Torsion Springs - Nomenclature

Torsion spring

Here are the usual limits for (cold manufactured) torsion springs:

  • d < 17 mm
  • D < 340 mm
  • LK0 < 630 mm
  • n ≥ 2
  • 4 ≤ w ≤ 20

Basic formulae for torsion springs

Symbol

Unit

Detail

Formulae

a

mm

Initial space between coils

a ≥ (0.24 w -0.64) d0.83

AD

mm

Tolerance on mean diameter

 

D

mm

Mean diameter

D = De - d

Dd

mm

Diameter of the shaft

De

mm

external diameter

De = D + d

Di

mm

Inside diameter

Di = De - 2 d

d

mm

Wire diameter

d = De-D

E

N/mm2

Elastic modulus

 

G

N/mm2

Torsion modulus

 

Lbr

mm

Length of ends

LK0

mm

Initial length of the body

LK0 = d (n + 1.5)

M1, M2

N.mm

External torque related to α1, α2

M1 = R (α1 - α0)

M2 = R (α2 - α0)

Mn

N.mm

Maximal allowable torque

N

-

Number of cycles

 

n

-

Number of active coils

q

-

stress correction factor

R

N.mm/°

spring rate

 

R'

N.mm/°

spring rate related to the body

Ra, Rb

mm

radius to apply external loads

 

Rm

N/mm2

Ultimate tensile strength

 

w

-

spring index

w = D / d

α0

°

initial external angle

 

α1, α2

°

Operating angles related to M1, M2

α1 = M1 / R + α0

α2 = M2 / R + α0
αh1, αh2

°

angular defelctions

αh1 = M1 / R

αh2 = M2 / R
αh

°

Operating angular travel between M1 and M2

αh = α2 - α1
αhn

°

Greatest allowable deflection

αhn = Mn / R
α n

°

Greatest allowable angle

αn = Mn / R + α0
γ

°

angle between ends

γ = 360 ( n - E(n) )

r

Kg/dm3

Density

 

σzul

N/mm2

Maximum allowable flexion stress

 

σq2

N/mm2

Corrected stress related to M2




Manuel Paredes