# Technical Information

## Basic Relations

Free Height = Travel + Solid Height

## Basic Equations

For Round Bar:
Load Rate (R) = (Gd4) / (8ND3)
Stress (S) = (PD / .393d3)K or (GdF / (Pi)ND2)K
Curvature Correction (K) = (4C - 1) / (4C - 4) + (0.615 / c)
Spring Index (c) = D / d

Where:
G = Modulus of Elasticity (11,200,000 for steel)
d = Bar Diameter
D = Mean Diameter (O.D. minus Bar Size)
N = Active Turns (Total Turns less 1.5)
F = Axial Deflection
c = Spring Index (D / d)
K = Curvature Correction Factor
Pi = Pi (3.14)

## Suggested Limits on Proportions

In designing springs, certain practical limits on proportions should be followed whenever possible. These are as follows:

• Outside diameter = 4 to 8 times bar diameter
• Free height = 1 to 4 times outside diameter
• Minimum solid height = 5 times bar diameter

Readily available bar sizes should be used unless large quantities are involved. Double and triple concentric nests may be used for more capacity in limited space.

### Glossary

COMPRESSION SPRINGS: A compression spring is an open-coil helical spring that offers resistance to a compressive force applied axially. Compression springs are usually coiled as a constant-diameter cylinder.

EXTENSION SPRINGS: Extension springs are springs which absorb and store energy by offering resistance to a pulling force. Various types of ends are used to attach the extension spring to the source of the force.

TORSION SPRINGS: Torsion springs, whose ends are rotated in angular deflection, offer resistance to externally applied torque. The wire itself is subjected to bending stresses rather than torsional stresses, as might be expected from the name.

SOLID HEIGHT: Height of spring when loaded to bring all coils in contact.

STATIC LOAD: The dead weight supported by the spring, no motion being involved.