Aircraft engine bearing skid specific reasons - bearing knowledge

Understands China bearing network, general machinery used in the rolling bearing because of the low speed, and there is always load act on it, rarely appear skid phenomenon. But the aviation gas turbine main bearing is easy to slip, this is because: ( 1) High speed. Under the effect of high speed, the roller under the effect of large centrifugal force is from the inner ring raceway contact trend; ( 2) The load is small. Aeroengine rotor are doing lighter, make effect on bearing radial load is small, and a maneuvering flight plane when in some cases, the effect on the bearing load of smaller, appear even zero load, as well as the rotor unbalance force in some cases would offset some effect on the bearing radial load, bearing caused by light load or no load. These two factors make produced by friction drag power is small, even to zero, in this way, it will inevitably cause bearing sliding, sliding ceng damage. For ball bearing, because it also carry axial load, so the general is not easy to skid. Aircraft engine bearing some measures to prevent the skid with drag power increased measures to prevent the bearing slide ceng reduce bearing clearance, the roller under the action of centrifugal force can still keep contact with the inner ring groove. For example, the CFM56 engine bearing high pressure turbine roll bearing ( Intermediate bearing) With the small clearance or even negative clearance to reduce slippage; And as WJ6 engine compressor forward roll bar in serious slide bearing in the long run after injury, the bearing clearance by 0. 070-0. 095 mm decrease to zero. 045-0. 065 mm, eliminates the phenomena of ceng. But, using the measures for decreasing the clearance will lead to other serious problems, so should be treated with caution, especially for the engine hot end bearing, should be more careful. In the early days of aviation gas turbine engine, in order to solve the problem of the balance of the cage, the main bearing cage positioning in the outer ring, but this design is easy to cause the bearing slide injury. This is because when the cage positioning in the outer ring, exists in the oil film between outer ring and cage under the effect of viscosity of obstruction of roll bar cage for normal movement to trigger a skid. If the cage positioning in the inner ring, in the inner ring and maintain the oil film between the frame under the action of viscous drag to a roller and cage assemblies to power its normal movement. In this way, will be scheduled in the outer ring of cage to locate on the inner ring, not only reduce the resistance, but also increase the drag power, will obviously reduce sliding ceng damage, of course it must also improve the machining precision of the cage to improve its balance. Assembly, impose an additional on bearing radial or axial load, namely on bearing 'preloading', make the bearing work, always, and between the outer ring raceway and roller has load effect, not a light load or zero load, to increase the drag force. On bearing preloading method are: using non-circular bearing and axial spring on bearing preloading and roll adopts the hollow rod and adjust the fuel injection direction of bearing, etc. The bearing outer ring made of circular cylindrical, and for the installation of bearing seat hole still make it round. Commonly used non-circular bearing with elliptical bearing outer ring and bearing outer ring of 3 valve type. Press the elliptical bearing, for example, into the bearing hole, the axis of the ellipse ( Outside the ring protruding parts) I. e. , one of the roller to here additive loads, such as the long axis in a horizontal position as shown in figure 3, make a few roller in horizontal position and keep contact and effect between inner and outer ring with a certain load, therefore, in addition to the lower roller by the gravity load, a few 90 ° around the roll bar, are all influenced by a certain amount of load, which makes the load roller number increased to about 60% of the total number of roller, can produce certain power, overcome the sliding bearing. 'Skid' is used to show that the severity of the rolling bearing is sliding and sliding when keep the actual speed is equal to the speed cage theory, bearing no skid and the skid degrees to zero; As long as you keep the actual speed is lower than the theoretical, bearing the skid, when keeping the actual speed is zero, skid degree is 100%. Commonly used to determine the actual speed cage for bearing the skid. Angelo, a firm, when developing the RB211 engine USES to detect radioactive isotope sliding bearing. In keeping the shelf fixed a small with cobalt or iridium ( Co 60,Ir 192) Silk source, using the inverse square law ( That reached a certain point of radioactivity is the square of the distance from source to point) Cage in the work of the principle of measure speed, bearing to discover whether a skid, and can calculate the skid. Can also be used for cutting the magnetic line of force principle to measure the rotational speed of the cage. To prevent axial load acting on the ball bearing to as mentioned above, the RB211 fan rotor bearing thrust bearing as a intermediary, due to the rotor of the fan will appear in the job direction of axial force, thus put into use in ( In April, 1972) Less than half a year after first appeared in the ball bearing slide injury. Then take the foregoing will maintain the orientation of outer to the inner ring measures, to a certain extent, solve the problem, but because of axial load commutation problem not solve, so for a long time, in all sorts of retrofit RB211 ( 524 b, 524 c, 524 d4 and 524 d4upgrade, etc. ) , or the occasional slip of the bearing damage events. Therefore, at the end of the RB211 retrofit RB211524G/H ( By the year 1989) , the diameter of the unloading chamber sealing YanHuan place by 556. 20 mm increase for 731. 52 mm, eliminates the rotor axial load commutation problems in the work. Basically can solve the problem of the bearing of the skid. Derived from 524 g/H RB211 development trent of engine, in addition to the large diameter of the balance of the cavity sealing YanHuan outside, still in the low pressure turbine shaft back-end install on rotor preloading springs and small bearings, fundamentally solve the problem of sliding bearing. 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