Basic knowledge of spring

1、 Functions, types, common symbols and units of spring:
Functions of spring: positioning, restoring, buffering or damping, impact, power, application of force, adjustment of pressure and measurement of force
Type of spring:
According to the material is divided into: metal spring (steel spring, non-ferrous metal spring), non-metallic spring
According to the spring shape, it can be divided into coil spring, leaf spring, volute spring, plate spring, ring spring and torsion bar spring
According to the service conditions of spring, it can be divided into:
Class I: the number of times subjected to alternating load is more than 106, which belongs to the category of infinite life calculation, and fatigue strength calculation should be carried out;
Class II: the number of times of alternating load is between 103 and 105, and the impact load is within the scope of finite life calculation;
Class III: under the action times of alternating load less than 103 times, it belongs to the category of static load strength calculation.
Common symbols and units of spring:
C — spiral spring winding ratio; disc spring diameter ratio; coefficient
D — spring pitch diameter
D1 — spring inner diameter (ID)
D2 — outer diameter of spring (OD)
D — diameter of spring material (wire diameter)
G — shear modulus of material (MPA)
F “- spring stiffness (n / mm)
H — working height of spring
H0 — free height of spring
T — spring torque
T — spring pitch

2、 Basic performance of spring
Spring is a kind of mechanical parts. It uses the elastic and structural characteristics of materials to produce deformation when working, and transforms mechanical work or kinetic energy into deformation energy (potential energy), or deformation energy (potential energy) into mechanical work or kinetic energy.
Spring applications:
Buffering or damping, such as support spring of crusher and suspension spring of vehicle, etc;
Mechanical energy storage, such as clocks, meters and automatic control mechanism on the original spring;
Control movement, such as valves, clutches, brakes and springs on various regulators;
A force measuring device, such as a spring scale and a spring on a dynamometer.
Characteristic line of spring: the relation curve between load and deformation is called spring characteristic line.
There are three kinds of characteristic lines of spring: 1) linear type 2) increasing type 3) decreasing type
Spring stiffness: the ratio of load increment to deformation increment, that is, the load required to produce unit deformation, is called spring stiffness.

The stiffness of compression and tension spring is k = (p2-p1) / (h1-h2)
The stiffness of torsion spring is k = (t2-t1) / (torsion angle 2-torsion angle 1)
The stiffness of the spring increases with the increase of load;
For the decreasing spring, the stiffness decreases with the increase of load;
The stiffness of linear spring does not change with the load, which is also called spring constant.
Deformation energy of spring
The deformation energy of the spring is inversely proportional to the shear modulus G and elastic modulus E of the spring material. Therefore, the low modulus is beneficial to the large deformation energy required. The size of the deformation energy is directly proportional to the square of the maximum working stress. Increasing the stress means that the material is required to have a high elastic limit, and a high elastic limit also corresponds to a high modulus (stress plays a decisive role).
In order to obtain large deformation energy, the volume or stress of spring material can be increased, or both can be increased.
Fatigue strength of spring

In mechanical equipment, there are two kinds of stresses in the working process of parts of machinery: static stress and variable stress.
The failure of parts or materials subjected to static stress is plastic deformation or brittle fracture, so their strength is measured by the elastic limit or yield strength and displacement limit of the material. The failure of parts or materials subjected to variable stress is fatigue fracture, so their strength is measured by fatigue strength.
The fatigue strength is lower than the static stress strength such as elastic limit or yield strength.
The types of variable stress are: stable cyclic variable stress, unstable cyclic variable stress, random variable stress.
The factors influencing fatigue strength are yield strength, surface state, size effect, metallurgical defects, corrosive medium and temperature
The factors affecting the spring fatigue test are internal factors, such as chemical composition, metallographic structure, etc;
External factors, such as surface state, shape and size, temperature and surrounding media.