In many cases, the inner bore size of the bearing has been specifically defined by the construction of the machine or device. Regardless of the working life, the static load safety factor and the economy are all required, the size calculation must be carried out before the final selection of the remaining dimensions and structural form of the bearing. This calculation involves comparing the actual bearing load to its load capacity. The static load of a rolling bearing means that the bearing is stationary after loading (no relative movement between the inner and outer rings) or the rotation speed is very low. In this case, the safety factor of excessive plastic deformation of the raceway and the rolling element is calculated. Most of the bearings are subjected to dynamic loads, the inner and outer rings are relatively moved, and the dimensional calculations check the safety factors of early rolling damage of rolling raceways and rolling elements. Nominal life calculations are performed on the actual achievable working life according to DIN ISO 281 only in special cases. For economic performance-oriented designs, the bearing capacity of the bearing should be utilized as fully as possible. To make full use of the bearings, the more accurate the calculation of the bearing size is.
Static load bearing
Calculating the static load safety factor Fs helps determine if the selected bearing has sufficient static load rating. FS =CO/PO FS static load safety factor, CO rated static load [KN], PO equivalent static load [KN] Static load safety factor FS is a safety factor to prevent permanent deformation of the rolling parts contact area. For bearings that must run smoothly and have extremely low noise, the value of FS is required to be high; in the case of medium running noise, a smaller FS can be used; the following values are generally recommended: FS=1.5~2.5 for low noise level FS =1.0~1.5 is suitable for conventional noise level FS=0.7~1.0 for medium noise level. Static load rating CO[KN] is listed in the table for each type of bearing. The load (radial force for radial bearings and axial force for thrust bearings), the theoretical pressure generated at the center of the rolling element and raceway contact area is: -4600 N/MM2 self-aligning Ball bearing-4200 N/MM2 Other ball bearings-4000 N/MM2 All roller bearings have a total plastic deformation amount at the maximum load-bearing part of the rolling element and raceway contact area under the action of static static load CO. It is one ten thousandth of the diameter of the rolling element. The equivalent static load PO[KN] is a theoretical value, which is a radial force for a radial bearing and an axial and centripetal force for a thrust bearing. The stress generated by the PO at the center of the maximum load-bearing contact area of the rolling elements and raceways is the same as the stress generated by the actual load combination. PO=XO*F r+Ys*Fa[KN] where PO equivalent static load, Fr radial load, Fa axial load, unit is kilonewton, XO radial coefficient, YO axial coefficient.
Dynamic load bearing
The basis for the calculation of the dynamic load bearing standard method specified in DIN ISO 281 is material fatigue failure (pits), and the life calculation formula is: L10=L=(C/P)P [106 rpm] where L10=L nominal rating life [106 rpm] C rated dynamic load [KN] P equivalent dynamic load [KN] P life index L10 is the nominal rated life in units of 1 million revolutions [106 rpm] C rated dynamic load [KN] P life index L10 is The nominal rated life of 1 million rpm. For a large group of bearings of the same type, 90% of them should meet or exceed this value. The rated dynamic load C [KN] can be found in the parameter table of each type of bearing. Under this load, the bearing can reach the rated life of 1 million revolutions. The equivalent dynamic load P [KN] is a theoretical value, which is a radial force for a radial bearing and an axial force for a thrust bearing. Its direction and size are constant. The bearing life under the equivalent dynamic load is the same as the actual load. P=X*Fr+Y*Fa where: P equivalent dynamic load, Fr radial load, Fa axial load, unit is kilonewton, X radial coefficient, Y axial coefficient. The X, Y value and equivalent dynamic load calculation basis for different types of bearings can be found in the tables and prefaces of various types of bearings. The life index P of a ball bearing and a roller bearing is different. For ball bearings, P=3 for roller bearings, P=10/3
Variable load and variable speed
If the value and speed of the dynamic load of the bearing changes with time, then there must be a corresponding consideration when calculating the equivalent load. Continuous load and speed curves are replaced by piecewise approximations. The formula for calculating the equivalent dynamic load becomes:
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Minimum load of rolling bearings
Too small a load and insufficient lubrication can cause the rolling elements to slip and cause bearing damage. The minimum load factor of the cage bearing is P/C=0.02, and the minimum load factor of the full bearing is P/C=0.04 (P is the equivalent dynamic load and C is the rated dynamic load)
Bearing accuracy and grade
The accuracy of the rolling bearing is divided into (main) dimensional accuracy and rotation accuracy. The accuracy level has been standardized and is divided into five levels: P0, P6, P5, P4, and P2.
The accuracy is increased from the 0th level in order, and is sufficient for the general purpose 0 level, but when used in the conditions or occasions shown in Table 1, an accuracy of 5 steps or higher is required.
Although the above accuracy level is based on the ISO standard, its name is different in national standards.
Table 2 lists the accuracy levels applicable to the various bearing types and the comparison between national standards. Dimensional accuracy (items related to shaft and housing installation)
1. Allowable deviation of inner diameter, outer diameter, width and assembly width
2. Allowable deviation of the diameter of the compound circle and the diameter of the outer complex circle in the roller group
3, the allowable limit value of the chamfer size
4. Allowable variation of width Rotation accuracy (item related to the rotation of the rotating body)
1. Allowable radial runout and axial runout of the inner and outer rings
2, the inner ring allows lateral runout
3. Allowable variation of the inclination of the outer diameter surface
4. Allowable variation of the thickness of the thrust bearing raceway
5. Allowable deviation and allowable variation of tapered bore
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