Effect of Residual Shaft Bow on Unbalance Response and Balancing of a Single Mass Flexible Rotor—Part II: Balancing

Three methods of balancing a rotor with a residual shaft bow were presented. Method I balanced the total shaft amplitude to zero at the balance speed. Method II balanced the elastic deflection to zero at the balance speed leaving the residual bow amplitude. Method III balanced the total shaft amplitude to zero at the critical speed without actually operating the rotor at the critical. After balancing by Method I, a large amplitude remained near the critical. Method II balanced the rotor to the residual bow amplitude at all speeds except near the critical where the amplitude is slightly larger than the residual amplitude. The optimum balance resulted from balancing by Method III. In this case, the amplitude was less than or equal to the residual bow amplitude for all speeds except at the critical where the amplitude was zero. Method III required that the critical speed be known prior to balancing. For all three balancing methods, the unbalance influence coefficient must be determined. Two procedures for determining this coefficient were discussed. One was the familiar trial weight influence coefficient method and the other was the direct method which does not require trial weights. Part I of this paper discussed the effect of shaft bow on unbalance response.