About effect of shaft unbalance and supports misalignments to the border of rotation stability of the experimental four support shaft


The paper shows the influence of the technical condition of the shaft on the stability boundary of the shaft motion on the experimental four support stand. The influence of the bearings ' misalignment and rotor unbalance on the occurrence of self-excited oscillations is experimentally investigated. It is shown that with a minimum unbalance, the acceleration of the shaft to 50 Hz does not lead to a loss of stability. While increasing unbalance boundary of self-excitation is reduced from 52 to 55 Hz up to 35-37 Hz. Also it is found that when the perfect rotors alignments the boundary of self-excitation is higher than the rotation frequency of 50 Hz. With the mutual displacement of adjacent supports № 2 and № 3, the stability boundary gradually decreases and with critical misalignments, when shaft - bearing rubbing appears, subharmonic resonances may occur under certain conditions. It is also shown that when the temperature of the oil in the bearings changes, the loss of stability occurs at lower speeds, both with a decrease in temperature and with its increase. Thus, there is an optimal value of the oil temperature at which the stability of the system is the highest. The oil temperature at the inlet of the bearing, at which the stability of the system is the highest, is within 40-43 degrees. The experiments qualitatively confirmed the previously obtained calculated data for the turbine units.