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4. Machine balancing in situ.

Question 4.1.

Why are the rotors balanced in situ if they are already balanced on special balancing machines? The question was asked by the specialists of the plant operations service of the gas transportation enterprise in Saint Petersburg (Russia).

The question is answered by Alexander G. Shablinsky.

The question is answered by Alexander G. Shablinsky:

There are many reasons why it is necessary to balance a rotor after its mounting into a machine or during its operation because of the increased vibration. They can be divided into three groups:

  1. The influence of the limited accuracy of assemblage and mounting of rotating assemblies into a machine on the residual unbalance.

  2. The influence of the environmental conditions and defects on the rotor unbalance.

  3. The appearance of noninertial oscillation forces on the rotation frequency in some types of machines.

The first group of reasons includes first of all the inaccuracy of coupled rotors alignment and the inaccuracy of the coupling workmanship.

The second group includes such reasons as rotor disbalance due to non-uniform thermal expansion, the wear of some rotating elements, sticking on them some external particles, looseness of supports and so on.

The third group includes the reasons defined by such technological deviations during making or assemblage of different types of machines, or defects, that lead to the appearance of non-inertial oscillation forces with the rotor rotation frequency. These forces can be of the electromagnetic, hydrodynamic, mechanic or aerodynamic origin, and they are not always compensated by the centrifugal forces even during balancing the assembled machines.

 

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