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XingHua donghua gear co., LTD

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Analysis and Prospect of China's Gear Development Trend

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[Abstract]:
Internationally, the power transmission gear unit is developing along the direction of miniaturization, high speed and standardization.
Internationally, the power transmission gear unit is developing along the direction of miniaturization, high speed and standardization. The application of special gears, the development of planetary gears, the development of low-vibration, low-noise gears are some of the characteristics of gear design. In order to achieve the purpose of miniaturization of the gear device, the load bearing thrust of the existing involute gear can be improved. Hard tooth surface technology is widely used in various countries to increase the hardness to reduce the size of the device; special tooth shapes represented by circular gears can also be applied. The main drive system of the ship-borne helicopter developed by the UK and France adopts a circular arc gear, which greatly reduces the height of the reducer. With the trend of replacing the power of ships with medium-speed diesel engines, the use of high-power planetary gears on large ships has been effective; nowadays, in large-scale transmissions such as metallurgy, mining and cement mills, planetary gears are small in size and good in coaxiality. The advantages of high efficiency and more and more applications.
 
Due to the large-scale development of mechanical equipment, the working parameters of the gears have been improved. For example, the transmission power of high-speed gears is 1000-30000kw. The peripheral speed of the gear is 20~200m/s (1200-12000r/min), and the design working life is 5X104-10X104 hours; the circumferential speed of the rolling mill gear has been increased from several meters per second to 20m/s, even 30~50m/s. Passing the twisting torch up to l00~200t.m, the service life is required to be 20~30 years. The accuracy of these gears is generally in the order of 3 to 8. It has high requirements for stationarity and noise. For high speed gears (including turbo mechanical gears). When the peripheral speed exceeds 100 m/s, it is required to correct the thermal deformation generated at the beginning of the design due to the thermal effect in operation, so that the gear reaches a normal meshing state during operation. Especially for high speed heavy duty gears. More to be considered. Secondly, for low-speed heavy-duty gears such as rolling mill gears, the elastic deformation of the entire gear unit system becomes prominent due to the increase in the tooth surface load factor of the hard-toothed gears, so it is sometimes reflected to the tooth surface. The elastic deformation is corrected. This technique of shaping the gear teeth is an important trend in the manufacture of high-power, high-speed, heavy-duty gears. In the aspect of gear manufacturing technology. The focus is on hard tooth surface machining, especially the development of cutting and heat treatment processes for large hard toothed gears, such as super hard cutting teeth, rolling internal teeth, forming grinding teeth, large modulus gear teeth, elastic grinding wheel polishing, gear tooth repair New processes such as shape and deep sand carbon are being continuously tested and applied in production.
 
The development of the gear manufacturing process is largely reflected in the improvement of the accuracy level and production efficiency. Since the 1970s, the manufacturing precision of various gears has generally increased by about one level. Some even have 2 to 3 levels. Generally, the accuracy of low-speed gears has been improved from the past 8-9 to 7-8. Machine gears are increased from 6 to 8 to 4 to 6. The rolling mill gear is increased from 7 to 8 to 5 to 6.
 
For small and medium-sized gears with small modulus, due to the development of high-performance gear hobbing machines and the improvement of tool materials, the hobbing efficiency has been significantly improved. With a multi-head hob, the cutting speed is 90m/s under large feed conditions. If the super-harded hob is used to process the quenched and tempered steel gear with a modulus of about 3, the cutting can be over 200m/s. To improve the efficiency of the gear insertion, it is limited by the reciprocating mechanism of the gear shaping machine. Recently, the development of tool unloading, the use of hydrostatic bearings, and the new structure such as the rigidity of the tool post and the column have been improved, and the efficiency has been significantly improved. The new gear shaping machine can reach 2000 strokes per minute.
 
Due to the wide application of hardened gears and the increasing number of gears required for high speed and high performance, the grinding of teeth is required, and the efficiency and quality must be improved. Generally speaking. It is more common to use the method of grinding. The forming method has less grinding teeth. The MAAG grinding method has high precision but low efficiency. Not suitable for heavy grinding. The single-grinding gear grinding machine produced by Niles and Hofler has good rigidity and reliability, and is suitable for large feed processing with high efficiency. In recent years, in order to improve efficiency, the grinding method has also been improved, such as reducing the number of grinding times, compressing the length of the formation, and shortening the tailing stroke; for this reason, the "K" one grinding method proposed by MAAG and the "double-sided" proposed by Niles The grinding method "increased the actual grinding efficiency. At present, for the grinding of medium and small gears in batches, the worm wheel grinding machine is preferred, and the grinding efficiency is very high. For the grinding of large modulus gears, in addition to the grinding of single grinding wheels that can be reground, The forming pattern cutting method is adopted. It is also an effective way to efficiently grind.
In addition, there are some new methods, such as the G-TRACNo765 orbital gear cutting machine developed by Gleason Corporation of the United States, which can process 88 gears per hour, which is 3 to 4 times higher than that of ordinary gear hobbing machines. Double cutter high efficiency cutting process. Cutting speed up to 137m / s, rough, finishing a helical gear with m = 1.5mm, outer diameter of 24.43mm, tooth width of 19mm, only 6 seconds, the efficiency is 5 to 10 times the tooth. The multi-tool head of the American company has a 5 to 10 times higher efficiency than ordinary gears. The cold forming process of the gear industry in the automotive industry, such as cold extrusion and hot rolling, has continued to gain new development.
 
About gear materials and heat treatment. With the development of self-faceted gears, it has gradually gained people's attention.
 
The development trend of gear steel; one is low alloy steel containing Cr, Ni, Mo; the other is boron steel; the third is carbonitriding steel; the fourth is free cutting steel. Due to the lack of Ni and Cr in China, 20CrMnTi carburized steel or boron-containing rare earth steel is commonly used. 18CrMnNiMo carburized steel or medium carbon alloy steel is commonly used in heavy machinery. In the machine tool industry, 40Cr, 38CrMoAl and other steels and high-speed gears are nitrided with 25Cr2MoV steel.
 
Gear heat treatment process generally has four types of carbon infiltration (or carbonitriding), nitriding, induction hardening, quenching and tempering. The current general trend is to improve the hardness of the tooth surface. The bearing capacity of the carburized and quenched gear can be increased by 2~3 times compared with the tempered gear. Table 111# uses gears made by different processing methods. Comparison of center distance, weight and safety factor.
 
Carburized and quenched gears can achieve high surface hardness, wear resistance, toughness and impact resistance, and provide high resistance to pitting and fatigue. The performance of the heart and carburizing layer depends mainly on which heat treatment process is used. For example, when the gear is quenched and tempered to 360HB, the tooth surface contact fatigue limit stress ph. -750N2, such as surface quenching to HRC56-60-, pJ1500N2, such as surface carburizing to the same hardness yi.-1200N2, for quenching and tempering gears. Due to the improvement of gear tool materials. The tooth surface hardness of the pinion has been increased to 360HB, and the large gear has been increased to 280HB or more.
 
Most of the gear carburizing uses gas carburizing. The propane gas generator is used to generate gas and is sent to a carburizing furnace. It is also useful as a liquid injection type carburizing furnace to vaporize the organic liquid in the furnace. This method occupies less land, and the raw materials and processing costs are low: the unstable working time of the furnace is also short, which is conducive to saving energy and cost. Recently developed vacuum carburizing methods, especially for deep carburizing requirements, can further reduce time and reduce distortion.
 
The application of electronic computers in various industrial fields; promoted the development of various technologies. Similarly, the progress in the design and calculation of gears is also very fast. People can use computers to calculate, analyze and compare various possible design methods, and obtain better results through optimization. For example, in the analysis of the tooth surface contact area and the angle between the meshing line and the relative speed, a program is prepared for the calculation of the elastohydrodynamic lubrication and the calculation of the geometric parameters. Also, there are programs in the calculation of gear shaping and calculation of gear bearing capacity. China has compiled the program software for GB3480-83 involute cylindrical gear bearing capacity calculation standard for production applications. In gear machining, the entire cutting process can be controlled by a computer. Make the manufacturing quality stable and reliable. At present, the domestic research and application of microcomputer to calculate the cutting gear adjustment card of the spiral bevel gear can adjust the processing deviation in time. The tooth surface contact is brought to a desired position, and the work efficiency is greatly improved. In addition, according to the principle of numerical control, the application of a microcomputer to parabolic shape modification of the toroidal worm helical tooth surface has been applied to production. Although this work is still in its infancy in China, it is of great significance to improve the quality and technical level of gear manufacturing.