US1802892A - Electric furnace - Google Patents

Description

April 28, 1931. F. A. HANSEN ELECTRIC FURNACE Filed April 18. 1929 2 Sheets-Sheet ALUNDUM MOLYBENUM IHalllllv Il JNVENTOR. (/W,

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F. A. HANSEN 1,802,892 ELECTRIC FURNACE Filed April 18, 1929 2 Sheets-.Sheet 2 b j E: i- 7 INVENTOR. ccd/: a fama/M,

BY @76 TTORNEY Patented Apr. 1931 UNITED STATES PATENT OFFICE FRED A. HANSEN, OF MILWAUKEE, WISCONSIN, ASSIGNOR TO HEVI DUTY ELECTRIC COMPANY, OF MILWAUKEE, WISCONSIN, A CORPORATION OF WISCONSIN' 4inseriert.' FURNACE Application filed April 18,

My invention relates broadly to electric furnaces and more particularly to an arrangement of heating element and terminal system for use in electric furnaces.

One of the objects of my invention is to provide an electric furnace construction havinga heating resistor which is constructed for operation at a verf.T high temperature of the order of 28000 F. and which will withstan-d such temperatures without deteriorating.

An object of this invention is to prevent by means of a protective gas, deterioration of the terminal of an electric furnace heating element, which would otherwise result in eX cessive oxidization.

Another object of this invention-is to prevent the overheating of a terminal by an enclosure of comparatively large radiating surface.

Another object of the invention is to provide means for cooling the terminal of the resistor by meansI of an inflowing protective gas.

Still another object of the invention is to secure the combined cooling effects of a large radiating surface in the form of an enclosure around the terminal of an electric furnace and the cooling action of intlowing gas therein.

Still another object is to permit the use of a comparatively small diameter terminal on the heating coil of an electric furnace to reduce the cost where an enlarged size terminal of such metal as tungsten, platinum, molyb- Clenum, etc., which results in an excessive cost.

Other and further objects of my invention reside in the construction of a heating system for electric furnaces as set forth in the following specification and shown in the accompanying drawings in which:

Figure 1 is a rear elevation of an electric furnace embodying the improvements of my invention with a part of the furnace broken away andy shown in cross-section; Fig. 2 is a horizontal cross-sectional view taken through the furnace structure of Fig. 1; Fig. 3 s a detailedv view of the heating coil showing the terminals thereof; Fig. 4 is an enlarged cross- 1929. Serial No. 356,268.

jectcd, but insulated therefrom, and through which an inilowing protective and cooling gas is iiowing by means of pipe connections to the enclosure.

Referring to the drawings, Fig. 1 shows a furnace chamber formed by a Inutile indicated by reference character 1 of any suitable material such as alundum, on which in helical form is wound the heating coil 3, and all surrounded by heat insulating material 4 preferably porous through which gas may circulate, enclosed in the furnace shell 5, such as steel. Terminal G-A is the terminal extlending from the front end of the furnace co1 Reference character 7-A designates a ceramic refractory tube of any suitable ma.- terial such as alundum surrounding terminals 6--A and G-B or like material.

Reference character 8 shows a connection block of any suitable material such as brass having means of making electrical contact to the terminal of heating coil 3 as indicated. The resistor G-A has its end fitted within the terminal block 8 and secured by screw members 9.. The projecting portion of terminal block 8 extending beyond the balance 0f the structure is used for connecting the electrical circuit by any suitable means such as clamps or lugs.

Reference character 10 shows a gas-tight enclosure of any suitable material such as a malleable iron T. The enclosure 10 is internally screw threaded at one end to receive an insulated plug 11 of any suitable material such as fibre, and having lug 12 with flat side faces 13 therein to form a wrench hold for inserting part 11 into part 10.

Reference character 14 denotes a gland made of any material such as brass forming a stuffing box in conjunction with plug 11, having compression means such as machine screws 15 forming a means of compression of any compressive packing 16 such as asbestos cord.

Reference character 17 shows a wrought iron pipe connection which extends to screw threaded extension 21 on enclosure 10 through which any inflowing gas takes the path of iiow indicated by arrow lines 18. This gas drives` oxygen from the chamber 19 through any suitable exit port in the furnace wall (not shown) until the chamber becomes saturated with the iniiowing gas such as hydrogen. Enclosure 10 is made gas-tight to the furnace shell by means of weld 20.

I preferably use molybdenum for furnaces operating up to 40000 F. The nature of molybdenum at elevated temperatures re,- quires protection against oxidization, and hydrogen is commonly used for such purpose. Due to the comparatively high cost of molybdenum, and further due to its heat resisting qualities molybdenum will carry approximately ten times the number of ampcres that can be successfully applied to another commonly used resistor element such as chromel, an alloy of 80% nickel-20% chroi mium.rk The high amperage thus applied would `'cause an overheating of the terminal of a heating coil where the terminal passes through the wall of the furnace unless a cooling means is provided. The same high amperage applied would also tend to overheat the terminal where it extends beyond the furnace shell unless a cooling means is applied. Such cooling means is secured preferably by the combined eifect of the cooling intlowing gas and the radiating effect from the comparatively large external surface of the terminal enclosure. A further heat distribution effect result due to the welded junction between the terminal enclosure and the furnace shell, as heat conduction from the fitting of the shell results in added radiation.

By the use of an enlarged connection plug, such as 8, having ample current carrying capacity, and when preferably made of a material such as brass, has sutcient combined conduction and radiating qualities as to keep the terminal .of the heating coil cool where the terminal is lodged in the connecting plug. W'hile I have specifically mentioned the use of alundum and molybdenum, I desire that it be understood that other metals having similar properties may be used. It will be understood that gases other than hydrogen may be used to effect cooling of the conductor terminals and to prevent oxidization.

In the terminal construction of my invention the effect of the gas is to cool the terminal commencing at the point that the terminal conductor G-A and G-B enters the enclosure 10 so that by the time the terminal wire reaches the tubes T-A and 7-B the wire is at relatively low temperature. Between the enclosure 10 and the furnace chamber, if the conductor 6A or 7--A is at red temperatures, the hydrogen gas prevents any chemical change taking place, which would take place by the union of oxygen with molybdenum, if the oxygen had not previously been displaced by the inowing hydrogen was.

lVhile I have described my invention in o ne of its preferred embodiments, I desire that it be understood that modifications may be made and that no limitations are intended other than those imposed by the scope of lthe appended claims. l

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1, In an electric furnace, an enclosing shell, a furnace chamber enclosed by said shell and having a wall substantially porous to the passage of gas, a heating coil in said furnace chamber, said heating coil having its endsextending through said shell, enclosing casings secured to the furnace shell and surrounding the ends of the conductor comprising said heating coil, and means for introducing a cooling medium of gas into said enclosing casings for reducing the temperature, and preventing oxidization of the terminals comprising part of said heating coil at points adjacent said furnace shell, said gas being directed through the porous wall of said furnace chamber.

2. In an electric furnace, a heating chamber, a shell surrounding said heating chamber, a heating coil disposed within said heating chamber with thel ends of the conductor extending through the walls of said heating chamber, said walls being substantially porous in structure, enclosing casings secured to said shell and surrounding the ends of said conductor, and means connected. to each of said enclosing casings for introducing a cooling medium of gas therein for reducing the temperature and preventing oxidization of the said ends of said conductor constituting part of said heating coil at points adjacent said furnace shell, said as being directed through the porous walI of said furnace structure.

3. In an electric furnace, an enclosing wall structure having suiiicient porosity for the passage of gases therethrough, a heating coil disposed within said enclosing wall structure, tubular members extending through said wall structure, a furnace shell enclosing said wall structure, enclosing casings connected with said furnace shell and surrounding said tubular members, the ends of said heating coil passing through said tubular members and through said enclosing casings,

and means for introducing gases into said enclosing casings and into said tubular members for reducing the temperature and preventing oxidization of the conductor forming said heating coil at points adjacent said furnace shell, said gases being directed through said wall structure.

4. In an electric furnace, an enclosing casin@ including a wall structure having a sufficient degree of porosity for the passage of gases therethrough, a heating chamber within said casing, a heating coil surrounding said heating chamber and having its ends eX'- tendng through said enclosing casing, hollow terminal members secured adjacent the exterior of said enclosing casing and surrounding the said ends of said conductor forming part of said heating coil at points adjacent the ends thereof, and means for introducing a cooling and protective gas into said hollow terminals for lowering the temperature and preventing oxidization of the ends of said heating coil at points adjacent the exterior of said furnace, said gas being directed through said wall structure to said heating chamber.

5. An electric furnace comprising a substantially porous refractory casing, a, heating chamber disposed within said refractory casing, a heating coil within said heating chamber, a heat resisting lining in said chamber, heat resisting tubes extending through said refractory casing and terminating eX- teriorly of the walls of said furnace, hollou7 terminal members enclosing the ends of said heat resisting tubes and surrounding the ends of the conductor forming part of said heating coil, and meansfor introducing a cooling and protective gas into said hollow terminals and into said heat resisting tubes, said gas being directed through said tubes and through said substantially porous refractory casing to said heating chamber.

6. In an electric furnace, a refractory casing, a shell-like wall structure surrounding said refractory casing, tubular members protruding through said refractory casing, hollow terminal members surrounding the ends of said tubular members and connected to said shell-like wall structure, a heating chamber within said refractory casing, a heating coil disposed around said heating chamber, said coil having the ends thereof protruding through said tubular members and said hollow terminal members, and means for introducing a cooling and protective gas into said hollow terminal members for reducing the ten'iperature of the conductor forming said ends of said heating coil at points adjacent the shell-like Wall structure of said furnace, said gas being directed through said tubular members and through the refractoryv casing vand into said heating chamber.

7. An electric furnace comprising a refractory casing, a heatingr chamber within said refractory casing, a heating coil disposed around said heating chamber, a heat resisting lining for said heating chamber, heat resisting tubular members protruding through said refractory casing from the eX- terior of said furnace, hollow terminal members enclosing the ends of said tubular members, the conductor constituting part of said heating coil passing through said heat resisting tubular members and through said hollow terminals, and means connected to said hollow terminals for introducing a cooling and protective therein surrounding the conductor substantially throughout the length thereof in the course of its passage through said refractory casing, said gas being directed through said tubular members and through said refractory casing into said heating chamber.

8. An electric furnace comprising a substantially porous refractory casing, a heating chamber within said casing, a heating coil within said chamber, a heat resisting lining of porous ceramic refractory for said chamber, tubularmembcrs of porous ceramic refractory passing through said refractory casing, hollow terminal members secured to the exterior of said casing, surrounding said tubular members and enclosing the ends of the Pconductor forming part of said heating coil,'s'aid hollow terminal members having means for introducing a cooling and protective gas therein for passage into said porous tubular members, saidf'gas being directed through said porous refractory casing into said heating chamber.

9. In an electric furnace, a porous refractory casing, a heat-ing chamber within said casing, a heating coil of molybdenum disposed within said heating chamber, tubular members of heat resisting porous ceramic refractory passing through said refractory casing and surrounding the ends of the molybdenum conductor, hollow enclosing terminals positioned exteriorly of said refractory casing and surrounding the ends of said heat resisting tubular members and said ends of said conductor, and means for introducing a cooling and protective gas into said hollow terminals for passage intosaid heat resisting tubular members for reducing the temperature and preventing oXidif/.a'tion of said ends of molybdenum conductor at points adjacent the exterior of said' chamber, said gas being directed throughsaid tubular members and through said porous refractory casing into said heating chamber.

l0. In an electric furnace, a substantially porous refractory casing, a heating chamber within said casing, a heat resisting lining of porous alundum for said chamber, a heating gcoil of molybdenum disposed within said heating chamber, porous tubular members of alundum passing through said refractory casing, for receiving the ends of the molybdenum conductor and surrounding said conductor throughout the passage thereof to a point exteriorly of the furnace, hollow terminal members surrounding the ends of said tubular members, and means for introducing la gaseous medium into said hollow terminal members for penetration through said porous tubular members and through said porous lining by passage directly through said refractory casing.

11. In an electric furnace, a refractory casing, a heating chamber Within said casing, a heating coil within said chamber, tubular members extending through said refractory casing for receivin and enclosing the ends of said heating coil,- terminal members located exteriorly of said refractory casing and surrounding said -tubular members, and means for introducing into said tubular members and into said terminal members a gas for cooling, and for preventing oxidization of the said ends of said conductor forming part of said heating coil, said gas being directed, through said tubular members and through said refractory casing.

12. In an electric furnace, a refractory casing, a heating chamber within said casing, a heating coil of molybdenum disposed within said casing, heat resisting tubular members passingfthrough said refractory casing for receiving the ends of the molybdenum conductor forming part of said heating coil, hollow enclosing terminals located exteriorly of said refractory casing surrounding the ends of said tubular members, and means for introducing a gas into said terminals and tubular members for cooling, and for preventing oxidization of said ends of the conductor constituting said heating coil at points adjacent the entry of the conductor into said heating chamber, said gas being directed through said ltubular members and through said refractory casing.

13. In an electric furnace, a refractory casing, a heating chamber within said casing, a heating coil of molybdenum disposed within said casing, heat resisting tubular members passing through said refractory casing for receiving the ends of the molybdenum conductor forming part of said heating coil, hollow enclosing terminals located exteriorly of said refractory casing surrounding the ends of said tubular members, and means for introducing hydrogen gas into said terminals and tubular members for preventing oxidization and for cooling of said ends of the conductor constituting said heating coil at points adjacent the entry of the conductor into said heating chamber, said hydrogen gas being directed through said tubular member and through said refractory casing into said heating chamber.

14. A terminal structure for the ends of the resistor in a resistor type furnace comprising a tubular member extendino through the furnace Wallandsurrounding tthe end of the resistor, said tubular member projecting beyond the limits of the furnace wall, a cylindrical member secured to the side of the furnace wall concentrically with respect to the projection of said tubular member therefrom, said cylindrical member being screw threaded at its extremity, an insulated bushing having screw threads engaging the screw threads on the extremity of said cylindrical member, connecting means extending through said insulating bushing and establishing connection with the. end of said resistor, and means for introducing a cooling gas in said cylindrical member for passage through said tubular member around the resistor throughout the length of the passage of said resistor through said tubular member.

l5. A terminal for the ends of a heating resistor in an electric furnace comprising a tubular member extending through the furnace Wall and surrounding the end of the resistor substantially throughout the length of its passage from the electric furnace, said tubular member projecting beyond the limits of the furnace wall, a cylindrical member having one end thereof secured to the furnace wall concentrically around the projection of the tubular member from the furnace wall, said cylindrical member being enlarged at the opposite end and interiorly screw threaded, an insulated plug having screw threads engaging the screw threads in the interior of the "enlarged end of said cylindrical member, a connector extending through said plug and establishing electrical connection with the end of said resistor, and means for introducing a cooling gas into said cylindrical member and surrounding the end of said resistor throughout its passage through said tubular member.

In testimony whereof I a-iiix my signature.

FRED A. HANSEN.

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