Through the analysis of the failed parts by the method of factor diagram, the reasons for the fracture of the working face of the guide wheel caused by sand casting are as follows.
1) Sand casting produces defects such as sand holes and pores (see Figure 1), which will lead to the risk of potential cracks.
At present, the molding process of sodium silicate sand is widely used for cast steel guide wheels, and the sand mold is required to be dried thoroughly before pouring. In order to further improve the surface quality of steel castings, the surface of surface sand shall be painted to improve the surface strength of sand mold, close the surface gap of 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 will not be discharged in time. In addition, if the pouring speed control is unreasonable, the gas in the mold cavity will not be discharged in time and pores will be formed. On the other hand, 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 pouring. During turning, the sand is released to form pits. Moreover, incomplete mold repair and floating sand on the surface of sand mold lead to sand mold casting pits. The above situations will cause 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 very different. The liquid steel cools too fast at this position, which is easy to produce stress cracks (see Figure 2).