Through the analysis of the failure parts by using the main factor diagram method, the causes of the fracture of the working face caused by the casting of the guide wheel are as follows.
1) Casting defects such as sand holes and air holes (see Figure 1) will lead to the risk of potential cracks.
At present, water glass sand molding process is widely used for cast steel guide wheel, and the sand mold is required to be thoroughly dried before pouring. In order to further improve the surface quality of steel castings, the sand surface should be coated to improve the surface strength of sand mold, close the surface gap between sand mold and sand core, and improve the sand inclusion and sand hole caused by sand flushing during pouring. On the one hand, if the sand mold is not dried sufficiently, a large amount of gas generated in the pouring process can not be discharged in time. In addition, if the pouring speed is not controlled reasonably, the gas emission in the mold cavity can not be discharged in time, resulting in the formation of pores. On the other hand, if the sand mold is not cleaned or the strength of the sand mold is low, small pieces of sand are wrapped by liquid steel to the guide wheel body or tread during the pouring process, and the sand is released to form pits during turning. Moreover, incomplete mold modification and sand floating on the surface of sand mold lead to casting pockmarks. The above situations will cause the potential failure risk of the guide wheel, which needs to be solved.
2) The thickness of working face is too small.
Compared with the middle part, the thickness of the working face is greatly different, and the cooling speed of the liquid steel at this position is too fast, which is easy to produce stress cracks (see Fig. 2).