Calculation method of leaf spring stiffness

In comparison, “Common Curvature Method” and “Concentrated Load Method” are traditional calculation methods for leaf spring stiffness. In addition, the Chinese scholar Kong Hui proposed a calculation method for some inherent defects in the common curvature method-the main piece analysis method. The scholar Tian Guangyu put forward his own ideas for some inherent shortcomings of the concentrated load method. The starting point of both of them is to regard each leaf spring as a cantilever beam of equal cross-section, without considering the friction between the leaf springs and the large deformation characteristics during the deformation of the leaf spring, the classical beam formula is used to calculate the first leaf The end deflection of, and then the stiffness of the leaf spring.
The common curvature method was proposed by Parsilowski of the former Soviet Union. The basic assumption is that after the leaf spring is loaded, each blade has the same curvature in any section, that is, the entire leaf spring is regarded as a variable section beam. The formula for calculating the stiffness of the symmetrical leaf spring is as follows:

The basic assumption of the concentrated load method is that the leaves of the leaf spring only contact each other at the ends, that is, it is assumed that there is only one contact point at the end between the ith piece and the i-1th piece, the contact force is Pi, and the contact point is The deflection of two adjacent blades is equal. Among them, P1 is the external load on the first piece. Therefore, there are n-1 unknown forces in the system P2, P3,…, Pn, n-1 equations can be obtained by equal deflection at the contact point, and the unknown forces P2, P3,…, Pn, and then obtain the end deflection of the first piece based on the load on the first piece, and then the stiffness of the leaf spring can be obtained.

Based on the above assumptions, the formula for calculating leaf spring stiffness is as follows: an+2=an+1=l1.

The concentrated load method assumes that each leaf of the leaf spring is in contact with each other only at the ends, but in fact the points in the leaf spring may also be in contact with each other. Based on this idea, the improved concentrated load method puts forward the following assumptions: a. There are not only interactions at the endpoints, but also several contact points. As shown in Figure 2, there are Ni contact points between the ith piece and the i-1th piece. Record the distance between these points and the symmetry plane of the leaf spring Is lij,j=1,2,…,Ni; b. The interaction between the i-th slice and the i-1th slice only has a concentrated force at the preset Ni contact points, denoted as Pi1, Pi2, PiNi, as shown in picture 2.

Similar to the concentrated load method, there are total unknown forces in the system. From the equal deflection at the contact points, one equation can be obtained. Solving this equation system can obtain the magnitude of each unknown force. According to the force on the first piece, the end deflection of the first piece can be obtained, and then the stiffness of the leaf spring can be obtained.

Unlike the concentrated load method, the results calculated by this method cannot guarantee that each unknown force is greater than or equal to zero (that is, there can only be pressure between the contact points). For this reason, iterative algorithms are needed to solve this problem.

The formula for calculating the stiffness of the leaf spring is as follows:

The common curvature method assumes that after the leaf spring is loaded, each blade has the same curvature on any cross section. There is an obvious discrepancy in this assumption, that is, there is no concentrated bending moment at the free end of each piece. It is also impossible to have the same curvature as the previous one at the same section. For this reason, the main film analysis method has made the following assumptions. a. Each leaf spring is divided into a constrained part and a non-constrained part. The definitions of the constrained part and the non-constrained part of the i-th leaf spring; Curvature assumption, that is, the curvature of each section is the same as the previous one in this section.

The common point of the above calculation methods is that the leaves of the leaf spring are approximately equivalent to a cantilever beam, and the contact between the leaves is simulated by different methods. In fact, the leaf spring has large deformation characteristics when it is working, and there is a certain deviation in the linear cantilever beam simulation, and the contact simulation method between the leaf springs is also rough. Using the finite element method to calculate the leaf spring stiffness can overcome the above shortcomings and make the calculation more accurate, and the working stiffness of variable section springs, less leaf springs and gradient stiffness leaf springs can be obtained very well, which has practical significance.

Mechanical use and changes in the state of technology

The machine is subjected to various energies in use, and the functions of these energies mainly include: (1) The function of the surrounding medium energy, including the function of the operators, repairers and environmental conditions performing tasks;
(2) Internal energy sources related to the operation of machinery and the work of various institutions, such as various loads, vibrations, temperature, etc.;

(3) Latent energy (internal stress of castings and internal stress of assembly) accumulated in mechanical materials and parts during manufacturing and assembly.

These energies mainly exist in the form of mechanical energy, thermal energy, and chemical energy. When the energy reaches a certain value, it will cause harmful processes to appear, causing changes in the initial performance and state of mechanical parts, such as when matched with a certain power and speed. At this time, a harmful friction process will occur with each other, and the result of friction will cause wear of the mating pair and change the movement of the mating pair. It can be seen that with the development of harmful processes, the parts will be damaged first, which is specifically manifested as wear, deformation, cracks, fatigue, corrosion, etc. The appearance of damage causes changes in the structural parameters of mechanical parts, such as dimensional tolerances and geometric tolerances. , Change of fit clearance, etc.

Changes in structural parameters have led to changes in mechanical function output parameters, such as changes in mechanical output power and speed. With the further expansion of the damage degree, the structural parameters of mechanical parts gradually exceed the allowable value. If the structural parameters of the mechanical parts exceed the allowable value and the function output parameters do not exceed the allowable limit range, it is considered that the machine has a potential failure and the corresponding state is an abnormal state. At this time, it should be eliminated through maintenance; if the structure parameter exceeds the limit , The function output parameter also exceeds the allowable value, it is considered that the machine has a functional failure, and the corresponding state is the failure state. At this time, the corresponding failure should be eliminated through repair. If the machine is used for a long time, the structural parameters of its main parts have reached the limit value, and the system function output parameter is seriously exceeded, and the economic efficiency of use will be significantly reduced. At this time, the machine is in a state of extreme technology and needs to be overhauled or updated.

Characteristic analysis of mechanical failure

Mechanical failures are inseparable from mechanisms such as wear, corrosion, fatigue, and aging. According to the general process of mechanical failure formation, mechanical failures mainly have the following characteristics:

(l) Potentiality. Various damages will occur to the machinery in use, and the damage causes changes in the structural parameters of the parts. When the damage develops to the extent that the structural parameters of the parts exceed the allowable value, the machine will have potential failures. Because there is a certain margin (safety factor) in the mechanical design, even if the structural parameters of some parts exceed the allowable value, the function output parameters of the machine are still within the allowable range, that is, the machine does not have a functional failure. It usually takes a long period of time to develop from potential failure to functional failure, because through lubrication, cleaning, tightening, adjustment and other means, the development of damage can be eliminated or slowed down, so that potential failures can be controlled or even eliminated to a certain extent. The potential of mechanical failures can be reduced through maintenance to reduce the occurrence of functional failures, thereby greatly extending the service life of the machinery.

(2) Gradual onset. Since the occurrence of processes such as wear, corrosion, fatigue, and aging are closely related to time, the occurrence of mechanical failures is mostly related to time. In use, mechanical damage is gradually generated, the structural parameters of parts and components are also slowly changed, and the mechanical performance gg# number also gradually deteriorates. Most of the failures may be tested and monitored by the instrument in advance. The probability of failure is related to the time of machine operation. The longer the machine is used, the greater the probability of failure. The gradual occurrence of failures makes most mechanical failures preventable. Failure diagnosis and condition-based maintenance are based on this foundation.

(3) Wearability. The processes of mechanical wear, corrosion, fatigue, and aging are accompanied by changes in energy and quality, and the process is irreversible. It is manifested as the degree of mechanical aging gradually intensified, and more and more failures. With the increase of use time, although the elimination of local faults can restore the performance of the machine, the failure rate of the machine is still rising, and new faults will continue to appear. At the same time, the elimination of damage is also incomplete, and maintenance cannot restore the performance of the machine to the state before use. The wearability of mechanical failure determines the difference between the level and depth of mechanical maintenance, and the mechanical failure distribution model cannot be simply described by exponential distribution.

(4) Fuzziness. In the use of machinery, due to the influence of various use and environmental conditions, the damage and the change of output parameters have a certain degree of randomness and dispersion. At the same time, due to the influence of factors such as materials and manufacturing, various limit values, The initial value also has a different distribution. The output parameters of the same machine under different use environments also have different distributions over time, which leads to a certain degree of dispersion in parameter changes and failure judgment standards, which makes the occurrence and judgment of mechanical failures The standards have a certain degree of ambiguity. The ambiguity of mechanical faults adds a certain degree of difficulty to the diagnosis and discrimination of mechanical faults, and it also requires that the research of mechanical faults must be combined with macroscopic and microscopic.

(5) Diversity. In mechanical use, due to the simultaneous effects of wear, corrosion, fatigue, and aging, the same component often has multiple failure mechanisms, resulting in multiple failure modes, such as shaft bending, wear, and fatigue fracture. These faults are not only different in fault mechanism and manifestation, but also in different distribution models and different levels of influence at all levels, which makes the faults show diversity. The diversity of mechanical failures requires separate studies of failures according to different mechanisms and modes.

Steel telescopic guide rail guard

The steel telescopic guide rail guard is the traditional form of protection for machine tools. It plays an effective protective role in preventing chips and other sharp objects from entering. Certain structural measures and suitable scrapers can also effectively reduce the penetration of coolant.
Its characteristics are summarized as: anti-cold, anti-heat, anti-corrosion, wear-resistant, smooth operation and no noise.

The number of sections of the steel telescopic guide rail guard is important to its ratio, weight and operating characteristics. Each single section should be as long as possible, so that the number of sections can be reduced and the cost can be reduced. In general, the maximum stretch The minimum compression ratio should be between 3:1 and 5:1. Compared with other materials of machine tool guide rail guards, steel machine tool guards have the following advantages and disadvantages. Advantages of steel machine tool guide guards: high mechanical strength, High tensile strength. Extreme high temperature resistance. When tools or workpieces fall, because there is a protective cover to protect the guide rail, avoiding the possibility of smashing the machine tool guide rail. Disadvantages of the steel machine tool guide rail protection cover: the extension and compression ratio is small, and the cost is relatively small , The steel machine tool protective cover produced is widely used in heavy-duty machine tools such as CNC boring and milling machines, modular machine tools, machining centers, and gantry milling machines.

The steel telescopic guide rail protective cover is equipped with polyurethane or brass sliding block under the running speed of 10m/min. A roller is installed under a medium speed of 30m/min. In addition, a buffer system is required between the drive plate, scraper plate and scraper. The purpose of the slider buffer system is to reduce collisions, noise and friction.

Pneumatic manipulator components and their operating principles

Our common manipulator is a mechanical equipment that is commonly used in industrial production for horizontal/vertical displacement. Its action is driven by an air cylinder, which is controlled by a corresponding solenoid valve. The following describes the components and movement of the pneumatic manipulator.
The pneumatic manipulator is mainly composed of three parts: the frame, the mechanical arm and the air claw that play a fixed support role. The movement that drives the first shoulder joint is composed of 2 pneumatic muscles, the frame arm is composed of 4 pneumatic muscles, the upper arm is equipped with 4 pneumatic muscles, and the forearm is equipped with 4 pneumatic muscles.

Classification of manipulators:

1. According to the driving mode, it can be divided into hydraulic, pneumatic, electric and mechanical manipulators;

2. According to the scope of application, it can be divided into two types: special manipulator and general manipulator;

3. According to the motion trajectory control mode, it can be divided into point position control and continuous trajectory control manipulator.

Pneumatic manipulators can realize 4 degrees of freedom movement, and the driving of their respective degrees of freedom is all realized by pneumatic muscles. The air claws at the front end grab the objects and realize the rotation of their respective joints through the drive of pneumatic muscles, so that the objects can move in space. According to reasonable control, the motion requirements of the manipulator are finally realized.

The concept of various pressures of safety valves and the regulation of opening pressure

The nominal pressure of the safety valve represents the maximum allowable pressure of the safety valve at room temperature. The safety valve used in high temperature equipment should not consider the reduction of the allowable stress of the material at high temperature. The safety valve is designed and manufactured according to the nominal pressure standard.
Cracking pressure: also called set pressure, it is the medium pressure when the safety valve disc starts to rise under operating conditions.

Discharge pressure: the pressure on the inlet side when the disc reaches the specified opening height.

Re-seat pressure: After the safety valve is discharged, the disc re-presses the valve seat and the inlet pressure when the medium stops discharging. The return pressure is an important parameter that characterizes the quality of the safety valve. Generally, it is required to be at least 80% of the working pressure, and the upper limit is not to produce frequent flapping.

Opening and closing pressure difference: the difference between opening pressure and return pressure.

Regulations on the opening pressure of safety valves

The opening pressure of the safety valve of the boiler drum and superheater is specified as follows:

(1) When the rated steam pressure is less than 1.27MPa, the opening pressure is working pressure +0.02MPa and working pressure +0.04MPa;

(2) When the rated steam pressure is greater than 1.27MPa but less than 3.82MPa, the opening pressure is 1.04 times the working pressure and 1.06 times the working pressure respectively;

(3) When the rated steam pressure is greater than 3.82MPa, the opening pressure is 1.05 times the working pressure and 1.08 times the working pressure respectively.

The opening pressure of the economizer safety valve is 1.5 times the working pressure of the economizer. The opening pressure of the pressure vessel safety valve shall not exceed the design pressure of the pressure vessel.

Selection of crushing machinery

When users choose crushing machinery, they are often confused and do not know how to choose many crushing machinery. This article introduces the classification method of crushing machinery and common types of crushing machinery: one of the selection of crushing machinery
1. Classification and scope of application of crushing machinery

(1) The method of material crushing

Although there are many types of crushing machinery, according to the different methods of applying force, there are methods for crushing materials such as extrusion, bending, impact, shearing and grinding. In the crushing machine, the force application is very complicated, and several types of force are often present at the same time. Of course, there are one or two main forces in a crushing machine.

Because the shape of the material particles is irregular and the physical properties of the materials are different, the crushing methods used are also different. There are several methods for using mechanical force to crush the materials according to the external force applied.

1. crushed

Place the material between two working surfaces. After applying pressure, the material will be broken due to the compressive stress reaching its compressive strength. This method is generally suitable for crushing large pieces of material.

2. Chopping

Put the material between a plane and a working plane with sharp edges. When the working plane with sharp edges squeezes the material, the material will split along the direction of the pressure action line. The reason for splitting is that the tensile stress on the splitting plane reaches or exceeds the tensile strength limit of the material. The tensile strength limit of the material is much smaller than the compressive strength limit.

3. Broken

The material is broken by bending stress. The simply-supported beam or multi-support beam with two fulcrums under the concentrated load of the crushed material is broken and broken when the bending stress of the material reaches the bending strength of the material.

4. Impact crushing

The material is broken by the impact force. Its crushing force acts instantaneously. Its crushing efficiency is high, the crushing ratio is large, and the energy consumption is small. Impact crushing has the following situations:

(1) The impact of the moving work body on the material;

(2) High-speed moving materials impact on a fixed working surface;

(3) Tell the moving materials to impact each other;

(4) The high-speed moving body impacts the suspended materials.

5. Grind (grind)

After a certain pressure and shear force are applied between the material and the moving working surface, when the shear stress reaches the shear strength limit of the material, the material will be smashed; or the shearing and grinding effect of the friction between the materials And crush the material.

(2) Classification of crushing machinery

1. Types of crushing machinery

According to the different structure and working principle, the commonly used crushing machinery has the following types.

(1) The jaw crusher (jaw crusher) relies on the periodic reciprocating movement of the movable jaw to crush the material entering between the two jaws.

(2) Hammer crusher (hammer crushing) The material is crushed by the impact of the high-speed rotating hammer and the material itself impacts the fixed liner at high speed.

(3) The cone crusher (cone crusher) relies on the eccentric rotation of the inner cone to crush and crush the material between the two cones.

(4) Impact crusher (reaction crusher) The material is hit by the high-speed moving hammer, causing the material to hit the impact board at high speed, and the materials collide with each other to be crushed.

(5) Roller crusher (roller crushing) The material falls between two parallel and oppositely rotating rollers (rotating toward each other). The material is pulled into between the rollers under the action of the friction on the surface of the rollers and is subjected to the rollers. Squeezed and broken.

Another point worth noting is that the crushing ratio and unit power consumption (energy consumption per unit mass of crushed products) are the basic technical and economic indicators of crushing machinery. The unit power consumption is used to distinguish whether the power consumption of the crushing machine is economical, and the crushing ratio is used to describe the characteristics of the crushing process and identify the crushing quality. Even if the unit power consumption of two crushers is the same, but the crushing ratios are different, the two crushing machines The economic effect is still different. Generally speaking, machinery with a large crushing ratio has a higher working efficiency. Therefore, to identify the working efficiency of the crushing machine, the unit power consumption and the size of the crushing ratio should be considered at the same time.

Application of Hardware Spring in Agricultural Machinery

In the maintenance of agricultural machinery, some parts are not restricted by the structure, and they will be installed backwards or incorrectly when assembling with a little carelessness. This will leave potential troubles for the agricultural machinery. Therefore, attention must be paid to the assembly.
Cylinder head gasket: If there is an oil hole, it must be aligned with the corresponding oil passage hole on the body and cylinder head to avoid dry friction of the air distribution mechanism on the cylinder head due to oil cut. There is no oil passage hole and the front and back shapes are the same, which is determined by the material of the cylinder head: for aluminum alloy cylinder heads, the curled side of the cylinder head should face the cylinder block; for cast iron cylinder heads, the curled side of the cylinder head should face the cylinder head .

Pistons and piston rings: Pistons with upward arrow marks on the top should be installed in the direction specified by the marks; if there is no mark, the vortex pit or the small notch beside the pit on the piston top should be facing the injector side to ensure The mixture is evenly mixed. When assembling the piston ring, the top with “up”, “UP” and other marks should face up; for twisted rings with no marks on the top, the inner groove or chamfer should face down; the chrome-plated ring (shiny shell) should be installed In the first piston ring groove. Each ring opening should be staggered by 120 to 180 degrees to ensure its sealing and oil distribution effect.

Connecting rod and connecting rod cover: The large end of the connecting rod of the horizontal diesel engine is divided by 45 degrees, and the section should be downward to improve the force of the connecting rod bolt. The connecting rod cover and the connecting rod are processed in pairs. The matching marks should be on the same side during assembly to ensure that the roundness and cylindricity of the connecting rod bearing meet the specified requirements.

Main bearing cap, bearing bush or bushing: The main bearing cap and the housing of the machine body are all processed by matching boring. They should be seated according to the matching mark. Do not interchange or change the assembly direction at will, so as not to damage the coaxiality and size of the main bearing seat hole Accuracy. Bearing bushes or bushings with oil holes should be aligned with the corresponding oil passage holes on the bearing seat and bushing holes to ensure a smooth lubricating oil path.

Cylinder head bolt: If one end of the bolt is coarse thread and the other end is fine thread, then the coarse thread end should be screwed into the body; if both ends of the bolt are fine threads, the shorter end should be screwed into the body , To ensure that the cylinder head can be pressed tightly.

Oil pump and fuel injection pump: The oil adopts planetary rotor type. The outer rotor should be chamfered toward the pump body to prevent the oil from circulating in the pump and lowering the pump oil pressure. The crescent-shaped positioning groove on the injector shaft plug sleeve should be aligned with the positioning hole on the pump body, and the mark on the plunger (or oil return groove) should be installed upwards to avoid no fuel supply or diesel engine runaway.

Foamed plastic filter element: The air filter using foamed plastic filter element should be installed in the same direction as the winding direction of the filter and the flow direction of the intake air to reduce the pressure of the intake air.

Clutch friction plates, disc springs, brake shoes, bearings: If the lengths of the two hubs of the clutch friction plates are inconsistent, the two long hubs should be installed opposite to each other (the short hubs are opposite), otherwise the clutch will not be engaged; the friction plate is riveted For the oil slinger, the oil slinger should be directed toward the flywheel to avoid oil pollution. For double-acting clutches that use disc springs as the compression element, the small ends of the two disc springs should be opposed to ensure reliable compression of the friction plates. For unbalanced wheel brakes, the brake shoe with the longer friction lining should be the front brake shoe, otherwise it will cause uneven wear of the brake shoe and reduce the braking effect. The 60204 (outside) and 60206 (inside) semi-enclosed bearings are used for support. The closed surfaces with rubber rings should be opposite to each other, and other bearings should not be substituted, otherwise it will cause oil and water in the clutch cavity.

Drive shaft and drive chain: The drive forks at both ends of the drive shaft should be in the same plane to avoid torsional vibration and damage to the drive components. If the drive chain adopts hardware spring clips, the direction of the opening end should be opposite to the direction of chain movement to avoid collision and fall off during movement.

Driving wheel: If the driving wheel is marked with an upward arrow, it should point to the direction of rotation of the tire when moving forward; if there is no mark, the driving wheel should be pointed upward when viewed from the back of the locomotive.

Introduction of 304 stainless steel composite plate

Stainless steel composite plate material is a new type of material, which combines the performance advantages of stainless steel and carbon steel, and is a new generation of environmentally friendly products that save energy and reduce emissions. Although it does not have a market share as large as 304 stainless steel, it complies with the general trend of energy saving and high efficiency, and the emerging potential cannot be underestimated.
Product brand:

Common base materials: Q235, 20g, 16MnR, etc.

Commonly used composite materials: 0Cr13, 0Cr17, 0Cr18Ni9, 1Cr18Ni9Ti, 00Cr17Ni14Mo2, etc.

Specifications:

Thickness:> 3mm, where the multilayer thickness is 0.5mm -3mm, and the base layer thickness is> 3.5mm

Width: 1500mm -2600mm

Length: <12000mm

Executive standard: GB/T 8165-1997<Stainless steel clad steel plate and steel belt>

Product advantages:

Low production cost: because the proportion of stainless steel is small, material costs are reduced and precious metals are saved.

Good performance: It has multiple advantages of stainless steel, non-ferrous metals and carbon steel.

There are many types of steel involved: different combinations can be selected according to user requirements.

High interface bonding strength: bonding between two metal sawtooth atoms to ensure performance.

It is true that 304 austenitic steel, as a widely used steel, has good corrosion resistance and heat resistance. 304 composite plate also covers the grain boundary corrosion resistance of ferrite, austenite, and duplex stainless steel. Resistance to stress corrosion and pitting corrosion.

304 austenitic stainless steel is mainly used in household products, auto parts, medical equipment, building materials, etc. And 304 composite board can also be widely used in petroleum, chemical industry, city construction and so on. It can be used in pressure vessels, pipelines, reaction tower engineering equipment under various corrosive conditions. Among them, pressure vessels mainly focus on the first and second types of the three types of pressure vessels.

Especially in some special industries, 304 composite board has very important irreplaceability. How can such a new material with excellent performance not let people pay more attention?

Research and development of plastic spring

Because plastic springs have the advantage that steel springs are difficult to replace, the United States, Britain, Japan and other countries are racing to develop and have achieved many research results, and some have been put into practical applications. Its development has generally gone through three stages.
Before 1970, it was the exploration stage of principle experiments. At this stage, there are more published applied theory analysis articles and phased research reports. During this period, because the thermosetting plastics suitable for engineering applications are still in the early stage of development, the development of engineering plastic springs encountered many problems, such as poor temperature resistance, low hardness and wear resistance, high prices, and difficulty in making a wide range of Coil springs, coupled with design procedures, processing equipment, and process parameters have encountered some new problems to be solved, thus delaying the progress of plastic springs to practical applications.

Before 1980, it was the stage of practical development. At this stage, due to the development of the plastics industry, fiber-reinforced plastics (FRP=Fiberglass Rein-forced Plastics) that are temperature-resistant, wear-resistant and reasonably priced have been successfully developed, coupled with the development of automobile design in the direction of miniaturization and light weight, especially for petroleum Since the crisis, in order to reduce the weight of auto parts and save fuel, auto manufacturers have actively developed plastic leaf springs, which has promoted the development of plastic springs to practical applications. The outstanding development result at this stage is the practical application of FRP leaf springs in the United States.

Measures to improve spring quality

(1) Thermomechanical heat treatment–combining steel deformation strengthening and heat treatment strengthening to further improve the strength and toughness of steel. Thermomechanical heat treatment is divided into high, medium and low temperature. High temperature thermomechanical heat treatment is quenched immediately after deformation occurs in a stable austenite state, and can also be combined with forging or hot rolling, that is, quenched immediately after hot forming. Thermomechanical treatment has been used in the production of automobile leaf springs. (60Si2Mn)
(2) Austempering of springs-Austempering can be used for springs with small diameters or sufficient permeability. It can not only reduce deformation, but also improve strength and toughness. It is best to perform tempering again after austempering. The elastic limit can be increased, and the tempering temperature is the same as the austempering temperature.

(3) Spring relaxation treatment-the spring works under the action of external force for a long time, and the result of stress relaxation will produce a small amount of permanent (plastic) deformation, especially the spring that works at high temperature, the stress relaxation phenomenon is more serious at high temperature. Reduce the accuracy of the spring, which is not allowed for general precision springs. Therefore, this kind of spring should be relaxed after quenching and tempering-pre-load the spring so that its deformation exceeds the deformation that may occur when the spring is working. Then heat it at 20C higher than the working temperature for 8-24h.

(4) Low-temperature carbonitriding-the process of combining tempering and low-temperature carbonitriding (soft nitriding) can significantly improve the fatigue life and corrosion resistance of the spring. This process is mostly used for coil springs.

(5) Shot peening-surface defects such as scratches, folds, oxidative decarburization, etc. tend to become stress concentration places and sources of fatigue fracture during spring operation. If a small steel shot is used to spray the surface of the spring at high speed, it will not only improve the surface quality of the spring, increase the surface strength, and put the surface in a state of compressive stress, thereby increasing the fatigue strength and service life of the spring.

Operation precautions

(1) Check the surface for defects such as decarburization and cracks before heat treatment. These surface defects will seriously reduce the fatigue limit of the spring.

(2) The quenching heating should pay special attention to prevent overheating and decarburization, do a good job in salt bath deoxidation, control the furnace gas atmosphere, and strictly control the heating temperature and time

(3) In order to reduce the deformation, the method of loading the spring during heating, the form of fixture and the method of quenching during cooling.

(4) Tempering as soon as possible after quenching, and heating as much as possible. Quick cooling after tempering can prevent temper brittleness and cause surface compressive stress, and improve fatigue strength.

quality inspection

Before heat treatment–

(1) The rolled surface of steel is often the surface after the spring is made, so there should be no cracks, folds, scars, hair lines, bubbles, interlayers, and pressed oxide scales.

(2) Surface decarburization will significantly reduce the fatigue strength of the spring. The depth of the decarburized layer should be inspected as required.

After heat treatment–

(1) There should be no cracks, corrosive pitting and severe quenching deformation when observing the spring watch with the naked eye or low-power magnifying glass.

(2) The hardness and its uniformity meet the requirements. In mass production, it is allowed to use a file to sample the hardness, but it must be noted that the position of the file mark should not affect the final accuracy of the spring.

(3) The metallographic structure should be troostite or a mixed organization of troostite and sorbite.

(4) After the leaf spring is assembled, the permanent deformation and static deflection test under working load are usually carried out.