# Elastic force calculation method of compression spring and tension spring

Pressure spring
·In addition to the spring size, the design data of pressure spring need to calculate the maximum load and the load of deflection size;

·Spring constant: expressed by K, when the spring is compressed, the load (kgf / mm) of each increase of 1 mm distance;
·Spring constant formula (unit: kgf / mm)
G = steel modulus of wire: Piano steel wire g = 8000; stainless steel wire g = 7300, phosphor bronze wire g = 4500, brass wire g = 3500
D = wire diameter
Do = od = outer diameter
Di = id = inner diameter
DM = MD = pitch diameter = do-d
N = total number of turns
NC = effective number of turns = n-2
Calculation example of spring constant:
Wire diameter = 2.0 mm, outer diameter = 22 mm, total number of turns = 5.5 coils, steel wire material = piano wire

Tension spring
The K value of tension spring is the same as that of pressure spring
·The initial tension of tension spring: the initial tension is equal to the force required to pull apart the tightly attached spring and coil. The initial tension occurs after the spring is rolled and formed. When the tension spring is made, the initial tension of each tension spring is uneven due to the difference of steel wire material, wire diameter, spring index, static electricity, lubricating grease, heat treatment and electroplating. Therefore, when installing the tension spring of various specifications, it should be pre pulled until the parallel coils are slightly separated. The force required is called the initial tension.
·Initial tension = P – (K × F1) = maximum load – (spring constant × tensile length)

Torsion spring
·Spring constant: expressed in K, when the spring is twisted, the load (kgf / mm) of each additional 1 ° torsion angle
·Spring constant formula (unit: kgf / mm)
E = steel modulus of wire: Piano steel wire e = 21000, stainless steel wire e = 19400, phosphor bronze wire e = 11200, brass wire e = 11200
D = wire diameter
Do = od = outer diameter
Di = id = inner diameter
DM = MD = pitch diameter = do-d
N = total number of turns
R = arm of force under load
p=3.1416