Technological Study On Quality Control Of Thin-long Rod And Thin Thickness Ductile Iron Casting

As shrinkage defects are usually existed in the ductile iron segment casting, several feeding schemes are adopted to test in the practical conditions. Optimal technology is obtained to eliminate shrinkage porosities and improve the mechanical properties by comparing microstructures and mechanical properties. Feeding distances of the end riser were studied for different length segment casting. In order to meet the requirements of shrinkage porosity inspection of ductile iron casting, the supersonic inspection method was investigated and validated. The technology of controlling cementite in the thin-thickness ductile iron castings was experimentally studied as well. From the investigation, the conclusions are as follows.When the twin lateral thermal risers were located in one-third of the ductile iron segment casting, it can get the best feeding effect to eliminate shrinkage and shrinkage porosity, obtain the dense microstructure and improve the mechanical properties significantly. The tensile strength can reach above 476Mpa, the elongation is above 10%, and the maximum elongation can reach up to 15%. Based on the optimal riser feeding, the corresponding ferrite in the casting and Y type specimen can be obtained by instantaneous inoculation, which can solve the large difference of mechanical properties between segment casting and Y-type specimens.The ultrasonic detection technology was used to inspect the defects of the ductile iron segment rod castings with different thickness and different sizes of risers, the results are in good accordance with those of practical dissection. Subsequently, it is reasonable for 8 times supersonic-echo method to detect defects of the ductile iron castings.For the small modulus long rod casting of nodular iron segment, there is a problem of shrinkage distance if the lateral thermal risers are set on the end. If the modulus is in the range of 0.47～0.56cm, the effective shrinkage distance of the lateral thermal risers is approximately 320mm through adopting the reasonable riser size. If the length of casting is above 400mm, it is difficult for the lateral thermal end risers to provide the effective feeding. Hence, it should choose other riser setting. The descending order to affect the amount of graphite and cementite in the thin thickness nodular iron casting obtained from the orthogonal test is Si/C, carbon equivalent and the mass fraction of inoculants. The cementite of the thin thickness nodular iron casting can be eliminated effectively when the carbon equivalent, Si/C and the mass fraction of inoculants are 4.3%～4.6%, 0.6 and 1.2%～1.4% respectively. Instantaneous inoculation is an effective measure to improve the solidification structure of nodular iron casting with thin thickness.