Abstract: Referring to the calculation method of dynamic load rating of four-row tapered roller bearings of TIMKEN and other foreign bearing companies, a method for calculating the dynamic load rating of domestic four-row tapered roller bearings is proposed.
1 The calculation method in the national standard
In GB/T6391-2010 “Rated Dynamic Load and Rated Life of Rolling Bearings”, the calculation of rated dynamic load and rated life of single-row and double-row radial roller bearings is clearly specified, and the situation of combined bearings is also explained. The calculation of the rated dynamic load of the combined bearing is as follows: 2 or more sets of single-row roller bearings are installed on the same shaft and run as a whole in a tandem configuration. The manufacturing and installation accuracy can ensure uniform load distribution. The radial direction of the bearing The dynamic load rating is equal to the 7/9th power of the number of bearing sets multiplied by the dynamic load rating of a set of single-row bearings.
Where: Cr is the radial dynamic load rating; bm is the material coefficient; fc is the geometric coefficient; i is the number of rows of rollers; Lwe is the effective contact length of the rollers; α is the angle between the outer raceway and the center line; Z is the Number of rollers per row; Dwe is the average roller diameter.
2 Foreign calculation methods
The dynamic load rating of TIMKEN’s bearings is based on the rated life of 9 × 107r revolutions or working 3000h (500r/min). The calculation of the dynamic load rating of the double-row and four-row tapered roller bearings of SKF is also based on the rated life of 9×107r or working 3000h (500r/min).
TIMKEN believes that it is more practical to use 9×107r as the rating life, because most bearings are equal to or exceed this value. Based on this formula, TIMKEN has carried out extensive bearing fatigue life tests, and the results have proved that this method is an effective method to evaluate the actual life of bearings.
For a double-row bearing, when the loads of the two bearing rows are equal, the rated dynamic load C90(2) of the double-row bearing considering the service life of the component system can be obtained from the formula (2), at this time, i=2 in the formula.
When ni=0.1r/min, axial load Fa=250kN, radial load Fr=140kN, and overturning moment M=1300kN·m, calculate the fatigue life, take the bearing clearance as 0, -0.01, -0 .02, -0.03, -0.04, -0.05, -0.06 and -0.1mm, substitute the above parameters into equations (14) to (16), and use the Newton-Raphson iteration method to calculate δa , δr and θ, and calculate the normal contact load of the bearing at different position angles according to (13). Substitute the required results and parameters into equations (17) to (25) to calculate the rated life of the bearing ring and the complete set of bearings. The results are shown in Table 1. It can be seen from the table that with the increase of the absolute value of the negative clearance of the bearing, the rated life of the pitch bearing first increases and then decreases. The pitch bearing generally requires a service life of 20 years , which is equivalent to 175200h, and can meet the requirements when the bearing clearance is -0.04 ~ 0mm. Therefore, in order to meet the requirements of bearing life when designing pitch bearings, a reasonable bearing clearance should be selected.
When the bearing clearance is 0 and different bearing groove curvature radii are used, the calculation results of the rated life of the ring and the entire bearing are shown in Table 2. It can be seen from Table 2 that the larger the curvature radius coefficient of the pitch bearing groove, the shorter the bearing life. This is mainly because with the increase of the groove curvature radius coefficient, the tightness of the steel ball and the groove decreases, and the contact ellipse area is relatively small under the same load, and the contact stress is large, thereby reducing the bearing life.
3 The proposed calculation method
Referring to the calculation method of dynamic load rating of four-row tapered roller bearings of TIMKEN company, and comparing with the Cr value of four-row tapered roller bearings of other companies in the world, it is considered that the rated dynamic load of four-row tapered roller bearings in China should be calculated according to the following method. calculate.
In the Chinese bearing industry, when calculating the dynamic load rating of the four-row tapered roller bearing, most of them only take i in the formula (1) as 4, so the calculated Cr is too small. By referring to the calculation methods of TIMKEN and other foreign bearing companies, a new method for calculating the dynamic load rating of four-row tapered roller bearings is proposed.