EP1907828A1 - Method for analyzing liquid metal and device for use in this method - Google Patents

Method for analyzing liquid metal and device for use in this method

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Publication number
EP1907828A1
EP1907828A1 EP06776373A EP06776373A EP1907828A1 EP 1907828 A1 EP1907828 A1 EP 1907828A1 EP 06776373 A EP06776373 A EP 06776373A EP 06776373 A EP06776373 A EP 06776373A EP 1907828 A1 EP1907828 A1 EP 1907828A1
Authority
EP
European Patent Office
Prior art keywords
bath
casing
pipe system
purge gas
submerged pipe
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP06776373A
Other languages
German (de)
French (fr)
Inventor
Paul Alexander De Vries
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Aleris Switzerland GmbH
Original Assignee
Aleris Switzerland GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Aleris Switzerland GmbH filed Critical Aleris Switzerland GmbH
Publication of EP1907828A1 publication Critical patent/EP1907828A1/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/15—Preventing contamination of the components of the optical system or obstruction of the light path
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/66—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light electrically excited, e.g. electroluminescence
    • G01N21/69—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light electrically excited, e.g. electroluminescence specially adapted for fluids, e.g. molten metal
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/71—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light thermally excited
    • G01N21/718—Laser microanalysis, i.e. with formation of sample plasma
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/15—Preventing contamination of the components of the optical system or obstruction of the light path
    • G01N2021/151—Gas blown
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/66—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light electrically excited, e.g. electroluminescence
    • G01N21/69—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light electrically excited, e.g. electroluminescence specially adapted for fluids, e.g. molten metal
    • G01N2021/695—Molten metals

Definitions

  • the invention relates to a method for analyzing the composition of a bath of liquid metal and to a device for use in this method.
  • a probe which is provided with means for transporting a beam of laser light is positioned above a bath of liquid steel. That part of the steel which the laser light impinges on emits element-specific radiation.
  • the radiation emitted is passed via an optical system, which is likewise accommodated in the probe, to a spectrometer for analysis.
  • the composition of the steel can be derived from the results of the analysis. This method is also known as LIBS (Laser Induced Breakdown Spectroscopy).
  • the probe On the side facing the bath, the probe is provided with a ceramic tube which protects the probe from being affected by liquid steel and by slag which is present on top of the liquid steel.
  • a gas pressure is applied inside the tube by a stream of a gas which is supplied via an inlet port of the probe and is discharged along outlet ports of the probe with a limited passage.
  • laser light is to be understood as meaning any form of electromagnetic radiation which is generated by a laser.
  • metal is also to be understood as encompassing an alloy which substantially comprises one or more metals and other metals or non-metals.
  • One problem of the known method is that the material which the laser beam impinges on at the surface of the bath, such as steel and alloying elements in the prior art, reacts with the gas or with impurities which are inevitably present in the gas, such as oxygen if the gas is an inert gas.
  • the impurities react with the material and form compounds which in turn, on account of the energy of the laser beam, at least in part generate radiation, and thereby distort the measurement of the composition of the bath.
  • Another problem is that compounds which have such a high melting point or boiling point that they do not melt or evaporate, but rather form a solid crust where the laser beam is supposed to meet the bath, may form. This problem plays a significant role in particular in the case of reactive metals. If the composition of the bath fluctuates, the solid crust shields the bath from further analysis, with the result that it is not possible to measure the correct current composition of the bath.
  • a method for analyzing the composition of a bath comprising liquid metal in which a laser beam is directed onto a surface of the bath and in which at least part of the metal forms a sample which is analyzed, characterized in that, at least at the location where the laser beam meets the bath, impurities at the surface of the bath are removed by purging with a stream of a purge gas.
  • the stream of the purge gas entrains impurities in the form of undesirable reaction products which have been formed and carries them outside the region of the surface where the laser beam meets the bath. Tests have shown that removing impurities can be carried out so effectively that it is possible to carry out measurements continuously, so that even accurate measurement and determination of a changing composition of the bath is possible.
  • the method according to the invention is particularly advantageous if the liquid metal is a liquid aluminium alloy.
  • Aluminium has a particularly high affinity for oxygen, in such a manner that even the very low oxygen potential of 10 "7 in argon, which is customarily used as purge gas, is too high to allow analysis of the composition of an aluminium bath, certainly if low concentrations of alloying elements or impurities need to be determined.
  • LIBS was unsuitable for determining the composition of a bath of liquid aluminium continuously or with a high level of accuracy, as required for the production of aluminium alloys.
  • a further improvement to the method according to the invention is achieved in an embodiment which is characterized in that the velocity and direction of the stream of the purge gas are selected in such a manner that the surface of the bath adjacent to the location where the laser beam meets it has a convex meniscus. It has been found that by selecting the direction in which the gas is fed to the surface and the quantity of gas, it is possible to promote the formation, maintenance and height of a convex meniscus. It is particularly effective to supply the purge gas in such a manner that the purge gas is discharged radially over the convex meniscus and thereby entrains impurities.
  • a submerged pipe system provided with a top side, an underside and a casing is at least partially placed in the bath, and the stream of the purge gas is fed into the submerged pipe system above the bath and is directed onto the bath at least at the location where the laser beam meets the bath.
  • the submerged pipe system extending into the bath of liquid metal causes a convex meniscus of the molten metal inside the casing of the submerged pipe system. Solid or liquid impurities which form on the meniscus are discharged by the stream of purge gas to the region outside the laser beam.
  • a further embodiment of the method according to the invention is characterized in that purge gas in the submerged pipe system is discharged from the submerged pipe system below the surface of the bath.
  • the liquid metal is a liquid aluminium alloy.
  • Liquid aluminium is particularly reactive and forms a crust of aluminium oxide, which distorts the measurement, even in the presence of very small quantities of oxygen, originating from the purge gas or from leaks.
  • aluminium oxide which is formed is discharged by the purge gas to outside the region where the laser beam meets the aluminium surface.
  • the invention is also embodied by a device for use in the method for analyzing the composition of a bath comprising liquid metal, which device is provided with a submerged pipe system provided with a top side, an underside and a casing having an inner wall and an outer wall, a source for generating a beam of laser light and a gas supply tube for feeding purge gas into the submerged pipe system, characterized in that the gas supply tube is provided with a passage having a reduced bore size, in order to at least locally increase the flow velocity of the gas in the direction of the bath, and runs inside the casing in such a manner that during use the bath inside the casing forms a convex meniscus. It is preferable for the gas supply tube inside the casing to at least in part be concentric with the casing.
  • the submerged pipe system When the device is in use, the submerged pipe system is submerged in the bath of liquid metal, forming a convex meniscus. It has been found that the height of the convex meniscus can be increased by discharging the purge gas along the underside of the submerged pipe. It is preferable for the purge gas to be supplied with a selected velocity in the direction of the highest point of the convex meniscus.
  • the purge gas One additional advantage is that impurities are entrained along the meniscus by the purge gas.
  • the momentum which the laser beam imparts to the molten metal causes drops of molten metal to jump out of the bath and be deposited on, inter alia, the optical system which is used to guide the laser beam to the bath and to guide any element-specific radiation to an analysis apparatus, or on a gas pipe for discharging the gas sample to an analysis apparatus.
  • This embodiment of the invention also prevents drops of liquid metal from reaching the optical system or a pipe for the gas sample, on the one hand on account of the reduced size of bore and on the other hand on account of the higher gas velocity.
  • a further improvement to the device according to the invention is achieved with an embodiment which is characterized in that the casing of the submerged pipe system is provided, in the part which in use extends into the bath, with outlet openings and/or with slots arranged in the underside of the casing.
  • the meniscus is self-stabilizing or is at least more self-stabilizing than without this measure, i.e. the meniscus has a symmetrical profile in the submerged pipe, in particular if the casing has a circular cross section.
  • oscillations which occur in this embodiment caused by the momentum of the laser beam are more successfully attenuated in an embodiment in which slots and/or openings run with an increasing cross section from the inside of the casing towards the outside thereof.
  • a further preferred embodiment of the method according to the invention is characterized in that at least part of the inner wall of the casing of the submerged pipe system is made from a material which is not wettable by the liquid metal.
  • This embodiment promotes the formation and height of a convex meniscus still further. Moreover, it has the effect of providing the submerged pipe with a longer service life on account of reduced chemical attack, since the casing does not come into contact with the material to the same extent.
  • the invention will be explained in more detail below on the basis of a diagrammatic drawing of a measurement arrangement suitable for carrying out the method according to the invention. In the drawing:
  • Fig. 1 shows a diagrammatic cross section through a measurement arrangement for measuring the composition of a bath according to the invention
  • Fig. 2 shows a view of the underside of the casing of a submerged pipe system for use in the method according to the invention.
  • Fig. 1 denotes part of a bath of molten metal, such as a bath of a molten aluminium alloy.
  • a submerged pipe system 2 which in the embodiment shown is provided with a casing 3, extends into the bath.
  • a gas supply tube 4 runs concentrically inside the casing.
  • the casing 3 and the gas supply tube 4 are coupled to one another by means of O-rings 5, which also provide a gastight seal.
  • a convex meniscus 6 is formed inside the casing.
  • a laser beam 15, generated by a laser source (not shown), meets the meniscus at the location of the meeting plane 7, which is located above the focal point of the laser beam in order to prevent positioning problems and in order to prevent gas located above the meniscus from forming a plasma.
  • the gas supply tube 4 is provided with a passage 8 with a central narrowed section 9.
  • the direction of the stream of the purge gas originating from a gas source (not shown in more detail) is denoted by arrows 10, 11 and 12.
  • the purge gas acquires an increased velocity as it flows through the bore.
  • the stream of purge gas flows along the meniscus and entrains solid and possibly liquid particles in the direction indicated by arrow 13, so that it is always a clean meeting plane 7 which is exposed to the laser beam.
  • the gas stream promotes the maintenance and height of the convex meniscus. The process of keeping the meeting plane 7 clean is further promoted by the downward curvature of the meniscus.
  • the purge gas leaves the submerged pipe in the form of gas bubbles 14 and entrains the solid particles.
  • Fig. 2a shows a side view of the submerged pipe; in this case of the bottom pipe 3 in the form of a cylindrical pipe.
  • Fig. 2b shows a view of the underside of the submerged pipe.
  • the wall 20 of the casing 3 is provided with toothed slots 21. It is preferable for the cross section of the slots to increase from the inside outwards, as shown in
  • the flow velocity of the gas on the inside of the submerged pipe is greater than on the outside, which has a stabilizing effect on the position of the meniscus and also ensures that the metal in the submerged pipe continues to move and is therefore a good reflection of the metal in the molten bath.
  • the casing may be provided with holes 22 which are submerged in the bath when using the method. The slots and holes have a stabilizing and homogenizing effect on the shape of the meniscus. Moreover, it is assumed that they cause an additional flow around the underside of the submerged pipe, which contributes to the liquid metal in the submerged pipe being constantly refreshed and therefore being a good reflection of the molten metal in the remainder of the bath.

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  • Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • Pathology (AREA)
  • Immunology (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • General Health & Medical Sciences (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Plasma & Fusion (AREA)
  • Engineering & Computer Science (AREA)
  • Optics & Photonics (AREA)
  • Investigating And Analyzing Materials By Characteristic Methods (AREA)
  • Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)

Abstract

Method for analyzing the composition of a bath comprising liquid metal, in which a laser beam is directed onto a surface of the bath and in which at least part of the metal forms a sample which is analyzed, wherein, at least at the location where the laser beam meets the bath, impurities at the surface of the bath are removed by purging with a stream of a purge gas.

Description

METHOD FOR ANALYZING LIQUID METAL AND DEVICE FOR USE IN
THIS METHOD
The invention relates to a method for analyzing the composition of a bath of liquid metal and to a device for use in this method.
A method and device of this type are known from British Patent Application GB 2154315 A. Said publication describes a method and device for analyzing the composition of molten steel.
According to the method described, a probe which is provided with means for transporting a beam of laser light is positioned above a bath of liquid steel. That part of the steel which the laser light impinges on emits element-specific radiation. The radiation emitted is passed via an optical system, which is likewise accommodated in the probe, to a spectrometer for analysis. The composition of the steel can be derived from the results of the analysis. This method is also known as LIBS (Laser Induced Breakdown Spectroscopy).
On the side facing the bath, the probe is provided with a ceramic tube which protects the probe from being affected by liquid steel and by slag which is present on top of the liquid steel.
To prevent liquid steel from penetrating into the ceramic tube, a gas pressure is applied inside the tube by a stream of a gas which is supplied via an inlet port of the probe and is discharged along outlet ports of the probe with a limited passage.
In the context of the present description, the term laser light is to be understood as meaning any form of electromagnetic radiation which is generated by a laser. Furthermore, the term metal is also to be understood as encompassing an alloy which substantially comprises one or more metals and other metals or non-metals.
One problem of the known method is that the material which the laser beam impinges on at the surface of the bath, such as steel and alloying elements in the prior art, reacts with the gas or with impurities which are inevitably present in the gas, such as oxygen if the gas is an inert gas. The impurities react with the material and form compounds which in turn, on account of the energy of the laser beam, at least in part generate radiation, and thereby distort the measurement of the composition of the bath. Another problem is that compounds which have such a high melting point or boiling point that they do not melt or evaporate, but rather form a solid crust where the laser beam is supposed to meet the bath, may form. This problem plays a significant role in particular in the case of reactive metals. If the composition of the bath fluctuates, the solid crust shields the bath from further analysis, with the result that it is not possible to measure the correct current composition of the bath.
The problems are significant in particular in the case of measurements which last for a prolonged period of time on account of the requirement for statistical accuracy.
It is an object of the invention to provide a method for analyzing a metal, in which the measurement accuracy is not affected by impurities in the gas.
It is another object of the invention to provide a method for analyzing a metal which is also suitable for analyzing reactive metals. Yet another object of the invention is to provide a method for analyzing a metal which is also suitable for measuring low concentrations of an element in a bath of a metal or for long-term measurements.
These and other objects are achieved by a method for analyzing the composition of a bath comprising liquid metal, in which a laser beam is directed onto a surface of the bath and in which at least part of the metal forms a sample which is analyzed, characterized in that, at least at the location where the laser beam meets the bath, impurities at the surface of the bath are removed by purging with a stream of a purge gas.
The stream of the purge gas entrains impurities in the form of undesirable reaction products which have been formed and carries them outside the region of the surface where the laser beam meets the bath. Tests have shown that removing impurities can be carried out so effectively that it is possible to carry out measurements continuously, so that even accurate measurement and determination of a changing composition of the bath is possible. The method according to the invention is particularly advantageous if the liquid metal is a liquid aluminium alloy.
Aluminium has a particularly high affinity for oxygen, in such a manner that even the very low oxygen potential of 10"7 in argon, which is customarily used as purge gas, is too high to allow analysis of the composition of an aluminium bath, certainly if low concentrations of alloying elements or impurities need to be determined. Prior to the invention, therefore, LIBS was unsuitable for determining the composition of a bath of liquid aluminium continuously or with a high level of accuracy, as required for the production of aluminium alloys.
A further improvement to the method according to the invention is achieved in an embodiment which is characterized in that the velocity and direction of the stream of the purge gas are selected in such a manner that the surface of the bath adjacent to the location where the laser beam meets it has a convex meniscus. It has been found that by selecting the direction in which the gas is fed to the surface and the quantity of gas, it is possible to promote the formation, maintenance and height of a convex meniscus. It is particularly effective to supply the purge gas in such a manner that the purge gas is discharged radially over the convex meniscus and thereby entrains impurities. According to one particularly effective embodiment of the invention, a submerged pipe system provided with a top side, an underside and a casing is at least partially placed in the bath, and the stream of the purge gas is fed into the submerged pipe system above the bath and is directed onto the bath at least at the location where the laser beam meets the bath. The submerged pipe system extending into the bath of liquid metal causes a convex meniscus of the molten metal inside the casing of the submerged pipe system. Solid or liquid impurities which form on the meniscus are discharged by the stream of purge gas to the region outside the laser beam. It has been found that, in the case of a flat top side of a bath of, for example, molten aluminium, a depression up to 10 mm deep can form at the location where the laser beam meets the surface of the bath. Dross collects in this depression, making reliable measurement impossible. This embodiment of the invention avoids this problem.
A further embodiment of the method according to the invention is characterized in that purge gas in the submerged pipe system is discharged from the submerged pipe system below the surface of the bath. For a selected diameter of the casing pipe, the depth to which the casing is submerged and the velocity of the stream of gas, it is in this way possible that the impurities are discharged out of the submerged pipe system. The method according to the invention is of particular benefit if the liquid metal is a liquid aluminium alloy. Liquid aluminium is particularly reactive and forms a crust of aluminium oxide, which distorts the measurement, even in the presence of very small quantities of oxygen, originating from the purge gas or from leaks. With the method according to the invention, aluminium oxide which is formed is discharged by the purge gas to outside the region where the laser beam meets the aluminium surface.
The invention is also embodied by a device for use in the method for analyzing the composition of a bath comprising liquid metal, which device is provided with a submerged pipe system provided with a top side, an underside and a casing having an inner wall and an outer wall, a source for generating a beam of laser light and a gas supply tube for feeding purge gas into the submerged pipe system, characterized in that the gas supply tube is provided with a passage having a reduced bore size, in order to at least locally increase the flow velocity of the gas in the direction of the bath, and runs inside the casing in such a manner that during use the bath inside the casing forms a convex meniscus. It is preferable for the gas supply tube inside the casing to at least in part be concentric with the casing.
When the device is in use, the submerged pipe system is submerged in the bath of liquid metal, forming a convex meniscus. It has been found that the height of the convex meniscus can be increased by discharging the purge gas along the underside of the submerged pipe. It is preferable for the purge gas to be supplied with a selected velocity in the direction of the highest point of the convex meniscus. One additional advantage is that impurities are entrained along the meniscus by the purge gas. It has been found that the momentum which the laser beam imparts to the molten metal causes drops of molten metal to jump out of the bath and be deposited on, inter alia, the optical system which is used to guide the laser beam to the bath and to guide any element-specific radiation to an analysis apparatus, or on a gas pipe for discharging the gas sample to an analysis apparatus. This embodiment of the invention also prevents drops of liquid metal from reaching the optical system or a pipe for the gas sample, on the one hand on account of the reduced size of bore and on the other hand on account of the higher gas velocity. A further improvement to the device according to the invention is achieved with an embodiment which is characterized in that the casing of the submerged pipe system is provided, in the part which in use extends into the bath, with outlet openings and/or with slots arranged in the underside of the casing. Surprisingly, it has been found that in this embodiment the meniscus is self-stabilizing or is at least more self-stabilizing than without this measure, i.e. the meniscus has a symmetrical profile in the submerged pipe, in particular if the casing has a circular cross section.
Moreover, it has been found that oscillations which occur in this embodiment caused by the momentum of the laser beam are more successfully attenuated in an embodiment in which slots and/or openings run with an increasing cross section from the inside of the casing towards the outside thereof.
A further preferred embodiment of the method according to the invention is characterized in that at least part of the inner wall of the casing of the submerged pipe system is made from a material which is not wettable by the liquid metal.
This embodiment promotes the formation and height of a convex meniscus still further. Moreover, it has the effect of providing the submerged pipe with a longer service life on account of reduced chemical attack, since the casing does not come into contact with the material to the same extent. The invention will be explained in more detail below on the basis of a diagrammatic drawing of a measurement arrangement suitable for carrying out the method according to the invention. In the drawing:
Fig. 1 shows a diagrammatic cross section through a measurement arrangement for measuring the composition of a bath according to the invention, and
Fig. 2 shows a view of the underside of the casing of a submerged pipe system for use in the method according to the invention.
In Fig. 1, 1 denotes part of a bath of molten metal, such as a bath of a molten aluminium alloy. A submerged pipe system 2, which in the embodiment shown is provided with a casing 3, extends into the bath. A gas supply tube 4 runs concentrically inside the casing. The casing 3 and the gas supply tube 4 are coupled to one another by means of O-rings 5, which also provide a gastight seal. As a result of part of the casing 3 being submerged in the bath 1, a convex meniscus 6 is formed inside the casing. It is preferable for at least part of the inner wall of the casing to be made from a non-wetting material. A laser beam 15, generated by a laser source (not shown), meets the meniscus at the location of the meeting plane 7, which is located above the focal point of the laser beam in order to prevent positioning problems and in order to prevent gas located above the meniscus from forming a plasma.
The gas supply tube 4 is provided with a passage 8 with a central narrowed section 9. The direction of the stream of the purge gas originating from a gas source (not shown in more detail) is denoted by arrows 10, 11 and 12.
As a result of the reduced size of bore, the purge gas acquires an increased velocity as it flows through the bore. The stream of purge gas flows along the meniscus and entrains solid and possibly liquid particles in the direction indicated by arrow 13, so that it is always a clean meeting plane 7 which is exposed to the laser beam. Moreover, the gas stream promotes the maintenance and height of the convex meniscus. The process of keeping the meeting plane 7 clean is further promoted by the downward curvature of the meniscus.
The purge gas leaves the submerged pipe in the form of gas bubbles 14 and entrains the solid particles.
Fig. 2a shows a side view of the submerged pipe; in this case of the bottom pipe 3 in the form of a cylindrical pipe.
Fig. 2b shows a view of the underside of the submerged pipe.
The wall 20 of the casing 3 is provided with toothed slots 21. It is preferable for the cross section of the slots to increase from the inside outwards, as shown in
Fig. 2b. The result of this is that the flow velocity of the gas on the inside of the submerged pipe is greater than on the outside, which has a stabilizing effect on the position of the meniscus and also ensures that the metal in the submerged pipe continues to move and is therefore a good reflection of the metal in the molten bath. In addition or as an alternative, the casing may be provided with holes 22 which are submerged in the bath when using the method. The slots and holes have a stabilizing and homogenizing effect on the shape of the meniscus. Moreover, it is assumed that they cause an additional flow around the underside of the submerged pipe, which contributes to the liquid metal in the submerged pipe being constantly refreshed and therefore being a good reflection of the molten metal in the remainder of the bath.

Claims

1. Method for analyzing the composition of a bath comprising liquid metal, in which a laser beam is directed onto a surface of the bath and in which at least part of the metal forms a sample which is analyzed, characterized in that, at least at the location where the laser beam meets the bath, impurities at the surface of the bath are removed by purging with a stream of a purge gas.
2. Method according to Claim 1, characterized in that the velocity and direction of the stream of the purge gas are selected in such a manner that the surface of the bath adjacent to the location where the laser beam meets it has a convex meniscus.
3. Method according to Claim 1 or 2, characterized in that a submerged pipe system provided with a top side, an underside and a casing is at least partially placed in the bath, and the stream of the purge gas is fed into the submerged pipe system above the bath and is directed onto the bath at least at the location where the laser beam meets the bath.
4. Method according to Claim 3, characterized in that purge gas in the submerged pipe system is discharged from the submerged pipe system below the surface of the bath.
5. Method according to one or more of the preceding claims, characterized in that the liquid metal is a liquid aluminium alloy.
6. Device for use in the method for analyzing the composition of a bath comprising liquid metal according to one or more of the preceding claims, which device is provided with a submerged pipe system provided with a top side, an underside and a casing having an inner wall and an outer wall, a source for generating a beam of laser light and a gas supply tube for feeding purge gas into the submerged pipe system, characterized in that the gas supply tube is provided with a passage having a reduced bore size, in order to at least locally increase the flow velocity of the purge gas in the direction of the bath, and runs inside the casing in such a manner that during use the bath inside the casing forms a convex meniscus along which purge gas flows.
7. Device according to Claim 6, characterized in that the casing of the submerged pipe system is provided, in the part which in use extends into the bath, with outlet openings and/or with slots arranged in the underside of the casing.
8. Device according to Claim 7, characterized in that slots and/or openings run with an increasing cross section from the inside of the casing towards the outside thereof.
9. Device according to one or more of Claims 6-8, characterized in that at least part of the inner wall of the casing of the submerged pipe system is made from a material which is not wettable by the liquid metal.
EP06776373A 2005-07-26 2006-07-24 Method for analyzing liquid metal and device for use in this method Withdrawn EP1907828A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NL1029612A NL1029612C2 (en) 2005-07-26 2005-07-26 Method for analyzing liquid metal and device for use therein.
PCT/EP2006/007261 WO2007012440A1 (en) 2005-07-26 2006-07-24 Method for analyzing liquid metal and device for use in this method

Publications (1)

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EP1907828A1 true EP1907828A1 (en) 2008-04-09

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US (1) US20070023110A1 (en)
EP (1) EP1907828A1 (en)
CN (1) CN101263380A (en)
CA (1) CA2614790A1 (en)
FR (1) FR2889313A1 (en)
NL (1) NL1029612C2 (en)
RU (1) RU2008102370A (en)
WO (1) WO2007012440A1 (en)

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WO2007012440A1 (en) 2007-02-01
RU2008102370A (en) 2009-07-27

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