New spring testing machine

Spring testing machine is a special instrument for testing springs. In recent years, the speed of development is very rapid, and there are many new spring models. Here is a brief introduction about the characteristics and maintenance knowledge of the new spring testing machine.

The new spring testing machine has the following characteristics:
1. The load deformation characteristic curve is nonlinear.
2. The disc spring is in sheet shape and easy to form a combination. It can be assembled and replaced by building blocks, so it is convenient for maintenance.
3. The disc spring with radial groove has zero stiffness. This characteristic can be used in some deformation range where the spring force is basically stable.
4. The vibration absorption performance of the disc spring is not lower than that of the cylindrical spiral spring. When the laminated combination is adopted, the disc spring has greater damping and dissipates the impact energy due to the friction between the disc springs.
Spring testing machine and other types of testing machine need regular maintenance, so how to maintain it, this is a lot of testing machine operators are concerned about. I would like to share this problem with you, hoping to bring help to the operators.

1. During maintenance, please do not wipe with water, alcohol or acetone, which will damage the spring tester and the electronic components.
2. Make sure that the fuselage is clean and not placed in a place with high humidity, so that the accuracy will not be damaged.
3. The coating part of the machine is often cleaned with a clean cloth.
4. The electroplated part is wiped with a little oil.
5. Add a little oil to each moving part.
6. Do not get dust and water on the key part of the panel.

Wire twisting machine

Main application of wire twisting machine:
The torsion testing machine is mainly used to measure the plastic deformation ability of metal wire with diameter of 0.1-1 mm in one direction or two directions. The surface defects of wire rod can be displayed during the test. The testing machine consists of manual loading, high-precision torque sensor detecting torque, photoelectric encoder detecting angle, and digital display of test results. It is mainly applicable to the Mechanical Laboratory of relevant scientific research departments, colleges and universities and industrial and mining enterprises to measure the torsional properties of materials; it is very suitable for on-line inspection of wire rod production units and incoming inspection of wire rod using units

The main technical parameters of wire torsion testing machine are as follows
Maximum diameter of sample of wire torsion tester (mm): 1 – ¢ 3 ¢ 0.1 – ¢ 1
Sample length (mm): 100-300, 50-200
Sample tension (n): 2-350 0.2-30
Sample speed (R / min): 60, 90, 120
60, 120, 180,300
Counting mode: digital display, digital display
Motor power (kw): 0.250.25
External dimension (length × width × height mm)
877 × 350 × 1082
Net weight: 200kg (floor type)
Power supply voltage (V): 380 wire twisting machine

Clever use of spring return function

According to the mechanical properties, the spring can be divided into precision spring, tension spring, compression spring, torsion spring, bending spring and spiral spring. The spring deforms under the action of external force, and the spring can recover after the external force is removed. Many tools and equipment are reset by using the property of precision spring. For example, the hinges of many building doors are equipped with reset springs, and the doors will reset automatically after people enter and leave. People also make use of this function to make automatic umbrella, automatic pencil and other supplies, very convenient. In addition, all kinds of buttons and buttons also need a return spring.

To be engaged in the production and manufacturing of various cold coil stretching, compression, torsion spring and special-shaped spring and hardware stamping parts with wire diameter less than 8mm, the main equipment such as CNC 620 CNC spring machine and cnc-8 CNC spring machine are directly imported from Taiwan, with an annual production capacity of more than 2 billion.

The products are widely used in mechanical instruments, automobile and motorcycle accessories, household appliances, office supplies and other fields, heat treatment The equipment adopts rjc-315 numerical control tempering furnace and zx-12-9 oxygen free quenching furnace. The main testing equipment includes 23ta desktop projector, tld50 tension and compression tester, tl-1000 spring tension and compression testing machine, tns-1000 spring torsion testing machine and so on.

What is a coil spring

A spiral spring made of spring wire. There are many types of spiral spring, which can be divided into ordinary cylindrical spiral spring and variable diameter spiral spring according to the shape, and can be divided into left-hand spring and right-hand spring according to the helix direction. The cylindrical spiral spring has the advantages of simple structure, convenient manufacture and wide application. Its characteristic line is straight line and can be used as compression spring, tension spring and torsion spring.

When the load is large and the radial size is limited, two compression springs with different diameters can be used together to form a combined spring. There are taper coil spring, volute coil spring and concave spiral spring. The conical spiral spring has good cushioning performance and can bear large load. Volute spiral spring can store more energy and bear larger load, but the manufacturing process is more complex. The performance of concave spiral spring is similar to that of conical spiral spring, which is mostly used for cushion and mattress. The load surface of spring steel wire includes circle and rectangle, and circular section is the most commonly used.

Spiral spring, namely torsion spring, is a spring that bears torsion deformation, and its working part is also tightly wound into a spiral shape. The end structure of torsion spring is processed into various shapes of torsion arm, not hook ring. Torsion spring is often used in balancing mechanism of machinery, and is widely used in automobile, machine tool, electrical appliance and other industrial production.

About spring shoes

The appearance of spring shoes is very similar to that of dry skates, except that the bottom of the shoes is equipped with elliptical springs instead of pulleys. When you first put on the shoes, you need to bounce in place several times to get used to the “rebound” feeling, and then you can use them on the beach, roadside and even on the snow to enjoy the novel “weightlessness” rebound movement.

Spring shoes can play a good bounce effect, but people have different opinions on him
It is reported that the spring shoes were originally developed to help those injured in sports recover. Manufacturers claim that the shoes can cushion up to 80% of the bounce impact, protect joints from injury, and also have the function of weight loss and shape building. At present, the manufacturing process of this kind of rebound shoes is still a secret. Kangoo jumps only disclosed that the shell of the rebound shoe is made of polyurethane compound, the black arc spring bracket on the sole is made of a material called “space plastic”, and the orange tension spring between the two spring supports can adjust the elasticity according to the user’s weight.

Gas spring

It is a mechanism composed of a closed cylinder, a piston assembly and a piston rod which can slide in the cylinder and takes compressed gas as the energy storage medium.
A cycle
It refers to the air spring piston rod once in the stroke specified in the drawing.
Dynamic internal resistance (g)
It refers to the dynamic friction force produced when the piston rod moves back and forth within the stroke specified in the drawing.
technical requirement
general requirements

The gas spring shall meet the requirements of this standard and be manufactured according to the drawings and technical documents approved by the specified procedures.
The installation length tolerance of gas spring shall conform to grade A of QC / t29087.
The shape of the gas spring should be smooth and smooth without burr.
The coating of air spring piston rod should be uniform, and no visible cracks, blisters, pockmarks, delamination and other defects are allowed.
The coating of other parts except piston rod should be uniform: no local coating, obvious crack, blister, roughness and other defects are allowed.
The coating layer of gas spring should be uniform, and no defects such as exposure, wrinkling, blistering and peeling are allowed.

Working temperature range: 40 ℃~ 80 ℃.
mechanical property
When the air spring is tested according to 5.1, its force displacement curve is shown in Fig. 1. The nominal value of the force shall meet the requirements of the drawing, and the limit deviation of the nominal value of the force shall comply with the provisions in Table 1.
When the piston rod of the air spring is reciprocating, its dynamic internal resistance g shall meet the requirements of the drawing, and no clamping stagnation and obvious vibration are allowed.
Air tightness

Durability
The change rate of initial force value of air spring after 5.3 test shall not be greater than 8%.
Corrosion resistance
After the air spring is tested according to 5.4, the coating of the gas spring shall comply with the provisions of Article 5.2 B in gb6461, and the coating layer of the gas spring shall meet the requirements of grade I in gb1740.
tensile strength
The overall tensile strength of the gas spring shall meet the requirements of Table 2. After the test according to 5.5, all connectors shall not be broken or fall off, and their mechanical properties shall meet the requirements of Table 1.
test method

Mechanical property test
Test conditions: the temperature is 20 ± 2 ℃, and the measurement is carried out after 4 hours. The test speed is 500 mm / min.

Test method: the piston rod of the air spring is vertically clamped on the testing machine with the piston rod downward for at least three cycles, and the piston rod of the gas spring is observed for clamping or obvious vibration. If there is no abnormality, start to measure and record the force displacement curve, and measure the f force at each point according to the following method:
Compress the air spring piston rod to point a according to the distance L specified in the drawing, stay for 3S; record the value of F3 force.
Compress the piston rod of the gas spring to point B and stay for 3S; record the value of F4 force.
Stretch the piston rod of air spring to point C and stay for 3S; record the value of F2 force.
Stretch the piston rod of air spring to point D and stay for 3S; record the value of F1 force.

Air tightness test
The gas spring was placed in a high-temperature test chamber at 80 ± 2 ° C for 4h, then moved to 20 ± 2 ℃ for 2h, and then placed in a low-temperature test chamber at 40 ± 2 ° C for 4h, and then moved to 20 ± 2 ℃ for 2h. After two times of high and low temperature tests, the mechanical properties were tested according to 5.1.

Durability test
The gas spring was loaded on the testing machine according to the actual loading state, and the gas spring was continuously and evenly cycled for 25000 times at the frequency of 4-6 times / min. 2500 times per cycle, test and record according to 5.1.

Corrosion resistance test
The piston rod of the air spring is in the minimum compression state specified in the drawing, and the test shall be conducted for 48h according to the provisions of GB 6458. After the test, the corrosion resistance of 4.5 shall be checked.

tensile strength test
Fix the connection parts of both ends of the gas spring on the testing machine, and apply the tensile test specified in 4.6. After the test, the mechanical properties were tested according to 5.1.

60Si2Mn 60simna spring steel, oil quenching spring steel, tempering spring steel

60crmnba 30W4Cr2VA spring steel is a kind of steel used to make spring or similar spring performance parts. It has high elastic limit, fatigue limit (especially notch fatigue limit) and certain impact toughness and plasticity. It is mainly used under dynamic load such as impact and vibration or long-term periodic alternating stress. Therefore, the springs working in various conditions should have good surface quality and high fatigue resistance. In terms of process performance, the spring steel which needs quenching and tempering should have certain hardenability, not easy to decarbonize, low overheat sensitivity and high plasticity, and easy to form in hot state. The steel wire for making small size spring should have uniform hardness and certain plasticity.

According to the production method, spring steel can be divided into hot-rolled spring steel and cold drawn (rolled) spring steel. The hot-rolled spring steel includes the round steel or trapezoidal steel used for manufacturing coil spring, torsion bar and flat steel for making leaf spring; the cold drawn (rolled) spring steel includes the cold drawn steel wire for manufacturing small-sized spiral spring and the cold-rolled steel strip for making spring and various spring sheets. Alloy spring steel usually contains manganese, silicon, chromium, molybdenum, tungsten, vanadium and trace boron. These alloy elements can improve the hardenability of the steel, and manganese and silicon dissolved in ferrite can improve the yield strength. Chromium, tungsten and vanadium can improve the elastic limit, yield ratio and heat resistance of steel. According to the alloy elements, the commonly used spring steels can be divided into:

Carbon spring steel is cheap and widely used. If the surface state and heat treatment microstructure are the same, the fatigue limit is not lower than that of alloy spring steel. The disadvantage is that the hardenability and yield strength are low; the spring with large cross-section can not be quenched through oil quenching, but easy to crack when water quenching. If the carbon content is increased, the strength and elastic limit can be increased, but the impact toughness and plasticity will be reduced, especially the low temperature toughness. There are four grades of carbon spring steel in China: 65, 70, 75 and 85.
The content of manganese is 0.90-1.20% in pure manganese bearing spring steel such as 65Mn. The increase of manganese content can improve the hardenability and strength of steel and reduce decarburization tendency; the disadvantage is that it has overheat sensitivity and temper brittleness, and is easy to produce quenching cracks, so it is only suitable for manufacturing various small size flat spring and round spring.

Silicon manganese spring steel is the main hot-rolled alloy spring steel. There are four grades of 55si2mn, 60Si2Mn, 60Si2MnA and 70si3mna in China. The contents of silicon and manganese are 1.50-2.80% and 0.60-0.90% respectively. The addition of silicon in steel can significantly improve the elastic limit and yield ratio, and improve the tempering stability, but it is easy to form inclusions such as silicate and increase the decarburization sensitivity. When the content of carbon and silicon in steel is high, carbon is easy to graphitize. This kind of steel is widely used in the production of damping leaf springs and coil springs for automobiles, tractors and locomotives, as well as springs requiring high stress.

Chromium containing spring steel is widely used in the world. There are two grades of steel 50CrMn and 50CrVA in China. 50CrMn, containing about 1% chromium and manganese, has high hardenability and low decarburization tendency; its disadvantage is that both chromium and manganese aggravate the tendency of temper brittleness, and it needs rapid cooling after tempering, which is mainly used to manufacture leaf spring and spiral spring with larger cross section and more important. The results show that 50CrVA steel has good hardenability; adding vanadium can refine the structure, not easy to overheat, and improve the strength and toughness of the steel, and reduce the notch sensitivity. This kind of steel has low decarburization tendency, good impact toughness at low temperature and stable performance when working at higher temperature. It is mainly used for making valve spring, safety valve spring and spring working at higher temperature. The mechanical properties and hardenability of 50CrVA spring steel are better than those of the above two kinds of spring steel by adding other alloy elements properly.

The 60Si2CrVA steel with silicon content of 1.40-1.80%, chromium content of 0.90-1.20% and vanadium content of 0.10-0.20% has high hardenability and low overheat sensitivity. When the plasticity index is similar, the tensile strength and yield strength of 60Si2CrVA steel are higher than those of silicon manganese spring steel. It is mainly used to make high stress spring.

The tungsten content of 65si2mnwa steel is 0.80-1.20%. Like 60Si2CrVA steel, it can be used to make high load, heat resistant (≤ 350) and impact resistant spring. 30W4Cr2VA steel with high alloy content is a kind of high strength heat-resistant spring steel with high hardenability. It is mainly used to manufacture control valve spring used under 500. The production process of these steels is complex and the price is high.

Heat resistant steel and heat-resistant alloy can be selected for springs working under high temperature conditions; stainless steel of corresponding brands shall be selected for springs working in corrosive medium according to the properties of medium (oxidizability and reducibility).

Spring material type

The spring steel (SUP) is the most widely used spring material, and the other steel or copper alloy wires listed in table a are available according to the purpose of use.
Table a is generally used for spring materials
Category JIS number symbol
Spring steel g 4081 sup
Hard steel wire g 3521 SW
Qin steel wire g 3522 swp
Oil tempered steel wire——
Stainless steel wire g 4309 sus-wh
Brass wire h 3521 BSW
White copper wire h 3721 hsws
Phosphor green copper wire h 3751 pbw
Beryllium copper wire h 3803 becuw

A. Carbon steel and alloy steel: when making springs, metal elements such as silicon, manganese, chromium, vanadium and molybdenum are often added to the steel to increase the elasticity and fatigue limit of the spring and make it impact resistant.
a. Large springs are usually processed by hot working, that is, the spring material is rolled into bars at high temperature, and then processed at high temperature, quenched in oil or water at 780 ~ 850 ℃, and tempered at 400 ~ 500 ℃.
b. Small springs are annealed first, then cold worked, rolled and then hardened and tempered, such as steel wire, piano wire or steel strip.
c. Piano steel wire is made of high carbon steel (0.65 ~ 0.95%), with less impurities and diameter less than 1 / 4. After bremsstralization, it is drawn into a line at room temperature. It has good mechanical properties, high tensile strength and toughness, and is an excellent spiral spring material.
d. Stainless steel wire is used in corrosion prone areas, high-speed steel and stainless steel can be used to withstand high temperature.
e. 0.6 ~ 0.7% of carbon content of oil return line should contain manganese, and 0.6 ~ 1.0% is usually used for coil spring,
f. 0.9-1.0% ordinary steel is commonly used for plate spring, and CR-V steel and Si Mn steel are used for higher grade plate spring.

2. Non ferrous and non-ferrous alloy steels:
a. The alloy can not be hardened by heat treatment, only rolled.
b. Copper alloys for springs include phosphor bronze, brass, etc., which are inferior to steel in elasticity and corrosion resistance. They are generally used in springs for chemical machines and also for springs for electrical measuring instruments due to their non-magnetic properties.
c. Monel is an alloy of copper and nickel, used in the food industry, denoted by K.
d. Inconel (75% Ni, 15% Cr, 10 ° C) has no relaxation at high temperature (within 700 ° f). It is used in boilers, turbines and jet engines.

3. Rubber spring:
a. Its function is to absorb vibration and shock motion.
b. Many resin materials can also be used as spring materials.

Standard and application of spring steel wire

Table 4 GB / t4357-89 carbon spring steel wire
Note: ① grade D steel wire of Φ≤ 4.0mm and grade B and grade C steel wire of Φ≤ 6.0mm shall be wound on the mandrel with the diameter of steel wire for 2 turns, and the surface of the sample after winding shall not produce crack and fracture.
② The D-grade steel wire with a diameter of more than 4.0 mm is wound on the mandrel of twice the diameter of the steel wire for 2 times, and the surface of the sample after winding shall not have cracks and fractures.
③ The steel wire with diameter > 6.00mm shall be subject to bending inspection. The sample shall be bent 900 along the arc of R = 10mm in different directions, and no crack and fracture shall be produced after bending.

Grade B and C steel wires are generally 70 (67a, 72A) or 65Mn (67b), and grade D are produced by t9xta and t8mna (82B).
This standard steel wire is mainly used to make static mechanical spring, its service life vibration frequency is higher than that of non mechanical spring, there are certain requirements for fatigue life, and the torsion performance of finished products is also increased. Therefore, the wire rod for steel wire should be smelted by EAF or EAF + secondary refining method, with P ≤ 0.030%, s ≤ 0.020%, etc. If there is free ferrite in the microstructure of the finished steel wire, the fatigue life of the spring will be reduced. However, 5% – 1.5% of the free ferrite exists in the controlled rolling and controlled cooling coil, so it is not suitable to use wire rod to produce finished steel wire directly. In principle, the steel wire supplied according to this standard should be treated with lead bath before forming to eliminate free ferrite structure, and the microstructure of finished steel wire should be fibrotic sorbite structure.

(3) GB / t4358-1995 carbon spring steel wire for important purposes
The steel wire supplied according to the standard is mainly used to make dynamic spring working under various stress states. According to the working stress state of the spring, the steel wire is supplied in three groups: Group E is suitable for medium stress dynamic spring, group F is suitable for high stress dynamic spring, and group G is suitable for dynamic spring with high fatigue life. The tensile strength, torsion, winding, bending and decarburization are tested for finished steel wire. The mechanical properties of common specifications are shown in Table 5.

Because the steel wire supplied according to this standard is used to make dynamic spring working under medium and high stress state, the finished steel wire must not only maintain high elastic limit and good toughness index, but also consider fatigue limit and fatigue life of spring. Therefore, there are higher requirements for the purity of steel, the content of nonmetallic inclusions and gases, the content of ferrite and the degree of surface decarburization. The wire rod for steel wire must be smelted by electric furnace + secondary refining method. The chemical composition of wire rod should be higher: P ≤ 0.025%, s ≤ 0.020%, Cr ≤ 0.10%, Ni ≤ 0.15% (0.12%), Cu ≤ 0.20%. In order to improve the fatigue life, Mn is often controlled in the high limit in practical production. 70 or 70 Mn (72B) is selected for Group E, t8mna or t9rta is selected for group F, and 65Mn (Mn can be adjusted to 0.9-1.2%) or 67b is selected for group G. The purpose of reducing P and s content in steel, increasing Mn content and adopting secondary refining is to reduce the content of non-metallic inclusions in steel, improve inclusion morphology and gas content, and increase fatigue limit and fatigue life. If there is free ferrite in the microstructure of steel wire, the fatigue life will be greatly reduced. The steel wire supplied according to the standard must be subject to lead quenching before being finished.

Group G steel wire is used to make valve spring working in severe vibration state, which requires very high fatigue life. Therefore, 65Mn wire rod with better toughness is selected. Although the tensile strength is decreased, the fatigue life is guaranteed. The steel wire surface decarburization will form ferrite structure, which will seriously affect the fatigue performance. The standard increases the inspection of decarburization layer for group G steel wire, and stipulates that the total decarburized layer depth shall not be greater than 1.0% d. however, for large size steel wire (Φ > 4.0 mm), the decarburization layer caused by hot-rolled wire rod is difficult to be completely eliminated. The supplementary regulation of the standard is: “with the consent of the demander, the steel with decarburized layer no more than 1.5% d in diameter can be supplied Silk “.
Table 5 GB / t4358-1995 carbon spring steel wire for important use
Note: ① the steel wire with diameter less than 4.0 mm shall be wound on the mandrel equal to the diameter of steel wire, and the steel wire with diameter greater than or equal to 4.0 mm shall be wound for 5 turns on the mandrel with twice the diameter of steel wire, and there shall be no crack or fracture.

② The steel wire with diameter greater than 1.0 mm shall be subjected to bending test. The sample shall be bent 900 along the R arc in different directions, and there shall be no crack or fracture at the bending part, with Φ ≤ 4.0 mm, r = 5 mm, and Φ > 4.0 mm, r = 10 mm.
③ The decarburized layer of group G steel wire is ≤ 1.0d%.
(4) Gjb1497-92 specification for special purpose carbon spring steel wire
In some special occasions, it is required that the spring has the elasticity beyond the conventional requirements. For example, for the convenience of carrying and using, the space occupied by the spring is very small, and the elastic force should be large enough. The steel wire with extra high tensile strength and good toughness must be selected to make the spring. The carbon spring steel wire for special purposes meets this requirement.

The standard stipulates that steel wire shall be supplied in groups a, B and C. Group C is suitable for high stress spring, group B is suitable for high stress spring, group A is suitable for ultra-high stress spring. T9A, T10A and t8mna steel wires are recommended in the standard. In fact, the tensile strength of steel wire increases with the increase of carbon content, while the torsional property (toughness index) decreases with the increase of carbon content. Considering comprehensively, the three wire companies of Dalian special steel group select T9A steel wire added with rare earth to produce group A, B and C steel wire. The tensile strength, torsion, torsional fracture, winding, tensile strength uniformity and size uniformity of finished steel wire are evaluated. The mechanical properties of common specifications are shown in Table 6.

It should be pointed out that the ultra-high tensile strength of steel wire is obtained by sacrificing part of plasticity and fatigue life. It is only suitable for springs with simple shape and low requirements for fatigue life. This standard should not be popularized.

Standard and application of spring steel wire

Spring is the most commonly used part in mechanical industry and daily life. The spring should return to its original position after unloading. The smaller the plastic deformation, the better. Therefore, the steel wire should have high elastic limit, yield strength and tensile strength. The higher the yield ratio is, the closer the elastic limit is to the tensile strength, so the higher the strength utilization ratio is, the stronger the spring elasticity is.

 

The spring absorbs the impact energy by elastic deformation, so the spring steel wire does not have to have high plasticity, but at least it must have the plasticity that can bear the spring forming and enough toughness to bear the impact energy.
Spring usually works under alternating stress for a long time, so it should have high fatigue limit and good creep and relaxation resistance.

 

Spring used in specific environment, there will be some special requirements for steel wire, for example: the spring used in corrosive medium must have good corrosion resistance. The spring used in precision instrument should have long-term stability and sensitivity, low temperature coefficient, high quality factor, small aftereffect effect and constant elastic modulus. The spring working at high temperature is required to keep enough elastic limit and good creep resistance at high temperature.
In addition, the forming process and heat treatment process of spring steel wire should also be considered. Both cold drawn spring steel wire and oil quenched and tempered spring steel wire are directly wound with steel wire in supply state, and the spring is directly used after stress relief treatment after forming. The tensile strength of cold drawn spring steel wire is slightly higher than that of oil quenched and tempered steel wire. The elasticity of large size cold drawn steel wire is too large, and it is difficult to wind spring. Therefore, the specification of cold drawn spring steel wire is generally less than 8.0 mm, and that of oil quenched and tempered steel wire is generally less than 13.0 mm. In fact, spring steel wire in light drawing state is mostly used for spring with diameter of 13.0 mm, which is cold drawn, wound and then quenched and tempered. Most of the steel wires with diameter above 15.0 mm are made by heating winding process.

 

The spring can be divided into static spring and dynamic spring according to the running state. Static spring refers to the spring with limited vibration times in service, such as safety valve spring, spring pad, scale spring, fixed load spring, mechanical spring, watch hairspring, etc. Dynamic spring refers to the spring whose vibration times are more than 1 × 106, such as engine valve spring, vehicle suspension spring, shock proof spring, coupling spring, elevator buffer spring, etc. Static spring material selection mainly considers tensile strength and stability, while dynamic spring material selection mainly considers fatigue, relaxation and resonance performance.

According to the load condition, the spring can be divided into three states: light load, general load and heavy load. Light load refers to the spring which bears static stress, low stress and small deformation, such as spring for safety device, spring for vibration absorption, etc. The designed service life is 103 ~ 104 times.
The general load refers to the common spring which has a design life of 105 ~ 106 times and is used under the condition of vibration frequency of 300 times / min. The lower the load stress, the longer the life.
Heavy load refers to the spring which works for a long time and vibrates frequently. Such as valve spring, air hammer, press, hydraulic controller spring, its load is high, often less than 10% of the allowable stress, service life is more than 1 × 106 times, usually 107 times.

The principle of spring material selection is: first, meet the functional requirements, then the strength requirements, and finally consider the economy.
Carbon spring steel is widely used in spring steel and its consumption is the largest. The steel contains 0.60% ~ 0.90% carbon and 0.3% ~ 1.20% manganese, so the cost is relatively low. After proper processing or heat treatment, high tensile strength, sufficient toughness and good fatigue life can be obtained. However, the carbon steel wire has low hardenability, poor relaxation resistance and corrosion resistance. The temperature coefficient of elastic modulus is large (up to 300 × 10-6 / ℃). It is suitable for manufacturing springs with small cross-section and low working temperature (120 ℃ >).

Alloy spring steel generally contains 0.45% – 0.70% carbon and a certain amount of Si, Mn, Cr, V, W and B alloy elements. The addition of alloying elements can improve the relaxation resistance and toughness of spring steel, and significantly improve the hardenability and service temperature of the steel. It is suitable for manufacturing springs with larger cross-section and higher temperature. The comparison of common grades of spring steel at home and abroad is shown in Table 1. Table 1 Comparison of common grades of spring steel at home and abroad