# Definition of coil spring

A spiral spring made of spring wire. There are many types of spiral spring, which can be divided into ordinary cylindrical spiral spring and variable diameter spiral spring according to the shape, and can be divided into left-hand spring and right-hand spring according to the helix direction.
The cylindrical spiral spring has the advantages of simple structure, convenient manufacture and wide application. Its characteristic line is straight line and can be used as compression spring, tension spring and torsion spring. When the load is large and the radial size is limited, two compression springs with different diameters can be used together to form a combined spring.

Name and dimension relationship of each part of cylindrical spiral compression spring:
1. The diameter of spring wire D is the diameter of steel wire for manufacturing spring.
2. Outer diameter of spring d0, the maximum diameter of spring.
3. Inner diameter of spring D1, minimum diameter of spring, D1 = d-2d.
4. Mean diameter of spring D2, average diameter of spring, D2 = d-d.
5. Pitch T, the axial distance between two adjacent rings except the supporting rings at both ends.
6. The effective number of turns n, the number of supporting rings N2 and the total number of turns N1. In order to make the compression spring stable and evenly loaded, both ends of the spring will be tightly and ground flat during manufacturing. The tightly ground part only plays a supporting role, so it is a supporting ring. There are three kinds of supporting rings: 1.5, 2 and 2.5 rings, and 2.5 rings are used most. The remaining cycles maintain the same pitch, which is called the effective number of turns. The total number of turns N1 is the sum of the effective number of turns N and the number of supporting rings N2.
7. Free height H0, the total height of spring without external force, H0 = NT + (n2-0.5) d.
8. The developed length L is the length of the blank used to make the spring, l ≈ N1 √ (π D2) &amp; sup2; + T &amp; sup2;.
There are taper coil spring, volute coil spring and concave spiral spring. The conical spiral spring has good cushioning performance and can bear large load. Volute spiral spring can store more energy and bear larger load, but the manufacturing process is more complex. The performance of concave spiral spring is similar to that of conical spiral spring, which is mostly used for cushion and mattress. The load surface of spring steel wire includes circle and rectangle, and circular section is the most commonly used.

Spiral spring, namely torsion spring, is a spring that bears torsion deformation, and its working part is also tightly wound into a spiral shape. The end structure of torsion spring is processed into various shapes of torsion arm, not hook ring. Torsion spring is often used in balancing mechanism of machinery, and is widely used in automobile, machine tool, electrical appliance and other industrial production.