Before the mass-produced coupler products are finally put into storage, they need to go through one preliminary surface inspection, two flaw detection and other process inspections. The primary surface inspection is to detect whether there are obvious shrinkage porosity, surface crack, air hole and other defects on the surface of steel castings after unpacking and sand dropping; The two flaw detection tests include the flaw detection in the casting workshop (detecting the superficial crack condition of steel castings after pre normalizing and air gouging welding repair) and the flaw detection in the finishing workshop (detecting the superficial crack condition of steel castings after quenching and tempering after finishing welding repair and low-temperature tempering).
| Casting number | Test quantity (PCs.) | Number of defects (PCs.) | Defect rate (%) | Remarks |
| 957-1006 | 50 | 0 | 0 | No obvious surface defects |
| 1007-1058 | 52 | 3 | 5.8 | 1039、1041、1053，Scrap |
| 1059-1110 | 52 | 5 | 9.6 | 1074、1075、1087、1088、1093，Scrap |
| Total | 154 | 8 | 5.2 | Scrapping reason: sand inclusion |
The initial inspection of surface defects of steel castings after unpacking and sanding is mainly to detect whether there are obvious shrinkage, shrinkage, cracks, pores and other defects on the surface of steel castings, as well as whether the printing on the surface of coupler products is clear. Several preliminary inspection reports of hook body and tongue within half a month are randomly selected. The surface defects of steel castings are shown in Table 1 and table 2.
| Casting number | Test quantity (PCs.) | Number of defects (PCs.) | Defect rate (%) | Remarks |
| 713-769 | 56 | 3 | 5.3 | 732、748、752，Scrap |
| 770-824 | 55 | 3 | 5.4 | 788、809、811，Scrap |
| 825-880 | 56 | 0 | 0 | No obvious surface defects |
| 881-936 | 56 | 0 | 0 | No obvious surface defects |
| Total | 223 | 6 | 2.7 | Scrapping reason: sand inclusion |
It can be seen from Tables 1 and 2 that the steel castings have no obvious surface defects except that the steel castings are scrapped due to the penetration of sand. The main reason for the formation of sand inclusion penetration is that during the molding of molding sand, the sand mold strength at the gate and the corner of complex curved surface is insufficient or the sand box is improperly combined, resulting in a large amount of loose sand. During pouring, it is enriched due to the scouring of liquid steel, forming serious sand inclusion, resulting in penetration and scrapping of steel castings.