Page 12 - Rotating Machinery Pratical Solutions to Unbalance and Misalignment

Introduction to Vibrations
Chapter
Chapter
Chapter
Chapter
Chapter
Introduction to Vibrations
Introduction to Vibrations
Introduction to Vibrations
Introduction to Vibrations
Introduction to Vibrations

ibration is the back and forth or repetitive motion of an
object from its point of rest. Simple vibration can be illus-
V V V V V trated with a mass suspended by a constant force spring,
as shown in Figure 1-1.
When a force is applied to the mass, it stretches the spring
and moves the weight to the lower limit. When the force is re-
moved, the stored energy in the spring causes the weight to move
upward through the position of rest to its upper limit. Here, the
mass stops and reverses direction traveling back through the po-
sition of rest to the lower limit. In a friction-free system the mass
would continue this motion indefinitely.
In real situations, there is always some form of friction or
dampening which causes the mass to not quite reach the upper
and lower limits, and gradually lowers the motion until the mass
returns to the position of rest.
However, if the force were applied again, the mass would
again move to its lower limit. By successively adding and remov-
ing the force, the mass would continue to vibrate. Although this is
a very simplified example, all machine parts exhibit the same
basic characteristics.

Upper limit
Force
Rest position

M Lower limit

Figure 1-1. Simple Vibratory Motion