US2283188A

US2283188A - Electric furnace

Info

Publication number: US2283188A
Application number: US373228A
Authority: US
Inventors: Anders E A S Cornelius
Original assignee: Hartford Empire Co
Current assignee: Hartford Empire Co
Priority date: 1941-01-06
Filing date: 1941-01-06
Publication date: 1942-05-19
Anticipated expiration: 1959-05-19
Also published as: NO65715A

Description

HLEUE 3 Sheets-Sheet l A.. E. A. S. CORNELBUS ELECTRIC FURNACE Filed Jan. 6, 1941 'May i9, 1942.

May 39 1942- A. E. A. s. coRNELuus 2,283,188

ELECTRIC FURNACE Filed Jan. 6, 1941 3 Sheets-Sheet 2 ,ff ff /////n///////// May 19, 1942.

A. E. A. s. co'RNELlus ELECTRI G FURNACE Filed Jan. 6, 1941 3 Sheets-Sheet 5 Patented May 19, 1942 UNITED STATES PATENT OFFICE ELECTRIC FURNACE Anders E. A. S. Cornelius, Stockholm, Sweden, assigner to Hartford-Empire Compan Hartford, Conn., a corporation of Delaware Application January 6, 1941, Serial No. 373,228

11 claims.

This invention relates to improvements in electric furnaces for making glass, water soluble silicates, vitreous enamels and similar substances and to methods of making such substances therein. It relates more particularly to the construction and use of electric furnaces of the type having a submerged throat beneath a transverse bridge wall for the passage of molten glass or other molten substance being made from a melting and plaining section of the furnace to the working or delivery section thereof.

In designing electric furnaces of the character described, care should be taken to provide for desirable life and durability of the furnace walls in contact with the molten material in the melting section of the furnace and of the electrodes employed therein while also producing and maintaining a high thermal eillciency so as to permit the use of electric power despite the relatively high cost thereof. 'I'hese -considerations have led to spacing from the transverse bridge wall and other transverse walls of the furnace of the electrodes employed to pass electric current transversely through the conductive bath oir molten material in such furnace and the further expedient of covering the molten bath in the melting chamber or portions of the furnace with a heat absorbing blanket of the raw materials or batch so as to cool and protect the upper portions of the electrodes,

which may project into such blanket or lie immediateiy therebeneath. Also, a space of substantial depth may be provided in the furnace chamber into which the raw materials are supplied so that plaining of the molten glass or other molten material being made may be effected in the lower portion of such chamber in a zone of lower temperature than the superjacent melting zone.

A furnace of the construction and mode of operation just described has a disadvantage or shortcoming which will now be explained in connection with the making of glass. At the transverse bridge wall beneath which the molten glass passes through the submerged throat to the delivery or working end of the furnace, a surge develops which tends to draw molten material directly from the melting zone and also incompletely fused or raw material from the overlying blanket of raw materials. This causes partially fused raw materials to penetrate to and mix with the completely molten, refined material leaving the melting and refining chamber of the furnace so that the glass arriving at the working or delivery end of the furnace will be 65 of' lower quality than would be the case if the surge had been prevented.

An important object of the present invention therefore is to prevent penetration of the partially or inadequately fused materials into the completely molten, refined material that is ready to be withdrawn from the melting and refining chamber.

A further object of the invention is to improve the condition vof the material in the lower portion oi' the melting and refining chamber so as to obviate need of any special rening chamber or to permit the, use of a refining chamber of substantially reduced size.

Other objects of the invention relate to the provision of suitable electrodes suitably located in the melting and refining chamber for high efficiency without undue deterioration of or attack on the walls of such chamber or the electrodes therein.

In carrying out the invention, premature mixing of partially fused or inadequately refined materials with the completely molten and refined material arriving at the intake end of the submerged throat beneath the transversely extending bridge wall may be prevented by increasing the electrical density in a vertical zone in the melting and refining chamber adjacent to the intake end of the submerged throat so as to increase the temperature of the molten material in this zone and thus produce therein convection currents counter to the out-surge at the throat. The additional heat produced in this zone in accordance with the prsent invention will be carried by the convection currents to the actual melting zone and there utilized in the process of melting raw materials so that practically no additional heat loss is' caused by the improved method.

Other objects and advantages of the invention will be explained or will become apparent from the following description of the construction and operation of a numberof practical embodiments of the invention, as shown in the accompanying drawings, in which:

Fig. 1 is a longitudinal vertical section through the melting and refining portion and part of the remainder of an electric furnace constructed according to the present invention and adapted to carry out the method thereof, the view being substantially along the line indicated at I-I in Fig. 2;

Fig. 2 is a horizontal section through the Structure shown in Fig. 1 as viewed in plan;

Fig. 3 is a transverse vertical section along the line 3--3 of Fig. 1;

Fig. 4 is a similar section along the line 4--4 of Fig. 1:

Fig. 5 is a view similar to Fig. 1 but showing a second form of furnace structure having a delivery end portion provided with a glass feeding forehearth, the view being along the line 5--5 of Fig. 6;

Fig. 6 is a horizontal section along the line 6-6 of Fig. 5, as viewed in plan;

Fig. 7 is a transverse section through an approximately half portion of the furnace at the plane indicated by the line 1-1 of Fig. 5, looking in the direction of the arrows;

Fig. 8 is a similar view but taken at the plane indicated by the line 8--8 of Fig. 5;

Fig. 9 is a like view but taken at the plane indicated by the line -9 of Fig. 5;

Fig. `10 is a view generally similar to views 1 and but showing a'third form of furnace structure, having at the delivery end thereof a chamber equipped to permit glass to be drawn therefrom in an upward direction in sheet form, the view being taken along the line |0-I0 of Fig. 11; Fig. 11 is a view along the line II-II of Fig.

Fig. 12 is a transverse section along the line IZ-IZ ofFig. 10;

Fig. 13 is a similar view but taken along the line Iii-I3 of Fig. 10;

Fig. 14 is a like view but taken along the line ll--H of Fig. 10; and

Fig. 15 is a perspective view of a form of electrode that is adapted for use in lieu of that shown in section in Fig. 13.

The furnace shown in Figs. 1 to 4, inclusive, may comprise a metal casing I Within which may be provided a layer or lining 2 of material having good heat insulating properties. A layer 3 on the floor of the lining 2 may be formed of fire clay bricks, placed on edge, or of any other suitable refractory material. A bottom 4 and vertical side walls 5 may be placed upon and supported by the layer 3. These may be made of refractory blocks.

Electrode supporting blocks or platforms 6 are located at the sides of the melting and refining section |00 of the furnace. and may be separate from or integral with the bottom blocks l. These blocks or platforms 6 serve to support electrodes 1 at opposite sides of the melting and refining section |00 so that the rearward ends of the electrodes are spaced a substantial distance from I,

the transverse rear wall 8 of the furnace and the forward ends of the electrodes are spaced, but a less distance, from the transverse bridge wall structure 9 at the forward end of the melting and refining section of the furnace.

The electrodes 1 may be made of iron having a low carbon content, of carbon or graphite, or of any suitable known metal or alloy having a sufficiently high melting point for the service intended. The inner or contact face of each electrode is of substantial vertical extent and extends longitudinally of the melting and refining section of the furnace for the greater part of the length thereof.

Each electrode 1 has its forward end portion enlarged downwardly at 1a, Figs. 1 and 4, so that a zone of relatively great or increased current density is provided in the glass bath between the relatively deep forward end portions of the electrodes. This zone extends from the bridge wall rearwardly for a substantial part of the length of the rening chamber, as from A to 1/3 of the entire length thereof. The forward ends of the electrodes 1 terminate at a distance from the adjacent side of the bridge wall structure sufficient to prevent destruction of the bridge wall structure by electric current when the electrodes are in use in the furnace. This distance is not sumciently great as to interfere substantially with the creation of the zone of relatively increased current density as aforesaid or as to permit downcurrents in the molten bath next to the bridge wall.

As shown, the downwardly enlarged forward end portions 1a of the electrodes extend to the level of the bottom of the bridge wall structure 9 and hence to the level of the top of the throat passage I0. The lower edges of the remaining longer portions of the electrodes are located at a substantially higher level in the molten bath.

The electrodes have reduced stem portions which may be in the form of plates 1b extending through the sides of the furnace structure for connection with a suitable source of electric current supply, as with a source of single phase alternating current or currents.

The structure of the delivery end portion of the furnace may be as desired or required for any particular use. The floor of the entire furnace `structure may be stepped upwardly at I I so that the bottom of the delivery end portion I2 of the furnace is substantially above the level of the bottom of the melting and refining section of the furnace. The delivery end portion of the furnace may be provided with any suitable cover or crown structure, represented by the structure indicated at I3.

The bridge wall may be cooled by a passage 9a extending therethrough or in any other suitable known way. Any suitable known means may be provided for heating or regulating the temperature of the molten material in the delivery portion of the furnace. As shown, the transverse wall I3a at the end of the crown or cover portion of the structure next to the bridge wall 9 has a burner opening, indicated at I4, with which a burner may be associated for applying heat to the glass in the delivery portion of the furnace.

The structural features of the furnace shown in Figs. 1 to 4, inclusive, and as just described, permit the raw materials or batch for making glass, for example, to be fed thereto so as to form a blanket, indicated at B, on the surface of the bath of molten material I5 in the melting and refining section |00. Beneath the blanket B of batch or raw materials is a horizontal zone, indicated at M, Figs. 1, 3 and 4, extending longitudinally of the melting and refining chamber between the electrodes 1 `from the transverse bridge wall structure 9 to the rear end wall 8. The forward portion of this melting zone M is merged into and includes the major portion of a substantially vertical zone C of relatively increased current density andtemperature, located between the downwardly enlarged or relatively deep forward portions of the electrodes. This zone extends from the bridge wall 9 rearwardly for a substantial distance, as from 1A to l/3 the length of the chamber |00 and downwardly from the level of the molten bath to the level of the top of the throat passage I0. This is below the level of the upper part of most of a horizontal zone P, which is located directly beneath the zone M. The zone P is designed and intended to accommodate the glass or molten material which is undergoing plaining or refining beneath'the zone M at a somewhat lower temperature than that existing in the zone M.

In using this furnace for the making of glass, for example, the batch is fed to produce the blanket B and batch is added thereto as required to maintain such blanket at the thickness desired vduring the continued operation of the furnace.

The electrodes may extend into or, if completely submerged in the bath, be sufficiently close to batch or raw materials of this blanket to be cooled and protected thereby. The most intense heat will be developed midway between the opposed electrodes so that convection currents will be generally in an upward direction midway between the electrodes anddownwardly adjacent to the contact faces of the electrodes. 'I'he convection currents in the melting zone'M may be as represented by the circles formed of arrows in Figs. 3 and 4. These arrows indicate the directions of the transverse convection currents when the temperatures of the portions of the glass bath next to the electrodes are less than the temperature of the portion of the bath midway between such electrodes. The directions of such transverse convection currents would of course be the reverse of those shown by the arrows if for any reason or at any time the temperatures of the portions of the glass bath next to such electrodes should be higher than the temperature of the intermediate portion of the bath.

The melting of raw materials from the blanket B will take place in the zone M so that molten material will finally descend, as indicated by the downwardly pointing vertical arrows in Figs. 1 and 3, to the lower plaining or refining zone P. In the latter, the glass will be at a lower temperature than in the zone M and will move forwardly toward the throat I0.

The zone C, in which the most intense heat will be developed and in which the convection currents are upward, as indicated by the arrows I6 in Figs. l and 4, opposes and prevents direct movement of raw materials from any portion of the blanket B or partially fused materials from the melting zone M to the throat I0. The temperature in zone C may be in the order of 100 C. higher than in the remainder of the melting zone. All raw materials acted on by heat in the melting zone must pass through the circulatory movements set up in melting zone and subsequently to and through the lower planing zone P before arriving at the throat I0. Thus, all glass will be completely fused and given a refining or plaining treatment for a substantial time during movement thereof for a substantial distance before such glass is permitted to pass through the throat I to the delivery end of the furnace.

After passing through the throat I0, the outgoing molten material, in a refined or plained condition, will rise to the higher delivery end portion I2 of the furnace, from which it may be conducted or removed in any suitable known manner for such use as is to be made thereof.

The materials and general structural features of the furnace shown in Figs. 5 to 9, inclusive, may be the same as have been pointed out in the description of the furnace of Figs. 1 to 4, inelusive, and therefore need not be further referred to herein.

The melting and refining section of the form of furnace shown in Figs. 5 to 9, inclusive, is designated 200. It comprises an upper zone for the reception of a blanket of batch B, a melting zone M beneath the blanket B, including a zone Cof relatively great current density and increased ytemperature, as in the melting and rening section of the furnace structure of Figs. 1 to 4, inclusive. Beneath the melting zone is a plaining or refining zone P. c

A throat ||0 beneath a bridge wall structure |09 may be located below the level of the floor of the melting and refining chamber proper. As shown, the top of this throat passage is level with the bottom of the floor of the melting and rening chamber proper.

The electrodes |01 in this form of construcf tion differ from the electrodes previously described, in that the forward portions thereof, dening the zone C of' relatively great heat, are enlarged not only in a downwardly direction as indicated at |0`|a in Figs. 1 and 8 but also inwardly or toward each other as indicated at |0'|b in Figs. 5, 6 and 8. The distance for the passage of electric current through the glass between the enlarged forward end portions of the electrodes is thus less than between the remaining, longer portions of such electrodes.

Delivery end portion ||2 of the form of furnace of Figs. 5 to 9, inclusive, has a glass feeding forehearth ||3 appurtenant thereto. The bottom of this forehearth is shown as having a glass discharge feed outlet I I4 and means, represented by the plunger and sleeve assembly ||5, may be provided in conjunction with this forehearth to control the feeding of glass through the outlet IIl.

The floor of the delivery section of this type of furnace may be stepped upwardly, in relation to the level of the floor of the melting and refining chamber, as indicated at I|6. Also, opposed electrodes II'I may be located in the vertical passage ||8 which connects the throat ||0 with the interior of the delivery chamber |I2. These electrodes preferably are located at the bottom of this vertical passage ||8 and may extend into the molten bath for a predetermined distance from the side walls of the furnace, as shown in Figs. 6 and 9. Other opposed electrodes IIS may be provided adjacent to the surface of the molten bath at the juncture of the vertical passage ||8 with the interior of the delivery chamber I|2. These electrodes may have their glass contact faces flush with the side walls of the delivery chamber.

The operation of the form of structure shown in Figs. 5 to 9, inclusive, will be substantially like that hereinbefore described. The fusion of the raw materials from the blanket B will be effected in the melting zone, in which there will be convection circulations substantially as hereinbefore described. Thefused and circulated glass will finally descend, as indicated by the downwardly pointing vertical arrows |20 of Fig. 5, to the lower plaining or refining zone P. In the latter, there will be a forward movement in a generally horizontal plane toward the throat I I0. At the entrance to the throat ||0, some of this forwardly moving molten material will come under the influence of the rising convection currents, indicated by the upwardly pointing arrows |2| Ain zone C in Fig 5, this being a zone of relatively high temperature. This zone C will guard the entrance to the throat IIO against the outflow through such throat of incompletely fused or raw materials or the direct passage to Such throat of incompletely fused materials from the melting zone orraw materialsfrom the blanket B It will ,be noted, that in the operation of this form of furnace, as in the case of the furnace of Figs. 1 to 4, inclusive, the stronger upwardly moving convection currents in the zone C at the bridge wall and above the entrance to the throat passage will cause some glass from the plaining zone to rise at the forward part of the melting and refining chamber and to be re-circulated in such chamber in a generally vertical plane extending longitudinally of the chamber. This circulation in a longitudinal vertical plane will modify the circulations in transverse vertical planes in the melting zone M so that the molten material in the melting zone will be forced toward the rear while it is undergoing treatment in the melting zone before and during its descent to the plaining zone P.

The electrodes ||1 at the juncture of the throat and upward passage H may be used only at the start of operation of the furnace or during interruption of such operation, to keep the glass in the throat molten, or they may be used during actual operation to adjust the temperature of the glass flowing from the melting and refining chamber to the delivery chamber ||2.

The upper electrodes IIS, in the delivery chamber are located close to the surface of the glass therein and have relatively little depth or vertical dimension. These electrodes may serve to create a hot spot at the surface to which the glass from the throat will rise by convection, as indicated by the arrows |22 in Fig. 5. Flames from a burner or burners may be employed to supplement the action of these electrodes so that any remaining bubbles or seeds in the glass may expand, rise to the surface and disappear. The glass in the delivery chamber may subsequently descend, as indicated by the arrows |23 in Fig. 5. From the delivery chamber, the refined glass may pass under a skimmer block |24, Fig. 5, into the forehearth ||3.

Except as hereinafter pointed out, the structural features of the embodiment of the invention shown in Figs. to 14, inclusive, may be substantially as have hereinbefore been described. This form of furnacestructure includes a melting and refining section or chamber 300, the bottom of which is stepped downwardly to provide a throat passage 3| 0 beneath a transverse bridge wall structure 309. An upwardly extending passage 3|0 at the other side of the bridge wall leads from the throat 3|0 to the interior of a, delivery chamber 3|2. The outer end portion of the delivery chamber is formed to provide a glass draw chamber 3|! which is suitably equipped for the drawing of glass upwardly at 320 in sheet form. Skimmers 32| are provided at the juncture of the delivery chamber 3|2 with the draw chamber 3|9.

The electrode at each side of the melting and refining chamber 300 comprises a main electrode part 301 and a supplemental electrode part 301a which is located below the level of and in advance of the electrode part 301 or in other words between the inner end of the electrode part 301 and the adjacent wall of the transverse bridge structur 309. The inner end of the supplemental electrode part 301a is however spaced from the transverse bridge structure 309 to avoid destruction of such bridge structure by electric current passing through the glass between the electrodes.

'I'his arrangement of electrodes and cooperative furnace walls provides the vertical series of horizontal zones in the melting and refining chamber, as in the previously described forms of furnace.` That is, there is an upper zone for the reception of a blanketB of batch, an immediately subjacent zone M in which melting of the raw materials takes place and in which the glass is circulated by convection currents and moves downwardly as indicated by the downwardly pointing arrows 330 in Figs. 10 and 12, and a lower zone P in which plaining or refining of the glass at a somewhat lower temperature is effected and in which the movement of the glass is forwardly toward the entrance of the throat 3|0 as indicated by the forwardly pointing arrows 33|. This arrangement also provides the zone C of increased current density and relatively high temperature adjacent to the bridge wall and directly above the entrance to the throat 3|0, in which the convection currents move upwardly as shown by the upwardly pointing arrows 332, Figs. l0 and 13. The arrangement of opposed electrodes at the sides of the melting and refining chamber and the provision of the zones therein as just described cause circulatory movements of the molten materials in side by side circular paths in generally transverse vertical planes aslindicated by the circles formed by arrows in Figs. l2 and 13 and also circulatory convection currents in generally longitudinal vertical planes in the chamber 300, as and for reasons which have been stated in the descriptions of the operations of the preceding furnace structures.

The furnace structure of Figs. 10 to 14, inclusive, may be provided with upper opposed electrodes 322 above the juncture of the vertical passage 3|8 with the interior of the delivery chamber 3|2 and opposed lower electrodes 323 at the juncture of the throat 3|0 with the vertical passage 3|8. Other means may be provided for heating the glass in the delivery chamber or for regulating the temperature thereof, if desired.

The operation of the form of the device that is shown in Figs. 10 to 14, inclusive, is similar to that of each of the previously described embodiments of the inventions. Glass is melted at the rate suitable for the service in which the structure is being used and passes downwardly to the plaining zone P whence most of the refined glass passes to the throat 3|0. The zone C functions to prevent direct passage of batch or inadequately fused raw materials to the entrance to the ,throat and to cause recirculation through the melting zone of some of the refined glass from the upper part of the zone P at the juncture of the latter with the entrance to the throat 3|0. Afer passing through the throat 3|0, the glass rises to the surface of the bath in the delivery chamber, later downwardly in such bath, and subsequently beneath the Skimmers 32| to the draw chamber JIS, as indicated by the arrows in this portion of the structure as shown in Fig. 10. In the delivery chamber, the glass may be additionally conditioned and the temperature thereof may be reduced to that desired for the drawing process.

There is a dependent relation between the temperature of the glass in the plaining zone P in each of the hereinbefore described practical embodiments of the invention and efficient functioning of the furnace so as to supply suitably refined or plalned glass continuously and efficiently to the delivery chamber of the furnace at the rate desired. Thus, if the temperature in the plaining zone is too high, the temperature in the immediately subjacent melting zone M must lbe still higher with a consequent increase in the rate of fusing of the raw materials from the covering blanket B. It therefore is desirable to effect melting of the batch at the desired rate without excessive temperature inthe kzone M and with a lower, although adequately high, temperature in the lowermost plaining zone P. This trodes, constructed and arranged to cause aA greater electric. current density in a portion of arrangement will prevent overheating of the electrodes and excessive melting or fusing of the raw materials from the blanket B. 'I'he zone of greatest heat is nearest to the transverse bridge wall and this will prevent lshortcircuiting of raw materials or inadequately fused batch to the throat by which molten material is conducted to the delivery chamber and also will insure desirable circulatory movements of the glass in the melting and refining chamber without inducing movement of an undue amount of glass from the refining or plaining zone P up into the hotter melting zone. -It is advantageous to maintain the temperature of the zone C at approximately 100 centigrade above the ternperature of the melting zone proper although this may vary with the dimensions of the structure provided and with the character and nature of the particular substance that is being made at any given time.

The embodiments of. the invention shown in Figs. 5 to 9, inclusive, and Figs. 10 to 14, inclusive, may operate on three-phase current by using two phases in series in the melting and refining chamber and the third in the delivery chamber. The load on the electrodes in the latter may be slightly below that on the electrodes in the melting and refining chamber lbut the reduction need not be greater than is permissible by the use of any modern electric power line.

Electric current passing through a wall made of burnt refractory will soon destroy such wall. In constructing furnaces according to the present invention, it may be advantageous to use electro-cast refractory for walls, such as the bridge walls, in the event such walls are in the zone of the electric current produced by the operation of the electrical elements of the complete structure. Such electro-cast material is more resistant to the attack of the electric current.

The electrodes for the zones of relatively high temperature may be made of material that is more resistant to high temperature than the electrodes in the melting zone or in the other zones of lower temperature. These electrodes may be made of graphite, tantalum or some other metal or alloy having a high melting point. The electrode part 401:1, shown in Fig. 15, is formed of tantalum and may be used in lieu of the low carbon iron electrode part 301a of the form of structure shown in Figs. to 14, inclusive. The member 40la differs from the electrode 30,1a in that the head thereof, instead of being solid, is of open form, comprising a laterally turned contact plate portion connected with the plate-like stem or body 41| of the electrode by side flanges M2.

I claim:

l. An electric resistance furnace, in which molten glass or other substance being made acts as a resistance to electric current, comprising a melting and refining chamber having an outlet passage at one end thereof in position to be submerged by a bath of the molten substance in the chamber, means for passing electric current transversely through the portion of the bath in the upper portion ofthe melting and refining chamber, and means, including opposed electhe'bath occupying Aa vertical zone in the melting and reilning chamber adjacent to the intake end of. said passage than inthe remainder of said bath, said vertical zone vextending longitudinally -of the melting and refining chamber for only a minor part ofthe entire length thereof.

2. An electric resistance furnace, in which molten glass' or other substance being made acts as a resistance to electric current, comprising a melting and refining chamber having an outlet passage at one end thereof in position to be submerged by a bath of the molten substance in the chamber, means for passing electric current transversely through the portion of the bath in 4the upper portion of the melting and refining f chamber, and means, including opposed elecmelting and refining chamber having a transsaid chamber and opposed adjacent verse bridge wall at one end thereof and a passage beneath said transverse wall for the egress of molten material from said chamber, opposed electrodes in the upper part of said chamber cooperating with the walls thereof to provide a melting zone in the upper portion only of said chamber and extending the greater part of the length thereof, and means, including opposed electrodes, constructed and arranged to provide' an increased electric current density in a vertical zone at the end of the melting zone nearest to the transverse wall above said passage and ex,- tending downwardly to a level below that of said melting zone.

4. An electric resistance furnace, in which molten glass or other substance being made acts as a resistance to electric current, comprising a. melting and refining chamber having an outlet passage at one end thereof in position to be submerged by a bath of the molten substance in said chamber, means for passing electric current horizontally through the portion of the bath in the upper portion only of said chamber and means, including opposed electrodes, constructed and arranged to cause greater downward penetration in the bath of heat created by the resistance of the bath to said electric current in a vertical zone closest to the intake end of said outlet passage than elsewhere in said bath.

5. An electric resistance furnace, in which molten glass or other substance being made acts as a resistance to electric current, comprising a melting and refining chamber having an outlet passage at one end thereof in position to be submerged by a bath of the molten substance in electrodes located at above the level of the end of said outlet passage, said electrodes having a greater extent in a downward direction at the end portions thereof nearest to the sides of said chamber said outlet passage than elsewhere along the length of the electrodes.

6. An electric resistance furnace, in which molten glass or other substance being made acts passage at one end thereof in. position to be sub merged by a bath of the molten substance in said chamber and opposed electrodes located at the sides of said chamber above the level of the ad- `iacent end of said outlet passage. said electrodes having a greater extent toward each other at the end portions thereof nearest to said outlet passage than elsewhere along the length of the electrodes.

7. An electric resistance furnace, in which molten glass or other substance being made acts as a resistance to electric current. comprising a melting and refining chamber having an outlet passage at one end thereof in position to be submerged by a bath of the molten substance in said chamber and opposed electrodes located at the sides of said chamber above the level of the adjacent end of said outlet passage, said electrodes having a greater downward extent and a greater extent toward each other at the end portions thereof nearest to said outlet passage than elsewhere along the length of the electrodes.

8. .An electric resistance furnace, in which molten glass or other substance being made acts as a resistance to electric current, comprising a melting and refining chamber having an outlet passage at one end thereof in position to be submerged by a bath of the molten substance in said chamber and opposed electrodes located at the p sides of said chamber above the level of the adjacent end of said outlet passage, said electrodes comprising parts nearest to said outlet passage located below the level of the lower portions of the remaining parts of said electrodes.

9. An electric resistance furnace, in which molaaa-8,188

' as a resistance to electriccurrent. comprising a melting and refining chamber having an outlet located below the level of the lower portions of the remaining parts of said electrodes and consistlng of a material of greater'resistance to high temperatures than the material of said remaining parts.

10. The method of making glass in a furnace having a melting and refining chamber provided with an outlet passage at its lower part at one end thereof, comprisingv the steps of providing a bath of molten glass in said chamber to submerge and extend substantially above the level of said outlet passage, providing a blanket of raw materials on the surface of said bath, passing electric current transversely through the upper portion only of said bath to provide av horizontal melting zone extending from the surface of the bath i'or only part of the depth thereof, and establishing a condition of greater electric current density in a portion of the bath in a vertical zone adjacent to the intake end of said outlet passage and of greater depth than said horizontal melting zone.

1l. The method of making glass in a furnace having a melting and refining chamber provided with an outlet passage at its lower part at one end thereof, comprising the steps of providing a bath of molten glass in said chamber to submerge and extend substantially above the level of said outlet passage, providing a blanket of raw materials on the surface of said bath, applying heat to said bath to eifect fusion of raw materials from said blanket and circulatory movements of molten material of the bath in generally transverse vertical planes in a melting zone extending from the surface of the bath for only part of the depth thereof. and applying relatively more heat to a portion of the bath in a vertical zone adjacent to the intake end of said outlet passage and of greater depth than said melting zone to cause upwardly moving convection currents in said vertical zone and circulatory movements of molten material of the bath in generally longitudinal vertical planes in said chamber.

ANDERS E. A. S. CORNELIUS.