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Ball Bearing Technology News: Clearance control dramatically improves the accuracy of steel ball bearings

wallpapers News 2020-04-23
Bearing clearance (internal clearance) refers to the total distance that a bearing ring can move in a specific direction relative to another ring before the bearing and shaft or bearing housing are not installed. According to the moving direction, it can be divided into radial clearance and axial clearance. The internal clearance of the bearing before installation must be distinguished from the internal clearance (operation clearance) of the bearing when the operating temperature is reached after installation. The original domestic removal (before installation) is usually more significant than the running approval. This is due to the difference in the degree of fit involved in the installation fit. The difference in the thermal expansion of the bearing inner and outer rings and related components causes the inner or outer circle to expand or contract.
 
Bearing internal clearance and the specified value
The size of the internal clearance (also called removal) during the operation of rolling bearings has a significant influence on the bearing performance such as fatigue life, vibration, noise and temperature rise.
Therefore, selecting the internal clearance of the bearing is an important research project for the taking that determines the structural size. Generally, in order to obtain stable test values, the 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 radial clearance, also known as geometric clearance), that is, an additional amount of elastic deformation caused by the test load (called the test clearance Show the difference). Generally, permission before the installation is specified by the theoretical internal clearance.
 
Choice of internal clearance
The following points should be considered when selecting the most appropriate clearance according to the conditions of use:
(1) The cooperation of the bearing, the shaft and the housing causes the change in consent.
(2) Due to the temperature difference between the inner and outer rings during bearing operation, the clearance changes.
(3) The material used for the shaft and the casing affects the change in bearing clearance due to the different expansion coefficients.
Bearings that usually work regularly should prefer the radial clearance of the primary group. But for bearings working under special conditions, such as high temperature, high speed, low noise, and low friction, the radial clearance of the auxiliary group can be selected. Use smaller radial clearances for precision bearings and bearings for machine tool spindles. If there are special requirements for bearing clearance, bearings can meet customer needs.
 
Clearance control
Clearance control of deep groove ball bearings
Aiming at the problem of radial clearance controlled by the axial clearance commonly used in the production of deep groove ball bearings, the radial clearance after the sleeve is out of tolerance, by strictly controlling the accuracy of the inner and outer channels and the steel ball, and calculating the axial clearance by compression The radial clearance range at the time of the gap, the lower limit value remains unchanged, and the upper limit value is compressed by 15%. The axial clearance obtained by this method is used as the reference to control the actual radial clearance after closing. The example verification shows that this method can meet the technological requirements.
Angular contact ball bearing clearance analysis
For angular contact ball bearings, the clearance also determines its fatigue life. If the consent is not selected correctly, it is straightforward to cause early failure of the bearing.
Angular contact ball bearings are generally used in pairs, and they are divided into two types: pre-clearance and preload. Machine tool bearings with higher stiffness require a preload configuration, and the interference fit of the shaft is petite (about a few microns). There is no need to consider the influence of the interference fit on the working clearance when pairing. However, for bearings with more considerable interference, the impact of the intervention on its radial clearance must be considered. In this case, the pre-clearance configuration is mostly used. However, JB / T 10186-2000 only stipulates the pre-clearance values ​​of the 7200B and 7300B bearing series, but does not specify the other set, so theoretical calculation is required to select a suitable clearance range.
Factors affecting the preload of angular contact ball bearings: If the preload of the bearing increases, the stiffness can be increased, but excessive preload will cause the bearing to generate abnormal heat, resulting in early failure of the bearing. In positioning preload, the preload force depends on the bearing installation conditions, including bearing fit, centrifugal effect and temperature rise during operation.
1. Coordination of bearings
For machine tool bearings, the inner ring is generally an interference fit, and the outer ring is a clearance fit. The interference fit between the inner circle and the shaft changes the radial dimension, increasing preload.
2. Centrifugal effect
When the bearing runs at high speed, the inner channel will expand due to the centrifugal force, causing the radial clearance of the bearing to change and increase the preload.
3. Temperature rise
When the bearing is running, due to its internal friction, lubricant stirring and other external factors, it will cause the bearing temperature to rise and the parts to expand.

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Tag: ball bearing