Sinter Strength and Pore Structure Development using Analogue Tests

Iron ore sinter quality is important for productive and efficient operation of the modern iron blast furnace. Understanding the driving mechanisms of industrial sinter quality is complicated by the variability in the product. Variability arises due to many factors including heterogeneous raw material distribution, spatial variation in temperature profile and gas atmosphere down the bed. To reduce product variability iron ore sinter analogues were created from the - 1.0 mm fraction of an Australian iron ore. Samples were fired under tightly controlled thermal and atmospheric conditions in an infra-red rapid heating furnace. Maximum temperature was found to have a strong influence on the porosity of the fired tablets and hence their strength. The more commonly used integrated time at temperature above 1100 degrees C (EA, enclosed area) was found to be not as useful a predictor of sinter strength for these analogue tests. Analogues fired to 1320 degrees C showed a minimum in porosity and maximum strength after holding for 1 min. With longer firing, over-sintering occurred caused by pore swelling, leading to a decrease in strength. The proposed mechanisms of pore swelling are bubble coalescence and gas generation from hematite decomposition to magnetite. Extrapolating these results suggests over-sintering may occur in the lower part of the industrial sinter bed if the temperature is too high for too long, leading to lower strength product.