Apparatus and system for measuring the temperature of molten metal

Abstract

The present invention relates to an apparatus and method for measuring the temperature of a molten metal bath. The apparatus according to the invention comprises a core wire and a detector, the core wire comprising an optical fiber, a first metal tube, a filler layer of organic material, and a second metal tube containing the filler layer.

Description

[Technical field]

[0001] The present invention relates to an apparatus and system for measuring the temperature of a molten metal bath.

[0002] There are several means and methods available for measuring the temperature of a molten metal bath in a metallurgical vessel during a metal manufacturing process. One of these means for measuring the temperature of a molten metal bath, particularly iron or steel in the melting environment of an electric arc furnace (EAF), involves immersing an optical fiber surrounded by a metal tube in the molten metal. The optical fiber surrounded by the metal tube is often also referred to as a core wire. The optical fiber can receive thermal radiation and transmit the thermal radiation from the molten metal to a detector, for example a pyrometer. An appropriate instrument can be associated with the detector to determine the temperature of the molten metal bath.

[0003] To measure the temperature of a molten metal bath, a core wire can be fed into the molten metal bath, where it can be consumed over a given time. The front end of the optical core wire is immersed in a metallurgical vessel and on its way to the molten metal bath first encounters a high-temperature atmosphere, then a slag layer and then the molten metal bath. Depending on the conditions of the melting process, the bath can also contain residual unmelted parts, e.g. obtained from scrap. The immersed part of the core wire melts in the molten metal bath. Once the temperature measurement is finished, the tip of the optical core wire can be partially withdrawn from the molten metal bath. The withdrawn tip of the optical core wire becomes the new front end for the next temperature measurement. Such an apparatus is therefore suitable for semi-continuous temperature measurement in the form of a series of immersion cycles.

[0004] It has generally been found that the use of unvitrified optical fibers is essential for accurate temperature measurements, especially the condition of the front end.

[0005] Many of the devices known in the prior art are typically constructed using an optical fiber installed in a tube. The gap between the optical wire and the metal tube is typically filled with a filler material to protect the optical fiber from the heat of the molten metal bath during immersion. The layered structure helps keep the optical fiber cool for a relatively long period of time. Devitrification due to high temperatures, which would destroy the optical fiber, is delayed.

[0006] US Patent No. 7,748,896 B2 discloses a device including an optical fiber with a laterally surrounding cover that surrounds the optical fiber in multiple layers, one layer including a metal tube and an intermediate layer formed of an inorganic material disposed below the metal tube, during immersion of the tube in a liquid metal bath, the outer tube melts and the loosely held filler material tends to float to the surface, exposing the centrally located optical fiber to the liquid metal bath.

[0007] Furthermore, consumable optical fibers with additional protective structures have been proposed. For example, JP 10-176954 A describes a fiber surrounded by metal tubes at intervals. A tube made of a thermal barrier coating is arranged around this metal tube, and this thermal barrier coating is surrounded by an outer metal tube. This structure prevents the inner metal tube from melting too quickly. The coating made of a thermal barrier material may contain carbon particles, so that the inner metal tube does not melt until the corresponding tube section is immersed in a molten metal bath. Although the devices proposed in the prior art serve to isolate the optical fiber from harsh conditions prior to measurement, the devices may undergo uncontrolled degradation of the thermal barrier coating under certain conditions.

[0008] It is well known in the art of accurate temperature measurement with immersed optical fiber that the optical fiber must be consumed at a rate equal to or faster than the devitrification rate of the optical core. The devitrification rate is a result of the amount of heat input to the optical core during immersion in the molten metal and from exposure to the surrounding environment. Thus, the core optical fiber must be consumed in proportion to the pre-exposure conditions, such as the radiant heat at the immersion location, the slag temperature, and the melting temperature of the particular furnace.

[0009] In both cases, the long core wire is already in the furnace during the previous measurement. Due to the continuous nature of the optical core wire, the adjacent unused parts of the optical core wire can be thermally altered due to high temperatures, either due to radiative heating from inside the furnace, convective heating from the evolved gases of the steelmaking process, or conduction from temporary contact with the molten slag cover and / or heat transfer along the uninterrupted metal cover from the hot to the cold parts of the optical core wire coil. Cutting off the unused but damaged parts was a solution taught, for example, by JP 10-176954 A. Such mechanical additional process steps create further demands on the measuring equipment and greatly increase the wear of the core wire.

[0010] Further improvements to the core wire are disclosed in EP 3156835(A1) and EP 3156834(A2). An intermediate layer comprising a low density refractory material that melts in a controlled manner when exposed to a molten metal bath is used to protect the optical fiber long enough to avoid devitrification before a temperature measurement can be taken. The material of the intermediate layer forms a gob and floats towards the surface of the molten metal bath. Although the proposed devices provide a solution for a more controlled decomposition of the intermediate layer, they may suffer from increased response times, which may be problematic for certain application scenarios.

[0011] As mentioned above, the structures known from the prior art are not able to provide accurate measurements of the required quality in the required response time over the entire application range. The term application range refers to the temperature range in which the temperature measurement of the molten metal bath is performed. This term also refers to successive multiple measurements, in which the core wire may be affected differently depending on the application environment.

[0012] The object of the present invention is to provide an improved device and system for measuring the temperature of a molten metal bath, which solves at least one of the above-mentioned problems. In particular, one of the objects of the present invention is to provide an improved device for obtaining more reliable temperature measurements over a wide range of applications. More particularly, the object of the present invention is to improve the melting and decomposition behavior of the device during and after the measurement. Another object is to provide a device which makes it possible to minimize the wear of the core wire.

[0013] These objects are achieved by a device and a system for measuring the temperature of a molten metal bath according to the independent claims. Preferred embodiments are defined in the dependent claims.

[0014] The device according to the present invention comprises: (a) a core wire having a immersed end and an opposite end, (a1) Optical fiber; (a2) a first metal tube that accommodates an optical fiber; (a3) a filler layer surrounding the first metal tube; and (a4) a second metal tube containing a filler layer; and (b) a detector for receiving a signal transmitted by the optical fiber, the detector being coupled to an opposite end of the core wire, wherein the first metal tube has a yield strength of at least 140 N and the filler layer has a yield strength of 0.3 to 1.1 g / cm 3 and a filler layer material that is an organic material having an ash content of 10% by weight or less.

[0015] Surprisingly, it has been found that the problems arising in the prior art can be overcome by appropriately selecting the properties of the first metal tube and the filler layer. In particular, a first metal tube having a yield strength of at least 140 N and a filler layer having a density of 0.3 to 1.1 g / cm 3 It has been found that by using a filler layer having a density in the range of 0.1 to 0.5, the optical fiber can be more controllably exposed to the bath, improving the quality of the measurements obtained.

[0016] The present invention provides an apparatus for measuring the temperature of a molten metal bath. As used herein, the term bath is used to describe a melt in a vessel, where it is envisaged that certain physical parameters of the melt are to be determined. The molten metal of the molten metal bath is not particularly limited. According to a preferred embodiment, the molten metal is molten steel. The term molten metal bath does not exclude the presence of solid or gaseous parts.

[0017] The temperature of the metal melt may vary and usually depends on the composition of the metal and the stage of the melting process. Typically, the temperature of the molten metal bath is between 1500 and 1700 °C.

[0018] The present invention includes a core wire, where the term "core wire" can be used to refer to an optical fiber contained within a casing, in particular a metal tube. The casing can completely surround the optical fiber, or can be at least partially open such that the casing does not completely surround the optical fiber.

[0019] The core wire according to the invention has a submerged end and an opposite end. The submerged end of the core wire is to be understood as a part of the device that is configured to submerge its front end in the molten metal bath during application. According to a preferred embodiment, the core wire is a consumable core wire. Preferably, when used to measure temperature, the core wire is consumed in a direction from the submerged end to the opposite end, such that after each measurement sequence, another part of the device becomes the submerged end. The opposite end is connected to a detector and is not consumed during measurements.

[0020] The core wire comprises an optical fiber. An optical fiber is a flexible, transparent fiber. Optical fibers are most often used as a means for transmitting light between two ends of the fiber. Optical fibers may be formed from glass or plastic, preferably quartz glass. Most commonly, graded index fibers are used for the intended application.

[0021] According to a preferred embodiment, the device may include a single optical fiber.

[0022] In a further embodiment, the device may comprise a plurality of optical fibers.

[0023] The optical fiber is housed in a first metal tube.

[0024] While immersed, the core wire is subjected to buoyancy forces due to the molten metal acting against the immersed device. For a reliable measurement, it is important that the optical fiber is immersed in the molten metal bath to a certain depth when the measurement is made. The first metal tube must resist these bending forces while keeping the optical core submerged in the immersion direction until it is completely melted, which requires a certain mechanical stiffness of the first metal tube.

[0025] According to the invention, the first metal tube has a yield strength of at least 140N.

[0026] The first metal tube can be defined by a first tube wall thickness (T1), an outer diameter (D1), an inner diameter (I1), a cross-sectional area defined by the wall thickness of the first metal tube (CW1), a total cross-sectional area defined by the outer diameter (TC1), and an inner cross-sectional area defined by the inner diameter (IC1).

[0027] The yield strength in the context of the present invention is defined as the product of the yield stress of the first metal tube and the cross-sectional area of ​​the first metal tube (CW1).

[0028] For common materials, yield stress values ​​are known in the art. For example, the yield stress of stainless steel SS304 is known to be 195 MPa.

[0029] The first metal tube may have a wall thickness (T1) of 0.15 to 0.3 mm, preferably a wall thickness (T1) of 0.2 to 0.25 mm.

[0030] The first metal tube may be formed from a sheet of metal. In a preferred embodiment, the metal may be iron or steel, preferably stainless steel.

[0031] In a preferred embodiment, the metal of the first tube may have a melting point in the range of 1400-1500°C, and even more preferably in the range of 1430-1480°C.

[0032] In a preferred embodiment, the linear density of the first metal tube may be in the range of 5 to 12 g / m, even more preferably 8 to 10 g / m. The linear density of a device is defined by its mass per unit length.

[0033] The first metal tube may have an outer diameter (D1) in the range of 1.5 to 2.5 mm. According to a further preferred embodiment, the first metal tube may have an inner diameter (I1) in the range of 1.2 to 2.2 mm.

[0034] According to a preferred embodiment, the first metal tube wall thickness (T1) is less than 15% of the first metal tube outer diameter (D1).

[0035] In a further preferred embodiment, the cross-sectional area defined by the wall thickness of the first metal tube (CW1) is less than 45% of the total cross-sectional area of ​​the first metal tube (TC1).

[0036] Preferably, the inner cross-sectional area (IC1) defined by the inner diameter of the first metal tube is 1.4 to 3.5 mm 2 is within the range.

[0037] In a preferred embodiment, the cross-sectional area of ​​the optical fiber may occupy no more than 4% of the total cross-sectional area defined by the outer diameter of the first metal tube (TC1).

[0038] The first metal tube of the core wire according to the invention is surrounded by a filler layer, which in a preferred embodiment may comprise a plurality of elements, more preferably the filler layer may comprise fibres.

[0039] In a preferred embodiment, the fibers of the filler layer may form a rope. It has been found that a rope formed from multiple groups of fibers can be advantageous as it ensures that no fibers can be released from the open end of the core wire as it is fed into the melt. A rope in the context of the present invention is a group of fibers that are twisted or braided together to combine into a larger and stronger form.

[0040] In further embodiments, the filler layer material may have the form of a web, net, woven or knitted structure.

[0041] In another preferred embodiment, the filler layer may be formed from at least two sublayers.

[0042] According to a preferred embodiment, the filler layer may or may not include an adhesive or resin. Preferably, the amount of adhesive or resin is less than 2 wt-% based on the total weight of the filler layer.

[0043] According to the present invention, the filler layer comprises an organic material.

[0044] Organic materials in the context of the present invention should be understood as materials that contain carbon (C) at the elemental level in the range of at least 30% by mass. For example, the total formula of the chitin base unit is CH, which has a molar mass of 203.2 g / mol. 13 NO5, resulting in a carbon content of 47.3% by mass.

[0045] Preferably, the organic material may be selected from the group consisting of naturally occurring materials, natural or synthetic polymers and combinations thereof. More preferably, the organic material may be a polysaccharide, most preferably selected from the group consisting of lignin, chitin, cellulose and combinations thereof. Even more preferably, the organic material may be selected from the group consisting of cotton, wool, jute, hemp, coir, sisal, wood, flax and combinations thereof.

[0046] In a preferred embodiment, the filler layer comprises at least two filler layer materials.

[0047] In a further embodiment, one of the at least two materials of the filler layer may be a flame retardant. Such a combination of materials may help control the decomposition behavior of the filler layer.

[0048] The organic material has an ash content of 10% by weight or less, preferably an ash content of 8% by weight or less, even more preferably an ash content of 6% by weight or less.

[0049] Ash content represents the non-combustible components of a material remaining after the material has been completely combusted. Organic materials can have an ash content of less than 100%. In contrast, inorganic materials, such as glass, can have a non-combustible content of 100% or less. The ash content of a material is determined by thermogravimetric analysis according to the currently valid version of ASTM 1131.

[0050] The low ash organic materials according to the present invention have been found to be non-slag forming combustible materials. Non-slag forming should be understood as meaning that the material does not melt, or does not substantially melt, in the molten metal bath and typically does not remain in a slag layer over the molten metal bath. In contrast, inorganic materials tend to melt and remain around the optical core for extended periods of time, eventually becoming a slag layer over the molten metal bath. However, it has been found that such organic materials do not stop burning after the device comes into contact with the molten metal bath after a measurement cycle. Devices that have undergone prolonged decomposition of such a filler layer are not suitable for obtaining accurate temperature measurements in successive measurement cycles, since the optical fiber with the new front end is left unprotected and prone to devitrification. The damaged parts must be removed, resulting in increased wear on the device.

[0051] Surprisingly, it has been found that the density of the filler layer material can affect this adverse decomposition behavior.

[0052] According to the present invention, the filler layer has a density of 0.3 to 1.1 g / cm 3 Density in the range of 0.4 to 1.0 g / cm 3 and even more preferably in the range of 0.4 to 0.8 g / cm 3 The density is in the range of

[0053] The density of the filler layer is to be understood as the density of the filler layer material occupying the volume between the first and second metal tubes when placed in the core wire. The density of the filler layer may generally be different from the density of the filler layer material before application to the core wire. The density of the filler layer may be achieved by compressing the filler layer material between the first and second metal tubes. Preferably, the density of the filler layer is higher than the density of the filler layer material before application.

[0054] A material may be characterized by its maximum density, which is the highest density that can be achieved when the material is compressed as far as possible.

[0055] In a preferred embodiment, the maximum density of the filler layer material is between 0.5 and 3 g / cm 3 and even more preferably 1.0 to 2.0 g / cm 3 It is.

[0056] The layer density of the filler layer may advantageously be 50% or less, even more preferably 40% or less, and most preferably 30% or less of the maximum density of the filler layer material. The layer density of the filler layer may advantageously be more than 10% of the maximum density of the filler layer material, even more preferably more than 20%. The density of the filler layer may preferably be in the range of 10-50% of the maximum density of the filler layer material, and more preferably in the range of 20-40%.

[0057] Advantageously, the first metal tube and the filler layer are in direct contact, i.e. there are no additional layers or gaps.

[0058] In a preferred embodiment, the thickness of the filler layer is greater than the wall thickness (T1) of the first metal tube.

[0059] According to the invention, a second metal tube contains a layer of filler material.

[0060] During a typical measurement sequence, the core wire reaches a specific location in the molten metal bath. Once immersed, the second metal tube melts and dissolves into the metal bath. The filler layer insulates the first metal tube and the optical fiber from direct heating. Upon contact with the molten metal, the filler layer decomposes, exposing the first metal tube. While the first metal tube melts, the optical fiber is directly exposed to the molten metal bath and a temperature measurement can be made.

[0061] The second metal tube may be defined by a second tube wall thickness (T2), an outer diameter (D2), an inner diameter (I2), a cross-sectional area defined by the wall thickness of the second metal tube (CW2), a total cross-sectional area defined by the outer diameter (TC2), and an inner cross-sectional area defined by the inner diameter (IC2).

[0062] The second metal tube may have a wall thickness (T2) of 0.5 to 1.0 mm, preferably 0.7 to 0.9 mm.

[0063] The second metal tube may be formed from a sheet of metal. In a preferred embodiment, the metal may be a steel with an iron (Fe) content of more than 50%, preferably a low carbon (C) steel or a stainless steel.

[0064] In a further preferred embodiment, the metal of the second metal tube may have a melting point of 1450-1550°C, and even more preferably in the range of 1480-1520°C.

[0065] In a further preferred embodiment, the linear density of the second metal tube may be in the range of 200 to 300 g / m, and even more preferably in the range of 220 to 260 g / m.

[0066] In a preferred embodiment, the edges of the sheet of second metal tube in the transverse direction may not form an overlap. The transverse direction is defined by an axis running from the immersed end of the apparatus to the opposite end.

[0067] In a further preferred embodiment, the edges of the sheet of the second metal tube in the transverse direction can overlap to construct a seam. Even more preferably, the seam can be mechanically formed, and most preferably, the seam can be closed without adhesive, glue or welding.

[0068] The second metal tube may have an outer diameter (D2) in the range of 9 to 14 mm. According to a further preferred embodiment, the second metal tube has an inner diameter (I2) in the range of 8 to 13 mm.

[0069] Advantageously, the second metal tube may be gas permeable. Such a design allows gases in the internal structure of the core wire to leave the inside of the metal tube. Gases may be generated during decomposition of the filler layer, which may escape. A gas permeable design also allows gases from the environment, for example oxygen contained in the surrounding air, to enter the core wire.

[0070] In a preferred embodiment, the optical fiber is placed in the center of the core wire which further improves the quality and reliability of the measurement results.

[0071] In a preferred embodiment, the filler layer is capable of uniformly filling the space between the first metal tube and the second metal tube.

[0072] Advantageously, the optical fibers are uniformly thermally isolated laterally.

[0073] It has further been found that in a preferred embodiment, the first metal tube is concentrically disposed within the second metal tube. Preferably, the second metal tube is not in direct contact with the first metal tube.

[0074] It may be advantageous for the melting point of the metal of the second metal tube to be higher than the melting point of the metal of the first metal tube. In a preferred embodiment, the melting point of the metal of the second metal tube is at least 20° C. higher than the melting point of the metal of the first metal tube, more preferably more than 40° C. higher, and most preferably more than 60° C. higher.

[0075] In a preferred embodiment, the outer diameter (D1) of the first metal tube is 30% or less, more preferably 20% or less, of the outer diameter (D2) of the second metal tube.

[0076] Furthermore, it may be preferable that the outer diameter (D1) of the first metal pipe is within a range of 10 to 30% of the outer diameter (D2) of the second metal pipe, and even more preferably within a range of 15 to 25%.

[0077] It has been found that it can be advantageous for the linear density of the first metal tube to be less than 10% of the linear density of the second metal tube.

[0078] In one embodiment, the thickness of the filler layer may be greater than the wall thickness (T1) of the first metal tube. In a further embodiment, the thickness of the filler layer may be greater than the wall thickness (T2) of the second metal tube.

[0079] In a preferred embodiment, the thickness of the filler layer is greater than the thickness of the layer formed by the first metal tube and the thickness of the layer formed by the second metal tube.

[0080] According to a further embodiment, the device may comprise a plurality of optical fibers, each of the fibers being surrounded by a first metal tube. According to another preferred embodiment, a plurality of optical fibers, each surrounded by a separate first metal tube, are disposed within the second metal tube.

[0081] In accordance with the invention, the apparatus includes a detector for receiving a signal transmitted by the optical fiber, the detector being coupled to an opposite end of the core wire.

[0082] A detector in the context of the present invention may be a pyrometer.

[0083] The invention also relates to a system comprising the device described herein and a supply means for supplying a front end of the device into a bath of molten metal. The front end of the device in the context of the invention may be understood as the tip of the immersed end of the device.

[0084] In the context of the present invention, a feeding means may be understood as a means allowing the feeding of the core wire into the molten metal bath. Such means may be selected from the group consisting of coils, feeders, straighteners, guide tubes and blowing lances.

[0085] The system may further include a furnace having an inlet for the apparatus and holding a bath of molten metal. [Brief description of the drawings]

[0086] The concepts underlying the invention are described in more detail below with reference to embodiments shown in the drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. [Figure 1]FIG. 2 is a schematic cross-sectional view of a core wire. [Diagram 2] 1A-1D are schematic diagrams of core wires according to different embodiments of the present invention. [Diagram 3] FIG. 1 is a schematic diagram of an apparatus incorporated in a system for measuring the temperature of a molten metal bath.

[0087] FIG. 1 shows a schematic cross-sectional view of a core wire 1 in cross section, comprising an outer metal tube 5 (second metal tube), a filling material layer 4 and an inner metal tube 3 (first metal tube) housing an optical fiber 2. In the embodiment shown, the outer metal tube is provided with vent holes 6 allowing for a gas permeable construction.

[0088] 2A-2E show schematic diagrams of core wires 1'-1''''' according to some embodiments of the present invention. It should be understood that combinations of the illustrated embodiments are also possible according to the present invention.

[0089] 2A shows a cross-section of a core wire 1' according to a first embodiment in which the edges of the sheets forming the outer metal tube 5' do not overlap. The fill layer material 4' uniformly fills the space between the first tube 3' and the outer tube 5'. FIG. 2B shows a cross-section of a core wire 1'' according to a second embodiment, in which the filler layer 4'' comprises fibers. FIG. 2C shows a cross-section of a core wire 1''' according to a fourth embodiment, in which the filler layer 4''' comprises several sub-layers. FIG. 2D shows a cross-section of a core wire 1'''' according to a third embodiment, in which the filler layer 4'''' comprises two different fibrous materials. FIG. 2E shows a cross-section of a core wire 1''''' according to a fifth embodiment having a preferred outer tube closure, where the edges of the sheets forming the outer metal tube 5''''' overlap to form a seam portion 7.

[0090] FIG. 3 shows a schematic diagram of an apparatus 8 incorporated in a system for measuring the temperature of a molten metal bath. The system includes an apparatus 8 with a core wire 1 and a pyrometer 12, the core wire 1 being at least partially placed on a coil 9 and at least partially unwound from the coil 9 for performing measurements. One end of the apparatus 10 is connected to the pyrometer 12, which can be connected to a computer system (not shown) for processing data obtained by the apparatus 8. The apparatus 8 has an inlet 15 and is fed at its immersed end 11, guided by a feeder 13, through a guide tube 14 into a vessel containing a molten metal bath 16. The temperature of the part of the apparatus 8 extending from the coil 9 to the inlet 15 is considered low and can range from room temperature to 100° C. Passing the inlet 15 in the direction of the molten metal bath 16, it first encounters a high temperature atmosphere of up to 1700° C. or more, then encounters a slag layer 17, and then encounters the molten metal bath 16. The entrance 15 to the vessel may be provided with an injection lance 18 to prevent ingress of metal and slag into the guide tube 14. The core wire is then fed into the molten metal bath 16 to the required immersion depth at which measurements can be made. Up to this point in the measurement sequence, the optical fiber 2 and its front end are mechanically protected and insulated by the layers surrounding it. When the front end of the device 8 is immersed in a molten metal bath 16 at a temperature of up to 1850°C, the outer tube melts first, exposing the filler layer to the molten metal bath 16. The filler layer, which contains organic material, begins to burn when exposed to such conditions, exposing the front end to the molten metal. After the measurement sequence, the portion 19 of the core wire which was immersed in the molten metal bath is melted and therefore consumed. After a measurement has been made, the portion of the apparatus 20 which is located in the high temperature atmosphere and extends through the slag layer can be sent back towards the coil 9 and reused for the next measurement.

[0091] Organic materials are generally suitable as filler layer materials because they largely decompose when exposed to molten metal. When utilized as a filler layer within the core wire, this combustion behavior must be carefully controlled. Degradation must be prevented further in the direction of the opposite end of the core wire than in the portion of the core wire that is immersed in the molten metal bath.

[0092] A device that has undergone such prolonged degradation of the filler layer may be unsuitable for obtaining accurate temperature measurements since the optical fiber with the new front end would be left unprotected against the harsh environment within the molten metal bath vessel. Tests have shown that the density and structure of the packing layer and the gas permeability of the outer metal tube significantly affect this undesirable decomposition behavior.

[0093] An exemplary construction of a core wire according to the present invention (Example 1) comprises a graded-index 62.5 / 125 μm jacketed optical fiber embedded in a stainless steel (SS316) tube having a thickness of 0.2 mm and a yield stress of 200 MPa, resulting in a yield force of 238 N. 3 A layer of cotton fiber insulation having a density of 0.01 mm surrounds the first metal tube. This assembly is surrounded by an outer layer of 0.8 mm thick stainless steel having an outside diameter of 10 to 16 mm.

[0094] In a prior art example (Example 2), the core wire was constructed according to Example 1, except that the tube containing the optical fiber had a thickness of 0.13 mm, resulting in a yield force of 94 N.

[0095] In a further example according to the prior art (Example 3), the density of the filler layer is 0.2 g / cm 3 The core wire was constructed according to Example 1, except that:

[0096] To test the measurement performance of the exemplary structure, the core wire was connected to a pyrometer and introduced into a molten metal bath in an electric arc furnace. The temperature data obtained were compared with the data received with a conventional immersion thermocouple. As shown in Table 1, the quality of the data obtained has improved.

[0097] [Table 1]

[0098] Moreover, such improved temperature measurements were obtained along the entire length of the coil of core wire. [Explanation of symbols]

[0099] 1. 1'~1''''' core wire 2. 2'~2''''' optical fiber 3, 3'~3''''' First (inner) metal tube 4, 4'~4''''' filler layer 5, 5'~5''''' second (outer) metal tube 6. Vent 7. Outer pipe joint 8 equipment 9 Coil 10 Opposite end 11 Immersed end 12 Pyrometer 13 Feeder 14 Guide tube 15 Entrance 16 Molten metal bath 17 Slag layer 18 Blowing Lance 19 The portion of the core wire immersed in the molten metal bath 20 Part of the core wire exposed to high temperature atmosphere and slag T1 wall thickness of first metal tube D1 Outside diameter of the first metal tube I1 Inner diameter of the first metal tube CW1 Cross-sectional area of ​​the wall of the first metal tube IC1 Internal cross-sectional area of ​​the first metal tube T2 wall thickness of the second metal tube D2 Outside diameter of the second metal tube I2 Inner diameter of the second metal tube CW2 Cross-sectional area of ​​the wall of the second metal tube IC2 Internal cross-sectional area of ​​the second metal tube

Claims

1. 1. An apparatus for measuring the temperature of a molten metal bath, comprising: (a) a core wire having a immersed end and an opposite end, (a1) an optical fiber; (a2) a first metal tube that accommodates the optical fiber; (a3) a filler layer surrounding the first metal tube; and (a4) a second metal tube containing the filler layer; and (b) a detector for receiving a signal transmitted by the optical fiber, the detector coupled to the opposite end of the core wire; the first metal tube having a yield strength of at least 140 N; the first metal tube has a cross-sectional area (CW1) defined by a wall thickness of the first metal tube and a total cross-sectional area (TC1) defined by an outer diameter of the first metal tube, the cross-sectional area (CW1) defined by the wall thickness of the first metal tube being less than 45% of the total cross-sectional area (TC1) of the first metal tube; The filler layer has a density of 0.3 to 1.1 g / cm 3 and a filler layer material that is an organic material having an ash content of 10% by weight or less, The filler layer material is formed from fibers. Device.

2. The device of claim 1 , wherein the optical fiber is disposed centrally in the core wire.

3. The device according to claim 1 or 2, wherein the filler layer comprises at least two filler layer materials. Place.

4. 4. The method according to claim 1, wherein the filler layer is formed from at least two sublayers.

3. The device according to claim 1 .

5. 5. The apparatus according to claim 1, wherein the first metal tube has a first wall thickness (T1) and a first outer diameter (D1), the ratio between the first wall thickness (T1) and the first outer diameter (D1) being less than 15%.

6. The device according to any one of claims 1 to 5, wherein the second metal tube is gas permeable.

7. A device according to any one of the preceding claims, wherein the cross section of the optical fibre occupies no more than 4% of the total cross sectional area (TC1).

8. The apparatus of any one of claims 1 to 7, wherein the first metal tube is concentrically disposed within the second metal tube.

9. The apparatus of any one of claims 1 to 8, wherein the linear density of the first metal tube is less than 10% of the linear density of the second metal tube.

10. An apparatus according to any one of the preceding claims, wherein the melting point of the metal of the second metal tube is higher than the melting point of the metal of the first metal tube.

11. The apparatus of claim 5 , wherein the thickness of the filler layer is greater than the first wall thickness of the first metal tube.

12. An apparatus according to any one of the preceding claims, wherein the thickness of the filling material layer is greater than the wall thickness of the second metal tube.

13. A system comprising an apparatus according to any one of the preceding claims and supply means for supplying a front end of said apparatus into a bath of molten metal.

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