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what is the ball bearing

Time:2021-10-08 14:24:39 View:0

TAGS: Ball Bearing  Koyo Bearing,NSK Bearing 

Ball bearing is a kind of rolling bearing. The ball is installed between the inner ring and the outer ring and can bear a large load. Also called ball bearings.
basic introduction:

Ball bearing is a kind of rolling bearing. The ball is installed between the inner ring and the outer ring and can bear a large load. Also called ball bearings.



Structure and composition
Ball bearings are mainly composed of four basic elements: ball, inner ring, outer ring and retainer, also called cage or retainer. General industrial ball bearings meet AISI 52100 standards. Balls and rings are usually made of high chromium steel, with Rockwell C-scale hardness between 61-65. The hardness of the retainer is lower than that of balls and rings, and its materials are metal (such as medium carbon steel, aluminum alloy) or non-metal (such as Teflon, PTFE, polymer materials). Ball bearings have lower rotational frictional resistance than journal bearings, so at the same speed, the temperature generated by friction will be lower.

use
The purpose of the ball bearing is to determine the relative position of two parts (usually the shaft and the bearing seat) and to ensure their free rotation, while transmitting the load between them. At high speeds (such as in gyro ball bearings), this use can be extended to include free rotation with almost no wear in the bearing. In order to achieve this state, an adhesive fluid film called an elastohydrodynamic lubricating film can be used to separate the two parts of the bearing. Denhard (1966) pointed out that the elasticity can be maintained not only when the bearing bears the load on the shaft, but also when the bearing is preloaded so that the positioning accuracy and stability of the shaft does not exceed 1 microinch or 1 nanoinch. Hydrodynamic lubrication film [1].
Ball bearings are used in various machines and equipment with rotating parts. Designers often have to decide whether to use a ball bearing or a fluid film bearing in a particular application. The following characteristics make ball bearings more desirable than fluid film bearings in many occasions,
1. The starting friction is small and the working friction is appropriate.
2. Can withstand combined radial and axial loads.
8. Not sensitive to interruption of lubrication.
4. There is no self-excited instability.
5. Easy to start at low temperature.
Within a reasonable range, changing the load, speed and working temperature has only a small effect on the good performance of the ball bearing.
The following characteristics make ball bearings less desirable than fluid film bearings.
1. The limited fatigue life varies greatly.
2. The required radial space is relatively large.
3. The damping capacity is low.
I. The noise level is high. ·
6. The alignment requirements are stricter.
6. higher cost.
According to the above characteristics, piston engines usually use fluid film bearings, while jet engines almost exclusively use ball bearings. Various types of bearings have their own unique advantages. In a given application, the most suitable type of bearing should be carefully selected. The British Engineering Scientific Data Organization (ESDU 1965, 1967) has provided useful guidelines for the important issue of bearing selection.

Bearing clearance

Bearing clearance (internal clearance) refers to the total distance that a bearing ring can move in a certain direction relative to another ring before the bearing is installed with the shaft or bearing housing. According to the direction of movement, it can be divided into radial clearance and axial clearance, as shown in Figure 1.
The internal clearance of the bearing before installation must be distinguished from the internal clearance (operating clearance) of the bearing when the operating temperature is reached after installation. The original internal clearance (before installation) is usually greater than the operating clearance. This is due to the difference in the degree of fit involved in the installation and the difference in the thermal expansion of the inner and outer rings and related parts of the bearing, which causes the inner and outer rings to expand or contract.
Bearing internal clearance and specified value
The size of the internal clearance (also called the clearance) in the operation of a rolling bearing has a great influence on the performance of the bearing such as fatigue life, vibration, noise, and temperature rise.
Therefore, selecting the internal clearance of the bearing is an important research project for the bearing that determines the structural size.
Generally, in order to obtain a stable test value, a specified test load is given to the bearing, and then the clearance is tested. Therefore, the measured clearance value is larger than the theoretical clearance (in the radial clearance, also called geometric clearance), that is, one more elastic deformation caused by the test load (called the test clearance Show the difference).
Generally, the clearance before installation is specified by the theoretical internal clearance.
Choice of internal clearance
The following points should be considered when selecting the most suitable clearance according to the conditions of use:
(1) The matching of the bearing, the shaft and the housing causes the change of the clearance.
(2) The clearance changes due to the temperature difference between the inner and outer rings when the bearing is working.
(3) The material used for the shaft and the housing affects the change of bearing clearance due to different expansion coefficients.
For bearings that generally work normally, the radial clearance of the basic group should be used first. But for bearings that work under special conditions, such as high temperature, high speed, low noise, low friction and other requirements, the radial clearance of the auxiliary group can be selected. Choose smaller radial clearances for precision bearings, bearings for machine tool spindles, etc. If there are special requirements for bearing clearance, the bearing can meet the needs of customers.

Clearance control

Clearance control of deep groove ball bearings
Aiming at the problem that the axial clearance is commonly used in the production of deep groove ball bearings to control the radial clearance, and the radial clearance after the sleeve is out of tolerance, the accuracy of the inner and outer channels and the steel ball is strictly controlled, and the axial clearance is calculated by compression. For the radial clearance range during clearance, the lower limit remains unchanged, and the upper limit is compressed by 15%. The axial clearance obtained by this method is used as the basis to control the actual radial clearance after the sleeve is fitted. The example verification shows that this method can meet the process requirements [2].
Analysis of the clearance of angular contact ball bearings
For angular contact ball bearings, the clearance also determines its fatigue life. If the clearance is not selected properly, it is very easy to cause early failure of the bearing.
Angular contact ball bearings are generally used in pairs, and the use occasions are divided into two types: pre-clearance and pre-load. Machine tool bearings with higher rigidity requirements adopt the preload configuration, and the fit interference of the shaft is small (about a few microns), and there is no need to consider the impact of the fit interference on the working clearance when pairing. However, for bearings with large matching interference, the influence of the interference on its radial clearance must be considered. At this time, the pre-clearance configuration is mostly used. However, JB/T 10186-2000 only stipulates the pre-clearance value of 7200B and 7300B bearing series, and does not stipulate other series. Therefore, theoretical calculation is required to select an appropriate clearance range.
Factors affecting the pre-tightening of angular contact ball bearings: If the pre-tightening force of the bearing is increased, the rigidity can be improved, but excessive pre-tightening force will cause abnormal heating of the bearing, which will lead to early failure of the bearing. In positioning preloading, the preloading force depends on the bearing installation conditions, including bearing fit, centrifugal effect and temperature rise during operation.
1. Matching of bearings
For machine tool bearings, generally the inner ring is an interference fit and the outer ring is a clearance fit. The interference fit between the inner ring and the shaft causes the radial dimension to change, which leads to an increase in the pre-tightening force.
2. Centrifugal effect
When the bearing is running at high speed, the inner raceway will expand due to the centrifugal effect, causing the radial clearance of the bearing to change and increase the preload.
3. Temperature rise
When the bearing is running, due to the combined action of its internal friction, lubricant stirring and other external factors, it will cause the bearing temperature to rise and the parts to expand.
(1) Among the bearing parameters, the contact angle has a greater influence on the change in axial clearance. (2) Among the influences of interference fit, centrifugal effect, and temperature rise on bearing clearance, interference fit has the greatest impact. (3) In actual applications, if the bearing has an interference fit, the influence of the fit interference on the bearing clearance needs to be taken into account, and a certain amount of clearance should be reserved to avoid excessive pre-tightening force and premature failure of the bearing. When the angular contact ball bearings are actually paired, the change in radial clearance should be converted into the change in axial clearance for consideration

Rolling bearing

In the design of mechanical parts, rolling bearings and sliding bearings are often used. Compared with sliding bearings, rolling bearings have the following advantages and disadvantages.
advantage
(1) In general working conditions, the friction coefficient of the rolling bearing is small, and will not change with the change of the friction coefficient, and is relatively stable; the starting and running torque is small, the power loss is small, and the efficiency is high.
(2) The radial clearance of the rolling bearing is small, and it can be eliminated by the method of axial preloading, so the operation accuracy is high.
(3) Rolling bearings have a small axial width, and some bearings can bear radial and axial composite loads at the same time, with compact structure and simple assembly.
(4) Rolling bearings are standardized components with a high degree of standardization and can be produced in batches, so the cost is low.
shortcoming
(1) Rolling bearings have a small contact area between rolling elements and pipes, especially ball bearings, which have poor impact resistance.
(2) Due to the structural characteristics of rolling bearings, vibration and noise are relatively large.
(3) The life of rolling bearings is reduced under high-speed and heavy-duty conditions.
(4) The inner and outer rings of the rolling bearing adopt an integral structure, and cannot adopt a partial structure, which makes it difficult to install the bearing in the middle of the long shaft.


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