Graduation design

Generally, there are gear teeth, tooth grooves, end faces, normal faces, tooth top circles, tooth root circles, base circles and indexing circles.

Tooth of cogwheel

Referred to as tooth, it is every protruding part on the gear, which is used for meshing. These convex parts are generally arranged radially, and the teeth on the paired gears are in contact with each other, so that the gears can run continuously during meshing.

pulmonary alveolus

Is the distance between two adjacent teeth on the gear; The end face is a plane on the cylindrical gear or worm, perpendicular to the axis of the gear or worm.

Normal plane

Refers to the plane perpendicular to the tooth line of gear teeth.

addendum circle

Refers to the circle where the tooth tip is located.

dedendum circle

Refers to the circle where the groove bottom is located.

base circle

The generatrix of involute is a circle with pure rolling.

Pitch circle

Is the reference circle for calculating the geometric dimensions of gears in the end face.

Edit this paragraph classification

Gears can be classified according to tooth profile, gear shape, tooth line shape, surface where gear teeth are located and manufacturing method. The tooth profile of gear includes tooth profile curve, pressure angle, tooth height and displacement. Involute gears are relatively easy to manufacture, so among the gears used in modern times, involute gears account for an absolute majority, while cycloidal gears and circular arc gears are less used. In terms of pressure angle, the bearing capacity of small pressure angle gear is small; The gear with large pressure angle has high bearing capacity, but it increases the bearing load under the same transmission torque, so it is only used in special circumstances. The tooth height of gears has been standardized, and the standard tooth height is generally adopted. Modified gears have many advantages and have been used in various mechanical equipment. In addition, gears can be divided into cylindrical gears, bevel gears, non-circular gears, racks and worm gears according to their shapes; According to the shape of tooth line, it is divided into spur gear, helical gear, herringbone gear and curved gear; According to the surface of gear teeth, it is divided into external gear and internal gear; According to the manufacturing method, it can be divided into casting gear, cutting gear, rolling gear and sintering gear. The manufacturing materials and heat treatment process of gears have great influence on the bearing capacity, size and weight of gears. Carbon steel was used for gears before 1950s, alloy steel was used in 1960s, and surface hardened steel was used in 1970s. According to hardness, tooth surface can be divided into soft tooth surface and hard tooth surface. The gear with soft tooth surface has lower bearing capacity, but it is easy to manufacture and has good running-in. It is mostly used in general machinery with no strict restrictions on the size and weight of transmission, and in small batch production. Because the small wheel bears a heavy burden in the paired gears, the tooth surface hardness of the small wheel is generally higher than that of the big wheel in order to make the working life of the big and small gears roughly equal. Hard tooth surface gear has high bearing capacity. After the gear is finely cut, it is quenched, surface quenched or carburized to improve the hardness. However, in the process of heat treatment, the gear will inevitably deform, so it is necessary to grind, grind or finish cut after heat treatment to eliminate the error caused by deformation and improve the accuracy of the gear.

Edit this material

The steels commonly used in manufacturing gears are quenched and tempered steel, hardened steel, carburized and hardened steel and nitrided steel. The strength of cast steel is slightly lower than that of forged steel, and it is often used for larger gears. Gray cast iron has poor mechanical properties and can be used for light load open gear transmission. Ductile iron can partially replace steel to make gears; Plastic gears are mostly used in places with light load and low noise requirements, and the matching gears are generally steel gears with good thermal conductivity. In the future, gears are developing in the direction of heavy load, high speed, high precision and high efficiency, striving for small size, light weight, long service life, economy and reliability. The development of gear theory and manufacturing technology will further study the mechanism of gear tooth damage, which is the basis for establishing a reliable strength calculation method and the theoretical basis for improving gear bearing capacity and prolonging gear life. Develop a new tooth profile represented by circular arc tooth profile; Research on new gear materials and new gear manufacturing technology: The elastic deformation, manufacturing and installation errors and temperature field distribution of gears are studied, and the gear teeth are modified to improve the stability of gear operation and increase the contact area of gear teeth when fully loaded, thus improving the bearing capacity of gears. Friction, lubrication theory and lubrication technology are the basic work of gear research. Studying the theory of elastohydrodynamic lubrication, popularizing the use of synthetic lubricating oil and adding extreme pressure additives to the oil can not only improve the bearing capacity of the tooth surface, but also improve the transmission efficiency.

In this section, the development of China gear industry is edited.

During the Tenth Five-Year Plan period, China's gear industry developed rapidly: in 2005, the annual output value of the gear industry increased from 24 billion yuan in 2000 to 68.3 billion yuan, with a compound annual growth rate of 23.27%, making it the largest industry in China. In terms of market demand and production scale, China's gear industry ranks fourth in the world, surpassing Italy. In 2006, all the gear, transmission and transmission parts manufacturers in China realized the total industrial output value of 102628 183000 yuan, a year-on-year increase of 24. 15%. Accumulated product sales revenue was 982,382,400 yuan, a year-on-year increase of 24.37%; The accumulated profit was 5,665,265,438+0,000 yuan, up by 26.85% year-on-year. From June 5438 to February 65438, 2007, all the gear, transmission and driving parts manufacturers in China achieved a total industrial output value of 13654284 1000 yuan, a year-on-year increase of 30.96%. From June 5,438+0 to June 5,438+0, 2008, all the gear, transmission and driving parts manufacturing enterprises in China achieved a total industrial output value of144,529138,000 yuan, a year-on-year increase of 32.92%. Compared with developed countries, there are still some problems in China's gear manufacturing industry, such as insufficient independent innovation ability, slow development of new products, disorderly market competition, weak enterprise management, low degree of informatization, and the comprehensive quality of employees to be improved. At present, the gear industry should improve its concentration through market competition and integration, and form a group of large, medium and small enterprises with assets of several billion yuan, 500 million yuan and 65.438+0 billion yuan; Through the design and development of independent intellectual property products, a number of leading enterprises in vehicle transmission system (gearbox and drive axle assembly) will be formed, and the capabilities and resources of the gear industry will be integrated with the supporting capabilities of leading enterprises; Realize specialization and networking, and form a large number of famous brand enterprises with distinctive technology, products and quick response; Through technical transformation, the transformation of modern gear manufacturing enterprises is realized. By the end of the 11th Five-Year Plan, the annual sales of China gear manufacturing industry will reach 654.38+03 billion yuan, and the per capita sales will rise to 650,000 yuan/year, ranking second in the world. In 2006-20 10, 654.38 million sets of new equipment were added, that is, the investment in new equipment was about 6 billion yuan, and 20,000 new machine tools were purchased, with an average unit price of 300,000 yuan. By 20 10, the number of various machine tools in China gear manufacturing industry should reach about 400,000, including 65,438+10,000, with a numerical control rate of 25% (higher than the industry average 17%).

Edit this paragraph type

drive ratio

Fixed transmission ratio-circular gear mechanism (cylinder, cone) variable transmission ratio-non-circular gear mechanism (elliptical gear)

Relative position of axle

Plane gear mechanism spur gear drive external gear drive internal gear drive rack drive helical gear drive space gear mechanism bevel gear drive staggered shaft helical gear drive worm gear drive.

craftsmanship

Bevel gear blank semi-finished gear spiral gear internal gear spur gear worm gear

Edit the main parameters of helical cylindrical gear in this section.

angle of helix

β& gt； 0 is left-handed and vice versa.

teeth space

Pn = ptcosβ, and subscripts n and t represent the normal plane and the end face respectively.

package

mn = mtcosβ

Standard middle diameter

d = mtz

center distance

a= 1/2*m(z 1+z2)

Correct meshing conditions

m 1 = m2，α 1 = α2，β 1 =？ β2

Edit this part of the diagnosis.

The purpose of simple diagnosis is to quickly judge whether the gear is in normal working condition, and further diagnose and analyze the gear in abnormal working condition or take other measures. Of course, in many cases, according to the simple analysis of vibration, some obvious faults can also be diagnosed. Simple diagnosis of gears includes noise diagnosis, vibration level diagnosis and shock pulse (SPM) diagnosis, among which vibration level diagnosis is the most commonly used. Vibration leveling diagnosis method is a diagnostic method to judge whether the gear is in normal working condition by using the vibration intensity of the gear. According to the different judgment indexes and standards, it can be divided into absolute value judgment method and relative value judgment method.

Absolute value judgment method

Absolute value judgment method is to directly evaluate the running state with the amplitude value measured at the same measuring point on the gearbox as the index. In order to identify the gear state by absolute value judgment method, corresponding judgment standards must be formulated according to different gearboxes and different use requirements. The main basis for determining the absolute value of gear is: 1) theoretical study of abnormal vibration phenomenon; (2) Vibration phenomenon analysis based on experiments; (3) Statistical evaluation of measurement data; (4) Refer to relevant standards at home and abroad. In fact, there is no absolute value criterion that can be applied to all gears. When the size and type of gears are different, the judgment criteria will naturally be different. When judging broadband vibration according to measured parameters, the standard value must change according to frequency. When the frequency is below 1kHz, the vibration is judged by the speed; If the frequency is above 1kHz, the vibration can be judged by the acceleration. The actual standard depends on the specific situation.

Phase value judgment method

In practical application, for gears whose absolute value judgment standard has not been worked out, we can make full use of the data measured in the field to make statistical average and formulate appropriate relative judgment standard, which is called relative value judgment method. The relative judgment standard requires that the amplitude measured in the same part of the gearbox at different times be compared with the amplitude in the normal state, and when the measured value is compared with the normal value to a certain extent, it is judged as a certain state. For example, the relative value judgment standard stipulates that when the actual value reaches 1.6~2 times of the normal value, attention should be paid, and when it reaches 2.56~4 times, it means danger. Whether it is classified by 1.6 times or by 2 times depends on the use requirements of the gearbox. Roughing equipment (such as mining machinery) usually uses higher multiple classification. In practice, in order to achieve the best results, the above two methods can be used for comparison and comprehensive evaluation.

Edit the terms in this paragraph.

Tooth-each convex part on a gear for meshing. Generally speaking, these convex parts are arranged radially. The teeth on the paired gears contact each other, which causes the gears to mesh continuously. Cogging-the space between two adjacent teeth on a gear. gear

End face-the plane perpendicular to the cylindrical gear or worm shaft. Normal plane-On a gear, the normal plane refers to the plane perpendicular to the tooth line of the gear. Tooth tip circle-the circle where the tooth tip is located. Tooth root circle-the circle where the groove bottom is located. Base circle-the circle on which the generatrix forming involute performs pure rolling. Dividing circle-the reference circle for calculating the geometric dimensions of the face gear. For spur gears, the modulus and pressure angle on the indexing circle are standard values. Tooth flank-the flank of a gear tooth between the cylindrical surface of the tooth top and the cylindrical surface of the tooth root. Tooth Profile-Tooth surface profile cut by a specific curved surface (the plane of cylindrical gear). Tooth line-the intersection line between the tooth surface and the indexing cylindrical surface. End tooth pitch pt- the length of indexing arc between two adjacent end tooth profiles on the same side. Modulus m- quotient obtained by dividing the pitch by π, in millimeters. Diameter pitch p- reciprocal of modulus, in inches. Tooth thickness s- the length of indexing arc between tooth profiles on both sides of gear teeth on the end face. Groove width e- the length of the indexing arc between the tooth profiles on both sides of the end tooth groove. Height of the tooth tip hι- the radial distance between the tooth tip circle and the indexing circle. Tooth root height HF- radial distance between indexing circle and tooth root circle. Full tooth height h—— the radial distance between the tooth top circle and the tooth root circle. Tooth width b—— the dimension of gear teeth along the axial direction. End pressure angle ι t-the acute angle between the radial line passing through the intersection of the end tooth profile and the dividing circle and the tangent line of the tooth profile passing through this point. Standard rack: a rack whose base circle size, tooth profile, full tooth height, tooth crown height and tooth thickness meet the standard spur gear specifications. Racks cut according to standard gear specifications are called reference racks. Standard pitch circle: the reference circle used to determine the size of each part of the gear. It is the number of teeth x standard pitch line: the specific pitch line on the rack or the tooth thickness measured along it. Half of the court. Action pitch circle: When a pair of spur gears mesh, each has a tangent line as a rolling circle. Standard pitch: If the selected standard pitch is used as a benchmark, it is equal to the pitch of the reference rack. Pitch circle: The track left on the meshing contact point of two gears is called pitch circle. Pitch circle diameter: pitch circle diameter. Working depth: the sum of the crown heights of a pair of spur gears. Also called working tooth height and crown height. : The radius difference between the tooth top circle and the pitch circle. Backlash: The gap between tooth surfaces when two teeth bite. Clearance: the clearance between the tooth top circle of one gear and the tooth bottom of the other gear when two teeth bite. Node: the point where a pair of gears bite and the pitch circle is tangent. Pitch: the arc distance of the corresponding point between two adjacent teeth. Standard spacing

Edit this plastic gear

With the development of science, gears have gradually changed from metal gears to plastic gears. Because plastic gears are more lubricated and wear-resistant. It can reduce noise, cost and friction. Commonly used plastic gear materials are: PVC, POM, PTFE, PA, nylon, PEEK, etc.

Edit the production enterprises in this paragraph.

The gear industry is mainly composed of three types of enterprises: vehicle gear transmission manufacturing enterprises, industrial gear transmission manufacturing enterprises and gear special equipment manufacturing enterprises. Among them, the vehicle gear stands out, and its market share reaches 60%; Industrial gear is composed of general gear, special gear and special gear, and its market share is 18%, 12% and 8% respectively. Gear equipment only accounts for 2% of the market. Main production enterprises: Hangzhou Qianjin Gear Box Group Co., Ltd., Chongqing Gear Box Co., Ltd., Zhejiang Hengjiu Machinery Group Co., Ltd., etc. The gear industry is mainly composed of three types of enterprises: vehicle gear transmission manufacturing enterprises, industrial gear transmission manufacturing enterprises and gear special equipment manufacturing enterprises. Among them, the vehicle gear stands out, and its market share reaches 60%; Industrial gear is composed of general gear, special gear and special gear, and its market share is 18%, 12% and 8% respectively. Gear equipment only accounts for 2% of the market. Examples of major manufacturers: Hangzhou Qianjin Gear Box Group Co., Ltd. Chongqing Gear Box Co., Ltd. Zhejiang Hengjiu Machinery Group Co., Ltd. Jiangsu Spacecraft Co., Ltd. Yashi Crawler (Tianjin) Co., Ltd. Nanjing High Speed Gear Manufacturing Co., Ltd. Zhengmao Group Co., Ltd. Sichuan Gear Factory Hangzhou Donghua Chain Group Co., Ltd.

Edit this picture

Spur gear (for CNC gantry milling machine)

Spiral bevel gear (used as the accessory milling head of CNC gantry milling machine)

Helical gear (for general milling machine)

Gear shaft (suitable for CNC vertical lathe)

Various molded gears (10 pieces)

Edit the gear profile of the heavy truck in this section.

There are many grades of gear steel for medium and heavy trucks in China, mainly to meet the requirements of introducing foreign advanced automobile technology at that time. In the 1950s, China introduced the production technology of Soviet medium-sized trucks (namely "Jiefang" brand original models) from the former Soviet Union's Rihachev Automobile Factory, and also introduced 20CrMnTi steel for automobile gears produced by the former Soviet Union. After the reform and opening up, with the rapid development of China's economic construction, in order to meet the needs of the rapid development of China's transportation industry, since the 1980s, China has introduced various advanced models from industrialized countries in a planned way, and various advanced medium and heavy trucks from abroad have also been introduced one after another. At the same time, China's big automobile factory cooperates with famous foreign automobile companies to introduce advanced foreign automobile production technology, including automobile gear production technology. At the same time, the technical level of iron and steel smelting in China is constantly improving. By adopting advanced refining technologies such as ladle secondary smelting, fine-tuning composition and continuous casting and rolling, steel mills can produce gear steel with high purity and narrow hardenability, thus realizing the localization of imported automobile gear steel and raising the production level of gear steel in China to a new level. In recent years, the domestic high hardenability steel for heavy-duty automobile gears containing nickel, which is suitable for China's national conditions, has also been developed and applied, and achieved good results. The heat treatment technology of automobile gear has also developed from well-type gas carburizing protection in 1950s and 1960s to computer-controlled continuous gas carburizing automatic line, box-type multi-purpose furnace and automatic production line (including low-pressure (vacuum) carburizing technology), gear carburizing pre-oxidation treatment technology, gear quenching controlled cooling technology (due to the use of special quenching oil and quenching cooling technology) and gear forging blank isothermal normalizing technology. The adoption of these technologies not only effectively controls the carburizing and quenching deformation of gears, improves the machining accuracy and service life of gears, but also meets the needs of mass production of modern gears by heat treatment. Relevant literature points out that the life of automobile gears is mainly evaluated by two indexes, one is the contact fatigue strength of gears, and the other is the bending fatigue strength of gears. The former is mainly determined by carburizing and quenching quality, while the latter is mainly determined by gear material. Therefore, it is necessary to fully understand the requirements, properties and heat treatment characteristics of carburized steel for automobile gears.

Chromium-manganese-titanium steel and boron steel

20CrMnTi is the most widely used steel for truck gears in China for a long time. This is a medium-sized automobile gear 18XTr steel (that is, 20CrMnTi steel) imported from the former Soviet Union in 1950s. The steel has fine grains, small grain growth tendency during carburizing, good carburizing and quenching performance, and can be directly quenched after carburizing. It is pointed out in the literature that before 1980, carburized alloy structural steel (including 20CrbinTi steel) in China only guaranteed the chemical composition and mechanical properties of the samples when leaving the factory. However, in automobile production, steel products with qualified chemical composition and mechanical properties often appear, and the excessive fluctuation range of hardenability affects the product quality. For example, the hardenability of 20CrMnTi carburized steel is too low, the hardness of gear center after carburizing and quenching is lower than the specified value of technical conditions, and the fatigue life of gear is reduced by half during fatigue test; The hardenability is too high, and the inner hole of the gear shrinks too much after carburizing and quenching, which affects the gear assembly. Because the hardenability of steel has a great influence on the hardness and distortion of the gear tooth center, in 1985, the Ministry of Metallurgy promulgated the Technical Specifications for Hardenable Structural Steel in China (GB52 16-85), which includes the chemical composition and hardenability of 10 carburized steels such as 20CxMnTiH and 20MnVBH. According to the standard, the hardenability index of 20CrMnTi steel used for gear manufacturing is 30-42HRC at 9 from the water cooling end. After that, the problems of low hardness and excessive tooth center distortion of gears produced by 20CrMnTi steel were basically solved. However, it is obviously unreasonable to use 20CrMnTi steel with the same steel grade regardless of the gear module and steel section thickness. In recent years, due to the improvement of iron and steel smelting technology and the supply of alloy structural steel, the hardenability band of gear steel can be further reduced, and new steel grades can be developed according to the requirements of different products (such as transmission gears and rear axle gears) to meet their requirements. Through negotiation with steel mills, Changchun FAW successively signed agreements with gear mill manufacturers to supply the hardenability of 20CrMnTi steel in stages. For example, the hardenability groups of 20CrMnTiH steel used for manufacturing the first shaft and intermediate shaft gears of smaller cross-section transmission and the driving and driven bevel gears of larger cross-section rear axle of Jiefang 5t truck are I and II respectively, and the corresponding hardenability is J9: 30 respectively. 1960 or so, the shortage of domestic nickel-chromium steel has affected the production of domestic nickel-chromium steel. At that time, China's automobile industry was imported from the former Soviet Union, which used a lot of steel containing nickel and chromium. Therefore, at that time, China's automobile industry vigorously developed the research and development of boron steel, and used 20MnVB and 20Mn2TiB steel instead of 20CrMnTi carburized steel to manufacture gears. This is because adding trace boron (0.000 1%-0.0035%) to structural steel can significantly improve the hardenability of steel, so adding trace boron to steel can replace a certain number of precious alloy elements such as manganese, nickel, chromium and molybdenum, so boron steel has been widely used. 20MnTiB and 20Mn2TiB steels were used in the production of Jiefang brand automobile gears by Changchun FAW. "Dongfeng" brand 5, truck transmission and rear axle gear produced by Dongfeng Motor Company are made of 20CrMnTi and 20MnVB steel respectively. Similarly, it also signed an agreement with steel mills to reduce the hardenability zone of steel products and supply them in stages. The steels used for driving and driven bevel gears of transmission and rear axle are 20CrMnTiH(3), 20MnVBH(2) and 20MnVBH(3) respectively, and the corresponding hardenability is J9 = 32 ~ 39hrc, J9 = 37 ~ 44hrc and J9 = 34 ~ 42hrc respectively. China Qijiang Gear Factory imported the production technology of heavy-duty automobile transmission gear from German company, and successfully trial-produced the company's Cr-Mn-B series boron-containing gear steel in China according to the standards of German company ⅲ. The hardenability of gear material is J 10 = 3 1 ~ 39 h RC. Of course, boron-containing steels such as 20CrMnTi steel, 20MnTiB steel and 20MVB steel also have shortcomings. Generally speaking, carburized steels such as 20CrMnTi are essentially fine-grained steels. After carburizing, the grains will not fall off and can be quenched directly. But in fact, due to the influence of iron and steel smelting quality, grain coarsening often occurs under normal circumstances. The actual grain size of many batches of materials was tested, and it was found that a considerable part of the actual grain size was only 2-3 grades (930℃ for 3 hours). It is considered in the literature that 20CrMnTi steel contains a lot of tin inclusions due to its high titanium content, especially the large-size tin inclusions are the fatigue sources of gears, and their existence will reduce the contact fatigue performance of gears. This kind of inclusion is cubic structure, and it is easy to cleavage and crack when stressed, which leads to the early failure of gear. Another problem is that the hardenability of steel is limited, which can not meet the requirements of large diameter and large module gears, and the effective hardened layer depth and carburized center hardness can not meet the requirements of heavy-duty gears. In addition, 20CrMnTi steel is easy to produce internal oxidation and non-martensite structure during heat treatment, which reduces the fatigue life of gears. But at present, there is no gear carburizing steel as mature and reliable as 20CrMnTi steel in carburizing process in China. Therefore, it is still the most widely used carburized steel in China. There are also some shortcomings in boron steels such as 20MnVB, 20MnTiB and 20Mn2TiB. For example, poor deoxidation and denitrification of boron during smelting can not improve hardenability, so the performance of boron steel is unstable, and the gear distortion increases after carburizing and quenching, which affects the product quality. At the same time, the mixed crystal and grain are easy to be coarse, the deformation is difficult to control, and the toughness is poor. The tooth root of boron steel gear is easy to produce torus structure and black mesh and black belt of carbonitriding gear. Therefore, many factories stop using this steel at present. But it can never be concluded that boron steel is not suitable for gear carburizing steel. Boron-containing carburized steel is still used abroad. For example, the famous German Ⅳ gear factory has been using the reserved steel ZF7, which is a low-carbon chromium manganese steel containing boron. The main chemical compositions (mass fraction,%) of this steel are 0. 15 ~ 0.20c, 0. 15 ~ 0.40s, 1.0 ~ 1.3cr,1.0 ~/. Some American automobile transmission gears and rear axle driving and driven gears also use boron-containing carburized steel, such as 50B 15, 43BVl4 and 94B 17. So as long as the smelting technology of steel mills keeps up, the above problems of boron steel can be solved. The forging blanks of 20CrMnTiH, 20MnVBH and 20MnTiBH steel gears can be treated in continuous isothermal normalizing furnace to ensure the uniform distribution of flaky pearlite and ferrite. This can greatly reduce the heat treatment deformation of the gear, improve the accuracy of the gear and prolong the service life. The isothermal normalized hardness of gear forging blank is 156 ~ 207 HB.

Cr-Mn-Mo steel and Cr-Mo steel

22CrMnMo, 20CrMnMoH and 20 CRM nmoh steels are used for medium-sized automobile gears because of their high hardenability. This steel can be quenched directly after carburizing. Because Cr-Mn-Mo steel and Cr-Mo steel contain carbide-forming elements such as Cr and Mo, the carbon content on the surface of gear teeth will increase during carburizing, and a large number of carbides will easily appear in the carburized layer, which will deteriorate the performance of carburized layer. Therefore, when carburizing Cr-Mn-Mo steel and Cr-Mo steel for gears, a weak carburizing atmosphere should be adopted to prevent the formation of excessive carbides. The forged blanks of 22CrMnMo and 20CrMnMoH gears are tempered at 650 ~ 670℃ after normalizing. The metallographic structure is fine pearlite+a little ferrite, and the hardness is 17 1 ~ 229 HB. The forging blank of 20CrMnH gear is best treated in a continuous isothermal normalizing furnace, heated to 935 ~ 945℃, precooled to 640 ~ 650℃ and then isothermal, so as to obtain a uniform ferrite+pearlite structure with a hardness of 156 ~ 207 HB. It is pointed out in the literature that the smelting process of 20CrMoH steel is stable, the hardenability band is narrow, and it is easy to control. Compared with 20CrMnTi steel gear, the heat treatment distortion is small. The carburized layer has good and stable hardenability; The metallographic structure, surface and core hardness after carburizing and quenching can well meet the technical requirements. Good fatigue performance, more suitable for small and medium module gears in automobiles. Considering the service conditions of gears comprehensively, the fatigue life of gears can be ensured and the heat treatment deformation of gears can be reduced. When used for manufacturing gearbox gears, it should be J9 = 30 ~ 36 HRC, and when used for manufacturing rear axle gears, it should be J9 = 37 ~ 42 HRC.

Localization of foreign advanced automobile gear steel

With the introduction of advanced foreign models and the localization of various gear steels, the level of gear steels in China has reached a new level. At present, German Cr-Mn steel, Japanese Cr-Mo steel and American SAE86 steel meet the requirements of medium and small module gear steel. Some domestic truck gears are made of American brand SAE8822H steel, such as 8t and 10t bevel gears. The main chemical compositions (mass fraction,%) of this steel are 0. 19 ~ 0.25c, 0.70 ~ 1.05mn, 0. 19~0.25C ~ 0. It is considered that controlling hardenability is the key to solve the problem of gear deformation. In order to reduce deformation, H steel with hardenability bandwidth lower than 4HRC should be selected. After heat treatment, the accuracy (contact area) of gears made of H steel is 70% ~ 80% higher than that of ordinary steel, and the service life is prolonged. Therefore, the hardenability zone of carburized alloy structural steel is stipulated in the developed countries. Limit the hardenability range to a very narrow range (4 ~ 5 hours℃) as required. 1) When ordering in Germany, the hardenability of steel can be required to be within a given range, or the hardenability of steel can be reduced. 17CrNiM06 is very suitable for manufacturing heavy-duty automobile gears with large modulus. The main chemical components (mass fraction,%) of this steel are 0. 15 ~ 0.20c, 0.40~0.60Mn, 1.50 ~ 1.80cr, 0.25~0.35Mo, which has been used in domestic production. According to the literature, during the carburizing process of 17CrNiM06 steel gear, the carbon potential in the late carburizing stage should be reduced, and the cooling rate after carburizing should be accelerated, instead of air cooling, to prevent the formation of large carbides, and then tempering at 630℃ at high temperature to precipitate some alloy carbides, so as to reduce the amount of retained austenite during secondary heating quenching at 820℃ and finally obtain a better metallographic structure. 2) Austrian "Steyr" heavy-duty automobile factory requires a hardenability bandwidth of 7HRC. 3) The transmission gear and rear axle gear of Japanese medium and heavy trucks, such as Hino KB222 truck 9t and Nissan CKL20DD truck 8t, are widely made of Cr-Mo steel, such as SCM420H and SCM822H steel, which are equivalent to domestic 20CrMnMoH and 22CrMoH steel. This kind of steel has high hardenability. In a certain range, the bending fatigue life of gears increases with the increase of hardenability. It is pointed out in the literature that when Changchun FAW started to produce the rear axle gear of Jiefang brand 9t truck, it used 20CrMnTiH steel. Even if the steel with hardenability of Group II (J9 = 36 ~ 42 HRC) is used, the hardness of the gear tooth center after heat treatment is only 22 ~ 24hrc, which can not meet the requirements of gear technical conditions. The driving and driven bevel gears of the rear axle are damaged in the early stage during the use of the automobile. Therefore, Ct-Mo steel with higher hardenability has to be selected, and its main composition refers to Japanese SCM822H gear steel. The main chemical compositions (mass fraction,%) of this steel are: 0. 19 ~ 0.25c, 0.55~0.90Mn, 0. 19~0.25C ~ 0.35Si, 0.85 ~ 65. After consultation with steel mills, a new domestic steel grade of 22CrMoH steel was produced, and its hardenability index was J9 = 36 ~ 42hrc, which met the requirements of automobile gears. However, the technological performance of this steel is poor, and the gear forging blank must be cut after isothermal annealing. The hardness is 156 ~ 207 HB, and the metallographic structure is pre-ferrite+pseudo pearlite. This kind of steel has high hardenability, and it is easy to produce granular bainite by ordinary normalizing. The appearance of granular bainite is extremely unfavorable to cutting, which not only greatly reduces the service life of the tool, but also is always accompanied by uneven metallographic structure due to the appearance of abnormal structure, which eventually leads to the increase of gear heat treatment distortion. 4) In recent years, American automobile manufacturers have tried to reduce production costs and improve the reliability and durability of parts, which requires that the geometric dimensions and mechanical properties of products are highly consistent. In order to improve the consistency of product performance of heat-treated parts, it is necessary to reduce the hardness dispersion after quenching, which is directly related to the hardenability band width of steel. The consistency of gear center hardness will reduce the distortion of heat treatment, thus improving the accuracy of gear and making the residual compressive stress distribution on the surface of gear teeth more uniform. Some steels used in American truck transmission gears and rear axle driving bevel gears are SAE8620 steel and SAFA820 steel. American brands such as SAE8620H and SAE8822H are also produced and used in China (such as Baosteel No.5 Plant, etc.). ), which are used for transmission gear and rear axle bevel gear of medium-sized trucks respectively.

China heavy-duty automobile gear steel.

At present, China's gear steel basically meets the requirements of localization in the process of use and technology introduction, while the gear steel for heavy-duty automobile transmission and the gear steel for medium and heavy-duty automobile rear axle have yet to be developed and produced. According to the analysis of the technical status of heavy-duty vehicles in China, overload and poor road conditions are two serious problems, which can not be overcome in a short time, making gears often bear a large overload impact load. Overload impact load is between fatigue and fracture stress, which has a great influence on the service life of gears and often leads to early failure of gears. From this point of view, Cr-Ni or Cr-Ni-Mo series steel should be selected for heavy-duty automobile gears with large modulus, such as German 17CrNiM06 steel and domestic 20CrNi3H and 20CrNiMoH steel. The appearance of high-power engine promotes the development of new Cr-Ni-Mo gear steel.