US3403212A

US3403212A - Electric furnace having a heating element of carbon or graphite for producing temperatures under high pressures

Info

Publication number: US3403212A
Application number: US487289A
Authority: US
Inventors: Sato Sennosuke
Original assignee: Japan Atomic Energy Research Institute
Current assignee: Nihon Genshiryoku Kenkyusho; Japan Atomic Energy Agency
Priority date: 1964-09-21
Filing date: 1965-09-14
Publication date: 1968-09-24
Anticipated expiration: 1985-09-24
Also published as: GB1117776A; DE1540987A1

Description

p 24, 1968 SENNOSUKE SATO 3, 03,

ELECTRIC FURNACE HAVING A HEATING ELEMENT OF CARBON OR GRAPHITE FOR PRODUCING TEMPERATURES v I I j UNDER HIGH PRESSURES Filed Sept. 14, 1965 2 Sheets-Sheet 1 INVENTOR Sept. 24, 1968 SENNOSUKE sATo 3,403,212

ELECTRIC FURNACE HAVING A HEATING ELEMENT OF CARBON OR GRAPHITE, FOR PRODUCING TEMPERATURES Filed Sept. 14; 1965 UNDER HIGH PRESSURES 2 Sheets-Sheet 2 1 qy J- Crap/lite 4 V L d f a Gas l l l 7mpera fave K INVENTOR BY I WQLMQLM United States Patent 3,403,212 ELECTRIC FURNACE HAVING A HEATING ELEMENT OF CARBON OR GRAPHITE FOR PRODUCING TEMPERATURES UNDER HIGH PRESSURES Sennosuke Sato, Ibaragi-ken, Japan, assignor to Nihon Genshiryoku Kenkyusho, Tokyo, Japan, a corporation of Japan Filed Sept. 14, 1965, Ser. No. 487,289 Claims priority, application Japan, Sept. 21, 1964, 39/ 53,572 2 Claims. (Cl. 13--31) ABSTRACT OF THE DISCLOSURE An electric furnace is provided and has a hollow carbon heating element core member, a furnace body including a casing enclosing the core member, and a heat insulation powdered carbon filling the casing and surrounding the hollow core member. A sealed pressure vessel is received in the furnace body, power leads connect to the core member, means supply the pressure vessel with an inert gas, and gas-permeable members of low density graphite are arranged close to inert gas introducing apertures formed in the casing.

This invention relates to electric furnaces of the resistance-heating type including a hollow core member of carbon or graphite as a heating element and has for its object to provide an electric furnace of the type described which is capable of producing superhigh temperatures under high pressures with the entire furnace body accommodated in a pressure vessel.

Electric resistance furnaces of the general type have an advantageous feature that they can be temperature-controlled with ease, but, in order to attain temperatures exceeding 3300 K., they are required to employ a core material which has sufficiently high softening and melting temperatures and is stable undergoing no chemical change in a high-temperature atmosphere. One metallic material satisfying this requirement is tungsten. Carbon or graphite is known to have a sublimation temperature of 3620 K. under normal pressure but its practical use is limited to the temperature range up to approximately 3400 K. One previous form of graphite tube furnace is the one designed by the inventor and disclosed in the Journal of the Society of Materials Science Japan, vol. 14, No. 137, pp. 93-94 (February 1965).

Under these circumstances, in order to provide an electric resistance furnace for producing superhigh temperatures it is a prerequisite to prevent softening and sublimation at such high temperatures of carbon or graphite, forming the heating element of the furnace.

Carbon or graphite forming a heating element has a gas-liquid-solid phase at 4l00 K. if placed in an atmosphere pressurized to approximately 100 atm. However, under pressures exceeding the critical pressure of carbon, though it has correspondingly higher melting and boiling points, its critical temperature in its solid-liquid phase has a value of approximately 4l00 K. irrespective of the pressure and no higher temperature is realizable. With regard to this, reference may be had to the constitutional diagram (FIG. 3), which corresponds to the one on page 118 of the book Nuclear Graphite by R. E. Nightingale, Academic Press, 1961.

In practice, the highest usable temperature is also limited due to the necessity of avoiding any softening of the furnace core or heating element. Experiments show, however, that the carbon or graphite core can withstand even a temperature as high as approximately 4100 K., if subjected thereto only for a limited period of time, in con- 3,403,212 Patented Sept. 24, 1968 trast to the normal working temperature of 3900 K. or under.

According to the present invention, a satisfactory result can be obtained by employing a commercially available carbon powder or carbon black as a heat-insulting material. Carbon powder is microscopically an electrical or heat conductor but forms a D001 conductor as a mass of powder, forming a peerless heat insulator at superhigh temperatures of the order of 3900 K.

The electric furnace according to the present invention is utilizable for melting and refining different metal and alloy materials as well as various ceramic materials at superhigh temperatures of up to approximately 3900 K. and is also highly useful in measuring different physical, chemical and electrical qualities of such materials and in their researches.

Further, according to the present invention, there is provided an electric furnace for producing superhigh temperatures which is highly helpful in high-temperature analysis of refractories and heat-resistant materials, formation of artificial jewel crystals, and researches on high-temperature gases including plasmas.

According also to the present invention, there is provided an electric furnace which can realize a wide range of superhigh temperatures with stableness and thus is highly valuable compared with conventional furnaces of the electric-arc or light-focusing type.

The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawing, in Which:

FIG. 1 is a longitudinal cross-sectional view of an electric furnace embodying the present invention, taken along the line I-I in FIG. 2, with a portion of the furnace body shown in external appearance;

FIG. 2 is a cross-sectional view of same, taken along the line IIII in FIG. 1; and

FIG. 3 is a constitutional diagram of graphite showing its state varying with temperature and pressure.

Referring to FIGS, 1 and 2, reference numeral 1 indicates a hollow tubular core member formed of graphite which is energizable for heat generation by an electric current fed through conductors 18 to metallic terminals 2. The tubular core member 1 is enclosed in a metallic casing 4 with end plates 3 of insulating material such as hard asbestos secured to the opposite ends of the casing. The casing 4, forming the furnace body, is encircled with coiled cooling tubes 5.

Cooling rings

6, 6 are arranged on the respective ends of the core member 1 and each communicate with a water inlet pipe 60 and a water outlet pipe 20 for circulation of cooling water through the cooling ring 6. Axially spaced spiders 7, formed of graphite, serve to support the core member 1 in the casing 4 coaxially therewith by way of ceramic insulating shoes 8 interposed between the inner wall of the casing and the adjacent ends of the respective spider legs. The tubular core member 1 is apertured to communicate with radially extending temperature-measuring tubes 9, through which radiant rays can be led from within the core member exteriorly of the furnace.

Carbon powder 10 is loaded in the space in the casing 4 surrounding the tubular core member 1. Arranged at the opposite ends of the casing 4 inside of the respective end plates 3 are gas-permeable rings 11, formed of lowdensity graphite, for the purpose of equalizing the inert gas pressures inside and outside of the casing 4. Each of the graphite rings 11 is formed on its outer end surface with an annular groove 11a, which is in communication with a plurality of through apertures 30 formed in the adjacent end plate 3. Tubes 19 are connected to the hollow tubular core member 1 at its opposite ends so that inert gas may be filled therein through the tubes as indicated at a. As indicated at 0, insert gas is also filled in a pressure vessel 14, which accommodates the furnace body, through an opening 15, connecting to a suitable pressure source, formed in the bottom wall of the vessel, as indicated at c. The inert gas is led into the heat-insulating material 10, loaded in the casing 4, through the apertures 30 in the end plates 3, groove 11a in the graphite rings 11 and through the gas-permeable texture thereof so that the gas pressures inside and outside of the hollow core member 1 are balanced with each other.

Reference numeral 12 indicates stays secured to the inner wall of the pressure vessel 14 to support the furnace body in place therein. Inert-gas preheating and directing members 13 of graphite are inserted in the hollow core member 1 at its opposite ends and are each externally helically grooved as at 13 so that the inert gas a fed through the adjacent pipe 19 into the core member 1 proceeds helically along the groove 13 while being preheated by the heat of the core member itself. In this manner, it will be apparent that in the core member 1 is obtained a uniform pressure distribution of the inert gas.

The wall of the pressure vessel 14 is designed to withstand a pressure of 105 atm. or over depending upon the working temperature of the furnace and is also designed to fully withstand not only the thermal stress caused by the differential temperature within the vessel but also any dynamic stresses such as the slow cyclic fatigue caused by the repetition of the thermal stress. The bottom opening 15 in the pressure vessel 14 is provided for introduction of electric conductors, cooling tubes, inert-gas supply and pressure-gage pipings, etc. into the furnace body. End covers 16 are secured to the wall of the pressure vessel at its opposite ends by bolt means and can be removed for insertion of the object to be heated into the hollow core member and its removal therefrom. Reference numeral 17 indicates observation windows formed in the wall 14 of the pressure vessel in alignment with the temperature-measuring tubes 9 secured to the core member.

The following table includes various data obtained with one practical embodiment of the present invention.

Core temperature, K.:

Working 3900.

Duration 100 hours (4100 K.).

Modifications of the structure herein disclosed may suggest themselves to those skilled in the art, and it is to be understood that the present disclosure relates to a preferred embodiment of the present invention which is by way of example only and is not to be narrowly construed.

What is claimed is:

1. An electric furnace of the resistance-heating type including a hollow carbon heating element core member, a furnace body including a casing enclosing said hollow core member, a heat insulation of powdered carbon filling said casing and surrounding said hollow core member for the length thereof with an inert gas sealed in said casing for equalizing the gas pressure inside and outside of said hollow core member, a heat resistant sealed pressure vessel receiving said furnace body therein, power supply leads connecting to said core member, means to supply said pressure vessel with an inert gas under pressure, said core member being designed to receive an object to be heated, said casing having a plurality of apertures for introducing inert gas into the interior of said closed casing, and

gas-permeable members of low-density graphite arranged close to said apertures and positioned in said casing.

2. An electric furnace of the resistance-heating type including a hollow carbon heating element core member, a furnace body including a casing enclosing said hollow core member, a heat insulation of powdered carbon filling said casing and surrounding said hollow core member for the length thereof with an inert gas sealed in said casing for equalizing the gas pressures inside and outside of said hollow core member, a heat resistant sealed pressure vessel receiving said furnace body therein, power supply leads connecting to said core member, means to supply said pressure vessel with an inert gas under pressure, means connect to the ends of said core member to supply the inert gas thereto and only release heated gas into said core member, and

graphite spiders engaging said core member intermediate the ends thereof to aid in positioning it in said casing.

References Cited UNITED STATES PATENTS 2,125,588 8/1938 Ridgway 1325 2,768,277 10/ 1956 Buck et al. 219-427 2,778,866 1/1957 Sanz et al. 132O 3,150,226 9/1964 Thorne et al. 13-25 3,244,141 4/1966 Weech et al. 13-31 X BERNARD A. GILHEANY, Primary Examiner.

VOLODYMYR Y. MAYEWSKY, Assistant Examiner,