Electroslag Furnace

a furnace unit designed for electroslag remelting. It has mechanisms for feeding a consumable electrode into the slag bath and a bottom plate, on which is mounted a crystallizer for ingot forming or mechanisms for moving the crystallizer and ingot with the bottom plate during the melting process (Figure 1). Electroslag furnaces usually operate on alternating current at the frequencies specified for mains used in industry or at lower frequencies; some types operate on direct current. The power rating of the furnace transformer may be as high as 5–10 megavolt-amperes.

Figure 1. Designs of electroslag furnaces: (a) the ingot and crystallizer are stationary, and the electrode is lowered as melting progresses; (b) the crystallizer is stationary, and the ingot and electrode are lowered during melting; (c) the ingot is stationary, the crystallizer is raised during melting, and the electrode is lowered during melting

A typical electroslag furnace is a batch unit; small, continuous-action types also exist. Distinctions are made between single-phase and three-phase, single-wire and two-wire, single-electrode and multielectrode, and single-position and multiposition, and specialized and universal (general-purpose) types. The slag is subjected to prior melting in a flux-melting electric furnace with a graphite lining and a graphite electrode. It is then poured into the crystallizer via a siphon device or directly from above. Electric current is switched on, and the consumable electrode begins to be fed into the slag bath. The process is automatically programmed. After an ingot has been melted over a specified length, the ingot head is fed completely into the bath, and the current is then switched off. The molten slag is poured off from the crystallizer, which is then raised and the ingot is stripped off. After the electrode butt has been removed and a new consumable electrode has been mounted in the electrode holder, the furnace is ready for the next cycle. The specific energy consumption of an electroslag furnace ranges from 1,000 to 1,500 kilowatt-hours per ton. The flux consumption may be as high as 5 percent of the weight of the ingot, and the water consumption for cooling the crystallizer, bottom plate, electrode holder, and current-conducting parts may reach 500 cu m/hr.

The world’s first industrial electroslag furnaces were designed and constructed at the E. O. Paton Institute of Electric Welding of the Academy of Sciences of the Ukrainian SSR. Electroslag furnaces were placed in operation in 1958 at the Dneprospetsstal’ and New Kramatorsk machine-building plants. Modern single-phase, four-electrode, two-wire electroslag furnaces for melting slab ingots weighing up to 40 tons (500 mm thick, 2,500 mm wide, and more than 4 m high) have two 3,500-kilowatt furnace transformers. They operate with electrodes and a crystallizer that undergo converging feed motions; the movable crystallizer is short, with a broad upper section. The units are equipped with systems for blasting gas mixtures through the slag and metal baths, secondary cooling, and heating of the bottom part of the ingot (Figure 2). The melting time for a 40-ton ingot may extend to 16 hr. The output G (in kg/hr) of an electroslag furnace is determined from the empirical formula G = D, where D is the side of a

Figure 2. Electroslag furnace for melting slab ingots: (1) transformers, (2) consumable electrodes, (3) crystallizer, (4) ingots

square (blooming-mill) ingot, the broad face of a slabbing-mill ingot, the diameter of a solid round ingot, or the outside diameter of a hollow ingot (in mm).

Many types of electroslag furnaces are in operation in the USSR in specialized shops of metallurgical plants (for the production of rolling-mill ingots weighing up to 8 tons and slab ingots weighing up to 20–40 tons) and heavy machine-building plants (for the production of foundry ingots weighing up to 200 tons).

After the initial installations in the USSR, electroslag furnaces were constructed in Great Britain, the Federal Republic of Germany, the USA, and Japan. Electroslag furnaces have also been constructed and operated under Soviet license in France, Japan, Sweden, Bulgaria, Poland, Rumania, and Yugoslavia. Automatic control systems for electroslag furnaces are being developed in the USSR, the USA, and the Federal Republic of Germany.