请教一个关于轴承故障的问题
如果轴承跑外圏的同时，轴承外圈有剥落之类的故障频谱图上外圈缺陷频率会出现转频的边带吗？
观察不到吧 再学习一下调制和边带的机理。自己想想就明白了！ 剥落的话那是高频了，上千赫兹 jayceefang 发表于 2017-1-4 23:42
剥落的话那是高频了，上千赫兹
是吗？能详细说一下吗 本帖最后由 18618180420 于 2017-1-9 11:25 编辑
很有可能会出现转频边带的
楼上的资料 我大致看了一下不错
DEFECT SEVERITYBearing BehaviorA properly selected and installed angular contact bearing should have anevenlydistributed thrust load on theentire surface of both races. Under such conditions thebearing typically developssmall defects all the way around the race. The combinationof a 360 degree load zone andmultiple small defects produces a series of harmonics ofball pass frequency. The numberof harmonics generated is related to the circumferenceof both races and/or the lengthof the load zone.A properly selected and installed deep groove ball bearing should carry aradial load inabout one third of thecircumference. Under these conditions, the bearing develops adefect in the load zone thatgenerates a single ball pass frequency. Two defects cangenerate the second harmonic ofball pass frequency. If the load -- as "felt" by thebearing -- is on the rotor, as occurs in imbalance, a spall shouldoccur on the inner race(if the inner race is rotatingand the outer race is stationary). The load zone is always atthe same spot on the innerrace. If the load is external to the rotor, as is the case withover-tight V belts, the defectshould occur on the outer race at the load zone, because theload zone is always at the sameplace on the outer race.If a thrust bearing is notevenly loaded over its circumference and has a radial load, itwill behave like a radialbearing; that is, it will produce a single ball pass frequency. Ifa radial bearing has anabnormal thrust load, it will behave like a thrust bearing; that is,it will generate severalharmonics of the ball pass frequency. Bearings that are subjectedto the type of loads for which they were not designed fail quickly.Excessive loads canbe identified with spectralanalysis. This is accomplished by accurately measuring thegenerated BPFO or BPFI and thencalculating the contact angle. The contact angleidentifies the amount of thrustload.A beginning defect on either race generates ball pass frequency. Early spallinformationcan be identified when hairlinecracks develop. Manufacturing defects, such as holes inthe race the size of a sharppencil point, can be identified. Ball pass frequency can bedetected in unloaded machines,for example an electric motor not connected to a drivenunit or a new motor on the shopfloor.After a defect has begun, itwill get larger, and the spectral bandwidth will get wideruntil the spectrum is modulatedwith the speed of the rotating unit. The ball passfrequency and the ball passfrequency plus or minus the unit speed may be generated.Modulation can continue untilthe ball pass frequency is no longer apparent. (In somecases the amplitudes of the sumand difference frequencies are equal to or exceed thoseof the ball pass frequency.)The spectrum then becomes a series of frequency peakswhose difference frequency isequal to the unit speed. These phenomena occur when agrowing fatigue spall ispresent on the race.The limits of a significantchange in vibration level depend on the type of equipment involved and thecause of the vibration. For a coupled pump and motor that normallyvibrate at 0.07 IPS, a changeof 0.05 IPS could be significant and should be inspected. Onthe other hand, a bucketelevator that normally vibrates within a range on either side of0.5 IPS could be checked on aperiodic basis or when a change of 0.2 IPS occurs. At theother extreme, a cracked innerrace may not cause a noticeable change in the vibrationamplitude.Defects in antifrictionbearings can be identified at 0.008 IPS; an increase of 0.1 IPS in abearing could thus beimportant, whereas an increase of 0.1 IPS in an imbalance conditionmight cause little concern.Excessive vibration can bedefined as that level of vibration that experience has shown tobe harmful to a particularpiece of equipment. For a directly coupled pump and motor,excessive vibration could be0.05 IPS at a bearing frequency. For a fan that weighs 2,000pounds, 0.25 IPS at runningspeed could be excessive. At the other extreme, a 20 poundfan could vibrate at 2.0 IPS atrunning speed for long periods without incident.Bearings in rotating machineryshould be periodically checked with a frequency spectrumand time signal to detect and studydeveloping defects on the outer and inner races. Anaccurate method for thecalculation of bearing defect length is needed to allow aquantitative determination ofthe defect severity. With the defect size and progressionof development determined, theremaining bearing life can be estimated.Empirical measurements indicatethat a 6313 bearing can generate six harmonics of BPFIif the bearing a) is in athrust load; b) is failing from a shallow flaking spall; and c) hasa defect all the way around therace. The same bearing can generate seven harmonics ofBPFO if the above threeconditions are met.When deep fatigue spalls arepresent, pulses are generated. The FTT contains severalharmonics when pulses arepresent. Etching, corrosion, and fluting can also cause manyharmonics.In spherical and tapered rollerbearings, the length of the defect on the outer race can beapproximated by harmoniccontent. If the bearing is failing from a shallow flaking spall,each true harmonic of BPFOequals about 0.5 inches of defect length. For example, aspherical roller bearing thatis generating six harmonics of outer race ball pass frequencyindicates an outer race defectabout three inches long.If the above knowledge and thefollowing information on the inner race are used toapproximate defect size, andapplied to your diagnostics, it is helpful in assigningpriorities for repair. Forexample, we may want to replace bearings with large defectsbefore we replace bearings with small defects.
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