Graduation design

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

Tooth

The gear teeth

Teeth for short, is the gear on each of the raised part for meshing, these projections are generally arranged in a radial manner, paired gear gear teeth in contact with each other, so that the gear continues to mesh operation;

Teeth groove

Teeth grooves

Teeth is the gear on the space between the two neighboring gear teeth; endface is a cylindrical gear or cylindrical worm gear on, perpendicular to the gear or worm axis

Normal plane

The plane perpendicular to the tooth line of the gear teeth

Top circle

The circle in which the top of the tooth is located

Root circle

The circle in which the bottom of the groove is located

Base circle

The circle that forms the incurved line that is purely rolled

Is the circle of the index circle

The circle in which the grooves are located

The circle of the index is the circle in which the groove is located.

Is the base circle for calculating the geometry of the gear within the end face.

Edit Classification

Gears can be classified by tooth shape, gear profile, tooth line shape, the surface on which the gear teeth are located, and manufacturing method. The tooth shape of a gear includes the profile curve, pressure angle, tooth height and variations. Involute gears are relatively easy to manufacture, so they account for the absolute majority of gears used in modern times, while cycloid gears and circular arc gears are used less often. In terms of pressure angle, small pressure angle gears have a smaller load carrying capacity; while large pressure angle gears, although the load carrying capacity is higher, but in the case of transmitting the same torque under the increased load on the bearings, and therefore only used in special circumstances. The tooth height of the gear has been standardized, generally using the standard tooth height. Shift gears have more advantages and have been used in all kinds of machinery and equipment. In addition, gears can also be divided into cylindrical gears, bevel gears, non-circular gears, racks, worm gears; the shape of the tooth line is divided into straight gears, helical gears, herringbone gears, curved gears; according to the surface of the gear teeth are divided into external gears, internal gears; according to the manufacturing method can be divided into casting gears, cut gears, rolled gears, sintered gears and so on. Gear manufacturing materials and heat treatment process on the gear's load-bearing capacity and size of the weight has a great impact. 1950s, gears more than carbon steel, 60s changed to alloy steel, while the 70s more surface-hardened steel. According to the hardness , the tooth surface can be distinguished into two kinds of soft tooth surface and hard tooth surface. Soft tooth surface of the gear bearing capacity is lower, but easier to manufacture, good running, mostly used for transmission size and weight without strict limits, as well as a small amount of production of general machinery. Because of the paired gears, small wheel burden, so in order to make the working life of large and small gears are roughly equal, small wheel gear surface hardness is generally higher than that of the large wheel. Hardened gears have a high load carrying capacity, it is in the gear after precision cutting, and then quenching, surface quenching or carburizing quenching treatment to improve the hardness. However, in the heat treatment, the gear will inevitably produce deformation, so after the heat treatment shall be grinding, grinding or fine cutting , in order to eliminate the error due to deformation, improve the accuracy of the gear.

Materials

The steel commonly used in the manufacture of gears are tempered steel, quenched steel, carburized quenched steel and nitrided steel. The strength of cast steel is slightly lower than forged steel, commonly used in larger size gears; gray cast iron mechanical properties are poor, can be used for light load open gear transmission; ductile iron can partially replace the steel manufacturing gears; plastic gears are used for light loads and low noise requirements, and its paired gears are generally used with good thermal conductivity of steel gears. Future gears are to heavy-duty, high-speed, high-precision and high-efficiency direction, and strive for small size, light weight, long life and economic and reliable. The development of gear theory and manufacturing process will be to further study the mechanism of gear damage, which is the basis for the establishment of a reliable strength calculation method, is to improve the gear load carrying capacity, gear life extension of the theoretical basis; the development of new tooth shape represented by arc tooth profile; research new gear materials and manufacturing gears of the new process; research on the elastic deformation of the gears, manufacturing and installation errors, as well as the distribution of the temperature field, to carry out the gear tooth modification, in order to improve the smoothness of gear operation, and increase the contact area of the gear teeth when fully loaded, so as to improve the bearing capacity of the gear. Friction, lubrication theory and lubrication technology is the basic work in gear research, research on elastic fluid dynamic pressure lubrication theory, promote the use of synthetic lubricants and oil in the appropriate addition of extreme pressure additives, not only to improve the bearing capacity of the tooth surface, but also to improve transmission efficiency.

Edit the development of China's gear industry

China's gear industry in the "Tenth Five-Year Plan" period of rapid development: in 2005, the annual output value of the gear industry from 24 billion yuan in 2000 to 68.3 billion yuan, a compound annual growth rate of 23.27%, has become China's machinery foundation parts in the largest industry. The largest industry. In terms of market demand and production scale, China's gear industry in the global ranking has exceeded Italy, ranking fourth in the world. In 2006, all of China's gears, transmissions and drive components manufacturing enterprises to achieve a cumulative total industrial output value of 102628183 thousand yuan, an increase of 24.15% over the same period last year; to achieve a cumulative product sales revenue of 98238240 thousand yuan, an increase of 24.37% over the same period last year; to achieve a cumulative total profit of 5665210 thousand yuan, an increase of 26.85% over the same period last year. From January to December 2007, all of China's gears, transmissions and drive components manufacturing enterprises to achieve a cumulative total industrial output value of 136542841 thousand yuan, an increase of 30.96% over the same period last year; from January to October 2008, all of China's gears, transmissions and drive components manufacturing enterprises to achieve a cumulative total industrial output value of 144529138 thousand yuan, an increase of 32.92% over the same period last year. China's gear manufacturing industry, compared with developed countries, there is still a lack of independent innovation, new product development, slow, disorderly market competition, weak enterprise management, low degree of information technology, the comprehensive quality of practitioners to be improved and other issues. At this stage, the gear industry should be through market competition and integration, improve industry concentration, the formation of a number of billions of yuan, 500 million yuan, 100 million yuan in assets, large, medium and small-scale enterprises; through independent intellectual property rights product design and development, the formation of a number of vehicle driveline (transmission, drive axle assembly) lead enterprises, with the lead enterprise supporting the integration of the gear industry's capacity and resources; to achieve specialization, networking Matching, the formation of a large number of distinctive processes, distinctive products and rapid response capabilities of the brand-name enterprises; through technological transformation, the realization of modern gear manufacturing enterprise transformation. "Eleventh Five-Year" end, China's gear manufacturing industry annual sales can reach 130 billion yuan, per capita sales rose to 650,000 yuan / year, in the world industry rankings to reach the world's second. 2006-2010 will add 100,000 sets of new equipment, that is, each year for the new equipment investment of about 6 billion yuan, the purchase of 20,000 new machine tools, each with an average unit price of 300,000 yuan. Average unit price of 300,000 yuan. By 2010, China's gear manufacturing industry should have a total of about 400,000 sets of various types of machine tools, of which 100,000 sets of CNC machine tools, CNC rate of 25% (higher than the average value of 17% of the whole industry machinery manufacturing).

Edit paragraph type

Ratio

Fixed ratio -- circular gear mechanism (cylindrical, conical) Variable ratio -- non-circular gear mechanism (elliptical gears)

Relative position of the wheel axis

Planar gear mechanism Straight-toothed cylindrical gearing External gearing Internal gearing Rack gearing Helical cylindrical gearing Herringbone gearing Space gear mechanism Bevel gearing Staggered-axis helical gearing Worm gearing

Processes

Bevel gears Rough semi-products gears Helical gears Internal gears Spur gears Worm gears

Edit Main parameters of helical cylindrical gears in this paragraph

Spiral angle

β > 0 for left-handedness and vice versa for right-handedness

Tooth spacing

pn = ptcosβ, with the subscripts n and t denoting the normal and the end face, respectively

Module

mn = mtcosβ

Diameter of indexing circle

d = mtz

Center distance

a=1/2*m(z1+z2)

Correct meshing conditions

m1 = m2,α1 = α2,β1 = ? β2

Edit Diagnosis

The purpose of carrying out a simple diagnosis is to quickly determine whether the gear is in a normal working condition, and to further carry out precision diagnostic analysis or take other measures for gears that are in an abnormal working condition. Of course, in many cases, based on a simple analysis of vibration, can also diagnose some obvious faults. Simple diagnosis of gears includes noise diagnostic method, vibration level diagnostic method, and shock pulse (SPM) diagnostic method, etc., and the most commonly used method is vibration level diagnostic method. The vibration level diagnostic method is a diagnostic method that utilizes the vibration intensity of the gear to determine whether the gear is in normal working condition. According to different judgment indicators and standards, it can be divided into absolute value judgment method and relative value judgment method.

Absolute value determination method

Absolute value determination method is the use of the amplitude value measured at the same measurement point on the gear box as a direct evaluation of the operating state of the indicators. Absolute value determination method for gear state identification, must be based on different gearboxes, different requirements for the use of the development of the corresponding determination of standards. The main basis for the development of absolute value determination standard for gears is as follows: (1) theoretical study of abnormal vibration phenomena; (2) analysis of vibration phenomena based on experiments; (3) statistical evaluation of measured data; (4) reference to domestic and foreign standards. In fact, there is no absolute value determination standard that can be applied to all gears, and when the size and type of gears are different, the determination standard is naturally different. When judging the vibration of broadband by a measurement parameter, the standard value must be changed according to the frequency. When the frequency is below 1kHz, the vibration is judged by the speed; when the frequency is above 1kHz, the vibration is judged by the acceleration. The actual standard also depends on the specific circumstances.

Phase time value determination method

In practical applications, for the absolute value of the gear has not yet been formulated to determine the standard, you can make full use of on-site measurement data for statistical averaging, the development of appropriate relative determination of the standard, the use of such standards for the determination of the relative value of the determination method is called. Relative judgment standards require the same part of the gear box measurement point at different times measured amplitude and normal state amplitude comparison, when the measured value and normal value compared to a certain extent, judged as a state. For example, the relative value judgment standard stipulates that attention should be paid when the actual value reaches 1.6~2 times the normal value, and danger is indicated when it reaches 2.56~4 times. As for the specific use of 1.6 times for grading or 2 times for grading, depending on the use of the gear box requirements, more rough equipment (such as mining machinery) generally use a higher multiple of grading. In practice, in order to achieve the best results, can be used at the same time the above two methods, in order to compare and contrast, comprehensive evaluation.

Editorial Terminology

The gear teeth (teeth) - each of the raised portions of a gear used for meshing. Generally, these projections are arranged in a radial pattern. The gear teeth on paired gears are in contact with each other, resulting in continuous mesh operation of the gears. Groove - the space between two neighboring gear teeth on a gear. Gear

End face - on a cylindrical gear or cylindrical worm, the plane perpendicular to the axis of the gear or worm. Normal plane - on a gear, the normal plane refers to the plane perpendicular to the tooth line of the gear teeth. Top Circle - the circle where the top of the tooth is located. Root Circle - the circle where the bottom of the groove is located. Base circle - the circle on which the line of incidence forming the involute makes a pure roll. Indexing circle - the reference circle for calculating the geometric dimensions of the gear in the end face, in the case of spur gears, the modulus and pressure angle are standardized on the indexing circle. TOOTH FLACE - the side surface on a gear tooth that lies between the top cylindrical surface and the root cylindrical surface. Tooth Profile - the intercept of a tooth face by a specified surface (flat for cylindrical gears). Tooth line - the line of intersection of a tooth face with an indexing cylindrical surface. Pitch pt - the length of the indexing arc between two adjacent end face profiles of the same side. Modulus m - the quotient obtained by dividing the tooth pitch by the circumference π in millimeters. Pitch p - the reciprocal of the modulus, in inches. Tooth Thickness s - the length of the indexing arc between the two side profiles of a gear tooth on an end face. Slot width e - the length of the indexing arc between the two side tooth profiles of one tooth slot on the end face. Top height hɑ - radial distance between the top circle and the indexing circle. Root height hf - radial distance between the index circle and the root circle. Full tooth height h - radial distance between top circle and root circle. Tooth width b - axial dimension of the tooth. Face pressure angle ɑt - the acute angle between the radial line through the intersection of the face profile and the indexing circle and the tangent line of the profile through that point. Standard Rack: A rack in which only the base circle dimensions, tooth shape, full tooth height, crown height, and tooth thickness are in accordance with standard spur gear specifications, and the rack cut according to the standard gear specifications is called a standard rack. Standard Pitch Circle: The reference circle used to determine the dimensions of gears. The number of teeth x module Standard Pitch Line: a specific pitch line on the rack or the thickness of the teeth measured along this line, one-half of the pitch. Action Pitch Circle: When a pair of spur gears bite together, each has a tangent rolling circle. Benchmark Pitch (Standard Pitch): Selected standard pitch as a benchmark, equal to the benchmark rack pitch. Pitch Circle (Pitch Circle): two gears on the centerline of the contact point of the bite of the gears left on the track known as the pitch circle. Section diameter (Pitch Diameter): the diameter of the pitch circle. Effective tooth height (Working Depth): a pair of spur gear crown height and. Also known as the work of the tooth height. Crown Height (Addendum): Difference between the crown circle and the pitch circle radius. Backlash: The gap between the tooth face and the tooth surface when two teeth are occluded. Clearance: the gap between the top of one gear and the bottom of the other gear when two teeth bite together. Node (Pitch Point): a pair of gears bite and pitch circle tangent point. Pitch (Pitch): the distance between two neighboring teeth corresponding to the point of the arc. Normal Pitch (Normal Pitch): involute gears along a specific section of the same vertical line measured by the pitch.

Edit paragraph plastic gear

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

Edit this section of the production enterprises

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 gears alone, its market share of 60%; industrial gears by the industrial general, special, special gears, their market share of 18%, 12%, 8%; gear equipment this piece of only 2% of the market share. The main manufacturers: Hangzhou Advance Gearbox Group Co. Chongqing Gearbox Co. Zhejiang Hengjiu Machinery Group Co. 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 gears alone, its market share of 60%; industrial gears by the industrial general, special, special gears constitute a market share of 18%, 12%, 8%; gear equipment, which accounts for only 2% of the market share. Examples of major manufacturers: Hangzhou Advance Gearbox Group Co. Chongqing Gearbox Co. Zhejiang Hengjiu Machinery Group Co. Jiangsu Spaceship Co. Nanjing High-speed Gear Manufacturing Co. Zhengmao Group Co. Sichuan Gear Factory Hangzhou Donghua Chain Group Co.

Edit the picture

Spurface Gear ( Applied in CNC Gantry Milling Machine)

Spiral Bevel Gear (Applied in Attachment Milling Head of CNC Gantry Milling Machine)

Helical Gear (Applied in Ordinary Milling Machine)

Gear Shaft (Applied in CNC Vertical Lathe)

Various Moulded Forming Gears (10 pcs)

Edit this paragraph Medium and Heavy-duty Vehicle Gears Overview

China Medium and heavy-duty truck gears with more steel grades, mainly to adapt to the introduction of foreign advanced automotive technology at the time of the requirements. 50 years China from the former Soviet Union Rikhachev Automobile Plant to introduce the Soviet Union at the time of medium-sized trucks (i.e., "liberation" original model) production technology at the same time, but also the introduction of the former Soviet production of automotive gears of the 20CrMnTi steel. 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, from the 80's, China's systematic introduction of various types of advanced models of industrialized countries, various types of foreign advanced medium and heavy trucks are also introduced. At the same time, China's large automobile factories cooperate with famous foreign automobile companies to introduce foreign advanced automobile production technology, including the production technology of automobile gears. At the same time, China's iron and steel smelting technology level is also improving, the use of ladle secondary smelting and composition fine-tuning and continuous casting and rolling and other advanced refining technology, enabling steel mills to produce high purity, hardenability with narrowing of the steel gears, thus realizing the introduction of the automotive gears with the localization of the steel, so that China's gears with the level of production of steel on a new level. In recent years, suitable for China's national conditions of domestic heavy-duty automobile gears with nickel-containing steel with high hardenability performance has also been developed and applied, and achieved better results. Automotive gear heat treatment technology from the original 50-60 years using well gas carburizing guard to the current widespread use of computer-controlled continuous gas carburizing automatic line and box-type multi-purpose furnace and automatic production line (including low-pressure (vacuum) carburizing technology), gear carburizing pre-oxidation treatment technology, gear quenching and control of cooling technology (due to the use of special quenching oils and quenching and cooling technology), gear forging billets, isothermal Normalizing technology, etc. The use of these technologies not only make the gear carburizing quenching distortion has been effectively controlled, gear processing accuracy has been improved, the service life has been extended, but also to meet the needs of the gear of the modernization of heat treatment of mass production. The literature points out that the life of automobile gears is mainly assessed by two major indicators, one is the contact fatigue strength of gears, and the other is the bending fatigue strength of gears. The former is mainly determined by the carburizing quenching quality, the latter is mainly determined by the gear material. To this end, it is necessary to have a more comprehensive understanding of the requirements of automotive gear carburized steel, performance and its heat treatment characteristics.

Chromium manganese titanium steel and boron steel

For a long time, China's cargo automobile gears use the most common type of steel is 20CrMnTi. this is the last century 50's China's introduction of medium-sized automobile gears from the former Soviet Union 18XTr steel (i.e. 20CrMnTi steel). The steel grain fine, carburizing grain growth tendency is small, with good carburizing quenching performance, carburizing can be quenched directly after. Literature pointed out that before 1980, China's carburized alloy structural steel (including 20CrbinTi steel) in the steel factory only to ensure that the chemical composition of the steel and the mechanical properties determined by samples, but in the production of automobiles often appear in the chemical composition and mechanical properties of qualified steel, due to the fluctuations in the range of quenching performance is too large to affect the quality of the product. For example, if the hardenability of 20CrMnTi carburized steel is too low, then made of gear carburizing quenching, the heart of the hardness is lower than the value of the technical conditions, fatigue test, the fatigue life of the gear is reduced by half; if the hardenability is too high, then the gear carburizing quenching bore shrinkage is too large and affects the assembly of gears. Due to the steel hardenability of the wheel tooth heart of the hardness and distortion have an extremely significant impact, in 1985 the Ministry of Metallurgy promulgated our guarantee of hardenability of structural steel technical conditions (GB5216-85), in this technical conditions included in the 10 kinds of carburized steel, including 20CxMnTiH, 20MnVBH steel, the chemical composition, hardenability performance data. The standard stipulates that: 20CrMnTi steel used for manufacturing gear hardenability indicators for the water-cooled end of 9 curry from the hardness of 30-42 HRC. after this, the use of 20CrMnTi steel production gears in the heart of the hardness of the tooth is too low and the problem of excessive distortion basically been solved. But regardless of the gear module size and steel cross-section thickness are used the same steel 20CrMnTi steel is obviously unreasonable. In recent years, due to the improvement of China's steel smelting technology and the supply of alloy structural steel to improve the conditions have been gear steel hardening performance band further narrowing, and according to different products (such as transmission gears and rear axle gears, etc.) the requirements of the development of new steel to meet its requirements. Through consultations with steel mills, in 1997 Changchun FAW has signed with the production of gear steel manufacturers will be 20CrMnTi steel hardening performance of the supply agreement, such as "Jiefang" brand 5t truck for the manufacture of smaller cross-sectional size of the transmission first shaft, intermediate shaft gears and rear axle gears and cross-sectional size of the rear axle main, Slave bevel gear with 20CrMnTiH steel hardenability group were I and II, corresponding to the hardenability were J9: 30-36HRC and J9 = 36-42HRC. Around 1960, due to the supply of nickel and chromium steel in China is tight, affecting China's production of nickel-containing and chromium-containing steel. And at that time, China's automobile industry was introduced from the former Soviet Union technology, the Soviet Union, a large number of applications containing nickel, chromium steel. Therefore, at that time, China's automobile industry vigorously developed the development of boron steel, research and development work, with 20MnVB and 20Mn2TiB steel instead of 20CrMnTi carburizing steel manufacturing gears. This is because the addition of trace boron in structural steel (0.0001%-0.0035%) can significantly improve the hardenability of steel, so the addition of trace boron in steel can replace a certain amount of manganese, nickel, chromium, molybdenum and other valuable alloying elements, and thus boron steels are widely used. Changchun FAW has used 20MnTiB and 20Mn2TiB steel in the production of "liberation" brand automobile gears. Dongfeng Motor Company produces "Dongfeng" brand 5, truck transmission and rear axle gears were manufactured using 20CrMnTi and 20MnVB steel. Similarly, also signed with the steel mill to narrow the steel hardening performance band and graded supply agreement. The steel used for transmission and rear axle master and slave bevel gears are 20CrMnTiH(3) and 20MnVBH(2), 20MnVBH(3), corresponding to the hardenability properties of J9 = 32-39HRC and J9 = 37-44HRC, J9 = 34-42HRC, respectively. China's Qijiang Gear Factory has introduced the German company's heavy-duty automobile transmission gears production technology in the China's Qijiang Gear Factory introduced the German company's heavy-duty automobile transmission gear production technology, in the country according to the German Ⅲ company's standard trial production of the company's Cr-Mn-B system of boron-containing gear steel was successful. The hardenability of the gear material can be J10 = 31 ~ 39HRC Of course, 20CrMnTi steel and 20MnTiB steel, 20MVB steel and other boron-containing steel is also deficient. It is generally believed that 20CrMnTi carburized steel is the essence of fine grain steel, carburization grain will not rent, can be quenched directly. But in fact, due to the influence of steel smelting quality, often under normal conditions, the phenomenon of grain coarsening occurs. The actual grain size test on a number of batches of material, found that a significant portion of the actual grain size is only 2-3 level (930 ℃ insulation 3h conditions). Literature that 20CrMnTi due to the high Ti content, the steel TiN inclusions, especially large TiN inclusions is a source of fatigue in gear fatigue, and its presence reduces the contact fatigue performance of gears. This kind of inclusions are cubic structure, easy to deconvoluted cracking when stressed, leading to early gear failure. Another problem is that the hardenability of the steel is limited, which cannot meet the requirements of large-diameter large-module gears, and the depth of the carburized effective hardening layer and the hardness of the heart cannot meet the requirements of heavy gears. In addition, in the heat treatment process 20CrMnTi steel is easy to produce internal oxidation and non-martensitic organization and reduce the fatigue life of gears. But at present in our country gear carburizing steel there is no steel in the carburizing process with 20CrMnTi steel so mature and reliable. Therefore, it is still the most commonly used carburizing steel. 20MnVB, 20MnTiB and 20Mn2TiB boron steel also has some shortcomings, such as in the smelting due to the deoxidation and denitrification is not good so that boron can not play a role in increasing the role of hardenability, so that the boron steel performance is unstable, carburizing and quenching of the gear aberration increases and affects the quality of the product. At the same time due to the mixed crystal and grain is easy to coarse, to deformation is not easy to control and poor toughness, and boron steel gear root is easy to produce Torrhenite organization and carbon and nitrogen **** seepage gear black network, black band. Therefore, many factories discontinued the use of the steel. However, it must not be concluded that boron steel is not suitable for gear carburizing steel conclusions. Boron-containing carburizing steel is still used abroad. For example, Germany's famous Ⅳ gear factory, has been used by the factory to formulate the reservation steel ZF7, which is a boron containing low carbon chromium manganese steel. The main chemical composition of the steel (mass fraction, %) is 0.15 ~ 0.20C, 0.15 ~ 0.40S, 1.0 ~ 1.3Cr, 1.0 ~ 1.3Mn, 0.001 ~ 0.003B. U.S. automobile transmission gears and rear axle master and slave gears are also boron carburizing steel, such as 50B15, 43BVl4 and 94B17. Therefore, as long as the steel mill smelting Therefore, as long as the steel smelting technology to follow up, boron steel is able to solve the above problems. 20CrMnTiH, 20MnVBH and 20MnTiBH steel gear forging billets in the continuous isothermal normalizing furnace treatment can be guaranteed to obtain a uniform distribution of lamellar pearlite + ferrite. This can make the heat treatment distortion of the gear greatly reduced, so that the precision of the gear is improved and the service life is extended. Gear forging billet isothermal normalized hardness of 156 ~ 207HB.

Chromium-manganese-molybdenum steel and chromium-molybdenum steel

22CrMnMo, 20CrMnMoH and 20CrMoH steel is used for medium-sized automotive gears because of its high hardenability. These steels can be hardened directly after carburizing. As chromium manganese molybdenum steel and chromium molybdenum steel contains chromium and molybdenum and other carbide-forming elements, in the carburizing process will contribute to the increase in the surface carbon content of the gear teeth, easy to carburizing layer in the organization of a large number of carbides, so that the carburizing layer deterioration of performance. Therefore, gears using chromium manganese molybdenum steel and chromium molybdenum steel carburizing, it is appropriate to use a weak carburizing atmosphere to prevent the formation of excessive carbides. 22CrMnMo and 20CrMnMoH gear forging billet normalized at 650 ~ 670 ℃ for high temperature tempering treatment, the metallurgical organization of the fine lamellar pearlitic + a small amount of ferrite, hardness of 171 ~ 229HB. 20CrMnH gear forging billet is best in the continuous Isothermal normalizing furnace treatment, 935 ~ 945 ℃ heating, 640 ~ 650 ℃ first pre-cooling and then isothermal, can obtain uniform ferrite + pearlite organization, hardness of 156 ~ 207HB. literature pointed out that the 20CrMoH steel smelting process is stable, the quenching band is narrower and easy to control, and compared with the 20CrMnTi steel gears, has a heat treatment distortion is small; the infiltration layer has good, stable Hardenability; metallurgical organization, surface and heart hardness after carburizing and quenching, can better meet the technical requirements; fatigue performance is good, more suitable for automotive small and medium modulus gears. Comprehensive consideration of the service conditions of the gear, both to ensure that the fatigue life of the gear, but also to reduce the heat treatment of the gear distortion in the manufacture of gearbox gears should be J9 = 30 ~ 36HRC, used to manufacture rear axle gears should be J9 = 37 ~ 42HRC.

The localization of foreign advanced automotive gear steel

With the introduction of advanced models from abroad, the introduction of a variety of gear steel, the localization of China's gear steel level, the gear steel level. Localization of China's gear steel level to a new level. At present, Germany's Cr-Mn steel, Japan's Cr-Mo system steel, and the U.S. SAE86 steel to meet the small and medium modulus gear steel. Domestic truck gears have adopted the U.S. grade SAE8822H steel, such as 8t and 10t bridge bevel gears using SAE8822H, the main chemical composition of the steel (mass fraction, %) for 0.19 ~ 0.25C, 0.70 ~ 1.05Mn, 0.15 ~ 0.35Si, 0.35 ~ 0.75Ni, 0.35 ~ 0.65Cr, 0.30 ~ 0.40Mo. ～The literature suggests that controlling hardenability is the key to solving the problem of gear distortion. In order to reduce distortion should be selected Jominy hardenability bandwidth of 4HRC below the H steel. Using H steel gear heat treatment accuracy (contact zone) than ordinary steel is 70% to 80% higher, service life is extended. Therefore, industrially developed countries have stipulated the hardenability band of carburized alloy structural steel. According to the need to limit the hardenability band in a very narrow range (4 ~ 5HRC). 1) in Germany when ordering, you can require the steel hardenability in the given range, you can also ask for narrowing the hardenability of the steel. 17CrNiM06 is very suitable for the manufacture of large modulus heavy-duty automotive gears, the steel's main chemical composition (mass fraction, %) of 0.15 to 0.20C, 0.40 to 0.60Mn, 1.50-1.80Cr, 0.25-0.35Mo, 1.40-1.70Ni. This steel has been produced and used in China. Literature that, in the 17CrNiM06 steel gear carburizing process, in the appropriate reduction of carburizing late carbon potential at the same time to speed up the cooling rate after carburizing, from air cooling to air cooling, to prevent the formation of large carbides, and then tempered at a high temperature of 630cC to precipitate part of the alloy carbides, in order to reduce the amount of residual austenite in the 820 ℃ secondary heating quenching, and ultimately obtain a better metallurgical organization. 2) Austria's "Styer" heavy-duty automobile factory requires a hardenability bandwidth of 7HRC. 3) Japan's medium- and heavy-duty trucks, such as the "Hino" brand KB222-type load 9t car and "Nissan" brand CKL20DD-type cargo 8t car transmission Gears and rear axle gears are widely used Cr-Mo system steel, such as SCM420H and SCM822H steel, equivalent to China's localized 20CrMnMoH and 22CrMoH steel. Such steels have high hardening properties. Within a certain range, the bending fatigue life of gears increases with the increase of hardenability. Literature pointed out that Changchun FAW began in the production of "liberation" brand 9t truck rear axle gears, the use of 20CrMnTiH steel, even if the use of hardenability for the Ⅱ group of steel (J9 = 36 ~ 42HRC), heat treatment gear wheel tooth heart hardness is only 22 ~ 24HRC, less than the gear technology conditions Requirements set forth in the car in use, the rear axle active and driven bevel gear early damage. Therefore, we have to choose a higher hardenability of Ct-Mo steel, its main component reference to Japan's SCM822H gear steel, the steel's main chemical composition (mass fraction, %): 0.19 ~ 0.25C, 0.55 ~ 0.90Mn, 0.15 ~ 0.35Si, 0.85 ~ 1.25Cr, 0.35 ~ 0.45Mo. After consultation with the steel mills to produce a localized new steel. After consultation with the steel mills, a new localized steel 22CrMoH steel, its hardenability index for J9 = 36 ~ 42HRC, better meet the requirements of the use of automotive gears. However, the process performance of the steel is poor, gear forging billet to be isothermal annealing treatment before cutting, hardness of 156 ~ 207HB, the metallurgical organization for the first **** precipitation ferrite + pseudo **** precipitation pearlite. This steel hardenability is high, ordinary normalizing is prone to produce granular bainite, granular bainite is extremely unfavorable to the cutting process, not only so that the service life of the tool has decreased significantly, and due to the emergence of abnormal organization, always accompanied by the non-uniformity of the metallurgical organization, and ultimately lead to an increase in the gear heat treatment distortion.4) In recent years, U.S. automobile manufacturers seek to reduce production costs and improve the reliability of the parts and durability, which requires a high degree of consistency in product geometry and mechanical properties. Heat-treated parts to improve the consistency of product performance, you must reduce the hardness of the parts after quenching the degree of dispersion, which is directly related to the degree of steel hardenability band width. Consistency of hardness in the heart of the gear will reduce heat-treated aberrations, thereby improving the accuracy of the gear and allowing a more uniform distribution of residual compressive stresses on the surface of the gear teeth. U.S. cargo vehicle transmission gears and rear axle active bevel gear steel with some of the SAE8620 steel and SAFA820 steel manufacturing. U.S. SAE8620H, SAE8822H and other grades of steel in China has also begun to produce (such as Baosteel Group Shangsteel five plants, etc.) and use, respectively, for medium-sized truck transmission gears and rear axle bevel gears.

Domestic heavy-duty automobile gear steel

At present, China's gear steel to meet the basic use and the introduction of technology process localization requirements, while the heavy-duty vehicle transmission gears and medium-heavy-duty car rear axle gear steel, has yet to be developed and produced. According to the analysis of the current situation of the use of domestic heavy-duty vehicle technology, overloading and poor road conditions, the two problems are more serious, and can not be overcome in the short term, which makes the gears are often subjected to a large overload impact load. Overload impact load between fatigue and fracture stress, it has a great impact on the service life of the gear, often resulting in early gear failure. From this point of view, large modulus heavy-duty automotive gears should be selected Cr-Ni or Cr-Ni-Mo system steel, such as Germany's 17CrNiM06 steel is the best, there are domestic 20CrNi3H, 20CrNiMoH steel. The introduction of high-power engines to promote the new Cr-Ni-Mo series of gear steel