Abstract

The service life of the impact pads installed in the bottom of ladles at Kimitsu Steel Works was not long enough. So it was necessary to extend the repair interval of the ladles to improve the bottom impact pad life, so three improvements were made for this purpose.

The first one was to improve the strength of the impact pad, because of the damage caused by the impact/abrasion of molten steel during charging. Alumina-magnesia castable, the material of the impact pad, was densified as one of the improvements. So an improved bottom impact pad refractory was developed for use, which had roughly two times higher strength than the previous impact pads.

The second one was better control of the thermal expansion of the bottom refractories installed around the impact pads. The thermal expansion was decreased to prevent the damage caused by high expansion pressure between the impact pads and the surrounding bottom refractories. That is to say, the amount of magnesia of the alumina-magnesia castable, the material of the bottom refractory, was decreased to suppress too much expansion which occurred when alumina and magnesia reacted over 1200℃ and formed Spinel.

 The third one was optimization of the structure of the bottom area refractories. The impact pad and the bottom refractories were installed to provide a flat bottom surface, because the height difference of these refractories generated stress concentration at the interface where the lower height bottom refractories contacted the side face of the higher height impact blocks.

 Success was achieved, with doubling of the life of the impact pads, by making three improvements.