Analysis and prevention of fatigue failure of wave spring

1、 Introduction
Although spring industry is a small industry in the whole machinery manufacturing industry, its role can not be underestimated. With the deepening of the opening degree, the imported industrial equipment such as machinery manufacturing, automobile, petrochemical and electric power has been widely used in China. Accordingly, we also know that some new components with superior performance, multi-layer wave spring is a relatively new elastic element.
Ordinary single-layer wave spring is an elastic element with several peaks and valleys on a metal ring. It seems that the multi-layer wave spring is composed of several common single-layer wave spring. The difference is that it is not simply superimposed, but processed by a special continuous winding process.

 

2、 Classification and working principle
Wave spring is usually divided into: A, single-layer wave spring
Single layer closed wave spring with “O” shape
The single-layer open-ended type is “C” shape wave spring;
b. Multi layer peak to peak (Series) wave spring;
c. The multi-layer stacked peak type is also called nested type (parallel type);
Single layer wave spring: suitable for working conditions of short displacement and low elastic force, with good reliability and high working principle: wave spring has the accuracy of double working principle of cylindrical spring and disc spring.
Multi layer wave spring opposite peak type (series type): the elastic force value is inversely compared with the number of coils. It is mainly used in large displacement, medium and low elastic requirements, and is the substitute of cylindrical spring. Nested type (parallel type): the force value of the spring is proportional to the number of turns. It can maintain all the accurate characteristics of the wave spring while generating huge elastic force. In many cases, the nested (parallel) wave spring can be used instead of the disc spring.

 

3、 Effect of material and temperature on fatigue failure
For the same material, the material with fine grain structure has higher yield strength and fatigue elasticity than that with coarse grain structure; the fatigue life of surface strengthened material is much higher than that without strengthening treatment; the smaller the surface roughness is, the smaller the stress concentration is, the higher the fatigue strength is; The fatigue life of the material with metallurgical defects will be greatly reduced, which makes the spring fatigue failure in advance.
The wave spring made of common spring steel has good elasticity, strong conductivity and wear resistance. The fatigue failure of the spring is within the normal range at normal temperature (at? 200?). However, with the increase of temperature, the spring elasticity will gradually decrease and the failure phenomenon will increase obviously.
The wave spring made of stainless steel has high fatigue life and good relaxation resistance. At the same time, stainless steel also has high corrosion resistance and non-magnetic properties. Generally, stainless steel will fail when the temperature is higher than 400?. special stainless steel has extremely high corrosion resistance, non magnetism and other characteristics. When the working temperature of special stainless steel reaches 650?, it also has high relaxation resistance and fatigue resistance, which is an irreplaceable material in special working conditions.

 

4、 Prevention of fatigue failure of wave spring
The following is the wave spring load, stress calculation formula, we can use the formula to design the wave spring stress in the low stress state, the waveform spring fatigue failure is not obvious.
(1) Calculation formula of single-layer wave spring: F = pkdm / ebt3n4 * ID / OD
S=3IIPDm/4bt2N2 ;
(2) Calculation formula of multi-layer series or peak to peak wave spring;
f=PKDm3Z/Ebt3N4*ID/OD ; S=3IIPDm/4bt2N2 ;
(3) The calculation formula of multi-layer stacked peak spring is also called nested or parallel wave spring;
F=PKDm3/Ebt3N4Z*IDOD ; S=3IIPDm/4bt2N2Z ;
Where: F = displacement; P = load; k = multi turn coefficient; DM = average diameter;
Z = number of turns; E = modulus of elasticity; b = width of material; t = thickness of material;
N = wave number; id = inner diameter; OD = outer diameter; s = bending stress;
Through the fatigue test of the wave spring, we get that the fatigue life of the wave spring is far more than 500000 times, and the normal life is more than 1 million times. The outer diameter d = 137mm, inner diameter d = 125mm, thickness t = 0.8mm, wave crest height h = 6mm, working force value f = 1225n when working displacement is 3.5mm. After more than three years of use in a petrochemical enterprise, the service life of this type of wave spring has reached 1.8 million times, and some of them are even longer.
Therefore, we should select reasonable wave crest height and material thickness according to load and displacement, effectively control the stress of wave spring, and use adjustable wave number to control the fatigue failure of wave spring more effectively.