Current situation and Prospect of induction heat t

2022-08-21
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Current situation and Prospect of induction heat treatment of locomotive gears

after updating the quenching equipment with high control accuracy and high automation, the production quality and efficiency of locomotive gears are expected to be further improved. When the dual frequency quenching equipment is popularized, it is necessary to complete the verification of Metro and urban rail locomotive gears. The industry association can strive for project approval and organize relevant units to improve the basic research work of locomotive induction gear, such as the measurement of stress distribution and fatigue strength of hardened layer

the application of induction heating technology in domestic locomotive industry originated in the 1960s. Induction hardened gears for locomotives generally require a hardened layer of 2~4mm deep, and China is a big textile country with 52~60hrc. After 40 years of development, induction hardened locomotive gears are widely used in passenger and freight locomotives (DF, SS series, etc.) below 200km/h, urban light rail and subway locomotives, and are used to replace imported locomotive gears

I. current situation of induction heat treatment of locomotive gears

1 Technical status

all domestic manufacturers adopt the medium frequency oil embedding quenching process along the tooth profile. From the 1970s to the mid-1990s, domestic locomotive induction gear manufacturers have experienced the stages of quenching process exploration, batch production of domestic locomotive gears below 120km/h, localization of imported locomotive gears, and the process has gradually stabilized. Since the mid-1990s, with the rapid development of the railway industry, the locomotive running speed and traction tonnage have increased year by year, and the failure rate of the induction gear during its service life has gradually increased, which is highlighted by the fact that the two ends of the gear are not hardened within the full tooth width, and bending fatigue cracks occur during use. After research and exploration in recent years, the relevant manufacturers have achieved hardening within the full tooth width of the gear after adopting new processes

the service speed of induction gears for locomotives has been increased from 80~100km/h to 140~160km/h, and the service life has been increased from 400000 km in the initial stage to more than 1million km

2. Equipment status

(1) at present, the equipment level of machine tools of domestic manufacturers is uneven. The first generation hydraulic lifting, infinite position, quenching transformer semi submersible machine tools, the first and fifth generation hydraulic lifting, finite position, PLC controlled machine tools, and the second generation screw stepping motor lifting and semi CNC controlled machine tools coexist. The first generation machine tools are still dominant. Because the first generation machine tools still use the design of the late 1960s, the positioning accuracy and stability are poor, which can no longer meet the requirements of gear generation. Therefore, it also determines that the single arm type can meet the requirements of production, and must be updated; At present, there is only one second-generation quenching machine tool, which was put into use in 2004 and basically meets the production requirements, but it still fails to reach the technical level of the general quenching machine tool of the same period in terms of technical level

(2) the mechanical medium frequency generator (set) is still used for power quenching power supply. A few manufacturers have tried the domestic thyristor medium frequency power supply, but it has not been popularized due to poor reliability. The third generation all solid state IGBT medium frequency power supply has not been used in the domestic locomotive gear induction heat treatment industry

II. Problems in induction heat treatment of locomotive gears

1 Basic research is seriously insufficient

(1) the design theory of using gears with a speed of less than 160km/h has a lot of reserves, while whether induction gears can be used for locomotives with a speed of more than 160km/h is still in a blank stage in theory

(2) the induction gear has not been demonstrated by physical contact and bending fatigue strength tests, so that the service life of the gear cannot be accurately estimated

(3) the stress distribution in the hardened layer of induction gear has not been studied in depth

(4) dual frequency quenching of induction gears of urban rail and Metro locomotives with modulus less than 6mm is the development trend, but dual frequency quenching is still in the research stage. Designers have many blind spots in the application scope and service life of dual frequency quenched gears, and failed to carry out the physical test verification of dual frequency quenched gears on the test bench

2. Equipment aging

(1) induction hardening machine tools of domestic locomotive gear manufacturers are generally aging, and CNC numerical control, screw rod servo motor precise running, real-time monitoring and other technologies are not adopted. However, many domestic induction equipment manufacturers' gear quenching machine tools are still at the technical level of 10 years ago

(2) the medium frequency power supply is still a machine type medium frequency generator (set), while the full solid-state IGBT medium frequency power supply has not been successfully used in the railway industry

(3) heavy heat and light cold, ignoring the influence of cooling medium on quenching quality. Now domestic locomotive induction gear manufacturers still talk about the global requirements on the moral dimension of energy use in recent years. New energy vehicles require new development of lithium batteries. Oil is the main quenching medium, and the hardness distribution of gear tooth surface is not ideal

(4) the coordination between cold and hot machining of gears is not enough, and the influence of machining items such as chamfer size, shape, tooth root roughness and tooth root arc shape on induction heating and final quality is ignored

III. prospect of induction heat treatment of locomotive gears

(1) after updating the quenching equipment with high control accuracy and high automation, the production quality and efficiency of locomotive gears are expected to be further improved

(2) when the dual frequency quenching equipment is popularized, it is necessary to complete the verification of Metro and urban rail locomotive gears

(3) the industry association can strive for project approval and organize relevant units to improve the basic research work of locomotive induction gear, such as the measurement of stress distribution and fatigue strength of hardened layer

mechanical workers (end)

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