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Distribution of bearing load and calculation of equivalent dynamic load

by:JNSN     2021-12-25
In order to distribute the load acting on the shafting to each supporting bearing, the radial component force of each load can be obtained first, and then the vector sum can be obtained according to the direction of the component force. An example of radial load distribution is shown in Figure 5.1. In most cases, while the bearing bears the radial load, it also bears the axial load, that is, bears the combined load of the two. At this time, it is converted into an equivalent dynamic load, and its value is taken as the bearing load. FA u003d l2 · Fl FB u003d l1 · F. Distribution of bearing load. Bearings mostly bear the combined load of radial load and axial load, and the load conditions are varied, such as changes in size. Therefore, it is impossible to directly compare the actual load of the bearing with the basic dynamic load rating. Therefore, the actual load is converted into an imaginary load passing through the center of the bearing and having a fixed size and direction for analysis and comparison. Under this imaginary load, the bearing has the same life as the actual load and speed. The imaginary load converted in this way is called the equivalent dynamic load (P). Calculation of equivalent dynamic load The radial equivalent dynamic load (Pr) of radial bearing (including component ball bearings) bearing a combined load with a certain size and direction can be calculated by the following formula. Pru003dXFr + YFa. In the above formula, Pr: radial equivalent dynamic load, NFru003d: radial load, NFAu003d: axial load, NXu003d: radial load factor (refer to Table 5.4). Y u003d Axial load factor (refer to Table 5.4). Table 5.4 Radial load factor (X) and axial load factor (Y). Remarks) 1. The values u200bu200bof C0r (radial basic static load rating) and f 0 (factor) are shown in the dimension table. 2. When the value of f 0 Fa / C0r does not match the above table, use the interpolation method to calculate. Average equivalent dynamic load when load changes 5.4 Basic static load rating and equivalent static load 5.4.1 Basic static load rating ① Self-aligning ball bearing 4 600 MPa ② Other ball bearings 4 200 MPa (including component ball bearings) ③ Roller bearings 4 000 MPa Table 5.5 Calculation method of average equivalent dynamic load when load changes (1) Step change (2) Monotonous change (3) Sine change Pm u003d P1 pn1t1 +P2 pn2t2 + +Pn pnntnn1t1 +n2t2 + +nntn p Pm = Pmin + 2 Pmax Pm u003d 0.68 Pmax (4) sinusoidal change (the upper half of the sine curve) in (1) ~ (4) Pm P1 P2 Pn Pmin: minimum equivalent dynamic load, N Pmax Σniti: total revolutions during t1 ~ ti When the number Pm u003d 0.75 Pmax bears the load of changing size or direction, it is necessary to calculate the average equivalent dynamic load to make the bearing have the same life as the actual changing conditions. The calculation method of the average equivalent dynamic load under various changing conditions is shown in Table 5.5. : Average equivalent dynamic load, N: equivalent dynamic load at speed n1 and action time t1, N: equivalent dynamic load at speed n2, action time t2, N: equivalent dynamic load at speed nn, action time tn , N: Maximum equivalent dynamic load. When the N bearing is subjected to excessive static load or impact load at very low speed, the contact surface of the rolling element and the raceway will produce local permanent deformation. The amount of deformation increases with the increase of the load, if it exceeds a certain limit, it will affect the normal rotation. The so-called basic static load rating refers to the static load that generates the calculated contact stress as shown below in the center of the contact surface between the rolling element and the raceway subjected to the maximum load. Under this contact stress, the total permanent deformation of the rolling elements and raceways produced is about 0.0001 times the diameter of the rolling elements. The basic static load rating of the component ball bearing is expressed by (C0 r ), and its value is shown in the dimension table.
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