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Working conditions of bearings

Working conditions of bearings


(1) bearing load

The size, direction and nature of the load on the bearing are the main basis for the selection of the bearing type. 

When choosing the type of bearing according to the size of load, because the main components in the roller bearing are in line contact, it is appropriate to bear a large load, bearing deformation is small.And ball bearing is mainly for point contact, suitable for carrying light or medium load, so in the load is small, should be preferred to choose ball bearing. 

When choosing the type of bearing according to the direction of load, the thrust bearing is generally selected for the pure axial load.Thrust ball bearings can be used for small pure axial load.Thrust roller bearings can be used for larger pure axial loads.For pure radial load, usually choose deep groove ball bearing, cylindrical roller bearing or needle roller bearing.When the bearing is subjected to radial load R at the same time, there is A small axial load A, you can choose the deep groove ball bearing or angular contact ball bearing or tapered roller bearing with A small contact Angle;When the axial load is large, angular contact ball bearings or tapered roller bearings with a large contact Angle can be selected, or the structure combined with centripetal bearings and thrust bearings can be selected to bear radial load and axial load respectively. 

(2) the speed of the bearing

In the general speed, the speed of the high and low on the type of choice does not have any impact, only when the speed is higher, there will be a more significant impact.The nlim values of the limit speed of bearings of various types and sizes are included in the bearing samples.This speed refers to the maximum allowable speed when the load is not too large (P≤ 0.1c, C being the basic rated dynamic load), the cooling condition is normal, and the bearing is of grade 0 tolerance.However, since the limit speed is mainly limited by the temperature rise during operation, the limit speed in the sample cannot be considered as an absolutely unsurpassable limit.If the working speed of the bearing exceeds the limit speed, the measures set out in clause 5 below may be taken. 

From the working speed of the bearing requirements, can be determined as follows:

1) compared with roller bearing, ball bearing has a higher limit speed, so ball bearing should be preferred at high speed. 

2) under the condition of the same inner diameter, the smaller the outer diameter is, the lighter and smaller the rolling body will be. During operation, the centrifugal inertia force added by the rolling body on the outer ring raceway will be smaller, so it is more suitable for working at a higher speed.At high speed, it is advisable to choose ultra-light, ultra-light and light series bearings.Heavy and extra-heavy series bearings are only used for low-speed and heavy-duty applications.If the bearing capacity of a light series of bearings is not up to the requirements, consider using a wide series of bearings, or two light series of bearings together for use. 

3) the material and structure of the cage have a great influence on the bearing speed.The solid cage allows a slightly higher rotational speed than the ram cage. 

4) the permission speed of thrust bearing is very low.When the working speed is high, if the axial load is not very large, the angular contact ball wheel can bear the pure axial force. 

5) if the working speed slightly exceeds the limit speed specified in the sample, the high-speed performance of the bearing can be improved by increasing the tolerance level of the bearing, or appropriately increasing the radial clearance of the bearing, selecting circular lubrication or oil mist lubrication, and enhancing the cooling of the circulating oil, etc..If the working speed exceeds the limit speed more, should choose the special high-speed rolling bearing. 

(3) the centering performance of the bearing

When the center line of the shaft does not coincide with the center line of the bearing seat and there is an Angle error, or when the shaft is bent or tilted due to the force on the shaft, the axis of the inner and outer rings of the bearing will be deflected.At this time, should be used to have certain centering performance of aligning ball bearings or roller bearings.This kind of bearing can work normally when there is not much relative deviation of the inner and outer ring axis. 

Cylindrical roller bearings and needle roller bearings are most sensitive to the deflection of the bearings. The bearing capacity of such bearings may be lower than that of ball bearings in the deflection state.Therefore, when the stiffness of the shaft and bearing seat hole support stiffness is low, should try to avoid the use of this type of bearing. 

(4) installation and disassembly of bearings

Ease of assembly and disassembly is also a factor to be considered in the selection of bearing types.When the bearing seat has no dividing surface and must be installed and disassembled along the axial direction, the bearings with detachable inner and outer rings (such as N0000, NA0000, 30000, etc.) should be selected preferentially.When the shaft is mounted on the long shaft, bearings with the inner ring hole of 1:12 (for mounting on the fixed bushing) can be selected for easy disassembly. 

A bearing mounted on a fixed bush

In addition, the choice of bearing type should also consider the requirements of the overall design of the bearing device, such as the configuration and use requirements of the bearing, swimming requirements. 

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