FR2778909A1 - Glass furnace and an installation with such a furnace - Google Patents

Abstract

The furnace serves for production of glass by electric melting, with the melting energy dissipated in the molten mass by Joule effect. The furnace is provided with means for delivery of the raw materials which are placed as a layer (13) on the surface of a molten glass bath, while the electrodes (15) pass through this layer. The height (h) of the bath is less than 800 mm. The ratio h/S of the height (h) to the bath surface (S) is less than 0.5 m/m<2>.

Description

d-f 2778909

GLASS OVEN AND INSTALLATION

INCLUDING THE OVEN

The present invention relates to electric glass melting techniques in which the conductivity of molten glass is used to develop by Joule effect the energy necessary for the melting of materials.

1 0 firsts.

In a first type of electric glass melting furnace, the energy supply is produced by means of electrodes totally immersed in the mass of molten glass (hereinafter referred to as the bath), arranged vertically on the bottom of the glass. furnace and / or horizontally on the side walls of the furnace, the composition to be melted being introduced from above so as to maintain a surface layer constituting both a permanent reserve of raw materials and protection of the bath against loss

superficial calorifics.

The molten glass bath is the seat of convection movements, due to changes in the density of the glass according to its degree of heating, which participate in the transport of heat to the surface layer where the melting must take place as well as in the rest. the volume of the bath. These movements are particularly intense along the electrode due to the gradient of

temperature existing with the surrounding glass mass.

In this configuration where the electrodes are completely immersed, the energy exchange surface between the electrode and the bath is distributed over almost the entire height of the bath. Consequently, the difference in temperature of the glass according to the height of the bath is not very pronounced and the convection movements are of a very great amplitude, the current of hot glass rising along the electrode then following the layer of materials to be melted to bring it the fusion energy. This circulation results in a continual stirring of the bath which makes it possible to homogenize the mass.

of molten glass both in composition and in temperature.

Generally, furnaces of this type comprise a very deep refractory material tank, usually of the order of at least 1.5 m, in which a thickness of molten glass of the order of at least 1.2 at 1.4 m is provided so that the materials which melt under the surface layer have a residence time in the bath sufficient to reach a state of homogeneous composition and temperature, and thus to produce a satisfactory glass. The total immersion of the electrodes considered advantageous because allowing a fairly uniform energy input throughout the entire volume of the bath, however, proves to be restrictive because the violent stirring movements mentioned above cause erosion of the sole and measures must be taken to protect the sole against this wear which can also affect the

i 5 electrodes themselves.

More recently, the technique of electric fusion has undergone a major modification, consisting in immersing the electrodes in the bath through the free surface of the latter, instead of making them spring inside the bath from the bottom. . This made it possible to solve the delicate problems of replacing worn electrodes and sealing linked to the passage of the electrodes through the refractory of the hearth. The wear of the refractories could also be reduced because the use of immersed electrodes eliminates the direct heating at the level of the hearth, the hot zones being located in an upper part of the molten bath, and therefore makes it possible to limit the development of currents. convection in contact with the sole. This configuration also made it possible to increase the possibilities of adjusting the production parameters. For more details on this technique and its

advantages, reference may be made in particular to document FR-A-2 599 734.

The dimensioning of the furnaces has not been appreciably modified with the use of the immersion electrodes, and a minimum of depth was until now recommended to properly develop the temperature gradient necessary to establish the temperature at the bottom. relatively low desired: the temperature profile in the bath is in fact such that the temperature is higher near the electrode and decreases relatively slowly in the direction of the sole. This minimum depth was also considered necessary for the production of good quality glass. The object of the invention is to improve the definition of electric melting furnaces with immersed electrodes, so as to optimize the production conditions in particular by reducing, for equal production, the cost.

investment and / or operation, for improved profitability.

Completely surprisingly, it appeared to the present inventors that, with equal production capacity, the volume of the molten bath and equivalently the residence time of the materials in the bath could be significantly reduced compared to the art. prior without the qualities of the glass being appreciably affected. Thus, contrary to the received idea that a minimum bath height is necessary to produce a glass that is homogeneous in composition and temperature, the inventors have succeeded in developing glasses that are completely satisfactory in an oven whose depth has been reduced. in a way

very meaningful.

In this regard, the invention relates to a furnace for the preparation of glass by electric melting in which the melting energy is dissipated by the Joule effect in the melt, comprising means for supplying vitrifiable materials depositing said materials in layer on the surface of a molten glass bath and submerged melting electrodes submerged from the surface of the bath through the layer of composition to be melted covering the molten bath, characterized in that the height h of the molten bath is less than 800 mm and the ratio of the height h to the surface S of the bath is less than 0.5 m / m2.

For the purposes of this description, the height h of the molten bath denotes

in fact the useful height of the molten bath, namely the height between the upper level of liquid in the tank and the bottom of the furnace, or possibly in certain cases where the glass is drawn off at a higher level than that of the bottom , between the upper level of the liquid in the tank and the lower level of the glass draw-off opening. Indeed, for certain reasons, in particular when pollutants are liable to be deposited at the level of the sole and soil the mass of glass at the bottom of the bath, it may be preferable to draw off the glass in an area situated a little above the level. sole. It is established that the mass of glass thus isolated in the lower part of the furnace does not participate in

the elaboration of the glass and does not enter the useful mass of the bath.

It is generally difficult to measure with precision the exact level where the liquid phase begins in the tank, due to the fact that the surface layer of matter covering the bath (called "crust") is the seat of balances between several phases ( solids, liquids, gases) resulting from the fusion of the composition. An indirect measurement is generally carried out by the principle of communicating vessels, by detecting the upper level of liquid

in a compartment located downstream of the tank.

Against all expectations, it has been observed by the present inventors that by carrying out the electric melting in a furnace with immersing electrodes much shallower than usual, all other things being equal, a completely elaborated glass is produced, not containing no solid particles, and having a satisfactory homogeneity of composition, despite a residence time of the materials in the molten bath much shorter than in

the usual fusion techniques.

As a main advantage, the reduction in size of the furnace offered by the invention allows a substantial saving on the quantity of refractory material necessary for the constitution of the side walls of the furnace, and hence on the investment cost of the installation. The reduction in the quantity of glass present in the molten bath also allows a more rational use of energy by limiting energy losses in the mass of glass, hence saving on operating costs, in particular. when it comes to making glasses with low heat conductors. Others

advantages of the invention will become apparent in the remainder of this description.

The furnace according to the invention has a characteristic aspect ratio with a bath height limited to a value less than 800 mm and low with respect to the surface of the bath. In a preferred variant, the height h of molten glass can advantageously be reduced to a value less than 500 mm, in particular less than or equal to 450 mm, with a very significant reduction in the cost of the furnace. Heights less than or equal to 400 mm, in particular of

of the order of 300 mm or less, are particularly preferred.

In a particular embodiment, the h / S ratio defined above is moreover less than or equal to 0.05, for example of the order of

0.03 or less.

According to preferred variants where the furnace has a large surface for a high production capacity, the h / S ratio can even be less than or equal

at 0.02, or even 0.01 or 0.005.

The height of the tank will advantageously be limited accordingly, preferably to a value greater than the height of the bath from 100 to 200 mm,

in particular of the order of 150 mm.

No lower limit should theoretically be set for the height h of molten glass and a person skilled in the art should be free to choose heights as low as of the order of a few centimeters, subject to preserving a contact surface between. the electrodes and the molten glass sufficient to provide the necessary fusion energy. It has in fact been observed by the inventors that, as soon as one places himself more than 2 to 3 cm below the upper level of liquid in the tank (as defined above), no solid particle remains in the tank. the bath (that is, the melting is carried out) and the glass is completely elaborated. In this regard, it can be indicated that any bath height of 20 to 300 mm is included in the invention, the corresponding furnaces being essentially melting devices, producing elaborate glasses but relatively less refined than traditional furnaces. The invention is therefore remarkable in that it makes it possible to treat the same quantity of materials as a traditional oven with the same specific draft, but in an oven of reduced height: in fact, if the electrodes supply the same quantity of energy, they transmit it to a smaller bath volume. By thus modifying the conditions of energy input into the bath, the temperature profile in the bath is such that glass circulation currents are established in the mass of molten glass which are favorable to the production of a

homogeneous glass.

Thus, according to another aspect of the invention, the furnace is characterized by a bath height of less than 800 mm, in particular 500 mm, in particular 450 mm, and by an exchange surface between the electrodes and the molten glass ( this surface being formed by the lateral electrode surface immersed under the upper level of liquid present in the tank, per unit volume

bath) greater than 0.075 m2 of electrode per m3 of glass.

According to the invention, the mass of glass has a higher energy exchange surface than usual. There is therefore a relative amount of glass exposed to the electrodes greater than in traditional furnaces. The electrode surface area per unit of bath volume is advantageously greater than 0.1 m2 per m3, preferably greater than or equal to 0.15 m2 per

1 5 m3, in particular of the order of 0.2 m2 per m3 or more.

The depth of immersion of the electrodes in the molten bath is necessarily limited to a value less than the height of the bath to avoid contact between the electrode and the sole. This immersion depth must however be sufficient to provide the necessary exchange surface for

dissipate the desired power.

In particular to limit the wear of the sole, in particular by erosion caused by the convective currents of glass in the bath, it may be preferable for the immersed length of the electrodes to be less than or equal to two thirds of the height of the bath, preferably at half the height of the bath, the immersion depth also depending on the height of the bath. This makes it possible to locate the hottest zones near the surface of the bath, the fusion energy being dissipated where it is most needed. This precaution proves moreover favorable to a circulation of the molten materials following a path allowing the preparation and the rapid homogenization of the glass within the

shallow bath.

Advantageously, the shape of the electrodes can be adapted so that they have a very high lateral surface for a minimum of length. Advantageously, therefore, use will be made of electrodes, in particular of substantially cylindrical contour, the dimensions of which are such that their lateral surface Se, and their immersed length I are in a ratio Se. / I

greater than or equal to 0.45, advantageously to 0.6.

In a particularly advantageous embodiment, at least one electrode can comprise at least one substantially planar conductive element. In particular, such an electrode may have the shape of a plate or comprise several plates associated with one another. A substantially planar conductive element may nevertheless also have the shape of a strip or be

composed of a plurality of juxtaposed son.

Preferably, such plates are square or rectangular, in particular for reasons of ease of manufacture, although any other form of plate also makes it possible to supply the glass bath with current.

electric for the creation of a Joule effect.

Cylindrical type electrodes are in fact less preferred according to the invention as soon as the depth of the glass bath becomes smaller and smaller because, in order to obtain a sufficient lateral exchange surface with a short submerged length, it is necessary to use a large diameter cylinder, therefore relatively heavy. One solution may consist in using a hollow cylinder, since only the lateral surface of the electrode participates in the electrical exchange, the interior part being totally inert in this respect. This solution is however without economic interest in the current state of the technology of materials likely to constitute the electrodes (such as molybdenum) because a hollow cylinder can only be manufactured by milling, the material eliminated, lost, entering nevertheless in the cost of manufacturing such a hollow electrode. The use of flat or plate electrodes makes it possible, compared to conventional electrodes in the form of a cylindrical bar, to considerably reduce the weight of the electrode, for an equal lateral surface. This weight gain is a major advantage in the oven of the invention where the

electrodes are plunging, that is to say suspended from a support element.

The use of plates overcomes the economic handicap mentioned more

high for hollow cylinders.

The dimensions of the plates are chosen as a function of the desired exchange surface, the thickness being chosen to ensure sufficient longevity for the electrode as a function of the kinetics of wear by consumption of the conductive material constituting the electrode under the conditions. of

oven operation.

Advantageously, when the depth of the furnace is very small, the electrode comprises at least one plate, in particular rectangular, arranged such that its side of greatest dimension is oriented in a substantially horizontal direction. Thus, the support element is connected to the side of greatest dimension of the plate or plates. The thickness of the plate can be chosen to ensure a strong fixation when the support element penetrates

in the plate in particular by screwing.

It is possible to combine conductive plates in a wide variety of configurations: - two square or rectangular plates can be arranged in an L - three square or rectangular plates can be arranged in a U - four square or rectangular plates can be arranged for

forming a hollow parallelepipedal electrode.

Preferably, the associated plates for example as above are

assembled together, in particular by screwing or any other means.

Electrodes of different configurations can be used in combination in the same furnace to provide a particular distribution of current lines. It is thus possible to install in an oven, for example, both cylindrical electrodes and plate-shaped electrodes, or else both L-shaped electrodes and U-shaped electrodes. The electrodes made up of plate (s) can also be provided with means for adjusting the orientation of the electrical exchange surfaces, in particular by pivoting about at least one axis, in particular a horizontal axis and / or a vertical axis, so as to adjust the distribution of the lines current in the

molten glass bath.

As stated previously, an essential feature of the melting technique according to the invention is the low average residence time of the molten materials in the furnace within the bath, relative to the production rate which is generally expressed by the specific draw Tspéc which is the quantity of glass (in tonnes) withdrawn from the furnace per day relative to a furnace surface area of 1 m2. Indeed, for a constant specific draw, the residence time of the materials in the bath is proportional to the volume of the bath and the reduction in the height of the bath results in a corresponding reduction in

residence time.

In this regard, the invention also relates to a process for electrically melting glass in which the energy is dissipated by the Joule effect in the melt from immersed electrodes, comprising the steps of distributing the materials constituting the composition. melting in a layer on the surface of the bath, immersing the electrodes from the surface of the bath through said layer of composition to be melted, supplying the electrodes with an electric current, the materials melting and combining in the bath to form the glass and withdraw the molten glass with a flow rate expressed by the specific draw Tspéc, characterized in that the average residence time (in days) of the materials in the bath between the surface layer and the draw-off zone

2, 1.2 Og.

is less than, advantageously than, or even a -

T.pec Tspec Tspec As an indication, under preferred operating conditions, the average residence time of the materials in the bath between the surface layer and the withdrawal zone is less than or equal to 0.7 days, advantageously to 0, 5 day, for example of the order of 0.25 to 0.4 days, for a specific draw of

The order of 3 t / m2 / day.

The furnace according to the invention proves to be particularly advantageous for the production of glasses which are <opaque "to infrared radiation, such as, for example, glasses containing a relatively high proportion of iron oxide (for example of the order of at least 0 , 60% Fe203, up to 1 O - 12% or more) in which the radiation develops to a limited extent Usually in regular sized furnaces, the low conductivity of the radiation creates marked temperature differences between the zones of the bath, with in particular relatively cold zones at the bottom of the bath where the glass tends to devitrify. Due to its shallow depth, the furnace according to the invention allows the establishment of a thermal gradient avoiding the creation of these cold areas and limiting the risk of

devitrification of these particular glasses.

The melting technique according to the invention makes it possible to produce, with less expensive equipment and under more economical operating conditions, good quality glass which can be used for a very large number of applications with results as satisfactory as glass produced in traditional furnaces. . For example, the molten glass according to the invention can be transformed into glass wool, in particular for the production of products.

insulation, of a quality equivalent to existing wools.

Consequently, the invention also relates to an installation for the manufacture of glass wool comprising a glass melting furnace, a fiberizing device and means for supplying the fiberizing device with molten glass produced in said furnace, characterized in. in that the furnace is a low depth plunging electrode furnace as described above. Other possible applications are in particular the manufacture of

reinforcing fibers or glass substrates of various shapes.

For applications where a very high quality glass is required, it is possible to couple the furnace according to the invention with a complementary device which will carry out a rehomogenization and / or a refining at the last moment before the transformation of the molten glass. Such an installation can be advantageous compared to an installation comprising a very deep furnace calculated to produce directly at the furnace outlet the glass with the desired degree of homogenization and very high refinement: thus placing such an additional device just upstream. of the final processing device, any defects (inclusion of gas bubbles) liable to appear within the molten glass during its transport from the furnace to the final processing stage can be remedied. The use of two separate devices instead of a single high-performance oven is generally economically advantageous because of the substantial savings made on

the cost of building the furnace.

Other advantages and features of the invention will emerge from the

detailed description which follows, made with reference to the accompanying drawings, on

which: - Figure 1: schematically shows an installation for manufacturing glass wool using an electric furnace according to the invention - Figure 2: shows a schematic view in longitudinal section along axis 1-11 of the furnace of the figure 1; - Figure 3: shows a schematic view in longitudinal section along the axis 111-111 of the oven of Figure 1; - Figure 4: shows a side view in partial section of a plate-shaped electrode usable in an oven according to the invention; FIG. 5 represents another side view of the electrode of FIG. 4; FIG. 6 represents a side view and in partial section of an electrode consisting of an assembly of plates which can be used in an oven according to the invention; - Figure 7: shows an elevational view of the assembly of

plates shown in Figure 6.

It will be noted that the figures are schematic representations on which do not appear all the implementation details within the reach of a person skilled in the art and on which the scale is not necessarily

complied with, unless otherwise specified below.

The installation shown in Figure 1 is intended to produce glass wool for the production of thermal insulation materials. It essentially comprises a glass melting furnace 1 supplied with a mixture of vitrifiable materials by a supply system 2, a channel 3 for transporting the molten glass produced in the furnace 1 and a fiberizing machine 4 supplied with molten glass via the channel. 3. In the fiberizing machine, the molten glass falls into a fiberizing plate 5, the side wall of which is pierced with a multitude of orifices, rotated around a vertical axis 6, so as to be ejected centrifugally. molten glass through said orifices in the form of

glass filaments 7 solidifying by cooling.

The constitution of the furnace 1 is shown in detail in the two sectional views of FIGS. 2 and 3. The furnace comprises a tank 8 made of refractory material constituted by a floor 9 and vertical walls 10, and surmounted by a vault 11. The tank shown has a horizontal sole 9. The tank 8 of the furnace according to the invention can take all the traditional general shapes, but differs from traditional furnaces by the low height of the walls 10. By way of example, the tank shown has a surface area of approximately 10 m2 for a height.

0.4 m.

As shown in Figure 2, the tank 8 contains a mass of molten glass 12 constituting the molten bath, covered with a layer 13 of solid raw materials continuously distributed by the supply system 2. This layer as uniform as possible may be more or less thick depending on the operating speed. Under operating conditions, a thickness of at least 100 mm is preferably maintained in order to thermally insulate the molten bath from the atmosphere. Preferably, this thickness should not exceed about 300 mm as this does not provide any advantage for the fusion and would overload

therefore unnecessarily the surface of the bath.

The height h of the bath is calculated by measuring the difference between the

free glass level in transport channel 3 and bottom level 9.

In the mode shown, it is approximately 300 mm; the h / S ratio is therefore

of 0.03 (in m / m2).

In the mode shown, the molten material is discharged through a groove 14 located on one side of the tank 8 and at the same level as the sole 9, this

throat communicating with channel 3.

Melting electrodes 15, six in number in this example, are arranged in the upper part of the furnace, carried by supports 16 of the traditional type. Their arrangement, of the type described in EP-A-0 140 745, is more particularly suited to a three-phase current supply, the distribution of the phases (R, S, T) being as indicated in FIG. 3. This arrangement allows good phase balancing. Any other mode

usual power supply is however conceivable within the scope of the invention.

The electrodes 15 pass through the surface layer of raw materials and enter the molten bath. The lowest possible immersion depth is preferred, subject to offering the necessary exchange surface. In practice, an immersion depth less than 2/3 of the height of the bath and even preferably half of this height will be

generally advantageous.

In the embodiment shown, the electrodes are cylindrical in shape, short but of relatively large diameter to provide a large exchange surface. With a diameter of approximately 200 mm and a useful length I of approximately 150 mm, the lateral exchange surface Sei is approximately 0.095 m2 per electrode and the Sel / I ratio is 0.63. In operation, the electrodes are immersed over their entire useful length 150 mm, ie half the height of the bath, the exchange surface per unit of bath volume therefore being 0.190 m2 per m 3 of bath.

In general, this furnace can be supplied with a current density on

the electrode of the order of 1 to 3 A / cm2.

In a particular example of operation, the furnace supplied with a current density of 2 to 2.5 A / cm2, makes it possible to produce glass with a specific draft of the order of 3 t / d / m2, i.e. a total draft. 30 t / d: with a glass with a density of 2.4 t / m3, the volume of glass produced 3.3 is 12.5 m per day. Knowing that the volume of the bath is 3 m3, the residence time of the materials in the bath is approximately 0.25 days with a

bottom temperature in the usual range.

For comparison, compared to a furnace with standard plunging electrodes comprising a deep tank containing a glass bath 1 m high, the furnace according to the invention has a reduced construction cost.

approximately 40% corresponding to the reduction in the height of the side walls.

Moreover, in operation under the same production conditions (same specific draw), the advantageous distribution of energy in the bath according to the invention makes it possible to reduce energy consumption by approximately 5%. FIGS. 4 and 5 represent an electrode 19 in the form of a plate which can be used in the oven 1 in place of at least one of the cylindrical electrodes

15.

The actual electrode consists of a rectangular molybdenum plate 20 connected to a steel extension 21 by screwing. The plate 20 is provided with an internal thread 22 formed in the thickness of the plate in the middle of the side of greatest dimension (length). Extension 22 is

1 0 provided with a corresponding threaded end 23.

The extension 21 is the means of connection between the electrode and the support arm of the assembly: its function is to support the electrode and to bring the electric current to the electrode. In operation, it passes through the layer 13 of raw materials surmounting the bath, the lower portion with the thread 23 inserted into the plate 20 lying approximately at a

level corresponding to half the thickness of the surface layer 13.

In order to avoid melting of the attachment between the electrode and the steel extension, and to avoid the wear of the molybdenum in the attachment zone in the upper part of the plate 20, a system of

cooling 24 of the <"water-jacket>" type integrated in the extension 21.

This system comprises a circuit 25 for circulating cooling water inside the extension between an inlet orifice 26 and a

outlet port 27.

The extension 21 provided with the cooling system 24 is equipped with a plate 28 for connection to a support element (arm), not shown.

penetrating through the side walls of the oven.

By way of example, a plate electrode 1 9 functionally equivalent to the cylindrical electrode 15 described above has a length

of 300 mm, a height of 150 mm and a thickness of 45 mm.

The diameter of the thread 22 should preferably be as large as possible in order to have the strongest possible electrode attachment. This further results in better cooling of the entire supported electrode area since the threaded end 23 of the extension 21 enclosing the end

of the cooling system 24 provides a higher water flow.

In these circumstances, it is preferable that the shoulder 29 on the extension 21 is such that it projects beyond the thickness of the plate 20. In fact, it is on this front contact surface that the electrical contact supplying the electrode. It is therefore advantageous for this contact surface to be as large as possible to avoid excessively high current densities.

important on this electrode connection surface.

With the dimensions indicated above, the side surface of the plate 20 is 0.103 m per electrode, which is very close to the side surface.

Salt electrode 1 5.

On the other hand, the weight of the plate 20 is only about 21 kg instead

of approximately 50 kg for the cylindrical bar 15.

For the same current supply capacity, the plate electrode 19 is

more than 2 times lighter than the cylindrical electrode 15.

The reduction in the weight of the electrode leads to a reduction in the lever arm on the electrode support and therefore allows a simplification of the

construction of the furnace.

This electrode 19 was tested under the same operating conditions as those described above with the electrode 15 with

a current density at the electrode of about 2 A / cm2.

Under these conditions, the fusion has the same qualities with the two types of electrodes. While cylindrical electrode 15 wears with a loss of 3.1 grams of molybdenum per tonne of glass produced, electrode 19 wears with a loss of 2.9 grams of molybdenum per tonne of glass produced. Thanks to the cooling of the threaded end of the extension 21, the wear of the plate occurs from the external rectangular faces without

damage to electrical contact.

The thickness of 45 mm of the plate 20 is sufficient to ensure a satisfactory longevity of the electrode. This could be explained in particular by the fact that, with an equal loss of mass, the surface of a plate would decrease less quickly.

than the surface of a cylinder.

Figures 6 and 7 show a hollow electrode 30 of square section, consisting of the assembly of four molybdenum plates 31, 32, 33, 34 fixed to a molybdenum support plate 35 by screws 36

also molybdenum.

The support plate 35 is provided with an internal thread 37 making it possible to fix the electrode on an extension, not shown, which may be of the structure

analogous to the extension 21 provided with a cooling system.

Compared to the plate electrode 19 of Figures 4 and 5, the square electrode allows the diffusion of electric current in four directions

perpendicular instead of two opposite directions.

In a particular example, the dimensions of the plates 31, 32, 33 and 34 are such that each face of the electrode measures 160 mm wide by mm high, which gives a total lateral exchange surface of 0.096

m, that is to say of the order of that of electrode 15.

i15 With a total weight of 32 kg, electrode 30 is also twice

more efficient than the cylindrical electrode 15.

The electrodes 19 and 30 can be provided with means for adjusting their orientation, in particular by pivoting about a vertical axis or an axis

horizontal, to adjust the distribution of the current lines in the molten bath.

These means can in particular be carried by the extension 21 or by

the carrier element from which the extension is suspended.

In Figures 4 and 5, the electrode 19 comprises such orientation means about a vertical axis, in the form of the union 40 between

the extension 21 and the support 28.

The glass produced in the furnace 1, once passed to the fiberizing machine 4, is transformed into glass wool with such a low proportion of infibers

than with glasses from traditional ovens.

The step of transporting molten glass to the processing device

can advantageously be used to homogenize and refine the glass.

However, even if the transport conditions were not optimal or if the glass produced in furnace 1 was not sufficiently homogeneous or refined due to uncontrolled variations in production parameters, it was

observed that the fiber product nevertheless exhibits satisfactory qualities.

The association of the furnace according to the invention with a processing device such as an internal centrifugation fiberizing machine proves to be particularly advantageous, probably because the centrifugal force applied to the molten glass within the fiberizing machine gives the glass a higher degree of homogeneity, this ultimate homogenization improving

the ability of glass to be transformed into wool.

The ovens of very low height according to the invention, in particular in which the height h of molten glass can range from 20 to 300 or 400 mm, preferably from 200 to 300 or 400 mm, therefore find a particularly advantageous application in this type of glass. installation, which they reduce

considerably the costs (investment and operation).

The invention, which has just been described in the context of an installation for manufacturing insulation materials based on glass wool, is in no way limited to this particular embodiment, and other glass products can be manufactured using the fusion device according to the invention,

coupled with the appropriate means of transformation.

Claims (10)

1. Furnace for the preparation of glass by electric melting in which the melting energy is dissipated by the Joule effect in the melt, comprising means for supplying vitrifiable materials depositing said materials in a layer on the surface of a bath of molten glass and submerged melting electrodes submerged from the surface of the bath through the layer of composition to be melted covering the molten bath, characterized in that the height h of the molten bath is less than 800 mm and the ratio of the height h to the surface S of the bath is less than 0.5 m / m2. 2. Furnace for the preparation of glass by electric melting in which the melting energy is dissipated by the Joule effect in the melt, comprising means for supplying vitrifiable materials depositing said materials in a layer on the surface of a bath of molten glass and submerged melting electrodes submerged from the surface of the bath through the layer of composition to be melted covering the molten bath, characterized in that the height h of the molten bath is less than 800 mm and the surface of immersed electrode per unit bath volume is greater than 0.075, advantageously 0.1, especially 0.15. 3. Oven according to claim 1 or 2, characterized in that the height h of the bath is less than 500 mm, in particular less than or equal to 450 mm, in particular of the order of 200 to 400 mm. 4. Oven according to any one of the preceding claims, characterized in that the electrodes have a shape such that their lateral surface Sé and their useful length I are in a ratio Se. / I greater than or equal at 0.45, advantageously at 0.6. 5. Oven according to any one of the preceding claims, characterized in that at least one electrode (19, 30) comprises at least one substantially planar conductive element (20; 31, 32, 33, 34). 6. Oven according to claim 5, characterized in that the electrode (19) has the shape of a plate (20) or comprises several plates (31, 32, 33, 34) associated with each other. 7. Oven according to claim 5 or 6, characterized in that the electrode comprises at least one plate, in particular rectangular (20), having its side of larger dimension arranged substantially horizontally. 8. Oven according to any one of claims 5 to 7, characterized in that at least one electrode (1 9, 30) is provided with means for adjusting the orientation of the electrical exchange surfaces, in particular by pivoting around at least one axis. 9. Installation for manufacturing glass wool comprising a glass melting furnace, a fiberizing device and means for supplying the fiberizing device with molten glass produced in said furnace, characterized in that the oven is an oven according to any one of claims 1 to 8. 10. Installation according to claim 9, characterized in that the fiberizing device is of the internal centrifugation type.