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.

TECHNICAL TERMS :-

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.

LOADED HEIGHT
Height of the spring when carrying the static load.

SOLID LOAD
The load required to bring the coils in contact with each other.

TRAVEL
The movement between free height and solid height.

DIAMETERS
Outside diameter must be given if spring is fit into a tube. Inside diameter must be given if spring is to fit over a rod or another spring.

LOAD RATE
The load per unit of deflection-normally expressed in kg/mm. This is a basic property of the spring.

SOLID STRESS
The stress range between spring free and spring solid.

TECHNICAL DETAILS

Free Height = Travel + Solid Height
Load = Load rate x Deflection
Solid load = Load rate x Travel

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)
R = Load Rate
d = Bar Diameter
D = Mean Diameter (O.D. minus Bar Size)
N = Active Turns (Total Turns less 1.5)
P = Applied Load
F = Axial Deflection
c = Spring Index (D / d)
K = Curvature Correction Factor
Pi = Pi (3.14)
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.