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Rated fatigue life of motor bearings

by:JNSN     2022-03-13
When the bearing rotates under load, due to the constant alternating load on the raceway surface of the ring and the rolling surface of the rolling element, even if the operating conditions are normal, the raceway surface and the rolling surface will be damaged due to material fatigue. do peeling or peeling). The total number of revolutions before this rolling fatigue damage occurs is called the (fatigue) life of the bearing. Even if the structure, size, material, processing method, etc. are exactly the same bearing, when rotating under the same conditions, the (fatigue) life of the bearing model will still be quite different. This is because material fatigue itself is discrete and should be considered from a statistical point of view. Therefore, when a batch of identical bearings are rotated separately under the same conditions, the total number of rotations in which 90% of the bearings do not suffer from rolling fatigue damage is called the basic rated life of the bearing (that is, the life with a reliability of 90%). It can also be expressed by the total rotation time when rotating at a fixed rotational speed. However, in actual work, damage other than rolling fatigue damage will also occur. These damages can be avoided by proper bearing selection, installation and lubrication. Basic dynamic load rating The basic dynamic load rating indicates the bearing's ability to resist rolling fatigue (that is, load capacity), which refers to a pure radial load (for radial bearings) with a certain size and direction, and the inner ring rotates and the outer ring is fixed (or inner ring). Under the condition of fixed outer ring rotation), the basic rating life under this load can reach 1 million revolutions. The basic dynamic load rating of the radial bearing is called the radial basic dynamic load rating, which is represented by Cr, and its value is entered in the bearing dimension table (represented by C in the following formula). The basic rating life formula (2) represents the calculation formula of the basic rating life of the bearing; the formula (3) represents the life formula expressed in time when the bearing speed is fixed. (Total number of revolutions) L10 u003d( C )PP (2)(time) L10ku003d (3)10660n( )CPP: basic rating life, 106 revolutions: basic rating life, h: equivalent dynamic load, N{kgf}: basic Rated dynamic load, N{kgf}: rotational speed, rpm: life index L10pnCPL10k ball bearing Pu003d3 roller bearing Pu003d310 Therefore, as the operating conditions of the bearing, set the equivalent dynamic load as P and the rotational speed as n, it will meet the design life The required basic dynamic load rating C of the bearing can be calculated by formula (4). Select the bearing that satisfies the C value from the bearing size table, and then determine the bearing size Cu003dP(L10k x )10660n p1(4) is expressed by the life coefficient (fh) and the speed coefficient (fn) The calculation formula is as follows: L10k u003d500fhf(5) Life coefficient: fhu003dfn (6C P speed coefficient: u003d(0.03n) p (7)-1fnu003d( )500x60n106Using the calculation chart [reference diagram], fh, fn and L10h can be easily obtained When choosing a bearing, it is intended to increase the fatigue life. To choose a large bearing, it will be uneconomical, and the strength, rigidity, installation size, etc. of the shaft are not necessarily based on the fatigue life. The bearings used in various machinery, according to the conditions of use, There is a baseline design life, that is, the experimental fatigue life consolidation will be taken below N 1.5 10 0.9 0.8 0.7 0.6 0.5 0.4 0.35 0.3 0.25N 10 20 30 40 50 70 100 200 300 500 1000 2000 3000 5000 100000.6 0.7 0.8 0.9 10 1.5 2.0 2.5 3.0 3.5 4.0 5.0 6.0100 200 300 3000 5000 10000 20000 30000 50000 100000H10H1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.4 0.4 0.5 0.3 0.25 0.20.190.1810 20 40 50 70 100 200 300 500 1000 2000 3000 5000 10.6 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.71.81.92.0 2.5 3.0 3.5 4.0 4.5 4.9100 200 300 400 500 700 1000 2000 3000 5000 10000 20000 30000 50000 100000H 10H [Bear Bearings] Speed u200bu200bLife Sites [ Roller bearing] empirical fatigue life coefficient fh and use of machinery correspondence table Table 3 conditions fh value and use of machinery ~ 3 2 ~ 4 3 ~ 5 4 ~ 7 6 ~ Frequent or short-term use Not often used, but it is required to ensure that the operation is not continuous , but the operation time is longer than 8 hours a day, or continuous operation for a long time for 24 hours, and it is not allowed to stop the operation of household vacuum cleaners, washing machines and other small electrical appliances due to accidents; ; small construction machinery Type electric motors; deck cranes; general cargo starters; gear bases; automobiles; escalator conveyor belts; elevator factory motors; lathes; general gear units; vibrating screens; crushers; grinding wheels; centrifugal separators; air-conditioning equipment; fan bearings; woodworking Machinery; large motors; axle cranes for passenger cars; compressors; mine cranes with important gear devices; inertia wheels (flywheels) for punching machines; main motors for vehicles: locomotive axle papermaking machinery water supply equipment; power plant equipment; mine drainage equipment.
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