A gear is a mechanical component that has a gear on the rim that continuously meshes to transmit motion and power. The use of gears in transmissions has long appeared. At the end of the 19th century, the principle of the incision method and the special machine tools and tools that used this principle to cut the teeth appeared one after another. With the development of production, the smoothness of the gear operation was taken seriously.
Gear accuracy:
Gear accuracy refers to a grade that is divided into the comprehensive error of the shape of the gear, including some important parameters such as tooth shape, tooth direction, and jump. The tooth shape refers to the radial shape of the tooth, and the tooth direction refers to the longitudinal direction of the tooth. The shape and the diameter jump refer to the error of the distance between two adjacent teeth. Generally, the gears used in our automobile can be processed by the hobbing machine, and can be used in grades 6-7. Some presses require high precision because of the need for high speed operation and batch printing. The gear reduces the error caused by the gear accumulation, and the printing effect is reduced. The domestically produced gear grinding machine can be processed to 4~5 grades. The high-precision gear grinding machine imported from abroad can be processed to 3,~4, and more Some can be processed to level 2. The Japanese standard DIN 0 is equivalent to the Chinese rating of 4, the general error is in μm, 1μm = 0.001mm
Note the problem:
The purpose of the simple diagnosis is to quickly determine whether the gear is in normal working condition and
Gears with abnormal working conditions are further subjected to sophisticated diagnostic analysis or other measures. Of course, in many cases, some obvious faults can be diagnosed based on a simple analysis of the vibration. Simple diagnosis of gears includes noise diagnosis, vibration diagnosis, and shock pulse (SPM) diagnostics. The most common is the vibration diagnosis method. The flattening diagnostic method is a diagnostic method that uses the vibration intensity of the gear to determine whether the gear is in a normal working state. According to different judgment indicators and standards, it can be divided into absolute value judgment method and relative value judgment method.
Absolute value judgment method:
The absolute value determination method uses the amplitude value measured at the same measuring point on the gear box as an index for evaluating the operating state.
The absolute value judgment method is used to identify the gear state. It is necessary to formulate corresponding judgment standards according to different gearboxes and different use requirements.
The main basis for setting the absolute value judgment criteria for gears is as follows:
1) Theoretical study of abnormal vibration phenomena;
(2) Analysis of vibration phenomena according to experiments;
(3) Statistical evaluation of the measured 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 the gears are different, the judgment criteria are naturally different.
When making a judgment on the vibration of a broadband according to a measurement parameter, the standard value must be changed according to the frequency. The frequency is below 1 kHz, the vibration is determined by the speed; the frequency is above 1 kHz, and the vibration is determined by the acceleration. The actual criteria will depend on the specific situation.
Phase time value determination
In practical applications, for gears that have not yet been developed with absolute value criteria, statistical measurements can be made using the data from the field measurements to determine appropriate relative criteria. The use of such criteria is called relative value determination.
The relative judgment standard requires that the amplitude measured at different points in the same part of the gearbox be compared with the amplitude in the normal state, and when the measured value reaches a certain level compared with the normal value, it is determined to be a certain state. For example, when the relative value judgment standard stipulates that the actual value reaches 1.6 to 2 times of the normal value, attention should be paid, and when it is 2.56 to 4 times, it indicates danger. As for the specific use, the classification is performed according to 1.6 times or the classification according to 2 times, depending on the use requirements of the gear box, and the relatively coarse equipment (for example, mining machinery) generally uses a higher classification.
In practice, in order to achieve the best results, the above two methods can be used simultaneously for comparison and comparison.
China's gear industry has developed rapidly during the 10th Five-Year Plan period: 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%, which has become the largest of China's mechanical basic components. Industry. In terms of market demand and production scale, China's gear industry has surpassed Italy in the global ranking, ranking fourth in the world.
manufacturer:
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 is unique, its market share is 60%; industrial gear is composed of industrial general, special, special gears, its market share is 18%, 12%, 8%; gear equipment only accounts for 2% of the market share .
Lubrication features:
The movement of a pair of reducer gears is achieved by a pair of tooth surface engagement movements. The relative motion of a pair of split tooth surfaces involves rolling and sliding. For gears that transmit power, the force of the gears should be studied. Deformation. Knowledge of applied mechanics is required. There is lubrication between the two tooth faces of the gear, and it also involves the knowledge of fluid mechanics. If you study the surface film generated by the interaction between the belt and the gear surface, you need physical and chemical knowledge. Therefore, in the presence of lubricants, the existence of lubricants must be considered in order to truly and comprehensively reflect the kinematics and dynamics of gear drives. The gear design of the man-made lubricant is a more comprehensive and complete gear design.
Failure form:
1, tooth surface wear
For open gear transmission or closed gear transmission with unclean lubricating oil, due to the relative sliding between the meshing flank surfaces, some hard abrasive grains enter the friction surface, so that the tooth profile changes and the backlash increases. As a result, the gear is excessively thinned and the teeth are broken. Under normal circumstances, only when the abrasive particles are mixed in the lubricating oil, the wear of the tooth surface will be caused during the operation.
2, tooth surface glue
For high-speed and heavy-duty gear transmission, the friction between the tooth surfaces is large and the relative speed is large, which causes the temperature in the meshing zone to be too high. Once the lubrication conditions are poor, the oil film between the tooth surfaces will disappear, making the metal of the two teeth. The surfaces are in direct contact and thus bond to each other. When the two tooth surfaces continue to move relative to each other, the harder tooth surface tears a part of the material on the softer tooth surface in the sliding direction to form a groove.
3, fatigue pitting
When the intermeshing two teeth contact, the force and reaction force between the tooth surfaces cause contact stress on the two working surfaces. Since the position of the meshing point is changed and the gear is made to perform periodic motion, the contact stress is According to the pulsation cycle. Under the action of such alternating contact stress for a long time, a small crack will appear at the tooth mark of the tooth surface. With the passage of time, the crack gradually expands in the lateral direction of the surface layer, and the crack forms a ring shape, so that the wheel The surface of the tooth produces a slight area of spalling to form some fatigue shallow pits.
4, tooth broken
Gears that are subjected to load during operation, like cantilever beams, whose roots are subjected to periodic stresses of the pulse that exceed the fatigue limit of the gear material, will crack at the root and gradually expand, and will occur when the remaining part cannot withstand the transmission load. Broken teeth. Gears may cause broken teeth due to severe impact, eccentric load and uneven material in the work.
5, tooth surface plastic deformation
Under impact load or heavy load, the tooth surface is prone to local plastic deformation, which deforms the curved surface of the involute tooth profile.
Processing methods:
There are two types of involute gear processing methods, one is the profiling method, and the gear groove of the gear is milled out by the forming cutter, which is “imitation shape”. The other is Fan Chengfa (Exhibition Method).
(1) Hobbing machine hobbing: It can process helical teeth below 8 modules
(2) Milling machine milling: can process straight rack
(3) Inserting teeth: can process internal teeth
(4) Cold punching machine: can be processed without debris
(5) planing machine planing teeth: can process 16 modulus large gears
(6) Precision casting teeth: can process cheap pinions in large quantities
(7) Grinding machine grinding gear: can process the gear on the precision machine
(8) Die casting machine casting teeth: most processing non-ferrous metal gears
(9) Shaving machine: It is a metal cutting machine for gear finishing
Use application:
Plastic gear
With the development of science, gears have gradually changed from metal gears to plastic gears. Because plastic gears are more lubricious and wear resistant. It can reduce noise, reduce costs and reduce friction.
Commonly used plastic gear materials are: PVC, POM, PTFE, PA, nylon, PEEK and so on.
Car gear
China's medium and heavy-duty trucks use more steel grades for gears, mainly to meet the requirements of introducing advanced foreign automotive technology at that time. In the 1950s, China introduced the production technology of the Soviet medium-sized truck (the original model of the "liberation" brand) from the former Soviet Union's Rikhov Automobile Factory. At the same time, it also introduced the 20CrMnTi steel 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 rapid development of China's transportation, from the 1980s, China has systematically introduced various advanced models of industrial developed countries, all kinds of foreign advanced medium and heavy loads. Cars are also being introduced. At the same time, China's big automobile factory cooperates 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 steel smelting technology level is also constantly improving, using steel smelting secondary smelting and composition fine-tuning and continuous casting and rolling and other advanced smelting technology, enabling steel mills to produce high-purity, hardenable performance with narrowed gears The use of steel, thus achieving the localization of the introduction of automotive gear steel, so that China's gear steel production level has reached a new level. The high-hardenability steel containing nickel for domestic heavy-duty automobile gears suitable for China's national conditions has also been applied and achieved good results. The heat treatment technology of automobile gears has also evolved from the well-type gas carburizing protection in the original 50s-60s to the current widespread use of computer-controlled continuous gas carburizing automatic lines and box-type multi-purpose furnaces and automatic production lines (including low pressure (vacuum) carburizing). Technology), gear carburizing pre-oxidation treatment technology, gear quenching control cooling technology (due to the use of special quenching oil and quenching cooling technology), gear forging blank isothermal normalizing technology. The adoption of these technologies not only makes the gear carburizing and quenching distortion become effective control, the gear processing precision is improved, the service life is prolonged, but also meets the mass production requirements of modern heat treatment of gears.
Chromium manganese titanium steel and boron steel
For a long time, the most common steel used in China's truck gears is 20CrMnTi. This is a medium-sized automobile gear 18XTr steel (ie 20CrMnTi steel) imported from the former Soviet Union in the 1950s. The steel grain is fine, the grain growth tends to be small when carburizing, and has good carburizing and quenching properties, and can be directly quenched after carburizing. According to the literature, before 1980, China's carburized alloy structural steel (including 20CrbinTi steel) only guaranteed the chemical composition of steel and the mechanical properties measured by samples when it was shipped from the factory, but chemical composition and mechanical properties often appeared in automobile production. Qualified steel, due to excessive fluctuation range of hardenability, affects product quality. For example, if the hardenability of 20CrMnTi carburized steel is too low, the hardness of the core after the carburized and quenched is lower than the value specified in the technical conditions. When the fatigue test is performed, the fatigue life of the gear is reduced by half; if the hardenability is over If the gear is high, the shrinkage of the inner hole after the carburizing and quenching is too large, which affects the gear assembly.
Since the hardenability of steel has extremely significant influence on the hardness and distortion of the heart of the gear teeth, in 1985 the Ministry of Metallurgy promulgated the technical conditions for ensuring hardenable structural steel in China (GB5216-85), which was included in this technical condition. The chemical composition and hardenability data of 10 kinds of carburized steel including 20CxMnTiH and 20MnVBH steel. The standard stipulates that the hardenability performance index of 20CrMnTi steel used for manufacturing gears is 30-42HRC from the water-cooled end 9 coffee. After that, the problem that the hardness of the tooth core portion of the 20CrMnTi steel production gear is too low and the distortion is excessively large has been basically solved. However, it is obviously unreasonable to use the same steel No. 20CrMnTi steel regardless of the gear module size and the steel section thickness. Due to the improvement of the level of steel smelting technology in China and the improvement of the supply of alloy structural steel, there are conditions to further narrow the hardenability performance of gear steel and develop according to the requirements of different products (such as transmission gears and rear axle gears). New steel grades meet their requirements.
Domestic heavy-duty vehicle gear steel
China's gear steel basically meets the requirements of national demand and localization of imported technology, while heavy-duty vehicle transmission gears and rear axle gear steels for medium and heavy-duty vehicles have yet to be developed and produced. According to the analysis of the current state of use of heavy-duty vehicles in China, the two problems of overloading and poor road conditions are more serious and cannot be overcome in the short term, which makes the gears often subject to large overload shock loads. The overload shock load is between the fatigue and the fracture stress, which has a great influence on the gear life and often causes the gear to fail early.
In order to improve the service life of the power transmission gear and reduce its size, in addition to improvements in materials, heat treatment and structure, the arc-toothed gear has been developed. In 1907, the British FRANK HUMPHRIS first published a circular tooth profile. In 1926, the Eritrean EHREST WILDHABER obtained the patent right of the circular arc-toothed helical gear. In 1955, the Soviet Union’s M. L. NOVIKOV completed the practical study of the arc-toothed gear and won the Lenin medal. In 1970, R.H., ROHCE, UK engineer R. M. STUDER has obtained a US patent for double arc gears. Such gears are now increasingly valued and have shown significant benefits in production.
Gears are toothed mechanical parts that can mesh with each other and are used in a wide range of applications in mechanical transmission and in the entire mechanical field. Modern gear technology has reached: gear module 0.004 ~ 100 mm; gear diameter from 1 mm to 150 m; transmission power up to 100,000 kW; speed up to hundreds of thousands of rev / min; the highest peripheral speed of 300 m / second.
With the development of production, the smoothness of gear operation has been taken seriously. In 1674, the Danish astronomer Romer first proposed the use of the outer cycloid as a tooth profile curve to obtain a smooth running gear.
During the industrial revolution of the 18th century, gear technology was developed at a high speed, and people have carried out extensive research on gears. In 1733, the French mathematician Kami published the basic law of tooth profile engagement; in 1765, the Swiss mathematician Euler suggested using the involute curve as the tooth profile curve.
The hobbing machine and gear shaping machine that appeared in the 19th century solved a lot of problems in producing high-precision gears. In 1900, Pffort installed a differential gear for the gear hobbing machine, which can machine the helical gear on the gear hobbing machine. Since then, the hobbing gear of the gear hobbing machine has been popularized, and the processing gear has become the overwhelming advantage. The involute gear has become the most widely used gear. .
In 1899, Rashe first implemented the solution of the displacement gear. The displacement gear not only avoids the root cutting, but also can match the center distance and improve the bearing capacity of the gear. In 1923, the United States Wilder Haber first proposed the gear with a circular tooth profile. In 1955, Sunovikov conducted an in-depth study on the circular arc gear, and the arc gear was applied to the production. The gears have high load carrying capacity and efficiency, but they are not as easy to manufacture as involute gears, and further improvements are needed.
