Application and failure countermeasures of bearings for multi-roll mills (3)
Load and life analysis: Generally, the life calculation of imported bearings is only applicable to bearings mounted on a solid shaft and placed in a rigid bearing housing. For multi-roll mills, the outer ring of the bearing is directly used as a support roller, and the part of the outer diameter is in contact with the intermediate roller. Under the action of external load, the thick-walled outer ring will undergo a certain elastic bending deformation, which affects the load distribution on the raceway and thus affects 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 torus, the differential equation of radial deflection at any angular position is d2 W/de +IVu003d一MR/ (1) where: is the radial deflection at the corner; E1 is the bending stiffness, and is the cross section Upper bending moment; R is the radius of curvature. The radial deflection ()l2J of the outer ring can be solved by the formula (1). In addition, the contact deformation between the rolling element and the raceway at any position is u003d cos~+ () (2) where: is the relative displacement of the inner and outer rings, and n is the number of the rolling element. Establish the deformation equation of each rolling element, plus the force balance equation of a ferrule. There are a total of +1 equations. Solving the above nonlinear equations can calculate the contact deformation of each point. Then the contact load at each point is Q u003d k (3) where: k is the bearing load deformation constant. Calculate the rated load Q small Q of the inner and outer ring of the bearing and the equivalent load Q small Q of the inner, outer ring and rolling element of the bearing according to the rated calculation formula of the line contact, and obtain the rated life of the inner and outer ring of the bearing as Llolu003d( Q JQ f) (4) Llo u003d (Q ／Q) (5) Then the rated life of the whole set of bearings is L1ou003d(￡1o. One wish+L1o -9/8)-(6) The calculation shows that the load of the supporting bearing The distribution is different from the bearings of the rigid seat. Due to the elastic deformation of the outer ring of the supporting bearing, the rolling element load area becomes smaller, and the load on the top roller of the load area increases. Therefore, the equivalent load of the supporting bearing increases significantly, and the service life is greatly reduced. Due to the elastic deformation, the life of the bearing is approximately 75% lower than the conventional calculation. For the special application of backup roll bearings, the structural design of THOMSON bearings must help to improve the load distribution. The wall thickness of the outer ring of the bearing must not only ensure that the outer ring has sufficient rigidity, so as not to undergo large bending deformation due to heavy load, but also take into account that the bearing has a large dynamic load capacity (the experience value of foreign bearing companies is that the outer ring is rolled The ratio of channel diameter to outer diameter D/Du003d0. 7). Relevant studies have shown that the design of large-diameter rollers is more reasonable than the design of small-diameter rollers with a slightly larger number; for applications with low speed and heavier loads, a full-load rolling structure without cage can be adopted to increase The load capacity of the bearing is large, and the load at the contact point of the raceway is reduced at the same time, and the rigidity of the bearing is improved. The force analysis of the roller system: In order to effectively calculate the bearing capacity of the STIEBER bearing of the backup roll, the force analysis of the roller system is required. In order to facilitate the calculation, a simplified force analysis method is adopted, the elastic deformation and friction loss of the roll are ignored, and the direction of the force is assumed to be on the connecting center line of the two rolls, as shown in Figure 3. Figure 3 Force analysis of the roller system P1u003dP/(2sina) (7) P2u003dP1sin(口一3)/sin(90~+ —) (8)P3u003dP1sin(口一p)/cos( —p) (9)P4u003dP3cos3/sin~ (10)P5u003dP2sin(90~一j5-7)/sin(90~+sound one y)(11)P6u003dP2 sin(Lu Yi),)/cos(jl One),) (12) P7u003d, /P6 +P +2P6P4cos(90~一+j5) (13) The load F of a single supporting bearing is calculated as follows: Fu003d(Ibn/L)P (14) where: f6 is the bearing width; is the number of bearings on the spindle; L is the length of the entire support roll. The calculation shows that the load distribution on the roller system is extremely uneven, and the load of the two support rollers A and D is larger than the load value of the middle support rollers B and C. For some types of rolling mills, the relative difference between the load value on the A and D backup rolls and the load on the B and C backup rolls can reach 40%. As a result, the support rollers located on the side of the roller system wear more serious, and the bearing life of the support rollers on both sides is greatly reduced.