# Design and calculation of spring

Name and designation compression coil spring tension coil spring
The spring diameter D / mm is determined by the strength calculation formula
Spring pitch diameter D2 / mmd2 = CD
Spring inner diameter D1 / mmd1 = d2-d
Spring outer diameter D / MMD = D2 + D
Spring Index C C = D2 / D, generally 4 ≤ C ≤ 6
For compression spring, g = 5 ° to 9 ° is recommended
The effective number of turns n is determined by the calculation of deformation conditions, generally n > 2
The total number of turns N1 compression N1 = n + (2 ~ 2.5); stretching N1 = n
N1 = n + (1.5-2) (y I type hot coil); the mantissa of N1 is 1 / 4, 1 / 2, 3 / 4 or the whole circle, and 1 / 2 coil is recommended
When N1 = n + 1.5, H0 = NP + DLI type H0 = (n + 1) d + D1
When N1 = n + 2, H0 = NP + 1.5dl type Ⅱ H0 = (n + 1) d + 2D1
When N1 = n + 2.5, H0 = NP + 2DL Ⅶ H0 = (n + 1.5) d + 2D1
When N1 = n + 2, H0 = NP + 3D
When N1 = n + 2.5, H0 = NP + 3.5D
Working height or length HN / mmhn = H0 lnhn = H0 + LN, LN deformation
Pitch P / mm P = D
Spacing D / MMD = p-dd = 0
Compression spring height diameter ratio BB = H0 / D2

Development length L / MML = pd2n1 / cosgl = pd2n + unfolded length of hook
Calculation formula of spring force: the design data of pressure spring, in addition to the spring size, needs to calculate the maximum load and the load of displacement size; spring constant: expressed by K, when the spring is compressed, the load of every 1mm increase (kgf / mm); spring constant formula (single position: kgf / mm): k = (g × D4) / (8 × DM3 × NC) 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 = medium diameter = do-d n = total number of coils NC = effective number of coils = n-2 spring constant calculation example: wire diameter = 2.0mm, outer diameter = 22mm, total number of coils = 5.5 coils, steel wire material = piano wire k = (g × D4) / (8 × DM3 × NC) = (8000 × 24) / (8 × 203 × 3.5) = 0.571kgf/mm. 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. The formula of spring constant (unit: kgf / mm): k = (E × D4) / (1167 × DM × P × n × R) e = steel modulus of wire: e = 21000 for Piano steel wire, e = 19400 for stainless steel wire, e = 11200 for phosphorus bronze wire, Brass wire e = 11200 d = wire diameter do = od = outer diameter Di = id = inner diameter DM = MD = medium diameter = do-d n = total number of turns r = arm of force under load p = 3.1416 Hooke’s law f = – KX K is spring coefficient X is tensile type variable f = kx, K is stiffness coefficient, X is elongation.