Preface

The planetary gear reducer matched with the Spearman mixer reducer was found to be damaged when it was used for more than nine months, which resulted in the failure of its normal use. The reducer model is YNF1110, transmission ratio is 500 and assembly type is V11. The YP250M-4 motor matched before the damage of the reducer works continuously in one direction for 25 K W, 1450 r/min, nominal transmission ratio i=500, 24 hours, ambient temperature is room temperature, and the working medium of the mixer is liquid or semi-liquid. In this paper, the causes of gear shaft damage of reducer are analyzed.

1 Physical and chemical examination

The macroscopic picture of the damaged reducer gear shaft is shown in Figure 1. It can be seen from the figure that the main shaft of the gear shaft has not been obviously damaged, but many teeth on the shaft have been broken. Careful observation of the damaged teeth reveals that the crack initiation zone and the extended radiation zone can be clearly seen on the cross section of all the broken teeth. The crack initiation zone extends from the same side of the teeth to the other side, and the fracture surface extends directly from the crack initiation zone, as shown in Fig. 2a. There is obvious extrusion damage in the upper part of the gear teeth without fracture, as shown in the arrow of Fig. 2b. At the same time, the shape of the gear teeth crushed by extrusion is also observed, as shown by the arrow of 2c, which shows that the gear teeth are subjected to a great deal of external force in the process of using.

2 microstructure

Sampling on the gear teeth and observing the microstructures, the results are shown in Figure 3. There is a layer of penetrating layer on the surface of gear teeth. The penetrating layer depth at the top, the meshing surfaces on both sides and the root of gear teeth are 571, 1102 and 910 microns respectively (see Fig. 3a, 3b and 3c, respectively). The microstructure of the infiltrated layer is fine-needle tempered martensite. The microstructure of the tooth center is acicular tempered martensite, as shown in Fig. 3D.

1.3 hardness test

The hardness of the gear teeth is tested and the results are shown in Table 1.

2, comprehensive analysis

Reducer is a power transmission mechanism, which reduces the number of rotations of motor, internal combustion engine or other high-speed power to the desired number of rotations and obtains a larger torque. Generally, the gears on the input shaft with fewer teeth engage the large gears on the output shaft to achieve the purpose of deceleration. In the process of working, the gears of the reducer generally have to bear large alternating or even impact loads. The contact stress is large and the tooth surface is easy to wear. Therefore, the requirement of the gears is that the surface of the gear shaft is hard and wear-resistant, and the center is strong and tough [1-2]. From the point of view of the gear shaft analyzed in this paper, it is found that after carburizing (nitrogen) treatment, the top, meshing surface and root of the gear have thicker penetrating layer thickness. Hardness test shows that the surface layer has higher hardness and the core hardness is moderate, which meets the technical requirements of the product and meets the application conditions of the gear.

However, the macro analysis shows that the crack initiation zones of all fracture teeth are on the same side of the teeth, and all of them extend directly from the crack initiation zones to the other side to form extended fracture. At the same time, there are obvious extrusion damage or even crushing in the upper part of the gear teeth, which indicates that the gear teeth are subjected to a great deal of external force in the use process. It is concluded that the damage of the gear belongs to pure mechanical overload damage. In actual production, the type of reducer should be determined according to the transmission ratio and use requirements, the specifications should be determined according to the mechanical strength, and the allowable thermal power should be checked. The calculated power of the reducer can be calculated by the following formula.

According to the actual working parameters of the reducer analyzed in this paper and looking up the table, the calculated power of the mixer when the working medium is liquid or semi-liquid is 82.5 kW and 99 kW, respectively. The YNF1110-500 reducer can not meet the strength requirements of the mixer. Improper selection is the main cause of pure mechanical overload damage of the reducer gear shaft.

Concluding remarks

The microstructures, penetration depth and hardness of the gear shaft all meet the design requirements. The damage of the gear shaft of the reducer belongs to pure mechanical overload damage. Therefore, in order to make the mixer work properly, it is necessary to re-select the reducer, and its mechanical strength must meet the working needs of the mixer. When the working medium of the mixer is liquid, YNF1240-500 reducer is selected to meet the strength requirements; when the working medium of the mixer is semi-liquid, YNF1400-500 reducer is selected to meet the strength requirements.