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
• • 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
  • B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
  • B22D11/0637—Accessories therefor
  • B22D11/0697—Accessories therefor for casting in a protected atmosphere
• • 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
  • B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
  • B22D11/0622—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars formed by two casting wheels
• • 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
  • B22D11/16—Controlling or regulating processes or operations

Definitions

• the invention relates to the casting of thin metallurgical products obtained directly from liquid metal. More specifically, it relates to installations for casting thin strips, in particular steel, by solidifying the liquid metal against two close cylinders with horizontal axes, rotated in opposite directions and internally cooled.
• the thickness profile of the strip depends closely on the shape of the external surfaces of the cylinders in the casting space.
• this profile of the strip should be rectangular or slightly convex to ensure the smooth running of the cold rolling step and a satisfactory regularity of the thickness of the final product.
• the generatrices of each cylinder should remain rectilinear or slightly concave, in particular at the level of the neck, ie of the region of the casting space where the cylinders are closest to each other. other. In practice, this is not the case, due to the intense thermal stresses to which the cylinders are subjected.
• this expansion is usually anticipated by giving the exterior surface of each cylinder a slightly concave profile, having a "domed" in the center of the cylinder, that is to say a difference in radius relative to the edges.
• the optimum value of this cold convex varies according to the dimensions of the cylinder, and can be, for example, around 0.5 mm. In this way, during the expansion of the cylinder, there is a reduction in this convexity, and the profile of the cylinder in the casting space tends to approach a rectilinear profile.
• this convex during casting depends on the materials of the cylinders and the cooling system of the cooled ferrule which constitutes the periphery of the cylinder, of the geometry of this ferrule, and also of its method of attachment to the core of the cylinder, which can allow greater or lesser expansion of the ferrule. But it also depends on operating conditions which can vary from one casting to another, or even also during the same casting, such as the height of liquid metal present in the casting space and the intensity of the heat flow extracted from the metal. by the cylinder cooling means.
• Document JP-A-58-23549 shows an installation for casting a thin strip by depositing liquid metal on a single cylinder.
• the cylinder is cooled by sending on its surface, upstream of the casting zone, a fluid whose flow can be modulated along the width of the cylinder, so as to control the convexity of the cylinder.
• Data collected by thickness gauges measuring the thickness of the strip cast at different points are used for this purpose.
• the object of the invention is to provide operators with a means enabling them to adjust the convexity of the cylinders during casting with sufficient latitude.
• the subject of the invention is a process for casting a metal strip, in particular steel, according to which the said strip is solidified by adding liquid metal between two counter-rotating cylinders with horizontal axes cooled by internal circulation. of a cooling fluid, defining between them a pouring space, and the external surfaces of which have a roughness, and an inerting of said pouring space is carried out by insufflation of a given quantity of a gas or of a mixture of gases through a cover covering said pouring space, characterized in that the convexity of said cylinders is adjusted by modulating the quantity supplied and / or the nature of said gas or the composition of said gas mixture, at least in the vicinity of the surface of each cylinder upstream from its contact zone with liquid metal.
• the invention also relates to an installation for casting a metal strip, in particular steel, of the type comprising two counter-rotating cylinders with horizontal axes, cooled by an internal circulation of a cooling fluid, defining between them a casting space intended receiving the liquid metal, and the external surfaces of which have a roughness, a device for blowing a gas or a mixture of gases through a cover covering said pouring space, and means for modulating the quantity blown in and / or the nature of said gas or the composition of said gas mixture at least in the vicinity of the surface of each cylinder upstream from its zone of contact with the liquid metal, characterized in that it comprises means for measuring or calculating the bulge cylinders in said casting space, or a quantity representative of said convexity of the cylinders - in said casting space, and means - for automatically controlling said modulation of the quantity supplied and / or of the nature of said gas as a function of the data collected by said means for measuring or calculating the crown of the cylinders in the casting space, or of a quantity
• the invention consists in modulating the quantity and / or the composition of the gas present in the immediate vicinity of the surface of each cylinder, just before the latter comes into contact with the meniscus of liquid metal. , or these two parameters, in order to adjust the convexity of the cylinders.
• the quantity and composition of the gas present in the hollow parts of the surface of the cylinder have a direct influence on the coefficient of heat transfer between the metal and the cylinder. It is through this that we will vary the heat flow extracted from the metal on which the expansion of the cylinder, and therefore its crown, depends. This variation of the crown of the cylinders can be carried out during casting, depending on the particular conditions at the time.
• A is a heat transfer coefficient, expressed in MW / m 2 .s 0.35 , the value of which depends on the conditions prevailing at the metal-cylinder interface.
• A depends on the conditions at the metal-cylinder interface.
• One of the most important features of this interface is the roughness of the surface of the cooled cylinder shell. It has been found that a perfectly smooth ferrule surface and having a uniform thermal conductivity could cause the appearance of defects on the cast strip. The reason is that the effect of contraction of the skin of the strip during its cooling opposes the adhesion forces of this same skin on the shell. This competition is a source of tension inside the skin, which can lead to the appearance of superficial micro-cracks.
• the recessed areas are filled with the gas which constitutes the boundary layer of the atmosphere overhanging the rotating cylinder, and which the latter carries with it.
• the gas which filled them is trapped there. It is by means of this gas that the cooled walls of the hollows which are not in contact with the skin will nevertheless participate in the extraction of the heat flux from the metal.
• the calculated value of the coefficient A takes into account the effect of the roughness of the shell on the overall heat transfer between the metal and the cylinder.
• the surface of the liquid steel is not exposed to the ambient air, otherwise there would be pollution of the metal by the formation of oxidized inclusions. This formation would also lead to consumption of the most easily oxidizable elements present in the steel.
• the pouring space is most often capped with a device forming a cover. Under this cover, a gas totally inert towards the liquid metal (for example argon) is blown in the direction of the surface of the liquid steel, or a gas which it is tolerable for it to partially dissolve. in liquid metal (for example nitrogen in the case where a stainless steel is poured into which a low nitrogen content is not particularly sought after), or a mixture of such gases.
• both of the cylinders and of the cover does not generally bear on the cylinders, but is kept at a very short distance from their surface (a few mm).
• the disadvantage of such an arrangement is that the cylinders carry with them, in particular in the hollows of their surface, a boundary layer of air whose oxidizing power is unfavorable to the quality of the metal which comes into contact with it at the meniscus. and below.
• this problem is remedied by carrying out, in addition to the insufflation directed towards the surface of the liquid steel, an insufflation of argon and / or nitrogen in the immediate vicinity of the surface of the cylinders, where it is overhung by the cover.
• the quantity of gas present in the recesses is also a function of the flow of blown gas, in particular in the immediate vicinity of the cylinders.
• the quantity of gas remaining present in each recessed range is therefore lower in the case of the use of nitrogen than in the case of the use of argon.
• nitrogen cannot hinder the penetration of the metal into the hollows as much as argon, and we find us in solidification conditions closer to those of a smooth cylinder.
• it is argon which essentially constitutes the gaseous boundary layer entrained by the cylinders up to the meniscus, the heat transfer coefficient A between the cylinder and the metal skin during solidification is lower than in the case where the boundary layer is constituted by nitrogen.
• a 0 can for example vary between 4.2 and 4.8 and K is of the order of 0.025 in the range of lower argon contents or equal to 30%. Beyond this limit, there is a marked decrease in the influence of the argon content on the value of A. In the case of ferritic stainless steels, the influence of the argon content on A is less marked, and it becomes relatively weak in the case of carbon steels.
• the variant of the process according to the invention in which the crowning of the cylinders is adjusted by varying the nature of the inerting gas or the composition of the inerting gas mixture finds its preferred application in the casting of stainless steels, in particular austenitics.
• the variant according to which the setting of the convex is obtained only by modulating the gas flow blown is intended more particularly for carbon steels. It is understood that it is also possible to play on both parameters, bit rate and composition.
• the operator can experimentally determine the value of the thermal flux passing through the cylinder, and deduce therefrom by calculation the value of A, knowing the casting speed. From this value of A, thanks to previous experiences or modeling techniques, for each type of roughness of the cylinders and for each grade category, it deduces the curvature of the cylinder which would be to be expected if the cylinder had a perfectly straight generator when cold.
• the operator finally deduces the shape correction which it is preferable to apply construction to the cylinder so that, in at least most of the real experimental conditions, it is possible to obtain a cylinder whose generatrices would take, hot , the rectilinear or slightly concave shape desired, just by playing on the composition and / or the flow rate of the inerting gas, in accordance with the invention.
• the operator has the possibility of using either pure nitrogen or pure argon in order to be able, for a given gas flow rate and casting conditions, to have the choice between two rounded cylinders. But of course, it is preferable to give the possibility of using a mixture of these two gases (or of any other suitable gases) in respective proportions varying at will according to the needs of the setting of the convex, so as to carry out this setting as precisely as possible.
• the casting installation comprises two cylinders 1, 1 'brought together, energized internally cooled and rotated in opposite directions around their horizontal axes by means not shown, and means for supplying liquid steel 2 into the 'pouring space defined by the external surfaces 3, 3' of the cylinders 1, 1 'and closed laterally by two refractory plates, one of which 4 is visible in FIG. 1.
• These supply means comprise a nozzle 5 connected to a distributor not shown, and whose lower end plunges under the surface 6 of the liquid steel 2 which contains the casting space.
• the liquid steel 2 begins its solidification on the external surfaces 3, 3 'of the cylinders 1, 1' by forming skins 7, 7 ', the junction of which at the neck 8, that is to say of the zone where the difference between the cylinders 1, 1 ′ is the smallest, gives rise to a solidified strip 9 a few mm thick, which is continuously extracted from the casting installation.
• the inerting of the pouring space is provided by a cover 10 crossed by the nozzle 5, and which is supported on two blocks 11, 11 'extending over the entire width of the cylinders 1, 1'.
• the lower faces 12, 12 'of these blocks 11, 11' are shaped so as to match the curvatures of the external surfaces 3, 3 'of the cylinders 1, 1' and to be defined with them, when the inerting device is in service , a space 13, 13 ′ of width "e" equal to a few mm.
• the inerting gas is first supplied by a pipe 14 passing through the cover 10 and opening above the surface 6 of the liquid steel 2 present in the casting space.
• This pipe 14 is connected to a gas tank 15, containing for example nitrogen or argon, and the flow rate and the blowing pressure of which are controlled by a valve 16.
• a blowing of gas with controlled flow rates and composition is carried out through the blocks 11, 11 ′.
• a nitrogen tank 17 provided with a valve 18 and an argon tank 19 provided with a valve 20 are connected to a mixing chamber 21. It is from this mixing chamber 21 that the gas or, more generally, the gaseous mixture which, according to the invention, will constitute the boundary layer entrained by the external surfaces of the cylinders 1, 1 ′ up to their zones of contact with the surface 6 of the liquid metal contained in the pouring space which constitute the meniscus.
• a pipe 22 provided with a valve 23 leaves the mixing chamber 21 and brings a portion of the gas mixture which is there in the block 11, where a slot 24 (or a plurality of close holes, or a porous element) distributes it as uniformly as possible in the space 13 defined by the lower face 12 of the block 11 and the external face 3 of the cylinder 1.
• the valve 23 makes it possible to adjust the flow rate and the pressure of the mixture gaseous.
• a symmetrical device, comprising a line 22 'provided with a valve 23' also brings the gas mixture into the block 11 'then, through a slot 24', into the space 13 'separating the block 11' and the cylinder 1 ' .
• Another variant of the device according to the invention consists, as in the French application 94 14571 already cited, in providing inside each block 11, 11 'a second slot (or another functionally equivalent member) similar to the slot 24 , 24 ', and opening upstream of the latter in the space 13, 13' relative to the progression of the surface 3, 3 'of the cylinder 1, 1'.
• This second slot directs the gas which comes from it towards the outside of the space 13, 13 ', while the slot 24, 24' directs the gas which leaves there towards the casting space, therefore in the direction of progression. from the surface 3, 3 'of the cylinder 1, 1'.
• the regulation of the convexity of the cylinders 1, 1' finds it easier.
• the gas or the gaseous mixture brought into the spaces 13, 13 ′ separating the blocks 11, 11 ′ and the cylinders 1, 1 ′ can be found not only in the state gaseous, as has been implicitly assumed so far, but also in the liquid state.
• the inerting device which has just been described constitutes only one example of implementation of the invention, and that any other device making it possible to control the composition of the gas present above the casting space, and in particular of the gaseous boundary layer entrained by the external surface of each cylinder up to the meniscus could also be suitable.
• the operator which is responsible for the operation of the casting installation must have a certain amount of information for s 'ensure that the composition and the flow rate of the inerting gas adopted effectively lead to the desired convexity, and therefore to an adequate quality for the product.
• one possibility consists in continuously collecting the data (flow rate of cooling water, variation of its temperature between inlet and outlet of the cylinder) making it possible to calculate the heat flux passing through the cylinder, to calculate it at close intervals and to deduce the curvature such as mathematical models and / or prior calibrations make it possible to predict it.
• Another way of proceeding is to continuously measure the volume of the cylinders in an area as close as possible to the casting space, to deduce therefrom the value of the volume in these contact zones and to adjust the composition of the gas. inerting accordingly.
• This curved measurement can be carried out using, for example, a set of non-contact shape measurement sensors, such as capacitive sensors or laser sensors, distributed along at least one generator of one of the cylinders. , or better, of two sets of such sensors each installed on a different cylinder.
• the single figure shows schematically such sensors 25, 25 ', which are connected to a calculation unit 26.
• This also receives the information cited above which allows it to calculate the heat fluxes passing through the cylinders 1, 1', and it consequently controls the respective openings of the valves 18, 20, in order to regulate the flow rate and the composition of the gas mixture to the values which provide a convex considered optimal to the cylinders 1, 1 ′.
• the measurement of the thermal profile of the strip along its width, carried out at the outlet of the cylinders, can also give at least qualitative indications on the bulge imposed by the cylinders, since the temperature difference between the center of the strip and the areas closer to the banks is an index of variations in the thickness of the strip.
• the invention is, of course, not limited to the casting of steel strips, and can be applied to the casting of other metallic materials.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Continuous Casting (AREA)
• Metal Rolling (AREA)
• Output Control And Ontrol Of Special Type Engine (AREA)
• Forging (AREA)
• Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)
• Sorption Type Refrigeration Machines (AREA)
• Compressor (AREA)
• Alcoholic Beverages (AREA)

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• 1995
  • 1995-04-07 FR FR9504139A patent/FR2732627B1/fr not_active Expired - Fee Related
• 1996
  • 1996-03-22 PT PT96400602T patent/PT736350E/pt unknown
  • 1996-03-22 DK DK96400602T patent/DK0736350T3/da active
  • 1996-03-22 DE DE69615250T patent/DE69615250T2/de not_active Expired - Lifetime
  • 1996-03-22 EP EP96400602A patent/EP0736350B1/fr not_active Expired - Lifetime
  • 1996-03-22 AT AT96400602T patent/ATE205760T1/de active
  • 1996-03-22 ES ES96400602T patent/ES2160782T3/es not_active Expired - Lifetime
  • 1996-03-27 ZA ZA962428A patent/ZA962428B/xx unknown
  • 1996-03-27 US US08/622,783 patent/US5787967A/en not_active Expired - Lifetime
  • 1996-03-28 AU AU50340/96A patent/AU698709B2/en not_active Ceased
  • 1996-04-02 SK SK433-96A patent/SK282371B6/sk not_active IP Right Cessation
  • 1996-04-03 CA CA002173391A patent/CA2173391C/fr not_active Expired - Fee Related
  • 1996-04-03 MX MX9601307A patent/MX9601307A/es unknown
  • 1996-04-04 KR KR1019960010256A patent/KR100425968B1/ko not_active IP Right Cessation
  • 1996-04-04 CZ CZ19961002A patent/CZ289395B6/cs not_active IP Right Cessation
  • 1996-04-05 RU RU96106418A patent/RU2147969C1/ru not_active IP Right Cessation
  • 1996-04-05 RO RO96-00737A patent/RO115944B1/ro unknown
  • 1996-04-05 UA UA96041353A patent/UA43352C2/uk unknown
  • 1996-04-05 PL PL96313657A patent/PL180531B1/pl not_active IP Right Cessation
  • 1996-04-05 CN CN96104575A patent/CN1066364C/zh not_active Expired - Fee Related
  • 1996-04-05 TR TR96/00294A patent/TR199600294A2/xx unknown
  • 1996-04-08 JP JP11126496A patent/JP4016297B2/ja not_active Expired - Lifetime
  • 1996-04-08 BR BR9601286A patent/BR9601286A/pt not_active IP Right Cessation

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