Hooks and Loops Extension springs make use of hooks or loops. Loops are closed while hooks have an open side or section.
C ommon E xtension S pring T erminology Symbol Units Description Formula A L0 mm, in Free length tolerance 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, Mpa, PSI Modulus of elasticity E = δ/ε F0 N, Lbf Initial tension Pi = 2P1 - P2 L1, L2 N, Lbf Target loads (related to target heights/lengths) Fc Th N, Lbf Theoretical load/force at set solid Fn N, Lbf Load/force related to Ln (smalled length) 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
Machine Hook and Loop Machine hooks are a common type of extension spring hook. These hooks are stronger than cross over center hooks because the radius of the bend to make the hook is not as pronounced.
No Hooks These types of ends have o
stress or fatigue on the ends of the extension spring. The amount of pulling force and distance increases and the life cycles re longer. No hooks have the ability to use a bolt to thread into the inner diameter of the extension or tension spring thus securing the ends of the spring
Ld = p D [ 2 + nm + n / Cos(z)]
LK
mm, in Buckling length
Ln
mm, in Smallest allowed operating length (gemometric) Ln = d (n + ni +nm) + Sa
Lr
mm, in Smalled allowed operating length (stress)
M =Ld p π d 2 10 -3 / 4
M g, lb Mass
m mm, in Spring pitch
m = [ L0 - d (ni + nm) ]/n
N n ni
Number of cycles
n = G d 4 / (8 R D 3 )
Number of active coils Coils related to the ends Number of dead coils Total number of coils
nm
nt
nt = n + nm + 2
Extended Hooks Extended hook extension springs are very useful when you need a long length inside hooks but a short body length to get more force out of the spring through less coils. It is the most expensive hook type.
Crossover Center Hooks Crossover center type extension springs are very common. This type of hooks is made by lifting the last coil and twisting the coil towards the middle therefore crossing the center.
R = G d 4 / (8 n D 3 ) or (L1-L2) / (D1-D2)
R, KSR N/mm, Lbf/in Spring Rate
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
Side Hooks This hook type is used when
the body of the spring must not interfere with the components of a mechanism. This is due to the fact that the hooks are on one side of your spring therefore the other side of the spring is offset. They are made by simply bending the last coil so they are more economical than cross over center hooks
19
starrett .com
Made with FlippingBook - professional solution for displaying marketing and sales documents online