Though there are many types of the springs, yet the following, according to their shape, are important from the subject point of view.
The helical springs are made up of a wire coiled in the form of a helix and is primarily intended for compressive or tensile loads. The cross-section of the wire from which the spring is made may be circular, square or rectangular. The two forms of helical springs are compression helical spring as shown in Fig (a) and tension helical spring as shown in Fig (b).
The helical springs are said to be closely coiled when the spring wire is coiled so close that the plane containing each turn is nearly at right angles to the axis of the helix and the wire is subjected to torsion. In other words, in a closely coiled helical spring, the helix angle is very small, it is usually less than 10°. The major stresses produced in helical springs are shear stresses due to twisting. The load applied is parallel to or along the axis of the spring.
In open coiled helical springs, the spring wire is coiled in such a way that there is a gap between the two consecutive turns, as a result of which the helix angle is large. Since the application of open coiled helical springs are limited, therefore our discussion shall confine to closely coiled helical springs only.
The helical springs have the following advantages:
These are easy to manufacture.
These are available in wide range.
These are reliable.
These have constant spring rate.
Their performance can be predicted more accurately.
Their characteristics can be varied by changing dimensions.
Conical and volute springs-