Condition Monitoring of Axial Fan Blades

Condition monitoring of axial fan blades plays an important role for their long-term and reliable operation. From a short-term point of view, it provides information about their current state, and from a long-term point of view, it helps to detect such operating conditions that would lead to a reduction in the residual life of the rotating components. In the past, some cases were revealed where the crack occurred in the rod of the turning mechanism of the blades. In this paper the results of the experimental modal analysis are presented. From the point of view of operational measurement, the used BTT method is also described. The BTT method measures the passage times of the blades using stationary sensors mounted in the fan stator. The times of blade passage are largely determined by the projection of the overall blade vibration in the tangential direction. It has been shown that due to the change in blade rotation, different apparent levels of blade vibration can be detected even when the actual vibration level is constant. For this reason, a method of blade vibration compensation was proposed, where the actual angle of the blades is obtained from the measurement of blade passes under two BTT sensors located next to each other. The suitability of the proposed method is demonstrated on a case study.