INTRODUCTION

A Spring is an engineering component which when deflected by a force tends to return to its unloaded shape. Ideally the energy input to cause the deflection is usefully recovered. Springs are used extensively throughout mechanical engineering in a number of forms;

Metal Springs

• Helical Compression Springs

• Helical Extension Springs

• Helical Torsion Springs

• Coil Springs

• Disc Springs

• Leaf Springs

• Spiral Springs

Other spring Types

• Air Springs

• Elastomer Springs

Metal springs are generally fall into one of three classes of duty;

1. High Duty..Springs subject to rapidly reciprocating loads e.g. engine valve springs

2. General Duty..Springs that work infrequently for limited periods

3. Static Load Springs..Springs that are used to apply a fixed load throughout their life

Spring Rate and Stress

Generally springs are designed to have a deflection proportional to the applied load (or torque -for torsion springs).

The "Spring Rate" is the Load per unit deflection.... Rate (N/mm) = F(N) / d_e(deflection=mm)

For General purpose springs a maximum stress value of 40% of the steel tensile stress may be used. However the stress levels are related to the duty and material condition (ref to relevant Code/standard)

For a helical coil spring made from round wire the spring rate and the stress is calculated as follows;

• F = Force (N/mm)

• G = Modulus Of Rigidity (N/mm²>

• d = dia of wire.(mm)

• D = Mean dia of spring (mm)

• N = Number of Active Springs.

• K = Wahl Correction = [(4C - 1)/(4C - 4)] + 0.615/C

• C = Spring Index = D/d

• d_e = deflection (mm)

Extension Spring Initial Tension
An Extension spring can have an initial tension which must be exceeded before any deflection can take place. When the load exceeds the initial tension the spring behaves according the the formulae above.
The initial tension load can be calculated from the formula.... W_i = p S _i d³/ ( 8 D)

Spring Rate and Stress

• b = largest section dimension(mm)

• t = Smallest Section dimension(mm)

• K₁ = Shape Factor (see table)

• K₂ = Shape Factor (see table)

• C = Spring Index = D/(radial dimension = b or t)

Disc Spring are generally standarized according to DIN 2092 Calculations or DIN 2093 (dimensions /quality).
Din 2093 differentiate spring in three groups:

• Group 1: Disc Spring thickness t < 1 mm Cold Formed

• Group 2: Disc Spring thickness 1 <= t < 6 mm Cold Formed with inner/outer rings machined and inner edges rounded

• Group 2: Disc Spring thickness 4 <= t < 16 mm Hot Formed, All surfaces machined and inner/outer edges rounded, bearing flats




• t = Thickness (mm)

• u = Poissens Ratio (mm)

• E = Youngs Modulus N/mm²

• K₃ = Shape Factor (see table/Graph)

• K₄ = Shape Factor (see table/Graph)

• K₅ = Shape Factor (see table/Graph)

F = [ 4 E d_e / (1 - u²) K₃ Do²] . [( h - d_e) . (h -d_e/2).t + t³]

s = [4 E d_e / (1 - u²)K₃ Do²] x [K₅ (h - d_e / 2) + K₄ t ]




Do/Di	1.5	1.6	1.7	1.8	1.9	2.0	2.1	2.2	2.3	2.4	2.5	2.6	2.7	2.8	2.9	3.0
K3	.52	.57	.61	.65	.67	.69	.71	.73	0.74	0.75	0.76	0.77	0.77	0.78	0.78	0.79
K5	1.1	1.12	1.15	1.17	1.20	1.22	1.24	1.26	1.29	1.31	1.33	1.35	1.37	1.39	1.41	1.43
K4	1.18	1.22	1.26	1.30	1.34	1.38	1.42	1.45	1.49	1.53	1.56	1.6	1.63	1.67	1.7	1.74