Research On Anti-cracking Castables For Iron Trough

Al₂O₃-SiC-C based castables are currently often used and promising castables fortrough of blast furnace. It has the good performances of pass of large amount of molteniron, long service life, low refractory material consumption and convenient construction.However, it is unable to be adopted at median or small sized blast furnace with a singletaphole, mainly because the requirement of fast baking and anti-cracking of castablescould not be met.The performances and anti-cracking mechanisms of Al₂O₃-SiC-C based castableswere investigated on the basis of Secar71cement, silica micropowder and silica sol-gelas binders respectively. The main raw materials were brown corundum of various particlesize, silicon carbide, white corundum （-325mesh）, ball pitch, silicon powder and AC wasused as foaming agent. The comprehensive thermal analyses were carried out todetermine the anti-cracking performance. Factory experiments were also carried out. Theresults showed that the addition of AC foaming agent could decrease the dewatertemperature and enlarge the temperature range. Therefore, the anti-cracking performancewas improved. The mechanism was as follows: foaming agent AC will decompose torelease gases with the help of cement and water. As the gas escapes, superfine open poreswill generate in the castables. The formation of open pores at a lower temperature favorsthe expulsion of water and reduces the possibility of cracking of the castables. However,with increase of AC foaming agent, the apparent porosity of samples increased whilebulk density, modulus of rupture, crushing strength and slag resistance decreased. Takeall the properties into consideration, the optimum addition were2a%of AC.Adding fused magnesia powder into silica micropowder binded castables could formM-S-H gel, which could not only improve the strength but also anti-crackingperformance of the castables. This is because slow dehydration took place during heating,which was helpful for rapid roasting. The castables exhibited low strength when smallamount of fused MgO powder was added. If the addition amount is overmuch, MgOwould react with SiO₂protective film existed on the surface of the samples to produceMg₂SiO₄and lead the expose of surperficial aggregates. Therefore the optimum additionwas3-6%of MgO. Silica sol-gel-binded castables expulsed physical held water slowly at100℃, whichwas helpful for improving anti-cracking performance. The castables exhibited goodflowability and anti-cracking performance with addition of0.05%of sodium tri-polyphosphate （STP） as dispersant. The castables could form-Si-O-Si-web structure andhas high medium temperature strength. No low melting phase produced at hightemperature but generated mullite could improve the strength. However, the castableshave big volume expansion and poor slag resistance.