Motor Balancing Issues and Myths


Motor unbalance can cause any of a number of undesirable outcomes from machine downtime to equipment breakdown.  Motor unbalance can also be a symptom of deeper problems in the motor or the equipment. It is important to detect and correct unbalance in a timely manner.

Unbalance occurs when the rotor’s mass is no longer at the center of rotation. Unbalance can be caused by many factors:

  • Assembly error
  • Machine tolerances
  • Eccentric components
  • Wear
  • Corrosion
  • Thermal distortion
  • Mechanical distortion
  • Material buildup
  • Bent components
  • Broken components

Many things can prevent the successful correction of unbalance. Equipment resonance, bearing issues, product buildup and many more equipment problems can prevent a successful balancing job from being completed. All Equipment defects should be corrected before attempting to balance equipment.

There are two pervasive myths about motor unbalance.

MYTH: “1x RPM is always caused by unbalance.”

TRUTH: Unbalance always causes vibration at 1x RPM. However, 1 x RPM is not always caused by unbalance. Many other problems can exhibit vibration at this frequency. Examples are:  misalignment, bent shaft, bowed shaft, cracked shaft, eccentricity, open rotor bars in the motor, rubs, looseness, belt issues, and resonance.

MYTH: “The run time and lifetime of the equipment can be extended by performing a balance job on the equipment.”

TRUTH: Problems such as misalignment, bad bearings, looseness, and the like cannot be corrected by balancing the machine. It is almost impossible to correctly balance a machine that has other defects affecting its performance. Misalignment, bad bearings, looseness, and the like should be corrected before attempting to balance equipment.


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