Doctor of Philosophy
Department of Materials Engineering
Wells, Lisa, The rheology of a composite polymer ceramic plastic refractory, Doctor of Philosophy thesis, Department of Materials Engineering, University of Wollongong, 2002. http://ro.uow.edu.au/theses/1533
Taphole clays are a plastic ceramic-polymer composite used in iron making blast furnaces to control the casting of hot metal and slag from the blast furnace. They also protect the sidewall refractories in the blast furnace from erosion and corrosion. Taphole clays generally consist of liquid binder, refractory matrix, and refractory aggregate. A novolak resin solution has been used in this study because it is a common binder used in industry. The matrix material is usually a mixture of fine particles of silicon carbide, coke, alumina, and other special additives. The aggregate materialconsists of coarse particles of alumina or alumino-silicates.
Studies on taphole clays to date have generally focused on the effect of compositional variations on their performance. Extrusion behaviour is known to highly influence the performance of taphole clays but has not been previously studied in depth. In this thesis the rheology of the taphole clay mixtures and their components are studied. The binder was aged at various temperatures with and without the addition of the curing agent hexamethylenetetramine (HMTA). The effect of temperature and curing time was assessed based on the binder's viscosity. Extrusion pressure variation in the mixture of binder and matrix material due to ageing, temperature and binder composition was also studied. The Benbow-Bridgwater model for paste extrusion was used to evaluate the extrusion pressures. The aggregate material was not added in this study and will be the focus of future work.
Major findings of this study were that the binder was found to react with HMTA at temperatures above 40°C producing an increase in viscosity. This reaction occurred at temperatures much lower than had previously been reported. Without the addition of HMTA there was found to be no significant change in the viscosity of the binder. When the binder and HMTA mixture was heated to temperatures of 70°C and above, the reaction was rapid, taking less than 12 hours to observe a significant viscosity increase. Again, these cure temperatures were lower than reported in previous studies. It is proposed that the increased mobility of the polymer chains due to the addition of the solvent is the reason these reactions were occurring at relatively low temperatures.
The extrusion behaviour of different taphole clay compositions was performed by comparing parameters from the Benbow-Bridgwater equation. This study has extended the application of the Benbow-Bridgwater equation, which was previously applied to the extrusion behaviour of ceramic pastes. Studying the matrix binder material variation found that ageing at 50°C, mixing technique and temperature all had a significant effect on the extrusion pressure. The effect of temperature of extrusion was also examined and found to be a significant factor in extrusion behaviour. A novel variation to the Benbow-Bridgwater equation is proposed to account for these temperature changes.
It is envisaged that this work will be used to modify blast furnace taphole clay storage and utilization procedures to obtain more consistent taphole clay behaviour. This work also provides an understanding of the factors that can contribute to the variability observed in the extrusion pressures of taphole clays. Having a greater understanding of the external factors that can lead to significant differences in taphole clay performance will lead to better operating conditions in the blast furnace and a longer furnace life.