SK149399A3 - Electrode type soderberg for making silicon alloys and silicon metal - Google Patents

Abstract

The self-baking electrode suitable for use in an electric arc furnace comprises an elongated open ended electrically conductive casing for extending generally vertically within the furnace. A central core made of a heat conductive material is disposed within and spaced from the casing. A framework within is securing the central core to an inner surface of the casing for holding centrally the central core within the casing and for preventing an extrusion of the central core downward. The central core is surrounded by a carbonaceous electrode paste devised to cure into a solid electrode upon heating and to bond to the central core. This self-baking electrode allows the production of silicon metal in a Söderberg-type furnace without any modification to the usual slipping system or addition of another slipping system. An electrode according to the invention allows the same furnace to produce both FeSi of any grade and Si metal without any downtime between the gradual change from one product to the other and each time at the lowest electrode cost.

Description

Technical field

The present invention relates to a self-baking electrode for producing silicone alloys and silicone metal.

BACKGROUND OF THE INVENTION

The use of self-baking electrodes (also "Soderberg electrodes") for the production of ferrous alloys has been known for about 75 years (see U.S. Patent No. 1,440,724 of September 1919 and U.S. Patent No. 1,441,037 of January 1923 both under the name of Söderberg). The self-baking electrodes consist essentially of a carbon-containing material such as anthracite, coke, tar and pitch which fills the steel casing in position inside the electric arc furnace by means of contact tips and a suspension and sliding device. The use of the high voltage and the glow of the arc ignited by the electrode during furnace operation generates sufficient heat to melt the material filled into the package and form the sealant and then coke the resulting sealant and finally burn the electrode.

The steel sheaths of the Soderberg electrodes now in use are mostly round and equipped with a series of internally projecting ribs positioned radially toward the center of the electrode in order to obtain the mechanical force of the electrode, the penetration of heat in the electrode through the conductivity of the ribs. It behaves like a normal driver. Ribs and casing are usually made of perfect steel and their t

quantity, length and physical shape depend on what is considered to be the optimum for perfect firing on any geometric design.

Since the electrode consumes during the production of silicone or ferrous alloy, both the sealant and the casing can be replaced. This action takes place high at the top of the electrode column in such a way that there is sufficient static pressure for coherence and to run through the various degrees of the temperature model from softening the sealant to the heat generated by the current flow.

Electrode consumption is replaced by perfect sliding of the electrode through the contact tips. The iron casing and the ribs passing through the nibs burn and oxidize or melt each time they slide, thereby sinking into the mixture. Because of this consumption / oxidation, the iron recovery is in such an amount that Söderberg technology cannot be used to produce a commercial grade silicone metal where, according to the grade for Si, Fe content should be below 1%, below 0.5%, below 0.35% or even below 0.2%.

Therefore, the silicone metal is produced exclusively using a so-called "pre-bake" electrode, which is an amorphous carbon or semi-graphitized electrode made in special manufacturing plants and then supplied in parts of a typical length of 2 to 2.5 m. These pre-baking electrodes, which are typically 4 to 6 times more expensive than the Söderberg electrodes, are to be connected to each other by certain devices such as plugs and sockets or a set of male / female structural cuts at the ends of each electrode piece. In the operation of a silicone metal furnace, these relationships between electrode fragments are limiting factors for the transfer of energy from one electrode to the other below the contact tip.

For the heat and current transfer of the model, the plugs and sockets are susceptible to breakage due to sudden changes in the furnace energy - which is caused by any type of power cut - so breakage of the electrode is part of an unwanted negative impact in operation.

Moreover, their strength is relatively low when compared to Söderberg electrodes, which do not contain weak points in connectors or plugs, making it stronger and capable of receiving energy per square piece.

Therefore, reducing the cost of an electrode using the self-baking principle is one of the major visions of any silicone metal manufacturer.

Many attempts have been made to develop a type of Söderberg electrode that would allow cheaper production of silicone metal while meeting all the criteria for reducing the amount of iron in the metal produced.

In 70 ', Nippon Denko in Japan developed a system in which the packing and ribs, usually made of steel, are replaced by packing and ribs made of aluminum (see Japanese Patent Nos. 951,888 and 835,596). This attempt to use aluminum on the casing and ribs has never been used industrially because of the lack of mechanical stability and substantially different conductivity of aluminum compared to steel.

Another approach was taken by M. Cavigli (see Italian Patent No. 606,568 of July 1960). This patent proposed to remove the ribs from the outer packaging and to adapt the movement of the sealant relative to the outer packaging by sliding or extruding the outer contents of the packaging as a centrally necessary component. Iron crosses were introduced inside the package to support the firing electrode. These iron crosses held the electrode as long as relative displacement between the sheath and the electrode was allowed, either by injecting or reducing the weight of the suspension. This system was in operation in a factory in Italy. It makes it possible to reduce the contamination of iron; However, it does not allow to achieve the same low level of iron contamination as is done with conventional pre-firing electrodes.

Another approach was taken by Bruff (see U.S. Patent No. 4,527,329 of July 1985). This patent proposes to separate the baking of the sealant from that which occurs by using heat by means of Ohm resistance and conductivity, and below the contact tips. Thus, a special firing device is positioned above the contact tips. In addition, the invention is provided for cutting and removing the iron wrapper below the firing system, above the contact tips, such that a base-shaped firing electrode enters and connects to the contact tips. This system is converted in a small furnace around 10 MW in Elkem Kristiansand. However, there are some limitations to the use of higher voltage furnaces with larger diamond electrodes, which are the production standard for price efficiency in the developed world.

A similar solution has been disclosed in German patent no. No. 4,036,133 of May 1991 under the name E. Svana.

Another system based on the proportional development of a self-baking electrode with respect to the outer sheath was disclosed by Persson in U.S. Pat. No. 4,575,856, Mar. 1986. In this patent, the iron crosses used by Caviglim in its system are replaced by smaller graphite electrodes introduced into the center of the package. The small electrodes were supported and were driven by a special slip / hold device that allows relative movement within the package.

An improved system based on the "transfer" of a conventional pre-firing electrode of one of the designated types described by Cavigli and Persson in Canadian Patent No. 5,201,549. 2,081,295.

The disadvantages of this system result from the physical force of the graphite electrode core limitations and their limited potential for absorbing voltage indentation and braking forces, since the electrode core is substantially uncontrolled to a length of 14 m and can be held in a perpendicular position for various reasons. Further, the wrapper, which in this system is essentially an extrusion paint, needs to slide downward for replacement, for thermal damage between and below the contact tips. Without such periodic rearrangement, the damage would reach high levels in the contact tips, and the liquid sealant would start to drip, causing a failure called "green" breakage of Söderberg technology. Periodic rearrangement of the packaging contaminates Si not only with the furnace iron, but also with the alloy elements used in the packaging material and the determination of maximum heat to protect oxidation. These contaminants have the effect that the silicone metal produced in this way is unsuitable for use in the chemical industry for the production of methyl chlorosilanes from the silicone metal. Packaging made of stainless steel also has drawbacks such as reducing the heat important properties for operation, the furnace environment and the time at which they are exposed to this.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a new and improved self-baking electrode.

Another object of the present invention is to provide a new electrode assembly that enables the production of silicone metal in a Söderberg-type furnace of any modification of an existing shear assembly or the addition of another shear assembly. Thanks to the electrode of the invention, the same furnace can also produce FeSi of each stage and the metal Si without any deterioration between the gradual change of one product to another at any time at the lowest cost of the electrode.

The electrode as the invention overcomes the problems associated with the preferred field: contamination of the silicone metal by core breakage as a result of the displacement forces, deformation of the shell, loss of production and substantial expense for the establishment of a new shear system. It also provides a method for converting larger and more efficient Söderberg type ferrosilicon furnaces into existing silicone metal furnaces with pre-firing technology.

Accordingly, the present invention relates to a self-baking electrode in a position suitable for use in an electric arc furnace comprising:

an elongated electrical conductive casing open at the end, which normally extends perpendicular to the furnace during operation;

a central core housed in a furnace and separated from the packaging, a central core made of a heat conducting material;

at least one structural frame, a structural package securing the central core to the inner surface of the package to retain the central core within the package and prevent the central core from being pushed downwards; and a carbon electrode sealant surrounding the central core, the sealant is intended to wrap a solid electrode for heating and attachment to the central core.

The present invention also relates to an electric arc furnace comprising a self-baking electrode as described above. More specifically, the electric arc furnace comprises:

the furnace itself comprising a charge for igniting the furnace; self-baking electrode containing:

a longitudinally electrically conductive wrapper open upwardly having an upper and a lower end, say, a wrapper generally expanded perpendicularly within the furnace and released to slide perpendicularly through the derailleur mechanism;

a central core located within the furnace and away from the package, the central core being made of a heat conducting material;

at least one structural frame in the package, a structural frame that maintains the central core to the inner surface of the package to maintain the center of the central core within the package and to prevent the central core from being pushed downwardly through the lower end of the package;

a carbon electrode sealant surrounding the central core, the sealant for wrapping a solid electrode for heating and attachment to the central core;

the packaging retaining components are generally perpendicular to the interior of the furnace; and electrical components for generating an electric arc in the furnace, electrical components comprising a connection to the package.

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Another object of the invention is to provide a process for forming a self-baking electrode in an electric arc furnace, the process comprising the steps of:

(a) the procurement of an electrically conductive container opened upwards;

b) positioning the longitudinal central core of the heat conducting material to the furnace and away from the package;

c) maintaining the central core to the inner surface of the package to be kept centrally within the package;

d) shifting the elongate electrically conductive wrapper in the furnace to expand generally perpendicularly;

e) introducing a certain amount of carbon electrode sealant into the envelope and surrounding the central core, the sealant is intended to coat the solid electrode for heating and attachment to the central core

f) coupling the package to a power source; and

g) generating by electric power to the electric power source of the electric arc in the furnace.

The central core of the electrode consists predominantly of carbon rods or rods connected to each other such that the heat transfer is in substantially continuous connection. Metal bars or rods may also be used.

However, the material used to produce the central core, such a core in the form of rods or rods, should be perforated to allow cooling by injection of biatomic or other gases. Thus, it is useful for controlling and influencing the electric arc on the electrode type and on the electrode firing.

In accordance with the invention, the packaging material is selected as being electrically conductive to transfer electrical energy from the contact tips to the Söderberg sealant to prevent unwanted metallic contamination or Ti, V, Ta, Cr, Zr or Ni. As an advantage, the casing can be made of Cu or brass, or an aluminum alloy or aluminum of sufficient strength to support the filling pressure of the Söderberg sealant without deformation or indentations.

Such selection makes the invention useful for producing suitable grade silicone metal for use in Rochow-direct synthesis. Indeed, it is only necessary to select the material forming the conductive core and the support shell so that the resulting metal melting additions contain appropriate amounts of Al and / or Cu and / or zinc and / or tin as required in the silicone so produced.

As an advantage of the invention, the electrode allows the user to switch from the production of ferrosilicon using a conventional Söderberg electrode to produce silicone metal using the technology described above, without any downtime, and since no additional graphite core guiding devices are required, switching to Söderberg technology is possible and unique.

As appreciated, an important improvement in the electrode is that the central core of the electrode that is attached to the sheath is "deprived" of its function of transferring pressure forces to the extrusion as described for the electrode as described in the preferred art, as indicated above. Consequently, the core material is not exposed to the risk of bulging or deformation during indentation and v

also breaking. Furthermore, it eliminates the need for a special sliding device, for performing the functions of the central core, and thus a substantial expense for irreversibly reassembling existing furnaces, with a carbon electrode prior to the baking electrode as described above. Furthermore, it permits a much safer use of the pierced electrode core, where, in the case of the extrusion principle, the presence of such a central opening in the central core weakens the core mechanically in cross-section, especially at plug or socket level with more pronounced susceptibility to furnace damage.

An unbounded description of this preferred representation will be given with reference to the accompanying drawings.

Overview of the figures in the drawing

In FIG. 1 is a side cross-sectional side view schematically illustrating an electric arc furnace in which an electrode such as the present invention is used;

Fig. 2 is a side cross-sectional view of the electrode as a preferred embodiment of the invention illustrated above with a conventional Söderberg electrode; and

Fig. 3 is a cross-sectional view of the electrode of FIG. 2 taken along line II-II of FIG. Second

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, an electric arc furnace 2 in which an electrode 4 such as the present invention can be used as illustrated. The furnace 2 is of ordinary design and can be used to melt, for example, ferrosilicon and silicone metal. As is well known, the furnace 2 comprises a furnace 6 itself made of an outer steel jacket and a suitable fire-resistant material. The curtain 8 extends upwardly from the furnace and has an upper end provided with a lid 10 or furnace lining 6. The electrode 4 extends perpendicularly inside the furnace 6 through an opening 12 in the lid 10. The furnace 2 comprises electrical components for generating an electric arc in the furnace 2. and the hub 14 in the furnace 6 itself. The electrical components have contact so that the contact tip 16 is connected to the electrode 4. The contact tip 16 is mounted on the electrode 4 with a plain semi-ring 18. The furnace 2 may also be provided with a water cooled jacket 20, for cooling. The holding components are preferably to hold the electrode 4 vertically in the furnace 2. The holding components preferably comprise control cylinders 22 and two slide belts 24 mounted on the top door 26 of the furnace and supporting the electrode 4.

Referring in more detail to Figures 2 and 3, the self-baking electrode 4 as the present invention comprises an elongate electrical conductive wrapper open upwards 30, for expansion in a generally perpendicular manner in the furnace 2, in operation. This sheath 30 has an upper end 31 and a lower end 33. A central core 32 made of a heat conducting material, predominantly made of carbon material, is placed in the furnace and spaced from the package 30. The sheath 30 and the central core 32 define an annular channel 34 in which the carbon electrode sealant 36, predominantly Söderberg sealant, can be filled, melted and heated. In other words, the carbon electrode sealant 36 surrounds the central core 32, the sealant 36 is designed to encapsulate the solid electrode for heating and attachment to the central core 32.

The central core 32 may be in the form of a rod or other intended shapes and maintained in the center within the shell 30, by at least one frame 37 that prevents relative displacement of the central core 32 relative to the shell 30 by being a sealant displacement between the core 32 and the shell 30th

Preferably, the wrap 30 is made of thin-walled plain steel or thick-walled Dural in such a way that the strength of the walls can withstand the radial pressure of Söderberg sealant 36 as a filler. The filling of the Sodserberg sealant 36 into the electrode sheath 30 is carried out in a continuous manner so as to minimize the "decreasing" height as well as the total length between the contact tips.

In the case where the silicone metal is to be produced in the furnace 2, the container 30 is preferably made of a material unalloyed with a metal selected from the group consisting of titanium, vanadium, tantalum, chromium, zirconium and nickel to prevent contamination of the silicone metal to be produced in the furnace 2, with one, say, metal while the package is ingested in the furnace 2.

More often in this case, the container 30 is made of a metal selected from the group consisting of copper, brass and aluminum.

As seen in FIGS. 2 and 3, the frame 37 securing the central core 32 to the inner surface of the wrapper 30 comprises a pair opposite the lying rods 38, each rod 38 generally laid horizontally having a first end 40 inserted into the central core 32 and a second end 42 fastened to the inner surface of the package 30. The rod 44 penetrates through the central core 32 below the pair of rods 38, the rod 44 has opposing outer ends 46 projecting from the central core 32. The frame 37 further comprises two lateral components 48, each connected to the other end. 42 of each rod 38, to the corresponding outer end 46 of the rod 44. According to FIG. 3, two further rods 60 may be provided to prevent distortion or rotation of the central core 32. Each of the rods 60 includes a first end 62 secured to the central core 32 and a second end 64 attached to the inner wall of the package 30, the two rods 60 contact the central cores 32.

Although not substantially, the stretched sheets 47 may be secured to the inner surface of the wrap 30 to better prevent the baking sealant 36 being pushed downwards. However, experiments have shown that the frame 37 itself prevents the baking electrode 36 from being pushed down very efficiently while the baking electrode is attached to the frame 37.

According to FIG. 2, an ordinary Soderberg electrode 49 is shown below the electrode 4 as the present invention. This common Soderberg electrode 49 comprises a shell 50 and ribs 52 mounted on an inner wall of the shell 50. The self-baking electrode 54 is formed in the shell 50 and the electrode 54 and the shell 50 are moved downwardly. This type of electrode is well known in the art and does not need further description. As appreciated by this ordinary Soderberg electrode 48, it should have the same diameter as the electrode diameter 4 according to the invention, showing that it is easy to move from ferrosilicon production using conventional Söderberg electrode 49 to silicon metal production using the electrode of the invention , without any downtime or closure of the entire furnace.

The detailed structure of the electrode of the invention allows a large reduction in the volume of the metal, such as steel, which is normally used to prevent the self-baking electrode from being pushed down. In fact, with the electrode of the invention, it is possible to obtain a silicone metal which contains less than 0.5% Fe, with a coating still made of steel.

Extensive studies of both the conventional electrode and the mixed electrode firing sample, where the center of the electrode is made of a solid material having substantially different thermal and electrical conductivity, have shown that when the electrode contains a high conductivity central core, the heating and firing sample is higher in the contact area. compared to conventional Söderberg technology. In particular, the baking of the binder passes from the solid core of the conductivity of the large heat, compared to the surrounding Söderberg binder towards the sheath, as opposed to the conventional Söderberg electrode; and Söderberg material.

The present invention uses, in a very well balanced system, the high conductivity of the central core to burn the surrounding Söderberg sealant 36. It does not need a relative displacement of the baking electrode 36 relative to its surrounding sheath 30 since this is the case with mixed electrodes known in the prior art and for use in production of silicone metal.

The process for forming the self-baking electrode 4 in the position of the electric arc furnace 2 according to the present invention comprises the following steps.

(a) The elongated, open-ended, electrically conductive container is within easy reach.

b) The elongate central core 32 of the conductive thermal material is located inside the furnace and away from the package 30.

c) The central core 32 is fixed to the inner surface of the container 30 and kept centered with the container 30.

d) The elongate electrically conductive casing 30 slides within the furnace 2 to expand in a generally perpendicular direction.

e) A certain amount of carbon electrode sealant 36 is introduced in a package 30 surrounding the central core 32. The sealant 36 is designed to wrap a solid electrode for heating and attachment to the central core 32.

f) The electric arc is located in the furnace 2 according to a well known method which does not need further description.

Individually in step c), the central core 32 is secured to the package 30 by introducing the two opposite sides of the central core 32, the first end 40 of the matching rod 38, the pair opposite the lying rods 38 and securing the second end 42 of each, say, lying rods 38, to the inner surface of the package such that each rod is pulled generally horizontally inside the package 30. The rod 44 is folded over the central core 32 by two rods 38 in such a way that opposite the lying outer ends 46 of each rod 44 protrude from the central core 32. The rod 38 is individually coupled to the corresponding outer end 46 of the rod 44 with the structural lateral frame 48.

In the case where the electrode 4 is used to produce silicone metal, the sheath 30 in step d) may be advanced to the top of a previously produced Soderberg type 49 self-baking electrode used to produce the ferrosilicon as shown in FIG. 2. In this case, the sheath 30 used to produce silicone may have substantially the same diameter as the outer sheath 50 of the Söderberg electrode 48. As mentioned above, it can be seen that it is easy to switch from ferrosilicon production by using an ordinary Söderberg electrode 48 to produce silicone metal using the electrode of the invention without stopping and shutting down the entire furnace.

Claims (15)

NEW CLAIMS: A self-baking electrode (4) suitable for the production of silicone metal and silicone alloys and for use in an electric arc furnace (2), characterized in that it comprises: an extended heat-conductive wrapper with an open end (30) extending perpendicular to the furnace (2) in operation; a central core (32) disposed in the furnace and spaced from the package (30), the central core being made of a heat conducting carbon material; at least one frame (37) in the package (30) securing the central core (32) to the inner surface of the package (30) to maintain the center of the central core (32) in the package (30) and prevent the central core (32) from down; and a carbon electrode sealant (36) surrounding the central core (32), the sealant (36) is intended to wrap an electrode for heating and attachment to the central core (32). A self-baking electrode (4) according to claim 1, wherein the casing (30) is made of a non-alloyed metal material selected from the group consisting of titanium, vanadium, tantalum, chromium, zirconium and nickel to prevent contamination of the product produced in the furnace with any of said metal for the ongoing consumption of the package (30) in the furnace (2). The self-baking electrode (4) according to either of claims 1 and 2, characterized in that the central core (32) is made of carbon rods connected to each other. The self-baking electrode (4) of any one of claims 1 to 3, wherein the sheath (30) is made of a metal selected from the group consisting of copper, brass and aluminum. A self-baking electrode (4) according to any one of claims 1 to 4, characterized in that the at least one frame (37) comprises: a pair of opposing rods (38), each rod (38) extending horizontally and having a first end (40) inserted into the central core (32) and a second end (42) secured to the inner surface of the package (30); a rod (44) penetrating the central core (32) below the pair of rods (38) and having opposed outer ends (46) protruding from the central core (32); and two lateral construction frames (48) connecting the second end (42) of each rod (38) to the corresponding outer end (46) of the rod (44). A self-baking electrode (4) according to any one of claims 1 to 5, characterized in that the central core (32) is punched to allow injection of cooling gases. 7. An electric arc furnace for the production of silicone metal and silicone alloys (2), comprising: a furnace (6) comprising an ignition cartridge (14); a self-baking electrode (4), comprising: an elongated, open-ended electrical conductive wrapper (30) having an upper end (31) and a lower end (33), said wrapper (30) being expanded perpendicularly in the furnace (6) and released to slide perpendicularly through the slide mechanism (24); a central core (32) disposed in the furnace and spaced from the package (30), the central core (32) being made of a heat conducting carbon material; at least one frame (37) inside the package (30), a frame (37) securing the central core (32) to the inner surface of the package (30) to maintain the center of the central core (32) in the package (30) and prevent extrusion a central core (32) downwardly at the lower end (33) of the package (32); a carbon electrode sealant (36) surrounding the central core (32) for wrapping the electrode for heating and for attachment to the central core (32); means for maintaining (22, 24) the package (30) in a completely perpendicular position in the furnace (6); and electrical means for generating an electric arc in the furnace comprising a connection (16) to the enclosure (30). Electric arc furnace (2) according to claim 7, characterized in that the casing (30) is made of a non-alloyed material with a metal selected from the group consisting of titanium, vanadium, tantalum, chromium, zirconium and nickel to prevent contamination of the product a furnace (2) with one of said metal on the ongoing consumption of the package (30) in the furnace (2). Electric arc furnace (2) according to claim 7 or 8, characterized in that the central core (32) is made of carbon rods connected to each other. Electric arc furnace (2) according to any one of claims 7 to 9, characterized in that the casing (30) is made of a metal made from the group comprising copper, brass and aluminum. 4-b Electric arc furnace (2) according to any one of claims 7 to 10, characterized in that the at least one frame (37) comprises: a pair of opposing rods (38), each rod (38) disposed completely horizontally and having a first end (40) inserted into the central core (32) and a second end (42) secured to the inner surface of the package (30); a rod (44) penetrating the central core (32) below the pair of rods (38) and having opposed outer ends (46) protruding from the central core; and two lateral construction frames (48), each connecting together the second end (42) of each rod (38) to the corresponding outer end (46) of the rod (44). An electric arc furnace (2) according to any one of claims 7 to 11, characterized in that the central core (32) is punched to allow injection of cooling gases. Process for forming in the position of a self-baking electrode (4) for producing silicone metal and silicone alloys in an electric arc furnace (2), a process comprising the following steps: a) procuring an extended electrical conductive package (30) with an open end b) placing a central core (32) of carbon-heat conducting material in the furnace and away from the package (30); c) attaching the central core (32) to the inner surface of the package (30) and keeping it centrally in the package (30); d) sliding the perpendicularly longitudinally electrically conductive envelope (30) in the furnace (2); e) introducing a plurality of carbon electrode sealant (36) into the sheath (30) such that said sealant (36) surrounds the central core (32), the sealant (36) enveloping the electrode to heat and connect to the central core (32); and f) connecting the package (30) to a power source; and (g) introducing, with the aid of an electric power source, an electric arc into the furnace (2). The process of claim 13, wherein step c) comprises the steps of: - introducing successively into two opposing sides of the central core (32), introducing a first end (40) of the matching bar (38) of the pair of opposing bars (38) and securing the second end (42) of each of the opposite bars (38) to the inner surface of the package ) in such a way that each rod (38) is completely horizontal in the packaging (30); Λ * - introducing a rod (44) through the central core (32) below said two rods (38) and in such a way that the outer opposing ends (46) of said rods (44) protrude from the central core (32); and - interconnecting with the lateral frame (48), the second end (42) of each rod (38) to the corresponding outer end (46) of the rod (44). The process of claim 13, wherein: - in step d), the sheath (30) is connected to the top of a prior Söderberg-type (49) self-baking electrode used to produce ferrosilicon, said Söderberg electrode (49) comprising an outer sheath (50); and by that - the electrode sheath (30) which is formed has substantially the same diameter as said outer sheath (50) of the Söderberg electrode (49).