A spiral spring consists of a strip or wire wound in a flat spiral . This is subject
to a torque to produce an angular deflection. A typical spiral spring is a clock spring
Nomenclature
D = Outside diameter of spring (m)
b = Width of spring strip (m)
d = Inside diameter of spring (m)
t = thickness of spring strip (m)
n = Number of turns of spring
k = Spring rate = M /θ Nm/rad.
E = Young's Modulus (N/m2)
M = Moment/torque on spring = F.D / 2(Nm)
L = Length of strip (m)
G = Modulus of Rigidity (N/m2)
I = Second moment of intertia of spring strip (m4)
F = Force to deflect spring N
y = distance from neutral axis to outer fibre of wire/strip = y/2 (m) θ = Deflection (radians) α = Tensile/compressive stress resulting from spring deflection (N/m2
Note: metres (m) have been shown as the units of length in all of the variables above
for consistency. In most practical calculations milli-metres will be more
convenient.
Spring Rate
The spring rate k is defined on this webpage as the torque (Nm)per unit angular deflection (θ ).
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Roy Beardmore passed away on 9th March 2013. He is sadly missed. This website, Roymech, has been an invaluable resource for engineers around the world and we hope to maintain this incredible legacy going forward.
