There are three ways to improve the bearing capacity of gears, namely, ① improving the structure of reducer, such as adopting planetary transmission reducer, etc.; ② improving the tooth profile, such as adopting modified tooth and arc tooth profile, etc.; ③ improving the strength of gears, such as improving the material and heat treatment of gears, so as to improve the allowable stress value of gears.
A lot of research work has been done in these three aspects at home and abroad, and continuous innovation has promoted the continuous development of gear bearing capacity. Among the three ways mentioned above, the potential of improving gear strength is the biggest, and the effect is also remarkable, and the research and development in this field is also fast.
Large low-speed and heavy-duty gears are bulky and have less batch production, so it is difficult to carry out experimental research, which is slower than the development of small gears such as automobiles and machine tools.
In the 1950s, hard tooth face gears were widely used in automobiles and machine tools, while soft tooth face gears were mostly used in low-speed and heavy-duty large gears. In the late 1950s, with the improvement of cutting ability of cutting tools and the guarantee ofaccuracy, medium hardness gears were developed, and the tooth surface hardness was increased from hb260 to hb340-360. The bearing capacity is increased by 30%. In the early 1960s, after solving the chemical heat treatment, gear grinding process and hobbing process of high hard tooth surface of large gear, the low-speed and heavy-duty large gear with hard tooth surface appeared, the bearing capacity was more than doubled, and the volume and weight of reducer were reduced. Since the early 1970s, the United States and Japan have adopted the advanced technologies of heavy-duty gear grinding, carbide hobbing and carburizing heat treatment.
With the continuous development of heavy mining machinery manufacturing level in our country, we have mastered the manufacturing technology of soft tooth face gear since the 1960s, and also conducted a lot of research work on hard tooth face gear, and achieved certain results in reducer structure and tooth shape. People pay more and more attention to the selection of gear materials and the reform and improvement of heat treatment technology. The hardness of a single-stage transmission gear reducer for an ordinary rolling mill which transmits 10000 horsepower torque is increased from hb260 to HRC60 after carburizing and quenching. The original weight is reduced from 91t to 45t, and the average service life is increased from 3-5 years to 10-15 years. It can be seen that the material and heat treatment of large low-speed and heavy-duty gears can bring great economic benefits.