OUT OF THE MOULD AND INTO THE FERE - A NEW PERSPECTIVE ON THE OPTIMISATION OF DEFLOCCULATED CASTABLES

摘要

The recent developments in refractory castable technology based upon calcium aluminate cement (CAC) bonding systems have contributed to their increased usage rate compared to other monolithic refractory types. Most of this growth in recent years can be attributed to the arrival of new placing technologies. The continuing growth of monolithic refractory castables is expected to rely increasingly on the development of monolithic castables, which offer both improved durability as well as a more rapid and reliable processing prior to use. It is considered that one of the key routes to further optimise castable processing will be through a greater understanding of the hardening, dry out and heat up phases. A major constraint has been the lack of necessary analytical techniques which can be used to first investigate and then optimise these processing steps. This paper will present an approach by which deflocculated castable systems can be optimised through a better understanding of the role that the calcium aluminate cement (CAC) plays during the hardening stages of castable use. Existing measurement techniques such as conductimetry, calorimetry and mechanical strength have been used together with a new technique, based upon ultrasonic measurement, to investigate deflocculated castable systems. This ultrasonic technique allows a continuous measurement of the castable hardening phase. Results are presented, from placing at 20°C through to the hardened and dried state, of various model castable systems based on a 70% Alumina cement as well as a new type of 80% Alumina cement. From the observed data, important structural changes in the castables can be seen to occur throughout the hardening process. The role of different fine fillers within these castable systems is investigated and clear differences are seen depending upon the choice of fine reactive fillers and accompanying additives. Mechanisms are also proposed to account for the different hardening rates that are found within each specific system An assessment is also made of the impact of the CAC type upon the castable behaviour during hardening. Conclusions are drawn as to differences in the hardening and elastic properties of these model castable systems and how such systems might be optimised.