Bearing types and technical characteristics
Bearing type is selected depending on the technical characteristics required by a certain application.
A suggestive graphic symbol has been determined for each main technical characteristic. Thus, a proper bearing for each purpose can be easily chosen. According to the specifications in this catalogue, the proper type and size of bearing can be selected, together with all manufacturing and operating technical conditions
In most cases, while operating, bearings should have a small radial clearance that can be defined as "the possible value of displacement in radial direction of one bearing ring in relation to the other without parts deformations"
While operating, bearing internal clearance is different from the one at delivery, since the latter is reduced when mounting bearings with a certain tight fit.
Under operating conditions, internal clearance change is also caused by different temperatures between the outer and inner ring. Bearings types are generally delivered with a normal radial or axial clearance according to the values shown for each rolling bearing group.
The decrease in radial clearance due to the tight fit and operating temperature is considered to be between 60-80% of the tightening value, depending on bearing series and size.
After the clearance in bearings has been decreased, a large enough operational clearance should remain, so that the lubricant film shouldn't be destroyed.
Deep groove ball bearings should have an operational clearance close to zero. There may be often a light preload, due to the point-contact between the rolling elements and raceways.
Small-sized cylindrical roller and needle roller bearings should have an operational clearance of 5-10 urn and larger-sized bearings a clearance of 10-30 urn.
Bearing producers can also manufacture - at request-bearings with radial and axial clearance smaller (C1 and C2) or larger (C3, C4 and C5) than normal, so that the most favorable operating conditions for bearings should be assured.
Cylindrical and needle roller bearings can be manufactured with interchangeable rings (no special designation) and with non interchangeable rings (suffix NA).
Bearings with non interchangeable parts have a smaller radial clearance than bearings with interchangeable parts. Changing rings from one bearing to another is not allowed.
In case of bearings with interchangeable parts, the rings may be changed and the values of radial clearance will not be altered.
Angular misalignments occur generally when the shaft bends under the operating load or when bearings adjoint parts have form or position deviations.
In such cases, self-aligning ball bearings, cylindrical roller bearings or spherical roller thrust bearings should be used.
A certain bearing bent angle can compensate for errors of alignment and maximum angle values are shown for each type in the introductory texts of the table sections.
When misalignments should be compensated, radial and axial clearance are important. The larger the clearance, the greater the possibility of self-aligning.
The misalignment exceeds the permissible values shown in the introductory texts of the bearing tables, the bearing rating life decreases. The greater the ratio Fr/C0r, the shorter the rating life. If 0,1 < Fr/C0r < 3, the rating life decreases with about 25%.
