US3147328A - Electric glassmaking furnace - Google Patents

Description

p 1, 1954 J. M. Y. LE CLERC DE BUSSY 3,147,328

ELECTRIC GLASSMAKING FURNACE 3 Sheets-Sheet 1 Filed May 7, 1962 m y N m m w VIE A hi r ,ac MflM 5 0C 8 M 6 1m p 1964 J. M. Y. LE cLERc DE BUSSY 3,147,328

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I ELECTRIC GLASSMAKING FURNACE Filed May '7; 1962 3 Sheets-Sheet 3 VI 4 w w A64 v a a v r a M m mm c a a m... i W L United States Patent 3,147,328 ELECTRIC GLASSMAKHNG FURNACE Jacques Marie Yves Le Clerc de Eussy, Paris, France,

assignor to Verreries Pcchet et du Courval, Paris,

France, a French body corporate Filed May '7, 1962, Ser. No. 192,663 Claims priority, application France May M9, 1961 14 Claims. (Cl. 13-6) The invention relates to an electric glassmaking furnace.

A glassmaking furnace of conventional type is generally constructed in the form of a rectangular trough a vat whose wall is constituted by an air-cooled refractory ceramic material; such a trough is generally divided into two compartments separated by a cooled refractory wall. In the first compartment the melting of the charges and the refining are carried out and in the second compartment the glass stands before use.

The refining is a delicate operation and is very long to carry out in these units; owing to the viscosity of the liquid solution, the glass must travel very slowly toward the point of utilization; during this period of translation the glass is made to undergo controlled movements so as to render it homogeneous and cause the bubbles to rise and for this reason a volume is generally adopted for the furnace which is three times greater than that of the glass daily extracted from the chamber. Thus a furnace allowing a daily production of ten tons generally contains thirty tons of glass.

Furnaces of this type have a number of disadvantages and in particular the following:

(a) The refractory materials employed are sensitive to thermal shocks and this precludes stoppages in furnace operation.

(b) These materials are subjected to rapid wear due to their corrosion by the molten glass and for this reason the normal life of these linings generally does not exceed two years.

(c) It is difficult to change the type or quality of the glass manufactured by this furnace.

(d) Owing to the enormous masses handled, the glassmaking operation lacks flexibility and is often remote from the points of utilization.

(e) Such installations are very costly.

The object of the present invention is to provide a glassmaking furnace in which these disadvantages are avoided or restricted to the bare minimum. The invention provides in particular a glassmaking furnace whichalthough giving a result comparable to those obtained with conventional furnaces from the point of view of quantities and qualities of molten glass-permits obtaining glasses which are much harder than the glasses obtained with conventional units while utilizing only a minimum amount of melting agents; is flexible in operation and can be stopped and started up in the course of operation in a very short period of time; and gives these results with investments much less than those normally necessary and with lighter and smaller units and charges of molten glass which are about one tenth to one twentieth of those in conventional units.

Some of the aforementioned disadvantages can be avoided in the known manner in utilizing electricity for heating the mass of glass by the Joule effect, the electrical energy being supplied by electrodes in the very centre of the molten mass and the wall of the furnace being water-cooled.

The furnace of the invention belongs to this type of furnace but these known improvements in glass furnaces are insufficient in themselves to solve the problem of the refining of the glass, since, to permit a rapid refining, it is always necessary to raise a large mass of glass to a 3,147,328 Patented Sept. 1, 1964 "Ice high temperature and to maintain it at this temperature during the duration of the refining.

The furnace according to the invention comprises a refining device disposed within the trough in the hottest region of this chamber, said device comprising means for withdrawing in the course of the continuous pouring a portion of the molten glass in said region and thus removing it from the large movements due to the convection currents in said chamber, means for rapidly raising the temperature of said portion so as to diminish the viscosity and increase the size of the bubbles which are thus separated from the fine glass, means for evacuating to the exterior as production proceeds the fine glass just obtained, and means for returning to the bath within the furnace the bubbles thus separated.

In one embodiment of said device, said refining device comprises two horizontal discs having substantially flat or conical surfaces near one another at least on their edges, the space between said discs communicating with one or a plurality of escape apertures for the bubbles and with a fine-glass extracting aperture.

The bubble-escape aperture communicates with the interior of the trough and the fine-glass extraction aperture communicates with the exterior of the trough.

Said means subjecting the withdrawn portion of glass to a rapid temperature rise comprise a source of electric current whose terminals are respectively connected to the two discs of said device.

Further features and advantages of the invention will be apparent from the ensuing description, with reference to the acccompanying drawings to which the invention is in no way limited.

In the drawings:

FIG. 1 is partly an elevational view of a furnace according to the invention and partly a vertical sectional view taken along line 11 of FIG. 2;

FIG. 2 is a plan view of said furnace in which the upper part shows the furnace in the filled condition seen from above, a second part shows the empty furnace revealing the electrodes and the discs and a third part shows a horizontal sectional view taken in the plane of the refining system;

FIG. 3 is an axial sectional detail view of the lower part of the extracting device;

FIG. 4 is an electric diagram of said furnace;

FIG. 5 is an axial sectional view of one embodiment of a part of the refining device;

FIG. 6 is a view similar to FIG. 3 of a modification of a detail of the invention;

FIG. 7 is a partial axial sectional view of a modification of another detail of the invention;

FIG. 8 is a sectional view taken along line 88 of FIG. 7, and

FIGS. 9 and 10 are sectional views of two modifications of the refining device.

In the embodiment shown in FIGS. 1-5, the furnace comprises a chamber 1 which can be suspended or mounted, as shown, on legs, for example three legs 2, interconnected by a ring of tubes 3 supporting an angle-iron structure 4 from which the chamber is suspended.

The chamber ll comprises a copper trough or vat 5 for example three millimetres thick; the bottom of this trough I is provided with an aperture 6 whose diameter is about twenty centimetres. Brazed on the outer surface of the trough are copper tubes 7 which are individually connected to input and output collectors 7a and 7b and in which a cooling liquid circulates at high speed. In the drawing, the connections for the collectors have only been shown for one tube. The inner face of the trough is provided with a linning 8 consisting of zircone, zirconia, clay, alumina and a binder. This lining for-ms a screen adapted to stop the infra-red rays directed toward the wall of copper and to decrease the losses by conduction. The cooled trough is adapted to afford sufficient cooling to permit the lining 8 to resist corrosion due to the molten glass owing to the drop of the temperature in the region of the inner face of the lining; this temperature drop is such that the glass becomes almost stationary, this glass reaching very high degree of vicosity in this region.

The lining 8 has a thickness of about 3 to 4 cm. Owing to its fragility it performs no glass-retaining function; however fluidtightness is obtained by. the combination of this lining and the glass itself. The copper trough 5 provides a support for the molten mass and its inner surface cools the lining.

The lining 8 is merely laid in the trough 5 without any mechanical or other connection with the copper, and this allows it to expand and contract freely.

In normal operation, the charge of glass is heated by the Joule effect within the molten 'mass, the electric energy being supplied by three melting electrodes 9 composed of molydenum and connected to copper electrode carriers 9a which extend through the wall of the chamber, approximately midway of the height of the latter, through insulating sleeves 10. They terminate in segments 11 constituting the electrodes proper and having a part-cylindricalsurface 12 coaxial with the trough. The electrodes can be fixed or adjustable in position and are angularly spaced 120 apart.

The furnace further comprises superheating electrodes forming part of the refining device, and starting electrodes. These special electrodes will be described hereinafter. I A refining device 13 is disposed in the chamber on the axis of the trough. It comprises:

(a) A molten glass withdrawing device.

(b) A device superheating the withdrawn glass.

() A device extracting the fine glass obtained.

'(d) Preferably a device at least partially restoring the heat energy used in the refining operation.

The glass withdrawing device comprises (see FIG. two horizontal coaxial discs, namely an upper disc 14 and a lower disc 15 whose edges are at a short distance from each other so as to provide a circular slit 16 for the withdrawn glass, the space between the lips being in normal operation for example about mm. The faces of these two discs are similar to one another and have preferably a certain conicity so as to provide an inner chamber 17. The discs are composed of a metal which is not attacked by the molten glass and preferably molybdenum.

The upper disc, forming the electrode, is connected toan axial molybdenum bar 18 carried by an electrode carrier 18a supported by an adjusting device, such as an insulating sleeve 19 which is threadedly engaged in a nut 20 supported by a fixed plate 21 carried by a fixed support insulated from the fixed stand supporting the trough. For instanc'e, this support can consist of pairs of rails 22 supported by the fixed stand of the furnace through the medium of insulating plates 22a, these rails 22 receiving in the known manner carriages 23 carrying auxiliary starting electrodes 24 shown in dot-dash line in FIG. 1. As these electrodes are only used for starting the furnace operation the carriages and the electrodes carried thereby are withdrawn as soon as the furnace reaches normal operation. as explained hereinafter.

The upper disc 14 is provided with an axial passageway 25 communicating with the inner space of the trough by way of radial passageways 26 (FIG. 5).

- The lower disc forming the second refining electrode is connected to a molybdenum rod 27 provided with an axial passageway 28 (FIGS. 3 and 5) constituting the passageway through which the fine glass is extracted, this rod being secured in position in the manner shown in FIG. 3. This securing device comprises in particular three coaxial membersof sintered alumina, namely two members 29 and 30 in the form of truncated cones, the member 29 27 are such that the slit 16 is substantially on being disposed within the member and the latter within a conical aperture 31 formed in the bottom of the lining 8. The member 30 and the members supported thereby are carried by a third member of alumina 32 which is maintained by a portion of a copper wall 33 detachably assembled with the trough 5 by screws 34 and bars 35. The hollow molybdenum rod 27 is surrounded by a tubular sleeve 36 of platinum whose upper end is located a little above the level of the alumina member 29 and lower end terminates in a conical portion 36a receiving the end of the rod 27 having a corresponding conical shape. The lower end of the sleeve 36 terminates in an orifice formed by a circular bead 36b; this platinum bead borders the lower outlet orifice of the passageway 28.

This platinum sleeve is provided with a skirt 37 clamped between, on the one hand, the member 32 and, on the other hand, the lower ends of the members 29 and 30. The level of the upper disc 14 and the length of the rod the same level as the median plane of the electrodes 11.

The refining device, constituted by the two discs and the elements connected thereto, is supplied with electric current by a conductor (not shown) connected to the electrode carrier 18a which is connected to the upper electrode and by a molydenum bar 38 connected at 39 to the hollow rod 27 of the lower disc and to an electrode carrier 40 (FIG. 1) extending through the wall of the trough.

The electric assembly (FIG. 4) comprises three single 1 phase transformers 41 capable of supplying a secondary voltage of about 60 v. and a current of, for example 3 to 4,000 A. and supplying power to the melting electrodes 11, and a refining transformer 42 supplying power to the discs 14, 15, this transformer being capable of supplying for example 20,000 A. at 26 v. e

The secondary windings of the transformers 41have regulable power take offs which permit regulating the voltage applied to the electrodes 11.

The assembly is completed by various measuring apparatus and switches.

The furnace according to the invention is started and operated under normal conditions in the following manner:

With the upper disc 14 in separated position, the fur nace is filled with cullet (glass particles) up to for example a level 30 cm. above the disc 15. The starting electrodes 24 are moved together so as to be about 3 cm. from each other and are then placed on the cullet. The electrodes 24 are put under tension (for example 60 v.) and the glass between these electrodes is heated with a blow pipe; as soon as the operation has started the blow pipe is withdrawn.

The furnace is supplied with a composition P and the starting eelctrodes are gradually withdrawn. The melting electrodes are put under tension and as soon as they have started up, the starting electrodes are removed.

When the glass is well liquid in the centre the upper disc 14 is placed in position and the two refining discs 14, 15 are put under tension at moderate intensity.

When the entire mass is hot enough, the flow in the extracting passageway 28 is initiated by means of a blow pipe.

The furnace is continued to be supplied with thecomposition by pouring the latter preferably in the pouring zone of the furnace and the'furnace is controlled by means of the available voltage regulation.

In the course of operation, when the furnace is operating normally, the major part of the current in the melting electrodes 11 travels from the electrodes to the glass, from the latter to the two refining discs, then to the glass and finally to another electrode.

In the molten glass'the hottest region is created between the discs and the melting electrodes; this creates high convection currents which, in occurring between the eleccurrents encounter the central layer of composition and then travel horizontally until they encounter a thicker layer of composition. They are then made to descend and it is this which melts the composition in the most efiicient manner. When these currents reach the furnace walls they are already highly cooled and have entrained glass in formation.

They then descend slowly in the vicinity of the walls and are taken up by the central action.

A small part of the glass is then withdrawn by the refining device which draws this glass through the slit 16 owing to the fact that the molten glass is sucked through the pouring oriflice 36b (FIG. 3) of the extracting tube.

The glass is withdrawn in the hottest region of the furnace; the chemical and homogenization reactions of the glass are complete. The glass, having been removed from the vertical movements of convection of this region, then moves horizontally toward the centre while it is superheated by the high current intensity between the discs. Its temperature therefore rises to for example 1,800 or 2,000 C. before the glass is extracted from the chamber. Consequently, this glass is rendered fluid and the size of the bubbles increases owing to the expansion of the included gases, these two causes acting in the same direction to increase the rising speed of the bubbles; the latter rise through the central aperture of the disc 14 whereas the glass descends in the passageway 28 under the action of the suction through the aperture 36b (FIG. 3).

The element consisting of the platinum sleeve 36 and skirt 37 performs the following functions:

(a) It acts as a pouring orifice.

(b) It protects the end of the molybdenum tube 27 against the action of oxygen.

(0) It retains, and acts as an abutment for the tube 27.

(d The skirt 37 extends up to a region which is sufficiently cooled to prevent any possibility of escape of glass coming from the furnace.

(e) The end of the platinum tube extends into the chamber and is. wetted by the glass and thisv prevents any oxidation of the molybdenum within the alumina members in that the hot glass is prevented from passing through any passageway other than the passageway 28.

This passageway serves to conduct the fine glass of the refining device to the extracting orifice. The mass of the walls of this passageway firstly serves to facilitate the start of the pouring owing to the heating by conductibility and thereafter serves to pass the current toward the refining device and finally to consume heat stored in excess in the fine glass toward the interior of the furnace.

The device fixing the molybdenum rod 27 shown in FIG. 3 can be arranged in accordance with a modification of the invention shown in FIG. 6.

In this modification the alumina members 29 and 30 disposed in the conical aperture 31 of the lining are supported as in the first embodiment by a lower annular member also of alumina, but this member 32a has a shape different from that of the member 32 so as to support the hollow molybdenum rod. The latter, which carries the reference character 27a in FIG. 6, has a shape similar to that of the rod 27 but the platinum member 37a has a shape different from that of the member 37 since it is secured to the end of the sleeve 36a (similar to the sleeve 36) and it rests on a member 43 which is also of platinum and is provided at its centre with an opening coinciding with the extracting passageway 28, a platinum nozzle 44 coaxial with the passageway 28 extending the latter through an axial aperture in the annular member 32a.

In this assembly, the platinum member 43 is also dismountable and it is therefore possible to replace it by another similar member having a nozzle 44 and whose dimensions and shape are different from those of the nozzle previously in use.

The member 36a-37a remains fixed and assembled with the molybdenum rod which it protects from oxidation as in the first embodiment.

The refining requires energy but the latter is limited owing to the fact it is expended in the very centre of the chamber in the region where the glass is already the hottest. Furthermore, this energy is partially recovered in the furnace. For instance, if the temperature of the glass is brought to, for example, 2,000 C. the glass issues at a temperature of for example only 1,500 O; the outlet passageway is heated by the passage of the fine glass and expends its energy by radiation and convection in the bath of molten glass.

As the heat exchange between the molybdenum rod and the bath is therefore advantageous, this exchange can be enhanced by providing the rod with a heat exchanger 45 as shown in FIGS. 7 and 8. This heat exchanger consists of fins 46 or other radial projections secured to the rod 27 below the refining device.

The current supply bar 38a is welded to the exchanger.

This exchanger can be in one piece with the rod 27 or can be formed by a separate member attached to the rod 27. In order to increase the area of the surface of contact between, on the one hand, the fine glass which passes through the inner passageway of the rod 27 and, on the other hand, the inner wall of the exchanger, the latter cancomprise a plurality of passageways 47 instead of a single passageway (FIG. 8).

The furnace according to the invention has principally the advantage of an inert mass/flow ratio which is considerably reduced relative to conventional furnaces; the relatively light weight of its charge; as the copper walls and refractory walls are independent of each other, the furnace also permits frequent and rapid stoppages without risk of deterioration of the assembly; it is therefore easy to change from one type of glass to another.

The shape of the glass-withdrawing device of the refining device is not limited to the shape shown in FIGS. 1 and 5; in particular, this device could be for example in the forms shown in FIGS. 9 and 10.

In the device shown in FIG. 9, the upper disc 14a has an annular recess 48 which traps the gases and an evac nation through the centre as in the embodiment shown in FIG. 5.

In the device shown in FIG. 10, the lower disc 15a is highly conical and upwardly flared and the lower face of the upper disc 14b is also upwardly divergent so that the bubbles rise from the centre toward the slit 16 in opposite direction to that of the glass current.

Although specific embodiments of the invention have been described, many modifications and changes may be made therein without departing from the scope of the invention as defined in the appended claim.

Having now described my invention what I claim as new and desire to secure by Letters Patent is:

1. An electric glassmaking furnace comprising a trough having an inner wall defining a glass-melting chamber, at least two lateral melting electrodes spaced from said inner wall and defining between these electrodes a region which is the hottest region of the furnace, the periphery of this region being nearer from the center of the furnace than from said inner wall; and a glass-refining device positioned between said electrodes, inside said region; said refining device comprising: current-conducting means arranged between the electrodes, at a short distance therefrom and surrounding a refining cavity, fineglass discharge means communicating with said cavity and with the outside of said trough, and bubble conduit means communicating with said cavity and with the portion of the glass-melting chamber which is outside said refining device.

2. An electric furnace as claimed in claim 1, wherein said trough comprises a copper wall, an inner refractory lining supported by said copper Wall, and water tubes brazed to the outer surface of said copper wall.

3. An electric glassmaking furnace comprising a trough having an inner wall defining a glass-melting chamber, at least two lateral melting electrodes spaced from said inner wall and defining between these electrodes a region which is the hottest region of the furnace, the periphery of this region being nearer from the center of the furnace than from said inner wall; and a glass-refining device positioned between said electrodes, inside said region; said refining device comprising: two current-conducting elements extending horizontally respectively from two vertically aligned geometric axes, said elements having edges which are close to one another, but not contiguous, so as to define a cavity which communicates with the glass-melting chamber through the interval between said edges, said cavity further communicating with a refinedglass discharge orifice outside said trough, and with the glass-melting chamber outside said refining device through a bubble-conduit. t

4. The electric glassmaking device as claimed in claim 3 further comprising a support for supporting the upper element of said refining device, and adjusting means for adjusting the position of said upper element relative to said support, whereby the width of the slit between said elements can be varied. v

5. A glassmaking device as claimed in claim 3 further comprising a set of rails fixed abovethe trough of the furnace to support carriages for supporting starting elec trodes; said rails further carrying'a support supporting the upperelements of said refining device; and adjusting means for adjusting the position of said upper elements relative to said support whereby thewidth of the slit between said elements can be varied. 1

6. An electric glassmaking furnace as claimed in claim 3, wherein said two current-conducting elements are substantially flat horizontal elements.

7. An electric glassmaking furnace as claimed in clai 3, wherein said two current-conducting elements are substantially discoid. a

8. An electric glassmaking furnace as'claimed in claim 3, wherein one of said elements is substantially plane and the other element is conical.

9. An electric glassmaking furnace comprising a trough having an inner wall defining a glass-melting chamber, at leasttwo lateral melting electrodes spaced from said inner wall and defining between these electrodes a region which is the hottest region of the furnace, the periphery of this region being nearer from the center of the furnace than from said inner wall; and a glass-refining device positioned between said electrodes, inside said region; "said refining device comprising: current conducting means arranged between the electrodes, at a short distance there-' from and surrounding a refining cavity, bubble conduit means communicating with said cavity and with the portion of the glass-melting chamber which is outside said refining device, and a fine-glass discharge tube extending through the bottom of said trough and supported by this bottom.

10. An electric furnace as claimed in claim 9, wherein said current conducting means and said discharge tube are made of molybdenum.

11. An electric furnace as claimed in claim 9, further comprising a heat exchanger fixed on said discharge tube.

12. An electric furnace as claimed in claim 9, wherein a lower portion of said discharge tube is maintained by members composed of sintered alumina fitted in an aperture in the bottom of the trough and the portions of the rod which are in contact with the alumina or which would be in contact with the atmosphere are protected by a cylindrical lining of platinum.

13. An electric furnace as claimed in claim 12, wherein said cylindrical lining comprises a substantially plane skirt extending horizontally around said lining, said skirt being clamped between members of alumina which consequently support said skirt.

14. An electric furnace as claimed in claim 13, wherein said platinum skirt restson a support plate also of platinum, the assembly ofthe members of platinum being clamped between the members of alumina supporting said tube, and said support plate being provided with a pouring nozzle of platinum which downwardly extends at the lower end in the passageway of the discharge tube.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. AN ELECTRIC GLASSMAKING FURNACE COMPRISING A TROUGH HAVING AN INNER WALL DEFINING A GLASS-MELTING CHAMBER, AT LEAST TWO LATERAL MELTING ELECTRODES SPACED FROM SAID INNER WALL AND DEFINING BETWEEN THESE ELECTRODES A REGION WHICH IS THE HOTTEST REGION OF THE FURNACE, THE PERIPHERY OF THIS REGION BEING NEARER FROM THE CENTER OF THE FURNACE THAN FROM SAID INNER WALL; AND A GLASS-REFINING DEVICE POSITIONED BETWEEN SAID ELECTRODES, INSIDE SAID REGION; SAID REFINING DEVICE COMPRISING: CURRENT-CONDUCTING MEANS ARRANGED BETWEEN THE ELECTRODES, AT A SHORT DISTANCE THEREFROM AND SURROUNDING A REFINING CAVITY, FINEGLASS DISCHARGE MEANS COMMUNICATING WITH SAID CAVITY AND WITH THE OUTSIDE OF SAID TROUGH, AND BUBBLE CONDUIT MEANS COMMUNICATING WITH SAID CAVITY AND WITH THE PORTION OF THE GLASS-MELTING CHAMBER WHICH IS OUTSIDE SAID REFINING DEVICE.

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