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Basic load ratings
There is no standardized method for determining the load ratings of spherical plain bearings and rod ends, nor is there any standardized definition. As different manufacturers define load ratings differently, it is not possible to compare the load ratings of bearings produced by one manufacturer with those published by another manufacturer.
Basic dynamic load ratings
The basic dynamic load rating C is used, together with other influencing factors, to determine the basic rating service life of spherical plain bearings and rod ends. As a rule it represents the maximum load which a spherical plain bearing or rod end can sustain at room temperature when the sliding contact surfaces are in relative motion. The maximum permissible load in any individual application should always be considered in relation to the desired service life. The basic dynamic load ratings quoted for SKF spherical plain bearings and rod ends are based on the specific load factor K and the effective projected sliding surface. Values of K for the various sliding contact surface combinations can be found in table 1.

The basic dynamic load rating C is used when calculating dry sliding bearings which are to be dynamically loaded. It is defined as that load, constant in magnitude and direction, under which a given basic rating life (corresponding to a given total distance travelled) can be achieved under constant rotation or oscillating movement at a defined sliding velocity at room temperature. It is assumed in this definition that the load acting on bushings and flanged bushings is purely radial, and the load acting on thrust washers is purely axial and applied at the center. Dynamic load conditions are essentially oscillating movement or rotation under load, but also include micro-sliding under variable load (e.g. as a result of vibration) or operation under high-frequency alternating loads. Often a combination of these conditions will be encountered. Whereas oscillating movement or rotation under load usually produces wear, the other conditions may result in fatigue.
The actual load ratings quoted by various manufacturers depend on the way in which they are defined so that it is not always possible to make direct comparisons between them.
The method for calculating the Basic Dynamic Load Rating can be found in JIS B1518 / ISO 281  and is based on an endurance test of 1,000,000 revolutions.
Basic static load ratings
The basic static load rating C[sub]0[/sub] represents the maximum permissible load which may be applied to a bearing when there is no relative movement of the sliding contact surfaces. Values of C[sub]0[/sub] may be different for a spherical plain bearing and a rod end incorporating the corresponding bearing.
For spherical plain bearings the basic static load rating represents the maximum load which the bearing can accommodate at room temperature without its performance being impaired as a result of inadmissible deformations, fracture or damage to the sliding contact surfaces. The basic static load ratings quoted for SKF spherical plain bearings are based on a specific static load factor K[sub]0[/sub] and the effective projected sliding surface. It is assumed that the bearing is adequately supported by the associated components of the bearing arrangement. In order to fully exploit the static load rating of a spherical plain bearing it is generally necessary to use shafts and housings of high-strength materials. The basic static load rating must also be considered when bearings are dynamically loaded if they are also subjected to additional heavy shock loads. The total load in such cases must not exceed the basic static load rating.
For rod ends it is the strength of the eye-shaped head of the rod end (housing) at room temperature under a constant load acting in the direction of the shank axis which is the determining factor. The basic static load rating represents a safety factor of at least 1,2 relative to the tensile limit of the material of the rod end head under the above conditions.
The basic static load rating C[sub]0[/sub] is defined as the maximum load which an SKF composite bushing, flanged bushing or thrust washer can support when stationary at room temperature without permanent deformation of the sliding layer being produced which would jeopardise its performance. It is assumed here that the components surrounding the bearing prevent its deformation. At elevated temperatures it is necessary to modify the basic load ratings of the various materials by multiplying the C[sub]0[/sub] value by the temperature factor c[sub]3[/sub] (also valid for dynamically loaded bearings). The permissible operating temperature range should also be considered.
The formula for the Basic Static Load Rating and the Static Equivalent Radial Load Rating of ball bearings is defined in specification JIS B1519 / ISO 76.
The Basic Static Load Rating is the amount of static radial load that will cause a total permanent deformation (ball and raceway) on the most heavily stressed ball/raceway contact area (the center) that equals to 0.0001 of the ball diameter under a stress level of 4200 MPa.
 
پاسخ
 سپاس شده توسط Hamid Jafary Pooya


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