When discussing bearing systems in motor products, it is obviously unscientific to talk about bearings in isolation, especially since the design, processing, installation, and subsequent use of the bearing housing are all crucial factors.
Selection and requirements for bearing housing design
● The fit between the bearing outer race and the bearing inner race should not be excessive, but the clearance should not be too large either. For basic series motors, the standards adopted by many motor manufacturers and the tolerances for the bearing inner race recommended in this article are shown in the table below.
When a bearing is heated during operation, its working clearance will decrease compared to before use. The degree of reduction varies under different temperature conditions, and different materials will also correspond to different reduction amounts.
To prevent the outer ring of the bearing from rotating in the bearing housing (i.e., running out of the bearing), the cumulative axial clearance of the components in the bearing housing should be moved from the outer ring of the bearing to the end cover or bearing sleeve. In other words, the outer ring of the bearing should be locked by the inner and outer covers of the bearing. For explosion-proof motors, this clearance should be less than 0.2 mm.
● The bearing housing should be located as far away from the stator and rotor windings as possible, and good ventilation and heat dissipation are essential. For motors with internal circulation ventilation, if the temperature of one bearing is too high, cooled air should be directed to that bearing first. To improve heat dissipation, when using grease-lubricated bearings, avoid using two bearings at the same end.
● Lubrication-related components at bearing locations should be designed to both hold sufficient grease and allow excess grease to drain away. For example, a sloping "oil slinger" can throw waste grease from the bearing housing into the oil reservoir of the outer cover. For high-speed, high-power electric motors, thin oil lubrication can be used to address bearing overheating.
● Facilitates assembly and disassembly. When designing motor components, efforts should be made to ensure that the bearing is first introduced into the bearing housing before the rear cover enters the frame stop during assembly, so as to avoid damage to the bearing during assembly; when disassembling, space should be left at the bearing inner cover to place disassembly tools.
● Add a temperature monitoring device, but the alarm temperature should be selected according to the location where the temperature sensing element is buried. No matter where it is buried, it should not be close to the maximum allowable temperature of the bearing, such as 95℃ for ordinary bearings.
Other countermeasures to reduce bearing system problems
● The bearing distance should not be too large, otherwise the bearing will be damaged faster due to the increased deflection of the shaft.
● The center height of the motor should be as low as possible. Firstly, a lower center of gravity ensures smoother operation; secondly, it minimizes changes in center height due to thermal expansion after installation and operation. For motors with a center height greater than 400mm, after successful installation and commissioning at room temperature, the center height should rise by 0.1-0.3mm after heating up under load. If the driven equipment cannot rise accordingly, or if the rise is less than this value, the bearings will bear additional forces, inevitably leading to accelerated damage.
● The motor itself should have good rigidity and should not generate or approach resonance during operation.
● The bearing area must be well-sealed. The protection level of the inner and outer covers of the motor bearings must meet the requirements of the actual operating environment.
●For larger motors, measures should be taken to prevent shaft current from causing electro-corrosion and accelerating bearing damage.
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