Electron-Beam Furnace

an electric furnace in which electric energy is transformed into heat directly in a metal being remelted as a result of bombardment with electrons emitted from an electron gun. The electrons are accelerated by a high-voltage electric field (10–35 kilovolts) under low-pressure conditions (less than 10 millinewtons per m²).

Electron-beam furnaces used in the metallurgy of pure metals and alloys consist of the following units and systems (Figure 1): an electron emitter (electron gun) with a cathode, accelerating anode, and magnetic focusing system; a melting chamber with gating devices and a crystallizer (a mold or crucible) for the metal; a vacuum system; mechanisms for transporting the metal to be remelted; and a power supply with an automatic control system. The metal to be remelted is introduced into an electron-beam furnace through a vacuum seal in the form of a consumable electrode, ingot, single crystal, or powder. The molten metal runs off in drops either into a water-cooled crystallizer—a mold (in ingot melting) or crucible (in melting in crucibles with a skull, for the production of shaped castings, and in the growing of single crystals)—or into cold, water-cooled hearth reservoirs (in refining molten metal).

In industry, electron-beam furnaces with capacities in excess of 1 megawatt are used for remelting steel ingots with diameters up to 1,000 mm, heat-resistant alloy ingots with diameters up to 500 mm, and refractory metal ingots with diameters up to 280 mm. The electrical efficiency of electron-beam furnaces ranges from 0.6 to 0.8. The specific power consumption is 1–2 kilowatt-hours per kg (kW-hr/kg) for steel, 10–15 kW-hr/kg for niobium, tantalum, and molybdenum, and 20–40 kW-hr/kg for tungsten. As of

Figure 1. Designs of electron-beam furnaces: (a-e) and (g) with electrostatic electron guns, (f) with magnetron electron gun; (EG) electron gun, (AC) annular cathode, (LC) linear cathode, (SC) spiral cathode, (DC) disk cathode, (AA) accelerating anode, (MFS) magnetic focusing system, (MDS) magnetic deflection system, (CE) consumable electrode, (Ch) free-flowing charge, (C) single crystal, (I) ingot, (Cry) crystallizer, (CWS) crucible with skull, (Cru) crucible, (CM) casting mold, (CH) cold hearth, (VS) vacuum system

1978, a 7.2-megawatt electron-beam furnace was in the planning stage, designed to remelt steel ingots with diameters up to 2,000 mm (with a cold hearth).