ES1077019U - Graphite electrode (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Monolithic graphite electrode having first and second terminal positions and a non-terminal body part, a first zone disposed in the first terminal position of the electrode, a second zone disposed in the non-terminal body part of the electrode and a third zone in the second terminal position of the electrode, characterized in that the first zone and the third zone have a concentration of carbon fibers comprised between 1% and 10% by weight, and the concentration of carbon fibers in the second zone comprises at least 20% less than the concentration of carbon fibers in the first and third zones, so that the concentration of fibers in the first zone and in the third zone is sufficient to increase the resistance of the electrode in the first terminal position and in the second terminal position, respectively, and the concentration of the fibers in the non-terminal body part is insufficient to increase the resistance the electrode of the non-terminal part of the electrode. (Machine-translation by Google Translate, not legally binding)

Description

GRAPHITE ELECTRODE

FIELD OF THE INVENTION

The present disclosure relates to a graphite electrode that shows improved properties by providing zones of different characteristics, and to a process for preparing the described graphite electrode. More particularly, the disclosure refers to a graphite electrode having one or more zones that differ substantially from other areas of the electrode in terms of resistance, electrical characteristics, composition, etc.

STATE OF THE TECHNIQUE

Graphite electrodes are used in the steel industry to melt metals and other ingredients used to form steel in electrothermal furnaces. The heat needed to melt metals is generated by passing current through a plurality of electrodes, usually three, and forming an arc between the electrodes and the metal. Electric currents that exceed 100,000 amps are frequently used. The resulting high temperature melts metals and other ingredients. Generally, the electrodes used in steel furnaces are present in the form of electrode columns that are a series of individual electrodes joined together to form a single column. Thus, when the electrodes are depleted during the thermal process, replacement electrodes can be attached to the column to maintain the length of the column that extends into the oven.

Generally, the electrodes are joined in columns through a spike (sometimes called a nipple) that works to join the ends of adjacent electrodes. Typically, the spike takes the form of opposite male threaded sections, at least one electrode end comprising female threaded sections capable of matching the male threaded section of the spike. Thus, when each of the opposite male threaded sections of a pin is threaded into the female threaded sections of the ends of the two electrodes, the electrodes are joined together forming a column of electrodes. Commonly, the joined ends of the adjacent electrodes, and the spike between them, are referred to in the art as joint (or, more specifically, spike junction).

Alternatively, the electrodes may be formed with a machined threaded boss or tail at one end and a mechanized threaded connection part at the other end, such that the electrodes can be joined by threading the tail of an electrode into the connection part of a second electrode and thus form a column of electrodes. The joined ends of two adjacent electrodes in such an embodiment are also referred to in the art as a spikeless joint. In the production of an embodiment of a spikeless electrode, the threads of the joint may include so-called "locked" threads, also referred to in the industry as "completely stuck" threads, which are frequently used. In locked threads, both thread flanks of one of the elements (such as the male tail) are in contact with both thread flanks of the other element (such as the female connecting part). On the contrary, in "unblocked" or "unlocked" threads, referred to in the industry as "stuck" or "partially stuck" threads, only one thread flank of each element makes contact with the threads of the other element, and are commonly used in spike joints.

Given the extreme thermal stress experienced by the electrode and the joint (and indeed the electrode column as a whole), mechanical / thermal factors such as resistance, thermal expansion and cracking resistance must be carefully balanced to avoid damage or destruction of the column of electrodes or individual electrodes. For example, the longitudinal thermal expansion (that is, along the length of the electrode / electrode column) of the electrodes, especially at a different speed from that of the spike, can force the joint to separate, reducing the effectiveness of the column of electrodes in the conduction of the electric current. A certain amount of transverse thermal expansion (ie, across the diameter of the electrode / electrode column) of the electrode that exceeds that of the spike may be desirable to form a firm connection between the spike and the electrode; however, if the transverse thermal expansion of the electrode greatly exceeds that of the pin, damage to the electrode or a separation of the joint may result. Again, this may result in reduced efficiency of the electrode column or even 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 literal unscrewing of the electrodes that form the joint (or the electrodes and spikes that form the joint) due to vibrations and other stresses. This unscrewing can decrease the efficiency of the electrode column by reducing the electrical contact between the adjacent electrodes. In the most severe case, unscrewing can result in the loss of the electrode column below the affected joint.

Therefore, what is desired is a more qualified graphite electrode to resist the thermal and mechanical stresses to which it will be exposed in an electric arc furnace, compared to graphite electrodes conventional in the art. It is also highly desirable to achieve these benefits, while maintaining the commercial practicability of the manufacture of the present graphite electrodes.

SUMMARY OF THE INVENTION

One aspect of the present disclosure is to provide a graphite electrode having different zones, at least one area having a measurable difference when compared to other areas of the same electrode.

Another aspect of the present disclosure is to provide a graphite electrode having at least one area with a measurable difference when compared to other areas of the same electrode, where the at least one such zone is located in a terminal part of the graphite electrode

Another aspect of the present disclosure is to provide a graphite electrode having at least one area with a measurable difference when compared to other areas of the same electrode, where the at least one such zone is located on an outside part of the graphite electrode

Yet another aspect of the present disclosure is to provide a graphite electrode having at least one area with a measurable difference when compared to other areas of the same electrode, where such measurable difference constitutes the level of the fibers in the at least one area of this type.

These and other aspects that will be apparent to the person skilled in the art after reviewing the following description can be realized by providing a carbon article having a first zone and a second zone, the first zone being formed from a first mixing design and the second zone from a second mixing design and the first and second mixing designs have at least one difference selected from the group of differences of a presence of a certain material, a concentration of a certain material, the size of a certain material and combinations thereof. In some embodiments, the disclosure includes a carbon article having a first zone and a second zone, the first zone having a concentration of carbon fibers greater than a concentration of carbon fibers in the second zone, and the first comprising zone at least one of an outer part or an end part of the article, advantageously in which the concentration of carbon fibers in the second zone comprises approximately 20% less than the concentration of carbon fibers in the first zone. A third zone can optionally be included, in which the third zone can be located opposite the first zone and constructed from substantially the same mixing design as the first mixing design.

Also, in the present disclosure there is included a process for manufacturing a carbon article, such as those described above, including mixing the resource of combining a first mix design and a second mix design in a segregated manner, differing the first design mixing the second mixing design in at least one way; Form a raw article and carbonize it. The formation may include at least one of coextrusion or hot pressing; if hot pressed, the combination comprises installing a separator in a mold and removing the separator before a pressure application.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In certain embodiments, graphite electrodes are manufactured by first combining a particulate fraction comprising calcined coke, pitch and, optionally, carbon fibers in the form of a mixture of raw materials. Carbon fibers based on mesophase pitch or PAN are two examples of suitable types of carbon fibers. The description of this report is not limited to the above types of carbon fibers. Other types of fibers, such as cotton, rayon or carbon fibers derived from biomass, can be used. Additionally, the carbon fibers may or may not be graffiti. More specifically, calcined, crushed, calibrated and ground petroleum coke is mixed with a coal tar pitch binder to form the mixture. Generally, in graphite electrodes for use in steel processing, particles with an average diameter of up to 25 millimeters (mm) are used in the mixture. The particulate fraction preferably includes a small particle charge comprising coke powder. Other additives that can be incorporated into the small particle charge include iron oxides to inhibit swelling (caused by the release of sulfur from its carbon bond within the coke particles), coke powder and oils or other lubricants for facilitate the extrusion of the mixture.

After mixing the particulate fraction, pitch binder, etc., the body is formed (or shaped) by extrusion through a matrix or molded into forming molds to create what is called raw raw material. Forming, either by extrusion or molding, is carried out at a temperature close to the softening point of the pitch, usually at about 100 ° C or more. The die or mold can form the article in substantially final shape and size, although machining of the finished article is usually necessary, at a minimum to provide structures such as threads. The size of the raw raw material may vary; For electrodes, the diameter can vary between about 220 mm and 800 mm.

After extrusion, the raw raw material is heat treated by cooking it at a temperature of between about 700 ° C and about 1100 ° C, more preferably between about 800 ° C and about 1000 ° C, to carbonize the pitch binder turning it into a solid pitch coke, give the article remains in shape, high mechanical resistance, good thermal conductivity and comparatively low electrical resistance and thus form a carbonized raw material. The raw raw material is cooked in relative absence of air to prevent oxidation. Cooking should be done at a rate of approximately 1 ° C to approximately 5 ° C elevation per hour to the final temperature. After cooking, the carbonized raw material can be impregnated one or more times with coal tar or oil pitch or other types of breasts or resins known in the industry, to deposit additional coke in any open pores of the raw material. Each impregnation is then followed by an additional cooking step.

After cooking, the carbonized raw material is then graphitized. The graphitization is carried out by heat treatment at a final temperature of between about 2500 ° C and about 3400 ° C for a sufficient time to cause the carbon atoms in the coke and in the pitch coke binder to transform from a poorly ordered state in the structure Graphite crystalline Advantageously, the graphitization is carried out by keeping the carbonized raw material at a temperature of at least about 2700 ° C and, more advantageously, at a temperature between about 2700 ° C and about 3200 ° C. At these temperatures, different elements of carbon are volatilized and these are escaped as vapors. The time required for graphite temperature maintenance using the method of the present disclosure is not more than about 18 hours and, in fact, no more than about 12 hours. Preferably, the graffiti is performed for about 1.5 to about 8 hours. Once the graffiti is completed, the finished article can be cut to size and then machined or otherwise transformed into its final configuration.

In an alternative embodiment, the formation of a graphite electrode can be carried out by the use of resistance heating of the particulate fraction mixture, pitch binder, etc. in a hot pressing stage. During the hot pressing stage, resistance heating is accompanied by the application of mechanical pressure ("hot pressing") to increase the density and carbonization of the mixture. Optionally, after hot pressing, the preform electrode or pin can be subjected to one or more densification stages using a carbonizable pitch to further increase the density of the preform before the graphitization stage.

During the hot pressing stage, the hot pressing mixture or raw material is hot pressed to create a preform body, such as a preform electrode or pin. In the hot pressing process, the hot pressing mixture is heated to a temperature sufficient to melt at least a portion of the raw material. This heating stage includes the application of an electric current to the hot pressing mixture, such that heat is generated within the mixture. While the hot pressing mixture is heated, a pressure is applied to the mixture to form a preform electrode or pin that is at least partially carbonized.

In one embodiment, a hot pressing hydraulic assembly suitable for resistively heating and hydraulically compressing a hot pressing mixture (i.e., the dry mixed raw material or, optionally, the heat softened raw material or the electrode or spigot crude) is used to make a preform carbon body, such as a preform electrode or spike. An example of a hot pressing hydraulic assembly includes a hydraulic press having an integrally attached hot pressing mold, the mold having a cavity formed to receive the hot pressing mixture and configure the desired preform. Preferably, the hot pressing mold is shaped with the appropriate dimensions of the desired graffiti carbon body, such as a graphite spike or electrode. Additionally, the hot pressing mold is preferably contained within a thermally insulated housing. Pressure is applied to the hot pressing mixture by means of hydraulic pistons and is preferably applied to achieve a uniform pressure throughout the mixture. The pressure application is preferably also performed in a molding direction perpendicular to the longitudinal axis of the preform to obtain a longitudinally preferred carbon body, that is to say that it has a crystalline structure oriented to provide the greatest tensile strength along the axis. longitudinal of the body. In a preferred configuration, the hot pressing mold will be oriented to mold the preform with its longitudinal axis in a horizontal plane. Pressure is then applied to the hot pressing mixture by means of upper and / or lower vertical hydraulic pistons that operate with a single effect or with double effect.

In a preferred embodiment, the ends of the hot pressing molds are stainless steel end plates that are in electrical contact with the hot pressing mixture. A resistive heating system applies an electric current to the hot pressing mixture through these end plates. In a more preferred embodiment, the pistons and the hot pressing mold each have a silicon carbide surface lining and both are electrically isolated from the hot pressing hydraulic assembly frame. The resistive heating system includes an electrical power source to provide a high current at low voltage, such as a direct current supply. Alternating currents of high intensity are also contemplated. The direct current or alternating current supply is electrically connected with the stainless steel end plates. The construction of the hot pressing hydraulic assembly is such that all parts of the hot pressing mixture within the cavity of the hot pressing mold are subjected to a substantially uniform flow of current. The resources of resistively heating and compressively molding the hot pressing mixture under current and pressure conditions that are generally uniform throughout the hot pressing mixture result in substantially uniform characteristics throughout the preform electrode or pin and result in also a significant reduction of fissures or other irregularities that tend to result in a fracture during use. Preferably, a programmed application of the current and pressure provides, among other things, temperatures, pressures, heating rates and pressurization rates of the hot pressing mixture according to a desired cooking procedure, the calculations of which are based on kinetics of the specific raw material. More preferably, a programmable control system integrated in the hot-press hydraulic assembly provides such a programmed application of current and pressure.

After carbonization, during the hot pressing operation, the carbonized raw material is then graphitized, as discussed above. Again, the graphitization is 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 in the coke and in the pitch coke binder to pass from a poorly ordered state to the Graphite crystal structure. Advantageously, the graphitization is carried out by keeping the carbonized raw material at a temperature of at least about 2700 ° C and, more advantageously, at a temperature between about 2700 ° C and about 3200 ° C.

In an embodiment of the present disclosure, the graphite article, whether it is a graphite electrode, a graphite electrode spike or a graphite billet, has a plurality of zones in which at least one zone is substantially different from At least another area. By "zone" it is intended to refer to an area or part of the electrode, spike or graphite billet. By measurably different it is intended to mean that the difference for said at least one characteristic is substantially different in the first zone compared to the second zone of the final article. By way of example only, in terms of concentration of a material, this may mean that the concentration of a certain material may differ from the first zone with respect to the second zone by at least about 20%, preferably, at least about 25% and, more preferably at least about 50%. In certain preferred embodiments, this is achieved with different mixing designs, that is, combinations of different mixtures or masses of raw material, as described in more detail below.

For example, in certain embodiments at least one area of the electrode

or graphite spike may include fibers to improve electrode or spike resistance in high stress regions. In some embodiments, the fibers are carbon fibers based on mesophase pitch or fibers derived from PAN (polyacrylonitrile). The fibers used should advantageously have a Young's modulus (after carbonization) of about 15 x 106 psi to about 40 x 106 psi. They preferably have an average diameter between about 6 to about 15 microns and a tensile strength of about 200 x 103 psi to about 400 x 103 psi, and preferably have an average length of about 4 mm to about 32 mm in length on average . Suitable fiber lengths include an average length of about 6 mm or less, about 12 mm or less, about 18 mm or less or about 25 mm or less. It is also preferred that the carbon fibers are not longer than the largest coke particle. Very advantageously, the fibers are added to the mixture as bundles containing between about 2000 and about 20,000 fibers per beam, compacted with the use of a sizing action.

Carbon fibers are preferably included in one of the areas of the graphite electrode or spike at a level of about 1% to about 10% by weight, more preferably from about 1.5% to about 7.5% and even more preferably approximately 5.0% or less. However, in other areas of the electrode, spike or graphite article the fibers are present at levels of at least about 20% less or even about 25% less, or even more preferably about 50% less; consequently, the zone or zones that have fibers constitute very different zones in the electrode or the spike. In fact, in certain embodiments at least one other zone has no fiber and, therefore, is a very different zone compared to an area that has 1% by weight of fibers or more. By way of example in terms of an electrode, in a first area of the electrode, for example, a first area of the electrode connection part, the fiber concentration may be about 10%. In a second zone of the electrode, for example, a central part of the electrode, the concentration of fibers in the second zone is no more than about 8.0%. This embodiment may include an optional third zone of the electrode, in which the fiber concentration is substantially the same as in the first zone. In this embodiment, the third zone may include a second area of the connection part located opposite the first area of the connection part.

In a certain additional embodiment, the electrode may include one or more segments that are substantially devoid of carbon fibers, which means that they have an insufficient amount of fibers to affect the desired property of the electrode. Even more preferred, the electrode segment may be completely devoid of carbon fibers. The above embodiments can be implemented in any combination of them.

It has been recognized that the inclusion of fibers in graphite electrodes or spikes can improve the resistance of a graphite electrode or spike (see, for example, Kortovich et al. In International Publication No. WO 2004/020185, Singer in US Pat. No. 4,005,183 and Shao et al. in US Patent No. 6,280,663, the description of which is incorporated herein in its entirety by reference). However, it has also been recognized that the inclusion of fibers in electrodes or graphite spikes at sufficient significant levels is prohibitive from a cost point of view. Allowing the inclusion of fibers in only those areas of the graphite electrode or spigot that are regions of high stress, such as thread regions, the advantages of fiber inclusion can be obtained with lower cost implications, thus retaining the commercial feasibility of the Article.

In other embodiments, one area of the graphite article may include sulfur to inhibit swelling, while other areas do not include it. For example, it would be useful to include sulfur in those areas of a graphite electrode or spike that include the thread regions, but it would be disadvantageous to include sulfur inside a spike or electrode, where it can lead to a split. The practice of the present disclosure can be used to "manipulate" an electrode or graphite spike such that sulfur is preferably contained in an area that includes the thread regions, but not an area that constitutes the inner part of the article. Also, in other embodiments, advantages can be obtained through the control of the size of the coke particles in certain areas compared to others, or in the presence of iron oxide in certain areas compared to others. Again, this can be done using the present disclosure.

In one embodiment, especially useful when the body is formed (or configured) by extrusion of the raw material mixture through a matrix, as described above, very different areas are formed by a coextrusion process. In coextrusion, very different raw material mixtures, such as a first raw material mixture containing at least 1% fiber by weight and a second raw material mixture containing at least 25% less fiber by weight, each of them is extruded through adjacent extrusion tubes and these then converge to form a single article. In this way, two very different zones are formed in the article; for example, a first zone can include at least 1% of fibers by weight and a second zone can include at least about 25% less fibers by weight than the first zone. In another embodiment, the difference in the amount of fibers is at least about 50%; In a further embodiment, the difference is at least 75%. The extrusion tubes can be located in various arrangements, depending on the way in which the user wishes to group very different areas neatly. For example, in the case of fibers, it may be desirable to have an area of increased fiber level (sometimes referred to as fiber loading) on an external part of the graphite electrode or spike to achieve improved resistance, but it is less desirable to have an area of increased fiber loading in an internal part or core of the graphite or spike electrode for cost reasons. In this circumstance, the article can be formed by coextrusion, where two extrusion tubes are arranged coaxially around each other.

In a coextrusion embodiment to produce an electrode having an increased fiber load on an external part compared to the electrode core, a first raw material mixture having at least 1% by weight of fibers and it is extruded through the outer extrusion tube of a coextrusion apparatus, and a second mixture of raw material is prepared that has at least 25% less fiber load (or, more preferably, has no fibers) and is extruded through the central extrusion tube of the extrusion apparatus. In this way, the extruded body has a very different zone of more fibers in the outer part and a very different zone of less fibers (or without them) in the core or inner zone.

In another embodiment, especially useful when the body is formed (or configured) by hot pressing, a plurality of mixtures of hot pressing raw material are fed to the mold, each forming a very different area in the final body For example, in the case of fiber loading, a first mixture of hot pressing raw material having at least 1% by weight of fibers is prepared, and a second mixture of hot pressing raw material is prepared with the minus 25% less fiber load or no fiber at all. These two mixtures of hot pressing raw material can then be fed to the hot pressing mold in a specific order, specific locations and / or specific quantities to create the desired areas. As an example, it may be desirable to have a greater fiber load in the areas of an electrode or graphite spikes where there are threads, that is, the end positions or the ends of the article because they are high stress areas where it is desirable greater resistance In this situation, a mixture of hot pressing raw material having at least 1% by weight of fibers is fed first to the mold to form a first terminal part of the article; a mixture of hot pressing raw material that has at least 25% less fiber load, or that has no fibers at all, is then fed to the mold to form the central part of the article; A mixture of hot pressing raw material having at least 1% by weight of fibers is then fed to the mold to form a second terminal part of the article. In some embodiments, a separator can be placed between the areas in the mold before the application of heat and pressure, and this can then be removed to form a unit article when heat and pressure are applied.

In this way, an economical carbon article, such as a graphite electrode or spike, having very different regions or zones with different characteristics from those of other regions or areas, can be prepared in order to provide an article more capable of resisting the thermal and mechanical stresses to which it will be exposed in, for example, an electric arc furnace, as compared to conventional art articles, while maintaining the commercial practicability of manufacturing the present graphite electrodes.

Figure 1 is a view of an electrode according to the description of this memory and shows the internal connection parts at the terminal ends of the electrode.

As shown in Fig. 1, electrode 12 includes two (2) terminal end sections 14, each of which includes a section of an electrode commonly known as an end face. As shown in the cut of Fig. 1, each section 14 includes a connection part 16. The connection part 16 includes threads 18. The threads 18 can be designed as completely stuck threads or partially stuck threads. In addition, Figure 1 illustrates that each section includes a quantity of carbon fibers. Preferably, the amount of fibers in section 14 is sufficient to increase the resistance of the electrode in such section. On the other hand, electrode 12 includes a non-terminal or central section 10. The concentration of carbon fibers in section 10 is at least that of one of sections 14, preferably both. It is preferred that the amount of fibers in section 10 is not sufficient to increase the strength of section 10. In a particular embodiment, the concentration of fibers in section 10 may be minimal to trace amounts and, furthermore, to be substantially devoid of such fibers. The embodiment shown herein is not limited to any particular exact size of sections 14 and / or section 10. The exact sizes of such sections 14 and 10 may be modified as desired.

Descriptions of all patents and publications cited mentioned in this application are fully incorporated herein by reference. The above percentages concerning concentration are percentages by weight if nothing else is specifically indicated.

The above description is intended to allow the person skilled in the art to implement the disclosure. Said description is not intended to detail all possible variations and modifications that will be apparent to the person skilled in the art after reading the description. However, it is intended that all such modifications and variations mentioned be included within the scope of the disclosure defined by the following claims. The claims are intended to understand the elements and steps indicated in any arrangement or sequence that is effective to achieve the objectives of the disclosure, unless the context specifically indicates otherwise.

Claims (1)

 R E I V I N D I C A C I ON E S 1. Monolithic graphite electrode presenting a first and second 5 terminal positions and a non-terminal body part, a first zone disposed in the first terminal position of the electrode, a second zone disposed in the non-terminal body part of the electrode and a third zone in the second terminal position of the electrode, characterized in that the first zone and the third zone have a carbon fiber concentration between 1% and 10% by weight, and the The concentration of carbon fibers in the second zone comprises at least 20% less than the concentration of carbon fibers in the first and third zones, so that the concentration of fibers in the first zone and in the third zone is sufficient to increase the resistance of the electrode in the first terminal position and in the second terminal position, respectively, and the concentration of the fibers in 15 the non-terminal body part is insufficient to increase the resistance of the electrode of the non-terminal body part of the electrode.