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Rated fatigue life of motor bearings

by:JNSN     2021-12-26
When the bearing rotates under a load, because the raceway surface of the ring and the rolling surface of the rolling element are constantly subjected to alternating loads, even if the conditions of use are normal, the raceway surface and rolling surface will appear fish-scale damage due to material fatigue (called Do peeling or peeling). The total number of revolutions before this rolling fatigue damage occurs is called the (fatigue) life of the bearing. Even for bearings with exactly the same structure, size, material, processing method, etc., when rotating under the same conditions, the (fatigue) life of the bearing model will still show a big difference. This is because material fatigue is inherently discrete and should be considered from a statistical point of view. Therefore, when a batch of the same bearings are rotated separately under the same conditions, the total number of rotations at which 90% of the bearings do not have rolling fatigue damage is called the basic rating life of the bearing (that is, the life of 90% reliability). It can also be expressed by the total rotation time when rotating at a fixed speed. However, in actual work, damage phenomena other than rolling fatigue damage may also occur. These damages can be avoided by making good bearing selection, installation and lubrication. Basic dynamic load rating The basic dynamic load rating indicates the bearing's ability to withstand rolling fatigue (ie load capacity), and refers to a pure radial load (for radial bearings) with a certain size and direction. The inner ring rotates and the outer ring is fixed (or the 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 a radial bearing is called the radial basic dynamic load rating, expressed by Cr, and its value is entered into the bearing size table (indicated by C in the following formula). The basic rating life formula (2) expresses the basic rating life calculation formula of the bearing; the formula (3) expresses the life formula expressed in time when the bearing speed is fixed. (Total number of revolutions) L10 u003d (C) PP (2) (time) L10k u003d (3) 10660n () CPP: basic rating life, 106 revolutions: basic rating life, h: equivalent dynamic load, N{kgf}: basic Rated dynamic load, N{kgf}: speed, rpm: life index L10pnCPL10k ball bearing Pu003d3 roller bearing Pu003d310 Therefore, as the service condition of the bearing, set the equivalent dynamic load to P and the speed to n to meet the design life The required basic dynamic load rating C of the bearing can be calculated by equation (4). Select the bearing that satisfies the value of C from the bearing size table to determine the size of the bearing Cu003dP(L10k x )10660n p1(4) Expressed by the life factor (fh) and speed factor (fn), the calculation formula is as follows: L10k u003d500fhf(5) Life Coefficient: fhu003dfn (6C P Speed u200bu200bCoefficient:u003d(0.03n) p (7)-1fnu003d( )500x60n106 Use the calculation chart [reference diagram] to easily find fh, fn and L10h in When choosing a bearing, it is intentional to increase the fatigue life. It will be uneconomical to choose a large bearing. The strength, rigidity, and installation dimensions of the shaft are not necessarily based on the fatigue life. The bearings used in various machines are based on the conditions of use. Reference design life, that is, the empirical fatigue life coefficient refers to the following table n 1.5 10 0.9 0.8 0.7 0.6 0.5 0.4 0.35 0.3 0.25 02019018017 016 015n 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 6.0 100 200 300 400 500 700 1000 2000 3000 5000 10000 20000 30000 50000 100000h10h1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.55 0.5 0.45 0.4 0.35 0.3 0.25 20 40 50 70 100 200 300 500 1000 2000 3000 5000 10000nn0.62 0.7 0.6 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 2.5 3.0 3.5 4.0 4.5 4.9 100 200 300 400 500 700 1000 2000 3000 5000 10000 20000 30000 50000 100000h 10h [Ball bearing] Speed u200bu200blife Speed u200bu200blife [ Roller bearing] Correspondence table of empirical fatigue life coefficient fh and used machinery Table 3 Condition fh value and used machinery ~ 3 2 ~ 4 3 ~ 5 4 ~ 7 6 ~ Frequent or short-time 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 24 hours continuously. It is not allowed to stop operating household vacuum cleaners, washing machines and other small appliances due to accidents; electric appliances, calenders, agricultural machinery, household air conditioners, motors ; Small construction machinery Type motor; deck crane; general cargo starter; gear frame; automobile; escalator conveyor belt; elevator factory motor; lathe; general gear device; vibrating screen; crusher; grinding wheel; centrifugal separator; air conditioning equipment; fan bearing; woodworking Machinery; large motors; cranes for passenger car axles; compressors; important gears and mine cranes; punch inertia wheels (flywheels); main motors for vehicles: locomotive axles, paper-making machinery, tap water equipment, power plant equipment, and mine drainage equipment.
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