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ChangSha lkerui gear machinery CO.,LTD.

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Analysis and Prospect of gear development trend in China

Analysis and Prospect of gear development trend in China

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The application of special gears, the development of planetary gears, the development of low vibration and low noise gears are some characteristics of gear design. In order to achieve the goal of miniaturization of gears, the existing involute teeth can be improved. Wheel bearing thrust. Hard tooth surface technology is widely used in many countries to improve the hardness to reduce the size of the device; special tooth profile represented by circular arc gear can also be applied. The main transmission system of Shipborne helicopter developed by Britain and France adopts circular arc gear, which greatly reduces the height of the reducer. With the trend that marine power is replaced by medium-speed diesel engines, the use of high-power planetary gears on large ships is indeed effective; now in large transmission devices such as metallurgy, mining, cement mill, planetary gears with its advantages of small size, good coaxiality and high efficiency are used more and more.
Because of the development of mechanical equipment, the working parameters of gears have been improved. For example, the transmission power of high-speed gear is 1000-30000kw. The circumferential speed of the gear is 20-200m/s (1200-12000r/min), and the design service life is 5X104-10X104 hours. The circumferential speed of the gear of the rolling mill has been increased from several meters per second to 20m/s, or even 30-50m/s. The torsional torch reaches l00~200t.m and requires a service life of more than 20~30 years. The accuracy of these gears is generally 3~8. It has higher requirements for stationarity and noise. For high speed gears (including turbomachinery gears). When the circumferential velocity exceeds 100m/s, the thermal effect in operation requires that the thermal deformation should be corrected at the beginning of design, so that the gear can reach a normal meshing state at work. Especially for high-speed and heavy loaded gears. More consideration should be given to it. Secondly, for low-speed heavy-duty gears such as rolling mill gears, the elastic deformation of the whole gear system caused by the increase of the load coefficient of the tooth surface becomes prominent after the hard-tooth surface gear is used, so sometimes the elastic deformation reflected to the tooth surface should be corrected. This technology of gear tooth modification is an important trend in the manufacture of high power, high speed and heavy load gears. In gear manufacturing technology, the emphasis is on the development of hard tooth surface machining, especially the cutting and heat treatment processes for large hard tooth surface gears, such as superhard cutting, hobbing, forming grinding, honing of large modulus gears, polishing of elastic grinding wheels, tooth profile modification, and deep sand carbon. And application.
Since the 1970s, the manufacturing accuracy of all kinds of gears has been improved by about one grade, some even by 2-3 grades. The precision of low speed gears has been improved from 8-9 grades to 7-8 grades. The gear of the machine tool is increased from 6~8 to 4~6. The gear of the mill is raised from 7~8 to 5~6.
For small and medium-sized gears with small modulus, the hobbing efficiency has been greatly improved due to the development of high-performance gear hobbing machine and the improvement of tool materials. Using multi head hob, the cutting speed can reach 90m/s under large feed and condition. For example, if the quenched and tempered steel gears with modulus about 3 are machined with superhard hobs, the excessive cutting can reach 200m/s. To improve the gear shaping efficiency, it is restricted by the cutter reciprocating motion mechanism of the gear shaping machine. Recently, new structures such as tool unloading, hydrostatic bearing, and stiffness enhancement of tool holder and column have been developed, resulting in significant improvements in efficiency. The stroke number of the new gear shaper can reach 2000 times / minute.
Because of the wide application of hard face gear and the increasing demands of high speed and high performance, grinding is required to improve the efficiency and quality. Generally speaking. Generation grinding is widely used, while shaping grinding is less. MAAG grinding method has high grinding accuracy but low efficiency. It is not suitable for heavy grinding. Niles and Hofler's single grinding wheel grinding machine has good rigidity, reliable precision, suitable for large feed processing, high efficiency. In recent years, grinding methods have also been improved to improve grinding efficiency, such as reducing grinding times, compressing growth and shortening tailing stroke; therefore, the "K" grinding method proposed by MAAG and the "double-sided grinding method" proposed by Niles have improved the actual grinding efficiency. At present, for batch grinding of medium and small-sized gears, the worm grinding wheel grinding machine is preferred. The grinding efficiency is very high. For grinding large modulus gears, besides single wheel grinding which can be re-grinded, the forming drawing grinding method is adopted. It is also an effective way to efficiently grinding.
In addition, there are some new technological methods, such as the G-TRACNo765 rail type gear cutter developed by Gleason Company of the United States, which can process 88 gears per hour, 3-4 times higher than the ordinary hobbing machine. The cutting speed can reach 137m/s, and a helical gear of m=1.5m m, 24.43m m in diameter and 19 m m in width can be machined roughly and finely. Its efficiency is 5-10 times that of the helical gear in 6 seconds. Cold extrusion, hot rolling and other cutting processes have also been developing continuously.
With regard to gear material and heat treatment, with the development of the self face gear, it has also been gradually taken seriously.
The development trend of gear steel is: low alloy steel containing Cr, Ni and Mo, boron steel, carbonitriding steel and free cutting steel. Due to the lack of Ni and Cr in China, 20CrMnTi carburizing steels are often used or boron containing rare earth steels are used. 18CrMnNiMo infiltration for heavy machinery