Refractories slagging

Blasting. Using this procedure, scale is removed by high-velocity particles impelled by an air blast or by a high-velocity wheel. Blast materials usually consist of sand, or sometimes of steel grit, silicon carbide, alumina, refractory slag,... 

The equilibrium phases and phase eompositions in dependence of the refractory/slag ratio have been determined. For this purpose a variable has been introduced which is defined by the mass ratio of the refractory material to the total mass of refractory plus slag. = 0 represents the composition of the slag with no contact to the refractory material and = 100 represents the composition of the refractory material with no slag contact. 

Ti Temperature where i = slag surface (s), refractory-slag interface (r),... 

The equilibrium thickness increases as the of the refractory-slag system increases, i.e., as more slag-resistant refractories are used. This usually means the use of higher-purity refractories, namely higher alumina content or higher MgO purity. 

However, the enrichment of refractory constituents resulting from this dissolution could lead to precipitation, at the refractory-slag interface, of new phases less soluble than the initial oxides, and these corrld slow down any subsequent dissolution. Thus, the process of corrosion by dissolution is dependent on precipitation which can be interpreted only based on the knowledge of phase diagrams with more than three corrstitnents. 

Open-Arc Furnaces. Most of the open-arc furnaces are used in melting and refining operations for steel and iron (Fig. 1). Although most furnaces have three electrodes and operate utilizing three-phase a-c power to be compatible with power transmission systems, d-c furnaces are becoming more common. Open-arc furnaces are also used in melting operations for nonferrous metals (particularly copper), slag, refractories, and other less volatile materials. 

Fig. 8. Magnetherm reactor central electrode, A secondary circuit, B grounding electrode, C refractory lining, D carbon lining, E primary material feed, F slag taphole to FeSi recovery, G vacuum line, H water spray ring, I condenser, cmcible, K trap, L filter, M and transformer, N.

Mechanical Properties. The physical properties of a particular refractory product depend on its constituents and manner in which these were assembled. The physical properties may be varied to suit specific appHcations. For example, for thermal insulations highly porous products are employed, whereas dense products are used for slagging or abrasive conditions. 

Standardized appHcations of different refractory types are Hsted ia an excellent series compiled by the ASTM (36). These surveys cover the principal iadustrial appHcations of refractories and furnish a description of furnace operations and destmctive influences such as slagging, erosion, abrasion, spalling, and load deformation. 

Fireclay refractories are used in kilns, ladles, and heat regenerators, acid—slag-resistant apphcations, boilers, blast furnaces, and rotary kilns. They are generally inexpensive. 

Forsterite Refractories. Refractories made from forsterite, Mg2Si04, resist alkah attack and have good volume stabiUty, high temperature strength, and fak resistance to basic slags. Uses include nonferrous metal furnace roofs and glass-tank refractories not in contact with the melt, ie, checkers, ports, and uptakes. 

Refractory lining life was at one time an important maintenance cost, but developments using a nitrogen lance to splash slag over the walls have increased lining life by a factor of -- 10 (2000 to 20,000 heats). 

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