PART 1: TYPES OF SPRING

1: HELICAL SPRING

If a wire is wound on cylindrical workpiece along its length, the spring made by this method is called helical spring.
A helical spring is classified as; 

(a) Closely coiled helical spring.

(b) Open coiled helical spring.

A helical spring is said to be closely coiled when spring wire is coiled so close so that there is no gap between two adjacent turns or it can be said that each turn is nearly at right angle to the axis of spring.
The spring wire of closely coiled helical spring is subjected to shear stress. 
In a closely coiled helical spring, the helix angle is usually less than ten degree.
 In a open coiled helical spring, the spring wire is coiled in such a way that there is a large gap between two adjacent turns. 
These types of springs are usually used to withstand compressive loads.