Application and failure countermeasures of bearings in multi-roll mills (3)
Load and life analysis: Generally, the life calculation of imported bearings is only applicable to bearings installed on solid shafts and placed in rigid bearing housings. For multi-roll mills, the outer ring of the bearing is directly used as a backup roll, and the part of the outer diameter is in contact with the intermediate roll. Under the action of external load, the thick-walled outer ring will have a certain elastic bending deformation, which will affect the load distribution on the raceway, thereby affecting 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 +IVu003d-MR/ (1) where: is the radial deflection at the corner; E1 is the bending stiffness, and is the section at the corner Upper bending moment; R is the radius of curvature. The radial deflection ( )l2J of the outer ring can be solved by equation (1). And 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 rolling element number. Establish the deformation equation of each rolling element, plus a force balance equation of the ferrule, a total of +1 equations, and solve the above nonlinear equations, the contact deformation of each point can be obtained. Then the contact load of each point is Q u003d k (3) where: k is the bearing load deformation constant. Calculate the rated load Q of the inner and outer rings of the bearing according to the rated calculation formula of the line contact, and the equivalent load Q of the inner and outer rings and the rolling elements of the bearing. 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) One (6) The calculation shows that the load of the support bearing The distribution differs from bearings with rigid seats. Due to the elastic deformation of the outer ring of the support bearing, the load area of u200bu200bthe rolling elements becomes smaller, and the load on the top rollers in the load area increases, so the equivalent load of the support bearing increases significantly, and the service life is greatly reduced. Due to elastic deformation, the life of the bearing is approximately 75% lower than conventional calculations. For the special application of backup roller bearings, the structural design of THOMSON bearings must help to improve the distribution of the load. The wall thickness of the outer ring of the bearing should not only ensure that the outer ring has sufficient rigidity to prevent large bending deformation due to heavy load, but also take into account the large dynamic load capacity of the bearing (the experience value of foreign bearing companies is that the outer ring is rolled. The ratio of channel diameter to outer diameter D / D u003d 0.7 ). 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. The load capacity of the large bearing, while reducing the load on the contact point of the raceway, improves the rigidity of the bearing. Force analysis of the roll system: In order to effectively calculate the bearing capacity of the STIEBER bearing of the backup roll, the force analysis of the roll system is required. In order to facilitate the calculation, a simplified force analysis method is adopted, the elastic deformation and friction loss of the rolls are ignored, and it is assumed that the direction of the acting force is on the concentric line of the two rolls, as shown in Fig. 3. Fig. 3 Force analysis of roller system P1u003dP/(2sina) (7)P2u003dP1sin(1-3)/sin(90~+) (8) P3u003dP1sin(1-p)/cos( p) (9 )P4u003dP3cos3/sin~ (10)P5u003dP2sin(90~one j57)/sin(90~+sound one y)(11)P6u003dP2 sin(Lu one),)/cos(jl one),) (12) P7u003d、/P6 +P +2P6P4cos(90~一+j5) (13) The load F of a single support bearing is calculated as follows: Fu003d(Ibn/L)P (14) In the formula: f6 is the bearing width ; is the number of bearings on the mandrel; L is the length of the entire backup roller. The calculation shows that the distribution of the load on the roll system is extremely uneven, and the load of the two backup rolls A and D is larger than that of the middle backup rolls B and C. For some types of rolling mills, the relative difference between the load values u200bu200bon the A and D backup rolls and the loads on the B and C backup rolls can reach 40%. As a result, the wear of the backup rollers on the side of the roller system is more serious, and the bearing life of the backup rollers on both sides is greatly reduced.