EP2536988B1 - Support arm for an electrode of a melt metallurgic furnace - Google Patents

Description

The invention relates to a Elektrodentragarm a molten metallurgical furnace, in particular an electric arc furnace, wherein the electrode support arm is provided with at least one measuring element for measuring a physical quantity.

The DE 198 56 765 discloses a method for detecting the degradation of electrically-energizable or energetically-connectable components of electric arc furnaces that arc burning from an electrode during operation.

From the DE 27 50 271 A1 an electrode arrangement with a generic electrode support arm is known. In melting metallurgical furnaces, in particular in electric arc furnaces, holding devices for the required electrodes are used. These devices usually consist of a support pole, which carries a Elektrodentragarm; the electrode support arm runs in horizontal direction. At the end remote from the support pole of the electrode support arm, an electrode is arranged, which extends vertically downwards, ie it hangs at the end of the electrode support arm. The flow guide from a power connection to the electrode is usually done by copper-plated steel sheets, which make up the support arm. The steel sheet essentially performs the mechanical support function, with the copper applied conducting the current.

The cited document also already explains that the electrode support arm can be provided with sensor elements, with load cells or strain gauges being used. With these sensors, the deformation of the support arm is detected. The determined sensory determined data are compared with setpoints, for which a measured value evaluation device is used.

Similar electrode arrangements are in DE 27 50 186 A1 , in the DE 36 08 338 A1 , in the EP 1 537 372 B1 and in the EP 0 094 378 B1 described.

A disadvantage of the prior art systems - as far as they go at all to the question of data acquisition in Elektrodentragarm - that high electrical interference due to the high current through the Elektrodentragarm present that disturb both thermocouples and strain gauges sensitive. Accordingly, it is difficult to accurately determine thermal data (that is, temperatures) and mechanical data (ie, strains), which, however, is the prerequisite for optimally driving the electrode operation.

The present invention is based on the object, a Elektrodentragarm of the type mentioned in such a way that it is possible to detect thermal and / or mechanical loads on the Elektrodentragarms as accurately as possible and to improve the operation of the electrode assembly to improve. So it should be provided an efficient monitoring for the electrode support arm. In this case, a continuous and precise monitoring of the temperatures or the mechanical stresses of the electrode support arm should be possible, which can be realized inexpensively.

The solution of this object by the invention is characterized in that the measuring element is formed in the electrode support arm for measuring the temperature and / or mechanical strain of the electrode support arm, wherein the measuring element comprises at least one optical waveguide which extends at least in sections along the longitudinal extent of the electrode support arm.

The optical waveguide can be arranged in a surrounding tube.

The optical waveguide and the tube possibly surrounding it can be arranged in a bore in the electrode support arm.

Alternatively, it is possible that the optical waveguide and possibly surrounding him tube are arranged in a groove in the electrode support arm. The groove can be closed by a closure element which holds the optical waveguide and the possibly surrounding tube in the groove base, wherein the closure element is in particular a metal part inserted into the groove or cast into the groove. The closure element is preferably connected to the groove by friction stir welding. In friction stir welding, advantageously, the welding temperature can be well controlled, whereby it can be prevented that the optical waveguide inside the groove becomes too hot.

A further alternative provides that the optical waveguide and / or, if appropriate, the tube surrounding it are arranged in a layer, wherein the layer is arranged on or in the electrode support arm. The layer may consist of metal or of a temperature-resistant non-metallic material. The optical waveguide and the possibly surrounding tube can be completely surrounded by the material of the layer. The layer may be applied galvanically to or in the electrode support arm. It can be made of copper, chrome or nickel. It may be a spray coating or a chemical coating, as for example from the DE 10 2009 049479.0 is known.

By introducing optical waveguides into the walls and supporting elements of the electrode support arms, temperatures and / or stresses or strains in the components of the electrode support arm can be measured as a temperature or stress profile over the surface of the electrode support arm. Also included are dynamic changes due to flows in the melt, which is located in the vessel under the arm. As a result, an assessment of the state of wear and the present load situation of the support arm by the temperature and / or the voltage is possible. The proposed concept enables a representation of the thermal or mechanical loading of the components over their surface in the respective operating state.

In order to be able to carry out precise temperature measurements with the optical waveguide, it is advantageous for the optical waveguide or the metal tube surrounding the optical waveguide to rest tightly against the component or medium, if possible without (insulating) air gap, thus ensuring good temperature transmission can take place on the optical fiber. However, the fiber optic cable must not be mislaid during the temperature measurement, so that it can expand or contract when the temperature changes.

In contrast, it is necessary for a strain measurement with the optical waveguide, that the optical waveguide is firmly connected to the component whose elongation or its temporal strain curve to be measured, so that the mechanical strain of the component transmits to the optical waveguide.

So that an expansion (tension) of the wall of the electrode support arm can be measured, it is advantageous if the optical waveguide or the tube surrounding it is firmly connected to the bore or groove base.

If a groove is provided in which the optical waveguide or the tube surrounding it is laid, it is preferably provided that a filler for closing the groove is used, which may consist of metal. It can be made to fit the shape of the groove. It can also be provided that the filler is produced by casting or spraying the material of the filler into the groove. After that, therefore, the material from which the filling piece is made pourable or sprayable and then poured or injected into the groove, in which the optical waveguide, if necessary, including tube was inserted.

The proposed embodiment thus offers the possibility to detect stress states in the measured plane and thus to detect the mechanical stress of the components.

The technology of measuring temperatures, strains or stresses and / or accelerations from the temporal distribution of the measured strains is known as such (also under the name "optical Dehmessstreifen"), so that reference is made in this respect to the prior art.

For this purpose, the optical waveguide is preferably connected to an evaluation unit in which the temperature distribution in the electrode support arm can be determined. With this evaluation, the mechanical stress on the wall of the electrode support arm can also be detected accordingly.

Fig. 1

schematisch in der Seitenansicht eine Elektrodenanordnung eines Lichtbogenofens mit einem horizontal verlaufenden Elektrodentragarm,

Fig. 2

die Einzelheit "X" gemäß Fig. 1 in geschnittener Darstellung,

Fig. 3

den Schnitt A-B gemäß Fig. 1 und

Fig. 4

den Bereich einer Bohrung gemäß Fig. 3 in vergrößerter Darstellung.

In the drawing, an embodiment of the invention is shown. Show it:

Fig. 1

schematically in side view an electrode assembly of an arc furnace with a horizontally extending electrode support arm,

Fig. 2

the detail "X" according to Fig. 1 in a cutaway view,

Fig. 3

the section AB according to Fig. 1 and

Fig. 4

the area of a hole according to Fig. 3 in an enlarged view.

In Fig. 1 is an electrode assembly 6 can be seen, which is used in an electric arc furnace. The electrode assembly 6 has a support pole 8 extending vertically. At its upper end an electrode support arm 1 is arranged, which extends horizontally. At the end remote from the support pole 8 of the electrode support arm 1, an electrode 7 is arranged hanging, over which the arc is generated in the electric arc furnace. The electrode support arm 1 extends in a longitudinal extension L, which in the present case corresponds to the horizontal direction. The power supply of the electrode 7 via a power connector. 9

The electrode support arm 1 is made of sheet steel, with which a sufficient mechanical strength is achieved. For the electrical conduction of the current from the power connection 9 to the electrode 7, plating with copper is provided.

As the sectional view according to Fig. 2 and according to Fig. 3 can be removed, the Elektrodentragarm 1 is liquid-cooled. For this purpose, the electrode support arm 1 has a cooling channel 10, which flows through a coolant becomes. The media supply lines required for this purpose are not shown.

In order to be able to detect precisely both the temperature in the electrode support arm 1 and the mechanical strains in the same, the electrode support arm 1 has a respective bore 5 in its upper and in its lower region (see FIG. FIGS. 2 and 3 ), in which a measuring element 2 is housed, with which the temperature and the voltage can be measured. This is an optical waveguide 3, which is housed in a protective tube 4. The two, still empty holes are in Fig. 3 to see; in this, the optical waveguide is introduced together with tube 4, as it is made Fig. 4 evident.

The optical waveguide 3 typically has a diameter of z. B. 0.12 mm; with cladding tube 4 usually results in a diameter in the range of 0.8 mm to 2.0 mm.

The optical waveguide 3 consists of a base fiber, which is introduced into the holes 5 or in similar channels or grooves in the electrode support arm 1. The optical waveguide 3 can withstand temperatures up to 800 ° C continuous load. The tube 4 is only optional, not mandatory. In this case, the optical waveguide 3 without tube 4 by the connection to the base material of the electrode support arm 1 expansions is particularly favorable; the same applies to the temperatures that can be well detected by the optical waveguide 3 in the cladding tube 4.

In Fig. 3 is shown that a respective bore 5 is provided in the upper and lower region of the electrode support arm 1, in each of which an optical waveguide 3 is introduced. It is also possible in all four side sections of the profile how it looks Fig. 3 indicates to bring holes and place optical fiber 3.

In order to increase the robustness of the signal transmission in the optical waveguide 3 and to evaluation devices, not shown, the light waves are guided via lens plug from the electrode support arm in the respective rest position to the evaluation unit.

In addition to the illustrated possibility of accommodating the optical waveguide 3 in holes 5 is also the preferred way to incorporate a groove in the Elektrodentragarm 1 and the optical waveguide 3 - possibly together with pipe 4 - to lay in the groove bottom. The groove can then be closed again, to which the above-mentioned measures can be used.

Also possible is the introduction of the optical waveguide 3 - possibly together with tube 4 - in a layer of metallic material or temperature-resistant non-metallic material, which is applied to the electrode support arm 1.

Alternatively, the optical waveguide fiber optic sensors in modules, that is, enclosed in prefabricated structural units. For a temperature measurement the optical fibers are loosely laid in the modules, so that a temperature-induced change in length of the optical waveguide within the module is possible stress-free. On the other hand, for a strain measurement, the optical waveguides are preferably permanently connected over their entire length to the material of the module or to the housing of the module, so that an expansion of the module or of its housing is transmitted to the optical waveguides. The modules with the optical waveguides are glued or welded onto the electrode support arm and thus actively connected. An elongation or temperature change of the electrode arm is therefore transmitted to the optical waveguide via the module. The modules or the optical waveguides in the modules are suitable to measure the temperature, the mechanical stress or strain and / or - over the time course of the elongation - also the acceleration behavior of the component, in particular of the electrode support arm. For the acceleration measurement, a special measuring device may be required, which may be integrated into the module. In particular, the strain or acceleration measurements can be used to dampen unwanted vibrations of the component control technology, that is, to correct.

The layer can be galvanized (in the case of metal), wherein the optical waveguide 3 together with the tube 4 are completely encased. The galvanic layer may for example consist of copper, chromium or nickel.

The optical waveguide 3 is connected to a temperature detection system, not shown, or to a detection system for mechanical stresses or strains. By means of the detection system laser light is generated, which is fed into the optical waveguide 3. The of the optical fiber 3 collected data are converted by means of the detection system into temperatures or voltages and assigned to the different measuring locations.

The evaluation can be carried out, for example, according to the so-called fiber Bragg grating method (FBG method). In this case, suitable optical waveguides are used, the measuring points with a periodic variation of the refractive index or grating get impressed with such variations. This periodic variation of the refractive index leads to the fact that the optical waveguide represents a dielectric mirror as a function of the periodicity for specific wavelengths at the measuring points. By changing the temperature at one point, the Bragg wavelength is changed and exactly this is reflected. Light that does not satisfy the Bragg condition is not significantly affected by the Bragg grating. The different signals of the different measuring points can then be distinguished from one another on the basis of propagation time differences. The detailed structure of such fiber Bragg gratings and the corresponding evaluation units are well known. The accuracy of the spatial resolution is given by the number of impressed measuring points. The size of a measuring point can be, for example, in the range of 1 mm to 5 mm.

Alternatively, the "Optical Frequency Domain Reflectometry" method (OFDR method) or the "Optical Time Domain Reflectometry" method (OTDR method) can also be used to measure the temperature. These methods are based on the principle of fiber optic Raman backscatter, taking advantage of the fact that a temperature change at the point of a light guide causes a change in the Raman backscatter of the optical waveguide material. By means of the evaluation unit (eg a Raman reflectometer) The temperature values along a fiber can then be determined in a spatially resolved manner, with this method averaging over a specific length of the conductor. This length is about a few centimeters. The different measuring points are in turn separated by differences in transit time. The structure of such systems for evaluation according to the said methods is well known, as are the necessary lasers which generate the laser light within the optical waveguide 3.

1. 1. Der stromführende Kupferleiter des Elektrodentragarms verändert seine Leitfähigkeit mit der Temperatur. Durch die genau ermittelten Temperaturmesswerte und die Kenntnis der zugehörigen Leitfähigkeit des Kupfers kann ein konstanter Stromfluss eingestellt bzw. geregelt werden.
2. 2. Weiterhin ist ein Selbstschutz des Elektrodentragarms durch Kenntnis von Temperatur und Dehnung möglich. Diese ermittelten Daten können in einer Steuerung bzw. Regelung mit zulässigen Werten verglichen werden; die Regelung kann dann Korrekturen für den Stromfluss und die Positionierung des Tragarms vorgeben, so dass die zulässigen Werte eingehalten werden können.
3. 3. Eine weitere sehr vorteilhafte Anwendung ist die Vermeidung von Schwingungen in der Elektrodenanordnung. Schwingungen im Elektrodentragarm, auch Grenzzyklen, können durch die Dehnungsmessung erkannt werden. Als Konsequenz können kritische Arbeitspunkte vermieden werden, es können namentlich die Einstellwerte für Strom und Spannung so angepasst werden bzw. es kann das Signal so moduliert werden, dass der Schwingung entgegengewirkt und diese kompensiert wird.

With the equipment of the electrode support arm 1 in the manner explained, a monitoring of temperatures and / or strains is possible, which can be used in the following manner during operation of the electrode assembly:

1. 1. The current carrying copper conductor of the electrode support arm changes its conductivity with temperature. Due to the precisely determined temperature measured values and the knowledge of the associated conductivity of the copper, a constant current flow can be set or regulated.
2. 2. Furthermore, self-protection of the electrode support arm by knowledge of temperature and strain is possible. This determined data can be compared in a control or regulation with permissible values; the control can then provide corrections for the current flow and the positioning of the support arm, so that the permissible values can be maintained.
3. 3. Another very advantageous application is the avoidance of vibrations in the electrode assembly. Vibrations in the electrode support arm, including limit cycles, can be detected by the strain measurement. As a consequence, critical operating points can be avoided, in particular the setting values for current and voltage can be adapted in this way or the signal can be modulated in such a way that the oscillation is counteracted and compensated for.

The largest adjusting lever for vibration compensation is usually the regulation of the adjusting cylinder of the height control of the support arm (see in particular the above-mentioned DE 36 08 338 A1 ). This height control can be used to compensate for the vibrations and deformations identified by the strain measurement. For this procedure, which is known per se, reference is made to the article by Prof. Dr.-Ing. Klaus Krüger "Requirements for a modern electrode control for three-phase electric arc furnaces" in "elektrowärme international" 4/2007, Vulkan-Verlag GmbH, Essen, ISSN 0340-3521-K 5548 F, referenced.

LIST OF REFERENCE NUMBERS

1. 1 electrode support arm
2. 2 measuring element
3. 3 optical fibers
4. 4 pipe
5. 5 hole
6. 6 electrode arrangement
7. 7 electrode
8. 8 support pole
9. 9 power connection
10. 10 cooling channel

• L length extension

Claims (13)

1. Electrode support arm (1) of a smelting metallurgical furnace, particularly an arc furnace, wherein the electrode support arm (1) is provided with at least one measuring element (2) for measuring a physical variable, characterised in that the measuring element (2) is constructed for measuring the temperature and/or the mechanical elongation of the electrode support arm (1), wherein the measuring element (2) comprises at least one optical waveguide (3) which at least in a section extends along the length direction (L) of the electrode support arm (1).
2. Electrode support arm according to claim 1, characterised in that the measuring element, in the form of the optical waveguide (3), for the purpose of the temperature measurement is arranged loosely free of stress or movement in or at the electrode arm or for the purpose of elongation measurement - preferably over the entire length thereof - is arranged in operative connection with the material of the electrode support arm for ascertaining the elongations thereof.
3. Electrode support arm according to one of the preceding claims, characterised by a measuring device for detecting the time plot of the elongations of the electrode arm and for determining the acceleration behaviour of the electrode arm from the detected time plot of the elongations.
4. Electrode support arm according to one of the preceding claims, characterised in that the optical waveguide (3) is arranged in a module disposed in fixed operative connection with the electrode arm, wherein the optical waveguide for the purpose of the temperature measurement is arranged to be free of stress and movement in the module or for the purpose of the elongation measurement is arranged to be fixedly embedded in the module.
5. Electrode arm according to claim 3 and 4, characterised in that the measuring device for determining the acceleration behaviour of the electrode arm is integrated in the module for elongation measurement.
6. Electrode support arm according to claim 1, 2 or 3, characterised in that the optical waveguide (3) and/or a tube (4) optionally surrounding it is or are arranged in a bore (5) in the electrode support arm (1)
7. Electrode support arm according to claim 1, 2 or 3, characterised in that the optical waveguide (3) and a tube (4) optionally surrounding it are arranged a groove in the electrode support arm (1).
8. Electrode support arm according to claim 7, characterised in that the groove is closed by a closure element which holds the optical waveguide (3) and the tube (4) optionally surrounding it in the groove base, wherein the closure element is, in particular, a metal part which is inserted into or cast in place in the groove and which is connected with the groove preferably by friction stir welding.
9. Electrode support arm according to claim 1, 2 or 3, characterised in that the optical waveguide (3) and/or the tube (4) optionally surrounding it is or are arranged in a layer, wherein the layer is arranged at or in the electrode support arm (1).
10. Electrode support arm according to claim 9, characterised in that the layer consists of metal, preferably of copper, chromium or nickel, or of a temperature-resistant non-metallic material.
11. Electrode support arm according to claim 9 or 10, characterised in that the optical waveguide (3) and the tube (4) optionally surrounding it are completely surrounded by the material of the layer.
12. Electrode support arm according to any one of claims 9 to 11, characterised in that the layer is applied to or in the electrode support arm (1) by plating.
13. Electrode support arm according to any one of claims 9 to 11, characterised in that the layer is applied to or in the electrode support arm in the form of an injection-moulded coating or a chemical coating.

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