TM 5-805-4/AFJMAN 32-1090
CHAPTER 8
VIBRATION CONTROL
8-1. Introduction.
that adjacent coils are solid against one another,
and is not binding against its mounting bracket,
This chapter provides the details of vibration
and to ensure that all springs of a total installa-
isolation mountings so that the desired vibration
tion are uniformly compressed and that the equip-
conditions discussed in chapter 2 can be met for
ment is not tilting on its base. For reasons of
most electrical and mechanical equipment. In addi-
safety, steel springs are always used in compres-
tion typical forms of vibration isolators are given,
sion, not in tension.
five general types of mounting systems are de-
b. Neoprenein-shear isolators. Neoprene is a
scribed, and summary tables offer suggested appli-
l o n g - l a s t i n g material which, when properly
cations of five mounting systems for the mechani-
shaped, can provide good vibration isolation for
cal equipment commonly found in buildings. A
the conditions shown in table 8-1. Typically,
discussion of the general consideration for effective
neoprene-in-shear mounts have the appearance of
vibration isolation is presented in appendix B.
a truncated cone of neoprene bonded to bottom and
8-2. Vibration Isolation Elements.
top metal plates for bolting to the floor and to the
Table 8-2 lists the principal types of vibration
supported equipment. The mount usually has an
isolators and their general range of applications.
interior hollow space that is conically shaped. The
This table may be used as a general guide for
total effect of the shaping is that for almost any
comparing isolators and their range of static de-
direction of applied load, there is a shearing action
flections and natural frequencies as applied to two
on the cross section of neoprene. In this shearing
equipment categories (rotary and reciprocating)
configuration, neoprene serves as a vibration isola-
and two equipment locations (noncritical and criti-
tor; hence, the term "neoprene-in-shear." A solid
cal). Additional details are required for actual
block of neoprene in compression is not as effective
selections of mounts. Vibration isolator types are
as an isolator. Manufacturers' catalogs will show
discussed in this paragraph, and equipment instal-
the upper limit of load-handling capability of large
lations are discussed in the remaining paragraphs
neoprene-in-shear mounts. Two neoprene-in-shear
of this chapter.
mounts are sometimes constructed in series in the
same supporting bracket to provide additional
to support heavy equipment and to provide isola-
static deflection. This gives the double deflection
tion for the typical low-frequency range of about 3
mount referred to in table 8-1.
to 60 Hz (180- to 3600-rpm shaft speed). Steel
c. Compressed glass fiber. Blocks of compressed
springs have natural frequencies that fall in the
glass fiber serve as vibration isolators when prop-
range of about 1 Hz (for approximately lo-inch
erly loaded. The manufacturers have several dif-
static deflection to about 6 Hz (for approximately
ferent densities available for a range of loading
1/4-inch static deflection). Springs transmit high-
conditions. Typically, a block is about 2-inches
frequency structureborne noise, so they should be
thick and has an area of about 10 to 20 in.2. but
supplemented with a high-frequency pad-type iso-
other dimensions are available. These blocks are
lator when used to support equipment directly
frequently used in series with steel springs to
over critical locations in a building. Unhoused
remove high-frequency structureborne noise, and
"stable" steel springs are preferred over housed
unstable or stable springs. Unstable springs tend
they are often used alone, at various spacings, to
to tilt over when they are loaded and to become
support floating concrete floor slabs (fig 6-6). The
short-circuited when they bind against the inside
manufacturer's data should be used to determine
walls of the spring housing. Stable steel springs
the density and area of a block required to achieve
have a diameter that is about 0.8 to 1.2 times
the desired static deflection. Unless otherwise indi-
their compressed height. They have a horizontal
cated, a static deflection of about 5 to 10 percent of
stiffness that is approximately equal to their verti-
the uncompressed height is normal. With long-
cal stiffness; therefore, they do not have a ten-
time use, the material might compress an addi-
dency to tilt sideways when a vertical load is
tional 5 to 10 percent of its height. This gradual
applied. The free-standing unhoused spring can
change in height must be kept in mind during the
easily be inspected to determine if the spring is
designing of floating floors to meet floor lines of
compressed correctly, is not overloaded to the point
structural slabs.
8-1
Previous Page
