US2777891A - Electric melting furnace - Google Patents

Description

Jan- 15, 1957 s. D. WILLIAMS ELECTRIC MELTING FURNACE 2 Sheets-Sheetl F'iled June 4, 1954 amid/Ummm.

HTOB/VE YS S. D. WILLIAMS ELECTRIC MELTING FURNACE Jan. 15, 1957 2 Sheets-Sheet 2 Filed June 4, 1954 INVENTOR. Sha ,40. Wazaa/M BY l - ,4 7 roe v5 ys United States Patent O ELECTRIC MELTING FURNACE Steele D. Williams, Avalon, Pa. Application June 4, 1954, Serial N o. 434,367 14 Claims. (Cl. 13-6) This invention is for an electric melting furnace and pertains to a melting furnace designed to continuously receive charges of so-called raw material at one end and during operation, to discharge a nished product at the other. The invention constitutes an improvement on the invention disclosed in my copending application Serial No. 303,314, tiled August 8, 1952.

The furnace herein described is especially designed for the production of glass fibers and will hereinafter be particularly described in that connection, but this is by way of illustration and not limitation, and the furnace may be used for the heating or melting of other materials.

Glass melting furnaces are generally large structures designed to handle large charges so that the glass will have an adequate time to age or mature after the ingredients are melted, but glass used in the making of fibers does not require the same degrees of optical perfection that is necessary in most glass and can therefore be quickly produced after the ingredients are melted. The present invention has for its object therefore to provide a furnace of compact construction designed to hold a relatively small charge, but in which the charge is quickly brought to the desired molten condition and may thereafter be quickly withdrawn, and which, if desired, may be continuously operated. That is to say, a charge of glass-making constituents either in the dry or molten state, may be continuously or intermittently delivered to the furnace so as to accomplish a continuous delivery of bers from the furnace.

A further object of the invention is to provide a furnace in which the melting chamber is included within a hollow electric resistance which provides a isource of heat for the chamber.

A further object is to provide a resistance furnace of tubular form with one end of the tube elevated above the other end so as to obtain a continuous flow of the molten glass formed within the furnace by the glassmaking constituents charged into the elevated end thereof in such a way as to cause turbulence in the material Within the tube and to thereby assist in the elimination of seeds and other objectionable characteristics of the molten mass within the furnace.

A further object is to maintain a temperature in the resistance tube which is much higher than that of the molten glass initially delivered to the tube and to, in that way, subject the melt within the melting or refining chamber to a rapid increase in temperature and also to maintain it at a relatively high temperature for a sufficient period to produce tough glass.

A further object of the invention is to provide a furnace of novel construction, and which is small and compact, and in which the elements are protected from the high heat and oxidation.

A further object of the invention is to provide a furnace having an improved outlet tube for the discharge of the nished product.

2,177,891 Patented Jan. 15, 1957 These and other vobjects and advantages are obtained by my invention, as will be more fully apparent from the following description and reference to the accompanying drawings, in which:

Figure 1 is a longitudinal vertical section through a furnace embodying my invention, certain accessories being schematically shown;

Figure la is a fragmental sectional view of a portion of the furnace structure illustrated in Figure l and discloses a structural detail employed in connection with the glass melting chamber;

Figure lb is a fragmental sectional view of a portion of the apparatus illustrated in Figure l and discloses auxiliary means for heating the glass delivery tube forming a part of that apparatus;

Figure 2 is a side elevation, on a larger scale of the discharge tube;

Figure 3 is a perspective View with showing the discharge tube;

Figure 4 is a perspective view of the top of one of the carbon supports with the terminals and connectors, the water cooling system not being shown; and

Figure 5 is a view similar to Figure 4, showing the terminals with the water-cooling system, but for the purpose of clarity the connectors have not been included.

Referring to the drawings and particularly Figure 1, the structure comprises a supporting frame made of metal sections designated generally as 2. On this frame is supported an enclosing casing having one end higher than the other, the uppermost portion of the bottom being designated 3, and the lowermost portion of the bottom being designated 4, and 5 is the inclined connecting portion of the bottom between 3 and 4. The structure has end walls 6 and 7, and parallel side walls 8. There is a removable cover 9, the casing being rectangular in plan, and this cover has a close t on the top of the casing.

The enclosure is preferably formed of heavy gauge sheet metal, and the entire interior is covered with a heavy lining of asbestos or other relatively light heat insulating material, this lining being designated 10.

Within the casing is the furnace structure itself, and this includes a block or pedestal 11 of a refractory material which sets on the elevated portion 3 of the bottom. Set on this pedestal is a heavy carbon block or column 12, and it may be secured to the base 11 in any suitable parts broken away f manner.

Set into the top of the column 12 are a plurality of electric terminals in the form of copper tubes, these preferably being arranged as shown in Figures 3 and 4, the several tubes being designated 13. They extend down into the carbon column for several inches and have a close lit in the top of the column so as to make good electrical contact with the carbon. A multiple connector 14, best shown in Figure 4, is attached to the several copper tubes and connects the terminal of a cable 15 which leads to a source of electric current.

Provision is preferably made for cooling these copper terminals. This cooling system is best shown in Figure 5, and includes a manifold 16 connected with a source of water supply, and from this manifold there are a plurality of long tubes 17 terminating near the bottoms of the copper terminals 13. A second manifold 18 is positioned below the manifold 16 and has small pipes or tubes 19 extending down into the terminals 13, and terminating just below the tops of these terminals. There is one tube 19 for each of the terminals. The manifold 18is connected with a suction pump (not shown). By means of this system, cold water can be introduced into the bottom of each of the several copper terminals or tubes and be drawn olf at the top.

On thelower level 4 of the bottom there is a similar pedestal 2u supporting a similar carbon column 21. Set into the top of this column are similar terminals 13 with connectors 14, and there is a similar Water circulating system including manifolds i6 and 1S with the tube arrangement as previously described. The supply cable connected to the terminals at the top of the lower carbon column is designated 1:3', and is of course connected to the other side of the source of current supply (not shown).

The carbon block 1 2 has a downwardly opening inclined socket 22 in the face thereof which confronts the column 21, and the column 21 has an upwardly-opening inclined socket 23 in the face confronting the upper column 12. The areas of carbon block electrodes 12 and 21 may be reduced at any desired rate and in any desired` manner adjacent the region of contact with tube 24, to thereby change the current density at the delivery end of the block to near or equal that of resistance tube 24.

Tightly fitted into the sockets 22 and 23 and extending between the two columns is a dense carbon tube 24. is tightly fitted into the sockets 22 and 23 in order to make good electrical contact therewith, and it comprises the electrical heating resistance of the furnace extending as. it does between the two carbon columns 12 and 21. Fitted within the carbon tube 24 is the receiving cylinder or tube 2S which is formed of a high refractory material such as an aluminum oxide refractory. I have found a tube of a refractory sold under the trade-mark Alfrax to be satisfactory for this purpose. ln Figure la I have shown the tube 25 coated on both the inside and outside with fused zirconium oxide. Such coatings are optional but desirable.

The upper end of the tube 25 is closed by a plug 26 of a refractory material similar to 25, and in the lower end of the tube 25 there is a plug 27 having an opening therethrough, the axis of which opening is horizontal.

Near the upper end of the receiving tube 25 there is an upwardly-extending refractory tube 28 terminating in a funnel-like hopper 29 in its upper end, and this tube 28 passes through an opening in the top 9 so that materials to be melted in the furnace can be intermittently or continuously charged into the funnel and flow down the tube 28 into the upper part of the refractory tube 25. The opening in the cover has a close fit about the tube 28. The inclination of the tubular furnace chamber is steep, so that the upper end is well above the lower end, assuring a small area over which dross or slag may form and a substantial depth of molten material, sutncient to maintain a good hydrostatic head or pressure in the discharge tube.

Leading from the lower end of the receiving cylinder 25, and passing through the plug at the bottom thereof is the discharge tube assembly designated generally as 30. This assembly includes a horizontally-extending inner tube 31 formed. either of a highly heat-resistant material, or of refractory and supported at. its inner end by a refractory block 31A shown. as set into carbon column 21. It is almost completely surrounded by a close fitting heat insulating shell 32 which may be of the same material as the tube 25. Along one side of the shell there is a continuous slot through which the tube 31 is exposed, and the tube 31 is provided at spaced intervals with smallV outlet openings 33. The outer end of the tube 31 is closed by a removable refractory plug 3d. rlhe inner discharge tube 31 may be heated from one or both ends by a separate current supply, such as ll() volts 60 cyclecurrent having a standard rheostat in the line to control the current input and to thereby regulate the temperature in the discharge tube.

ln Figure lb l have diagrammatically shown the discharge tube 31 so heated. A source of electric current 55 delivers current to heating elements 5l and 52 which are located in series and coupled together by a wire 53 which forms a part of `the current delivery circuit. A rheostat 54 is located in the circuit for controlling the amount of current delivered to the heating elements 51 and 52.

Extending along the outside of the shell 32 are a number of parallel resistance heating wires or rods 35 which are in close contact with the shell 32. Corrugated straps 36 around each end of the assembly make contact with the rods 35 and hold them in spaced relation around the periphery of the tube, and these strips constitute connectors for connecting the resistance wires or rods to electric cables 37 and 38.

By means of these resistance heaters the discharge tube assembly can be brought up to a high temperature and the tube can be maintained at the proper degree of heat after the furnace has been put into operation by means of the resistor rods. The outer end of the discharge tube assembly may be supported on an A frame or other suit able supporting stand 30a.

To retard the dissipation of heat from the melting tube or melting chamber, the casing is partly filled with nely divided insulating material. l may use for this purpose nely divided carbon as indicated at 39, but if nely `divided loose carbon is employed there is a transverse partition 40 across the inside of the casing which is formed of an electrical non-conducting material so that the loose carbon cannot conduct current from one of thc carbon columns -to the other. instead of using loose carbon or carbon black, I may use some other low bulkdensity heat insulating material, and if necessary, additional molded insulation can be provided around the outside of the tube 24.

To protect the furnace from temperatures, provision is made mosphere of inert gas therein. To this end there is a manifold 41 extending along one or both sides of the casing having discharge pipes 42 that open into the casing at intervals. This manifold may be connected to a source of inert gas 43. A suitable inert gas is nitrogen, and it is delivered under just suicient pressure to assure of the atmospheric air being displaced from the casing. Since the casing is practically closed aga-inst the escape of gas, very little gas is required during operation to protect the furnace.

Also the high bulk density material is most effective if it is kept loose and liuifed up. To accomplish this there Amay be a suction manifold 45 with a number of pipes 46 leading therefrom to various locations in the casing. A combined suction, blower and storage unit, schematically illustrated at 47, has its intake or suction side connected to the manifold 45. A discharge pipe 48 leads from this unitv to a manifold 49 having a plurality of branch pipes 50 through which the insulating material is blown back into the casing where it will settle, thus being loosened and aerated. The drawings are intended to be schematic as to the exact. location of the pipes 46 and 50.

In the starting up of the furnace, a charge of materials, as for example a boro-silicate glass-forming mix, is introduced into the furnace chamber through the hopper 29 and tube 28, and the material will gravitate to the lower end until the furnace is filled up to the bottom of the tube 28. After the furnace has been charged with the meltable or molten material, the chamber is purged by displacing the air with an inert gas as explained above, and current is then applied to the two carbon blocks, whereupon the carbon tube 24 is heated by resistance to the flow of current therethrough, and this heat of course is communicated to the charge on the interior. After the melting of the initial charge has been accomplished, theV further rate of melting can be closely regulated by regulating the supply of current to the two carbon columns 12 and 21.

At the proper time the resistance wiresl or rods 36 are heated to bring the discharge tube 31 up to a temperature where the melt will not be chilled to a point' where it solidies, and as the operation continues, the melt will tlowthrough thetubes and emerge fromthe small openings 33.v r[he openings 33 will preferably' all be of uniform size so that the rate of discharge from each opening oxidation under operating for maintaining an atis the same, and in the case of making glass fibers, a blast of high velocity air may be blown against the streams of glass discharging from the holes 33 in a manner well understood in the art to attenuate the glass into fibers.

In other instances the tube 31 may be shorter and the holes 33 may not necessarily be provided, in which case the plug 34 at the discharge end of the tube is removed and the melted material can discharge from the end of the tube.

Once the operation of the furnace is commenced, material is supplied to the hopper 29 and ows into the melting chamber by gravity and the rate of ow of course is controlled by the rate at which the melted material is withdrawn from the bottom of the melting tube. Considerable heat is necessarily generated in the carbon columns or carried by conduction from the tube 24 into the columns, and the water cooling system hereinbefore described for the several copper terminals 13 protects these terminals from the high heat. The loss of heat by radiation from the tube 24 is retarded by the low bulk density insulating material 39, and if, after a period of operation, this mate- -rial tends to become densely packed, it may be fluffed up through the system hereinbefore described, including the manifold 45, the pipes 46, the suction and blower unit 47, and the manifold 49 and discharge pipes 50.

The furnace described is relatively compact and light so that it does not require special foundations, and it can be located in a plant area suited to the subsequent operations of drawing the glass fibers or other procedures that are to be carried out on the melted material without extensive alteration of the floor area of the building or the incorporation of special foundations. By supplying current to the carbon tube 24 through the carbon columns 12 and 21, the presence of metal terminals directly at each end of the melting tube is avoided, thus eliminating any need for cooling equipment immediately adjacent the ends of the carbon tube, while simultaneously eliminating the problem of maintenance of the metal terminals. The copper tubes 13 are located suiciently far from the ends of the furnace tube so that the cooling of them does not affect the temperature of the tube at its ends. At the same time any of the elements of the furnace can be quickly replaced if necessary with very little lost time for cooling down the furnace, and with a minimum of down time while the repair or replacement is being made. All parts are standard so that bricklayers or other skilled labor are not required either in the erection of the furnace or in its subsequent maintenance.

While I have shown and described one particular ernbodiment of my invention it will be understood that various changes and modifications may be made in the construction shown Within the contemplation of my invention and under the scope of the following claims.

What I claim is:

l. A melting furnace of the class described comprising a tubular shell constituting an electric resistance unit, carbon columns in which the ends of said tube are ernbedded and with which the tube ends are in good electrical contact, metal terminal assemblies on each of the carbon columns, said tube being supported in said columns with one end higher than the other, a discharge tube leading from the lower end of the tubular shell, and means for introducing material to be melted into the upper end of the tubular shell.

2. A melting furnace as described in claim l in which said carbon columns are surrounded by an enclosure, and there is means for maintaining a non-oxidizing atmosphere in the enclosure.

3, A melting furnace as defined in claim 1 in which the terminal assemblies comprise a plurality of metal tubes embedded in each of the carbon columns with a common connector attached to all of the tubes of each column, and means for circulating a cooling fluid through said metal tubes.

4. A melting furnace as dened in claim 2 in which the enclosing casing also contains a low bulk` density in\ sulating material surrounding the tubular shell and the carbon columns.

5. A melting furnace of the class described comprising a tubular Ishell constituting an electric resistance unit, said shell being formed of carbon and having a refractory lining over the interior thereof, carbon columns in which the opposite ends of said tubular shell are embedded and with which the tubular shell ends are in good electrical contact, said tube having one end higher than the other, a metal terminal assembly on each of the carbon columns through which current is supplied to the opposite ends of the tubular shell, a horizontally-extending discharge tube extending from the lower end of the tubular shell, a casing enclosing the tubular shell and carbon columns and through which the discharge tube projects, means for maintaining a non-oxidizing atmosphere in the chamber, and a charging tube extending from the tubular shell upwardly through the casing and opening at its inner end into the interior of said tubular shell through which material to be melted can be introduced into the upper end of said tubular shell.

6. A melting furnace of the class described compris- -ing a tubular shell constituting an electric resistance unit, said shell being formed of carbon and having a refractory lining over the interior thereof, carbon columns in which the opposite ends of said tubular shell are embedded and with which the tubular shell ends are in good electrical contact, said tube having one end higher than the other, a metal terminal assembly on each of the carbon columns through which current is supplied to the opposite ends of the tubular shell, a horizontallyextending discharge tube extending from the lower end of the tubular shell, a casing enclosing the tubular shell and carbon columns and through which the discharge tube projects, means for maintaining a non-oxidizing atmosphere in the chambena charging tube extending from the tubular shell upwardly through the casing and opening at its inner end into the interior of said tubular shell through which material to be melted can be introduced into the upper end of said tubular shell, and electrical resistance means extending along said horizontal discharge tube for independently heating the same.

7. A melting furnace of the class defined in claim 6 wherein said discharge tube is enclosed in a refractory shell with said electric heating means outside of said shell, the shell being longitudinally slotted and the tube having spaced discharge orifices therein exposed through the slot in said shell.

8. A melting furnace as dened in claim 5 wherein said casing contains a loose low bulk density heat insulating material enclosing said tubular shell and surrounding the carbon columns, and means for withdrawing said low bulk density heat insulating material from the casing and discharging it back into the casing for liufling the same when it becomes compacted.

9. A glass melting furnace including a refractory tube located in an inclined position with one end elevated above the other and enclosing a tubular melting charnber and having a delivery port at the lower end thereof; batch-delivery means communicating with the interior of said chamber near the upper end thereof; and velectrical resistance element extending along and in contact with the exterior surface of said tube; current-delivery means in electrical contact with said element; a casing enclosing said tube and said element; a glass delivery tube communicating with said delivery port and extending through said casing; and means for delivering an inert atmosphere to the interior of said casing and around said tube and said element.

10. A glass melting furnace including a tubular melting chamber located in an inclined position with one end elevated above the other end and having a batchreceiving opening located adjacent the elevated end thereof and ya glass delivery port located adjacent the lower end thereof; an electrical resistance' element. extending along said'chamber-in heat imparting relation thereto; a horizontally extending delivery tube communieating With the interior of said chamber through said delivery port and provided'with at least one discharge aperture; electrical means for delivering yheat to said tube; 'and' separate means for delivering heating current to said element and to said electrical means.

11. A glass melting furnace including a tubular, inclined melting chamber with one end` elevated above the other and having a batch-receiving opening located adjacentfthe upper end thereof and a glass delivery port located at the lower end thereof; an electrical resistance element surrounding and extending along said chamber in heat imparting relation thereto; a separate current delivery means in electrical contact with each end of said element; a horizontally extending tube communieating with said delivery port of said chamber and having discharge apertures located in spaced relation along the length thereof; electrical heating means extending along said tube in heat imparting relationship thereto; and separate means for delivering heating current to said element and to said means.

l2. A melting furnace of the class described including a tubular shell constituting an electrical resistance unit surrounding a melting chamber; a separate carbon column in electrical contact with each end of said shell, said shell being supported by said columns with one end higher than the other; a discharge tube leading from the lower end of the chamber enclosed by said shell; means for introducing material to be melted through an open` ing in` said shell and into the upper end of said chamber; and means for delivering electric current to said columns and through said columns to said shell.

13. A glass melting furnace including a refractory tube located in an inclined position with one end elevated above the other and enclosing a melting chamber having a hatchrec'eiving opening "located adjacent the elevated end thereof 'and `a l,glass delivery port loca-ted adjacent .thev lower 'end thereof; 1an electrical resistance velement extending along and .surrounding said refractory tube; spaced'Y electrical conductor columns, each apertured to receive Aand :support an end of said element and said tube; and electrical 'terminal members secured to lsaid columns for delivering electric current to said `columns and to said element.

14. .A `glass. melting furnace including a refractory tube located in an inclined position with one end elevated above the other and enclosing a melting chamber having a batch-receiving vopening located adjacent the elevated end thereof and a glass delivery port located adjacent the lower end thereof; an electrical resistance element extending along and surrounding said refractory tube; spaced electrical conductor columns, each apertured to receive and support an end of said element and `said tube; electrical terminal members secured to said columns for delivering electric current to said columns and to said element; a casing enclosing said tube, said element and Said columns; and means for delivering an inert atmosphere to the interior of said casing.

References Cited in the rile of this patent UNITED STATES PATENTS 335,499 Bradley et al Feb. 2, 1886 388,645 Diehl f Aug. 28, 1888 984,119 Wood Feb. Y4, 1911 1,375,615 Soncini Apr. 19, 1921 v 1,481,228 Rondelli Jan. l5, 1924 1,528,542 Hancock et al Mar. 3 1925 1,610,376 Hitner Dec. 14, 1926 2,186,718 Ferguson I an. 9, 1940 2,188,927 Slayter Feb. 6, 1940 2,680,771 Kistler lune 8, 1954

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