Vacuum-arc furnace

Eig. 3. Coasumable-electrode melting ia the vacuum-arc furnace (13). A, arc B, buttoa E, electrode I, iagot L, Hd M, water-cooled mold and P, pool of... 

Allowed melting procedures vacuum arc furnace or electroslag remelting. 

Induction Furnace. The high frequency coreless induction furnace is used in the production of complex, high quaUty alloys such as tool steels. It is used also for remelting scrap from fine steels produced in arc furnaces, for melting chrome—nickel alloys and high manganese scrap, and more recentiy for vacuum steelmaking processes. 

Ladle metallurgy, the treatment of Hquid steel in the ladle, is a field in which several new processes, or new combinations of old processes, continue to be developed (19,20). The objectives often include one or more of the following on a given heat more efficient methods for alloy additions and control of final chemistry improved temperature and composition homogenisation inclusion flotation desulfurization and dephosphorization sulfide and oxide shape control and vacuum degassing, especially for hydrogen and carbon monoxide to make interstitial-free (IF) steels. Electric arcs are normally used to raise the temperature of the Hquid metal (ladle arc furnace). 

Metallic niobium is generally produced by aluminothermic reduction ofNb205. Generally an excess of A1 is used, producing a Nb-Al alloy to give Nb which may be melted in vacuum or by electron beam or arc furnace. 

Arc furnaces (cold crucible technique). Small, commercial, laboratory arc-melting equipment generally includes a high-vacuum/aigon atmosphere pumping... 

Refractory bricks composed of oxides of magnesium, chromium, aluminum and iron and trace amounts of silica and calcium oxide are used in roofs of open hearths, sidewalls of electric furnaces and vacuum apparatus and copper converters. Such refractories are made in an arc furnace by fusing mixtures of magnesite and chrome ore. 

High-carbon ferrochromium alloys are made by the reduction of chromite ore with carbon in an arc furnace. On the other hand, low-carbon ferrochromium is obtained by silicon reduction of the ore. The carbon content of ferrochromium can be reduced further by heating high-carbon alloys with ground quartzite or by oxidation in vacuum and removal of carbon monoxide formed. Ferrochromium alloys are used in the manufacture of stainless steel. 

Thorium metal also can he prepared hy thermal reduction of its hahdes with calcium, magnesium, sodium, or potassium at elevated temperatures (950°C), first in an inert atmosphere and then in vacuum. Fluoride and chloride thorium salts are commonly employed. Berzehus first prepared thorium by heating tetrachloride, ThCh, with potassium. Magnesium and calcium are the most common reductant. These metals are added to thorium halides in excess to ensure complete reduction. Excess magnesium or calcium is removed by heating at elevated temperatures in vacuum. One such thermal reduction of hahdes produces thorium sponge, which can be converted into the massive metal by melting in an electron beam or arc furnace. 

Further, there are dry processes in w/hich degassing in vacuum is the actual technical process. These include work in induction- and arc furnaces, steel degassing plants, and plants for the manufacture of pure metals and electron tubes. 

All the chemical reagents used in synthesis have been subjected to preliminary purification and rectification. Graphite of MPG-7 grade has been used. The graphite rods have been annealed preliminary in vacuum. The metallic rods have been remelted repeatedly in an arc furnace in argon medium of spectral purity. 

For temperatures above 1000°C, special high-temperature furnaces, including induction furnaces, vacuum furnaces, and arc furnaces, are used, but these are beyond the scope of this book. 

Boron oxide, B2O3, can be reduced by C above 1600°C. An electric arc furnace is used for large-scale production. Since this process takes place in two steps with CO as an intermediate, an overpressure of CO is necessary during the initial reaction. A final heating in vacuum at higher T is needed for purification. 

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