Induction Furnaces, Ladles

The requirements for refractories for the vanes of the degassing units do not differ from the requirements for the melting and holding furnaces (Table 3.6). They are high thermal shock resistance, low wetting by Al, and high erosion resistance. 

The same may be said about the refractories for the rotating furnaces for remelting of dross and wastes (Table 3.6). Such furnaces, having a diameter up to 4 m and a length of 8-10 m, are lined with bricks (in weir walls, inside the inner lining) and with LCCs (under hexagonal or octagonal inner cmistruction) (Fig. 3.17). 

The main interaction of the lining is mechanical action of the pieces of wastes and dross and chemical erosion. The service life usually doesn t exceed 1.5-2 years (Fig. 3.18). 

Induction furnaces are used for making alloys and master alloys and for remelting of scrap and noncondition billets. 

A crucible induction furnace (Fig. 3.19) consists of a refractory crucible, a water-cooled inductor around the cmcible, a steel shell (which takes most of the mechanical tensions), a pouring crucible lip, and a cup. 

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Almost all the materials just mentioned may be used in induction furnaces, ladles, and launders. 

The zinc is normally melted in a gas, oU, or coal-fired reverberatory furnace with a capacity up to 100 tons or in a low frequency induction furnace with a capacity of a few tons. The more highly aUoyed compositions are more effectively melted and mixed in low frequency induction furnaces. The furnace must be refractory-lined to eliminate iron pickup by the molten metal. The metal temperature is maintained below 500°C to minimize loss by oxidation. A ladle is used to transfer the metal for casting into molds the pouring temperature is usuaUy ca 440°C. Zinc scrap is not generaUy suitable for remelting because it may contain undesirable impurities. 

The coreless induction furnace is used for melting but cannot be used for refining. Therefore, in steel foundries the induction furnace has to be charged with raw materials of the correct chemical composition, i.e. that corresponding to the required composition of the melt hence steel scrap is mainly used. If necessary, the metal can be refined after melting in an AOD converter or in special treatment ladles (see Section 2.4.12). 

The metallurgical equipment of cast houses at smelters includes ladles for transporting raw A1 from the reduction shop to the cast house (Fig. 3.1), stationary or tilting holding furnaces, degassing units, induction furnaces for remelting of disposal or wastes and preparation of alloys, and gas-fired furnaces for remelting of disposal and wastes. 

Product C is based on chamotte and is used in aluminium foundries in ladles and smaller cmcible furnaces. The spinel-forming dry mix D is based on fused white alumina and is suited for inductive melting of special steel alloys at high temperatures. 

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