Aircraft engine bearing slide ceng injury and prevention measures - bearing knowledge

Aircraft engine bearing according to the principle of using function, typically using rolling bearing to work, because of the sliding friction coefficient is greater than the rolling friction coefficient, and some external factors make the roller and the inner and outer ring rolling forming dry friction, cause slippery, roller and inner and outer ring rolling on a rub marks and partial surface wear, etc. , the so-called 'ceng damage'. Bearing once appear smooth ceng damage, surface finish was damaged and friction coefficient increase, accelerate the wear process, make the roller diameter smaller, rolling path appear uneven slot mark, bearing damage, harm of rotor work, directly affects the normal work of the engine. 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. Bearing a smooth ceng damage has no direct relation with time, within a very short time, sometimes work in the engine, sometimes appear only after the engine working for a long time. In addition to bearing design, installation and the working conditions have an impact on bearing whether there will be a smooth ceng, engine assembly work sometimes play a major role. Such as turbine rotor assembly to the engine, in order to avoid rolling stick before turbine bearings roll bar block hoisting, commonly used vaseline coated between outer ring and the roll bar, to make the roll roll stick close to the outer ring road. It convenient for the engine assembly, but as a trial run for the first time in low temperature outdoor, may because of vaseline sticky hindered the normal movement of roll bar cage caused the bearing appears smooth ceng damage. Figure 1, applied to the rotor of a fighter engine on the ball bearing axial load with altitude, H) With the change of Ma after rolling bearing appears smooth ceng, the most common is the result of the surface abrasion wear, surface spalling, etc. Serious when, due to the friction between the roller and the inner ring produces too much heat can make the inner ring expansion, reduced the inside of the bearing clearance, bearing card to death. Therefore, in the aviation gas turbine on the main bearing, should pay special attention to prevent the bearing slide. At present, in most of the design, in order to reduce the sliding bearing, reduce the blocking roller can be use to maintain movement resistance method, also can adopt the method of increasing drag power, or both. 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.