.
When the motor bearing support system is a double fulcrum and dual bearing structure, the drive end is also used as the floating end when the radial load is large. Especially for low-voltage high-power and high-voltage motors, the cylindrical roller bearing at the floating end can meet the radial load requirements. Large load requirements.
The rollers and raceways of cylindrical roller bearings are in line contact or under-line contact. The radial load capacity is large. It is more suitable for bearing heavy loads and impact loads. The inner ring or outer ring can be separated for easy installation and disassembly. This series of bearings has a low coefficient of friction and is suitable for high-speed operating conditions with a limit speed close to that of deep groove ball bearings. The more commonly used N-type and NU-type cylindrical roller bearings 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 housing caused by thermal expansion or installation errors, and can be used as a free end support. However, the bearing has higher requirements for the machining of the shaft or the bearing chamber hole, and the relative deviation of the inner and outer ring axes after the bearing is installed must 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 selection of the bearing.
(1) When the floating end adopts a bearing with separable inner and outer rings, for the two-bearing structure motor, 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 cover of the bearing are axially free of gaps Cooperate.
(2) When non-separable bearings are used at the floating end, that is, the relatively common two ends of small and medium-sized motors are ball bearing structures. In view of the impact on the installation accuracy of the dragging equipment, the drive end is used as the fixed end, and the floating end is inside the bearing. The ring should be limited, and there is an axial gap between the outer ring and the stop of the inner and outer cover of the bearing; at the same time, in order to ensure the axial matching displacement requirement during the operation of the motor, the radial matching between the outer ring of the bearing 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.
Post time: Sep-13-2021