Spring constant: expressed in k, when the spring is stretched, the load for each additional 1mm distance (kgf/mm)
Spring constant formula (unit: kgf/mm): k=(G*d4)/(8*Dm3*Nc)
G: modulus of rigidity of the wire; d: wire diameter; Dm: middle diameter = outer diameter - wire diameter; Nc: effective number of turns = total number of turns - 2.
The initial tension of the tension spring: The initial tension is equal to the force required to pull apart the springs that are close to each other and the initial tension occurs after the spring is rolled and formed. During the production of tension springs, due to the difference in wire material, wire diameter, spring index, static electricity, lubricating grease, heat treatment, electroplating, etc., the initial tension of each tension spring is uneven. Therefore, when installing the tension springs of various specifications, it should be pre-tensioned to a slight distance between the parallel coils. The force required at this time becomes the initial tension.
Initial tension=P-k X l=maximum load-spring constant X tensile length
