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SKF Motor Bearing Configuration

Source:  skf bearing  Time:  2020-06-24

Bearings are the key components that support the normal operation of the motor. In addition to the manufacturing process control, the design and configuration of the motor bearings are very important. For example, different bearing configurations should be used for vertical motors and horizontal motors, and motors with different speed requirements should also be selected for different motors. Bearing.


1. Configuration of horizontal motor bearings


   A ball bearing and a column bearing should be used at both ends of the horizontal motor. At present, domestic two-pole small and medium-sized motors mostly use two ball bearings, although some manufacturers have adjusted the tolerance zone of the bearing inner diameter to the direction of the clearance fit, in order to alleviate the disadvantages of the balls squeezed after the bearing heats up. However, because the expansion coefficient of the bearing casing is larger than that of the cast iron parts that bear the bearing chamber-the end cover or the bearing sleeve, and the temperature at the bearing casing is also higher, the bearing casing can be axially in the bearing chamber at room temperature. Sliding a little bit, but the bearing may not be able to move when heated during operation. This is the main reason for the short bearing life and easy heating when using two ball bearings. After the temperature rise test, the motor using two ball bearings is shut down to measure the temperature rise. Sometimes the motor's bearings are burned out after the second drive. The reason is that the clearance of the ball bearings cannot bear the thermal expansion and contraction of the rotor. It can't creep in the bearing room, which causes the balls to bear large axial force.


   If you choose a ball bearing and a column bearing, the above problems can be avoided. A better motor factory in the same company changed the two-pole high-voltage motor of the H560 frame size from two ball bearings to one ball bearing and one column bearing. Except for replacing the bearings according to the regular maintenance cycle, no faults have occurred during normal operation. And the temperature measured at the bearing is only 20°C. This is the first successful case in China where the traditional use of two ball bearings in a two-pole motor has been changed to one ball bearing and one column bearing, and it has been gradually promoted on explosion-proof motors.


   In order to solve the problem of extreme speed heating and noise after replacing the ball bearing with a cylindrical bearing, a light series of cylindrical bearings can be used and placed on the end of the outer fan. The cooling condition is good, and the bearing noise can also be submerged by the fan noise. If the 2-pole motor with higher power has a larger bearing model and the light series of cylindrical bearings is also difficult to meet the limit speed requirements, the bearing grease can also be changed to thin oil.
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2. Configuration of vertical motor bearings


   When the vertical motor is used to drive the drum belt pump in the petrochemical system, due to the instantaneous upward axial force at the start of the multi-stage drum belt pump, plus the transportation requirements, and the bearing belt in order to eliminate the thermal expansion of the rotor For the damage caused by the vertical barrel with a pump motor (both 2 or 4 poles), the upper bearing of the motor should use two pairs of single-row radial thrust ball bearings, and the lower bearing uses cylindrical bearings. Series is appropriate. To prevent damage to the thrust ball bearing, the two bearing pairs should have a pre-applied axial force on the bearing jacket. The magnitude of its force is to ensure that during transportation and starting, the bearing will not be damaged due to the reverse axial force from the shaft extension end to the non-load end.
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3. Selection of bearing specifications and models


   2-pole motors should use light series bearings as much as possible; motors with 4 or more poles and non-positive and reverse rotation motors should choose series bearings; positive and reverse low-speed motors should choose heavy series bearings. A ball bearing and a column bearing should be selected for light, medium and heavy, and the ball bearing should be placed on the shaft extension end of the 2-pole motor.


   In recent years, some motor manufacturers have selected large clearance ball bearings on 2-pole motors that use two ball bearings. This is also a measure to alleviate bearing damage caused by the reduction of clearance due to bearing heat during operation. However, the mechanical noise of large clearance bearings should also increase. If one ball bearing and one column bearing are selected, the proper selection of the tolerance of the bearing chamber can also eliminate the above-mentioned disadvantages.

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