Page 24 - Rotating Machinery Pratical Solutions to Unbalance and Misalignment

Introduction to Vibrations

The characteristics of vibration due to unbalance and mis-
alignment are presented in the following chapters. These include
the frequency and the plane in which the vibration is present.
These simple measurements can be used to determine the condi-
tions of unbalance and misalignment.
In general, the vibration will exist in the radial direction, axial
direction, or both. The radial direction is usually broken up into
the vertical and horizontal planes to better describe the character-
istics of the vibration.
Figure 1-12 illustrates the two basic directions of vibration of
a machine shaft. Axial vibration occurs along the axis of the shaft,
while radial vibration acts outwardly from the center of the shaft.
It should be noted that the radial vibration may not be in the same
direction at opposite ends of the shaft. One end may be moving
vertically upward while the opposite end may be moving horizon-
tally to the left at the same moment in time. This is known as the
phase angle relation and will be useful in determining the cause
of the vibration.

Radial
Axial ➔
➔
➔
➔
➔

➔
Figure 1-12. Direction of Vibration

Phase angle relations as well as the direction of vibration are
discussed in the chapters on unbalance and misalignment, to as-
sist in identifying the source of the vibration.
Figure 1-13 shows the two directions of vibration with the
radial vibration broken down into the vertical and horizontal
planes.
Although a vibration analyzer is required to identify phase
angle relations and to perform field or shop balancing of machine
parts, many causes of vibration can be determined through in-
spections and proper assembly techniques.