1 From the application promotion, we chose the reducer of SGW-150 scraper conveyor widely used in current large and medium-sized coal mines as the design object of replacement.
2 tooth shape design According to the use requirements of coal mines, we designed a new type of reducer drive. 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 FSPH-79 ultra-short-tooth hard-toothed double-arc gear has a full tooth height coefficient of only 1.45, low tooth height, thick root and small deformation of the tooth after heat treatment, 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 profile has been tested in the operation of the spiral bevel gear. The test proves that the tooth profile has good performance and can guarantee the transmission strength of the spiral bevel gear.
3 gear parameter design reduces the volume of the reducer, first reduce the modulus. After repeated calculations, it is determined that the midpoint normal modulus of the bevel gear is mn=6, and the normal modulus of the second and third helical gears is mn=6 and mn=8, respectively. The third 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=260mm. According to this scheme, the axial force of the final stage is reduced by 20, but low speed. The tooth width of the stage has 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 total transmission ratio of this design is i=24.35033, which is 0.357 lower than the original transmission ratio of 24.4376, which meets the design requirements.
In the design, we start from the working characteristics of coal mine machinery, taking into account the bending strength of the coal mine reducer is the first requirement to ensure the project, followed by the wear resistance and contact strength. Through the strength check calculation of the above parameters, we can see the double arc safety factor comparison table designed by us.
4 Improvement of the reducer case 5 Improvement of the heat treatment process Now the tooth surface of the gear of the mine reducer is mostly carburized. Although the process is relatively simple, its heat treatment temperature is high, up to 920, heat treatment rear wheel The tooth deformation is large, and most of the gears of the mine reducer are not ground. Thus, 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 heat treatment deformation and reduce production costs, we decided to adopt a new heat treatment process for rapid carbonitriding; it only takes more than 2 hours to complete carbonitriding, while ordinary carbon treatment requires about 89 hours. The new process has a low heat treatment temperature of 780 840, which reduces the deformation of the heat treatment and ensures the depth of the hardened layer while reducing the energy consumption of the process. The hardened layer depth of the test gear is greater than 1.05mm, the hardness is 60HRC63HRC, the heat treatment deformation is small, and no grinding or shaving or scraping is required.
6 Test Results We jointly designed the arc gear reducer (materials 30CrMnTi and 20CrMnTi) of 75kW scraper conveyor manufactured by Shanxi Coal Mine Machinery Factory.
2 tooth shape design According to the use requirements of coal mines, we designed a new type of reducer drive. 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 FSPH-79 ultra-short-tooth hard-toothed double-arc gear has a full tooth height coefficient of only 1.45, low tooth height, thick root and small deformation of the tooth after heat treatment, 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 profile has been tested in the operation of the spiral bevel gear. The test proves that the tooth profile has good performance and can guarantee the transmission strength of the spiral bevel gear.
3 gear parameter design reduces the volume of the reducer, first reduce the modulus. After repeated calculations, it is determined that the midpoint normal modulus of the bevel gear is mn=6, and the normal modulus of the second and third helical gears is mn=6 and mn=8, respectively. The third 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=260mm. According to this scheme, the axial force of the final stage is reduced by 20, but low speed. The tooth width of the stage has 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 total transmission ratio of this design is i=24.35033, which is 0.357 lower than the original transmission ratio of 24.4376, which meets the design requirements.
In the design, we start from the working characteristics of coal mine machinery, taking into account the bending strength of the coal mine reducer is the first requirement to ensure the project, followed by the wear resistance and contact strength. Through the strength check calculation of the above parameters, we can see the double arc safety factor comparison table designed by us.
4 Improvement of the reducer case 5 Improvement of the heat treatment process Now the tooth surface of the gear of the mine reducer is mostly carburized. Although the process is relatively simple, its heat treatment temperature is high, up to 920, heat treatment rear wheel The tooth deformation is large, and most of the gears of the mine reducer are not ground. Thus, 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 heat treatment deformation and reduce production costs, we decided to adopt a new heat treatment process for rapid carbonitriding; it only takes more than 2 hours to complete carbonitriding, while ordinary carbon treatment requires about 89 hours. The new process has a low heat treatment temperature of 780 840, which reduces the deformation of the heat treatment and ensures the depth of the hardened layer while reducing the energy consumption of the process. The hardened layer depth of the test gear is greater than 1.05mm, the hardness is 60HRC63HRC, the heat treatment deformation is small, and no grinding or shaving or scraping is required.
6 Test Results We jointly designed the arc gear reducer (materials 30CrMnTi and 20CrMnTi) of 75kW scraper conveyor manufactured by Shanxi Coal Mine Machinery Factory.
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