EP2552625A1 - Method and device for manufacturing a bi-material ferrule and ferrule thus produced - Google Patents

Abstract

The invention relates to a method for manufacturing a bi-material ferrule, consisting of an outer annular ferrule (17) and an inner annular ferrule bonded together; the bottom pouring of the outer ferrule (17) is carried out in a casting space (7) defined by a wall of a first ingot mould and by an upwardly movable outer wall (8) of a second ingot mould that is concentric to the former; said movable wall (8) of the second ingot mould is raised such as to uncover the skin of the outer ferrule (17) which is solidified thereagainst; bottom pouring and solidification of the inner ferrule are carried out in a casting space defined by said skin and a stationary inner wall (9) of said second ingot mould, the bonding of the two ferrules being carried out by diffusion between said ferrules; and forging and/or one of said bonded ferrules is optionally carried out. The invention also relates to a device for using said method and to a ferrule thus produced.

Description

 Method and device for the manufacture of a bi-material ferrule, and ferrule thus produced.

 The invention relates to the field of metallurgy, and more particularly to the manufacture of bimaterial shells, that is to say of parts formed of two concentric solid parts of annular shapes made of two different materials and secured to each other. the other.

 The industry associated with the use of pressurized reactors - including the nuclear and petrochemical industry - uses such ferrules as constituents of reactor vessels or pressurizers. These ferrules may be manufactured by welding two ferrules initially separated and each manufactured by any method, or a ferrule and a band to be disposed on a surface of the ferrule. The outer shell may, for example, be low-carbon steel type 16MND5 and the inner ferrule be 304L type austenitic stainless steel initially in strip form.

 The outer shell of carbon steel may be obtained by forging, and the inner ferrule of stainless steel may, as has been said, be constituted by a band that is welded to the inner surface of the outer shell. Without limitation, the inner diameter of the inner shell may be between 2 and 9 meters, its height may be between 2 and 5 meters, the thickness of the ferrules may be of the order of 50mm to 600mm for the outer shell and from 5mm to 100mm for the inner shell.

 This relatively simple solution to implement is however not optimal because it is a long process to implement. For a reactor core ferrule having the aforementioned dimensions, welding and welding quality control can take between 5 and 10 weeks - the duration varying depending on the inner dimensions of the ferrule and the thickness of the weld layer desired. The quality of the welding must be checked very carefully and depends on the detection criteria applied.

 The object of the invention is to provide a method of manufacturing such bimaterial ferrules having a better productivity and an excellent reliability.

 To this end, the subject of the invention is a process for manufacturing a bimaterial shell consisting of an annular outer shell and an annular inner shell welded to each other, the two rings being in different materials, characterized in that:

- Source casting and solidification of the outer shell is carried out in a casting space defined by a casting base, a wall of a first mold arranged on the casting base and an outer wall, movable upwards, a second mold, disposed on said base and concentric with the first mold; said movable outer wall of the second mold is lifted so as to reveal the skin of the outer shell which has solidified against it;

 - Source casting and solidification of the inner ferrule is carried out in a casting space delimited by said skin of the outer shell which has previously solidified against the movable outer wall of the second mold and a fixed inner wall of said second ingot mold, the welding of the two rings being effected by diffusion of material between the surfaces of said ferrules which are in contact with one another during solidification;

 - And possibly forging and / or machining of the assembly formed by said welded ferrules.

 The outer wall of the second mold can be lifted when solidification of the outer shell is completed.

 One can start to lift said outer wall of the second mold while the casting of the outer shell is completed, but its solidification is not yet complete.

 One can begin to lift said outer wall of the second mold while the casting of the outer shell is not yet completed.

 The interface between the outer shell and the outer wall of the second mold can be lubricated.

 Forced cooling of the inner wall of the second mold can be achieved.

 The outer shell may be carbon steel and the inner shell of stainless steel.

 The invention also relates to a device for the manufacture of a bimaterial shell consisting of an annular outer shell and an annular inner shell welded to each other, the two rings being of different materials characterized in that it comprises:

 a source casting base;

 an inlet channel and its outlet channels for the liquid metal intended to constitute the material of the outer shell formed in said base, said outlet channels opening into a first casting space defined by the upper face of the base; inner wall of a first mold and the outer wall of a second mold;

an inlet channel and its outlet channels for the liquid metal intended to constitute the material of the inner ferrule formed in said base, said outlet channels opening into a second casting space defined by the upper face of the base, said outer wall of the second mold and the inner wall of the second mold;

 and means for lifting said inner wall of the second mold in a vertical direction, making it possible to discover the solidified inner surface of the outer shell and to put it in contact with the liquid metal intended to constitute the inner shell.

 It may comprise a chuck internally cooled and surrounded by the inner wall of the second mold.

 Said molds may comprise flyweights.

 The outer wall of the second mold may include means for lubricating its interface with the metal intended to form the outer shell.

 The subject of the invention is also a bi-material shell consisting of an annular outer shell and an annular inner shell welded to each other, the two rings being of different materials, characterized in that was obtained by the above method.

 The outer ferrule may be 16MND5 carbon steel and the inner ferrule may be 304L stainless steel.

 The ferrule may be a constituent of a nuclear or petrochemical reactor vessel

The ferrule may be a component of a nuclear reactor pressurizer.

 As will be understood, the invention aims to achieve successively, or almost simultaneously, the solidification of two hollow ingot whose shapes and compositions correspond to those of the two components of the bi-material shell that is desired to obtain. . The solidification of the outer face of the ingot constituting the inner ferrule takes place directly on the inner face of the ingot constituting the outer ferrule, or vice versa, and their joining is carried out by welding-diffusion or co-solidification of the metals constituting them.

 The invention will be better understood on reading the description which follows, with reference to the following appended figures:

 - Figure 1 which shows schematically front sectional view of an installation for implementing the method according to the invention;

 - Figure 2 which shows the same installation when the outer shell is being solidified;

 - Figure 3 which shows the same installation when the outer shell is fully solidified and the inner ferrule being solidified.

FIG. 1 represents an exemplary device according to the invention used for the manufacture of bi-material ferrule. It has as essential elements in the first place a base 1 for the casting source of a slightly conical annular shaped ingot in the example shown. This base 1, in the example shown, comprises in its central part a base 2 of substantially cylindrical shape and protruding from the remainder of the base 1.

 A first mold is defined in part by a cylindrical metal wall 3 deposited on the base 1, and whose lower part encloses the base 2, the upper face constitutes the bottom of the first mold. This wall 3 of the first mold may optionally be cooled externally or internally by circulation of a fluid, or be uncooled. The inner face of the first mold 3 serves to ensure the solidification of the outer portion of the ferrule. For this purpose, the base

1 comprises an inlet channel 4 for liquid metal (for example a low-carbon steel 16MND5), connected to a mother of casting not shown, that is to say to a vertical pipe for receiving the liquid metal s escaping from the bottom of the ladle where its temperature and composition have been regulated. The input channel 4 is divided into a plurality of output channels (of which two 5, 6 are visible in the figures) which open on the upper face of the base 2 and make it possible to send liquid metal to various parts of the annular casting space 7 delimited externally by the wall 3 of the first mold.

 A second mold is defined by the upper face of the base 2 of the base 1, two other cylindrical metal walls 8, 9 concentric, defining between them an annular space 10 for casting the inner part of the ferrule. For this purpose, the base 1 comprises another inlet channel 1 1 for liquid metal (for example a 304L austenitic stainless steel), connected to another casting mother (not shown) that the casting mother feeding the channel entry 4 previously cited. This other input channel 1 1 is preferably divided into a plurality of output channels (two of which 12, 13, located at the rear of the sectional plane of the figures, just like the input channel 1 1) are represented. in dotted lines in the figures. They open on the upper surface of the base

2 and make it possible to send liquid metal into the annular casting space defined by the walls 8, 9 of the second mold.

This second mold has, according to the invention, a feature which is that its outermost wall 8 which separates the two casting spaces 7, 10 (and therefore constitutes an inner wall for the first mold) is vertically movable to the control, in ways that will be seen later. Unrepresented lifting means, controlled by an operator or an automated device, provide this mobility. The innermost wall 9 of the second mold is indifferently fixed or removable. The installation is completed by a cooling system of the innermost wall 9 defining the second mold. For example, this cooling system may be a mandrel 14 cooled internally by circulation of a fluid (for example water) as described in documents FR-A-2,525,131, FR-A-2,543,031, FR-A- 2 676 670 or FR-A-2 676 671 This mandrel 14 is in contact with the innermost wall 9 defining the second mold to ensure its cooling and support during the use of the installation

 The installation is also preferably provided, in the upper parts of the casting spaces 7, 10, weights 15, 16, that is to say, circumferential pieces of refractory material disposed on the fixed walls of the molds:

 the internal face of the first mold 3;

 and the innermost wall 9 of the second mold.

 The role of these weights 15, 16, whose principle is well known in casting of ingots of liquid metal, is to delay the solidification of the metal in the zone facing them, so that it forms in this zone, the as long as possible, a reserve of liquid metal that can feed the axial portion of the ingot to ensure the most homogeneous solidification possible. Indeed, the solidified skins that form from the opposite walls of an ingot mold can grow irregularly and eventually meet locally in an anticipated manner, thus forming "bridges" that trap the still liquid metal. This, solidifying, will decrease in volume and leave empty spaces called "sinkholes" that may be prohibitive for the quality of the ingot and products that would come from it. In the case of ferrules of the type that the invention aims to manufacture, these sinkholes would be more harmful that the ferrules do not undergo or few subsequent plastic deformations that would certainly allow to close the sinkholes. The reserve of liquid metal maintained by the feeder feeds the central portion of the ingot during solidification, and to avoid the formation of the bridges at the origin of the sinkholes or to remelt after their formation.

 Figure 2 shows the installation during casting and solidification of the outer shell 17 made of carbon steel. A carbon steel in the liquid state has been introduced into the device through the inlet channel 4 and has entered the casting space 7 defined by the inner wall of the first mold 3 and the wall outer 8 of the second mold.

In Figure 2, the shell 17 is being solidified and a solidified skin 18 is formed against the walls of the first mold. Figure 3 shows the installation during casting and solidification of the inner ring of stainless steel. After having lifted the cylindrical wall 8 which separated the two casting spaces 7, 10 so as to reveal the solidified skin of the outer shell 7, a stainless steel was introduced through the inlet channel 11. liquid state. It has penetrated into the casting space defined by the outer shell 17 and the other wall defining the casting space of the second shell. This solidifies against the wall 9 cooled by the mandrel 14, and also against the inner surface of the outer shell 17. The temperatures of the two metals (the solidified shell 17 and the liquid metal 18 intended to form the inner annular shell) are chosen at the time of casting of the inner ferrule so that the chemometallurgical diffusion between the carbon steel and the stainless steel is carried out at their interface significantly, or that a co-solidification takes place at this interface. In this way, an excellent quality of the joining of the two ferrules is obtained by a welding-diffusion or co-solidification phenomenon.

 After complete solidification of the stainless steel 18, the first ingot mold 3 and the wall 9 of the second mold are removed, and the blank of the desired bi-material shell is obtained, ready to be forged and / or machined for obtaining the final shell, after also possible heat treatments.

 Advantageously, to facilitate the lifting of the wall 8 between the two casting spaces 7, 10, without damage to the surface of the ferrule 17 can be provided that its face intended to be placed in contact with the outer shell 17 is equipped with means such as oil injection ducts opening onto the surface of the wall, in a manner similar to that practiced for continuous casting molds of steel or pressurized gas injection ducts allowing rapid detachment of the wall 8.

The case where it is expected, for casting the stainless steel inner ferrule, that the outer ferrule 17 is fully solidified, has been described and shown. However, it would remain in accordance with the invention not to wait for this complete solidification and to raise the cylindrical wall 8 and then the casting of the stainless steel 18 while the solidification of the outer shell 17 is not yet fully completed. . It is sufficient that the solidified skin formed on the wall 8 is already strong enough not to be damaged by the movement of the wall 8 and to withstand the pressure that would exert on it the stainless steel 18 during its casting. This solution has the advantage of making the casting while the inner surface of the outer shell is at a relatively high temperature, which increases the intensity of the diffusion of the metals into each other. The cohesion of the two ferrules is thus even better ensured. In the same way, it is conceivable to start the lifting of the cylindrical wall 8 and the casting of the inner shell before the end of the casting of the outer shell 17, when the solidification of the outer shell 17 is nevertheless sufficiently advanced that the skin solidified against the cylindrical wall 8 is sufficiently thick and solid to withstand without damage the displacement of the wall 8 and the pressure exerted by the injected liquid metal 18 to form the inner shell. The solidification of the outer shell 17 can continue even when the wall 8 is in motion.

 The invention, as compared to the techniques known hitherto, makes it possible to eliminate the welding phase of the stainless steel strip and to verify the welds, and thus to gain at least 5 to 10% of the overall manufacturing time of a two-component shell of large size. For example, in a non-limiting way, this may represent 5 to 10 weeks on a manufacturing plan that may be spread over a hundred weeks

 The manufacture of a bi-material ferrule goes through the development of a two-component hollow ingot.

 The mold for making such a shell is predominantly cast iron, the removable internal device being made of cast iron or steel. A circular forging and / or rolling step allows the production of a blank having substantially the final length of the two-component shell, and a minimum blank thickness adapted to the subsequent machining phase. Finally a machining phase is performed to bring the bimetallic ferrule from the blank state to the finished part state with predefined dimensions.

 The invention has been described with reference to the manufacture of bi-material ferrules made of carbon steel for the outer part and stainless steel for the inner part. But of course this example is not limiting and other materials can be used. Similarly, the orders of magnitude of the dimensions that have been given as examples are not limiting.

 In the context of the invention, the rings 17, 18 annular may be cylindrical, frustoconical, rectangular section or other.

 It is also conceivable to cast the inner shell 18 before the outer shell 17, provided to provide cooling means which ensure that it is the inner shell 18 which cools first forcibly. In the same way as described above in the opposite case, the casting of the outer shell 17 can be performed on an inner shell 18 which is already partially or completely solidified or during casting.

Claims

 1. - A method of manufacturing a bi-material ferrule, consisting of an annular outer shell (17) and an annular inner shell (18) welded to each other, the two ferrules being of different materials, characterized in that  the source casting and the solidification of a first shell (17, 18) in a casting space (7, 10) delimited by a casting base (1), a first mold wall (3, 9) are carried out disposed on the casting base (1) and an upwardly movable wall (8) disposed on said base (1) and concentric with the mold wall (3, 9);  said movable wall (8) is lifted so as to reveal the skin of the first shell (17, 18) which has solidified against it;  the source casting and the solidification of the second ferrule (18, 17) are carried out in a casting space delimited by said skin of the first ferrule (17, 18) which has previously solidified against the wall (8) movable and a second mold wall (9, 3) fixed, the welding of the two rings being effected by diffusion of material between the surfaces of said ferrules which are in contact with each other during solidification or by co- solidification;  and the forging and / or machining of the bi-material shell formed by said welded ferrules is optionally carried out.  2. Method according to claim 1 characterized in that the first ferrule is the annular outer shell (17)  3. Method according to claim 1 characterized in that the first ring is the annular inner ring (18)  4. Method according to one of claims 1 to 3, characterized in that lifts said displaceable wall (8) when the solidification of the first ferrule (17, 18) is completed.  5. Method according to one of claims 1 to 3, characterized in that begins to lift said movable wall (8) while the casting of the first ferrule (17, 18) is completed, but its solidification n ' is not finished yet.  6. Method according to one of claims 1 to 3, characterized in that begins to lift said movable wall (8) while the casting of the first ferrule (17, 18) is not yet complete.  7. Method according to one of claims 1 to 6, characterized in that lubricates the interface between the first shell (17, 18) and the movable wall (8).  8. Method according to one of claims 1 to 6, characterized in that it blows a gas under pressure at the interface between the first shell (17, 18) and the movable wall (8). 9. Method according to one of claims 1 to 8, characterized in that a forced cooling of one and / or the other of the wall (s) (3, 9) of the mold.  10. Method according to one of claims 1 to 9, characterized in that the outer shell (17) is carbon steel and the inner shell of stainless steel.  1 1. Device for the manufacture of a bi-material shell consisting of an annular outer shell (17) and an annular inner shell (18) welded to each other, the two rings being of different materials, characterized in that it comprises:  a source casting base (1);  an inlet channel (4) and its outlet channels (5, 6) for the liquid metal intended to constitute the material of the outer shell (17) formed in said base (1), said outlet channels (5, 6) opening into a first casting space (7) defined by the upper face of the base (1), an inner wall of a first mold (3) and the outer wall (8) of a second mold;  an inlet channel (1 1) and its outlet channels (12, 13) for the liquid metal (18) intended to constitute the material of the inner ring formed in said base (1), said outlet channels (12) , 13) opening into a second casting space (10) defined by the upper face of the base (1), said outer wall (8) of the second mold and the inner wall (9) of the second mold;  and means for lifting said outer wall (8) of the second mold in a vertical direction, making it possible to discover the solidified inner surface of the outer shell (17) and to put it in contact with the liquid metal (18) intended to constitute the inner ferrule.  12. Device according to claim 1 1, characterized in that it comprises cooling means of the inner wall (9) of the second mold, such as a chuck (14) internally cooled and surrounded by the inner wall (9). ) of the second mold.  13. Device according to claim 1 1 or 12, characterized in that said molds comprise flyweights (15, 16).  14. Device according to one of claims 1 1 to 13, characterized in that the outer wall (8) of the second mold has means for lubricating its interface with the metal intended to form the outer shell (17).  15. Device according to one of claims 1 1 to 13, characterized in that the outer wall (8) of the second mold comprises means for blowing gas under pressure at its interface with the metal intended to form the outer shell (17). 16. Bimaterial shell consisting of an annular outer shell (17) and an annular inner shell (18) welded to each other, the two rings being in different materials, characterized in that it was obtained by the method according to one of claims 1 to 10.  17. Ferrule according to claim 16, characterized in that the outer ferrule is 16MND5 carbon steel and in that the inner ferrule is 304L stainless steel.  18. Ferrule according to claim 16 or 17, characterized in that it is a reactor vessel component of nuclear or petrochemical reactor.  19. Ferrule according to claim 16 or 17, characterized in that it is a component of a nuclear reactor pressurizer.