Low speed and heavy load gear transmission system is widely used in every lifeline of national economy, such as gantry crane and mining excavator in energy field, wind power gearbox in electric power industry, blast furnace airtight box and converter tilting mechanism in metallurgical field. In order to transmit heavy load, gears generally work at very low speed. Take the tilting mechanism of converter as an example: the dead weight of converter is 750-800 t in no-load condition, the weight of converter is 1000 t in working condition, and the working speed of trunnion bearing on both sides of supporting ring is only about 1 rpm. In this extreme condition, the gear is prone to fatigue microcracks, which lead to crack propagation and fracture, causing casualties and economic losses. Therefore, it is more and more important to study gear failure and fault detection.
Low speed and heavy load transmission equipment is the “key” of enterprises, especially for the process manufacturing industry. For example, once the smelting equipment such as blast furnace airtight box and converter tilting mechanism is shut down, in addition to the direct loss of equipment failure, it will also disrupt the production rhythm of downstream enterprises, and the loss is immeasurable. An air tight box at the top of a blast furnace in a steel plant broke down and the blast furnace was shut down for 5 days, resulting in an economic loss of more than 30 million yuan; A gear fracture accident occurred in the gear box of the secondary input shaft reducer on the north side of the No.3 converter in a steel-making plant. The converter was out of control and the molten steel overflowed, resulting in the burning of two slag tank cars and part of the rails, with a direct economic loss of more than 10 million yuan; The No.2 converter in No.1 Steelmaking Plant of an iron and steel group had a major failure of trunnion bearing ball rupture and gear box tooth beating, and was forced to shut down for 81 hours.
Most of the faults of transmission system are caused by the failure of gears. The failure forms of gears are various, such as tooth fracture, tooth surface pitting, tooth surface scuffing, tooth surface abrasive wear and plastic deformation. In particular, it should be pointed out that the fracture of gear teeth is often caused by the fracture of a gear tooth, which leads to the mutual meshing dislocation of gears, and even the phenomenon of jamming. There are many reasons for gear tooth fracture, generally divided into overload fracture and fatigue fracture from the fracture mechanism. In order to avoid overload fracture, it is necessary to design, manufacture and use the gear reasonably according to the actual working conditions of the gear, and introduce overload protection device into the transmission system when necessary. The fatigue fracture of gear teeth can be improved by controlling gear stress, reasonably selecting root fillet radius, polishing and shot peening, and reducing harmful residual stress Due to the influence of material defects and heat treatment, fatigue cracks often appear in gear teeth, forming fatigue sources. Under the action of long-term alternating stress, it will cause crack propagation, and finally lead to rapid crack propagation and fracture, causing accidents and losses.
Due to the special requirements of steel-making process, the tilting mechanism of converter starts and stops frequently, and the molten steel is poured regularly, so the equipment has to bear huge impact load. The production site of converter is shown in Figure 1. This paper takes a pair of heavy-duty gears in the secondary reducer of converter tilting mechanism in a steel plant as the research object, as shown in Fig. 2. In order to understand the changes of various working indexes of the gear teeth after the fatigue crack of the low-speed heavy-duty gear, the optimization design and anti fracture design of the gear structure are carried out, so as to improve the stability of transmission and prolong the service life of the gear, To ensure the safe operation of the machine, it is necessary to study the tooth fracture phenomenon. Therefore, it is of great significance to study the dynamic characteristics of cracked gears, as well as the stress field and propagation path in crack propagation.