DEVICE AND SYSTEM FOR MEASURING A TEMPERATURE OF A MOLTEN METAL

Abstract

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

Claims

1. A device for measuring a temperature of a molten metal bath, comprising (a) a cored wire having an immersion end and an opposite end, the cored wire comprising (a1) an optical fiber, (a2) a first metal tube accommodating the optical fiber, (a3) a filler layer surrounding the first metal tube and (a4) a second metal tube accommodating the filler layer, and (b) a detector to receive a signal transmitted by the optical fiber, the detector being coupled to the opposite end of the cored wire, wherein the first metal tube has a yield force of at least 140 N, and wherein the filler layer has a density in the range of 0,3-1,1 g/cm.sup.3 and comprises a filler layer material which is an organic material having an ash content of not more than 10 mass-%.

2. The device according to claim 1, wherein the optical fiber is arranged in the center of the cored wire.

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

4. The device according to claim 1, wherein the filler layer material is formed from fibers.

5. The device according to claim 1, wherein the filler layer is formed of at least two sub-layers.

6. The device according to claim 1, wherein the first metal tube has a first tube wall thickness and a first tube outer diameter, and wherein the ratio of the first tube wall thickness and the first tube outer diameter is less than 15%.

7. The device according to claim 1, wherein the first metal tube has a cross sectional area defined by the thickness of the walls of the first metal tube (CW1) and a total cross sectional area defined by the outer diameter, and wherein the cross sectional area defined by the thickness of the walls of the first metal tube is less than 45% the total cross sectional area of the first metal tube.

8. The device according to claim 1, wherein the second metal tube is gas permeable.

9. The device according to claim 1, wherein the cross-section of the optical fiber covers the total cross-sectional area by not more than 4%

10. The device according to claim 1, wherein the first metal tube is concentrically arranged in the second metal tube.

11. The device according to claim 1, wherein the linear density of the first metal tube is less than 10% of the linear density of the second metal tube.

12. The device according to claim 1, wherein the melting point of the second tube metal is higher than the melting point of the first tube metal.

13. The device according to claim 1, wherein the thickness of the filler layer is higher than the wall thickness of the first metal tube.

14. The device according to claim 1, wherein the thickness of the filler layer is higher than the wall thickness of the second metal tube.

15. A system, comprising the device of claim 1 and feeding means for feeding a leading tip of the device in a molten metal bath.

Description

[0096] FIG. 1 shows a schematic cross-sectional view of a cored wire.

[0097] FIG. 2 shows schematic views of cored wires according to different embodiments of the invention.

[0098] FIG. 3 shows a schematic view of a device embedded in a system for measuring a temperature of a molten metal bath.

[0099] FIG. 1 shows a schematic view of a cored wire 1 in cross-sectional view, comprising an outer metal tube 5 (the second metal tube), a filler layer 4, and an inner metal tube 3 (the first metal tube) accommodating an optical fiber 2.

[0100] In the shown embodiment, the outer metal tube comprises a vent 6 which allows a gas-permeable construction.

[0101] FIGS. 2A-E show schematic views of cored wires 1′-1″″′ according to several embodiments of the invention. It should be understood that combinations of the illustrated embodiments may also be possible according to the invention.

[0102] FIG. 2A shows a cross section of a cored wire 1′ according to a first embodiment, in which the edges of a sheet forming the outer metal tube 5′ do not overlap. The filler layer material 4′ is homogeneously filling the space between first tube 3′ and outer tube 5′.

[0103] FIG. 2B shows a cross section of a cored wire 1″ according to a second embodiment, in which the filler layer 4″ comprises fibers.

[0104] FIG. 2C shows a cross section of a cored wire 1′″ according to a fourth embodiment, in which the filler layer 4′″ comprises several sub-layers.

[0105] FIG. 2D shows a cross section of a cored wire 1″″ according to a third embodiment, in which the filler layer 4″″ comprises two different fibrous materials.

[0106] FIG. 2E shows a cross section of a cored wire 1″″′ according to a fifth embodiment with a preferred outer tube closure, in which the edges of a sheet forming the outer metal tube 5″″′ overlap and form a seam portion 7.

[0107] FIG. 3 shows a schematic view of a device 8 embedded in a system for measuring a temperature of a molten metal bath. The system comprises the device 8, comprising a cored wire 1 and a pyrometer 12, which is located at least partly on a coil 9 and is at least in part unwound from the coil 9 for conducting a measurement. One end of the device 10 is connected to the pyrometer 12 which in turn could be connected to a computer system (not shown) to process the data obtained with the device 8. The device 8 is fed with the immersion end 11 leading by means of a feeder 13 through a guide tube 14 in a vessel having an entry point 15 and containing the molten metal bath 16. The temperature of a part of the device 8 extending from the coil 9 to the entry point 15 can be considered to be low, which could be a temperature ranging from room temperature up to 100° C. Once passing the entry point 15 in the direction of the molten metal bath 16, a hot atmosphere of up to 1700° C. or even higher is first encountered, followed by a slag layer 17 which is in turn followed by the molten metal bath 16. The entry point 15 to the vessel could be equipped with a blowing lance 18 to prevent metal and slag penetration into the guide tube 14. Subsequently, the cored wire will be fed into the molten metal bath 16 to the required immersion depth where the measurement may be taken.

[0108] Up to this point of a measuring sequence, the optical fiber 2 and its leading tip is mechanically protected and thermally insulated by the layers surrounding it. When the leading tip of the device 8 is submerged into the molten metal bath 16 with temperatures up to 1850° C., first the outer tube will melt exposing the filler layer to the molten metal bath 16. A filler layer comprising organic material will start to burn when being subjected to such conditions, exposing the leading tip to the molten metal.

[0109] After the measurement sequence the part of the cored wire immersed in the molten metal bath 19 will be molten and thereby consumed.

[0110] After the measurement is taken, the part of the device 20 located in the hot atmosphere and extending through the slag layer can be fed back into the direction of the coil 9 and can be reused for the next measurement.

[0111] Organic materials are generally suitable as filler layer material since they largely decompose when exposed to a molten metal. When utilized as a filler layer in a cored wire, this burning behavior must be carefully controlled. A degradation further than in the part of the cored wire which is immersed into the molten metal bath in the direction of the opposite end of the cored wire has to be prevented.

[0112] A device which has been subjected to such a prolonged decomposition of the filler layer may not be suitable to obtain accurate temperature measurements since the optical fiber with the new leading tip is left unprotected to the harsh environment in a molten metal bath vessel. Tests have shown that the density and structure of the filler layer and the gas permeability of the outer metal tube dominantly influence this unwanted decomposition behavior.

[0113] An exemplary construction of a cored wire according to the invention (example 1) comprises a graded index 62,5/125 μm jacket optical fiber embedded in a stainless steel (SS316) tube with a thickness of 0.2 mm and a yield stress of 200 MPa, resulting in a yield force of 238 N. An insulating layer of cotton fibers with a density of 0,5 g/cm.sup.3 encloses the first metal tube. This assembly is surrounded by a 0.8 mm thick outer layer of a stainless steel with an outer diameter of 10-16 mm.

[0114] In an example according to the prior art (example 2), a cored wire was constructed according to example 1, except for the tube accommodating the optical fiber, which had a thickness of 0,13 mm resulting in a yield force of 94 N.

[0115] In a further example according to the prior art (example 3), a cored wire was constructed according to example 1, except for the density of the filler layer, which was 0,2 g/cm.sup.3.

[0116] To test the measurement performance of the exemplary constructions, the cored wires were connected to a pyrometer and introduced in a molten metal bath in an electric arc furnace. The obtained temperature data was compared to data received with conventional immersion thermocouples.

[0117] As shown in table 1, the quality of the obtainable data was improved.

TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Yield force first metal tube [N] 238 94 238 Density filler layer [g/cm.sup.3] 0.5 0.5 0.2 Data Quality +++ + +

[0118] Additionally, such improved temperature measurements were obtainable over the total coil length of the cored wire.

LIST OF REFERENCE NUMERALS

[0119] 1, 1′-1″″′ Cored wire [0120] 2, 2′-2″″′ Optical fiber [0121] 1, 3′-3″″′ First (inner) metal tube [0122] 4, 4′-4″″′ Filler layer [0123] 5, 5′-5″″′ Second (outer) metal tube [0124] 6 Vent [0125] 7 Outer tube seam [0126] 8 Device [0127] 9 Coil [0128] 10 Opposite end [0129] 11 Immersion end [0130] 12 Pyrometer [0131] 13 Feeder [0132] 14 Guide tube [0133] 15 Entry point [0134] 16 Molten metal bath [0135] 17 Slag layer [0136] 18 Blowing lance [0137] 19 Part of the cored wire immersed in the molten metal bath [0138] 20 Part of cored wire subjected to hot atmosphere and slag [0139] T1 Wall thickness of first metal tube [0140] D1 Outer diameter of first metal tube [0141] I1 Inner diameter of first metal tube [0142] CW1 Cross-sectional area of walls of first metal tube [0143] IC1 Inner cross-sectional area of first metal tube [0144] T2 Wall thickness of second metal tube [0145] D2 Outer diameter of second metal tube [0146] I2 Inner diameter of second metal tube [0147] CW2 Cross-sectional area of walls of second metal tube [0148] IC2 Inner cross-sectional area of second metal tube