WO1992003240A1 - Device for tapping vehicle for metal melts - Google Patents

Device for tapping vehicle for metal melts Download PDF

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Publication number
WO1992003240A1
WO1992003240A1 PCT/NO1991/000110 NO9100110W WO9203240A1 WO 1992003240 A1 WO1992003240 A1 WO 1992003240A1 NO 9100110 W NO9100110 W NO 9100110W WO 9203240 A1 WO9203240 A1 WO 9203240A1
Authority
WO
WIPO (PCT)
Prior art keywords
melt
tapping
electrodes
vehicle
drainpipe
Prior art date
Application number
PCT/NO1991/000110
Other languages
French (fr)
Inventor
Christian J. Simensen
Original Assignee
Senter For Industriforskning (Si)
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 Senter For Industriforskning (Si) filed Critical Senter For Industriforskning (Si)
Publication of WO1992003240A1 publication Critical patent/WO1992003240A1/en

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D3/00—Charging; Discharging; Manipulation of charge
    • F27D3/14—Charging or discharging liquid or molten material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D37/00—Controlling or regulating the pouring of molten metal from a casting melt-holding vessel
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D21/00—Arrangements of monitoring devices; Arrangements of safety devices
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B3/00—Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces
    • F27B3/08—Hearth-type furnaces, e.g. of reverberatory type; Tank furnaces heated electrically, with or without any other source of heat
    • F27B3/085—Arc furnaces
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D3/00—Charging; Discharging; Manipulation of charge
    • F27D2003/0034—Means for moving, conveying, transporting the charge in the furnace or in the charging facilities
    • F27D2003/0054—Means to move molten metal, e.g. electromagnetic pump
    • F27D2003/0056—Means to move molten metal, e.g. electromagnetic pump through a syphon in a vacuum chamber, e.g. involving aspiration or pressure on the bath
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D21/00—Arrangements of monitoring devices; Arrangements of safety devices
    • F27D2021/0057—Security or safety devices, e.g. for protection against heat, noise, pollution or too much duress; Ergonomic aspects
    • F27D2021/0078—Security or safety devices, e.g. for protection against heat, noise, pollution or too much duress; Ergonomic aspects against the presence of an undesirable element in the atmosphere of the furnace
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D2201/00—Manipulation of furnace parts

Definitions

  • the invention concerns a device used in connection with tapping of melt from a furnace or an oven or the like where it is important to avoid sucking up impurities of different kinds.
  • An example is tapping of aluminium from an electrolysis cell where it is important to avoid to drain molten bath (cryolite plus alumina), molten cryolite and sludge.
  • the liquid in the cell consists of a top layer of pure molten magnesium and a bottom layer of molten salt.
  • molten salt may be sucked up along with the molten metal.
  • a metal product which is enriched with such contaminant, is more corrosive than ordinary magnesium. Producers of magnesium therefore require equipment or methods to avoid that salt is tapped along with magnesium from the electrolysis cells.
  • the annual production of magnesium in Norway is about 50000 ton, and the world production is about 350000 ton (1991).
  • the main purpose of this invention is to solve this problem by using a device which is simple, reliable and economical in use, and which reacts so fast to impurities that the problem of sucking up the mentioned contaminants is reduced to a minimum.
  • the invention consists of a device for use with transfer pipes of melts, drainpipes for sucking up molten metal into crucibles on tapping vehicles used in the metal industry.
  • the device is characterized in that it comprises at least two electrodes (8) which are to be placed on the drainpipe (6) of the vehicle in such a way that said electrodes are in direct contact with the melt (3) during tapping, and that at least two of said electrodes are connected to an instrument (10) which is able to measure the variations in the electrical conductivity between the electrodes.
  • the difference in electrical conductivity between the pure, molten metal and the liquid contaminants of sludge, liquid bath or cryolite which are tapped with the metal, is so large that even small concentrations of impurities can be detected.
  • the electrical resistivity of molten aluminium is 3 • 10 " 7 ⁇ m at 950°C
  • the electrical resistivity of cryolite is 3.5 • 10 " 3 ⁇ m under the same conditions.
  • Detection of impurities which are pumped through the drainpipe can be used to generate and direct electrical signals. In its simplest form it can turn on a warning lamp while further intervention in the tapping process must be carried out manually. This is, however, not a practical solution in connection with industrial production, where the tapping rate of molten metal is high.
  • the device is set to control regulation devices necessary to stop the tapping of melt immediately and/or to return the impure melt to the electrolysis cell or the furnace or to redirect it to a separate receptacle, when some contaminated liquid is sucked up.
  • FIG. 1 shows a tapping vehicle without the use of the invention
  • Figure 2 shows a tapping vehicle where a device according to the invention is connected to the vehicle and the drainpipe
  • Figure 3 is a cross section of the drainpipe of Figure 2 with a preferred positioning of the electrodes.
  • An electrolysis cell comprising an anode(l) and a cathode(2) is shown in Figure 1.
  • a layer of liquid bath which is a mixture of alumina, cryolite and other salt components.
  • Lumps of sludge (alumina) (5) are located on the bottom of the furnace. The melt is transferred to a tapping vehicle (7) through a drainpipe (6).
  • a set of electrodes (8) is connected to the drainpipe.
  • Currentpulses or voltagepulses are supplied to the electrodes by means of a current generator (9) or a similar electrical device.
  • a detector (10) which is suitable for continuous measurement and registration of electrical conductivity, is connected to another set of electrodes placed not far from the first set.
  • the detector may be connected to a comparator (11) or equivalent devices which can detect deviations from the expected el- trical conductivity.
  • a control device (12) connected to the comparator (11) can by a certain, minimum deviation in electrical conductivity from that of the ordinary melt turn on a warning lamp (13) and/or give an electrical signal to devices (14) which produces an automatic stop of the tapping and/or provides that the contaminated melt is returned to the cell or furnace.
  • Such devices can involve pumps, valves, etc.
  • Figure 3 shows a cross section through a section of the drainpipe shown in Figure 2, and shows in detail the positioning of the electrodes on the pipe.
  • the device shown in Figures 2 and 3 includes 4 electrodes ( or 2 sets of electrodes) which are connected to the drainpipe (6). It is also possible to carry out continuous measurement of the electrical conductivity of the melt by means of only two electrodes connected to the drainpipe.
  • the operator of the tapping vehicle can change the position of the drainpipe in the cell or the furnace, and the melt transfer can continue.
  • the melt is delivered to the mixing furnace or the holding furnace in the casthouse.
  • the operator may temporarily put the described device out of function and let the melt transfer operation continue.
  • the tapping vehicle with crucible containing the contaminated melt is then sent to a cleaning station where the melt is treated specially.
  • a possible refining method is to purge the melt with active gas and skim the surface dross (oxide, cryolite and other salts) at low temperature.
  • a third possibility is to let the control signal automatically force the contaminated melt to flow into another chamber (crucible) on the vehicle so that the tapping of the cell can continue undisturbed without mixing the already tapped, pure melt with the contaminated one.
  • a fourth possibility is to return all the melt to the electrolysis cell and start the operation all over. This handling of the liquid may, however, also cause an unwanted turbulence in the metal bath in the cell or the furnace and lead to a lower temperature in the molten metal unless special precautions are taken to prevent such side effects.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Electrolytic Production Of Metals (AREA)
  • Manufacture And Refinement Of Metals (AREA)

Abstract

Device for use together with tapping vehicles for aluminium furnaces, magnesium furnaces, etc. The device comprises electrodes which are to be placed on the drainpipe of the vehicle in direct contact with the melt wich are sucked up, and an instrument able to measure the electrical conductivity between the electrodes. Additional devices which will automatically stop the tapping of the melt for a given variation in the electrical conductivity, is preferentially connected to the instrument.

Description

Device for tapping vehicle for metal melts
The invention concerns a device used in connection with tapping of melt from a furnace or an oven or the like where it is important to avoid sucking up impurities of different kinds.
An example is tapping of aluminium from an electrolysis cell where it is important to avoid to drain molten bath (cryolite plus alumina), molten cryolite and sludge.
When aluminium is produced by the Hall-Heroult process in an electrolysis cell, about one ton molten aluminium is tapped once a day. A drainpipe is then pierced into the melt, and the melt is tapped. Electrolysis bath which is a mixture of cryolite and alumina, or bottom sludge may also be tapped along with molten metal during this operation. The amount of these contaminants can be from 1 kg to 100 kg in an unsuccessful tapping. The temperature of the melt decreases continuously during the melt tranfer operation, first in crucible on the tapping vehicle and thereafter during transfer and holding in the mixing furnace. Presence of the above described contaminants will cause solidification of cryolite-alumina mixtures on the walls and the linings of both the transfer crucible and the mixing furnace, and on the surface of the aluminium melt. The result is a thick cover of contaminants on the linings of the transfer crucibles and the mixing furnaces with a repeated need for frequent internal cleaning of these devices. In particular serious circumstances nozzles may be blocked or rotors may fail due to these contaminants in the melt.
When aluminium - magnesium melts are contaminated with cryolite, the cryolite will react with the melt, and the melt is polluted with sodium. A high content of sodium may cause edgecracking of metal sheets during rolling of high alloyed aluminium - magnesium, resulting in a high rejection rate and an increased production cost.
The need for equipment or methods which can prevent or reduce the amount of sludge or bath sucked up from the electrolysis cell, is recognized by the aluminium industry. The Norwegian annual production of aluminium today is about 800000 ton from electrolysis cells, while the world production is 14 mill, ton per year.
When magnesium is produced by electrolysis t magnesiumcHoride, the liquid in the cell consists of a top layer of pure molten magnesium and a bottom layer of molten salt. When the cell is tapped, molten salt may be sucked up along with the molten metal. A metal product which is enriched with such contaminant, is more corrosive than ordinary magnesium. Producers of magnesium therefore require equipment or methods to avoid that salt is tapped along with magnesium from the electrolysis cells. The annual production of magnesium in Norway is about 50000 ton, and the world production is about 350000 ton (1991).
An apparatus for detection of water in a nonconducting liquid which is insoluble in water such as liquid hydrocarbons, is described in GB-patent no. 1.220.489.
An instrument for measurement of the absolute value of the electrical conductivity of liquids by means of electrodes which are situated in a cylindrical container filled with the liquid and connected to the required electronic device, is described in US patent no. 4.751.466.
A method for determination of electrical conductivity, pressure and temperature of liquids and in particular ocean water, is described in the German patent no. 3427050.
The published works show that the conductivity of liquids can be used for determination of contaminants in liquids and for other purposes. In spite of this, and in spite of the long recognized problem with tapping of sludge, molten bath, cryolite and other salts from the electrolysis cells, no proposal has been made, to our knowledge, for an effective method of preventing the tapping of contaminants.
The main purpose of this invention is to solve this problem by using a device which is simple, reliable and economical in use, and which reacts so fast to impurities that the problem of sucking up the mentioned contaminants is reduced to a minimum.
The invention consists of a device for use with transfer pipes of melts, drainpipes for sucking up molten metal into crucibles on tapping vehicles used in the metal industry. The device is characterized in that it comprises at least two electrodes (8) which are to be placed on the drainpipe (6) of the vehicle in such a way that said electrodes are in direct contact with the melt (3) during tapping, and that at least two of said electrodes are connected to an instrument (10) which is able to measure the variations in the electrical conductivity between the electrodes.
Preferential embodiments of the invention are disclosed by the dependent claim.
The difference in electrical conductivity between the pure, molten metal and the liquid contaminants of sludge, liquid bath or cryolite which are tapped with the metal, is so large that even small concentrations of impurities can be detected. For instance, the electrical resistivity of molten aluminium is 3 • 10 "7 Ωm at 950°C, while the electrical resistivity of cryolite is 3.5 • 10 "3 Ωm under the same conditions.
Detection of impurities which are pumped through the drainpipe, can be used to generate and direct electrical signals. In its simplest form it can turn on a warning lamp while further intervention in the tapping process must be carried out manually. This is, however, not a practical solution in connection with industrial production, where the tapping rate of molten metal is high. In a preferred embodiment of the invention the device is set to control regulation devices necessary to stop the tapping of melt immediately and/or to return the impure melt to the electrolysis cell or the furnace or to redirect it to a separate receptacle, when some contaminated liquid is sucked up.
The invention is described in more detail in the forthcoming paragraphs with reference to the accompanying drawings.
Figure 1 shows a tapping vehicle without the use of the invention,
Figure 2 shows a tapping vehicle where a device according to the invention is connected to the vehicle and the drainpipe,
Figure 3 is a cross section of the drainpipe of Figure 2 with a preferred positioning of the electrodes.
An electrolysis cell comprising an anode(l) and a cathode(2) is shown in Figure 1. On top of the molten metal (3) is a layer of liquid bath which is a mixture of alumina, cryolite and other salt components. Lumps of sludge (alumina) (5) are located on the bottom of the furnace. The melt is transferred to a tapping vehicle (7) through a drainpipe (6).
The same units comprising the device according to the invention are shown in Figure 2. A set of electrodes (8) is connected to the drainpipe. Currentpulses or voltagepulses are supplied to the electrodes by means of a current generator (9) or a similar electrical device. A detector (10) which is suitable for continuous measurement and registration of electrical conductivity, is connected to another set of electrodes placed not far from the first set. The detector may be connected to a comparator (11) or equivalent devices which can detect deviations from the expected el- trical conductivity. A control device (12) connected to the comparator (11) can by a certain, minimum deviation in electrical conductivity from that of the ordinary melt turn on a warning lamp (13) and/or give an electrical signal to devices (14) which produces an automatic stop of the tapping and/or provides that the contaminated melt is returned to the cell or furnace. Such devices can involve pumps, valves, etc. Figure 3 shows a cross section through a section of the drainpipe shown in Figure 2, and shows in detail the positioning of the electrodes on the pipe. The device shown in Figures 2 and 3 includes 4 electrodes ( or 2 sets of electrodes) which are connected to the drainpipe (6). It is also possible to carry out continuous measurement of the electrical conductivity of the melt by means of only two electrodes connected to the drainpipe.
Since there is a large difference in electrical conductivity between the pure aluminium melt and the mentioned contaminants, even small amounts of impurities (contaminants) can be detected by a device according to the invention.
When impurities are detected and the tapping operation is stopped, the operator of the tapping vehicle can change the position of the drainpipe in the cell or the furnace, and the melt transfer can continue. When the tapping of the pure molten metal is completed, the melt is delivered to the mixing furnace or the holding furnace in the casthouse.
As an alternative embodiment of the invention, the operator may temporarily put the described device out of function and let the melt transfer operation continue. The tapping vehicle with crucible containing the contaminated melt is then sent to a cleaning station where the melt is treated specially. A possible refining method is to purge the melt with active gas and skim the surface dross (oxide, cryolite and other salts) at low temperature.
A third possibility is to let the control signal automatically force the contaminated melt to flow into another chamber (crucible) on the vehicle so that the tapping of the cell can continue undisturbed without mixing the already tapped, pure melt with the contaminated one.
A fourth possibility is to return all the melt to the electrolysis cell and start the operation all over. This handling of the liquid may, however, also cause an unwanted turbulence in the metal bath in the cell or the furnace and lead to a lower temperature in the molten metal unless special precautions are taken to prevent such side effects.

Claims

Patent claims
1. A device for use together with a tapping vehicle for melting furnaces ch a ra ct erized in tha t it comprises at least two electrodes (8) which are to be placed on the drainpipe (6) of the vehicle in such a way that said electrodes are in direct contact with the melt (3) during tapping, and that at least two of said electrodes are connected to an instrument (10) which is able to measure the variations in the electrical conductivity between the electrodes.
2. A device as described in claim 1, ch a ra c t erized in t h a t devices (11,12) are connected to the instrument (10) and that said devices (11,12) responds to a given variation of conductivity by giving a control signal to another device (14) which causes the tapping of the melt to stop immediately and/or ensures that the impure melt is either returned to the furnace or redirected to a separate receptacle.
PCT/NO1991/000110 1990-08-15 1991-08-14 Device for tapping vehicle for metal melts WO1992003240A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NO903600 1990-08-15
NO903600A NO171118B (en) 1990-08-15 1990-08-15 DEVICE FOR METAL MELTS

Publications (1)

Publication Number Publication Date
WO1992003240A1 true WO1992003240A1 (en) 1992-03-05

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AU (1) AU8391491A (en)
NO (1) NO171118B (en)
WO (1) WO1992003240A1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5690888A (en) * 1995-06-07 1997-11-25 Molten Metal Technologies, Inc. Apparatus and method for tapping a reactor containing a molten fluid

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE178605C1 (en) *
US3078412A (en) * 1958-06-03 1963-02-19 Atomic Energy Authority Uk Apparatus for indicating the metal oxide content of a liquid metal
US3299706A (en) * 1964-04-03 1967-01-24 Latrobe Steel Co Apparatus for measuring molten metal levels in ladles
US3370466A (en) * 1965-09-24 1968-02-27 United States Steel Corp Method and apparatus for locating interfaces between fluids
US4173299A (en) * 1976-10-25 1979-11-06 Asea Ab Electromagnetic valve with slag indicator
US4602768A (en) * 1983-08-18 1986-07-29 Metacon Ag Apparatus for determining the presence of a metallic melt in a passage channel of a metallurgical furnace or of a casting ladle
US4887798A (en) * 1987-07-10 1989-12-19 Amepa Angewandte Messtechnik Und Prozessautomatisierung Gmbh Device for detecting slag flowing with molten metal through an outlet opening in a metallurgical vessel

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE178605C1 (en) *
US3078412A (en) * 1958-06-03 1963-02-19 Atomic Energy Authority Uk Apparatus for indicating the metal oxide content of a liquid metal
US3299706A (en) * 1964-04-03 1967-01-24 Latrobe Steel Co Apparatus for measuring molten metal levels in ladles
US3370466A (en) * 1965-09-24 1968-02-27 United States Steel Corp Method and apparatus for locating interfaces between fluids
US4173299A (en) * 1976-10-25 1979-11-06 Asea Ab Electromagnetic valve with slag indicator
US4602768A (en) * 1983-08-18 1986-07-29 Metacon Ag Apparatus for determining the presence of a metallic melt in a passage channel of a metallurgical furnace or of a casting ladle
US4887798A (en) * 1987-07-10 1989-12-19 Amepa Angewandte Messtechnik Und Prozessautomatisierung Gmbh Device for detecting slag flowing with molten metal through an outlet opening in a metallurgical vessel

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5690888A (en) * 1995-06-07 1997-11-25 Molten Metal Technologies, Inc. Apparatus and method for tapping a reactor containing a molten fluid

Also Published As

Publication number Publication date
NO903600L (en) 1992-02-17
NO903600D0 (en) 1990-08-15
AU8391491A (en) 1992-03-17
NO171118B (en) 1992-10-19

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