Extending the lining life in circulatory vacuum units at OAO EVRAZ NTMK

Abstract

In efforts to reduce metal costs, it is important to extend the lining life in metallurgical systems [1]. In particular, the linings of vacuum units account for a considerable portion of total refractory costs.Three groups of factors affect the lining life in cir culatory vacuum units [2]:(1) structural factors (the shape and size of the metal framework, the lining design, the format of the refractory pieces, and so on);(2) the physicochemical properties of the refracto ries, which depend on the quality of the raw materials, the manufacturing technology, and so on; (3) technological factors (the operating conditions of the metallurgical system, the slag composition and properties).Specialists at OAO EVRAZ NTMK have been studying these factors, in order to improve the refrac tory components and optimize their operating condi tions. The results assist in the development and intro duction of new lining configurations with improved performance and longer life.On that basis, measures have been taken to improve the operation of the vacuum units at OAO EVRAZ NTMK. STRUCTURAL FACTORSIn the converter shop at OAO EVRAZ NTMK, the lining configuration illustrated in Fig. 1 is employed in the vacuum unit. A deficiency of this configuration is that the junction of the refractory ring and the refrac tory concrete at the end is rapidly worn, as is the region where the transporting gas is supplied (Fig. 2). During operation, the liquid steel penetrates into the damaged surface and erodes the metallic plate that supports the refractory rings at the end of the tube. That leads to settling of the lower ring of the tube and the formation of a gap between the rows of components. In subse quent operation, metal melt leaks into the gaps, pro ducing local erosion around the circumference (Fig. 3). The vacuum chamber requires premature repair [2,3]. This problem at the junction of the refractory concrete and the refractory rings may be eliminated by adopting the design in Fig. 4. In that case, there is no horizontal junction between the concrete and the refractory ring, and the lower ring is rigidly fixed. In the course of operation, the modified structure does not permit per ceptible settling of the refractory rings. The mean life in experimental vacuum chambers was 106.0 melts (as against 102.0 melts for mass produced components). PROPERTIES OF THE REFRACTORIESSpecialists at OAO EVRAZ NTMK pay great attention to the refractory components obtained from suppliers and, in particular, their susceptibility to wear [4]. Research shows that the unit wear of refractories in the discharge tube does not depend on the overall properties but is largely determined by the characteris tics of the intake refractories. The operating condi tions are most intense at the intakes: additional cool ing of the refractory surface in the period between melts by neutral gas and considerable turbulence of the metal, which tends to erode the brick.It is evident from the table that the components dif fer considerably in properties and working life. For more detaile...

The Slag Regime of Equipment Used for the Secondary Treatment of Steel and the Durability of Its Refractories

“…It was determined experimentally that the longest-lasting products are those with good mechanical strength and low open porosity [2,3,5]. This linkage is probably due to the fact that use of the refractory products which have the best combination of strength and porosity characteristics makes it possible to alleviate the adverse effect of the slag on the refractories (impregnation and cracking) and more fully realize its protective properties through the formation of a slag crust.…”

“…At large modern factories such as the Nizhniy Tagil Metallurgical Combine (OAO EVRAZ NTMK), the cost of acquiring refractories for the secondary (ladle) treatment of steel accounts for more than 30% of the total expenditure on refractory materials [2,3]. The importance of improving the durability of secondary steel-treatment units stems from the decisive effect that these pieces of equipment have on the quality of the finished steel [3,4].…”

“…Experience shows that the composition of the refining slag affects the durability of the refractories [2,3,5]. It has this effect because most (roughly 2/3) of the wear of refractory products occurs chemically -by dissolution of the refractory in the slag [1].…”

“…The importance of improving the durability of secondary steel-treatment units stems from the decisive effect that these pieces of equipment have on the quality of the finished steel [3,4]. In ladle-furnace units (LFUs) and vacuum-degassing units (VDUs), liquid steel is treated by a refining slag that rids the steel of sulfur, oxygen, and nonmetallic inclusions (NIs).…”