Engineering Mechanics

Proceedings Vol. 22 (2016)

ENGINEERING MECHANICS 2016

Copyright © 2016 Institute of Thermomechanics, Academy of Sciences of the Czech Republic, v.v.i., Prague

 

Zachwieja J., Peszynski K.
pages 631 - 636, full text

Dynamic balancing of a rigid rotor should, at least in its final stage, be carried out at its operational speed, where its rotational frequency is often close to its resonance frequency. It is an adverse phenomenon, since even a minor constraint may induce high amplitude vibrations, limited by the attenuation. The service life of a rotor, mainly its bearings is thus significantly reduced. Balancing the rotor using the influence coefficient method at a frequency close to its resonance frequency is difficult due to the rapid changes in phase angle of a vector of the rotor response to constraints from the attached test weights. An optimal solution is to operate outside the rotor’s resonance zone. A quick and efficient method is to change its rotational speed, however, it may have some side effects. The rotors used in jet engines and power turbines, as well as rotors used in clinker cooler fans in cement plants and heating system fans in various types of furnaces used in the glass-making industry operate in high-temperature conditions. High temperature gradients during furnace start-up may result in thermal stresses at the rotor disc cross-sections. Strength of steel is also rapidly reduced at high temperatures. Cumulative effects of mechanical and thermal stresses at reduced rotor material strength may result in failure after a short period of operation. The study discusses those issues in relation to the rotors under mechanical and thermal stresses.

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