# Basic knowledge of spring

3、 Cylindrical helical compression spring
When the winding ratio is between 3 and 10, the spring end face is best ground flat; when the winding ratio is between 10 and 15, the end face can be ground or not; when the winding ratio is greater than 15, it can not be ground.
In order to avoid excessive additional force caused by eccentric load, the minimum number of working cycles is 2, but generally not less than 3.

Winding ratio C = spring pitch diameter / wire diameter
If the winding ratio C is too small, the bending deformation of the material is serious, and the required winding power is high. Sometimes the end of the cut mandrel is too thin and easy to break; if the winding ratio C is too large, the spring coil is easy to loosen and the diameter of the spring is difficult to control; in addition, due to the weight of the spring itself, the spring coil constantly vibrates. The ideal winding ratio is 4 ~ 9.
Spring stiffness F “= gd4 / 8d3n (n / mm)
In general, the number of effective coils of spring is more than 2.5, but for the spring with strict load requirement, the effective coil number is more than 4; the effective coil number is small and the load requirement is high, it is difficult to manufacture.
For the spring with small material diameter and strict load requirements, it is recommended to use support ring ≥ 2.
When there are two or more loads under the specified height, the free height shall not have tolerance requirements. The inner diameter and outer diameter of spring can not be marked with tolerance at the same time.

4、 Cylindrical spiral tension spring
Initial tension: when the tension spring is rolled and formed, the spring coils produce compression force with each other. When the external tensile load is applied to the spring, if the tensile force generated by the load does not reach this force, the spring will not deform, but will start to deform after reaching or exceeding the compressive force. The tensile load corresponding to this compressive force is the initial tensile force F0.
The bearing capacity of spring with initial tension is much higher than that without initial tension.
For the spring without initial tension, there will be more or less gap between the rings. When the number of coils of the spring is large, these gaps will affect the theoretical value of the free length of the spring, which needs to be negotiated with the customer.
The calculation formula of winding ratio and stiffness is the same as that of compression spring.
The total deformation of the tension spring is the sum of the deformation caused by the effective number of coils and the deformation caused by the hooks at both ends. It is equivalent to 0.1 turn for semicircular shackle and 0.25-0.5 turn for full circle shackle.
Springs with initial tension must be made of hardened steel wire.
It is difficult to ensure the quality of the spring with small diameter, large number of effective coils and large winding ratio.

5、 Cylindrical helical torsion spring
Spring type: ordinary torsion spring, parallel double torsion spring, in-line double torsion spring; two kinds of no gap and with space.
Generally, the number of effective working coils of spring shall not be less than 3;
The rotation direction of the torsion spring must be clear, and the rotation direction must be consistent with the direction of torque, so that the spring can be tightened when working.
The mandrel of the torsion spring must be 10% smaller than the inner diameter of the spring under the maximum working torque.
In order to avoid excessive stress concentration, the radius of each transition arc should not be less than 2 times of material diameter.
In order to prevent the torsion spring from instability, the maximum torsion angle should not be greater than the allowable value
The fourth power of the effective number of turns in the free state.
The tempering temperature of torsion spring with high precision should not be too high;
For the torsion spring to be electroplated, the radius of curvature of the bending arm should be as large as possible to prevent crisp.

6、 Spring manufacturing process
Coil spring – (correction) – stress relief tempering – rough grinding of end face – deburring inside and outside – (shot peening) – standing treatment (or strong pressure treatment) – fine grinding of end face – Inspection – antirust treatment – packaging
Shot Peening: increase fatigue life of spring
Standing or strong pressure treatment: the spring height is pressed to the working limit height or each coil is tightened several times or stayed for a period of time, so as to stabilize the size and improve the bearing capacity.