Balancing and Over-Speed Testing of Flexible Rotors

High-Speed Balancing and Over-Speed Testing Installations HS 16 to HS 29

In general the shafts of rotating machines are being balanced applying the methods for rigid rotors. Typically the unbalance of rigid rotors does not change within their speed range. However this is no longer valid for the rotors of turbomachinery (turbines, compressors, generator etc.). During run-up these rotors approach their first critical speed or they pass at least one critical speed. At the same time the vibrations and the dynamic bearing forces increase and the rotor unbalance is depending on the speed.

Those flexible rotors require specific balancing procedures (see ISO 11342). This also creates special demands on high-speed balancing and over-speed testing installations:

• When passing critical speeds of flexible rotors high vibrations and forces occur which must be controlled and monitored.
• The drive system has to be strong enough to rapidly accelerate the flexible rotors through critical speed conditions.
• The stiffness properties of the balancing bearings and the operational bearings must be comparable, thus the critical speeds and the beding modes of a flexible rotor are not being significantly modified.
• Flexible rotors carrying blades or impellers have to be balanced at reduced air pressure (vacuum) to minimize windage and warming of the rotor as well as the investment and operational costs of the drive system.
• Suitable safety buildings or safety enclosures have to ensure, that parts are being captured, which may fly off a flexible rotor revolving at very high speeds or occur as rotor fragments after a burst. Thus there is no further hazardous potential.
• The unbalance measuring system has to support the balancing specialist in applying the methods for flexible rotor balancing and during rotor acceptance.

The high-speed balancing and over-speed testing installations of HOFMANN meet all demands for balancing and over-speed testing of flexible rotors. The high-speed balancing and over-speed testing installations are being adapted to the specific requirements of a project for example by applying individual concepts for the drive system or the safety enclosure.

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