This document discusses static and dynamic balancing of rotating objects. It defines unbalance as the uneven distribution of mass about the rotating centerline, which causes vibratory forces. Static balancing ensures the center of gravity remains stationary during rotation by aligning it with the axis of rotation. Dynamic balancing accounts for inertia forces by balancing out couples and moments involved in accelerating moving parts, resulting in zero net force or moment. The objectives of balancing are minimizing vibration and ensuring balanced forces and couples. Balancing techniques counteract centrifugal forces from one mass with a second mass. Examples include balancing single or multiple masses rotating in the same or different planes.

1. Balancing - Static and Dynamic
COMPILED BY-
ANUJ JHA
B.TECH (FPE)
2014027007
FMP-201 THEORY OF MACHINES (2+1)

2. In Focus……
• Introduction (Need for balancing)
• What is Unbalance?
• Important Terms
• Cause of Unbalance
• Balance and unbalance video explanation
• Balancing- Introduction
• Balancing examples
• Objectives of Balancing
• Types of Balancing-
• Static
• Dynamic

3. Introduction
(need for balancing)
When man
invented the
wheel, he very
quickly learnt
that if it wasn’t
completely
round and if it
didn’t rotate
evenly about it’s
central axis, then
he had a
problem!
The wheel would
vibrate causing
damage to itself
and it’s support
mechanism and
in severe cases, is
unusable.
The mass had to
be evenly
distributed about
the rotating
centerline so that
the resultant
vibration was at
a minimum.

4. Unbalance……definition
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 centreline.

5. Important Terms….
Rotating centreline: The rotating
centreline being defined as the axis
about which the rotor would rotate if
not constrained by its bearings. (Also
called the Principle Inertia Axis or
PIA).
Geometric centreline: The geometric
centreline being the physical
centreline of the rotor.
When the two centrelines are coincident, then the rotor will be in a state of balance.
When they are apart, the rotor will be unbalanced.

6. Cause of Unbalance….
In the design of rotating parts of a machine every care is taken to eliminate any
out of balance or couple, but there will be always some residual unbalance left
in the finished part because of
1. slight variation in the density of the material
2. inaccuracies in the casting or
3. inaccuracies in machining of the parts.

7. Balance and unbalance video explanation

8. Balancing- Introduction
Balancing is the technique of correcting or eliminating unwanted inertia forces or
moments in rotating or reciprocating masses and is achieved by changing the
location of the mass centres.

9. Balancing examples….

10. Objectives of Balancing
The objectives of balancing an engine are to ensure:
1. That the centre of gravity of the system remains stationery during a complete
revolution of the crank shaft
2. That the couples involved in acceleration of the different moving parts balance
each other.

11. Types of balancing:
a) Static Balancing:
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 centre of gravity is in the
axis of rotation.
b) Dynamic balancing:
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 also met.

12. Balancing of Rotating Masses
The process of providing a second mass in order to counteract the
effect of centrifugal force of the first mass is called balancing of
rotating masses.

13. Different cases….
Balancing of single rotating mass rotating in the same plane.
Balancing of single rotating mass rotating in the different planes.
Balancing of different masses rotating in same plane.
Balancing of different masses rotating in different planes.

14. To be continued……..