After the trial production of the sample, the tooth anatomy was verified. The shrinkage defect at the center of the tooth was eliminated. Only a few upper teeth had slight porosity. The anatomical results met the requirements of the technical conditions of the drawing. The anatomical results are shown in Figure 1. However, there are large pores on the surface ofcastings, resulting in poor surface quality of ductile iron castings, as shown in Figure 2. Therefore, further process improvement is required for the surface quality of ductile iron castings.
Through analysis, the main reasons for the air hole defects on the surface of the driving wheel are that the air volume of the coated sand core increases, the wall thickness of the ductile iron castings is thin, and the exhaust is poor. In order to solve the blowhole defect, the following improvement measures have been taken:
(1) 50/100 coarse sand is used for 1 # and 2 # coated sand cores to reduce the gas generation of sand cores.
(2) The assembled 6 # sand core is put into the drying furnace for drying, and the process parameters are set as the holding temperature of 180 ℃ and the holding time of 4 h.
(3) Add exhaust passage, as shown in Figure 3. After implementing the improvement measures, more than 120 ductile iron castings of driving wheels were produced, and the defects of air holes were eliminated, and the surface quality was good.