Rotating parts in machines should be free of vibration to ensure their smooth operation and long service life. Reducing the vibration in your machinery relies on a number of factors, like a smooth rotating shaft, good bearing condition, and proper lubrication, but one of the most important ways to guarantee vibration-free operation is through symmetrical mass distribution.

Although designers strive to create machinery to be as symmetrical as possible, in practice, all rotating bodies have weight asymmetries about the axis of rotation, and this causes vibration. Vibrations cause the machine to be noisy and reduce the life of its parts, especially the bearings. Vibration can also cause structural fatigue stress, and excessive vibration can lead to dangerous operating conditions from unexpected catastrophic failures.

Static and dynamic balancing of motors and generators will make them run smoother and operate more efficiently for longer periods of time. Balancing will also improve the working environment of the machine operators by reducing noise, minimizing vibrations, and eliminating the risk of dangerous catastrophic failures.

Static Unbalance

Static unbalance is the simplest form of unbalance. It is equivalent to a single heavy spot in the rotor. It is called static because it will be present even when the rotor is not spinning. Static balancing is necessary to prevent a stationary object from rolling. When an object’s center of gravity is on its axis of rotation, it will remain stationary. But if the center of gravity is not on its axis of rotation, it tends to roll, and a braking force is necessary to keep it stationary. A rotating body at rest is in static balance if it continues to be at rest at all angular positions of its axis. Static unbalance can be corrected with a single plane balance.

Dynamic Unbalance

A rotor will actually have an infinite number of imbalances distributed at random along its axis of rotation. This can be expressed as 2 resultant unbalances acting in 2 arbitrary balance planes. They differ in magnitude and do not have clearly defined angular positions. As this state of unbalance can only be determined comprehensively when the component is rotating, it is referred to as dynamic unbalance. Dynamic unbalance can be corrected with a 2 plane balance.

Asymmetric mass distribution about the axis of rotation causes a rotating body to vibrate. Dynamic balancing is the method of measuring the imbalance with sensitive electronic equipment while a body rotates rapidly. This process also tests vibration by adding or removing weight from the rotating body to align the effective mass center with the axis of rotation. When the effective mass center is at the axis of rotation, there are no residual centrifugal forces, and vibration is eliminated.

What’s the Difference?

A rotating object must have static balance before it can have dynamic balance. But the object can have dynamic imbalance even when it is statically balanced. If that is the case, the object will tend to vibrate while rotating even though it has no tendency to roll while stationary.

In other words, dynamic balance can be thought of as the ability of an object to balance while in motion. A perfectly dynamically balanced body requires just the force supporting its weight to make it stay in place while rotating; a dynamically unbalanced body in rotation requires external forces to counter the wobble from vibrations.

Working With Renown

Correct balance and alignment of rotating parts are necessary to ensure optimal performance and long service life. Renown Electric has offered both on-site and in-house dynamic balancing services for over 30 years. We specialize in providing preventative and predictive maintenance services to minimize the wear and tear that can result from excess machine vibration. Our customers use our measurement and calibration services to dynamically balance rotating equipment, helping ensure that it works efficiently and maximizes its life span.

We are an ISO 9001:2015–registered company. Our ISO 18436-2–certified specialists conduct residual imbalance analysis per DIN ISO 21940. Our state-of-the-art dynamic balancing equipment includes the VIBXPERT II balancing system.

To learn more about the benefits of Renown’s dynamic balancing services and our other preventative and predictive maintenance programs, please contact us today. We’re available around the clock to assist you.

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