EP0594633B1 - Process and device for producing metal strip and laminates - Google Patents

Abstract

A stream (6) of superheated molten metal is deposited from a container (9), in a consolidated form by means of a pouring nozzle or separated into drops by a gaseous medium, at a casting point (5) on the inner surface of a wound strip or laminate rotating in and together with a mould (1). An initially liquid metal film (8) is thus produced to which a fluid coolant, preferably a deep-cooled liquefied gas such as argon or nitrogen, is applied from a cooling nozzle (12) at a cooling station (13) staggered in the direction of rotation in relation to the casting point (5), by means of which a substantial proportion of the superheating and melting heat of the metal film (8) is largely dissipated by evaporation. Depending on the residual heat reamining after the cooling cycle, the metal film (8) remains either insulated from the previously applied innermost metal layer (7), thus producing a strip, or melts with it, thus forming a substantially rotation-symmetrical laminate.

Description

The invention relates to a method for producing strips and composite bodies made of metal according to the preamble of claim 1 and an apparatus for performing the method.

Processes for the rapid solidification of metals have recently become increasingly important, since they allow the production of novel materials with in some cases improved or unusual structures and thus material properties. With increasing rate of solidification, there is an ever greater deviation from the equilibria, as determined by the state diagram, since the extremely short diffusion times make it difficult to set these equilibria. On the one hand, this leads to ever finer morphologies, e.g. B. the formation of finer dendrites or eutectics while reducing the interdendritic or cellular segregation and can lead to the formation of highly metastable structures with certain materials, up to the formation of metallic glasses in special cases. In the case of crystalline solidification, there is an advantage in the fact that the solubility range of certain desired elements is greatly expanded, while undesired precipitations can be suppressed.

The basis of all rapid solidification processes is the rapid removal of heat. This process is determined on the one hand by the thermal conductivity of the metal, on the other hand by the mechanism of heat transfer at the phase boundary to the heat-extracting medium. During the Heat transfer, characterized by the heat transfer coefficient, can be optimized in a wide range by choosing the right procedural conditions, the heat transport in the metal, which is characterized by the thermal conductivity coefficient, can only be improved by choosing small transport routes. For this reason, all of the methods of rapid solidification known today lead to castings which have a small thickness, at least in the spatial direction of heat transport. Examples of this are the gossip mold, where a drop of metal is suddenly formed into a film between two metal plates, the melt-spinning process, where a metal jet is usually applied to the outer surface of a rapidly rotating roller, which is continuously influenced by the acceleration and by the Heat removal from the roller used as a quenching body forms a thin metal film and certain powder atomization processes, where a metal jet is broken up into small drops under the influence of an atomization medium, which can be a gas or a liquid, which solidify in flight and are then fed to powder metallurgical compaction processes can be. The theoretical foundations of fast solidification processes are e.g. B. in a publication by R. Mehrabian, "Rapid Solidification", reproduced in "Rapid Solidification Technology Source Book", American Society for Metals 1983, pp. 186-209 in a clear manner. The most common methods can be found in chapters by G. Haour, H. Bode, "From Melt to Wire" and RE Maringer, "Payoff Decade for Advanced Material" from the same book, pp. 111-120 and p.121-128.

The process of spray compacting offers the possibility of producing larger cast structures, whereby semi-finished products can be produced in near-net-shape dimensions at higher cooling speeds. This is usually around 50 - 150 K above the liquidus temperature superheated melt usually atomized with the help of argon or nitrogen, similar to the case with powder production. During the flight, a substantial part of the overheating heat from the drops is taken up by the atomizing gas, so that the drops - depending on their size - hit the substrate in a more or less liquid state and weld there with the previously deposited material. The method is fundamentally suitable for the production of flat products, but in particular for the production of rotationally symmetrical semi-finished products such as round bars and tubes, in which case the substrate performs a rotational movement with a lateral offset during the spraying process. Since the metal drops only hit with very little overheating, the substrate, ie the material previously deposited, must be at a sufficiently high temperature so that it is still homogeneously welded. However, if the temperature is too high, a liquid layer builds up on the substrate surface, which on the one hand slowly solidifies in a conventional manner and on the other hand is thrown off the substrate under the influence of centrifugal force. Since the overheating of the sprayed-on metal particles is not constant due to their non-uniform particle size distribution, the so-called "overspray" is formed even if the process parameters are optimally set. This is the proportion of the spray particles which either fly past the substrate from the outset or are thrown off the substrate as a result of the temperature being too low. This leads to uneconomical application, especially in the case of expensive materials, and the fine metal powders deposited in the spray chamber are dangerous in many cases due to their explosiveness and toxicity. Although spray compacting has the advantage over classic powder metallurgy that all intermediate stages between powder atomization and powder compaction are eliminated - and thus possibilities for contaminating the Powder surface can be reduced - however, as with normal powder metallurgy, an enormous surface is still formed and, in the case of highly reactive materials or even with only slight contamination of the gas atmosphere in the spray chamber, this can lead to material damage despite the short reaction times.

A major disadvantage of spray compacting is the fact that cooling during flight takes place down to the range of the liquidus temperature, e.g. B. takes place relatively quickly with a few thousand Kelvin per second, but then on the substrate, where the critical area between liquidus and solidus temperature is passed, the cooling rate is only in the order of a few Kelvin per second. On the one hand, this enables the phenomena known from classic solidification, such as segregation and the formation of cavities and precipitates, but also a coarsening of the original cast morphology. Another disadvantage of the method is the fact that, as with all conventional solidification processes, the heat is removed via the layers which have already solidified beforehand, so that the heat transport is reduced with increasing thickness of the substrate, which leads to non-stationary solidification conditions. On the other hand, a great advantage of the spray compacting process is that large quantities of metal in the order of several kilograms per second can be converted, which makes it interesting to use in the context of large-scale semi-finished product production processes. The process engineering aspects of spray compacting are clearly presented in a work by W. Kahl and J. Leupp "Spray Deposition of High Performance Aluminum Alloys via the Osprey Process" in Swiss Materials 2/4 (1990), pp. 17-19.

A generic method is known from JP-A-61-119 355. In this process, several layers of molten metal are applied in succession to the top of a band passed over two rollers. Since very high speeds cannot be achieved with the belt and the melt is pressed onto it only by gravity, the applied layer is inevitably relatively thick, so that the desired very rapid cooling of the melt cannot be achieved in this way. The process is also only suitable for the production of a band-shaped laminate.

Compared to this known generic method, the object of the invention is to enable the production of metal strips with extremely rapid cooling, so that the metal strip produced has a structure which results from a rapid fixation of a metastable state. In addition, it should be possible to weld the metal strip to thick-walled, rotationally symmetrical composite bodies using the residual heat. Finally, a device suitable for carrying out the method is to be specified.

This object is achieved by the invention as characterized in the claims.

Compared to the known generic method, the invention permits a significantly higher speed of the substrate, since the placement and distribution of the melt is ensured by the centrifugal force that presses it against the inner surface. The same force also ensures that the melt is compressed and spreads very quickly in a relatively thin layer over a larger area and is pressed against the cold substrate - that is, the layer that was created immediately before and adjoins the outside - which creates the best conditions for rapid cooling. This is further supported by the fact that, as mentioned, heat flows from the applied melt into the substrate, which has been greatly cooled by the application of coolant, and is also removed from the surface by the coolant, preferably applied immediately after solidification. This heat removal from a thin layer over both interfaces leads to extremely high cooling rates.

The high speeds of the substrate mentioned also have the advantage of high output in front of an inevitably much slower moving belt.

While, as mentioned, the arrangement according to the known generic method is only suitable for the production of a tape - whereby, in contrast to the method according to the invention, a separate application device is required for each layer even with the same composition of the layers - a tape or a composite body can be produced according to the invention.

Another method is known from JP-A-57-156 863, in which the solidifying melt is applied to the outside of a wheel-shaped casting mold, which heats it from this side, while cooling it only by spraying water on the outside becomes. The substrate surface is always part of the Circumferential surface of the mold is formed. There are no successive layers and interaction between them. The purpose of the method is to produce a monocrystalline structure by setting an approximately constant temperature gradient.

Finally, from JP-A-57-070 062 a method is known in which melt is directed against a rotating inner surface, but coolant is not applied to the resulting metal strip or better metal wire, but is injected into the groove before the melt is applied. So there is only one-sided cooling. The wire does not go through a complete revolution either, but is deflected and drawn off by compressed air in the axial direction in front of the point at which coolant is injected, a process which may involve some difficulties and should preclude the production of wider strips. An interaction between successive sections of the tape thus produced is obviously impossible.

According to the invention, in a manner similar to the melt spinning process, an overheated metal melt in the form of a more or less closed jet is preferably applied to the inner surface of a rotating and essentially rotationally symmetrical mold cavity, similar to centrifugal casting. Deviating from melt spinning, where the heat is extracted exclusively from the rotating cooling roller, the heat removal in the present process takes place mainly by heat transfer into a liquid cooling medium which at one point is offset approximately at the same rotation level, but by a certain angle of rotation with respect to the location of the metal application is sprayed onto the metal film just deposited and forms a coolant film there. Both films are created on the one hand under the effect of the mechanical accelerations at the locations where they are applied, the heat transfer conditions in the metal layer formed in the course of the last revolution and between the films, and in particular as a function of the temperatures of the surfaces involved in mass transfer and the physical properties of those involved Phases such as thermal conductivity, density, solidification range, supercooling conditions etc.

Three areas can be distinguished in liquid cooling. A high cooling effect can generally be achieved at temperatures below the boiling point of the coolant, since the heat transfer directly into the liquid phase with its relatively high density and Heat capacity takes place. If the temperature is raised to a range above the boiling point, a second range is reached, where the Leydenfrost phenomenon occurs: at the phase boundary, partial evaporation of the coolant leads to the formation of a vapor film, which directly contacts the metal phase with the prevents liquid coolant. The heat transfer can therefore decrease by powers of ten. A third area, which is decisive in the sense of the present invention, is reached when the liquid cooling phase has a large temperature gradient on the one hand and a high relative speed compared to the hot surface to be cooled. Due to the turbulent conditions at the phase boundary of the coolant against the surface to be cooled, no vapor film can form, which guarantees the full cooling capacity directly in the coolant. Such conditions prevail in the liquid gas atomization process, where a melt is atomized into small powder particles by a rapidly moving jet of cryogenic liquefied gas. Practical tests have shown that heat transfer coefficients occur in this process, which can significantly exceed those of the melt spinning process.

The method according to the invention has two main differences from the classic melt spinning processes: on the one hand, part of the heat of the freshly applied metal film is transferred to an underlying solid metal layer, but this metal is the cast body formed in the course of the last revolution, on the one hand others, a substantial part of the heat is given off directly to the liquid cooling medium. An additional, but not essential, process feature is the fact that both films, ie metal and coolant, are pressed under the effect of centrifugal acceleration on the respective underlying layer, which improves the Leads heat transfer.

The method according to the invention also clearly distinguishes itself from conventional centrifugal casting by the fact that the solidification of the melt applied in the course of one revolution takes place essentially during this revolution.

Depending on the extent of the amount of heat that passes directly into the liquid cooling medium, there are significant and differential effects on the shape and structure of the resulting cast product. If the amount of metal supplied is chosen to be lower in relation to the rotational speed, for example as is the case with melt spinning, then at peripheral speeds z. B. in the range of 50 - 100 m / sec tapes with a thickness of the order of 0.05 mm. If the coolant is applied shortly after the metal film has been produced and the cooling effect is maintained for a longer period during the further rotation, then a substantial part of the heat of the freshly applied metal layer reaches the liquid cooling medium, which absorbs this heat with evaporation. When the rotation is complete, the coolant has completely evaporated so that the new metal film formation can take place on a clean and cryogenic substrate surface. Since the amount of heat in the film is not sufficient for welding to the last metal layer, a "coil" is created in this way. H. a "self-winding" tape winding. The cooling rates achieved in this way can be of the order of hundreds of millions of Kelvin per second.

According to the inventive method not a band, but a thicker, substantially rotationally symmetrical body z. B. be made in the form of a ring, then basically the procedure described above can be used, but in A smaller amount of the coolant is used in relation to the amount of metal, the amount of metal and the rotational movement preferably being matched to one another in such a way that the applied metal film generally has a thickness above 0.2 mm. It is also advantageous with this method of operation if the time at which the coolant is applied is delayed compared to the example above. In this way, the cooling effect starts later, so that the freshly applied film has more time to weld with the last layer applied, on the other hand, the reduced amount of coolant in relation to the amount of metal ensures that the cooling effect suddenly stops after the coolant has completely evaporated, so that a higher residual heat remains in the welded film, which favors a successful welding in the next film application.

The conditions in this welding thus lead to a type of "cast laminate" and lie between the slow solidification in the spray compacting described above and the rapid solidification in special processes, such as plasma spraying or laser treatment. While the comparatively cold metal drops can only be welded with a hot substrate during spray compacting, thin layers can also be combined with a cold base layer in the case of the high-energy surface treatments, since the high local energy density leads to welding before essential parts of the heat of fusion for the welding process can uselessly dissipate into deeper areas of the substrate.

Compared to spray compacting, there is another significant advantage in the method according to the invention. While spray compacting, a large number of small drops are formed with a huge cumulative surface, which contaminates the atmosphere of the usually voluminous and complex spray chamber The specific surface area of a closed film is considerably smaller and can react for a longer period of time at relatively high temperatures. In addition, the reaction time is very limited due to the short application distance and the higher cooling rate. However, a further advantage is of great importance: while part of the material is lost as so-called “overspray” during spray compacting, the process according to the invention largely results in a full application of the melt quantity in the product produced.

Fig. 1

den grundsätzlichen Ablauf des erfindungsgemässen Verfahrens anhand einer im Querschnitt dargestellten ersten Ausführungsform einer entsprechenden Vorrichtung,

Fig. 2

einen Schnitt nach der Linie II-II in Fig. 1,

Fig. 3a - 3c

radiale Temperaturprofile, wie sie bei einer ersten Variante des erfindungsgemässen Verfahrens auftreten,

Fig. 4a - 4c

radiale Temperaturprofile, wie sie bei einer zweiten Variante des erfindungsgemässen Verfahrens auftreten,

Fig. 5

eine zweite Ausführungsform einer Vorrichtung zur Durchführung des erfindungsgemässen Verfahrens im Querschnitt,

Fig. 6

eine dritte Ausführungsform einer Vorrichtung zur Durchführung des erfindungsgemässen Verfahrens im Querschnitt,

Fig. 7

eine vierte Ausführungsform einer Vorrichtung zur Durchführung des erfindungsgemässen Verfahrens im Querschnitt,

Fig. 8

eine fünfte Ausführungsform einer Vorrichtung zur Durchführung des erfindungsgemässen Verfahrens im Querschnitt,

Fig. 9

eine sechste Ausführungsform einer Vorrichtung zur Durchführung des erfindungsgemässen Verfahrens im Längsschnitt,

Fig. 10a

eine erste spezielle Ausführungsform des erfindungsgemässen Verfahrens anhand einer entsprechenden Vorrichtung in perspektivischer Darstellung,

Fig. 10b, 10c

zwei Phasen der Ausführungsform des Verfahrens gemäss Fig. 10a im Detail anhand von Längsschnitten,

Fig. 11a

eine zweite spezielle Ausführungsform des erfindungsgemässen Verfahrens anhand einer entsprechenden Vorrichtung in perspektivischer Darstellung und

Fig. 11b

die Ausführungsform des Verfahrens gemäss Fig. 11a im Detail anhand eines Längsschnitts.

The method according to the invention and devices for carrying it out are explained in more detail below with reference to figures which illustrate exemplary embodiments.
Show it

Fig. 1

the basic sequence of the method according to the invention on the basis of a first embodiment of a corresponding device shown in cross section,

Fig. 2

2 shows a section along the line II-II in FIG. 1,

3a-3c

radial temperature profiles, such as occur in a first variant of the method according to the invention,

4a-4c

radial temperature profiles as they occur in a second variant of the method according to the invention,

Fig. 5

a second embodiment of a device for performing the method according to the invention in cross section,

Fig. 6

a third embodiment of a device for performing the method according to the invention in cross section,

Fig. 7

a fourth embodiment of a device for performing the method according to the invention in cross section,

Fig. 8

a fifth embodiment of a device for performing the method according to the invention in cross section,

Fig. 9

6 shows a sixth embodiment of a device for carrying out the method according to the invention in longitudinal section,

Fig. 10a

a first special embodiment of the method according to the invention using a corresponding device in a perspective view,

10b, 10c

two phases of the embodiment of the method according to FIG. 10a in detail using longitudinal sections,

Fig. 11a

a second special embodiment of the inventive method based on a corresponding device in perspective and

Fig. 11b

the embodiment of the method according to FIG. 11a in detail using a longitudinal section.

1 and 2 show in cross section or longitudinal section an embodiment of a device according to the invention. Here, a cylindrical molded body 1 rotates in the direction of an arrow 2 about an axis of rotation, the rotary movement taking place within rollers 4 mounted on axes 3, two of which are shown as representatives. At least one of these roles must be designed as a drive role. In the present case and also in the following pictures, the axis of rotation is arranged horizontally, however, a vertical arrangement is also easily possible in the sense of the invention, since the acceleration due to gravity has only a slight influence compared to the acceleration due to rotation. At a casting point 5, a jet 6 of overheated melt strikes the inner surface of the outermost metal layer 7 formed in the course of the last revolution, a liquid metal film 8 being formed.

The jet 6 originates from the melt 10 located in a container 9, wherein the container 9 can either be a melting or holding furnace or just an unheated intermediate container for receiving the overheated melt. An outlet opening for the melt in the form of a pouring nozzle 11 can be designed analogously to the conditions during melt spinning, both in terms of its shape and in terms of its arrangement relative to the casting point 5, in such a way that optimal hydrodynamic conditions arise for the film formation. The pouring nozzle 11 can be a circular or a different from the circular shape, for. B. have a rectangular cross-section. As is known in the melt spinning process, it is also entirely possible to connect a plurality of casting nozzles 11 in parallel in order to produce wider band or ring structures. In addition, a certain pressure can be applied to the melt 10 in the container 9, so that it emerges from the pouring nozzle 11 at a desired speed or quantity per unit of time, it being possible at the same time for the melt to precede Contact with the outside atmosphere is protected.

The jet 6, as shown, can be directed towards the casting point 5 essentially as in melt spinning or, similarly to spray compacting, can be dissolved in drops by a stream of a fluid, preferably gaseous medium. In the former case there is a smaller surface of the melt with correspondingly fewer reaction possibilities of the same with the surrounding atmosphere, in the latter case a more even application of the melt. In contrast to spray compacting, the splitting of the jet 6 is not used for rapid cooling below the solidification temperature, the drops should remain liquid.

Coolant, e.g. B. liquid nitrogen, is applied from cooling nozzles 12a, b at points 13a, b to the metal film 8, each forming a coolant film 14 thereon, which is completely evaporated at a point 15. In many cases, a single cooling nozzle is sufficient. As in the case of molten metal, the coolant can also be applied from a plurality of nozzles arranged next to one another if a wider metal film 8 is desired. The device parts required for this would have to be congruent in FIG. 1 lined up behind the parts shown. They would perform analog functions like this. The metal film 8 is completely solidified at a point 16 in the present example. In most cases, the point 16 is in the direction of rotation in front of the cooling point 13, so that the liquid coolant only comes into contact with the completely solidified metal film 8.

It can be seen from FIG. 2 that the cylindrical molded body 1 has a groove-like depression on its inner wall, which is formed by a side wall 17a firmly connected to the inner wall and a removable side wall 17b is limited laterally. In this recess, the melt 10 is applied from the pouring nozzle 11 in the form of a jet 6 at the pouring point 5 to form the metal film 8 on the innermost metal layer 7 of the metal layers already formed in the course of the previous revolutions.

3a-c show three typical phases in a first variant of the method according to the invention, the production of a rapidly solidifying strip in a diagram which shows the radial temperature profile over several layers.

3a shows the moment at which a new metal film 8 with a melt of superheating temperature T _{1 has} just been applied, which is represented by the curve piece 18. The temperature drop 19 represents the heat transfer resistance to the innermost metal layer 7, which has formed and solidified in the course of the last revolution, the temperature of which is represented by the curve piece 20. The next lower layer - curve piece 21 - also shows a sharp drop in temperature to curve piece 20. In all cases, this sharp drop in temperature is caused by the existence of an air gap, ie by the fact that - in the sense of the strip production - no welding has occurred.

3b shows a phase which follows quickly, shortly after the application of the liquid coolant film 14 with a temperature T ₃ to the surface of the at least partially solidified metal film 8. The high temperature of the curve piece 18 shown in FIG. 3a as a result of the initial overheating has now increased , greatly reduced by heat transfer to the adjacent innermost metal layer 7, but in particular by heat transfer into the coolant film 14, the metal film 8 cooling in a zone 8b below the solidification temperature T ₂ and thus being completely solidified. During the whole process, the The temperature of the innermost metal layer 7 is increased somewhat in accordance with curve piece 20, but the heat in the liquid residual zone 8a is not sufficient to bring about welding with the adjacent innermost metal layer 7.

3c shows a phase immediately before the end of a revolution, shortly before the next superheated metal film 8 is applied, in accordance with FIG. 3a. The temperature of the metal film 8 may have dropped so far in this phase that the heat flow is reversed, i. H. The previously formed metal layers give off heat to the last-formed metal film 8. It is clear that between Fig. 3c and Fig. 3a, i.e. H. At least so much time must elapse from the beginning of the next cycle that the coolant film 14 has completely evaporated. Since the process according to the invention, on the one hand, similar to melt spinning processes, gives off the heat of the overheated melt to a metal substrate, but additionally transfers a substantial part of the heat into the liquid cryogenic coolant, there are potentially higher cooling rates.

4a-c show three phases in a second variant of the method according to the invention, the production of a composite body continuously welded from strips, in the form of a cast layered composite material.

In this case, an overheated metal film 8 with the temperature T ₁ corresponding to the curve piece 18 of the temperature curve is applied in FIG. 4a. Since the innermost metal layer 7 has not yet been welded, there is a sharp drop in temperature corresponding to curve piece 19 to the temperature of the last layer corresponding to curve piece 20. The course of the temperature curve 20, which decreases on both sides, results from the fact that in this area the Heat center of solidification in the course of the last revolution. The heat now flows into the sink from both sides Curve pieces 19 and 20, so that the surface of the innermost metal layer 7 heats up rapidly.

4b shows the moment immediately before the welding. The temperature of the last solidified innermost metal layer 7 now almost corresponds to the melting point, that of the liquid metal film 8 is still above the liquidus temperature T ₂ .

4c shows a point in time some time after the welding, precisely at the start of the application of the liquid coolant film 14. An edge region of the innermost metal layer 7 is no longer visible, which was melted again for a short time since the same has now solidified, just like the newly applied metal film 8 is. As a result of the welding, the solidified edge zone 8 finally merges into the innermost metal layer 7, which manifests itself in the continuous course of the curve branch 20 of the temperature curve.

FIG. 5 shows an embodiment of a device according to the invention, which has devices for applying two melts 10a and 10b in series in the course of one revolution as metal films 8a and 8b, which are then explained in connection with FIGS. 4a-c, which are welded together by corresponding means Metering of the coolant at the cooling point 13 is effected. A further coolant film with a more intensive cooling effect is applied behind the casting point 5b. Because of this intensive cooling effect, only the two metal layers 7a and 7b are welded, but not to the metal layer 7c underneath. If the composition of the two metal layers 7a and 7b is identical, a thicker strip is produced in this way at a high cooling rate. If the composition of these layers is different, a bimetallic strip is obtained. Of course, more than two liquid metal films are applied in succession, so that instead of a bimetal strips of more complex structure are created.

6 shows an embodiment of a device according to the invention, which is particularly suitable for the production of thin, rapidly solidified strips. In analogy to the melt spinning process, the distance 22 between the casting point 5 and the outlet opening of the casting nozzle 11 is to be kept as constant as possible. Since, in contrast to the melt spinning process, the innermost metal layer 7 produced in the course of the last revolution is used as the substrate, the casting point 5 is continuously shifted with respect to the original surface of the molded body 1. In the present example, the constant distance 22 is maintained by a Spacer roller 23 rolls on the innermost metal layer 7 formed last, which shifts the container 9 with the metal melt 10 via a holding device 24, so that the pouring nozzle 11 follows the movement of the winding structure. Deviating from this mechanical regulation, it is of course also conceivable to determine the distance of the pouring nozzle 11 from the pouring point 5 via an electronic measuring probe, a control circuit ensuring that the position of the pouring nozzle 11 is tracked, for example, via an electromechanical actuator.

7 shows an embodiment of a device according to the invention which is particularly suitable for the production of thicker strips or sheet metal, in particular if a larger width is desired. While the geometry of very thin strips is determined by the intrinsic dynamics of the metal film, i.e. its thermal and rheological properties as well as the acceleration forces when it hits the surface, the width and thickness of the strip depend on the material constants of the surface and the melt, their temperatures and the relative speeds are specified, this is at thicker strips or sheet metal less the case. In order to achieve a uniform distribution over the entire width of the casting zone, the casting point 5 is designed as a metal bath 25, the volume of this metal bath on the one hand through the side walls 17a, 17b of the rotating cylindrical shaped body 1 (FIG. 2) and the inner surface of the solidified innermost metal layer 7 produced in the course of the last revolution is limited in three spatial directions, while in the direction of rotation a baffle wall 27 made of a melt-resistant material and fixed by means of a holding device 26 forms the boundary, this baffle wall 27 on the one hand laterally against the walls 17a, b of the rotating molded body 1 forms a minimal gap which essentially prevents molten metal from flowing out of the bath 25, on the other hand forms a casting gap of a certain width with the inner surface of the innermost metal layer 7, which determines the thickness of the liquid metal film 8. In the interest of the constant width of this casting gap, the measures proposed in accordance with FIG. 6 can be used, ie the holding device 26 of the baffle wall 27 can be held at a constant distance from the respective inner surface either by a spacer roller 23 (FIG. 6) or by electronic means .

FIG. 8 shows a further embodiment of a device according to the invention with a similar objective as is the case with that according to FIG. 7. The supply of the jet 6 of the molten metal also takes place in a bath 25, the lateral limitation in the direction of rotation, however, in this case being formed by an accumulation roller 28 which, in the same way as the accumulation wall 27 described in FIG. 7, has a casting gap with the forms innermost metal layer 7 formed during the last revolution. At the cooling point 13, the cooling liquid is supplied via a cooling nozzle 12, the distribution of the cooling liquid, similar to the case for the metal melt in the present example, is accomplished by a roller 29. An arrangement (not shown in FIG. 7) is also conceivable, in which the cooling liquid is fed in behind the roller 29 in the direction of rotation. In such a case, the roller 29 serves on the one hand to roll the partially or fully solidified metal film 8 into the plane and also prevents liquid or gaseous coolant from flowing back into the area of the still liquid metal film 8.

FIG. 9 shows a further embodiment of a device for carrying out the method according to the invention, which is used specifically for producing complex-shaped, essentially rotationally symmetrical parts. For this purpose, the pouring nozzle 11 and the cooling nozzle 12 are fastened to a common holding device 30 and can be moved in the direction of an arrow 31 inside the rotating molded body 1. In the present example, the cooling point 13 is offset in the direction of rotation by half a turn in relation to the casting point 5 in the interest of clarity of the illustration. Of course, other dislocation angles are also possible, it only has to be ensured that the time period before the application of the coolant is sufficient to ensure sufficient pre-solidification of the metal film 8, so that impairments due to the possibly violent cooling reaction are avoided and that the time period after application of the coolant is sufficiently large that the coolant has evaporated before the next metal film is applied.

In the present example, apart from two end side walls 17a, b, the molded body 1 has a shaping inner wall 32 which must be made of a material which can withstand the attack of the melt thermally and mechanically. Since the main part of the heat is drawn in via the evaporating coolant, the inner wall 32 can consist of a ceramic material with low thermal conductivity, at least in an area adjacent to the surface. In such a case the rotating molded body 1 then consists approximately of an outer wall, which consists of a material that can absorb the mechanical forces occurring during the rotation process, for. B. metal, as well as from an inner part, which can endure thermal loads. The inner part can be a disposable part that is replaced after each casting process. This has the advantage that geometries with undercuts can also be cast without a dividing line, since the ceramic molding material can be removed from the molding 1 together with the essentially cylindrically symmetrical casting after the casting process.

The construction of an essentially rotationally symmetrical composite body then proceeds as follows: the molten metal applied at the casting point 5 forms a film 8 which, in the course of the further rotation, welds to the metal already deposited and at least partially solidifies. After a certain angle of rotation, the liquid coolant, for. As liquid nitrogen, applied, the amount being selected so that after complete evaporation of the coolant in the newly applied metal film 8, residual heat remains which allows welding with newly deposited material in the course of the following rotations. The holding device 30 can be moved along the axis of rotation, in the direction of the arrow 31, at a specific feed speed, but a back and forth movement is also possible which is matched to the amount of the deposited metal and in which the inner surface of the composite body is built up in a controlled manner . In the simplest case, such a device can be used to build a pipe. Both in this case, as in all of the examples described, it is readily possible to use other materials, e.g. B. ceramic or metallic phases in the form of powders or fibers or the like. Before, during or after the formation of the liquid metal film from a device, not shown, for. B. using a pneumatic conveyor on the rotating inner surface of the resulting composite body to apply so that a composite material is formed.

10a shows an embodiment of a device according to the invention for producing an endless tube, FIGS. 10b and 10c schematically demonstrating two characteristic situations from the course of the production process. The pouring nozzle 11 and the cooling nozzle 12 are fastened to a common holding device 30 as in FIG. 9, the pouring point 5 and the cooling point 13 being offset from one another by a certain angle of rotation. Said points do not necessarily have to be arranged in the same plane of rotation, but can be shifted relative to one another in the direction of the axis of rotation. The holding device 30 and with it the pouring nozzle 11 and the cooling nozzle 12 executes an oscillating movement in the axial direction according to the double arrow 34a relative to the rotating molded body 1. The tube 33 is pulled off in the direction of arrow 35.

FIG. 10b shows the time at which a new outer layer of the endless tube is built up, this moment corresponding approximately to the left end point of the oscillating movement of the holding device 30 in the direction of the arrow 34c in the present illustration. The melt passes from the pouring nozzle 11 in the form of a jet 6 onto the inner surface of the rotating shaped body 1, a liquid metal film 8 being formed which forms a solid edge layer 7a in direct contact with the externally cooled cylindrical shaped body 1, which forms at least one essential part is solidified so that it has sufficient mechanical strength. This largely solidified zone 7a merges into the subsequent fully solidified part of the tube 33.
FIG. 10c shows a point in time after the processes in FIG. 10b. The holding device 30 has made a movement to the right in accordance with arrow 34d and is located shortly before the point of reversal. At the same time, the tube 33 a rotational movement is carried out as indicated in Fig. 10a. The pouring point 5 is accordingly further to the right within the rotating molded body 1, and the cooling point 13 has also moved to the right, the cooling nozzle 12 being placed in the image plane in the interest of simplicity of illustration, like the pouring nozzle 11, although it is actually at a certain angle of rotation is offset in the direction of rotation. The effect of the coolant leads to a strong cooling of the initial zone of the pipe 33, so that the solidification now largely covers the entire pipe cross section built up in the course of the processes according to FIG. 10b. At the same time, the pipe 33 is built up by means of the pouring nozzle 11 shifted to the right for the application of the melt until the final inner diameter of the pipe 33 is reached. The extensive solidification of the tube 33 due to the heat removal from the inside by the coolant leads to a shrinkage of the outside diameter of the tube 33, which leads to the formation of a casting gap 36 with respect to the rotating molded body 1. This process takes place between the times corresponding to FIGS. 10b and 10c, that is to say in the course of the movement of the holding device 30 in the direction of the arrow 34d.

As soon as the contact between the freshly formed outer surface of the tube 33 and the rotating molded body 1 is lost, the rotary movement of the tube is only supported by a plurality of pull-out rollers 37 mounted on axes 38. The pull-out rollers 37 are movable in the direction of the axis of rotation and perform a brief movement in the direction of the arrow 34b at the moment the tube 33 loses contact with the rotating molded body 1, the tube 33 moving a distance which is of the order of magnitude of the oscillation amplitude cylindrical molded body 1 is pulled out. As soon as a new metal film 8 has been built up on the end face of the tube according to FIG. 10b, the pull-out rollers 37 can be lifted briefly from the tube 33 and shifted to the left by the same amount, where they then again with the tube 33 in Be brought in contact. Pieces of the desired length have to be cut from the continuous tube with a cutting device, not shown, at certain time intervals, similar to the case with classic continuous casting.

11a shows a further embodiment of a device according to the invention, which is suitable for producing an endless tube. However, while the tube 33 in the last example assumed the rotational speed of the rotating molded body 1, a case is shown here where only the actual zone of the structure is involved in the rotational movement, while the solidified tube 33 does not perform any rotational movement. Similar to the device according to FIG. 10a, the pouring nozzle 11 and the cooling nozzle 12 are arranged to be movable in the direction of the axis of rotation of the molded body 1 by means of a common holding device 30, the cooling point 13 being offset by a certain angle in the direction of rotation and also in the withdrawal direction corresponding to arrow 35 can be shifted by a certain amount relative to the casting point 5. While the roller 4 represents all the rollers that keep the rotating molded body 1 in motion, the two pull-out rollers 37 represent a larger number of pull-out rollers that move the tube 33 out of the rotating molded body 1.

Fig. 11b shows the process shown in Fig. 11a in principle in a schematic section. The rotating molded body 1 has a side wall 17, which is preferably made of a heat-insulating material and which prevents the melt from flowing away, which forms a liquid metal film 8, to the left. Since the rotating molded body 1, which preferably consists of a metallic mold material, is cooled from the outside, a partially solidified zone 7a is formed, in which, however, there is not yet any crosslinking of the Dendrites has come so that it still has the properties of a thixotropic liquid. At the same time, a cooling liquid is applied from a cooling nozzle 12 'to the inner surface of the largely solidified tube 33, the location of the formation of the coolant film 14' in the direction of rotation behind the image plane in which the pouring nozzle 11 is located to be imagined. The pulling-off movement of the tube 33 can take place in a continuous manner in the present case, since the strong cooling effect of the liquid coolant leads to the formation of a partially solidified zone 7b, which, however, adheres to the solidified tube 33 due to its higher degree of solidification and the resulting crosslinking of the dendrites, and the rotational movement of the zone 7a, which is carried along with the liquid metal film 8 by the rotational movement of the molded body 1, therefore does not participate. Incidentally, the transition between partially solidified zones 7a and 7b should not be thought of as a sharp transition, as shown in Fig. 11b for the sake of simplicity, but rather as a gradual transition from a partially fluid and still easily deformable zone to a partially rigid and essentially rigid Imagine zone.

When all of the previous embodiments spoke of a liquid coolant, it was generally a liquefied cryogenic gas, e.g. B. liquid nitrogen or liquid argon, because in most cases the coolant also has the task of protecting the freshly formed surface of the metal film 8 from contact with air. However, if there are materials which, due to their low oxidation readiness, e.g. B. can be sprayed with water as part of powder metallurgy, for. B. certain non-ferrous metals, water can also be used in the inventive method. The use of a reactive atmosphere, which leads to the formation of metal compounds, may be appropriate where a composite body is to be produced, in which, for. B. ceramic intermediate layers are embedded between the metallic layers. The ceramic intermediate layers then correspond to the former surfaces of the liquid metal film 8, which could partially react with oxygen to form an oxide layer before the application of a further layer.

Finally, the method according to the invention is to be explained using two concrete examples, the production of a steel strip in one case and the production of an annular composite body made of steel in the other. In both cases, a device was used which in principle corresponded to that shown in FIGS. 1 and 2. The rotating molded body 1 was a steel cylinder with an internal diameter of 600 mm, the width of the casting groove delimited laterally by the side walls 17a, b being 5 mm. In both cases, stainless chromium-nickel steel was used as the test melt. As it is difficult to meter a molten steel using a plug rod device or a miniaturized slide closure similar to an industrial scale in a small test due to the unfavorable surface / volume ratio, a special solution for the small test was found. In precision casting technology, so-called rocking ovens are known, with which steel can be melted in a pure form under protective gas and cast directly into hot precision molds - without contact with the outside atmosphere and without the need for a ladle. The rocking furnace consisted of a melt container rotatable about a horizontal axis in the form of a cylindrical barrel made of high-temperature-resistant magnesite, which contained two graphite electrodes that could be displaced relative to one another on the two end faces in the axis of rotation to form an arc. The steel alloy in the form of 15 mm rod material was introduced through an opening in the barrel, which was directed upwards during the melting process. During the melting process, the furnace rocked back and forth so that the walls in contact with the melt can get rid of their overheating heat. The upward loading opening of the furnace normally also serves to fasten the pouring funnel of the upward and preheated ceramic mold at the moment of pouring. In the present case, instead of a preheated mold, a preheated pouring funnel with an attached nozzle tube made of zirconium oxide with an inner diameter of 5 mm was attached. The entire rocking furnace was installed inside the rotating molded body 1, the rotating plane of the rocking furnace being identical to the rotating plane of the molded body and the pouring nozzle 11 of the furnace, when the same was rotated through 180 °, exactly in the center of the casting groove, at the same distance between the side walls 17a and 17b swung in.

After the melt had been brought to a temperature of 1550 ° C. in the furnace, the cylindrical shaped body 1 was brought up to a speed of 1200 rpm. At this point, the cooling nozzle 12, which was offset by 100 ° from the casting point 5, was still folded out of the casting device and was charged with liquid nitrogen a few seconds before the actual experiment began until the jet, which initially consisted of gas and liquid, only emerged in liquid form. this was done at a rate of 380 g / sec. Then the rocking oven was turned upside down, with which the casting process started and immediately thereafter - about 0.5 sec later, the cooling nozzle 12 was pivoted into the rotating plane of the shaped body 1, so that the cooling liquid got into the casting groove. Within the next 7 seconds, 1050 g of steel in the form of a band 0.09 mm thick and 5 mm wide were formed in this experiment, with 140 layers lying one above the other corresponding to the height of the winding of approx. 14 mm. At the same time, about 4 liters of liquid nitrogen were consumed. An immediate measurement of the metal winding showed a temperature below 250 ° C.

In a second experiment, a ring-shaped composite body made of stainless steel was produced using the same device. However, the bottom surface of the casting groove had previously been coated with calcium zirconate by means of a plasma spraying process in order to prevent undesired heat dissipation via the molded body 1, which prevents a steady welding state from being set quickly during a short-term test. In this case, the melt was overheated in the rocking furnace to 1800 ° C. and the molded body 1 was brought to a speed of 772 rpm. The cooling point 13, to which liquid nitrogen was applied as the coolant, was offset by a three-quarter turn of the wheel with respect to the casting point 5. In the same way as before, within a lead time, i.e. H. after a steady flow of the coolant had set in, the rocking oven was turned upside down and then a fraction of a second after that. Cooling nozzle 12 pivoted. The process was maintained for 9 seconds, resulting in a ring with a width of 4.5 mm, an inner diameter of 530 mm and an outer diameter of slightly less than 600 mm. The optical measurement of the temperature of the ring surface immediately after the end of the experiment showed a surface temperature of 1200 ° C. Due to the immediately restarted cooling, the ring was quickly brought to lower temperatures.

Claims (17)

1. Process for the manufacture of strip or a composite body of metal, in which at least one stream (6) of overheated metal melt is directed towards a surface moving transversely to the stream direction and thereby an initially liquid metal film (8; 8a, 8b) is produced on the same and subsequently liquid coolant is applied to the metal film (8; 8a, 8b) and the latter is cooled down at least into the solidification range, characterised in that the surface is a rotating inner surface approximately symmetric about the axis of rotation, which inner surface is formed in each case at least partly by solidified metal layers (7; 7a, 7b) produced during preceding revolutions.
2. Process according to Claim 1, characterised in that the cooling liquid is applied to the metal film (8; 8a, 8b) only after preliminary solidification of the same at least on the surface.
3. Process according to Claim 1 or 2, characterised in that the stream (6) of overheated metal melt strikes the surface in an essentially closed manner.
4. Process according to Claim 1 or 2, characterised in that the stream (6) of overheated metal melt is dispersed into drops by means of a fluid medium before striking the surface.
5. Process according to one of Claims 1 to 4 for the manufacture of a strip coil, characterised in that the cooling by the coolant is set in such a way that no melting occurs between the newly applied metal film (8; 8a, 8b) and solidified metal layers (7; 7a, 7b) produced during preceding revolutions.
6. Process according to one of Claims 1 to 4 for the manufacture of a composite body, characterised in that the cooling by the coolant is set in such a way that the newly applied metal film (8) melts with at least one of the metal layers (7) applied during the preceding revolutions.
7. Process according to Claim 6 for the manufacture of a pipe (33), characterised in that the newly applied metal film (8), by drawing off the metal layers (7) melted together and produced during the preceding revolutions, is displaced at least intermittently relative to the metal layers (7) in the direction of the rotational axis but is applied in an overlapping manner with them.
8. Apparatus for carrying out the process according to one of Claims 1 to 7 having a movable surface, having at least one container (9; 9a, 9b) for receiving metal melt (10; 10a, 10b), which container is connected to a pouring nozzle (11; 11a, 11b) which is directed towards the movable surface and having at least one coolant nozzle (12; 12a, 12b) which is likewise directed towards the movable surface and is arranged behind at least one pouring nozzle (11; 11a, 11b) in such a way as to be offset in the direction of movement of the surface such that it is suitable for cooling the surface of a metal film (8; 8a, 8b) applied by means of the said nozzle, characterised in that the movable surface is formed by the inner wall of a hollow mould body rotatable about an axis of rotation and the at least one pouring nozzle (11; 11a, 11b) and the at least one coolant nozzle (12; 12a, 12b) are arranged in the interior of the mould body (1).
9. Apparatus according to Claim 8, characterised in that a plurality of pouring nozzles (11; 11a, 11b) and a plurality of coolant nozzles (12; 12a, 12b) are successively arranged one after the other in the axial direction.
10. Apparatus according to Claim 8 or 9, characterised in that at least two pouring nozzles (11a, 11b) as well as between the same at least one coolant nozzle (12) are successively arranged one behind the other in the direction of rotation.
11. Apparatus according to one of Claims 8 to 10, characterised in that the pouring nozzle (11) is in each case suspended in such a way as to be movable at least in the radial direction and is rigidly connected to a spacer which is acted upon by a force directed towards the inner wall of the mould body (1).
12. Apparatus according to Claim 11, characterised in that the spacer is designed as a distance roller (23).
13. Apparatus according to Claim 11 or 12, characterised in that, to form a bath (25), it has a retaining element which is rigidly connected to the spacer, is arranged in such a way as to be offset in the direction of rotation relative to the at least one pouring nozzle (11), and forms with the respective inner surface an axially directed slot of constant width.
14. Apparatus according to Claim 13, characterised in that the retaining element is designed as a retaining wall (27).
15. Apparatus according to Claim 13, characterised in that the retaining element is designed as a retaining roll (28).
16. Apparatus according to one of Claims 8 to 12, characterised in that it has a device for drawing off in the direction of the rotational axis the already solidified section of a composite body produced in the apparatus.
17. Apparatus according to Claim 16, characterised in that the at least one pouring nozzle (11) and the at least one coolant nozzle (12) are fastened to a common holder (30) which is suitable for performing an oscillating movement, synchronised with the rotation of the mould body (1), in the axial direction.

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