Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
  • B22D11/041—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds for vertical casting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
  • B22D11/0401—Moulds provided with a feed head

Definitions

• the present invention relates to the continuous casting of metals, in particular steel.
• the continuous casting operation consists schematically of pouring a molten metal into an ingot mold, essentially consisting of a tubular element without bottom defining a passage for the cast metal, but the walls of which, in copper or more generally made of copper alloy, are energetically cooled by water circulation, and from which a product already solidified externally over a few centimeters in thickness is also continuously extracted. Solidification then progresses towards the axis of the product and ends during the descent of the latter downstream of the mold in the so-called "secondary cooling" zone under the effect of water spray bars. The product obtained, bloom, billet or slab, is then cut to length, then laminated before shipment to the customer or processing on site, into bars, wires, profiles, plates, sheets, etc.
• the ring contraction is all the more important that the heat extraction is strong and that the cast metal has a natural tendency to contract during cooling, for example by change of solid phase at the end of solidification, as it is the case in particular for grades of steel with 0.1% carbon or AISI 304 stainless steel.
• This perimeter contraction tends to cause a separation of the solidified skin relative to the wall of the mold, and therefore a reduction in the heat exchange due to the fact that the contact of said skin with the cold walls is degraded.
• This detachment is generally uneven depending on the perimeter of the solidified skin, which is a source of surface defects in the product finally obtained.
• an improvement consists in injecting into the ingot mold, at the level of said enhancement and at least just at the interface between it and the cooled metal walls. , an inert gas under pressure.
• This gas injection produced by a thin annular slot formed between said walls and the riser, forms jets perpendicular to the walls and directed towards the liquid metal, which shear any solidified skins which may have formed in contact with the refractory riser, so as to ensure an effective start to solidification precisely at the upper edge of the cooled walls.
• the present invention aims to solve these problems and aims particularly to allow, in the technique of continuous casting under vertical load, easy control and adaptation of the conditions of extraction of the heat flux, in particular in the zone where solidification begins. .
• the invention relates to a process for the continuous casting of metals according to which an ingot mold having metal walls is used.
• an ingot mold having metal walls is used.
• energetically cooled surmounted by an extension made of thermally insulating material the free surface of the molten metal contained in the ingot mold is maintained at the level of said enhancement during casting, and injected into the ingot mold, around its entire periphery, a gas under pressure, at the level of said riser and at least at the interface between the latter and the cooled walls.
• this process is characterized in that said injected gas is a gas or gas mixture having an adjustable thermal expansion capacity, to adjust, depending on the composition of the cast metal alloy and the casting conditions , the density of the heat flux extracted from said metal alloy in the zone where it begins to solidify at a specific predetermined value of the cast alloy.
• the method according to the invention thus offers a possibility of easily adapting as required the density of heat flux extracted from the cast metal to the level where the solidified skin is formed, in particular as a function of the composition of said metal, in particular the shade in the case of steel casting.
• the inventors have in fact observed, during casting tests carried out by injecting an inert gas, such as argon or helium, at the interface between the riser and the cooled metal walls, that the flux density extract was strongly influenced by the thermal expansion capacity of the gas.
• an inert gas such as argon or helium
• the flux density extracted over the first 40 millimeters from the upper edge of the metal walls was around 5 MW / m 2 when the temperature of the injected argon was around 500 ° C, and was only 4.2 or even 3.2 MW / m 2 when the temperature of the argon injected was around 100 ° C.
• the temperature of said gas is therefore adjusted.
• the temperature of the injected gas is adjustable between 50 and 600 ° C., this range of adjustment making it possible to fix the temperature of the gas at a predetermined value such that the density of extracted heat flux is between 2 , 5 and 6 MW / m 2 , thus providing wide possibilities for adaptation depending on the composition of the cast metal alloy and the various other casting parameters.
• the temperature of the gas is adjusted by mixing, in a determined volumetric ratio, gas coming from a hot source at a substantially constant temperature, for example at 700 ° C. with gas coming from a cold source also at a substantially constant temperature, by example at 20 ° C.
• the total gas flow injected is the sum of the gas flows from the two sources respectively. The report between these flows makes it possible to vary the temperature of the injected gas, while making it possible to maintain a substantially constant total flow. In practice, taking into account the inevitable heat losses, and with the temperatures of the two sources mentioned above, it will be possible to vary the temperature of the injected gas between 50 and 600 ° C.
• the gas mixing is carried out in a mixing chamber situated in the walls of the ingot mold and / or in the enhancement, the temperature of the injected gas being adjusted by adjusting the gas flow rates coming respectively from hot and cold sources and introduced into said chamber.
• the injected gas is a mixture of at least two gases constituting the mixture, for example argon and helium, the thermal expansion capacity of which is adjusted by adjusting the relative proportions of said gases constitutive.
• the gases constituting the mixture have different physical properties, in particular different densities, to adjust, as a function of their relative proportions, the density of the mixture.
• the invention also relates to a continuous metal casting installation comprising an ingot mold whose walls are formed by cooled metal walls surmounted by an extension in thermally insulating material, and injection orifices opening into the ingot mold for injecting into the ingot mold a gas under pressure in the form of jets distributed around the periphery of the ingot mold at the level of the extension and at least at the interface between said extension and the metal wall, characterized in that it comprises means for supplying said gases, connected to said orifices, making it possible to adjust the thermal expansion capacity of the injected gas.
• Said gas supply means may comprise means for adjusting the temperature of the injected gas, or means for adjusting the relative proportion of at least two gases constituting a gas mixture forming the injected gas.
• the casting installation comprises two sources of gas connected to a mixing chamber, itself connected to said orifices, and means for adjusting the gas flow rates coming respectively from said sources and introduced into the mixing chamber.
• the mixing chamber is located outside the mold and connected to a distribution channel arranged in the wall of the mold.
• the mixing chamber is located in the wall of the mold.
• the mixing chamber can in particular consist of a first distribution chamber arranged in the riser and connected to the source of hot gases and a second distribution chamber arranged in the metal walls and connected to the cold source.
• FIG. 1 is a schematic representation of a first variant, showing the upper part of the mold in partial longitudinal section,
• FIG. 2 illustrates a second alternative embodiment
• the walls 1 of the mold shown in FIG. 1 consist of metal walls 2, made of copper or copper alloy, surmounted by an extension 3 made of thermally insulating refractory material.
• the metal walls 2 are energetically cooled by an internal circulation of water in channels 4, shown schematically in the figure.
• the riser 3 consists of an upper part 5, of a height of 200 mm for example, made of a very insulating material and of a lower part 6 made of a refractory material possibly less insulating but having better mechanical resistance, for example the material known under the designation SiAlON, and having for example a thickness of 20 mm.
• the walls 1 of the ingot mold define a passage for the cast product, in which the molten steel 7 is conventionally supplied by a nozzle 8 comprising gills 9 situated at the height of said riser 3.
• the ingot mold also comprises gas injection orifices, opening onto the inner surface of the walls 1, at the interface between the extension 3 and the metal wall 2, preferably formed by a continuous slot around the periphery of the ingot mold, ensuring thus a regular injection of gas all around.
• This narrow slot 10 has a height of a few tenths of a millimeter, for example 0.2 mm, determined by a spacer 11 inserted between the lower part 6 of the extension and the metal wall 2, on the outside of the walls.
• the slot 10 opens onto the interior surface of the walls of the mold, around the entire periphery thereof.
• a distribution channel 12 is arranged in the metal wall 2, in the form of a groove made on the upper face of said metal wall and communicating with the slot 10 over the entire periphery of the mold.
• the casting installation also comprises a hot source 13 of inert gas, for example argon, heated to a temperature of around 700 ° C. by heating means known per se, and a cold source 14 of the same gas, maintained at room temperature, for example 20 ° C.
• a hot source 13 of inert gas for example argon
• a cold source 14 of the same gas maintained at room temperature, for example 20 ° C.
• the pressurized gas from the mixing chamber 17 is distributed in the channel 12 and is injected into the ingot mold through the slot 10.
• the temperature of the gas thus injected can be adjusted by means of the valves 15 and 16 by acting on the ratio of the gas flow rates coming from each source respectively.
• the distribution channel 12 could also be produced in the refractory riser 3, which has the advantage of limiting the heat losses of the gas due to the high temperature, of the order of 800 ° C., of the said riser. It is however easier to carry out the machining of the distribution channel in the metal wall 2, and in this case, to limit the cooling of the gas in contact with the metal of the wall, the temperature of which is only of the order of 100 ° C, the walls of said channel may be coated with an insulating material, such as zirconia or boron nitride.
• a second groove 22 is produced in the lower part 6 of the extension, opposite the groove 12 and also in communication with the slot 10.
• the hot source 13 of gas is connected via the valve 15 directly to this groove 22, and the cold source 14 is connected via the valve 16 to the groove 12.
• the volume defined by these two grooves constitutes both a distribution and a mixing chamber located entirely in the wall 1 of the mold.
• the invention is not limited to the variants described above solely by way of example, and in in particular, the temperature of the injected gas may be adjusted by other means than the mixture of hot and cold gases indicated above.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Continuous Casting (AREA)
• Forging (AREA)
• Treatment Of Steel In Its Molten State (AREA)
• Coating With Molten Metal (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)

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• 1996
  • 1996-04-05 FR FR9604303A patent/FR2747060B1/fr not_active Expired - Fee Related
• 1997
  • 1997-04-03 KR KR10-1998-0707947A patent/KR100449675B1/ko not_active IP Right Cessation
  • 1997-04-03 CA CA002251007A patent/CA2251007C/fr not_active Expired - Fee Related
  • 1997-04-03 EP EP97919471A patent/EP0958073B1/de not_active Expired - Lifetime
  • 1997-04-03 DE DE69714078T patent/DE69714078T2/de not_active Expired - Fee Related
  • 1997-04-03 JP JP9535904A patent/JP2000508244A/ja not_active Abandoned
  • 1997-04-03 ES ES97919471T patent/ES2176732T3/es not_active Expired - Lifetime
  • 1997-04-03 PT PT97919471T patent/PT958073E/pt unknown
  • 1997-04-03 AT AT97919471T patent/ATE220581T1/de not_active IP Right Cessation
  • 1997-04-03 BR BR9709160-0A patent/BR9709160A/pt not_active IP Right Cessation
  • 1997-04-03 WO PCT/FR1997/000596 patent/WO1997037795A1/fr not_active Application Discontinuation
  • 1997-04-03 AU AU23930/97A patent/AU2393097A/en not_active Abandoned
  • 1997-04-03 US US09/155,206 patent/US6260605B1/en not_active Expired - Fee Related

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