轴瓦乌金碎裂与碾压(Bearing+and+crushing+of+bearing)

轴瓦乌金碎裂与碾压（Bearing and crushing ofbearing）轴瓦乌金碎裂与碾压(Bearing and crushing of bearing)Bearing and crushing of bearingBearing shell sharply fracture is common in small and medium-sized units, sharply rolling on the large unit is relatively common, once appear, and these failures before did not find out the cause of the problem and find out some effective measures, will happen frequently, which have to frequent downtime check and replace the bearing shell. Therefore, these faults are not malignant, but have great influence on the utilization rate and safety of the unit.5.4.1 the general situation and characteristics of the axial and crushing accidentsThe crushing and crushing of axial ujin is generally found in the new machine, and some of the units have been repaired. The RCC can be formed at a time when the unit is stopped. The fracturing of the ujin is usually formed by the operation of 1-2 weeks, and the few units with special faults can be formed in one or two days.The image shows a 12MW back-pressure turbine with 2 watts of lower tiles, and the new tile is broken after 2 months of operation.It can be seen from the figure that the axial fragmentation isevenly distributed along the axial length, and the ujin fracture occurs in the highest oil film pressure region in the working state, and thedamaged edge is evenly distributed along the boundary line of the oil capsule. From the fragments, someof the pieces had fallen off completely from the tile, and a largegap had been formed between them. This phenomenon shows that after the fracturing of the ujin, after a long time running, the marginal small cracks develop and form the granules and are washed away by the oil flow.In general, the bearing of the group is not installed in the temperature measuring point, so the fracturing of the ujin is difficultto find in the operation of the unit. However, even if the temperature measurement points are installed on the ujin, if the measuring point is not in the zone of ujin, then the ujin temperature is not abnormal after the fracturing. And even though the temperature measurement points arein the ujin fragmentation area, the ujin temperature is no abnormalafter the fracturing. Only when the shaft neck and the temperature measurement point are directly touching the extremely short moment. Asthe temperature rises, the temperature measurement points are quickly damaged due to grinding. Temperature measurement point damage is a common fault of the running unit, and it is not usually caused by the disintegration of the uljin. So some units bearing cataclastic continues to run, after the debris area is decreasing, the journal with tiledirectly touching ground, thus not only make the journal serious wearand tear, and as the rotor, severe wear on flow passage.The bearing pressure of the bearing is that the ujin is subjected to excessive compressive stress (dynamic, static load), or the temperatureof the ujin is raised and softened, resulting in extrusion deformation under normal pressure. The extruded ujin first blocks the oil hole in the top of the roof, then squeezes the ujin into thin slices, which are brought toand accumulated in the mid-section oil gap by the rotating shaft neck.When the temperature of the ujin is too high, and the softening produces plastic deformation or wear, the high temperature of the ujinis attached to the shaft neck, which causes a gnawing of the ujin, which causes more serious damage to the bearing. If sharply plastic deformation and wear damage the normal oil wedge, lower oil to reduce or block can make sharply temperature rise sharply, so this kind of fault handling a bit not in time, can cause bearing shell burned. The falling of the ujin rotors causes severe mine grinding and a series of failures and accidents, but this failure can be effectively prevented by monitoring the ujin temperature.5.4.2 mechanism and cause of the bearing fracture of the bearingIn order to correctly understand the causes of ujin and to formulate effective countermeasures, it is necessary to find out the mechanism of the fracturing of the ujin.5.4.2.1 the mechanism and process of ujin fragmentationIn the working speed of the rotor, the oil film with a thickness of 100-300 mu m between the shaft neck and the ujin is determined by the diameter of the shaft, the shape of the shaft, the rotational speed,etc., and there is a relative vibration between the shaft neck and the shaft. Further, the excitation force on the rotor passes through the shaft neck and the oil film to the bearing seat, causing the oil film to produce alternating force. When the stress is too high, the surface of the ujin will form a small fatigue crack, and then the pressure of the oil film pressure will crack into the small crack, so that the small cracks will expand and penetrate, and the ujin will form the broken pieces. These fragments, under the influence of alternating oil wedge forces, fall off from the tile, causing the broken pieces to collide and change the pressure oil wedge into the small crack.The debris is continue to break into pieces, small pieces are constantly flow washed away, declining sharply bearing area, and finally so the pressure is too high, soften temperature rise sharply, the remaining bearing sharply extrusion into thin slices, squeezed out from the oil gap, rotor, shaft neck and tyres are mill directly. This is sharply during the process of fracture damage, but because of the sharply after fracture, journal on cataclastic sharply still can continue to run a long time, so most of the unit before the fractured sharply after melting, stop check the bearing shell can be found as shown in the situation, thereby preventing the damage of journal later. Therefore, it is more common in the field, but the accidents of the shaft neck and the flat tire are smaller.5.4.2.2 reasons for the fracturing of the ujinThe results show that there are two reasons for the fracturing ofthe bearing: one is that the relative displacement of the shaft neck is too large, which causes the pressure of the larger alternating oil film. The second is the stiffness and resistance of oil film, which can not effectively cushion and damp the oil film. The reasons for the relative displacement of the axial radial relative displacement, the stiffness of theoil film and the small damping are discussed.1. The axial radial relative displacement is too largeThe reasons for the relative displacement of axial radial relative displacement are:(1) the rotation axis is excessively vibratingThe relative amplitude of the rotation axis is proportional to the excitation force and the bearing stiffness of the bearing, which is inversely proportional to the stiffness of the oil film. The axial amplitude is proportional to the excitation force and inversely proportional to the dynamic stiffness of the bearing. Unit shaft amplitude commonly so, Jane ground reflects the relative vibration shaft size, but for small and medium-sized turbine bearing, as smaller quality of rotor, bearing support dynamic stiffness relative quality (rotor) is larger, and under the small shell amplitude, axis relative vibration is larger; Instead, large unit steam turbine, especially the low pressure rotor and generator rotor bearing, bearing support dynamic stiffness is low, under the small shell amplitude, axis relative vibration cannot toobig, so the bearing shell sharply rupture occurs mostly in small and medium-sized turbine bearing, large generator shaft fractured sharply rare defect.Causes of the shaft relative vibration exciting force is too large, the relative vibration caused by the rotation of exciting force and bearing vibration exciting force, the failure cause of these exciting force with its diagnosis method, in the second chapter has introduced in detail in section 2.There are two main kinds of excitation force that cause the relative vibration of the axis of rotation, one is the rotor unbalance force, which includes the rotor thermal variation and the permanent bending. The second is the axial half speed vortex.(2) the original swing of the bearing is too largeThe original pendulum value of the shaft is too large, and the rotation of the rotor is like the relative vibration of the rotating shaft, which can also lead to the large pressure of the alternating oil film. The reasons for the excessive pendulum swing are:1) axial machining error. The shaft neck processing is bad, make its ellipse passes big, sometimes in the neck axial length of a smallellipse through the big, will cause the ujin to break up. From a large number of measured data, when the ellipticity exceeds 0.05 mm, it will result in the disintegration of ujin. Therefore, the ellipticity should be less than 0.02 mm for the axial neck and the running of the new unit due to wear.Check shaft neck ovality, will on tile peel, axial length uniformly distributed along the axis neck 3-4 measuring plane, and the circumference of each measurement plane can be divided into eight parts, measured with a dial indicator along the vertical direction in turn each point of the circular flat machine shake pendulum value, and then calculate each plane in the direction of maximum diameter difference, the difference is called the ovality. Each plane ellipse should be less than 0.02 mm.2) rotor bending. The unbalance caused by permanent bending or thermal bending of the rotor can be compensated by aggravation, but it will increase the pendulum value of the shaft. There are some rotorsthat are bent, and by aggravating, the axis vibration is satisfied, but then the bearing is broken.The permanent bending of the rotor causes the rotation of the axles to be checked, which is the same as the concentricity method in the fourth section of the second chapter. The heat bending of the rotor causes the axial wobble to increase, and the relative vibration of the rotor is increased or not.3) axial connection concentricity bias. Shaft connectionconcentricity deviation, is mainly due to the coupling reaming installation and overhaul, the two rotor has failed to cause the concentric, so when the shaft after the bolt tightening, caused by the different heart of two rotor shaft neck set value is too large.2. The stiffness and damping of axial oil film are insufficientPantile normal circle and ellipse of oil film has good buffer and damping action, but for some needs and traditional habits of scraping tile, often under the will of the two bearings tile scraping into shape as shown in figure 5-5 oil capsule.A large number of field tests proved that this kind of bearing vibration resistance less oil scraper capsule shell is much lower, so some units after start-up and commissioning was put into operation, frequent sharply fracture, but the measuredaxis relative vibration is less than 50 microns, the journal each point set value is less than 0.02 mm. The vibration of the rotating shaft was found in the normal load process, and the vibration increased to 100-130 mu m, which lasted only 1-2min. Also, some of the units under the 3000 r/min and carrying load process, the rotor vibration are less than 50 microns, only in the process of the unit start-stop, through the critical speed, rotor shaft vibration of 100-160 microns, only 2 to 3 times of start-stop, jie tile inspection, found that sharply has obvious fracture, the fracture zone as shown in figure 5-4, along the oil sac border.For these units, it is more difficult to reduce the relativevibration of the shaft. A simple and effective measure is to improve the bearing vibration resistance, increase the oil film thickness and damping, the specific measures are bearing shell after the car, the fluctuation of tile edging slightly revised, slips do not make any repairs. Through the experiment of multiple machines, a new tile couldonly be used for half a month to break up and replace the bearing ofoil-free follicles. After 4-5 years of operation, there was no such accident. It is proved that the reason of the fracturing of the shaft of the oil bladder is caused by the relative vibration of the small axial neck, which is due to the significant decrease in the anti-vibration performance of the bearing.5.4.3 the causes and mechanism of the bearing of the bearingIf the fracturing of the ujin is caused by the dynamic load, the squeezing of the ujin is caused by the static load and the excessive temperature of the ujin. However, further researchhas found that the relative vibration of the short - time axial neck can cause the crushing of ujin in addition to the simple static load overload. The reasons and mechanism of the two kinds of loading are discussed in detail below.5.4.3.1 static loadThe axial static load mainly comes from the rotor; The second is the preload on the rotor. The preloading source on the rotor has been introduced in section 6 of chapter 3.The operation of large sets of imported, imported and domestic steam turbine low pressure rotor bearing, due to the design pressure is quite high, so the design though chose pantile carrying capacity of the highest circle, but the runtime these sharply rolling bearing often occur.The generation of this roller is suspected to be due to the failure of the oil film to establish the oil film in the disk and at low speed, and the shaft oil does not lift the rotor. It is proved by the measured axial buoyancy that it is not. FIG. 5-6 shows the relationship between the volume and rotational speed of a domestic 600MW unit (the front tile of low pressure rotor II).By figure 5-6, barring (start jacking oil pump) when the shaft neck float amount to 50 microns, bearing shell temperature sharply with imported oil temperature very close to, ran after the turn speed of more than 200 r/min, shaft neck float amount is more than 80 microns, at this time was not significantly elevated temperature sharply, clearly very sharply temperatureis above 2800 r/min and after loading, the general is 98-103 ?C.From the bearing pressure analysis, low pressure rotor bearing pressure are usually on the high side, numerical 1.401.7 Mpa, and than the pressure of the bearing surface area is calculated by journal (L.D) projection area, it is much bigger than the shaft neck confined area, so sharply actual bear is bigger than pressure is calculated. Assume that journal and the bearing contact Angle 60 ?, bearing and the bearing contact arc length is 0.524 D, considering both sides of the bearing contact with the journal the existence of the oil film pressure, also can undertake part of the load, to a conservative estimate,The actual pressure area of the axial neck is 0.7 DL, so the real ratio of ujin is 2.0-2.4 Mpa, which is 42% higher than the calculated value. General sharply at room temperature under the compressive stress will not produce plastic deformation, that is to say, in the operation of busbar sharply rolling deformation, temperature will rise, strength decrease after plastic deformation. After the long drive and low speed heating machine, the machine is checked and the ujin is intact, which indicates that the above analysis is realistic.The temperature rise of the general assembly is mostly at a higher speed. This is due to increased pressure, increase significantly under the high speed bearing friction calorific value, when its calorific value can not be oil flow away entirely, heat accumulation, as speed increases sharply temperature significantly higher; When the temperature rose to 110 ?, the sharply, though not soften, but its strength will decrease, which will produce a certain rolling deformation; If the deformation causes the wedge to be damaged, the oil content of the lower tile will decrease, the temperature of the ujin will rise rapidly, and the ujin will produce a larger plastic deformation. When the oil wedge is severely damaged, the temperature will increase sharply. Even if the brake stops, the temperature of ujin will continue to rise. Run a lot of experience has shown that when sharply raised to 110 ? C temperature, hits the brake, eventually sharply temperatures often exceed 130 ? C, and 150 ? C, sharply inevitably produce severe when rolling and wear; Sharply above 160 ? C temperature, finally, because of the sharplyserious wear and tear, damage of temperature measuring point, thus the final temperature sharply there has checked, but from the accident sharply after a large number of melting outflow phenomenon analysis, sharply temperature has more than 230 ? C in the end.Sharply to avoid a bearings rolling, wear, melting, axle bushsharply in the equipment operation temperature should not be only a maximum value, at the same time should also be stipulated temperature reaches a certain limit of allowable temperature rise rate, thus to ensure that when the temperature rise sharply to a certain limit, hits the brake process is still within the permitted temperature continues to rise.Field and some units bearing pressure is not high, but also can form sharply severe crush and wear and tear, this is due to the bearingrepair damaged the normal after scraping oil wedge or bearing gap is too small, caused by lower significantly reduce the amount of the oil that is scraping tile process and improper maintenance.At present, the low pressure rotor of the large unit is too high, and it is a prominent problem that the friction and wear are frequently produced. In terms of eliminating countermeasures, the factories have made more attempts, but the effect is not satisfactory. These measures include:1. Lower than pressureAt present, it is used to reduce the static load of this tile. However, the adjustment is not large due to the pressure limitation of the adjacent bearing.2. Reduce the oil temperature of the bearingAccording to several unit tests, the temperature of the ujin temperature decreases with the decrease of the oil temperature of the imported oil, but the adjustment amount is not large.3. Lower the oil scraperExperiments on several units, lower oil scraper capsule has some effects to sharply lower temperature, but not significantly, and can make larger mechanical impurity particles in oil into the next tile,tile sharply and shaft neck under serious scratches.4. Improve the scraping process, but the bearing is not to be shavenAlthough there are a lot of operating experience shows thatsharply temperature has great influence with scraping tile process, but if improve scraping tile process, sharply to reduce temperature, then the original high temperature is caused by improper scraping tile technology, and, arguably, it is a good blow a bricklayer's technique with bearing bush is better than machine finishing car to ensure oil wedge, thus the use of bearing bush should improve machining quality and technology, to improve the journal contact with sharply, try not to blow by building to improve the journal contact with sharply. But at the moment, in addition to the three oil wedge and tilting at the scene not blowing outside, other bearing shell are by different degree of repair,and many bearing bush once use, therefore scraping tile this technology in domestic in a relatively long period of time will also continue to be used. In addition to ensuring that the axial axial and ujin contacts are evenly distributed, it is more important to ensure that a good oil wedge is established in the operation.Therefore, the axial radial contact should take the weight of the lower tile center line and the principle of gradual reduction on both sides.5.4.3.2 the axial vibration is too largeJournal of relative vibration limit value is equal to the bearing clearance value, this phenomenon is called the limit cycle in vibration, its physical meaning is direct contact with the shaft neck and sharply and when the contact pressure over sharply material pressure can be sharply rolling deformation, deformation occurs first on the bad oilfilm formation and axial ends, due to the large vibration time is not long, so shaft neckis less vibration value is formed sharply rupture is much larger, but not sharply general fracture, and there is no impact bearing shell input, so will not rise sharply temperature.。