Electric resistor furnaces

Electricity generation Electric lighting Electric melting Electric power Electric resistor furnaces Electric vehicles... 

The most widely used and best known resistance furnaces are iadirect-heat resistance furnaces or electric resistor furnaces. They are categorized by a combination of four factors batch or continuous protective atmosphere or air atmosphere method of heat transfer and operating temperature. The primary method of heat transfer ia an electric furnace is usually a function of the operating temperature range. The three methods of heat transfer are radiation, convection, and conduction. Radiation and convection apply to all of the furnaces described. Conductive heat transfer is limited to special types of furnaces. 

Fig. 1. Main types of electric furnaces (a) resistance furnace, indirect heat (resistor furnace) (b) resistance furnace, direct heat (c) arc furnace (d) induction furnace. A, charge to be heated or melted B, refractory furnace lining C, electric power supply D, resistors E, electrodes F, electric arc G,...

There are large-scale operations using direct-heat resistance furnaces. These are mainly in melting bulk materials where the Hquid material serves as a uniform resistor. The material is contained in a cmcible of fixed dimensions which, coupled with a given resistivity of the material, fixes the total resistance within reasonable limits. The most common appHcation for this type of direct-heat electric resistance furnace is the melting of glass (qv) and arc furnaces for the melting of steel (qv). 

Use Electric resistors and heating elements, terminals, and other accessories for electric heating elements, electric heating appliances, electric furnaces. 

An isolated electrical resistor F is wound around the reactor to realize a furnace of 600 W, which is controlled by a thermocouple R. A sort of umbrella protects the specimen against possible water drops. The upper part of the reactor contains a Teflon ball used as an exhaust valve to control vapor pressure in the reactor. 

Figure 6.32. Thermistor DTA apparatus of Pakulak and Leonard (22) (o) sample holder and furnace (6) thermistor bridge circuit. ( )(/ A. output leads B, teflon sleeving C, electric resistor cement D. 1-mm centrifuge tube E. 1.5-mm centrifuge tube F. two-hole ceramic tube G. thermistor H, test tube, (ti) A. furnace B. furnace coil and well C. block, aluminum D, sample tubes E, thermistor containers T,. T>, T3 thermistors G, glass ring I in. x 3 in. (f>) JR, JR2, 100 G potentiometer R3, JR, 1000 Q 1% Rs, 2000 Q 1%. T T3, thermistors-100,000 Q at 25 C B, IA V dry cell.

Most electrically heated furnaces use the principle of Joule, or resistance, heating where current flowing through a resistor produces heat. The starting point is Ohm s law ... 

Crucible furnaces are indirectly heated using fuel-fired burners or electrical resistors. For fuel-fired crucibles, the thermal efficiency is not as high as for other melting furnaces, since it is difficult to make use of the heat of the combustion products. They are relatively inexpensive and since the flames are not in contact with the molten metal, metal losses are low and the melt quality is high, and also alloy changes can be readily carried out. [175, Brown, 1999]... 

Uses Catalyst in organic synthesis source of boron compounds refining of alloys soldering flux electrical resistors extinguishing magnesium fires in heat-treating furnaces mfg. of diborane semiconductor dopant boron vapor deposition raw material (boron fibers)... 

The most common types of sintering furnaces are electrical resistance furnaces in which a current carrying resistor, commonly called the furnace element or winding, provides the source of heat. In addition to size and cost, important considerations in the selection of a furnace are the maximum temperature capability and the atmosphere in which it can be operated for extended periods. Table 12.1 provides a selected list of common furnace elements. Several metal alloys (e.g., nichrome) can be used as furnace elements for temperatures up to 1200°C in both oxidizing and reducing atmospheres. For extended use in air, other furnace elements can deliver higher temperatures e.g., Pt (up to 1400°C) SiC (1450°C) ... 

A. G. E., Robiette, Electric Melting Practice, John Wiley Sons, Inc., New York, 1972, 412 pp., arc, induction resistor, and special melting furnaces are discussed. 

Resistance heating usually involves the highest electricity costs, and may require circulating fans to assure the temperature uniformity achievable by the flow motion of the products of combustion (poc) in a fuel-fired furnace. Silicon control rectifiers have made input modulation more economical with resistance heating. Various materials are used for electric furnace resistors. Most are of a nickel-chromium alloy, in the form of rolled strip or wire, or of cast zig-zag grids (mostly for convection). Other... 

Tammann Furnace. An electric high-temperature furnace having a carbon tube as resistor it is used without a protective atmosphere but is sealed to prevent ingress of air (G. Tammann see paper by E. Lowenstein. Z. Anorg. Chem., 154,173, 1926.). 

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