Bearings life and bearing load
Load and life analysis: The life calculation of general imported bearings is only applicable to the bearings installed on the solid shaft and placed in the rigid bearing housing. For the multi-roll mill, the bearing outer ring is directly used as the backup roller, and the outer diameter is partially in contact with the intermediate roller. Under the action of the external load, the thick outer ring will have a certain elastic bending deformation, which will affect the load distribution on the raceway and affect the bearing capacity. When calculating the contact deformation between the rolling element and the raceway, the influence of the radial deflection of the outer ring must be considered. According to the plane bending theory of thin-walled rings, the differential equation of radial deflection at any angular position is d2 W/de +IV=-MR / (1) where: is the radial deflection at the corner; E1 is the bending stiffness, which is the section Upper bending moment; R is the radius of curvature. The radial deflection ( ) l2J of the outer ring can be solved by equation (1). The contact deformation between the rolling element and the raceway at any position is = cos~+ ( ) (2) where: the relative displacement of the inner and outer rings, and n is the rolling element number. The deformation equation of each rolling element is established, and a force balance equation of a ferrule is added. A total of +1 equations are used to solve the above nonlinear equations, and the contact deformation of each point can be obtained. Then the contact load at each point is Q = k (3) where: k is the bearing load deformation constant. According to the rated calculation formula of the line contact, the rated load Q small Q of the inner and outer rings of the bearing and the equivalent load Q of the inner and outer rings of the bearing and the rolling element are calculated, and the rated life of the inner and outer rings of the bearing is Llol=( Q JQ f) (4) Llo = (Q / Q ) (5) The rated life of the complete bearing is L1o = (£1o. One will + L1o -9/8) - (6) calculation shows that the bearing load A bearing that is different from a rigid seat. Due to the elastic deformation of the outer ring of the support bearing, the load area of the rolling element becomes smaller, and the load on the top roller of the load zone is increased, so the equivalent load of the support bearing is significantly increased, and the service life is also greatly reduced. Due to the elastic deformation, the life of the bearing is reduced by approximately 75% compared to conventional calculations.
For the special application of the backup roller bearing, the structural design of the THOMSON bearing must help to improve the distribution of the load. The wall thickness of the outer ring of the bearing must ensure that the outer ring has sufficient rigidity, not to cause large bending deformation due to heavy load, and to take into account the bearing's large dynamic load capacity (the experience of foreign bearing companies is the outer ring rolling The ratio of the diameter of the track to the outer diameter is D / D = 0.7 ). Relevant research shows that the design of large-diameter rollers is more reasonable than the design with a small number of rollers. For applications with low speed and heavy load, a full-loaded roll-free structure without cage can be used. The load capacity of the large bearing reduces the load at the contact point of the raceway and improves the rigidity of the bearing.
Force analysis of the roller system: In order to effectively calculate the bearing capacity of the support roller STIEBER bearing, the force analysis of the roller system is required. In order to facilitate the calculation, the simplified force analysis method is adopted, and the elastic deformation and friction loss of the rolls are ignored. It is assumed that the direction of the force is on the connecting line of the two rolls, as shown in Fig. 3. Fig. 3 Force analysis of the roller system P1=P/(2sina) (7)P2=P1sin(mouth-1)/sin(90~+—) (8)P3=P1sin(mouth-p)/cos(-p) (9) P4=P3cos3/sin~ (10)P5=P2sin(90~一j5-7)/sin(90~+sound one y)(11)P6=P2 sin(Luyi),)/cos(jl a),) (12) P7=, /P6 +P +2P6P4cos(90~1+j5)(13) The load F of a single bearing is calculated by F=(Ibn/L)P (14) where: F6 is the bearing width; is the number of bearings on the mandrel; L is the length of the entire backup roll. The calculations show that the distribution of the load on the roller system is extremely uneven, and the load of the support rolls A and D on both sides is larger than that of the intermediate backup rolls B and C. For some types of rolling mills, the load on the A and D backup rolls is relatively 40% lower than the load on the B and C backup rolls. Therefore, the support roller on the side of the roller system is more worn, and the bearing life of the support rollers on both sides is greatly reduced.
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