Abstract: the article summarized the factors should be noticed in applying precision rolling bearing, such as precision, stiffness, load, speed, life, pre load, lubrication and seal; and illustrates the application examples given.
Keywords: precision rolling bearings; precision axis; stiffness; roller
1 Introduction
Correct application of precision rolling bearing in precision shafting involves different bearing characteristics and many external factors that affect the accuracy of bearing. If you consider not lose the use of precision bearing significance. Especially in the high-speed spindle rotation and the requirements of high precision, is associated factors of precision rolling bearing is more outstanding.
2 factors
2.1 accuracy
The use of precision rolling bearing, only the shaft and bearing seat tolerance of form and position accuracy and surface roughness with bearing precision is coordinated, to give full play to its performance. That is to say the installation precision of components is the main factor affecting the running accuracy of bearing. But the high requirements of installation precision of components will lead to difficulties in machining. In the application should be based on the "mechanical design manual" recommended value as the basis, combined with practical experience to make the rational choice. Can not be ignored is the bearing size precision, in the choice of matching installation parts and bearings, should consider this factor, combined with the selected will affect the bearing clearance or preload bearing.
2.2 stiffness
The bearing stiffness depends on its type and size. The main criterion is: roller element types (such as spherical or cylindrical), roller size and number and contact angle.
The roller is greater than the number of bearing size influence on rigidity. Bearing bearing the same number of rollers increase percentage increased rigidity than increasing the bearing size increased stiffness. For this reason, in order to increase the number of rollers to improve the precision of rolling bearing stiffness.
Contact angle effect on stiffness, is generally the contact angle is small, it meets the radial high stiffness; contact angle is large, then meet the axial high stiffness. In the arrangement of bearings, the same location to install two or more bearings can improve stiffness. Angular contact ball bearing is most suitable for this use and is often used in pairs.
The bearing stiffness will also be affected by the spindle and the bearing seat, its tolerance to choose; effect on bearing stiffness will be pre load.
The bearing stiffness expressed as elastic deformation and recovery ratio. The rolling bearing elastic recovery is not a linear relationship with load, so it is difficult to describe with a single function; linear relation can be estimated by approximation in application.
2.3 load
The use of precision shafting in equipment of precision bearings, bearing load capacity is not the key factor in selecting bearing the only consideration, and bearing inner diameter is shaft design. Other key factors such as the stiffness of the bearing, allowing the rotation speed and the accuracy are the decisive factor.
In application, selection of bearing type and layout, as a basic rule: roller bearing the same size with larger bearing capacity than ball bearings; can bear radial and axial complex load angular contact ball bearings and tapered roller bearings can withstand two-way load; double direction angular contact thrust ball bearing.
2.4 speed
Bearing rolling speed can be adjusted at the permissive temperature; with low friction properties of precision bearings, the resulting low heat characteristics. So the precision rolling bearings can be used for high speed working condition. Bearing the heat generated depends largely on the speed, also affected by the influence of bearing type, lubrication, pre load and work load and other factors.
2.5 life
In the application, as a basic requirement is to make the selection of bearing has a longer life. Determination of precision bearings basic life including the static load capacity and the load of two parameters. Also taking into account the effect of preload on the bearing life and main shaft strength and bearing its own factors. For the high speed working condition, the spindle with high wear resistance; centrifugal roller elements will also affect the service life of the bearing load and shorten.
For low speed rotation or slowly swing, bearing load can be considered as a static load equivalent effect, without any motion characteristics. In this case, due to load of the roller and track permanent deformation will affect the life; at the same time, bearing to withstand periodic heavy shock loads.
2.6 pre load
The pre load can improve the stiffness of the bearing, but also can improve the rotation accuracy. The general use of pre load bearing and the bearing pair group in the application of equipment spindle.
For the single row angular contact ball bearings and tapered roller bearing outer ring, usually regulate axial clearance and preload; for cylindrical roller bearing inner ring, the cone hole appropriate installation for pre load; for double direction angular contact thrust ball bearing, adjust the isolation sleeve dimensions, installation will be pre load.
Under the action of external force, the internal load distribution of bearing will change. Some roller elements will bear too much load, at the same time, another part of the roller element will be released, elastic deformation will change, as shown in figure 1.
Figure 1 shows the same preload F0 generated under the action of the same deformation under the action of external force; in Fa, bearing A δ a deformation, deformation of bearing B decreases; continue to increase the external forces acting to Fa ′, B bearing preloaded elastic deformation fully released. This is not conducive to the use of the bearings, the application should pay attention to consider the role of external force, in order to choose the appropriate pre load
In the application on the other hand, to limit the maximum bearing pre load. Because of increased preload friction will increase.
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