FR2666756A1 - CYLINDER FOR THE CONTINUOUS CASTING OF METAL STRIPS BETWEEN TWO CYLINDERS, PARTICULARLY STEEL, AND METHOD FOR MANUFACTURING THE SAME. - Google Patents

Abstract

Cylinder (1) for continuous casting of molten metal between two cylinders or onto a cylinder, in particular of steel, comprising an outer shell (3) intended to come into contact with the liquid metal and a rigid inner core (2) fixed to the ferrule, characterized in that the ferrule (3) and the core (2) are fixed together by a gasket (5) of a material whose melting point is inside that of the two constituent materials of the ferrule and the core, and which remains in the solid state at the local operating temperature of the cylinder. The core (2) is chosen from a material whose coefficient of expansion is substantially greater than that of the material of the shell (3). The connecting joint (5) can be made by brazing a suitable material or by tin soldering. The thickness of the ferrule (3) is much less than that of the ferrules used until now and fixed to the internal core by dovetail, which reduces its cost and its manufacturing difficulty.

Description

The present invention relates to the continuous casting of metal strips

  between two cylinders or on a single cylinder, in particular of steel, of the type comprising an energetically cooled outer ferrule intended to come into contact with the metal

  liquid, and a rigid inner core.

  We know that the cylinders used today-

  Lement, in devices for continuous casting of liquid metal between two cylinders with parallel axes and rotating in opposite directions or on a single rotary cylinder, comprise an outer ferrule in contact with which the molten liquid metal comes to solidify This ferrule is mechanically fixed by example by a "dovetail" type assembly to a rigid, solid, solid or hollow inner core, ensuring the mechanical strength of the assembly The ferrule is usually made of Cu or Cu alloy It must

  necessarily be thick, to allow control

  the deformations of the external surface, which ensure the geometry of the cast metal strip, while its useful part for heat exchange has a reduced thickness, less than 50 mm for example (30 mm of copper plus 12 mm of internal channels

  for circulation of a coolant).

  The blanks of such ferrules have an imposing mass, for example of 5 to 6 tonnes, and are extremely expensive, due to the cost and the

  mass of the aforementioned alloy, and also of its machining.

  In some cases, this very high cost alone could jeopardize the interest of using a

  continuous casting machine between cylinders.

  The invention therefore aims to provide a

  cylinder made in such a way that the manufacturing cost

  cation of its shell is considerably reduced, while adequately fulfilling its main functions of heat exchanger with metal

  liquid flow on the one hand, and on the other hand of dimen-

  correct operation of the cast product.

  According to the invention, the ferrule and the core are secured to each other by a joint of a material whose melting point is lower than that of the two materials constituting the ferrule and the core, and which remains at solid state at temperature

of local use of the cylinder.

  According to an embodiment of the invention

  tion, the joint is made by brazing and made up

  by a ribbon previously deposited on the former side

  of the core or on the inner face of the shell, for example a silver alloy with 56% Ag, 2% Ni and 42% Cu by weight, (designated B Ag 13 a according to the AWS standard), which has good wettability properties with liquid steel, or an alloy with

  copper, 68% Cu, 23% Mn and 9% Ni by weight.

  According to another possible embodiment of the invention, the seal is poured in the liquid state in a reserved space between the ferrule and the core. Such a weld seal can be

example of a tin alloy.

  According to a preferred variant of the

  vention, the core is chosen from a material whose coefficient of expansion is higher than that of

constituent material of the shell.

  According to one embodiment of the method of

  manufacture of the cylinder, also covered by the invention

  tion, a) the ferrule and the core are machined, b) the surfaces to be brazed are etched and optionally a fluxing of the said faces is carried out, c) an internal surface of the ferrule or on the external surface of the nucleus is put in place suitable brazing material, d) the ferrule is placed on the core, e) the brazing of the ferrule is carried out in an oven, f) to regenerate the properties of the ferrule's material if necessary, a hyper quenching is carried out, then a tempering, g) and finally, if necessary, machining is carried out

end of the shell.

  Other features and advantages of

  the invention will appear during the description

  which follows, made with reference to the appended drawing which illustrates an embodiment thereof by way of example

not limiting.

  The single figure is a partial axial sectional view of a cylinder for continuous casting of metal strips, in which the connection between the outer shell and the rigid internal core is achieved by

soldering.

  The cylinder 1 shown in the drawing is intended for the continuous casting of metal strips between two parallel cylinders, in particular steel strips. This cylinder 1, of axis XX, comprises a rigid internal core 2 and an external ferrule 3, the external face of which is intended to come into contact with the liquid metal and the thickness of which is of the order of 50-60 mm , is less than that of the core 2 The latter can extend radially either over only a part rn of the radius r of its external surface, in contact with the internal face of the ferrule 3, or, as shown in 2 a, over the entire radius r thus forming a

full room.

  The ferrule and the core 2 are fixed together by a joint of a material whose melting point is lower than that of the two constituent materials of the ferrule 3 and of the core 2, and which remains in the solid state at the temperature of local operation of

  cylinder 1, that is to say in the area of said seal.

  Cooling channels such as 4 are formed longitudinally in the shell 3 at one

  distance of 10 to 15 mm from the joint plane.

  In the embodiment shown in the drawing, the seal 5 is produced by brazing a suitably chosen material, which can be constituted for example in the form of a tape previously deposited, either on the external face of the

  core 2, either on the inside of the ferrule 3.

  As an example of an embodiment, the ferrule 3 can conventionally be made of a Cu-Cr-Zr alloy. The core 2 can be an austenitic nickel cast iron (for example the so-called "Ni-Resist" cast iron) or, more generally, in any material which can be brazed on the aforementioned copper alloy and whose coefficient of expansion is preferably

  higher than the material of the shell 3.

  The Cu-Cr-Zr alloy can also be replaced by copper reinforced with a dispersion of oxides, called

  by the "ODS copper" specialists, whose characteristics

  teristics as well as the manufacturing process are described in the patent application filed the same day as the present application in the name of the Applicant and entitled "Continuous metal casting cylinder,

especially steel. "

  According to a second embodiment of the cylinder 1, not illustrated in the drawing, the connection between the core 2 and the shell 3 is obtained by casting a seal in the liquid state in a space

  reserved interstitial between the shell 3 and the core 2.

  This preliminary space may for example have a width of 1 to 2 mm, and be provided with wires serving as spacers. Copper plating of the external surface of the core 2 is carried out beforehand to allow welding. In the two cases described above, the thickness of the ferrule 3 is significantly less than that of the massive dovetail ferrule used until now, which considerably reduces its

  cost and its manufacturing difficulty, and therefore

  quent facilitates its supply.

  A description will now be given of embodiments of the processes for manufacturing cylinder 1.

according to the invention.

  1 Cylinder manufacturing process by

brazen.

  The brazing operation consists in placing between the two parts to be assembled a thin layer of an alloy whose melting point is lower than that of the parts. The whole is brought to a temperature higher than the melting point of the alloy. brazing known as brazing temperature The brazing alloy melts and dissolves a little of the two parts, which raises the melting point of the bath, which re-solidifies in a few minutes The thickness of the brazed joint is very low and its mechanical resistance is general excellent. To properly solder the ferrule 3 on the core 2, the ferrule being made of Cu-Cr-Zr alloy, it is necessary to use brazing materials with high melting point, for example B Ag 13 a (according to AWS standard) which has the following composition: 56% Ag, 2% Ni, 42% Cu Furthermore, thanks to its coefficient of expansion greater than that of the shell 3, the core puts the seal 5 in compression

  and the ferrule 3 at the time of soldering.

  On the other hand, given the massiveness of the parts, the brazing must be done in the oven, which implies an initial placement of the brazing material in the form of tape (for example 1 to 2 kg of tape) Finally the oxidation and deformations associated with heat treatments mean that it will not be possible to recover core 2 after wear

  of ferrule 3, if not at its material value.

  The process for manufacturing a cylinder 1 according to the invention, the shell 3 of which is made of the aforementioned Cu-Cr-Zr alloy, is as follows: a) the blanks formed by the shell 3 and the core 2 are machined with a very tight tolerance, defined according to the dimensional characteristics of the device considered,

  b) the surfaces to be brazed are scoured, and event-

  tally a fluxing of these faces; c) an appropriate brazing material is placed on one of the surfaces facing the ferrule 3 and the core 2, for example a strip 5 or 10 thousandths of a mm thick, of "B Ag 13 a" , which is welded by points to make it hold; d) the ferrule 3 is placed on the core 2, and thermal shrinking is carried out to ensure provisional assembly; e) the cylinder 1 is brazed in an oven, for example at 1000 ° C. for 1 to 2 hours according to a two-phase operating mode which will be detailed below;

  f) and if necessary, to regenerate the properties of the ma-

  constituent material of the ferrule, quenching or rather hyperquenching at a minimum speed of 15 to 20 C / s from 1000 'C to at least 400' C, with water or oil (the choice must be done to avoid any risk of splitting), then the ferrule is subjected to an income, for example at 4800 C for 2 hours, g) and finally if necessary, it is machined

end of cylinder 1.

  The actual brazing operation is usually carried out at a heating rate of the order of 300 C / h to the brazing temperature, which of course depends on the brazing material used. It is for example 870 ° C. for B Ag

  13 a and 340 C for the copper alloy.

  This operation is followed, either later-

  ment, either directly if the oven allows, a diffusion phase by slower temperature rise, of the order of 100 ° C./h, from the brazing temperature to the hyper-tempering temperature of the shell , which is between 990 and 1000 'C This

  second phase is necessary to regenerate the pro-

  mechanical properties of the Cu-Cr-Zr alloy and thus avoid the subsequent risks of decohesion of the ferrule But it must be carried out more moderately at heating rate to prevent too sudden appearance of liquid which would escape from the joint by gravity, before the broadcast could take place

correctly.

  It will be noted that this post brazing heat treatment phase becomes unnecessary in the case of an ODS copper ferrule. It is then possible to use “B Ag-1” type brazings, containing zinc with a significantly lower melting point (700 ' C approximately) Quenching is no longer necessary, as is therefore the

income consecutive to this.

  2 Method of manufacturing the cylinder by

tin welding.

  In this second embodiment of the invention, the technique used is rather similar

  to that of the collage, due to the absence of veri-

  metallurgical bonding table As in the case of an adhesive, the metallic properties are correct in shear but less good in pulling out (traction) Of course the mechanical properties of a tin joint are much lower than that

of a brazed joint.

  The establishment of the tin alloy is done by casting between the ferrule 3 and the core 2 to be assembled, heated to a temperature T which can be

  250-300 ° C depending on the tin alloy chosen.

  The heating being very weak, it is possible to assemble completely machined parts, which can lead to simplifications of ranges. In the same way, disassembly by reheating is done very easily and the rigid internal core 2 can

normally be recovered.

  The invention is capable of various variants: thus any suitable material other than those mentioned above for brazing and welding the two parts of the cylinder 1 can be used, with the corresponding variants of the manufacturing process and assembly The cylinder can also be adapted to the casting of metals other than steel.

Claims (9)

  1 cylinder (1) for continuous casting of molten metal, in particular steel, between two cylinders, or on a cylinder, comprising an outer ferrule (3) intended to come into contact with liquid metal and a rigid inner core (2) fixed to the ferrule, characterized in that the ferrule (3) and the core (2) are joined to one another by a seal   (5) a material with a lower melting point   laughing at that of the two constituent materials of the shell and the nucleus, and which remains in the solid state at the   local operating temperature of the cylinder.   2 cylinder according to claim 1, charac-   terized in that the joint (5) is produced by brazing and consists of a tape previously deposited on the outer face of the core or on the inner face of the ferrule.   3 cylinder according to claim 1, charac-   terized in that the seal (5) is poured in the liquid state in a reserved interstitial space between the shell and core.   4 cylinder according to claim 1, 2 or 3, characterized in that the seal (5) is a brazed seal formed by a silver alloy at 56% Ag, 2% Ni and 42% Cu approximately by weight.   Cylinder according to claim 1, 2 or 3, characterized in that the joint (5) is a brazed joint formed by a 68% Cu, 25% copper alloy Mn and 3% Ni by weight approximately.   6 Cylinder according to any one of   previous claims, characterized in that the   ferrule (3) has a thickness of approximately 50 to 60 mm.   7 cylinder according to claim 6, charac-   terized in that the ferrule (3) has longitudinal internal cooling channels (4) formed at a depth of approximately 10 to 15 mm from its internal surface. 8 cylinder according to claim 1, 2 or 3, characterized in that the core is chosen in one   material with a higher coefficient of expansion   laughing at that of the constituent material of the shell.   9 Cylinder according to any one of   Claims 1 to 8, characterized in that the ferrule   (3) is made of a Cu-Cr-Zr alloy, or of reinforced copper by dispersion of oxides.   Method of manufacturing a continuous casting cylinder according to claim 2, characterized in that: a) the ferrule (3) and the core (2) are machined, b) the surfaces to be brazed are etched and optionally fluxed said faces, c) a suitable brazing material (5) is placed on the internal surface of the ferrule or on the external surface of the core, d) the ferrule (3) is placed on the core (2), e) the ferrule is brazed in an oven, for example at 1000 ° C. for 1 hour to 2 hours, f) to regenerate the properties of the constituent material of the ferrule if necessary, a hyper quenching is carried out, followed by tempering, g) and finally, if necessary, a machining is carried out end of the shell.   11 A method of manufacturing a continuous casting cylinder according to claim 3, characterized in that: a) the ferrule (3) and the core (2) are machined, 1 1 b) the core (2) is inserted into the ferrule (3) leaving between them an interstitial space and they are heated to an appropriate temperature (T), c) a solder joint made of a material found in the state is poured inside said space liquid at said temperature (T).   12 Method according to claim 9, characterized in that the solder joint is made of a tin alloy, and in that the temperature (T) is 250 'to 300 C.