Rotating machinery is widely used in modern industry. As a core component of rotating machinery, the installation process of bearings is directly related to the safe operation of rotating machinery. In this paper, the role of the pre-tightening force of the most common angular contact bearing in rotating machinery, the estimation method and the influence on the bearing performance are elaborated and discussed, which plays a guiding role in the installation of the angular contact bearing.
Rolling bearings are required to reserve a suitable working clearance for assembly depending on the application. In most cases, the working clearance should be positive, but if you need to improve the rotation accuracy or rigidity of the shafting, a negative working clearance is often used. Preloading is when the bearing is assembled
By applying a certain preload to the outside, the gap between the bearing rolling elements and the inner and outer rings is eliminated, and the bearing is elastically deformed to generate a negative working clearance. Pre-tightening is a measure to reduce the deflection of the shaft due to the force, to promote a more uniform load distribution in the bearing, and to improve the stress state under working conditions.
Preloading can also compensate the wear of the rolling elements and the inner and outer rings, reduce the noise generated by the equipment during operation, and prolong the service life of the bearings.
2 Where pre-tightening is required
In general, for high-speed precision operation where bearing positioning accuracy is high, rotation accuracy is required, shaft rigidity is required to be improved, and high-speed light load, large temperature change, reciprocating bearing arrangement or noise reduction and vibration reduction are required. In all cases, pre-tightening is required to provide minimum load on the bearings. For example, spindle bearings for precision machine tools, bearings for reducers, pinion bearings for automotive drive shafts, small motors, cryogenic equipment, bearings for fans, etc.
Often it is necessary to pre-tighten during assembly.
3 Determination of minimum load
The minimum load is affected by the basic static load rating of the bearing, the minimum axial load factor Ka, the rotational speed n, and the average diameter of the bearing. We can calculate according to the empirical formula provided in the bearing manual. For example, the minimum axial load of a single row angular contact bearing can be calculated by the formula.
Calculation. If the weight of the bearing support plus external force does not reach the minimum load, additional load must be applied by adjusting the preload of the bearing.
4 Determination of preloading
For angular contact ball bearings that can withstand both radial and axial loads, an axial force is generated in the bearing under radial load, and this axial force usually needs to be absorbed by another bearing with the opposite position. If there is a pure radial displacement between the inner ring and the outer ring,
Only the raceway halfway along the circumference of the bearing is under load. The axial force generated in a single row angular contact bearing can be calculated according to the formula Fa = R Fr . Fr in the formula is the radial load acting on the bearing, and the variable R is determined according to the contact conditions inside the bearing. The value is in accordance with the bearing manual.
The method of "determining the axial load experienced by a single or series of matched bearings" is determined,
5 The effect of preload force on bearing performance
If the external axial force is less than the above calculated minimum load value, the number of moving bodies subjected to the load will be less than half, the load capacity of the bearing will be correspondingly reduced, and the bearing rolling elements may slip and cause damage to the bearing. In practical applications, the axial force of the bearing is less than the minimum load required by the bearing due to the unlocked or inner ring fault of the bearing lock, resulting in deterioration of working conditions and bearing damage. So there is an external axis
In the case of load, it is necessary to consider pre-tightening the bearing to compensate for the play generated by the turbulence of the bearing itself subjected to the axial load and the play due to the elastic deformation, and to distribute the load evenly on the other end. Bearings without axial load. At the same time, assuming that the elasticity and the load are linear, then with the same external axial force Ka, with preloaded bearings
The axial displacement is smaller than that of the pre-tightened bearing arrangement, and the stability of the bearing is better. Of course, excessive bearing preload has a bad influence on the bearing, so the correct pre-tightening amount must be maintained. When determining the preload in the bearing arrangement, care should be taken when preloading exceeds certain
At a given optimum value, the rigidity can only be increased to a limited extent. Because the friction and the resulting heat will increase, the bearing life will be greatly reduced if there is additional load and long-term action.
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