Page 411 - Analysis and Design of Machine Elements

Springs
can be made from wire stock or from flat stock. Helical compression, extension and 389
torsion springs are wire springs; while flat springs are made from flat strip materials,
like leaf springs. Springs are mass produced and are commercially available from spring
manufacturers.
14.1.2.1 Helical Coil Springs
Helical coil springs, including cylindrical, conical, hourglass and barrel helical springs, as
shown in Figure 14.1, are probably the most widely used types. A cylindrical helical coil
spring, or cylindrical helical spring, is made of a round wire, wrapped into a cylindrical
form with a constant (Figure 14.1a) or variable (Figure 14.1b) pitch between adjacent
coils [2]. The load-deflection relationship of cylindrical helical springs with constant
pitch is linear, while the latter, together with conical, hourglass and barrel helical springs
are nonlinear, and they are designed to solve special problems.
When a cylindrical helical spring is subjected to a compressive force, a tensile force
or a torsional moment, the spring is termed as cylindrical helical compression spring,
cylindrical helical extension spring and cylindrical helical torsion spring, respectively.
The basic structure of these cylindrical helical springs is exactly the same except for the
end configurations.

Cylindrical helical compression springs
Figure 14.2 shows cylindrical helical compression springs with various end configura-
tions. Figure 14.2a has closed and ground ends and usually for medium- to large-size
springs. Such end configuration provides flat surfaces on which to seat the spring.

The support end surfaces are vertical to the spring axis, or the direction of compres-
sive loads. Figure 14.2b has closed ends by deforming the ends to a zero-degree pitch
angle without grinding. The closed end coils greatly enhanced the stability of springs.
Figure 14.2c has plain ends as if a long spring has been cut into sections without

(a) (b) (c) (d) (e)
Figure 14.1 Various helical compression springs. (a) Constant pitch, (b) variable pitch, (c) conical,
(d) hourglass and (e) barrel. Source: Adapted from Collins 2002, figure 14.1, p 516. Reproduced with
permission of John Wiley & Sons, Inc.