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
  • F27D27/00—Stirring devices for molten material
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B21/00—Obtaining aluminium
  • C22B21/06—Obtaining aluminium refining
  • C22B21/064—Obtaining aluminium refining using inert or reactive gases
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
  • C22B9/05—Refining by treating with gases, e.g. gas flushing also refining by means of a material generating gas in situ

Definitions

• the invention relates to a rotary gas dispersion device for the treatment of a bath of liquid metal, in particular aluminum, an aluminum alloy, magnesium or a magnesium alloy.
• the invention relates more particularly to a rotary injector (or "rotor") intended for the injection and dispersion of at least one treatment gas in a metal in the liquid state.
• Liquid aluminum leaving electrolytic cells or reflow ovens contains dissolved or suspended impurities.
• the most important of these impurities are hydrogen, alkaline elements such as sodium or calcium and oxides, in particular oxides originating from the oxidation of the metal during treatment.
• the liquid aluminum is subjected to various treatments for removing impurities.
• treatments which uses a combination of chemical reactions and flotation phenomena, consists in introducing into the bath, in the form of small bubbles, a gas called "treatment", which can be inert or reactive.
• a gas called "treatment” which can be inert or reactive.
• an argon bubble will bring with it to the surface of the bath a solid inclusion in suspension and / or capture, by diffusion, the hydrogen dissolved in the liquid metal.
• a chlorine bubble will react with the sodium contained and give a sodium salt which will also be transported to the surface of the bath.
• Mixtures are also used, such as argon which may contain a few percent of reactive gas of the chlorine type.
• Such treatments by gas action can be carried out batchwise in an oven or in a crucible (this is called a "batch” treatment).
• the treatments are most often carried out continuously between the oven and the casting machine in a chute or in a treatment tank (or “pocket”) of the type which is schematically represented in FIG. 1.
• the treatment efficiency is maximum when the exchange surface between the bath and the gas is itself maximum. This is achieved by designing the dispersing device so as to obtain very small bubbles, to project these bubbles throughout the volume of liquid metal (that is to say so as to produce the least possible dead volume) and to create recirculations of the bath itself so that it comes into contact with bubbles (always in order to obtain the least dead volume possible).
• the process gas can be dispersed in various ways in the liquid metal.
• static dispersing devices such as rods are used, or more frequently rotary dispersing devices which include one or more rotary injectors.
• a rotary injector or "rotor” is typically composed of a hollow drive shaft through which the gas arrives, gas emission orifices and blades.
• the blades are used to stir the bath, to disperse the gas therein and, sometimes, to split the bubbles into smaller bubbles by shearing effect.
• the openings are generally located near the rotor blades, for example between them or at their ends.
• International application WO 98/05915 (corresponding to American patent US 6,060,013) describes a rotary injector of this type.
• European application EP 819 770 (equivalent to American patent US 5,904,894) describes a rotary injector into which the treatment gas is injected using a porous material inert with respect to the liquid metal.
• Rotary injectors do not allow satisfactory control of the flow rate and the size of the gas bubbles emitted.
• Rotary injectors comprising emission orifices which present risks of blockage of the orifices and of evolution of the size of the orifices and of the blades by erosion, which modifies the quality of the dispersion of the gas.
• the pores are often too large. Consequently, on the one hand, the bubbles are too large, lack efficiency, the gas being insufficiently dispersed in the liquid metal, and cause harmful surface swirls; on the other hand, it is necessary not to stop the passage of gas in the pores to prevent the liquid metal from entering there, in particular during the periods of rest between two flows. On the other hand, when the pores are too small, the bubbles spread and remain large and it is difficult to introduce a high gas flow rate into the liquid metal.
• the invention relates to a rotary injector for injecting gas, called “process gas", into a liquid metal comprising a drive shaft, stirring means, means for conveying gas and means for emitting said gas. gas, and being characterized in that the emission means consist, in whole or in part, of at least one material wettable by said liquid metal, said material preferably being substantially inert to said liquid metal.
• said material can be made wettable by means of a coating of material wettable by liquid metal.
• the invention also relates to a rotary dispersion device comprising at least one rotary injector according to the invention.
• the invention also relates to a device for treating a liquid metal, such as a degassing bag, comprising at least one rotary injector or at least one rotary dispersion device according to the invention.
• Another subject of the invention is the use of the injector according to the invention for the treatment of a liquid metal, in batch or continuously, in particular in an oven or in a chute.
• the invention also relates to a process for treating a liquid metal, characterized in that at least one rotary injector according to the invention is used.
• Said metal can be aluminum or one of its alloys, or magnesium or one of its alloys. Description of the figures
• Figure 1 illustrates a typical liquid metal processing device using a rotary injector.
• FIG. 2 illustrates the wettability criterion within the meaning of the present invention.
• FIG. 3 illustrates four embodiments of the rotary injector according to the invention, seen in perspective.
• FIG. 4 illustrates two embodiments of the rotary injector according to the invention, seen in the axis of symmetry on the side of the part intended to be immersed in the liquid metal.
• FIG. 5 illustrates an embodiment of the rotary injector according to the invention, seen in longitudinal section, in a cutting plane passing through the axis of symmetry and corresponding to the cutting planes B-B of FIG. 4.
• FIG. 6 illustrates, in longitudinal section, in a cutting plane passing through the axis of symmetry, two embodiments of the rotary injector of the invention.
• FIG. 7 illustrates, in longitudinal section, in a section plane passing through the axis of symmetry, three embodiments of the rotary injector of the invention.
• a liquid metal treatment device typically comprises an enclosure (41) provided with inlet means (42) for the "raw" liquid metal (that is to say liquid metal to be treated) (421), means for leaving (43) the treated metal (431) and at least one rotary dispersing device (30).
• the inlet (42) and outlet (43) means are generally located either at the ends of the device, or on one and the same side.
• a rotary dispersing device (30) comprises a rotary injector (1), means for rotating (31) said injector, a source of process gas (32) and conduits (33) between said source ( 32) and the injector (1).
• the or each rotary injector (1) enters said enclosure (41) via an opening (44) which is generally provided with sealing means (45).
• the treatment enclosure (41) is generally a tank with one or more compartments (46, 47).
• the rotary injector (1) for injecting gas (2) into a liquid metal (3) said injector comprising a drive shaft (4), stirring means (5), means of delivery of gas (6, 7, 1 1), emission means (8, 9) of gas (2), said injector being characterized in that the emission means (8, 9) are, in all or part, consisting of at least one material wettable by the liquid metal (3).
• said wettable material is substantially inert to said liquid metal, that is to say that it has a lifetime in the liquid metal which is long enough to allow acceptable industrial use.
• a material is considered to be substantially inert to the liquid metal when it can be immersed in the liquid metal for a period of the order of 10 hours or more without significant alteration of the properties of the rotary injector and without prohibitive pollution of the treated metal.
• Ceramics generally fulfill this condition, in particular ceramics based on oxides, carbides, nitrides, borides and their mixtures. Certain refractory metals also fulfill this condition, such as tungsten.
• the emission means (8, 9) and / or the stirring means (5) and / or said drive shaft (4) and / or said insert (90) comprise a coating of wettable material on all or part of their surface exposed to liquid metal.
• Said porous material can also be made wettable by liquid metal using a coating of wettable material, that is to say that it can comprise a coating of wettable material.
• a material is considered to be wettable when the wetting angle made by the liquid metal in contact with it is less than 90 ° (see FIG. 2).
• the wetting angle (21) between the tangent T to the bubble (20) at its point of contact with the emission means (9) and the outer surface S of the transmission means is less than 90 °.
• the metal which then wets the material well near the emission orifice (8), counteracts the spreading of the bubble (20) and limits its diameter.
• the wetting angle (21) is greater than 90 °. In this case, the metal, which has difficulty wetting the emission means, allows the bubble to spread.
• the wettable material of the diffuser can be chosen from certain refractory metals which are substantially inert with respect to said liquid metals, molybdenum (Mo), tungsten (W ), vanadium (V), titanium (Ti), chromium (Cr), iron (Fe), steels, ..., or their alloys, or among ceramics such as titanium diboride
• TiB 2 TiB 2
• nitrides especially aluminum nitrides (such as AIN)
• carbides especially aluminum carbides (such as Al C 3 ) and titanium carbides (such as TiC ⁇ . X )
• BN boron nitride
• the emission and stirring means which constitute the so-called “active" part of the injector, are generally located at the so-called “lower” end of the injector, that is to say the end of the injector intended to be immersed in the liquid metal.
• the injector is normally intended to be used in a vertical position, with said lower part placed downwards.
• the active part normally includes at least one lower surface (120, 121, 122), at least one upper surface (130, 131) and side surfaces (140, 141, 142).
• the conveying means (6, 1, 1 1) typically comprise a main channel (6) in the shaft (4) of the injector and at least one secondary channel (7) to channel the treatment gas to the emission means (8, 9).
• the main channel (6) is typically in the axis of symmetry of said shaft.
• said emission means comprise at least one emission orifice (8) of said gas (2).
• the diameter of the orifice (8) influences the diameter of the bubble to be obtained.
• the diameter of each orifice (8) is preferably as small as possible. In practice, the diameter is preferably between 0.5 and 5 mm, and more preferably between 1 and 3 mm, which allows the size of the orifices to be well controlled at the time of their manufacture.
• said emission means comprise a porous material wettable by said liquid metal (3), and preferably also substantially inert to said liquid metal (3), for which the diameter of the open pores emerging at the surface of said porous material is preferably less than 0.5 mm.
• the rotary injector (1) may also include an intermediate cavity (1 1), typically between the main channel (6) and the secondary channels (7), which acts as a buffer volume, and / or a means for introducing a local pressure drop just upstream of the emission orifice, such as a porous material.
• the intermediate cavity (1 1) typically has a cylindrical shape and the secondary channels (7) extend radially therefrom to the emission means (8, 9).
• the emission orifices (8) are preferably located near the blades (5) of the injector, typically between them ( Figures 3a and 3b) or at the end thereof ( Figure 3c and 3d) .
• Emission ports may be provided at the end of the injector; for example, an orifice can be provided in the central part of said lower surface (120) of the injector.
• the number of emission ports (8) may be different from the number of blades (5). It is also possible to provide superimposed emission orifices. In practice, an emission orifice is provided for each blade.
• the emission orifices (8) preferably emerge on said lateral surfaces (140, 141, 142), for example on the external lateral surface (141) of one of the blades (5) or on the lateral surface (140) between the blades.
• the position of the emission orifices is preferably such as to allow maximum shearing of the bubbles during their formation.
• emission orifices are located between blades, they are preferably located halfway up the corresponding lateral surface (140); when emission orifices are located on blades, they can be located in the upper half of the corresponding external lateral surface (141) (that is to say in the part of said surface closest to the shaft (4)).
• Emission ports typically emerge at an angle to the side surface which is about 90 °; this angle can, in certain cases, be different from 90 °, in which case the axis of the secondary channels (7) can also form an angle with respect to the axis of the main channel which is different from 90 °.
• the stirring means (5) can also consist, in whole or in part, of at least one material wettable by said liquid metal (3), and preferably also substantially inert to said liquid metal (3), which material can be different that used for the transmission means (8, 9).
• the stirring means typically comprise blades (5). These blades are normally simple in shape, such as a plate shape.
• the stirring means can also comprise a complementary dispersing means, such as a disc (12) situated above the blades, typically in contact with the latter (as illustrated in FIGS. 3a, 3c and 4a).
• the drive shaft (4) may advantageously be made, in whole or in part, of at least one material wettable by said liquid metal, and preferably substantially inert to said liquid metal, which material may be different from that used for the transmission means (8, 9).
• the part of said shaft intended to be immersed in the liquid metal consists, at least on the surface, of said wettable material.
• the rotary injector (1) may consist of several separate parts (4, 5, 12, 13, 14, 90), as illustrated in Figures 6 and 7.
• the parts can be made of different materials.
• the rotary injector may advantageously include an insert (90) comprising said emission means (8, 9) and made of said wettable material, which allows it to be easily changed depending on the metal to be treated or in the event of breakage. accidental.
• the part of the injector intended to be immersed in the liquid metal may consist of a single piece.
• the injector comprises the following parts: a drive shaft (4), a disc (12), blades (5), a central core (13) and an assembly body (14).
• the central core comprises an intermediate cavity (11), routing channels (7) and emission orifices (8).
• the injector comprises the following parts: a drive shaft (4), blades (5) and an assembly body (14).
• the blades include routing channels (7), emission ports (8) and an intermediate cavity (11), said cavity being generally common to all the blades and enclosed in a central core (13) (not illustrated).
• the assembly body (14) comprises at least one central channel (60) and connection means (15a, 16a, 17a), typically a thread, which cooperate with complementary connection means ( 15b, 16b, 17b) of the other parts (4, 12, 13).
• connection means 15a, 16a, 17a
• complementary connection means 15b, 16b, 17b of the other parts (4, 12, 13).
• the central core (13) and / or the blades (5) are provided with removable inserts (90).
• the emission means (9) are made of a wettable material.
• the Applicant's tests have shown that it is particularly advantageous that the parts of the injector which are immersed in the liquid metal during the treatment are all made of a wettable material. The same material can be used for all these parts. Indeed, it has been noticed that, in this case, the bubbles emitted by the orifices (8) which are attracted in the blades and along the rotor shaft by a hydrodynamic effect do not remain trapped and do not have tendency to merge to form large bubbles, as is the case with non-wettable materials.
• the injector consists of several parts, the parts of the injector which are immersed in the liquid metal during the treatment are preferably all made of a wettable material. The same material can be used for all these parts.
• the injector may be provided with a ring (10) to allow coupling with rotation means (31).
• the axis of rotation of the rotary injector (1) is located in the axis of symmetry of the drive shaft (4).
• the rotary injector (1) of the invention can be used for the treatment of a liquid metal circulating in an enclosure, as illustrated in FIG. 1, which is typically a treatment bag, or in a circulation chute of liquid metal (not shown). It can also be used for batch processing, for example in an oven. In other words, a processing bag, oven or chute can be equipped with a rotary injector according to the invention for the treatment of a liquid metal continuously or in batches (batch treatment).
• Tests were carried out in a small experimental tank.
• the size of the bubbles formed was observed and determined using an X-ray camera.
• the method consists in irradiating the bath of liquid metal (3) in which the bubbles (20) are emitted using rays.
• X to visualize the said bubbles after recovery of the image by a camera and to measure them after calibration of the acquisition chain.
• the tests were carried out with rotary injectors comparable to those illustrated in FIG. 3.
• the blades and the emission means were made of graphite; in another case, representative of the invention, they were made of titanium. In both cases, the holes had a diameter of 1 mm.
• the Applicant has noted on the one hand that, with the injectors of the prior art, the bubbles had an average diameter of the order of 15 mm, part of the treatment gas could rise up along the rotor and of the injector shaft and 20% of the injected gas was not dispersed in the liquid metal. The part of the undispersed gas is practically useless because it does not contribute to the treatment of the liquid metal.
• the Applicant has also observed that, with the injectors according to the invention, the bubbles had an average diameter of the order of 6 mm and less than 0.5% of the gas injected (detection limit) was not dispersed in liquid metal.
• the Applicant has also noticed that, unlike the prior art, the bubbles emitted by the orifices located at the ends of the blades do not tend to form pockets of gas between the blades. The bubbles therefore preserve their small size, which results in greater treatment efficiency than the prior art.
• the injector according to the invention avoids the formation of gas pockets under the injector which could cause instabilities.
• the rotary injector according to the invention has the advantage of allowing a significant reduction in the speed of rotation required to obtain small bubbles by shearing effect.
• the speed of rotation can if be between 100 and 350 rpm, which also makes it possible to limit the surface agitation of the liquid metal and reduce wear on parts.
• the rotary injector according to the invention also has the advantage of having processing performance which is less sensitive to possible wear of the blades of the injector. Indeed, according to the invention, the size of the gas bubbles is largely determined by the emission orifices, and only a small part by the rotational movement of the blades, which then mainly have the function of dispersing the bubbles. in the largest possible bath volume and to stir it in order, in particular, to homogenize the treatment. Consequently, the wear of the blades over time does not cause an unacceptable crippling of the treatment performance of the injector of the invention.
• the orifice of the emission means of the injector according to the invention can be small enough to avoid the penetration of liquid metal.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Organic Chemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Manufacturing & Machinery (AREA)
• General Engineering & Computer Science (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Treating Waste Gases (AREA)
• Coating Apparatus (AREA)
• Waste-Gas Treatment And Other Accessory Devices For Furnaces (AREA)
• Physical Or Chemical Processes And Apparatus (AREA)
• Feeding, Discharge, Calcimining, Fusing, And Gas-Generation Devices (AREA)

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• 2000
  • 2000-10-20 FR FR0013468A patent/FR2815642B1/fr not_active Expired - Fee Related
• 2001
  • 2001-10-18 US US10/398,212 patent/US20040021257A1/en not_active Abandoned
  • 2001-10-18 EP EP01978568A patent/EP1332235B1/de not_active Expired - Lifetime
  • 2001-10-18 CA CA002426268A patent/CA2426268A1/fr not_active Abandoned
  • 2001-10-18 CN CNA018176321A patent/CN1469935A/zh active Pending
  • 2001-10-18 RU RU2003114738/02A patent/RU2270876C2/ru not_active IP Right Cessation
  • 2001-10-18 AU AU2002210668A patent/AU2002210668A1/en not_active Abandoned
  • 2001-10-18 ES ES01978568T patent/ES2218458T3/es not_active Expired - Lifetime
  • 2001-10-18 WO PCT/FR2001/003231 patent/WO2002033137A1/fr active IP Right Grant
  • 2001-10-18 DE DE60102832T patent/DE60102832T2/de not_active Expired - Fee Related
  • 2001-10-18 AT AT01978568T patent/ATE264406T1/de not_active IP Right Cessation
  • 2001-10-18 JP JP2002536105A patent/JP2004511661A/ja active Pending
• 2003
  • 2003-04-15 NO NO20031762A patent/NO20031762L/no unknown

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