Abstract: A method and apparatus for monitoring cracks of a rotatable body by detecting cracks by measuring accoustic emission signals and evaluating the depth of cracks from the result of the comparison of assumed vibrations of the rotatable body and its measured vibrations. By this method and apparatus not only the beginning of cracking of the rotatable body, but also the progress of cracking on an online basis can be detected and monitored.

Abstract: Disclosed is a method for detecting the condition of a crack generated in a rotor of a rotary machine during an operation thereof to check whether the crack is developing or not. The number of revolutions of the rotor and oscillations of journal end portions of the rotor born by the bearings are continually detected. The detection of the crack condition is made on the basis of the detected signal corresponding to the waveform of each half of at least one cycle of the detected rotor oscillation. Disclosed also is an apparatus for carrying out the method.

Abstract: A method of and a system for reducing an excessive amplitude of unbalance vibration occurring in a rotor by actually measuring and comparing the unbalance vibration amplitude of the rotor with a desired level for judgement as to whether the desired value is exceeded, selecting a certain correction plane combination in accordance with the measured unbalance vibration amplitude. A correction mass to be added to the rotor is calculated using an influence coefficient corresponding to the selected correction plane combination, assuming that the correction mass is added to the rotor, estimated residual vibration amplitudes and root mean squares thereof are calculated at respective correction plane position combinations each having at least any two of positions of a plurality of correction planes on the rotor.

Abstract: A vibration diagnosis method and apparatus for rotary machines adapted for measuring the vibration of rotor shaft of a rotary machine, extracting the vibration component synchronous with the revolution of the rotor shaft from the measured vibration data, comparing the amplitude of the extracted vibration component with the amplitude of the overall vibration, analyzing the causes of the synchronous vibration component when the result of the comparison meets a predetermined reference, judging, in accordance with the result of the analysis, whether the vibration due to mass unbalance is attributable to an abrupt generation of mass unbalance or to a thermal bow of the rotor shaft, and displaying the result of the judgment. The analysis of the vibration component is made in real time or making use of data stored in the past.

Abstract: A balancing method for use in a multiple-span rotor shaft system for a prime mover, such as a large-capacity, large-sized steam turbine and generator. A balancing influence coefficient representing the relationship between a unit weight and the resultant vibration, when the aforesaid unit weight is attached to a given balance-correcting plane of a multiple span rotor, is first determined, and then a balance-correcting plane, to which is to be attached a balancing weight, is selected, then a balancing weight is determined so as to minimize the value of the residual vibration amplitude, by using the method of least squares, which values are dependent on the value of the vibration amplitude, influence coefficients and balancing weights. Thus, a weight corresponding to the aforesaid balancing weight is attached to the aforesaid balance-correcting plane to reduce vibrations in a shaft.