In order to ensure the spring to work reliably, its material should not only meet the requirements of high strength limit and yield limit, but also have high elastic limit, fatigue limit, impact toughness, plasticity and good heat treatment process. Table 20-2 lists several main spring materials and their performance. Spring steel is widely used in practice, and its varieties include carbon spring steel, low manganese spring steel, silicon manganese spring steel and chromium vanadium steel. Figure 20-2 shows the tensile strength limit of carbon spring steel wire.
Category code allowable torsion stress [TT] allowable bending stress [σ b] / MPA shear modulus G / GPA elastic modulus E / GPA
Recommended hardness range HRC recommended temperature ° C characteristic and Application
Type I spring type II spring type III spring type I spring type II spring
Steel wire carbon spring steel wire
Ⅰ, Ⅱ, Ⅱ a, Ⅲ 0.3 σ b0.4 σ b0.5 σ b0.625 σ b81.5 ～ 78.5204 ～ 202 — 40 ～ 120 high strength and good performance, suitable for small spring
60Si2Mn
60si2mna47162778578598178.519745 ～ 50-40 ～ 200 has good elasticity, stable tempering and easy decarburization. It is suitable for spring under heavy load
65Si2MnWA
60si2crva560745931931116747 ～ 52-40 ～ 250, good strength, high temperature resistance and good elasticity
30w4cr2va44258873573592043-47-40-350 have good high temperature strength and hardenability.
50crva45-50-40-210 has high fatigue strength, good hardenability and tempering stability
Stainless steel 1cr18ni9ti32443254054067771.5193 — 250 ～ 300, corrosion resistant, high temperature resistant, suitable for small spring
4cr1344258873573592075.521548-53-40-300, corrosion resistant, high temperature resistant, suitable for making large spring
Co40crnitimo500666834834100076.5197 = – 40 ～ 500 corrosion resistance, high strength, no magnetism, low aftereffect and high elasticity
The bronze wire qsi-326535344244255040.293hb90-120-40-120 is corrosion-resistant and antimagnetic
QSn4-339.2
Qbe235344255055073542.2129.537-40 corrosion resistance, antimagnetism, good conductivity and elasticity
Note:
1. According to the number of force cycles n, the springs can be divided into three types: type i n > 106; type II n = 103-105 and impact load cases; type III n < 103.
2. According to different mechanical properties, carbon spring steel wire can be divided into four groups: group I, group II, group IIA and group III. group I has the highest strength, followed by group II, group IIA and group III.
3. Working limit stress TLIM of spring: type I: ￡ 1.67 [t]; type II: ￡ 1.25 [t]; type III: ￡ 1.12 [t].
4. The mechanical properties of rolled steel are the same as that of steel wire.
5. The shear modulus and elastic modulus of carbon steel wire are effective for the diameter of 0.5-4mm, and the lower limit is taken when the diameter is greater than 4mm.
2 material selection
Spring material selection must fully consider the use, importance, load nature, size, cycle characteristics, working temperature, surrounding media and other service conditions, as well as processing, heat treatment and economy, so as to make the selection results consistent with the actual requirements. Steel is the most commonly used spring material. Non ferrous metals can be used when the force is small and corrosion and magnetic properties are required. In addition, there are springs made of nonmetallic materials, such as rubber, plastic, cork and air.
3 spring manufacturing
The manufacturing process of spiral spring is as follows:
① Winding;
② Hook ring manufacturing;
③ Fabrication and finishing of the end;
④ Heat treatment;
⑤ For the important spring, strong pressure treatment should be carried out.
The winding method of spring is divided into cold coiling method and hot coiling method.
(1) Cold winding method: the spring wire diameter D ≤ 8mm shall be wound by cold winding method. The high-quality carbon spring steel wire which is cold drawn and pre heat treated is usually used for the spring wound in cold state. Generally, quenching treatment is not required after winding, and only low-temperature tempering is required to eliminate the internal stress during winding.
(2) Hot coiling method: the spring with larger wire diameter (d > 8mm) is wound by hot coiling method. The spring rolled in hot state must be quenched and tempered at medium temperature.