Basics of Balancing and Balancing Machines

What is an unbalance?

Unbalance occurs when the mass axis of a rotating object is not aligned with the axis of rotation. This can happen when the principal mass axis and the axis of rotation are not parallel or crossing. Dynamic unbalance is the most common type of unbalance and is a combination of static and coupled unbalance.

When a rotor is out of balance, it can cause the system to tilt or wobble, and can also result in vibration that becomes more harmful as the rotor speeds up. To compensate for unbalance, weights can be added in two or more planes along a shaft. Other methods for correcting unbalance include drilling, grinding, milling, and eccentric turning.

What causes unbalance?

Unbalance can be caused by centrifugal forces acting in different planes of rotation. Centrifugal force is an outward force that exists in rotating bodies and is proportional to the distance between mass and rotational axis, and the square of rotational speed. Dynamic unbalance occurs when masses are located in different planes of rotation and each mass tries to pull the drum in the direction of its centrifugal force.

What are the effects of unbalance on a machine?

Unbalance can lead to higher vibration and noise levels in machines, affecting their overall efficiency and quality. When left undetected, unbalanced rotors can lead to high maintenance and repair costs.

What is the relationship between unbalance and vibration?

Unbalance, or an uneven distribution of mass, causes vibration in machines. This is because the unbalanced mass interacts with the radial acceleration caused by rotation, which creates a centrifugal force. The force rotates with the components, and tries to move the rotor along the line of action of the force. This oscillation of the rotor around the axis can cause vibration.

What is balancing of a rotor

Rotor balancing is a process that involves analyzing a mechanical element's vibration profile to determine the amount and location of weight needed to correct an imbalance. The goal is to improve the mass distribution of a rotor so that it rotates in its bearings without uncompensated imbalance.

Here's how rotor balancing works:

1.Spin the rotor: Spin the rotor while using computer software to measure any unbalance.

2.Add or remove material: Add or remove counterbalancing material to correct the unbalance.

3.Spin again: Spin the rotor again to verify that the vibration has decreased.

4.Repeat: Repeat the process to further reduce the imbalance and vibration.

What are the effects / benefits of balancing a rotor?

Rotor balancing can help prevent issues caused by unbalance, which can compromise the safety and operational efficiency of a system. It can also improve the performance and lifespan of rotating machinery.

Rotor balancing involves removing or adding weight to the device so that the effective mass center reaches the true axis. This can be done using machines that determine the imbalance point and provide a correction.

What is a balancing machine?

A balancing machine is a tool that measures and corrects the imbalance of rotating components, such as rotors, fans, propellers, and turbines. The machine can detect the center of mass of a rotor by spinning it and using vibration sensors. The machine then calculates the position and amount of correction needed to reduce the imbalance, which can be done by adding or removing material or moving mass.

Balancing machines are important because they help ensure that rotating components are properly balanced, which can prevent noise, vibration, and energy waste. Vibration can also cause bearings to wear out more quickly and shorten the life of products.

How is unbalance interpreted on a balancing machine?

Unbalance is a vector quantity, i.e. it has a magnitude and a direction. The magnitude of the unbalance is defined as a composite product (multiplication) value of mass (m) times radius (r). m x r. This is the measured quantity internally in balancing machines. The user feeds a radius of correction desired r, and the machine computes the unbalance mass m based on the measured unbalance value. The direction of the unbalance is the angle measured from a known reference on the balancing machine. Thus the units in metric will be g-mm. An example of unbalance would be 10 g-mm @ 45 degrees. The reference could be fixed on the rotor, like a reflective sticker, or internally in the machine. In some literary references, the unbalance is referred in terms of eccentricity, measured in microns for the metric system. This measurement normalizes the unbalance with respect to the rotor weight. I.e, it is the unbalance divided by rotor weight or mxr/M, where M is the mass of the rotor. While doing the division, take care to use consistent units, i.e. if mxr is units of g-mm, M should be in grams.

For practical unbalance correction, one needs to know the unbalance value in a weight value say grams. This is achieved by dividing the unbalance value by the radius. Thus a 50 g-mm unbalance at 100 mm radius, needs a correction of 50 g-mm/100 mm, i.e. 0.5 grams. Modern balancing machines supplied by Precibalance indicates both the g-mm value as well as the value in grams as well as a combination of many other non metric mass and length units such as oz-in, lb-in etc.

What information do I need for specifying a balancing machine?

Choosing a balancing machine is a techno-commercial decision. Some of the considerations include