


1)
Overview

Space can be efficiently
used and the initial length of the spring
can be effectively used.
Extension spring is commonly used like compression
spring and has various hook shape
according to the application. 




2)
Application 
Components for automobile,
electrical, electronic, stationery, toy, industry,
and information
communication 



3)
Shape 
It has hooks at the both
ends. 

4)
Manufacturing
capability 
We manufacture extension
springs with a diameter of Ø 0.2mm to Ø
6mm. 

5)
Others 
Plating, coloring, power
coating etc available 

6)
Symbols used
for extension spring design 

Item 
Symbol 
Item 
Symbol 
shear modulus

G

mounting length

I 
wire diameter

d 
initial load

Po 
outside diameter

Do 
initial stress


mean coil diameter

Dm 
Load

P 
inside diameter

Di

spring constant

K 
total number of coils

Nt

index ratio

C 
number of active coils

Ne 
stress correction coefficient

k' 
free length

L 
shear stress


tensile strength






a) Spring constant : K = G * d
³ / 8 * Ne * Dm ³
b) Initial load : Po = π * d ³ *
/
8 * Dm (Refer to the graph below for .)
c) Load : P = K * (L  l) + Po
d) Stress correction coefficient : k' = {(4
* C1)  (4 *C4)}+(0.615/C)
e)
= k' * 8 * Dm * P/ π * d ³
f) Stress ratio = /



