1、 Improvement measures for defects such as sand hole and air hole are as follows.
1) Properly increase sand mold baking to 2 ~ 3 times to avoid wet gas residue.
2) Control pouring speed, standardize reasonable pouring time and final pouring temperature of each ladle.
3) In the process of pouring, small ladle pouring can be used to achieve stability and prevent sand washing.
4) Optimize the sand mixing ratio, reduce the surface roughness of sand mold, improve the compactness.
5) The paint should be applied evenly.
6) The temperature of molten steel is measured before each heat is discharged, and the temperature of molten steel is controlled at 1550 ~ 1650 ℃ before pouring.
7) Strengthen the inspection of product quality in the production process, and set up a full-time modeling inspector.
2、 Improvement of casting structure design: because the outer edge of wheel tread is thin, the middle part is thick, and the thickness change is too wide (see Fig. 1), the cooling speed is too fast in the, and the volume shrinkage of the outer edge and the middle part is different, so cracks and shrinkage are easy to occur (see Fig. 2). In the heating process of heat treatment, because the working face is thin and has good heat permeability, when the middle wall thickness is heated to the required temperature of 830 ℃, the temperature of the obviously thin working face will become higher, which makes the casting locally overheat, and the faster cooling rate in the cooling process is easy to produce cracks, or the over burning phenomenon will produce cracks, This kind of crack is zigzag distribution, accompanied by coarse surface martensite structure and intergranular cracking (see Fig. 3). In addition, through the establishment of mechanical mathematical model analysis, the tread can be regarded as a cantilever beam model. When the wheel tread is under the load, it will produce repeated deformation, which is easy to lead to fatigue fracture. Therefore, increasing the tread size can effectively alleviate or even eliminate the fatigue failure. Through the finite element analysis and calculation, it can be concluded that if the guide wheel body is properly thickened by 5mm, the maximum deformation is only 82.1% of that before the change. At the same time, it can slow down the thickness transition degree, slow down the cooling rate of liquid steel in the thin-wall position, further improve the pouring process, improve the fluidity and feeding capacity of liquid steel.