Exchangeability of rotor modules - a new balancing procedure for rotors in a flexible state

Exchangeability of rotor parts or modules without the need for a subsequent balancing step is a goal in design and production throughout the industry. it is not easy to handle this properly for rotors in a rigid state, and it is even more complex in the case of rotors in a flexible state. The discussion bases on low speed balancing methods for rotors in a flexible state. The new approach recommends some modal considerations to classical low speed balancing procedures of the individual parts, and adds a special balancing step in order to reduce the modal unbalance of the assembly. This step bases on the knowledge of the bending modes, the distribution of masses and moments of inertia along the rotor axis and on a separate measurement of the unbalance of each module. The recommended procedure will maintain the goal of modular exchangeability and good unbalance condition at low speed, and will simultaneously reduce the modal unbalances and consequently the deflection of the assembled rotor at high speed.