Hirth Coupling Modeling and Optimization on Rotor Assembly

Hirth couplings are widely used in turbomachinery to allow torque transmission along different rotor parts, guaranteeing precise centering, excellent structural stability, and reliable positioning. Except for some examples of rotors with disc and diaphragm usually rotating, machine design foresees to employee only few Hirth couplings. However, the increase of performance and efficiency in new developed products to satisfy the market, requires additional engineering and manufacturing complexity. This study, deals with rotor design of a turboexpander, using up to 16 Hirth couplings. Because each joint is crucial to minimize center misalignments and rotations during the assembly to prevent inconvenient rotordynamic behaviors, especially when the number of parts involved is high. Aim of this research activity is to define a stacking sequence procedure, which meet this target from direct measurements on the tooth geometry of each disc. After wide literature research on the manufacturing process, a design of experiment on a single joint was set and analyzed with FEM [1], changing the geometry parameters of the tooth. By comparing the results of the simulations with nominal and with incorrect profiles of the teeth, the model has been validated and the effects on actual rotor axis of each tooth design parameter has been combined together by means of a statistical analysis [2].