In such cases it is necessary to divide the bearing working cycle into several time periods in which the operational conditions are approximately constant see the picture. It is necessary to calculate the bearing life separately for each such period. The total bearing life can be determined using the relation. In an effort to design a bearing quickly, practical procedures use a simplified way of calculation of the bearing life for some types of loads.
In this calculation the external load of the bearing is replaced by a virtual mean permanent load that shows the same effects on the bearing as an actually acting variable load. The procedures for determination of the mean load for some common types of loads are given in the table.
Fluctuating load with sinusoidal course, at constant speed Rotating load, at constant speed Fluctuating load, at constant speed Fluctuating load, at variable speed where mean speed:. Oscillating motion Oscillating motion is replaced by virtual rotation at the speed equal to the frequency of oscillation:. Use of the simplified calculation is not suitable in case of a load with variable amounts and directions and with calculations of modified life.
In case of use of a bearing at permanently higher temperatures it is necessary to modify it during production to ensure its dimensional stability under operation. Bearings for use at high temperatures are produced with thermal treatment, usually with greater clearances and a differently designed cage, possibly with the use of special materials.
Requirements for the use, production and delivery of stabilized bearings must usually be consulted with the producer, where you can find detailed technical parameters of the bearing. For the purposes of preliminary designs it is possible to use the following orientation table. A bearing at static load is loaded by forces at standstill, at very slow speed or slow swinging movements. The load rating of the bearing is determined by permissible permanent deformations of orbital paths and rolling bodies.
The coefficient of safety s 0 gives the standard of safety of static-loaded rolling bearings and is defined by the following relation:. Basic static load rating of the bearing is defined as the external load that causes a permanent deformation of 0.
This permanent deformation usually has no adverse effects on the bearing function. Values of static load ratings are given for each bearing in the respective catalogues. Equivalent static load rating of the bearing is defined exclusively as radial load with radial bearings and axial load with axial bearings respectively, which causes a permanent deformation in the bearing and this deformation is of the same size as under actual conditions of loading.
The amount of the equivalent load is described by the relation. Values of the coefficient X 0 ,Y 0 depend on the type, design and size of the bearing. The friction moment of rolling bearings depends on many factors design of the bearing, method of lubrication, speed, etc. Practical calculations therefore use a simplified model with the use of an estimated coefficient of friction. Under the assumption of normal operational conditions and good lubrication an approximate friction moment can be calculated with rolling bearings operated at mean speed using the equation.
In case of sealed bearings the moment from the friction sealing must be added to the calculated friction moment. The resulting friction moment further determines the power loss N R that is equal to the heat produced in the seating:.
In case the shaft is seated in two single row angular contact ball bearings or in two tapered roller bearings, a mutual inner axial force is produced with radial load in the bearings. This force will naturally affect the bearing load rating and therefore it must be included in the calculation. The amount of the axial load of one bearing depends on the contact angle and arrangement of both bearings, on the amount of radial forces F rA , F rB and on the direction and amount of the external axial force K a.
The calculation must also consider the seating as a unit and both bearings must be designed at the same time.
Higher speeds create a danger of rolling elements slipping between the orbital paths of the rings with unloaded bearings due to centrifugal forces. This may adversely affect wear of the bearing and thus reduce its life. The bearing should be loaded by a certain minimum force under operation to ensure correct rolling.
The amount and size of this force depends on the type, design and size of bearing and operational conditions. The relations for determining the minimum load are usually given in catalogues of individual producers.
The heat that is produced by friction must be dissipated to achieve thermal balance. The operational temperature depends on many factors; its calculation is very complicated and leads to a system of non-linear equations. The following relation can be used for fast orientation:. For bearings seated in frame machines it can be determined approximately using the relation.
The speed of rolling bearings cannot be increased without any limitation. Centrifugal forces of the bearing increase its loading, inaccuracy of its run causes vibrations and friction in the bearing causes warming.
Limit speed depends on the type, design and size of bearing, its accuracy, and the design of the cage, inner clearances and operational conditions in its seating and, above all, the highest permissible temperature of the lubricant.
No specific and generally applicable limit of permissible speed can be determined exactly for rolling bearings.
Producers give in their dimensional tables guide values of limit speeds for individual bearings for the purposes of fast orientation. These values are based on practical experience and are applicable for bearings with normal clearances and produced at normal levels of accuracy provided that they are operated under normal conditions and with usual cooling.
The given limit speeds can be exceeded in certain individual cases, however, it is advisable to consult this with the producer. In addition to limit speeds, some producers also state in their catalogues of rolling bearings values of so-called thermal reference speeds. The reference speed gives the limit permissible speed of the bearing under exactly defined conditions and serves as an initial value for determining the permitted speed of the bearing for the given operational conditions.
The method of determining adjustment factors is described in catalogues of individual producers or in ISO The reference speeds given in the dimensional tables are defined for the following operational conditions:.
The registration number has been sent to the email address you entered. Download Free day trial : Users have 30 days after installation to test the installed product with no restrictions. Click here for further information. Privacy Policy. Two programs for the tolerance analysis of linear, 2D and 3D dimensional chains 1 Tolerance analysis of linear dimensional chains.
The program is designed for tolerance analysis of linear 1D dimensional chains. The program solves the following problems: -Tolerance analysis, synthesis and optimization of a dimensional chain using the arithmetic "WC" Worst case method, possibly the statistical "RSS" Root Sum Squares method. All solved tasks enable work with standardized tolerance values, both in designing and in optimization of the dimensional chain.
The program solves the following problems: -Tolerance analysis of a dimensional chain using the "Worst case" method. In designing a dimensional chain, the program enables work with standardized tolerance values. This module is a part of MITCalc - Mechanical and Technical Calculation Package for gear, belt and chain drives, bearings, springs, beam, shaft, bolt connection, shaft connection, tolerances and many others.
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