Shrinkage Distribution of Sintering Bed Evaluated by X-ray CT Observation

Abstract

Increasing sinter productivity, product yield, and sinter strength are important for more efficient processes. Because the sintering bed structure should strongly affect such sintering performances, evaluation techniques and controlling methods have been studied. X-ray computed tomography (CT) was used in several studies, because a sintering bed can be observed without destroying it. Sintering bed shrinkage has been also focused on as an index of product yield or sinter strength, because shrinkage should indicate structural change of the sintering bed. However, shrinkage was only evaluated as a cumulative value at the end of sintering, and material behaviour in the sintering bed has not been clarified. In this study, the correlation of shrinkage and sintering bed structure by X-ray CT observation was investigated. Tracers were located in the sintering bed, and the vertical shrinkage distribution was derived from their height change. The result was compared with the shrinkage change with time. Several factors for shrinkage were considered, and their influence degree was discussed. The main factor was sintering with melt formation. This result, however, contradicted the positive effect of ‘stand’, which prevents shrinkage and improves productivity and product yield. The reason is discussed, focusing on the support effect of the stand and difference in shrinkage distribution in the sintering bed. A quench test at a certain time during sintering was also carried out, and the transition state from granule to sinter was evaluated.