Double arc gear in scraper conveyor

Double Arc Gear in Scraper Conveyor 

Design Process and New Design Improvement of New Reducer for Coal Mine Scraper Conveyor

1 Introduction Double arc gear transmission has the characteristics of large bearing capacity and long service life. In the case of the same load and the same processing technology, the size and weight of the double arc gear transmission can be reduced compared with the involute gear transmission, and the service life is extended. The bearing capacity is more than double that of the involute gear transmission under the same conditions. And the processing cost is low, which can create greater economic benefits, and is an important means for solving the high-speed and heavy-duty gear transmission in China's transmission industry.
However, the soft-toothed and medium-hard-toothed double-arc gears have not been adapted to the requirements of certain high-performance transmissions. In the coal mine mechanical transmissions with heavy impact and heavy load, other engineering machinery, such as mines and petroleum machinery, are also facing extended use. An urgent problem with life. With the advent of new processing technologies such as boring, grinding and scraping, the processing of hard-toothed double-arc gears has matured, and its application is an inevitable trend.
At present, most of the various speed reducers used in China's coal industry are designed for analog products of previous Soviet products. The structure has many unreasonable features, large volume and short life. In order to promote the development of China's coal industry and improve economic efficiency, we have designed a new type of cone-column three-stage reducer for coal mine scraper conveyor, which is used to replace the cone-column three of the widely used involute gear transmission in coal mines. Stage reducer. In order to reduce the volume, reduce the cost, and improve the transmission quality and service life of the reducer, according to China's national conditions, we choose the double arc tooth shape as the new transmission tooth shape instead of the involute tooth shape. Considering the application promotion, we have selected the reducer of the SGW150 scraper conveyor widely used in current large and medium-sized coal mines as the replacement design object.
2 Toothed design The shape of the double circular arc gear is composed of four arcs. The center position and arc radius of the four arcs can be flexibly designed. In this way, in practical applications, the tooth profile of the double circular arc gear that meets the application requirements can be designed for specific application conditions.
The reducer used in the coal mine is poorly lubricated due to its poor working conditions. The unit is required to use hard-toothed gear transmission to increase its wear resistance. GB1275991 (type double arc gear transmission widely used in China, its full tooth height coefficient is 2 after heat treatment, so it is suitable for gear transmission without soft tooth surface or medium hard tooth surface without tooth finishing. The load carrying capacity is close to the hard toothed involute gear drive.
According to the requirements of the use of coal mines, the new reducer we designed is a hard-toothed double-arc gear transmission. When selecting the tooth shape, the analysis is carried out from the aspects of strength, anti-wear and elastohydrodynamic lubrication. After analysis and verification by various schemes, the FSH-73 short-tooth double-arc tooth profile and FSPH-79 type proposed by Professor Shao Jiahui are used respectively. Ultra-short-tooth hard-toothed double-arc tooth profile as the tooth profile of the cone and spur gear. The full tooth height coefficient of the FSPH-79 ultra-short-tooth hard-toothed double-arc gear is only 1.45, the tooth height is low, the tooth root is thick, and the tooth deformation after heat treatment is small, which is beneficial to the normal contact of the gear teeth.
This type of gear can be used directly after heat treatment by simply grinding and running (no grinding, no scraping). Its service life on a rolling mill gear base of a metallurgical plant has exceeded ten times that of the involute gear. In the design of the spiral bevel gear, since the spiral bevel gear adopts the contour tooth, considering the tooth height and the tooth thickness of the big end and the small end should have a reasonable ratio, the FSH-73 type with a full tooth height coefficient of 1.8 is adopted. Short tooth double arc tooth shape. The tooth shape has been tested in the operation of the spiral bevel gear. I have proved that the performance of this tooth shape is good, and the transmission strength of the spiral bevel gear can be guaranteed.
3 Gear parameter design The transmission ratio of the original reducer of SGW-150 scraper conveyor is 24.4376. In order to make the design of the new reducer not affect the working performance of the matching scraper conveyor, the gear ratio of the newly designed reducer is required. 24.4376±1% due to the bearing capacity of the reducer bearing, the center distance requirement is a2>230mm, a3> design life requirements pass the 1500h bench test (the same involute gear reducer design life requirements pass 1 000h The bench test), the volume requirement is not greater than the original reducer. The gear parameters of the original reducer are shown in Table 1. Table 1 The original SGW-150 reducer parameter desert number m/mm tooth number center distance / mm helix angle eight °) tooth width / mm first level second level third level according to the above A preferred design of the gear parameters is required. In order to ensure the service life of the gear transmission pair and reduce the volume of the reducer, first reduce the modulus. After repeated calculations, the midpoint normal modulus of the bevel gear is determined to be m=6. The normal modulus of the second and third helical gears is m=6 and m=8, respectively. The stage is changed from a spur gear to a helical gear, so the number of teeth, the helix angle and the center distance must be changed. The original first-stage bevel gear is a weak link, so we keep the number of teeth and the helix angle of the first stage unchanged, and the mid-point pitch and tooth width have a slight change, so that the first-stage bevel gear has higher strength.
In order to reduce the size to a minimum, the center distances of the second and third stages are respectively the required lower limit, that is, a2=230mm, a3=260, and the test is repeated according to the requirements of the modulus, the center distance and the transmission ratio. After the calculation, two options for the helix angle are proposed. The first scheme, that is, the high-speed P2 = 17.7791°, and the low-speed heart = 17.745. According to this scheme, the tooth width is small, so that the total volume can be reduced, but the final stage is the axis. The force is greater. In order to improve the bearing life, we chose the second option, that is, the high speed level is unchanged, the port 2 = 17.7919, the low speed stage takes 3 = 14.25. According to this scheme, the axial force of the final stage is reduced by 20%, but the low speed gear The width is increased. When the helix angle scheme is selected, two options of tooth width are selected. The first scheme has wider teeth, but ensures at least three points of contact, and the stress is small, which is beneficial to the formation of lubricating oil film, and the safety factor is 2 or more; the second scheme, the gear teeth are narrower, ensuring a minimum of two points of contact, which can reduce the volume of the reducer, but the stress is large, and the safety factor is less than 2. After careful consideration, it was decided to adopt the first scheme at the low speed level and the second scheme at the high speed level, so that the safety factor of the two-stage spur gears was all above 2. The final selected gear parameters are shown in Table 2. Table 2 The parameters of the new SGW-150 reducer The modulus of the number of teeth center distance / mm helix angle of eight °) tooth width / mm first level second level third level = 24.35033, than the original The transmission ratio of 24.4376 is reduced by 0.357% to meet the design requirements.
In the design, we start from the working characteristics of coal mine machinery, taking into account that the bending strength of coal mine reducer is the first requirement to ensure the second is the wear resistance and contact strength. Through the strength check calculation of the above parameters, we can see that the contact and bending strength of the double arc gear pair we designed are greatly improved. Table 3 compares the safety factors of the two deceleration tables 3 - A comparison table of the safety factors of the contact and bending strength of the second-stage third-stage involute gear contact curved double-arc gear contact bender. As can be seen from Table 3, the new design solutions have met or exceeded the original design indicators.
4 Improvement of the reducer case Due to the variation of the tooth profile and gear parameters, the structural size of the newly designed reducer case is reduced, and the total volume is reduced by 9% compared with the original design. In addition, from the perspective of lubrication, the reducer is considered. The ventilation and heat dissipation, as well as the viscosity of the lubricating oil used in coal mines at present, make the venting holes better and more compact, so that the air pressure in the tank is reduced, which is beneficial to lubrication and leakage prevention.
In order to facilitate the adjustment of the bearing during installation to ensure the contact area, the bearing installation is improved, which makes it easy for the worker to adjust the bearing to control the contact.
Considering that the leakage of the mine reducer is serious now, the sealing of the shaft seal and the joint surface is improved. First, the axial labyrinth seal at the shaft head is changed to a radial labyrinth seal, which not only reduces leakage but also reduces Reducer housing size. At the joint surface, we changed the sealant with poor sealing effect to 7903 oil-resistant seal grease. This seal grease has good oil resistance and is suitable for static sealing of assembly sealing surface and sliding at low speed and rotating sealing surface. Dynamic sealing, its use is very good.
5 Improvement of heat treatment process Nowadays, the tooth surface of gears of mine reducer is mostly carburized. Although this method is relatively simple, its heat treatment temperature is higher, and the tooth deformation is larger after 920Q heat treatment, while mine deceleration Most of the gears are not ground, so that although the tooth surface is hard, the contact of the gear pair is not good, which affects the transmission quality and service life of the gear pair. In order to reduce the heat treatment deformation and reduce the production cost, we decided to adopt a new heat treatment process - speed carbonitriding; it only takes more than 2 hours to complete the carbonitriding, and the ordinary carbon treatment needs about 8~9 h. The new process has a low heat treatment temperature, and the 780C~840Q can reduce the deformation of the heat treatment, ensure the depth of the hardened layer, and reduce the energy consumption of the process. The hardness of the hardened layer of the test gear is greater than 1.05mm, the hardness is 60HRC~63HRC, the heat treatment deformation is very small, and no grinding or shaving or scraping is required.
6 Test results We jointly designed with the Taiyuan Branch of the Coal Research Institute, the arc gear reducer (materials 30CiMnTi and 20QMnTi) of the 75kW scraper conveyor manufactured by Shanxi Coal Mine Machinery Plant, in accordance with the "Testing Specification for Reducer for Scraper Conveyor" The requirements of MT101 85" were carried out in the type test of the National Scraper Conveyor Quality Supervision, Inspection and Testing Center. After 1500h endurance test, the three pairs of gear pairs and the main parts of the gearbox are all in good condition to help achieve the test requirements of the reducer for the scraper conveyor.
Calculation of geometrical dimensions of angular displacement planetary gears (Furong Mining Bureau Electromechanical Equipment General Factory, Lixian 644501, Sichuan Province) Zhang Zuheng analyzed the correct calculation method.
Planetary gear transmission has the advantages of small size, light weight, large carrying capacity and high efficiency, and is widely used in various industries. Although China has produced standard planetary gear reducers, it still cannot meet the needs of actual use, and sometimes it is necessary to design according to actual conditions. The design of the planetary gear transmission includes a number of items, in which the calculation of the geometry of the part is essential. In the process of designing and mapping planetary gear transmissions, we often find that there are several methods for calculating the geometrical dimensions of the planetary gears in the angular displacement planetary gear transmission, but the results are different.
The 641 page example is an example. The calculation process is as follows: I know the NGW planetary transmission (for example), the modulus m=4 the number of the central gear teeth za=33, the number of internal ring gear teeth zb=85, the actual center distance a=103mm, try to calculate the planet Wheel geometry.
The calculation of the geometric parameters and dimensions of the 1A-C transmission planetary gears is the displacement of the center distance as the meshing angle NGW. The total displacement coefficient of the planetary transmission diagram is in the manual 111, which is beneficial to improve the gears. Contact strength and bending strength are available.
During the test, under the rated load, the mechanical efficiency is 0. 945 (forward and reverse) (0.920 for involute gear reducer), and the integrated noise for forward rotation is 89.dB(A), combined noise for reverse rotation. For 90.0dB(A), the balance oil temperature of the test reducer in the reverse operation is 79.7 C, and the equilibrium oil temperature during forward operation is 94.2 ° C. After the 500 h type test, the test is continued, after running 21 (1) h The second stage found a broken tooth and terminated the test. In this way, our double-arc gear reducer has more than doubled its service life when the size is reduced by nearly one-tenth of the size of the same involute gear reducer.
The project has been well received by experts organized by the Ministry of Coal. It is believed that the design and application of hard-tooth short-tooth spiral bevel gears and ultra-short-tooth hard-toothed cylindrical gears have reached the international advanced level.