Unbalance Forces Full

Описание: The forces (F) generated by an unbalance are equal to the unbalance mass (m) times the radius (r) from the center of rotation times the rotational speed (𝝎) squared.

F=mr𝝎2

The force (F) caused by a rotor unbalance can also be defined as the rotor mass (M) times the rotor eccentricity (e) times the rotational rate (𝝎) squared

F = Me𝝎^2

What is happening here is the rotor wants to rotate around it's center of mass, not its geometrical center. To visualize this, think about throwing a uniform wooden pole through the air so it flips end over end. It rotates around its geometric center. Now imagine throwing a hammer through the air the same way. Think about the motion it will create - it will not rotate around the geometrical center but around the head, eq the heavy part or center of mass.

The rotor eccentricity (e) is the distance between the geometric center and the mass center. This also explains why the rotor vibrates. If it was perfectly balanced and rotated around its geometric center, it wouldn't vibrate!

Because the unbalance forces are related to the shaft speed squared, it is important to make sure high speed shafts are precision balanced. Unbalance forces lead to premature machine failure. Unbalance forces cause damage to bearings and mechanical seals. Unbalance causes excess vibration which can lead to other problems.

We can rearrange the formulas for force:

F=mr𝝎2 = Me𝝎^2
mr = Me
e=mr/M

The last formula will be useful when we discuss balance standards and balance quality.

If you would like to learn more about unbalance and other mechanical faults or vibration problems please check out my website: https:\\www.ZencoVibrations.com

Sign up for a vibration Cat 1, 2 or 3 course with optional certification in accordance with ISO 18436-2. Course calendar: https://www.zencovibrations.com/events/

For quiz questions and other helpful content, follow me on LinkedIN:   / alanfriedmanvibe