MX2008003743A - Joint strengthening ring for graphite electrodes - Google Patents

Abstract

An electrode joint (50) is presented, the joint including two joined graphiteelectrodes (50a, 50b) and having a joint strengthening ring (10) interposedbetween the electrodes, the joint strengthening ring (10) composed of a compressible.

Description

GASKET REINFORCER FOR GRAPHITE ELECTRODES TECHNICAL FIELD The present invention relates to a joint reinforcing ring for graphite electrodes and to a process for preparing the reinforcing ring of the invention. More particularly, the invention relates to a ring, advantageously formed of expanded graphite particles, used on the end faces of graphite electrodes formed in a joint to improve the flexural strength in the upper column of an electrode column, of which the ring and the board of the invention are members. By "flexural strength in the upper column" is meant the ability of a column of graphite electrodes to resist cracking, cracking or other damaging effects that are formed by the bending forces to which the column is subjected during the operation of an electric arc furnace ("EAF"). The background technique Graphite electrodes are used in the steel industry to melt the metals and other ingredients used to form the steel in electrothermal furnaces. The heat necessary to melt the metals is generated by passing current through a plurality of electrodes, usually three, and forming an arc between the electrodes and the metal. Frequently currents of more than 100,000 amperes are used. The resulting high temperature melts metals and other ingredients. In general, the electrodes used in the steel furnaces each consist of columns of electrodes, that is, a series of individual electrodes, joined to form a single column. In this way, when the electrodes are depleted during the thermal process, replacement electrodes can be attached to the column to maintain the length of the column extending into the furnace. In general, the electrodes are joined to columns by means of a pin (sometimes called a nipple) that functions to join the ends of adjacent electrodes. Typically, the pin adopts the form of threaded male sections, opposite, with at least one end of the electrodes comprising female threaded sections, capable of engaging the threaded male section of the pin. Thus, when each of the opposite threaded male sections of a pin are screwed into the threaded female sections at the ends of two electrodes, those electrodes are joined in a column of electrodes. Commonly, the joined ends of the adjacent electrodes and the pin that is between them are referred to in the art as a gasket. Alternatively, the electrodes may be formed with a male or threaded boss, machined at one end, and a female threaded receptacle, machined at the other end; so that the electrodes can be attached by screwing the male pin of an electrode into the female receptacle of a second electrode, thereby forming a column of electrodes. The joined ends of two of said adjacent electrodes, in that embodiment, are also referred to in the art as a joint. Given the extreme thermal stress that the electrode and gasket (and actually the entire electrode column) can withstand, mechanical / thermal factors, such as physical strength, thermal expansion and cracking resistance, must be carefully balanced. In order to avoid damage or destruction of the electrode column or individual electrodes. For example, the longitudinal thermal expansion (ie, following the length of the electrode / electrode column) of the electrodes, especially at a different rate than that of the pin, can force the joint to separate, reducing the effectiveness of the electrode column to conduct the electric current. A certain amount of transverse thermal expansion (ie, following the diameter of the electrode / electrode column) of the electrode, greater than that of the pin, may be convenient to form a firm connection between the pin and the electrode; however, if the transverse thermal expansion of the electrode greatly exceeds that of the pin, the electrode or seal separation may be damaged. Again, this can result in the reduced effectiveness of the electrode column, or even the destruction of the column if the damage is so severe that the electrode column fails in the joint section.

In addition, another effect of the thermal and mechanical stresses to which an electrode column is exposed is the damage to the electrode that forms upwards the upper column, due to the "bending" forces applied to the column. This can result in cracks or fissures in one or more of the electrodes, or other detrimental effects. These conditions can reduce the efficiency of the electrode column by reducing the electrical contact between the adjacent electrodes. In the most severe case, cracks and fissures may result in breakage, with the resulting loss of the electrode column below the affected electrode. In U.S. Patent No. 3,540,764, Paus and Revilock suggest the use of an expanded graphite separator, disposed between the end faces of the adjacent electrodes, in order to increase the electrical conductivity and thermal stress resistance of the joint. However, the nature of the Paus and Revilock separator and its placement are such that a space is created in the joint when it was not created in other circumstances, thus contributing to the loosening of the joint and the potential of its failure. Therefore, what is desired is a joint reinforcing ring that can be used to reduce the tendency of the electrodes of a column to crack, crack or otherwise be damaged by the bending forces to which the column is subjected during the operation of the EAF. In other words, the desired reinforcing ring of the electrode joint increases the flexural strength of the upper column. It is also highly desirable to obtain those property benefits, without the use of high quantities of expensive materials, without requiring a substantial amount of effort on the site of the electric arc furnace. BRIEF DESCRIPTION OF THE INVENTION It is an aspect of the present invention to provide a joint reinforcing ring for the end faces of the graphite electrodes. It is another aspect of the present invention to provide a joint reinforcing ring for the end faces of the graphite electrodes, which improves the flexural strength of the upper column, in an electrode column formed by said electrodes. It is another aspect of the present invention to provide a joint reinforcing ring for the graphite electrode end faces, which produces electrode column seals that have improved physical strength and stability. Also an aspect of the present invention is a graphite electrode gasket having improved resistance to damage caused by bending forces, as compared to conventional graphite electrode gaskets in the art. These aspects and others that will be evident to those who have experience in the matter, when studying the following description, can be obtained by providing an electrode joint comprising two joined graphite electrodes and having a joint reinforcing ring interposed between the electrodes; the joint reinforcing ring comprising a compressible material, especially compressed particles of exfoliated graphite. In a preferred embodiment, the electrical conductivity of the joint reinforcing ring is greater in the direction that is extends between the electrodes, than what is in a direction orthogonal to it. In order to achieve this, the joint reinforcing ring must advantageously comprise a spirally wound sheet of compressed particles of exfoliated graphite. Each of the two joined electrodes forming the joint comprises a female threaded receptacle, and further comprising a pin comprising male, opposite threaded sections, which engage the female threaded receptacles of the electrodes, to form the joint. Alternatively, one of the electrodes may comprise a male threaded pin, and the other electrode may comprise a female threaded pocket; wherein the male threaded pin engages the female threaded receptacle to form the joint. Preferably, to form the joint reinforcing ring of the invention, a sheet of compressed particles of exfoliated graphite is provided, and then rolled (for example, around a head having a diameter equal to the internal opening of the joint reinforcing ring) to form a spirally wound joint reinforcing ring, suitable for use between the electrodes, in an electrode joint. The joint reinforcing ring must have an outer diameter generally equal to the outer diameter of the electrode joint and an internal opening, and may have, but not necessarily, an adhesive interposed between the layers of the spirally wound sheet of compressed graphite particles exfoliated.

In addition to being formed of a compressible material, such as the spirally wound sheets of compressed particles of exfoliated graphite, the reinforcing ring of the invention may be formed so as to increase its compression characteristic, such as by molding. . For example, the sheet can be molded so that it assumes a concave shape when viewed along the plane of the end faces of one or both electrodes, between which the joint reinforcing ring is located. The space between the tapered "arms" at either end of the concavity provides an even greater potential for the compression characteristic. In addition, a tamping paste, cement or other mastic-like material can be placed in the concave space. Another way in which the compression property of the exfoliated gellite sheets, wound in a spiral, can be increased is by forming a "corrugated" or "corrugated" surface of the joint reinforcing ring, also by molding. The concave or corrugated surfaces of the joint reinforcing ring, of course, are one or both surfaces that meet the respective end faces of the electrode. It should be understood that both the foregoing general description and the following detailed description give embodiments of the invention, and are intended to provide a general view or framework for understanding the nature and character of the invention, as claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated herein. descriptive memory constituting part of it. The drawings illustrate various embodiments of the invention and, together with the description, serve to describe the principles and operations of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective side view of an end face reinforcing ring for a graphite electrode, according to the present invention. Figure 2 is a perspective side view of a flexible, spirally wound graphite structure, from which the end face seal reinforcing ring of Figure 1 is derived. Figure 3 is a partial perspective side view of a male threaded graphite electrode, having an end face joint reinforcing ring, according to the present invention. Figure 4 is a partial perspective side view of a graphite electrode having a pin threaded therein, and having an end face joint reinforcing ring, in accordance with the present invention. Figure 5 is a side plan view of an electrode gasket having an end face joint reinforcing ring, in accordance with the present invention. Figure 6 is a sectional side view of an embodiment of an end face joint reinforcing ring for graphite electrodes, in accordance with the present invention. Figure 7 is a sectional view of another embodiment of an end face joint reinforcing ring for graphite electrodes according to the present invention. BEST MODE FOR CARRYING OUT THE INVENTION Graphite electrodes can be manufactured by first combining a particle fraction comprising calcined coke, resin and, optionally, mesophase resin or PAN-based carbon fibers, in a masterbatch. More specifically, calcined, dimensioned and milled calcined petroleum coke is mixed with a resin binder and coal tar to form the mixture. The particle size of the calcined coke is selected according to the final use of the article; and it is within the general experience of the technique. Generally, graphite electrodes for use in steel processing use particles up to an average diameter of about 25 millimeters (mm) in the mixture. The particle fraction preferably includes a small particle size charge comprising coke powder. Other additives that can be incorporated in the small particle size charge include iron oxides to inhibit puff emission (caused by the release of sulfur from its bond with the carbon within the coke particles), coke powder and oils or other lubricants to facilitate the extrusion of the mixture. After the mixture of the particle fraction, the resin binder, etc. is prepared. , the body is formed (or shaped) by extrusion through a die or molded into conventional forming molds to form what is known as a green material .. The forming, either by extrusion or by molding, is carries at a temperature close to the softening point of the resin, usually at around 100 ° C or more. The die or mold can form the article substantially in the final shape and size, although it will usually be necessary to machine the finished article, at least to provide a structure such as the threads. The size of the green material may vary; For the electrodes, the diameter can vary between 220 mm and 700 mm. After the extrusion the green material is heat treated by baking it at a temperature between about 700 ° C and about 1 100 ° C; more preferably, between about 800 ° C and about 1000 ° C, to carbonize the resin binder to solid resin coke; to give the article permanence of form, high mechanical strength, good thermal conductivity and comparatively low electrical resistance, and thereby form a carbonized material. The green material is baked in the relative absence of air to prevent oxidation. The baking must be carried out at a rate of approximately 1 ° C to approximately 5 ° C elevation per hour, up to the final temperature. After baking, the carbonized material may be impregnated one or more times with coal tar or with petroleum resin or other resins known in the industry, to deposit coke in any open pores of the material. Each impregnation is followed by an additional baking step. After baking, the carbonized material is graffitized. Graphing is carried out by heat treatment at a final temperature of between about 2500 ° C and about 3400 ° C for a time sufficient to cause the carbon atoms of the coke binder and resin-coke to be transformed from a poorly ordered state to the crystalline structure of the graphite. Advantageously, graphitization is carried out by keeping the carbonized material at a temperature of at least about 2700 ° C and, more advantageously, at a temperature of between about 2700 ° C and about 3200 ° C. At these high temperatures, the different elements of coal are vaporized and escaped as vapors. The time required for the graphitization temperature to be maintained using the process of the present invention is not greater than about 18 hours; not really more than about 12 hours. It is preferred that the graphite is performed for about 1.5 to about 8 hours. Once the graffiti is completed, the final article can be cut to size, and then machined or otherwise shaped to its final configuration. The joint reinforcing ring of the invention comprises a material that is disposed in an electrode joint between the end faces of the adjacent electrodes. The joint reinforcing ring preferably comprises a material having adequate dimensions to fill the gap between the adjacent electrodes. For this purpose, the joint reinforcing ring should have a thickness between approximately 1 mm and approximately 25 mm; plus advantageously, between about 3 mm and about 12 mm thick. Additionally, the joint reinforcing ring must extend radially from the perimeter of the electrode joint towards the center of the joint, ending between the perimeter and the threaded pin or the male threaded pin. More preferably, the radius of the joint reinforcing ring should be approximately equal to that of the electrodes between which it is disposed. Thus, the joint reinforcing ring of the invention should have a radius of between about 1 1 cm and about 37 cm (when used with graphite electrodes having a circular cross-section); more preferably, between about 20 cm and about 30 cm, with a central opening having a diameter approximately equal to, or greater than, the diameter of the threaded pin or the male pin (at its respective major point); more in particular, the diameter of the central opening of the joint reinforcing ring should be between about 50 percent and about 85 percent of the diameter of the electrodes between which it is disposed. In the most preferred embodiment, the central opening of the joint reinforcing ring should be approximately equal to the diameter of the threaded pin or male pin (at its respective major point). The material or materials from which or the joint reinforcing ring of the invention is produced, or the orientation or placement of the joint reinforcing ring must be such that the joint reinforcing ring is compressible to compensate for the differences and changes in the separation between the adjacent electrodes, which can vary based on the method used to connect the adjacent electrodes, as well as due to the different mechanical and thermal stresses to which the joint is exposed while in use in the oven . In addition, the compression capacity of the joint reinforcing ring material can help ensure that no air passes between the joint reinforcing ring and the electrodes, between which it is disposed. The material from which the joint reinforcing ring of the present invention is formed can also advantageously work to decrease the speed at which the threads of the electrode joint are oxidized. To do this, you must reduce (or physically block) the exposure of the threads to the hot air of the oven. More preferably, the material of the joint reinforcing ring must be oxidized at a rate equal to, or slower than, the speed of the electrodes forming the joint. What is most preferred is that the joint reinforcing ring material oxidizes at the slowest possible speed, while meeting the compression capacity requirements. Suitable materials useful for forming the joint reinforcing ring of the invention include: paper, cardboard, pulp, braided rope, etc. An especially preferred material is compressed particles of expanded (or exfoliated) graphite, sometimes called flexible graphite. Especially useful are sheets of compressed particles of exfoliated graphite.

The graphite useful for forming the joint reinforcing rings of the present invention is a crystalline form of carbon comprising atoms covalently bonded in flat, laminated planes, with weaker bonds between the planes. By treating the graphite particles, such as natural graphite flakes, with an interlayer, for example, from a solution of sulfuric and nitric acids, the crystal structure of the graphite reacts to form a graphite compound and the intercalant. The treated graphite particles are referred to below as "interleaved graphite particles". When exposed to high temperature, the interlayer within the graphite volatilizes, causing the interlaced graphite particles to expand in their dimensions up to about 80 or more times their original volume, in a manner similar to accordion, in the direction "c"; that is, in a direction perpendicular to the crystalline planes of the graphite. The exfoliated graphite particles are vermiform in appearance and, therefore, are commonly referred to as "worms". The worms can be compressed to flexible sheets that, unlike the original graphite flakes, can be formed and cut into various shapes. The graphite starting materials for the sheets, suitable for use in the present invention, include highly graphitic carbonaceous materials, capable of intercalating organic and inorganic acids, as well as halogen, and then dilate when exposed to heat. Those carbonaceous materials extremely graphites very preferably have a degree of graphite of about 1.0. As used in this description, the term "degree of grafitation" refers to the value g, according to the formula:? M? Tas - m 0.095 where d (002) is the separation between the graffitic layers of the coals in the crystal structure, measured in angstrom units. The "d" separation between the graphite layers is measured by common techniques and X-ray diffraction currents. The diffraction peak positions are measured, which correspond to the Miller index (002), (004) and (006). ) and standard minimum square techniques are used to derive the separation, which minimizes the total error for all those peaks. Examples of highly graphitic carbonaceous materials include graphites from various sources, as well as other carbonaceous materials, such as carbons prepared by chemical vapor deposition and the like. What is most preferred is natural graphite. Graphite starting materials for sheets, used in the present invention, may contain components other than carbon, as long as the crystalline structure of the starting materials maintains the desired degree of graphite, and is capable of exfoliation. In general, any material containing carbon, whose crystalline structure possesses the required degree of graphite and can be exfoliated, is suitable for use it with the present invention. Said graphite preferably has an ash content of less than twenty weight percent. More preferably, the graphite used for the present invention will have a purity of at least about 94 percent. In the most preferred embodiment, the graphite employed will have a purity of at least about 99 percent. A common method for manufacturing a graphite sheet is described by Shahe and co-inventors in U.S. Patent No. 3,404,061, the disclosure of which is incorporated herein by way of this reference. In the typical practice of the Shane method and co-inventors, natural graphite flakes are interspersed by dispersing the flakes in a solution containing, for example, a mixture of nitric and sulfuric acids, advantageously at a level of from about 20 to about 300 parts by weight. weight of intercalating solution per 100 parts by weight (pep) of graphite flakes. The intercalation solution contains oxidizing agents and other intercalating agents known in the art. Examples include those containing oxidizing agents and oxidizing mixtures, such as solutions containing nitric acid, potassium chlorate, chromic acid, potassium permanganate, potassium chromate, potassium dichromate, perchloric acid and the like, or mixtures, such as , for example, concentrated nitric acid and chlorate, chromic acid and phosphoric acid, sulfuric acid and nitric acid, or mixtures of a strong organic acid, for example, trifluoroacetic acid, and a strong oxidizing agent, soluble in the acid organic. Alternatively, an electrical potential can be used to effect the oxidation of the graphite. The chemical species that can be introduced into the graphite crystal using electrolytic oxidation include sulfuric acid as well as other acids. In a preferred embodiment, the intercalating agent is a solution of a mixture of sulfuric acid, or sulfuric acid and phosphoric acid, and an oxidizing agent, ie nitric acid, perchloric acid, chromic acid, potassium permanganate, hydrogen peroxide , iodic and periodic acids, or the like. Although less preferred, the intercalation solution may contain metal halides, such as ferric chloride and ferric chloride mixed with sulfuric acid, or a halide, such as bromine, as a solution of bromine and sulfuric acid or bromine, in an organic solvent . The amount of intercalation solution can vary from about 20 to about 150 pep and, more typically, between about 50 and about 120 pcp. After the scales are intercalated, any excess solution of the scales is drained and the scales are washed with water. Alternatively, the amount of the intercalation solution can be limited to between about 10 and about 50 pcp, which allows the washing step taught and described in US Pat. No. 4,895,713 to be eliminated, the description of which also it is incorporated here by means of this reference. The graphite flake particles treated with the intercalation solution can be contacted optionally, by example, by mixing, with an organic reducing agent, selected from alcohols, sugars, aldehydes and esters, which are reactive with the surface film of oxidizing intercalation solution, at temperatures within the range of 25 ° C to 125 ° C. ° C. Suitable specific organic agents include: hexadecanol, octadecanol, 1-octanol, 2-octanol, decyl alcohol, 1,10-decanediol, decylaldehyde, 1-propanol, 1,3-propanediol, ethylene glycol, polypropylene glycol, dextrose, fructose, lactose, sucrose, potato starch, ethylene glycol monostearate, diethylene glycol dibenzoate, propylene glycol monostearate, glycerol monostearate, dimethyl oxylate, diethyl oxylate, methyl formate, ethyl formate, ascorbic acid and lignin-derived compounds, such as lignosulphate sodium. The amount of organic reducing agent is suitably from about 0.5 to 4 weight percent of the graphite flake particles. The use of a dilation assistant, applied before, during or immediately after interleaving, can also provide improvements. Among these improvements may be the reduced exfoliation temperature and the increased dilated volume (also called "worm volume"). A dilation aid in this context will advantageously be an organic material sufficiently soluble in the intercalation solution to obtain an improvement in the dilation. More strictly, organic materials of this type, which contain carbon, hydrogen and oxygen, preferably exclusively, can be used. It has been found that Carboxylic acids are especially effective. A suitable carboxylic acid, useful as a dilation aid, can be selected from monocarboxylic acids, dicarboxylic acids and polycarboxylic acids, saturated and unsaturated, aromatic, aliphatic or cycloaliphatic, straight chain or branched chain; having at least 1 carbon atom, and preferably up to about 1 5 carbon atoms, which is soluble in the intercalation solution in effective amounts to provide a measurable improvement of one or more aspects of exfoliation. Suitable organic solvents can be employed to improve the solubility of an organic dilation aid in the intercalation solution. Representative examples of saturated aliphatic carboxylic acids, acids, such as those of the formula H (CH 2) nCOO H, wherein n is a number from 0 to about 5, include: formic, acetic, propionic, butyric, pentanoic , hexanoic and the like. Instead of the carboxylic acids, the anhydrides or the reactive carboxylic acid derivatives, such as their alkyl esters, can also be used. Representative of the alkali esters are methyl formate and ethyl formate. Its luric acid, nitric acid and other known aqueous intercalants have the ability to decompose formic acid, finally to water and carbon dioxide. Due to this, the formic acid and the other sensitive expansion aids are advantageously contacted with the graphite flake, before submerging the flake in the aqueous intercalant. Representative of dicarboxylic acids are aliphatic dicarboxylic acids having from 2 to 12 carbon atoms, in particular: oxalic acid, fumaric acid, malonic acid, maleic acid, succinic acid, glutaric acid, adipic acid, 1,5-pentanedicarboxylic acid, 1,6-hexanedicarboxylic acid, 1,1-decanedicarboxylic acid, cyclohexane-1,4-dicarboxylic acid and aromatic dicarboxylic acids, such as phthalic acid or terephthalic acid. Representative of the alkyl esters are dimethyl oxylate and diethyl oxylate. Representative of cycloaliphatic acids are cyclohexanecarboxylic acid and aromatic carboxylic acids representative of benzoic acid, naphthoic acid, anthranilic acid, p-aminobenzoic acid, salicylic acid, o-, m- and p- acids. tololic, methoxy- and ethoxybenzoic acids, acetoacetamidobenzoic acids and acetamidobenzoic acids, phenylacetic and naphthoic acids are representative of hydroxyaromatic acids: hydroxybenzoic acid, 3-hydroxy-1-naphthoic acid, 3-hydroxy-2-naphthoic acid, 4-hydroxy-2-naphthoic acid, 5-hydroxy-1-naphthoic acid, 5-hydroxy-2-naphthoic acid, 6-hydroxy-2-naphthoic acid and 7-hydroxy-2-naphthoic acid. Citric acid is prominent among the polycarboxylic acids. The intercalation solution will be aqueous and preferably will contain an amount of dilation aid of about 1 to 10 percent; the amount being effective to increase the exfoliation. In the modality in which the dilation assistant is contact with the graphite flake, before or after immersion in the aqueous intercalation solution, the dilation aid can be mixed with the graphite by suitable means, such as a V-mixer, typically in an amount of about from 0.2 percent to about 10 percent by weight of graphite flake. After intercalating the graphite flake, and after mixing the interleaved coated graphite flake with intercalator, with the organic reducing agent, the mixture is exposed to temperatures in the range of 25 ° C to 125 ° C to promote the reaction of the reducing agent and interlayer coating. The heating period is up to about 20 hours, with shorter heating periods, for example, at least about 10 minutes, for higher temperatures in the scale noted above. You can use times of half an hour or less, for example, in the order of 10 to 25 minutes, at the highest temperatures. The graphite particles thus treated are sometimes referred to as "interleaved graphite particles". By exposure to high temperature, for example, at temperatures of at least about 160 ° C and, especially, about 700 ° C to 1200 ° C and above, the interleaved graphite particles dilate to about 80 to 1000 or more times their Original volume, similar to an accordion, in the "c" direction, that is, in a direction perpendicular to the crystalline planes of the constituent graphite particles. The dilated graphite particles, ie Exfoliated, they are vermiform in appearance and, therefore, are commonly referred to as worms. The worms can be compressed with each other to flexible sheets which, unlike the original graphite flakes, can be formed and cut into various shapes, and can be provided with small transverse openings by mechanical deformation impact, as described below. The sheet and flexible graphite sheet are coherent, with good resistance to handling and are suitably compressed, for example, by pressing them with a roll to a thickness of approximately 0.075 mm to 3.75 mm, and with a typical density of approximately 0.1 to 1.5 grams per cubic centimeter (g / cc). Approximately 1.5 to 30 weight percent of ceramic additives may be mixed with the interlayered graphite flakes, as described in U.S. Patent No. 5,902,762 (which is incorporated herein by way of this reference) to provide impregnation increased resin in the final product of flexible graphite. The additives include ceramic fiber particles, which have a length of about 0.15 to 1.5 millimeters. The width of the particles is suitably around 0.04 to 0.004 mm. The ceramic fiber particles are non-reactive and non-adherent to graphite, and are stable at temperatures up to about 1 100 ° C, preferably up to about 1400 CC or more. Suitable ceramic fiber particles are formed from macerated quartz glass fibers, carbon fibers and graphite, zirconium oxide, boron nitride, silicon carbide and magnesium oxide fibers; mineral fibers that occur in nature, such as calcium metasilicate fibers, calcium and aluminum silicate fibers, aluminum oxide fibers, and the like. The flexible graphite sheet can sometimes be treated advantageously with resin, and the absorbed resin, after curing, increases the moisture resistance and handling resistance, ie the rigidity of the flexible graphite sheet as well as the "fixation" of the morphology of the sheet. Preferably, the suitable resin content is at least about 5 weight percent, more preferably, about 10 to 35 weight percent and, suitably, up to about 60 weight percent. Resins that were found especially useful in the practice of the present invention include: acrylic, epoxy and phenolic based resin systems; fluoro-based polymers, or mixtures thereof. Suitable epoxy resin systems include those based on diglycidyl ether or bisphenol A (DGEBA) and other multifunctional resin systems: the phenolic resins that may be employed include the resole resins and the phenolic novolac. Optionally, the graphite can be impregnated with fibers and / or with salts, in addition to the resin, or in place of the resin. The flexible graphite sheet material exhibits an appreciable degree of anisotropy due to the alignment of the graphite particles parallel to the parallel, opposite major surfaces of the sheet, with the degree of anisotropy increasing when pressed. with roller the sheet material at an increased density. In the roll-pressed anisotropic sheet material, the thickness, ie, the direction perpendicular to the parallel and opposite sheet surfaces, comprises the "c" direction and the directions indicating the length and width, i.e. along, or parallel to, the opposite major surfaces, it comprises the "a" directions and the thermal and electrical properties of the sheet are very different, in orders of magnitude, for the "c" and "a" directions. The flexible graphite sheet thus formed, formed to have the required central opening, can be used as such, or can be formed into a laminated structure of several flexible graphite sheets (with or without an adhesive between the layers) and can be used as the joint reinforcing ring of the invention, that way. However, what is most preferred, due to the anisotropic nature of the sheets of compressed expanded graphite particles, the orientation of the joint reinforcing ring, of graphite sheet, must be such that the "a" direction, which is the direction parallel to the opposite major surfaces of the sheet, is directionally stratified between the end faces of the electrodes. In that way, the greater electrical conductivity of the material, in the "a" direction, will improve the conductivity across the board, as opposed to the "c" direction. One embodiment of the joint reinforcing ring of the invention is illustrated in FIG. 1 and is designated by reference number 10. The joint reinforcing ring 10 comprises a sheet wound in spiral, of flexible graphite, and has its "a" direction through the thickness of the joint reinforcing ring 10, rather than along its surface. The joint reinforcing ring 10 can be formed, for example, by winding one or more flexible graphite sheets around a head 100, having a diameter equal to the desired diameter of the central opening "d" of the joint reinforcing ring 10. The sheets are wound around the head 100 until a radius equal to the desired radius of the joint reinforcing ring 10 has been obtained, resulting in a flexible spirally wound graphite cylinder 20, which can be sliced to individual rings 10, reinforcing. of the desired thickness (either through the head 100 or after removing the head 100). In this way, the direction "a" of greater conductivity is arranged stratified through the thickness of the ring 10 reinforcing joint. Optionally, an adhesive can be interposed between the turns of the ring-reinforcing ring 10, in order to prevent the ring-reinforcing ring 10, spirally wound, from unrolling. Alternatively, the joint reinforcing ring 10 can be formed by winding one or more flexible graphite sheets around a head 100, until a radius equal to the desired radius of the joint reinforcing ring 10 is obtained, and then the rolled cylinder 20 is compressed. spiral to the desired final thickness and shape. In fact, as discussed further below, the compression process can be used to mold (eg, by die casting or the like) a concave or corrugated shape, to the reinforcing ring 10 together, as illustrated in Figures 6 and 7, respectively, having arms 10a and 10b or ridges 10c, which abut the electrodes 30 and / or 40. These shapes can provide a still greater compression capacity for the ring 10 joint reinforcer. The joint reinforcing ring 10 is placed between the end faces of adjacent graphite electrodes, which form an electrode joint. For example, as illustrated in Figure 3, when a graphite electrode 30 having a male threaded, machined spigot 32 is employed, the seal reinforcing ring 10 may be placed on the end face 34 of the electrode 30, around the pin 32. When the electrode 30 is then cooperated with an adjacent electrode, having a female receptacle machined (not shown), therefore, the joint reinforcing ring 10 is placed between the end faces of the adjacent electrodes. The same applies to the electrode 40, illustrated in Figure 4, which uses a pin 42, instead of a pin. Advantageously, the joint reinforcing ring 10 is placed on the electrode 30 during the preparation of the electrode 30, either in the formation plant or in the furnace site, but before being put in its position on top of the furnace to load on the furnace. electrode column, to reduce the operation steps of forming the joint (which is often carried out in a relatively dangerous environment). Similarly, when the pin 42 is preset at the electrode 40, the joint reinforcing ring 10 can be placed on the electrode 40 at the same time. Also, when the ring 10 is formed joint enhancer with a concave shape, as shown in figure 6, and the concave portion is filled with a paste or cement, etc., a removable liner can be used to protect from dirt, dust or other substances, the dust or cement, thus preventing them from adhering to it. Consequently, in use, the seal reinforcing ring 10, for the end face of the electrode, is placed between the adjacent electrodes 50a and 50b, in an electrode joint 50, as illustrated in FIG. 5. The compressible nature of the joint reinforcing ring 10 increases the flexural strength of the upper column in a column formed using the electrodes 50a and 50b, by allowing compression during bending, thereby reducing the tendency of one or both electrodes 50a and 50b to crack, cracking, etc. Additionally, since the seal reinforcing ring 10 advantageously oxidizes at a rate equal to or less than that of the electrodes 50a and 50b, it reduces the oxygen input into the seal 50, between the end faces of the electrodes 50a and 50b and, in that way, it reduces or eliminates the oxidation of the threaded portions or the pin 32, or the male pin 42 and / or other joint surface 50, prolonging the life and functionality of the joint 50. The descriptions of all the patents and the cited publications, to which reference was made in this specification, are incorporated herein by means of this reference. The preceding description is intended to allow persons skilled in the art put the invention into practice. It is not intended to detail all possible variations and modifications that will become evident to the experienced worker, when reading the description. However, it is intended that all such modifications and variations be included within the scope of the invention, as defined by the claims that follow. The claims are intended to cover the elements and the steps indicated, in any arrangement or sequence that is effective to meet the intended objectives of the invention, unless the context specifically indicates otherwise.

Claims (13)

1. An electrode joint comprising two connected graphite electrodes and having a joint reinforcing ring interposed between the electrodes; the joint reinforcing ring comprising a compressible material that improves the flexural strength of the upper column, in an electrode column, of which the electrode joint is a component.

The gasket according to claim 1, wherein the compressible material comprises compressed particles of exfoliated graphite.

3. The gasket according to claim 2, wherein the electrical conductivity of the joint reinforcing ring is greater in the direction extending between the electrodes than it is in a direction orthogonal to it.

The gasket according to claim 3, wherein the gasket reinforcing ring comprises a spirally wound sheet of compressed particles of exfoliated graphite.

The gasket according to claim 2, wherein each of the two joined electrodes comprises a threaded female receptacle and further comprising a pin comprising threaded, opposite male sections, which engage the threaded female receptacles of the electrodes to form the joint.

6. The board according to claim 2, wherein one of the electrodes comprises a threaded male pin, and the other electrode comprises a threaded female receptacle; wherein the threaded male pin mates with the threaded female receptacle to form the joint.

7. A process for preparing a joint reinforcing ring for use in an electrode joint, the process comprising: providing a sheet of compressed particles, of exfoliated graphite, and winding the sheet to form a spirally wound joint reinforcing ring for use between the electrodes in an electrode joint.

The process according to claim 7, wherein the joint reinforcing ring has an outer diameter generally equal to the outer diameter of the electrode joint, and a central opening.

9. The process according to claim 8, wherein an adhesive is interposed between the layers of the spirally wound sheet of compressed particles of exfoliated graphite.

10. The process according to claim 8, wherein the sheet of compressed particles of exfoliated graphite is wound around a head having a diameter equal to the central opening of the joint reinforcing ring.

11. The process according to claim 10, wherein the sheet of compressed particles of exfoliated graphite, wound around a head, is cut to the desired thickness after rolling.

12. The process according to claim 7, in the that a surface of the joint reinforcing ring has a concave section. The process according to claim 12, wherein a surface of the joint reinforcing ring has a corrugated cross section.