Rotor balancing at work place

Rotor balancing (such as impeller of ventilator, pulley, half-coupling, crusher or separator barrel) at work place is the most common type of work during vibration adjustment of rotating machines. The concept of vibration adjustment includes removing the causes of elevated level of vibration of equipment in low-frequency region (close to rotational speed up to 1000Hz). Among main reasons of elevated level of vibration at low frequency are the following: imbalance, resonance, weakening of supports, shaft misalignment, defects of coupling etc.

Imbalance causes elevated level of vibration at rotational speed and as usual has the biggest energy of fluctuation able if not destroy but at least lower durability of support bearings or weaken construction of unit attachment to the base. Rotor balancing is being made at the end after a series of other preparatory adjustment works:

  • Recovery stiffness of elements of unit attachment to the base. It applies to situation with weld violation of framework structure or anchor bolt weakening. This defect shows itself as a vibration at a frequency equal to half the basic rotor rotational speed.
  • Weakening elimination of system rotor-bearing caused by bearing wear or its insufficient support. This defect also contributes to half, main and harmonic components of rotational speed.
  • Shaft alignment (pulley alignment). Vibration caused by shaft misalignment shows up on double rotational speed and also contributes to fluctuation on basic rotor rotational speed that greatly influenced the balancing quality.
  • Elimination of resonance influence. This defect is very guileful, because shows up only when the unit operates causing abrupt increase of vibration on basic rotational speed. Resonance – coincidence of rotational speed and natural oscillation frequency of all construction of unit or all its parts (e. g. chassis, spring etc.). To identify availability of resonance phenomena is possible by recording and analyzing nyquist plot (NP) during unit acceleration-rundown. As equipment works on fixed rotational speed, to reduce or eliminate influence of resonance is possible only by changing stiffness of system unit-base. This is usually achieved by welding additional stiffening rib in the case of framework structure or strengthen the base and unit affixtures to itself.
  • Rotor balancing. This procedure is being made at the end after a series of vibration adjustment work after removal other sources of vibration on basic rotational speed.

 

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