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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 choosing the bearing type. 

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

When the bearing type is selected according to the direction of load, the thrust bearing is generally selected for the pure axial load.Thrust ball bearing can be used for small pure axial load.Thrust roller bearing can be used for larger pure axial load.For pure radial load, deep groove ball bearings, cylindrical roller bearings or needle bearings are generally used.When the bearing is bearing radial load R, there is A small axial load A, can choose deep groove ball bearings or angular contact ball bearings or tapered roller bearings with small contact Angle;When the axial load is large, the angular contact ball bearing or tapered roller bearing with a large contact Angle can be selected, or the radial load and axial load can be borne by the combination of centripetal bearing and thrust bearing. 

(2) bearing speed

In the general speed, the speed of the high and low on the type of choice does not have any impact, only in the high speed, will have a more significant impact.Nlim values of 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 is the basic rated dynamic load), the cooling condition is normal, and the bearing with 0-grade tolerance is the maximum allowable speed.However, as the limit speed is mainly limited by the temperature rise during operation, it cannot be considered that the limit speed in the sample is an absolutely insurmountable limit.If the working speed of the bearing exceeds the limit speed, the measures mentioned in article 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 at high speed, ball bearing should be preferred. 

2) under the condition of the same inner diameter, the smaller the outer diameter is, the lighter and smaller the rolling body will be. The centrifugal inertia force of the rolling body on the outer ring raceway will be smaller during operation, 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 of bearings.Heavy and extra-heavy bearings, used only for low speed heavy loading.If the bearing capacity of one light bearing series is not up to the requirement, a wide bearing series can be considered, or two light bearing series installed together for use. 

3) the material and structure of the cage have great influence on the bearing speed.The solid cage allows a higher 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 improving the tolerance level of the bearing, or appropriately increasing the radial clearance of the bearing, choosing circular lubrication or oil mist lubrication, and strengthening the cooling of the circulating oil.If the working speed exceeds the limit speed more, should choose 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 housing 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 ball bearings or centering 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 the most sensitive to bearing deflection. The bearing capacity of such bearings may be lower than that of ball bearings under deflection condition.Therefore, when the stiffness of the shaft and the supporting stiffness of the bearing housing hole are relatively low, the bearing should be avoided. 

Installation and disassembly of bearings

Ease of assembly and disassembly is also a factor to be considered in the choice of bearing type.When there is no split surface of bearing housing and bearing parts must be installed and disassembled along the axial direction, bearings with detachable inner and outer rings (such as N0000, NA0000, 30000, etc.) shall be preferred.When the shaft is installed on the long shaft, bearings with 1:12 tapered holes in the inner ring (for mounting on the compact bushing) can be selected for ease of assembly and disassembly. 

Bearings mounted on a compact bush

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

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