METHOD FOR REGULATING OR CONTROLLING A MELTING FURNACE AND MELTING FURNACE, NAMELY A SHAFT FURNACE, FOR MELTING METAL

Description

[0001] The invention relates to a melting furnace, namely a shaft furnace, for melting metal, having at least one furnace chamber for receiving a molten metal bath, having at least one pumping device fluidly connected to the furnace chamber, which pumping device has at least one molten metal pump for pumping molten metal from the molten metal bath, and having a device for laser-induced plasma spectroscopy (LIBS), which has a laser source for emitting a pulsed laser beam onto the molten metal to generate a plasma of the material of the molten metal and which comprises a spectral analyzer for analyzing the radiation of the plasma to determine the composition of the molten metal.

[0002] JPS6042644A describes a melting furnace with a laser-induced breakdown spectroscopy (LIBS) system for recording metallurgical measurement data based on the molten metal in the molten metal bath in the furnace chamber. For this purpose, gas bubbles are introduced into the molten metal bath at the bottom of the furnace chamber and used for the LIBS process. The disadvantage of this method is that it requires relatively complex structural measures for the melting furnace and is relatively susceptible to contamination, which can reduce the stability of the laser-induced breakdown spectroscopy (LIBS) system or falsify its measurement results.

[0003] The document US2011 / 222057A1 discloses the monitoring of the composition of a melt bath for coating a steel strip, wherein a LIBS system is arranged at an opening of a line of the melt bath.

[0004] The invention therefore has the object of modifying the design of a melting furnace, namely a shaft furnace, in such a way that reliable laser-induced plasma spectroscopy (LIBS) can be carried out in order to be able to control or regulate the shaft furnace in an improved manner.

[0005] The invention solves the problem with regard to the melting furnace by the features of claim 1.

[0006] By having the pumping device with an access opening positioned higher than the molten metal and outside the furnace chamber, and by having the laser-induced plasma spectroscopy (LIBS) device act on the molten metal through this access opening, the tapping of measurement data on the molten metal can be relocated to a comparatively accessible area of ​​the melting furnace. Furthermore, the pumping device of the LIBS device can also provide a representative sample of the molten metal in the furnace chamber, which guarantees the accuracy of the measurement. For example, this can enable a reliable estimation of the further development of the element concentrations, which can be used for improved control / regulation of the melting furnace. According to the invention, not only can the design of the melting furnace be simplified in terms of LIBS measurement data acquisition, but the accuracy of LIBS measurement data acquisition can also be increased.

[0007] The construction can be further simplified if the pumping device has a pump pocket, wherein the access opening is provided on the pump pocket, in particular on its lid.

[0008] It is also conceivable for the pumping device to have a charge and / or side well, with the access opening being provided on the charge and / or side well, particularly on its lid. This also allows for stable measurement data acquisition in a user-friendly manner.

[0009] Preferably, the laser-induced plasma spectroscopy (LIBS) device comprises a measuring lance that is designed to be movable through the access opening toward the molten metal, enabling reliable measurement data acquisition in the vicinity of the molten metal. This can further improve the quality of LIBS measurement data acquisition.

[0010] Preferably, the measuring probe tapers to a conical shape at its free end to minimize the contact surface at the probe head. This can further increase the stability of the LIBS device.

[0011] Preferably, the wall of the measuring probe has or is made of a ceramic compound to withstand the comparatively high temperatures encountered during data acquisition. This also allows the measuring head to be moved close to the molten metal, which can further improve the accuracy of LIBS data acquisition.

[0012] The molten metal can be freed from floating impurities, such as aluminum dross, if the measuring lance has at least one outlet opening at its free end for a gas flowing through it. Furthermore, the measuring lance must also be cooled with the gas flowing through it to increase its stability.

[0013] If the measuring probe is hollow, this can facilitate the provision of optical components that are connected, for example, to the laser source and / or the spectrum analyzer.

[0014] Preferably, the pumping device is fluidly connected to its inlet and outlet on the furnace chamber for circulating or recirculating the molten metal in the molten metal bath within the furnace chamber. This allows for extremely precise determination of the molten metal in the molten metal bath within the furnace chamber. Measurement accuracy can thus be further increased.

[0015] It is also conceivable for the pumping device to be fluidly connected to the furnace chamber with its inlet and outlet at the shaft chamber of the melting furnace for introducing molten metal into the shaft chamber. This further increases the design simplicity.

[0016] Preferably, the pumping device is designed to circulate the molten metal in the molten metal bath. This allows the pumping device to ensure, for example, homogenization of the molten metal in the melting furnace.

[0017] It is conceivable that the shaft chamber contains a shaft with a column of metal to be melted. The metal to be melted is applied to the top of this column in the shaft.

[0018] The invention also has the object of improving a method for controlling or regulating a melting furnace in order to be able to precisely produce a semi-finished product with a predetermined target composition.

[0019] The invention solves the problem posed by the method with the features of claim 12.

[0020] By generating a plasma of the molten metal material with a pulsed laser beam through the access opening of the melting furnace and analyzing the plasma radiation with a spectral analyzer, a reliable and precise analysis can be performed. If this analysis is used to determine the actual composition of the molten metal, it is possible to adjust the actual composition to a target composition of the molten metal by adding melted metal. This opens up the possibility of precisely manufacturing semi-finished products with a specified target composition.

[0021] The analysis can be further improved if the measuring lance is advanced through the access opening to the molten metal at a distance from the metal melt, the metal melt is exposed to gas flowing through the measuring lance, and the plasma of the molten metal material is generated with the pulsed laser beam passing through the measuring lance. In this way, the control and / or regulation of the melting furnace can be further improved.

[0022] Preferably, before and / or after determining the actual composition of the molten metal, the laser-induced plasma spectroscopy (LIBS) is calibrated on a reference sample with a known composition in order to further improve the control and / or regulation of the melting furnace.

[0023] The method according to the invention can be particularly suitable for producing a semi-finished product, in particular made of an aluminum alloy, from the molten metal taken from the melting furnace.

[0024] The figures show, for example, the subject matter of the invention in more detail using an embodiment variant. Fig. 1 a schematic view of the melting furnace, Fig. 2 a sectional view of a first pumping device of the melting furnace according to Fig. 1 with a device for laser-induced plasma spectroscopy (LIBS) during a measurement data recording and Fig. 3 the device for laser-induced plasma spectroscopy (LIBS) according to Fig. 2 during a measurement calibration.

[0025] After Fig. 1 A melting furnace 1, namely a shaft furnace, for melting, preferably by immersion melting, metal, preferably non-ferrous metals, is schematically shown. Scrap, in particular aluminum scrap, is preferably also remelted in this furnace. The melting furnace 1 is heated by a burner system (not shown). The melting furnace 1 is an aluminum shaft melting furnace.

[0026] This multi-chamber, namely three-chamber, shaft furnace 1 has a furnace chamber 2 as the main chamber 3 and a shaft chamber 4 for metal supply, as well as a secondary chamber 5 between shaft chamber 4 and furnace chamber 2. In furnace chamber 2 there is a molten metal bath 6, which extends via the secondary chamber 5 into shaft chamber 4. A baffle 20 is provided between furnace chamber 2 and secondary chamber 5. A shaft wall 24 is provided between shaft chamber 4 and secondary chamber 5. In accordance with the furnace design as a shaft furnace, the metal to be melted is fed into shaft chamber 4, namely onto a column of metal to be melted in the shaft of shaft chamber 4. The metal to be melted sinks down the shaft, heats up in the process, and then enters the molten metal bath 6.

[0027] A first and a second pumping device 7a and 7b are fluidly connected to the furnace chamber 2. The two pumping devices 7a, 7b have metal melt pumps 8a to 8d for pumping the metal melt 9 from the metal melt bath 6. The pumping devices 7a, 7b serve to circulate the metal melt 9 of the metal melt bath 6. This circulation serves, for example, to homogenize the metal melt 9 of the metal melt bath 6.

[0028] Subsequently, the first pumping device 7a of the Fig. 1 This first pumping device 7a conveys the molten metal 9 back into the molten metal bath 6. For this purpose, the first pumping device 7a is in fluid communication with an inlet and an outlet 2a, 2b on the furnace chamber 2. Thus, the molten metal 9 of the molten metal bath 6 is conveyed in the furnace chamber 2 in the direction of flow (cf. Fig. 1 , direction of the arrow).

[0029] In addition, the melting furnace 1 has a device 10 for laser-induced plasma spectroscopy (LIBS). This LIBS device 10 is equipped with a laser source 11 and a spectral analyzer 12. The laser source 11 serves to transmit a pulsed laser beam 11a onto the molten metal 9 in order to generate a plasma of the material of the molten metal 9. The spectral analyzer 12 analyzes the radiation of the generated plasma and uses this to determine the composition of the molten metal 9.

[0030] According to the invention, the LIBS process is not carried out on the molten metal 9 in the furnace chamber 2, but outside this furnace chamber 2. For this purpose, the pumping device 7a, 7b has an access opening 13 arranged higher than the molten metal 9 (i.e. above its level) and outside the furnace chamber 2. Preferably, this access opening 13 is arranged directly above the molten metal 9, as in the Fig. 2 The LIBS device 10 now acts on the molten metal 9 through the access opening 13 to perform the measurement. The LIBS device 10 is thus protected from the adverse conditions in the furnace chamber 2 and can perform the measurement accurately and reliably. Furthermore, the molten metal 9 at the two pumping devices 7a and 7b is a comparatively representative sample of the furnace chamber 2 due to its direct removal from the furnace chamber 2, which increases the accuracy in determining the condition of the melt in the furnace chamber 2.

[0031] Through this optical access, the alloy composition is determined using the LIBS process and stored and made available in a corresponding system. The number of element determinations can be performed several times per second. This data is then output directly and linked to the data of the material used, enabling a statement to be made about the further development of the element concentrations in the molten metal 9 of the molten metal bath 6. Accordingly, for example, by adding more material to the molten metal 9, the actual alloy composition can be adjusted to a required target alloy composition. Such a closed-loop or closed-loop control of the melting furnace 1 enables the production of semi-finished products with an exact composition.

[0032] As in Fig. 1 and 2As can be seen, the first pumping device 7a has a pump pocket 14 on the molten metal pump 8d. The access opening 13 is also provided there, namely on the removable cover 14a of the pump pocket 14. The access opening 13 can be opened and closed with a closure 13a.

[0033] In addition, a charge well 23 is located downstream of the molten metal pump 8d on the first pumping device 7a, in the flow direction, for example, to directly supply metal to be melted to the molten metal bath 6 of the furnace chamber 2. An access opening 13 is also provided on this charge well 23, through which the LIBS device 10 can act on the molten metal 9.

[0034] To enable the LIBS device 10 to approach the molten metal 9, it has a ceramic measuring lance 16 with a measuring head 17 connected to it and mounted in a heat-protection housing. The measuring lance 16 is conical at its free end 16a. The measuring lance 16 has a measuring head 17 at its other end 16b, which is connected to the laser source 11 and the spectral analyzer 12 via a light guide 18 - which in the Fig. 2 is shown schematically. The measuring head 17 also includes an optical system 19, for example, for focusing the transmitted laser beam 11a and / or for receiving the plasma light.

[0035] The measuring lance 16 is designed to be vertically movable through the access opening 13 towards the molten metal 9 - as in Fig. 2 This allows the LIBS device 10 to independently adjust the distance to the molten metal 9, for example, by means of a distance control or regulation, to ensure permanent focusing of the laser beam 11a. Furthermore, gas 25 can be blown onto the molten metal 9 at the free end 16a of the measuring lance 16 via the central opening 26, through which the laser beam 11a also exits, in order to push floating contaminants away from the measuring point and thus remove them. Cooling is also possible using the gas. This ensures a precise analysis at all times.

[0036] Adaptation to the different filling levels is achieved, for example, by using displacement elements which position the LIBS device 10 based on the measured furnace filling level.

[0037] Focusing over the entire filling level range of molten metal 9 in the pumping device 7, for example in the pump pocket 14, charge well 23 or side well 15, can be achieved by arranging the entire LIBS device 10 on a vertically and horizontally movable platform which is fastened near the melting furnace 1 or directly to the melting furnace 1, which is not shown in the figures.

[0038] For regular calibration of the LIBS device 10, a validation station 21 with a reference sample 22 of known composition is provided - see Fig. 3 By calibrating the LIBS device 10 to the known composition of the reference sample 22, the reliability and repeatability of the measurement results of the metal melt 9 are ensured.

[0039] Alternatively, it is conceivable that the measurement is carried out at the second pumping device 7b which pumps the molten metal 9 from the furnace chamber 2 into the shaft chamber 4 of the melting furnace by means of molten metal pumps 8a, 8b or 8c and thus circulates it - as in Fig. 1 to recognize.

[0040] The second pumping device 7b can also have a sidewell 15, for example, between the metal melt pumps 8a, 8b, and 8c. The sidewell 15 can be used, for example, to remove oxide deposits from the melting process.

[0041] An alternative access opening 13 for LIBS measurement data acquisition is provided, for example, on the side-well 15, namely on the lid 15a.

Claims

1. Melting furnace for melting metal, having at least one furnace chamber (2) for receiving a molten metal bath (6), having at least one pump device (7a, 7b) in fluid connection with the furnace chamber (2), which pump device (7a, 7b) has at least one metal melt pump (8a, 8b, 8c, 8d) for pumping molten metal (9) from the molten metal bath (6), and having a device (10) for laser-induced plasma spectroscopy, LIBS, which has a laser source (11) for emitting a pulsed laser beam (11a) onto the molten metal (9) to generate a plasma of the material of the molten metal (9) and which comprises a spectral analyzer (12) for analyzing the radiation of the plasma to determine the composition of the molten metal (9), wherein the pump device (7a, 7b) has an access opening (13) arranged higher than the molten metal (9) and outside the furnace chamber (2), and that the device (10) for laser-induced plasma spectroscopy, LIBS, acts through this access opening (13) on the molten metal (9), characterized in that the melting furnace is a shaft furnace having a shaft chamber (4) for supplying metal.

2. Melting furnace according to claim 1, characterized in that the pump device (7a) has a pump pocket (14), wherein the access opening (13) is provided on the pump pocket (14), more particularly on its cover (14a).

3. Melting furnace according to claim 1 or 2, characterized in that the pump device (7a, 7b) has a charge well (23) and / or a side well (15), wherein the access opening (13) is provided on the charge well (23) and / or side well (15), more particularly on its cover (13a or 15a).

4. Melting furnace according to one of claims 1 to 3, characterized in that the device (10) for laser-induced plasma spectroscopy, LIBS, has a measuring lance (16) which is designed to be movable through the access opening (13) toward the molten metal (9).

5. Melting furnace according to claim 4, characterized in that the measuring lance (16) conically tapers toward its free end (16a) and / or in that the wall of the measuring lance (16) has a ceramic compound.

6. Melting furnace according to claim 4 or 5, characterized in that the measuring lance (16) has at least one blow-out opening (26) at its free end (16a) for a gas (25) conducted through the measuring lance (16).

7. Melting furnace according to one of claims 4 to 6, characterized in that the measuring lance (16) is hollow.

8. Melting furnace according to one of claims 1 to 7, characterized in that the pump device (7a) is in fluid connection with the furnace chamber (2) via its inlet and outlet (2a, 2b) for circulating or recirculating the molten metal (9) of the molten metal bath (6) in the furnace chamber (2).

9. Melting furnace according to one of claims 1 to 7, characterized in that the pump device (7b) with its inlet (2c) on the furnace chamber (2) and its outlet (2d) on the shaft chamber (4) of the melting furnace (1) is in fluid connection for introducing molten metal (9) into the shaft chamber (4).

10. Melting furnace according to one of claims 1 to 9, characterized in that the pump device (7a, 7b) is designed to circulate the molten metal (9) of the molten metal bath (6).

11. Melting furnace according to one of claims 1 to 10, characterized in that the shaft chamber (4) has a shaft with a column of metal to be melted.

12. Method for controlling or regulating a melting furnace (1) according to one of claims 1 to 11, in which a plasma of the material of the molten metal (9) is generated via the access opening (13) of the melting furnace (1) with the pulsed laser beam (11a), having a spectral analyzer (12) with which the radiation of the plasma is analyzed, and this analysis is used to determine the actual composition of the molten metal (9) in order to adjust the actual composition to a desired composition of the molten metal (9) by adding metal to be melted.

13. Method according to claim 12, characterized in that the measuring lance (16) is advanced through the access opening (13) to the molten metal (9) at a distance therefrom, the molten metal (9) is charged with gas (25) flowing through the measuring lance (16), and the plasma of the material of the molten metal (9) is generated by the pulsed laser beam (11a) passing through the measuring lance (16).

14. Method according to claim 12 or 13, characterized in that before and / or after determining the actual composition of the molten metal (9), laser-induced plasma spectroscopy, LIBS, is calibrated on a reference sample (22) with a known composition.

15. Method according to claim 12, 13 or 14, characterized in that a semi-finished product, more particularly made of an aluminum alloy, is produced from the molten metal (9) taken from the melting furnace (1).