Static & Dynamic Balancing
of Rotating Mass
Atish Kumar Sahoo(120101mer008)
• The condition which exists in a rotor when vibratory
force or motion is imparted to its bearings as a result
of centrifugal forces is called unbalance or the uneven
distribution of mass about a rotor’s rotating
•Balancing is defined as the process of designing
(or modifying) a machine in which unbalanced
forces is minimum.
•Balancing is the process of attempting to
improve the mass distribution of a body so that
it rotates in its bearings without unbalanced
Mass balancing is routine for rotating machines,
some reciprocating machines, and vehicles .
Mass balancing is necessary for quiet operation,
high speeds , long bearing life, operator comfort,
controls free of malfunctioning, or a "quality" feel .
The objectives of balancing an engine are to ensure:
1. That the center of gravity of the system remains stationery
during a complete revolution of the crank shaft and
2. That the couples involved in acceleration of the different
moving parts balance each other.
Balancing of Rotating Member :-
•Balancing means a process of restoring a
rotor which has unbalance to a balanced
state by adjusting the mass distribution
of the rotor about its axis of rotation
Types of balancing:
• Static Balancing
A rotating mass is said to be statically balanced if the rotating
mass can rest, without turning, at any angular position in its
bearings. This condition is attained when the sum of the
centrifugal forces on the rotating mass due to unbalanced
masses is zero in any radial direction.
i) Static balancing is a balance of forces due to action of gravity.
ii) A body is said to be in static balance when its center of gravity is in
the axis of rotation.
• Dynamic Balancing
A rotating mass is said to be dynamically balanced when it does not
vibrate in its running state. To make a rotating mass dynamically
balanced, it must first be statically balanced.
i) Dynamic balance is a balance due to the action of inertia forces.
ii) A body is said to be in dynamic balance when the resultant moments or couples,
which involved in the acceleration of different moving parts is equal to zero.
iii) The conditions of dynamic balance are met, the conditions of static balance are
Balancing of several masses rotating in different planes
A B C D
Benefits of balancing:-
Increase quality of operation.
Minimize audible and signal noises.
Minimize structural fatigue stresses.
Minimize operator annoyance and fatigue.
Increase bearing life.
Minimize power loss.
Need for Balancing:-
Rotating a rotor which has unbalance causes the following problems.
The whole machine vibrates.
Noise occurs due to vibration of the whole machine.
Abrasion of bearings may shorten the life of the machine.
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A Presentation prepared by me by simplifying the balancing of rotating mass.