Spring Number of Active Coils

Active coils are the open wound coils exerting energy while under a load of compression, extending, or deflection.  A coil is formed when it is wound one complete 360 degree helix starting with the second coil and count to the second coil on the other end.  The number of active coils should be 3 or more to stabilize spring charactacteistics.  Spring coils can either be left-hand or right-hand coils.

The spring number is a parameter in the design and analysis of helical springs.  It influences the spring's stiffness, load carrying capacity, and other mechanical characteristics.  Engineers use the spring number, along with other parameters such as wire diameter, coil diameter, and material properties, to design and select springs that meet specific requirements in terms of deflection, load capacity, and durability.

 

Spring Number of Active coils formula
\( n_a = G \; d^4 \;/\; 8 \; k_s \; D^3  \)
Symbol	English	Metric
\( n_a \) = number of active coils	\(dimensionless\)
\( G \) = shear modulus of material	\(lbf \;/\; in^2\)	\(Pa\)
\( d \) = wire size	\(in\)	\(mm\)
\( k_s \) = spring constant	\(lbf \;/\; ft\)	\(N \;/\; m\)
\( D \) = mean coil diameter	\(in\)	\(mm\)