C ommon C ompression S pring T erminology
Symbol
Units Description
Formula
D mm, in Mean diameter
D = De - d
De
mm, in External diameter
De = D + d
Di
mm, in Internal diameter
Di = D - d
d
mm, in Wire diameter
d = De - D
E = δ/ε
E,
Mpa, PSI Modulus of elasticity
L1, L2 N, Lbf
Target loads (related to target heights/ lengths) Theoretical load/force at set solid Load/force related to Ln (smalled length)
Fc Th N, Lbf
Closed and Squared Closed and squared end com- pression springs are the most common. This end type allows the spring to stand vertically when placed on a flat surface. The last coil on either end is closed. This end type is suited for compres- sion springs with a low slender- ness ratio.
Closed and Ground Closed and ground ended com- pression springs are also com- mon but they are more expensive. Closed and ground ends will help your compression spring stand vertically straight on a flat surface when the slenderness ratio is too large.
Fn
N, Lbf
fe
Hz
Natural frequency
k
-
Stress correction factor
L0, FL mm, in Free length/height D1, D2 mm, in Target Length/distance (related to target loads) Lc mm, in Solid length
Lc = d(n+ni+nm)
Ld
mm, in Length of wire
Ld = p D [ 2 + nm + n / Cos(z)]
LK
mm, in Buckling length
Ln
mm, in Smallest allowed operating length (geometric) mm, in Smalled allowed operating length (stress)
Ln = d (n + ni +nm) + Sa
Lr
M g, lb Mass
M =Ld p π d 2 10 -3 / 4
m mm, in Spring pitch
m = [ L0 - d (ni + nm) ]/n
N
Number of cycles
n
Number of active coils
n = G d 4 / (8 R D 3 )
ni
Coils related to the ends
nm
Number of dead coils
Double Closed Double closed ends are very simi- lar to closed and squared ended compression springs. Instead of the spring having one closed coil at the ends, it has two. They are used to provide stability when your spring has a high slender- ness ratio. This end type helps prevent buckling.
Open Ended Open ended compression springs are uncommon since the spring will not be able to stand unless supported by a shaft or mandrel. There is a pitch between each coil on an open ended compression spring.
nt
Total number of coils
nt = n + nm + 2
R, KSR N/mm, Lbf/in
Spring Rate
R = G d 4 / (8 n D 3 ) or (L1-L2) / (D1-D2)
Rm Mpa, PSI Ultimate tensile strength Sh mm, in Spring travel
Sh = D1 - D2
W Nmm, Joule
Stored energy
W = 0.5(L1+L2)(D1-D2)
w
-
Spring index
w = D / d
C ommon S pring D esign M aterials
Material
Stress
Corrosion Resistance
Application
Brass
Low
Yes Yes
Water resistant Electrical connectivity Corrosive environments Large diameters
Phosphor Bronze Low
Stainless Steel (302/304) Oil Tempered
Low
Yes
Medium
No No No
Hard Drawn MB Medium
Low cost
Music Wire
High
High stress
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