Cause analysis and detection of blade cracks of th

2022-08-21
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Cause analysis and detection of fan blade crack

rotor system is an important component of rotating machinery. Blade fracture caused by rotor crack propagation is very harmful to rotating machinery. At present, there are many researches on the vibration characteristics of rotor blade cracks, and few researches on the diagnosis and identification technology of rotor blade crack faults, while the identification of rotor blade cracks and their propagation. Visual inspection of the sample gauge distance will cause a certain deviation; Its 2 is of great significance for the final diagnosis of blade crack fault. In the fault diagnosis of mechanical equipment, the classical signal processing methods based on stationary process - Fourier transform analysis and windowed Fourier analysis are usually used at present. Compared with 2018, covestro will continue to strive to provide materials and expertise for the development of the industry, with an increase of more than 53%. The statistical average results of signals are given only in the time domain or frequency domain, respectively, which cannot take into account the overall picture and localization characteristics of signals in the time domain and frequency domain at the same time, These localization characteristics are often the characteristics of faults

the cause of crack is stress concentration. The finite element analysis shows that under the action of water pressure and centrifugal force, the large stress area of the runner is mainly distributed around the runner blade, and the equivalent stress calculated according to the third strength theory is distributed around the blade. Generally, there are four high stress zones in the runner blades, which are located on the front of the blade inlet side (pressure distribution surface) near the upper crown; The middle of the front of the blade outlet edge; The back of the water outlet edge of the blade is close to the upper crown; In the connection area between blade and lower ring. Casting defects and welding defects. Under the action of external stress, casting pores and sand holes may become the source of cracks, resulting in cracks. Due to the large thickness difference between the runner blade and the upper crown and lower ring, shrinkage and porosity are easy to occur during the cooling process. For the runner of cast welded structure, if the welding process is improper or the welder does not weld according to the requirements of the welding process, cracks will also appear in the weld and heat affected zone

due to the original design problem, the transition R angle between the runner blade and the upper crown and lower ring is designed to be small, causing stress concentration. Due to operation reasons, long-term low load, overload or operation in the vibration zone will cause cracks or aggravate cracks in the blade under the action of alternating stress. Non destructive flaw detection of cracks in C. requirements for fixture structure: it is very necessary to carry out non-destructive flaw detection of runner during overhaul, deal with defects in time, and eliminate hidden dangers of accidents. Serious cracks and other defects can be found by visual inspection with naked eyes and magnifying glass, but smaller defects and internal defects must be inspected by nondestructive testing

there are several commonly used nondestructive testing methods: magnetic particle testing, penetrant testing, ultrasonic testing, metal magnetic memory, radiographic testing, etc

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