US3419667A

US3419667A - Electric furnace

Info

Publication number: US3419667A
Application number: US625153A
Authority: US
Inventors: Walz Alfred
Original assignee: Sued Chemie AG
Current assignee: Sued Chemie AG
Priority date: 1966-03-25
Filing date: 1967-03-22
Publication date: 1968-12-31
Anticipated expiration: 1985-12-31
Also published as: GB1185194A; BE695928A; NL6704389A; DE1293972B; DE1293973B; DE1293399B

Description

Dec; 31, 1968 A. WALZ ELECTRIC FURNACE Sheet 2 of3 Filed March 22, 1967 INVENTOR.

A L FRED WA L Z FIG. 2

ATTORNEYS Dec. 31, 1968 A. WALZ ELECTRIC FURNACE Sheet Filed Ilarch 22, 1967 FIG. 3

FIG. 4

INVENTOR. ALF/?FD WA L'Z ATTORNEYS United States Patent O 15 Claims. (c. 3 23 ABSTRACT OF THE DISCLOSURE An electric furnace for melting materials includes a pair of coaxially arranged symmetrcal electrodes defining an annular space between them through which the materials to be melted are passed. To prevent sticking of the material in the sintering area the electrodes are maintained at a temperature above the sintering temperature of the material throughout their length of contact with the material. Where it is desired to form fibers and the like, the molten material may pass through difuser nozzles supplied with heated air. If it is desired to form a com-mon, flowing :melt of material, the individual strings of molten material may be combined in a funnel-like structure.

The present invention relates to electric furnaces in general, and more particularly to an electric furnace which is especially suited for melting of glass, minerals and other materials by direct resistance heating. The present invention is an improvement over the electric furnace disclosed in =my prior United States Patent No. 3,230,29l, granted Jan. 18, 1966.

The electric furnace disclosed in the above mentioned patent consists essentially of coaxially arranged symmetrical tubes or electrodes, which tubes at their upper ends are connected to the terminals of an electric current source and which tubes at their lower ends make conducting contact. An annular space is defined between the tubes through which the materials to be melted are passed. These materials are supplied to the upper end of the annular space and are steadily heated as they move downwardly between the tubes until they reach their melting temperature. Outlet openings are provided at the junction of the tubes for the molten material.

One of the problems encountered in electric furnaces of the type described is the sticking of the material in the region where it has just reached the sintering temperature, where it may bake together to form larger particles. consequently the homogeneous supplying of material in this area is impaired and the risk of obstruction is high.

It is'already known in the prior art to provide shielding cylinders in this area of sintering temperature. However this not only requires additional space in an area where one must employ 'more of the expensive precious metals, but the shielded region presents difficulties with the transfer of heat.

Moreover such electric furnaces may be used for the manufacture of fibers and threads by providing discharge nozzles for the molten material which operate according to the difuser principle. One difficulty which has been found for such installation is that the blast of air or other dfiusing medium directs cold air in the blowing nozzles and which hits the molten material, thereby raising its viscosity too high. Especially when the temperature of the molten material when it leaves the furnace is not too high, this quenching of the jet of melt prior to the fiber formation leads to an undesirable action upon the process of fi-ber formation.

It may sometimes be desirable to use a furnace of this type for the formation of materials other than fibers or threads. Since a melting furnace generally has outlet nozzles in the annular space which are located certain distances from each other, generally with compressed air ditfusers connected to them, diificulty is experienced in the production of small amounts of molten glass such as 'would be used for special purposes as photographic lens and the like.

Accordingly it is an object of the present invention to provide a new and improved electric furnace which overcomes the above difliculties.

Yet another object of the present inventon is to provide a new and improved electric furnace which minimizes diificulties created by sticking of the material in the sintering zone.

Yet a further object of the present invention resides in the provision of an improved electric furnace of the type provided with ditfuser nozzles wherein diiculties arising from the increase in viscosity of the molten metal when mixed with cold air of the blowing nozzles is minimized.

Yet a further object of the present invention is the provision of an improved electric furnace of the typedescribed wherein small amounts of molten material may be produced which are not fibrous in form.

In accordance with these and other objects there is provided an improved electric furnace of the type having a direct, electrical resistance heating for materials which can be molten and which preferably have a high melting point. Such a furnace consists of vertically arranged tubes defining elect-rodes which preferably are concentric and symmetrical. The upper ends of the tubes are connected to a source of current, and the lower ends of the tubes make conducting contact. The annular space between the tubes accom modates the material to be molten.

In accordance with one feature of the present invention, the inner tube is generally cylindrical, and the outer tube is defined by generally cylindrical portions at its upper and lower ends interconnected by an intermediate funnel-shaped portion so that the temperature of the inner tube along the region at which it makes contact with the material to be molten is equal to or higher than the melting temperature of the material and that the temperature of the external tube in all of the region where it makes contact with the material to be molten is higher than the sintering temperature of the material, and in the regions of the outlet nozzles defined at the juncture of the tubes the molten material will reach at least the melting temperature. Additionally it has been found that the provision of ar annular hopper concentric with the tubes and having an annular conical discharge intermediate the tubes narrower than the space between the tubes will produce a void beneath the hopper discharge. The temperature gradient along this void will be such that the tubes where they are engaged at the lower end of the cone of material are above the sintering temperature of the material and the hopper is below the sintering temperature of the material to be molten.

In accordance with another feature of the present invention, the air or fluid supplied to the diifuser nozzles first passes through one of the tubes for cooling the upper portion of the furnace, and thereafter the heated air is supplied to the ditfuser nozzles. Thus the heated air does not adversely aifect the viscosity of the molten material passing therethrough.

In accordance with yet another feature of the present invention, the nozzles formed at the juncture of the inner and outer tubes are of a relatively large diameter and run out into a collecting funnel which is located underneath the furnace, the streams of molten material being com bined in the collecting funnel so as to form one common,

flowing melt which then may be processed further in any known manner.

For a better Understanding of the present invention reference may be had to the accompanying drawings wherein:

FIG. 1 is `a central vertical section through an electric furnace which embodies one form of the invention;

FIG. 2 is a central vertical section through an electric furnace which embodies another form of the invention;

FIG. 3 is a central vertical section through the lower part of a modified furnace; and

FIG. 4 is a central vertical section through the lower part of yet another modified form of furnace.

Referring now to the drawings, and particularly to FIG. 1 thereof, there is provided an electric melting furnace formed essentially of two concentrical, vertical tubes from a noble metal of a high melting point, .such as platinum or a platinum alloy. More specifically there is provided an essentially cylindrical internal tube 11 defining an inner electrode and an external tube 12 defining an outer elec trode, which at its upper and lower end is formed of cylindrical sections of different diameters, and which external tube 12 has a funnel-shaped portion in its intermediate region tapering off from top to bottom. The upper edge of the external tube 12. is formed by an outwardly extending flange 13. At their lower edges the two

tubes

11, 12 are conductingly connected to each other and are equipped with a crown of outlet nozzles 14 for the discharge of molten material. The internal tube 11 and the external tube 12 are each attached to respective supporting devices by which they are maintained coaxially.

The supporting device of the external tube 12 is a ring 15 with an internal face which tapers off conically inwardly and downwardly and which is equipped `at its lower edge with an outwardly extending flange 16 with bores at its circumference to receive a plurality of attachment screws 17. The screws 17 pass through the corresponding holes in the fiange 13 of the external tube 12 and are screwed into the corresponding, threaded holes of a thrust collar 18. In this way the external tube 12 is rigidly connected with the ring 15 forming a good electrical contact. The upper, cylindrical section of the ring 15 is surrounded by a clamp collar 19 to which is connected an electrical lead 20. The lower internal diameter of the conical ring 15 is smaller than the internal diameter of the external tube 12, so that the lower edge 21 of the ring 15 protrudes beyond the annular space defined between the two

tubes

11, 12.

The supporting device of the internal tube 11 consists of an internally conical screw collar ring 22, the internal diameter of which tapers off upwardly from the outer diameter of the internal tube 11; it is filled in by the internal tube 11, which in this region is equipped with a slit 23. The internal tube itself is filled with a tapered shank 24 which has the same slope as the collar ring 22. A threaded end 25 of the shank 24 protrudes above and beyond the screw collar ring 22, and by aid of a tightening nut 26 is braced against the collar ring 22. This clamping produces both a thermally and an electrically good transition from the internal tube 11 to the .supporting device. Cooling tubes 27 pass through the tapered shank 24 and a cooling medium is directed therethrough. A clamp collar 28, to which a second electrical lead 29 is connected, surrounds the uppermost, cylindrical end of the tapered shank 24. Here too a lower edge 30 of the screw collar ring 22 protrudes beyond the annular space between the two

melting tubes

11 and 12, and is at the same height with the lower edge 21 of the ring 15.

An annular funnel-shaped hopper 31 is formed between the

rings

22 and 15 concentric with the

tubes

11 and 12 and having an annular discharge 33 intermediate the

rings

11 and 12 and narrower than the space between them and into which material 32 to be molten is poured.

A heat insulating layer surrounds the outer tube and prevents excessive thermal losses.

From the lower funnel discharge 33 the material to be molten drops in the shape of a freely standing cone 32a of poured material between the

tubes

11 and 12, til the goods at the base of this cone make contact with the tubes.

The cross section through the material between the tu bes 11, 12, through which a current flows, is dimensioned so that the temperature of the internal tube 11, where it makes contact with the material to be molten, is higher than the melting temperature of such material. Preferably the section close to the uppermost contact point at the base of the cone 3211 of poured material has the highest temperature. This simply means that the material to be molten is present as a melt and in this way make contact with the total surface of the internal tube 11. The best possible heat transfer to the material is created; thus the best thermal yield is obtained from 'the energy transformed in the internal tube 11. Furthermore the temperature regulation is very easy, the nelt from the inlet to the outlet nozzles 14 passes over a long enough path as a melt so that it will become degassed and fined.

At the outer cylinder however, the thermal balance shows different values, so that only the lower section which surrounds closely the outlet nozzles will reach the melting temperature of the batch to be molten. The temperature upwardly drops but at the base of the cone 32a it is still above the sintering temperature of the material to be molten. In this way the losses due to radiation towards the outside and the material to be employed for heat insulation remain within tolerable limits, and at the same time one prevents the batch sintering in the annular space between the tubes into the shape of large lumps, which would stop the flow of material and cause a ruination of the urnace, or at least a stoppage thereof.

On the other hand it is necessary to maintain the temperature of the melting tubes from noble metals so low at the Spots where they are clamped into the supporting parts from an ignoble metal, like a CrNi-steel, that no alloying will occur between these two classes of metals. This temperature, as a rule, will be below the sintering temperature of the material to be molten. One can bring this about by directing water, steam or other fluid against the tapered shank 24.

In this way the material to be melted will leave the hopper 31 when still granular and the range of temperatures at which these materials could become sintered is located in the cone 32a of poured material which stands free so that no flow of material will become interrupted.

With a PtRh alloy with about Pt and 20% Rh the temperature at the outlet nozzles 14 is in the range of 1400 C. to 1500 C. The hottest spot of the internal cylinder lies close to the base of the cone of poured material and is about 1600 C. The critical temperature at which the noble metal becomes alloyed With the ignoble metal of the supporting device will be about 600 C. Therefore one must bring about orcefully inside the internal tube 11 a temperature drop of about 1000 C. in the region of the freely standing cone 32a of poured material. The conditions for the handling of the outer tube are not so complicated. On the other hand the internal tube must be protected against overheating 'and melting, and if desred a thermocouple transmitter (not drawn) may be used at the hottest point of the internal tube, which switches off the installation as soon as the maximum permissible temperature is overstepped, i.e. approximately 1700 C.

The heat which flows from the supporting device goes automatically upwardly and will then become exploited for the preheating of the material in the funnel tube (not shown), and this too is a feature beneficial for the overall performance of the melting furnace.

As previously described, the melting furnace 38 consists essentially of two concentrical,

vertical tubes

11, 12 from a noble metal of a high melting point, preferably Pt or a Pt alloy. The two

tubes

11, 12 at their lower ends are connected with each other in an electrically conducting manner, and are equipped with a crown of outlet nozzles 14 for the molten goods. The internal tube 11 and the external tube 12 at their upper ends are each attached to a supporting device in the manner heretofore described and in this way are kept coaxial. The supporting device of the external tube includes the ring 15 around which a thrust collar 19 is placed. An electric lead 20 is Secured to the thrust collar 19. The supporting device of the internal tube 11 includes a conical bolt or tapered shank 39 which functions in the same manner as the tapered shank 24 described in the embodiment of FIG. 1. At the upper end of the conical bolt 39 is the clamping ring 28 which provides the connection for the second electric lead 29. The conical bolt 24 along its jacket surface is equipped with an helical cooling channel 42, which at its upper end is connected with the supply tube 27 for the coolant, and at its lower end is connected with a discharge tube 43 for the coolant. The external tube 12 from a no ble metal along its full length is equipped with the insulation jacket 3-1.

The removal tube 43 for the coolant is guided concentrically inside the internal tube to the lower end thereof and protrudes below beyond the opening of the internal tube 11, so that it may support an annular ditfuser discharge nozzle 44. This discharge nozzle 44 consists of the internal body 45 with rotation symmetry, -which is attached at the lower end of the discharge tube 43, and which has the shape of an urn, with a rounded-off, upper edge covered by a lid or plate 46. Between the edge of the urn structure and the lid 46 is defined an annular slot 47 for the removal of the heated cooling gas. The inside of the internal body 45 of the discharge nozzle is connected to the inside of the removal tube 43 by a plurality of holes 48 in the tube wall.

The external 'body of the discharge nozzle 44 is made up of a cylindrical annular sheath 49 which surrounds the internal body 45 in spaced relation. A jacketing 50` is located beyond and above the upper edge of the sheath 49 to define an annular slot 51. If the external supporting ring 15 is equipped With cooling Channels, then this air too, which became preheated in this external supporting device, may be drected to the ditfuser discharge nozzle 44.

By means of the airfiow through the ring-shaped (annular)

slots

47 and 51 into the annular jet slot, the molten material is first suoked in in the form of filaments and then, by means of turbulence, is separated into many individual filaments of very small diameter. By means of the unique enlargement of the difi'usor, and after the specific disintegration into filaments, the flow velocity is considerably diminished thereby improving the eficiency of the areodynamic effect.

In the embodiment of FIG. 3, the discharge (removal) tube 43 for the coolant, which runs concentrcally inside the internal tube 11 of a melting furnace, is closed by a plate 61 at its lower end which protrudes beyond the lower opening of the internal tube. Bores 62 are located in the cylinder wall of the discharge tube 43 at approximately the height of the outlet openings 14. The heated cooling gas is blown from the bores 62 against the streaming threads of melt, so that they are propelled outwardly in t-he shape of beads or little spheres.

In the embodiment of FIG. 4, there is provided a modified form of electric melting furnace adapted to provide a continuous flow of molten material. As therein illustrated, an improved melting furnace consists essentially of the two concentric, vertical tubes 11', 12' which are similar to the

tubes

11, 12 heretofore described except as t-o the manner of jointer at their lower ends. At their lower edges the two tubes 11', 12' are connected to each other in an electrically conducting manner, as by a ring or rim 65 provided with a plurality of outlet openings 14' for the molten goods.

The supporting of the internal tube 11' 'and of the external tube 12' and the manner of heating of the furnace 6 occurs as previously described for the embodiments of FIGS. 1, 2 and 3.

According to the present invention, a collecting funnel 66 is placed at the lower edge of the outer tube 12. This funnel 66 catches the melted streams which leave the outlet openings 14', combines them and discharges them at its outlet 67 as a common flow of melt. The diameters of the outlet openings 14' thereby are dimensioned so that the melt runs out of the furnace solely under the action of gravity; there is no nozzle effect. For melts of ordinary glass a diameter of about 2 mm. and more was found suitable for the discharge openings 14'. In order to bring about a good heat retention inside the funnel 66, it may be surrounded by a thermal insulation.

The flow of melt which leaves the outlet 67 of the funnel 66 may be passed into a processing machine, as this is commonly done.

Although the present invention has been described in conjunction with preferred embodiments thereof, it is obvious that numerous other embodiments may be devised by those skilled in the art. It is therefore intended in the appended claims to cover all such modifications as fall within the true spirit and scope of this invention.

What is claimed as new and desired to be Secured by Letters Patent of the United States is:

1. In a melting furnace of the type having direct electrical resistance heating for melting material and formed by vertically arranged concentric tubes defining electrodes, the tubes making conducting contact at their lower ends and provided with discharge nozzles at their junction, an annular space being defined between the tubes to accommodate the material to be melted; the improvement wherein the inner tube is generally cylindrical, and the outer tube is defined by generally cylndrical portions at its upper and lower ends interconnected by an intermediate funnelshaped portion so that the temperature of the internal tube along the full region at which it makes contact with the material to be melted is equal to or higher than the melting temperature of the material, and the temperature of the external tube in all of the region where it makes contact with the material to be melted is higher than the sintering temperature of the material, and in the region of the discharge nozzles the material will reach at least the melting temperature.

2. The improvement in a melting furnace as set forth in claim 1 wherein the temperature at the uppenmost point of contact between the material to be melted and said tubes is higher than the temperature close to the discharge nozzles.

3. The improvement in a melting furnace as set forth in claim 1 wherein said tubes are formed of platinum or of a platinum alloy.

4. The improvement in a melting furnace as set forth in claim 3 including support means supporting each of said tubes near their upper end and formed of ignoble metal the temperature of said tubes at said support means being less than the temperature at which said ignoble metal would become alloyed with the metal of said tubes.

5. The improvement in a melting furnace as set forth in claim 4 above wherein the support means for at least one of said tubes is provided with forced cooling means.

6. In a melting furnace of the type having direct electrical resistance heating for melting materials and fonmed by vertically arranged concentric tubes defining electrodes, the tubes making conducting contact at their lower ends and provided with discharge nozzles at their junction, an annular space being defined between the tubes to accommodate the material to be melted;

the improvement including an annular hopper concentrically positioned vertically above said tubes and havin-g an annular discharge intermediate said tubes and narrower than the space between said tubes so that a void is created between said hopper discharge and the upper side walls of said tubes.

7. The improvement in a melting furnace as set forth in claim 6 wherein there is formed 'an annular cone of poured material to be melted extending from said hopper discharge, said void providing an area in the side walls of said tubes having a temperature gradient such that the temperature of the tubes where they are engaged by the lower end of said cone is above the sintering temperature of said material and the temperature of said hopper is maintained below the sintering temperature of said material.

8. In a melting furnace of the type having direct electrical resistance heating for melting material and formed by vertically arranged concentric tubes defining electrodes, the tubes making conducting contact at their lower ends and provided with discharge nozzles at their junction, an annular space being defined between the tubes to accommodate material to be melted; the improvement comprising blast nozzles for directing a flow of fluid into the flow of molten material from said discharge nozzles, cooling means for the upper end of at least one of said tubes where it is supported, and a removal line from said cooling means extending through the inner one of said tubes and through the lower end thereof connected to said blast nozzles to serve as a supply line for the blast air to said blast nozzles.

9. The improvement in a melting furnace as set forth in claim 8 wherein said removal eonduit protrudes below the discharge nozzles for the molten material in said furnace and carries at its protruding end a hollow symmetrical hub provided with an annular slot, and an annular sheath around said hub defining a diffuser nozzle common to all the discharge nozzles.

10. In a melting furnace of the type having direct electrical resistance heating for melting materials and formed by vertically arranged concentric tubes defining electrodes, the tubes making conducting contact at their lower ends and provided -with discharge nozzles at their junction, an annular space being defined between the tubes to accommodate the material to be melted; the improvement defining a blast nozzle below said discharge nozzles for directing a flow of fluid into the outflow of molten material from said outflow nozzles, means for providing blast fluid to said blast nozzle, a hollow symmetrical hub being provided with an annular slot, and an annular sheath encirclin-g said hub' to form a diffuser nozzle which is common to all the furance discharge nozzles.

11. In a melting furnace as set forth in claim 10 including means for directing preheated air into said blast nozzle.

12. In a mixing furnace of the type having direct, electrical resistance heating for melting materials and formed by vertically arranged concentric tubes defining electrodes, the tubes making conducting contact at the lower ends and provided with discharge nozzles at their junction, an annular space being defined between the tubes to accommodate the material to be melted; the improvement including a blast nozxzle for directing a flow of fluid into the outflow of molten material from said discharge nozzles, said blast nozzles including a removal line extending through the inner one of said tubes and protruding below the outflow nozzles of the melting furnace, said removal line being closed at its bottom end and provided with a plurality of bores spaced across the periphery of its cylindrical wall and located at approximately the height of said discharge nozzles.

13. In a melting furnace of the type having direct electrical resistance heating for melting material and forrned by Vertically arranged concentric tubes defining electrodes, the tubes making conducting contact at their lower ends and provided with discharge nozzles at their junction, an annular space being defined between the tubes to accommodate the material to be melted; the improvement comprisng a collecting funnel placed underneath the furnace in the path of the flow from said discharge nozzles, said discharge nozzles having a cross sectional area sufficent to permit gravity flow of molten material therethrough.

14. The improvement in a melting furnace as claimed in claim 13 wherein the upper edge of said collecting funnel is connected to the lower edge of the outermost one of said tubes.

15. The improvement in a meltin-g furnace as claimed in claim 13 wherein each of said disc'harge nozzles have a diameter of at least 2 mm.

References Cited UNITED STATES PATENTS 2,233,435 3/1941 Snow 13-6 2,350,829 6/1944 Scharfnagel 13--6 X 2,600,490 6/1952 De Voe 13--34 2,680,772 6/ 1954 Skinner et al 13-34 3,109,045 10/1963 Silverman 13--6 3,230,29l 1/1966 Walz 13-6 3,212,871 10/1968 Vattrodt 13-6 X BERNARD A. GILI-IEANY, Primary Examiner.

H. B. GILSON, Assistant Exam'ner.

U.S. Cl. X.R.