Development of aerostatic bearing system for balancing of ultra-high speed turboexpander rotors used in helium liquefiers/refrigerators

Balancing of high speed turboexpander rotors is necessary to minimize vibration and noise, increase bearing life and to maintain stable operation of turboexpanders which can otherwise lead to cryogenic plant unavailability. In general, a dynamic balancing machine is based on mechanical roller bearing supports. This article reports an attempt to modify a dynamic balancing machine by replacing the existing line contact roller bearing system with a gas film supported aerostatic bearing system to eliminate erroneous and inconsistent unbalance readings. An aerostatic bearing system has been designed to balance a typical turboexpander rotor of 16 mm diameter. Experiments have been conducted to compare the performance of roller bearing and air bearing systems on the balancing machine. It has been found that consistency is improved by using air bearings and rotor can be balanced to a lower unbalance value.