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The following issues need to be considered in bearing design

wallpapers Tech 2020-05-27
The following issues need to be considered in bearing design:
· Dimensions · Load size direction · Rotation speed · Fixed speed, variable speed, high speed · Shaft and bearing seat materials · Load drive mode · Motor installation mode · Noise requirements · Temperature · Required bearing life · Lubrication · Maintenance · Status monitoring
 
Bearing design mainly includes two parts: bearing selection and bearing structure design. Bearing selection, mechanical design manuals and bearing manuals of major manufacturers all have detailed methods. The design of the bearing structure is very different for different types of motors. The bearing is also a vulnerable part. The failure of the mechanical part of the motor is mostly concentrated at the bearing. For the time being, there is no ability to fully elaborate the design of the motor bearing structure, but for the motor using rolling bearings, the following points can be achieved in the design of the bearing structure to improve the reliability of the safe operation of the motor!
 
(1) Do not squeeze the bearing
The balls or rollers can rotate freely in the raceway because they have clearance between the bearing and the outer sleeve. If the bearing sleeve is squeezed, the clearance will become smaller, because the value of the bearing clearance is very small, so it is very sensitive to the change of the clearance. Therefore, the bearing is most afraid of being squeezed. Among the many causes of bearing damage, extrusion ranks first.
 
(2) Do not overheat the bearing
If the bearing is not overheated, in addition to good heat dissipation at the bearing and reducing its own heat, it must also be kept away from the heat source-stator and rotor windings.
 
①Improve the ventilation and heat dissipation at the bearing
Ventilation and heat dissipation structure and path should consider the cooling of the bearing; the motor with internal circulation ventilation should make the internal circulation air flow cooled by heat exchange give priority to the bearings blown to the shaft extension end; the parts matching the bearing should be added as much as possible Radiating ribs; when the installation size allows, the airflow of the external air path can be blown to the bearing cover of the shaft extension end by the windshield before escaping to the surroundings.
 
② Try not to use the "three bearing" structure, the "three bearing" structure has two disadvantages: easy to heat; inconvenient to disassemble. Therefore, try not to use it.
 
③Quality, brand and filling amount of grease
a. Use high-quality products when choosing grease, not too expensive. Otherwise it will be lost due to small (not much applied to the bearing).
b. The grade of grease must be capable of the motor speed and operating environment.
c. The amount of fat should be appropriate.
④Other
a. When the tension of the pulley is too large, it should be adjusted to a suitable state;
b. If the bearing clearance is small, replace the large clearance bearing if necessary;
c. Strengthen the monitoring, embed the thermosensitive element in the hot part of the bearing room, and use the relay protection system to control the temperature at a certain value (preferably not exceeding 70 ℃ ~ 75 ℃).
d. Squeezing and stiffness of the bearing is also a hidden danger of fever and should be eliminated as soon as possible.
 
(3) Don't be uncomfortable
To ensure that the bearings are not stiff in use, the following 3 points should be noted (where ① and ③ are closely related to processing):
① The coaxiality of the parts related to the bearing must ensure that after the motor is assembled, the bearings at both ends must be on the same axis. This requires the rotor or shaft, end cover, bearing sleeve, and machine base to be carefully processed, and the coaxiality must be guaranteed. Among them, the bearing sleeve part is focused on ensuring the coaxiality, and it is better not to use it. Because when it is present, the bearing is first installed in the bearing sleeve, and then the bearing sleeve is inserted into the end cover. An extra diametrically matched dimensional chain is obviously not as good as the bearing directly inserted into the end cover to ensure the coaxiality.
② Bearing distance l should not be too large.
L try to follow L <10d, where, d-bearing inner diameter mm.
If the above formula cannot be guaranteed during design, try to make l smaller. At the same time take some remedial measures. Such as: improve the rotor stiffness (the iron core and the shaft adopt a heat sleeve); improve the dynamic balance accuracy.
③Do not deform the base during use
The larger cast iron frame and steel plate welding frame must be in place. Especially the welding base with asymmetric shape and relatively "thin" structure must not be ambiguous in terms of timeliness, otherwise there will be endless troubles.
 
(4) Don't "do research"
"Dry grind" means no grease (oil) in the bearing raceway. When the motor is shipped from the factory or reassembled after repair, it is more "generous" when refueling, and dare not idle the bearing. Although there are some accidental reasons, such as on-site workers failing to add grease in time, causing bearing dry research, the main reasons are the following two.
 
①Grease grade can not meet the requirements
Grease is sensitive to speed and temperature. Different grades of grease should be selected according to different usage conditions, and there is almost no "universal" grease. The five kinds of greases selected by Germany FAG company according to different temperatures, speeds, and load types are used on different motors, see the following table (grease grades and scope of application):
②The bearing structure fails to contain grease
 
 
 
(5) Don't be polluted
The following measures can be taken to prevent pollution
① Dust must not be allowed to enter the grease. Except for dust explosion-proof and submersible motors, most of the protection grades of domestic motors are IP44 and IP54. The latter are allowed to be used in dusty places. For the protection of the bearing part.

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