Forming mechanism and prevention and control measures of shrinkage defects of nodular cast iron in cylinder

During ut inspection, the main defects exceeding the standard were shrinkage cavity and porosity defect. In the subsequent finishing process, there were also serious shrinkage defects in the initial trial production castings.

UT inspection is carried out in accordance with the technical conditions for ultrasonic flaw detection of nodular cast iron castings (EN 12680-3), and 100% of the areas required by the casting drawings are detected by UT. The test results show that there are many serious shrinkage defects and porosity defects in the large thickness position of the inlet cylinder stator blade flange (the ultrasonic detection waveform shape is shown in Fig. 1 (a)), and the UT waveform is a typical shrinkage cavity and porosity defect waveform.

It can be seen from the UT inspection records that the shrinkage and porosity defects are densely distributed in the position of thick and large cross-section, and the defects are continuously distributed in flakes. The formation mechanism of shrinkage cavity and porosity in this part is relatively complex, which is an important research object in this part.