Open Coiled Helical Springs:

In these, the coils of the spring are not close to each other. The angle of helix is greater than 18.

Spring Subjected to Axial Load

Let us assume an open coiled helical spring subjected to axial load as in Figure (a). The geometry is described by R, d and α. These and other properties are explained below.

R = Mean radius of the coil.

d = Diameter of the wire,

n = Number of coils,

α = Angle of helix,

G = Modulus of rigidity,

Δ = Axial deflection of the spring, and

θ = Angle of twist.

An axial force, W behaves along the axis. The lowest coil is cut through a vertical plane through the axis, exposing a section AB of the wire. Because of helix angle α being considerable (> 180^o) AB, which is illustrated, enlarged in Figure (b) is not a circle. The circular cross- section is inclined at α to AB and illustrated as AO′C in Figure (b). Note down that normal to AB makes an angle α with normal to AC. Therefore, three lines

1. normal to section AB,

2. normal to cross-section AC, and

3. vertical axis of cross-section AC passing through its centre O′, are in the similar plane.