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What factors should different machines consider when choosing bearings?

wallpapers Tech 2020-05-26
Different types of bearings have different characteristics, which can be applied to various machines' use cases. When selecting a bearing type, the following factors should generally be considered. In general: thrust bearings and angular contact bearings are used when bearing thrust loads, ball bearings are usually used for high-speed applications, and roller bearings are used when carrying heavy radial loads.
What factors should different machines consider when choosing bearings?
 
1. The space and position of the machine occupied by the bearing
In mechanical design, generally determine the size of the shaft, and then select the rolling bearing according to the size of the shaft. Ball bearings are usually used for small shafts, and roller bearings are used for large beams. However, when the bearing is limited in the diameter direction of the machine, needle roller bearings, extra-light, and ultra-light series ball or roller bearings are used; when the axial position of the bearing is limited in the machine, narrow or special Narrow series of the ball or roller bearings.
 
2. The size, direction, and nature of the load on the bearing
A load is the most critical factor in choosing bearings. Roller bearings are used to bear heavy loads, ball bearings are used to carry light or medium burdens, and bearings made of carburized steel or bainite hardened can withstand shock and vibration loads.
In the direction of the load, when bearing pure radial loads, deep groove ball bearings, cylindrical roller bearings or needle roller bearings can be selected. When taking a small absolute axial load, a thrust ball bearing can be used; when bearing a large pure axial load, a thrust roller bearing can be used. When the bearing carries combined radial and axial loads, angular contact ball bearings or tapered roller bearings are generally used. For cantilever support structures, tapered roller bearings or angular contact ball bearings are often used and are used in pairs.
 
3. Self-aligning performance of bearings
When the centerline of the shaft is different from the centerline of the bearing housing, there is an angular error or the rigidity of the cylinder is small due to the considerable distance between the two supports of the beam, and it is easy to bend or tilt under force, you can choose a good adjustment Heart ball or spherical roller bearings, and outer ball bearings. This type of bearing can maintain regular operation when the shaft is slightly inclined or bent.
 
4. The rigidity of the bearing
The stiffness of the bearing refers to the amount of force required for the taking to deform per unit. The elastic deformation of rolling bearings is minimal, which can be ignored in most machines, but in some devices, bearing rigidity is an essential factor. Generally, cylindrical and tapered roller bearings should be used. Because these two types of bearings are under point load, their rolling bodies and raceways are in point contact, and their rigidity is reduced.
Various types of bearings can also be pre-tightened to increase the support rigidity. For angular contact ball bearings and tapered roller bearings, to prevent the vibration of the shaft and increase the support rigidity, a specific axial force is often applied in advance during installation to make them compact.
 
5. Speed of bearing
Each bearing model has its limit speed, which is determined by physical characteristics such as size, type, and structure. The limit speed refers to the maximum working speed of the bearing (usually r ∕ min). As a result, the bearing temperature rises, the lubricant dries up, and even the bearing gets stuck.
The speed range required in the application occasion helps to determine what type of bearing to use. D is the bearing size, which usually refers to the pitch circle diameter of the bearing. When selecting a bearing, use the average value of the bearing inner diameter and outer diameter, in mm. Multiply the pitch circle diameter D by the shaft rotation speed (unit r / min) to obtain a limiting speed factor (DN). DN is very important when selecting the bearing type and size. Most bearing manufacturers' product catalogs provide the limit speed value of their products. The practice has proved that it is better to work under the condition of a 90% lower limit speed.
 
6. Bearing travel and axial displacement
Typically, a shaft is supported by two bearings separated by a certain distance. To adapt to the different degrees of thermal expansion of the shaft and the casing, one bearing should be fixed in the axial direction during installation, and the other bearing should be able to swim on the shaft (i.e., floating support) to prevent the shaft from expanding or contracting Stuck phenomenon caused. Traveling bearings usually use cylindrical roller bearings (formerly 2000 and 32000) and needle roller bearings with no ribs in the inner ring or outer ring. This is mainly because the internal structure of such bearings allows the shaft and housing to have proper axial displacement. At this time, the inner ring and the shaft, the outer ring and the hole of the house can be tightly matched. When non-separable bearings are used for swimming support, such as deep groove ball bearings and spherical roller bearings, the outer ring must be allowed to fit the outer shell hole, or the inner circle and shaft should be loosely fitted to make it axially Free to swim. Tapered roller bearings, spherical roller bearings, and deep groove ball bearings are basically of the positioning type, and when used as non-positioning, loose fit installation is used. All thrust roller bearings are positioning bearings.
 
7. Facilitate the installation and disassembly of bearings
When choosing the bearing type, whether it is convenient to install and dismount the bearing must also be considered comprehensively, especially for the installation and disassembly of large and extra-large bearings. General angular contact ball bearings, tapered roller bearings, cylindrical roller bearings and needle roller bearings with the separable outer ring are easy to install and disassemble. Their inner and outer rings can be mounted on the shaft or the housing hole, respectively. Self-aligning roller bearings, double-row cylindrical roller bearings, and self-aligning ball bearings with tapered bores and tapered sleeves on the inner diameter are also easier to install and remove.
 
8. Other requirements
In addition to the above factors, the working environment temperature of the bearings, bearing seals, and special needs for friction torque, vibration, and noise should also be considered.

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