Heating inductive

Induced anisotropy Induction Induction furnaces Induction heating Induction melting... 

Fig. 2. Induction heating cod and load showing (a), current distribution in load, and (b), reference depth.

Power Supplies and Controls. Induction heating furnace loads rarely can be connected directiy to the user s electric power distribution system. If the load is to operate at the supply frequency, a transformer is used to provide the proper load voltage as weU as isolation from the supply system. Adjustment of the load voltage can be achieved by means of a tapped transformer or by use of a solid-state switch. The low power factor of an induction load can be corrected by installing a capacitor bank in the primary or secondary circuit. 

Some induction heating furnaces must operate at frequencies higher than the supply frequency. Formerly, rotating motor alternator frequency converters were used. Now the avadabdity of high speed, high power sdicon controlled rectifiers for use in frequency converters has made rotary converters obsolete. Modem units operate at higher efficiency, cost less, require less factory space, and coordinate readdy with process controls (2). 

Induction heating equipment installations can require significant investment in electric power components as well as the work handling equipment made necessary by the process. These costs can be offset by savings in plant space, reduction in metal loss, precise control of product temperature, and reduced in-process inventory. A typical continuous induction heating line consumes about 360 kW h/t heating carbon steel bars to 1230°C. 

A unique capability of induction heating is apparent in its abdity to heat the surface of a part to a high temperature whde the interior remains at room temperature. Proper selection of material, high frequency, and high power density can produce a thin surface hardness with a heat unaffected core (3). Figure 4 shows the cross section of a typical automotive shaft heated with 10 kH2 at various power densities. The required hardness depth is selected to... 

Induction heating using low frequency and low power density when apphed to a stationary or moving bar can produce a uniformly heated part suitable for introduction to a rolling mill (4). A cod line capable of producing 32 t/h of 17.8 cm (7 in.) diameter alloy steel bars heated to 1177°C is shown in Figure 5. 

Induction heating is used to heat steel reactor vessels in the chemical process industry (5). The heat produced in the walls is conducted to the material within. Multisectioned cods are used to provide controlled heat input to the process material as it passes through the reactor. Figure 6 illustrates a cross section of such a typical installation. 

High process temperatures generally not achievable by other means are possible when induction heating of a graphite susceptor is combined with the use of low conductivity high temperature insulation such as flake carbon interposed between the coil and the susceptor. Temperatures of 3000°C are routine for both batch or continuous production. Processes include purification, graphitization, chemical vapor deposition, or carbon vapor deposition to produce components for the aircraft and defense industry. Figure 7 illustrates a furnace suitable for the production of aerospace brake components in a batch operation. 

K. G. Webley, "Induction Heating of Steel Reactor Vessels," Chemical Process Industry Symposium, AlCHE, Philadelphia, Pa., June 5—8,1978. 

Materials Engineering Institute, Course 60, Induction Heating, American Society for Metals, Metals Park, Ohio, 1986. 

C. A. Tudbury, Basics of Induction Heating,]ohn Rider, New York, 1960. 

S. Zinn and S. L. Semiatin, Elements of Induction Heating, Electric Power Research Institute, Palo Alto, Cahf., 1988. 

For ordinary materials and higher production rates, P/M forging can be used (26,28). After parts are compacted and sintered to medium density, they are reheated, lubricated, and fed into a hot-forming or P/M-forging press. The part is formed by one stroke of the press in a closed precision die. A typical hot-forming press setup includes die sets, automatic die cooling and lubrication, transfer mechanism, an induction heating unit for preforms, and controls. 

Hot Pressing. Hot pressing may be used either to consoHdate a powder that has poor compactabiHty at room temperature, or to combine compaction and sintering in one operation. The technique is essentially the same as described for unidirectional die compacting. The powder is heated by either heating the entire die assembly in a furnace or by induction heating. In most instances, a protective atmosphere must be suppHed. 

S. L. Semiatin, D. E. Sutu2, and I. L. Harry, Induction Heat Treatment of Steel, American Society for Metals, Metals Park, Ohio, 1986. Carburic ng and Carbonitriding, American Society for Metals, Metals Park, Ohio, 1977. 

The CVD process is accomplished using either a hot-wall or a cold-wall reactor (Fig. 13). In the former, the whole chamber is heated and thus a large volume of processing gases is heated as well as the substrate. In the latter, the substrate or substrate fixture is heated, often by inductive heating. This heats the gas locally. 

A unique problem arises when reducing the fissile isotope The amount of that can be reduced is limited by its critical mass. In these cases, where the charge must be kept relatively small, calcium becomes the preferred reductant, and iodine is often used as a reaction booster. This method was introduced by Baker in 1946 (54). Researchers at Los Alamos National Laboratory have recently introduced a laser-initiated modification to this reduction process that offers several advantages (55). A carbon dioxide laser is used to initiate the reaction between UF and calcium metal. This new method does not requite induction heating in a closed bomb, nor does it utilize iodine as a booster. This promising technology has been demonstrated on a 200 g scale. 

Additional energy to sustain the endothermic reaction is provided chemically by the addition of siUcon carbide grain or electrically by use of electrothermal fluidized beds (33—34), induction heating, or resistance heating. Chlorine efficiencies are typically 98% or better. 

Carbide. Zirconium carbide [12020-14-3] nominally ZrC, is a dark gray brittle soHd. It is made typically by a carbothermic reduction of zirconium oxide in a induction-heated vacuum furnace. Alternative production methods, especially for deposition on a substrate, consist of vapor-phase reaction of a volatile zirconium haHde, usually ZrCl, with a hydrocarbon in a hydrogen atmosphere at 900—1400°C. 

Induction heating is thought to cause vigorous convection because of the spatially varying average force field imposed along the melt surface. 

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