Efficient Lining for Steel-Pouring Ladles

Abstract

An analysis was made of the reasons for the short service life of the lining of steel-pouring ladles and malfunc- tions of fountains used for bottom-pouring. A high-temperature adhesive was developed and the most chemi- cally stable refractory materials were chosen for it. The operating regime of steel-pouring ladles in the open-hearth shop at the Revda Hardware-Metallurgical Plant (in Revda) was studied, and based on the study results the shop replaced its fireclay bricks with MKRAP refractories. The authors used those results to also develop a mortar that has increased the life of the lining 30 - 50%. Use of the highly stable high-temperature adhesive in fountains has reduced metal loss during bottom-pouring operations. A project was undertaken in the open-hearth shop at Revda Hardware-Metallurgical Plant (in Revda) to lengthen the service life of its steel-pouring ladles. The lining of the walls and bottom of the 22.98-m 3 ladles at the plant are made up of three-four layers of refractory bricks. The refractory materials are fireclay bricks of grades ShB-9 and ShKu-32/16, fireclay mortars MSh28 and MSh31, refractory clay, and chromium-bearing concrete. The service tempera- ture of the working layer of the lining is 1600 - 1650°C, slag basicity CaO/SiO2 is 1.5 - 2.2, and the FeO content of the slag ranges from 10 to 25%. The lining is rapidly dried and heated over a 1-2h period during the beginning of use of the ladle. The horizontal joints of the walls are coated with a fireclay mortar on a sodium-silicate binder. There are no ver- tical joints in the linings of the walls. Study of wear of the lining of ladles after service showed that the wear takes place due to spalling of the bricks as a re- sult of thermal shocks which occur during the entry and dis- charge of molten metal and the heating that the lining under- goes after a repair. The refractory of the lining also reacts chemically with reactants in the melt, particularly in the re- gion of the vertical joints. There, reactants in the slag pene- trate the lining to depths of up to 50 mm. In addition, the working layer undergoes abrasive wear in the bottom of the ladle when incoming molten metal strikes the lining. The large amount of wear of the lining in the slag zone is due to oscillation of the melt during use of the ladle. In our opinion, a lining such as that described above has several shortcomings. The presence of three-four layers in the lining creates too many joints. Also, the use of short (230 mm) bricks in such linings creates 3-4m m oftaper in the working layer, which makes it more likely that some bricks will fall out of the layer during operation of the fur- nace. Another problem is the use of a fireclay mortar on a so- dium-silicate binder, which has poor physico-mechanical properties that do not meet the requirements for the given metallurgical conversion. The fireclay bricks operate at the limit of their physico-mechanical properties during use of the ladle. The vertical joints are not coated with the fireclay mor- tar during repairs to the lining, which allows reactants in the slag and metal to penetrate the joints and thus cause greater corrosive wear. Such penetration also creates thermal stresses in the lining during each introduction and discharge of molten metal due to the large coefficient of linear expan- sion of the metal and slag compared to the refractory prod- ucts. In addition, not enough time ( 1-3h ) isprovided for drying and heating the lining after the repair and use of a la- dle. The use of water to cool the lining after metal is cast pro- duces severe thermal shocks that crack the working layer af- ter 4 - 5 castings, i.e. after 2 - 3 heats. Such cracking occurs because, in accordance with their specifications, fireclay refractories need to undergo 3 - 4 water-cooling cycles (1300°C - water) and 20 - 25 air-cooling cycles (1200°C - air at 20°C) to perform properly. Cooling of a hot lining with water can cause accidents with ladles as a result of local dis- integration of the lining during service.