Production of semi-molten slurry using two or more mixing devices

Abstract

A method for producing a semi-molten metal slurry, comprising the steps of providing at least two stirring devices (111, 112; 211, 212, 213), each having a first end (111a, 112a; 211a, 212a, 213a) and an opposite second end (111b, 112b; 211b, 212b, 213b) and defining a central axis therebetween, (111a, 112a; 211a, 212a, 213a) are attached with cast metal pieces (121, 122; 221, 222, 223); and (S3) inserting a first end (111a, 112a; 211a, 212a, 213a) of each of the at least two stirring devices (111, 112; 211, 212, 213) into the liquid metal bath, the step of allowing the cast metal pieces (121, 122; 221, 222, 223) to be submerged in the liquid metal bath; after the insertion of the at least two stirring devices (111, 112; 211, 212, 213) into the liquid metal bath, a step (S4) of simultaneously rotating the at least two stirring devices (111, 112; 211, 212, 213) to which the cast metal pieces (121, 122; 221, 222, 223) are attached about their respective central axes, thereby rotating said cast metal pieces (121, 122; 221, 222, 223) in the liquid metal bath, wherein the rotation is continued until at least a majority of the cast metal pieces (121, 122; 221, 222, 223) have been melted to produce a semi-molten metal slurry.

Description

[Technical field]

[0001] Technical Field The present invention relates generally to a method for producing a semisolid metal slurry and an arrangement for doing so. [Background technology]

[0002] Background technology Metal casting processes using semi-molten metal slurries can be used when finely detailed, high quality components are required. Semi-molten metal slurries contain a mixture of metals in solid and liquid phases, which gives the slurries a higher viscosity compared to fully liquid melts. Furthermore, they often exhibit thixotropic properties, i.e., they flow more easily when under stress, for example during pressure casting processes. The use of semi-molten slurries is beneficial for many reasons compared to fully liquid metal melts. Semi-molten slurries solidify more slowly, which allows all cavities of the tool to be filled before solidification. Furthermore, a higher degree of control over the resulting microstructure is achieved, since nucleation points in the form of solid grains are already present in the slurry. Due to these and other beneficial properties, semi-molten slurries have attracted increasing attention from large-scale industries, for example the automotive industry. This inevitably increases the need to produce larger quantities of semi-molten metal slurries without compromising either cost, time or quality. Currently, this is a problem for companies that provide solutions for the production of semi-molten slurries.

[0003] One melt preparation process for semi-molten slurries is known as Rheocasting and is disclosed in Swedish Patent SE 538596. This patent discloses a method in which a liquid metal melt is cast with a mechanical stirrer, where a piece, sometimes known as an Enthalpy Exchange Material (EEM), and the stirrer are lowered into a liquid metal bath. The solid EEM has a lower temperature than the liquid metal bath, and in combination with the endothermic melting of the EEM, the liquid metal bath cools and begins to solidify. By simultaneously using a mechanical stirrer to break up the dendritic network that forms during solidification, a high quality semi-molten slurry is obtained.

[0004] The size of one batch of semi-molten slurry produced is known as the shot weight. The shot weight therefore includes both the weight of the liquid metal in the liquid metal bath and the piece on the stirrer when melted by the stirrer. If a larger shot weight is desired, both the weight of the liquid metal and the weight of the piece on the stirrer need to be increased to bring about the same amount of cooling from the piece to the liquid metal bath. However, increasing the weight of the piece on the stirrer presents many problems. For example, an increase in lead time of only a few seconds can lead to high costs, since the melting time of the piece in the liquid melt increases. Furthermore, the piece generally has a cylindrical shape, and an increase in the weight of the piece, and therefore the volume of the cylinder, results in a piece with a larger surface area, and therefore it becomes more difficult to break the solidified dendritic network and disperse the solid particles by cooling the melt more locally. This can also lead to the formation of a solid shell around the piece, which is too large to melt away. All of this can significantly reduce the quality of the semi-molten slurry. Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, there is a need for improvements in the semi-molten slurry production process to make it suitable for larger shot weights, shorter lead times, and higher quality slurries. [Means for solving the problem]

[0006] Summary of the Invention It is an object of the present invention to overcome at least some of the above problems.There is therefore provided a method for producing a semi-molten metal slurry, comprising the steps of: providing at least two stirring devices, each having a first end and an opposite second end defining a central axis therebetween, with a piece of cast metal attached to each first end; inserting the first ends of each of the at least two stirring devices into a liquid metal bath such that each piece of cast metal is submerged in the liquid metal bath; and after insertion of the at least two stirring devices into the liquid metal bath, simultaneously rotating the at least two stirring devices with the cast metal pieces attached thereto about their respective central axes, thereby rotating the cast metal pieces in the liquid metal bath, the rotation being continued until at least a majority of the cast metal pieces have been melted to produce a semi-molten metal slurry.

[0007] Providing at least two stirring devices has many advantages. The stirring can be improved at least due to the increased shear of the slurry provided by having at least two stirring devices rotating simultaneously. The improved stirring results in finer solid particles and faster and more even distribution of the solid particles in the slurry. Furthermore, stirring enhances and / or improves homogenization of the components, for example, when the cast metal pieces do not have the same chemical composition as the liquid metal bath. More efficient homogenization can also be related to temperature distribution in the slurry. The improved stirring can be due to the stirring device attached to the cast metal pieces providing cooling. Therefore, high stirring / shear is essentially provided at the same location where the solidified material forms on the surface of the cast metal pieces, thus effectively breaking up and distributing the solidified material into the melt. Furthermore, having at least two stirring devices provides the possibility to change the size of the cast metal pieces. That is, the shot weight can be increased by increasing the number of stirring devices rather than increasing the size of the cast metal pieces. Smaller cast metal pieces lead to smaller surface area of ​​each piece and therefore reduced melting time, avoiding problems associated with too high initial cooling and increased shear between cast metal pieces. Hence, a more time, cost and energy efficient process can be achieved. A higher quality semi-molten slurry is also achieved.

[0008] The desired solid particle content is an important characteristic of the semi-molten slurry, i.e., the share of solid particles in the finished semi-molten slurry. What solid particle content is desired may depend on the intended use of the slurry. The relationship between the weight of the liquid metal in the liquid metal bath and the weight of the cast metal pieces influences the solid particle content. It is generally said that a higher share of solid weight relative to the liquid weight gives a higher solid particle content due to increased cooling from the solid metal. Therefore, in the prior art, when a higher solid particle content is desired, a higher share of the injection weight needs to come from the cast metal pieces. Therefore, if only a single stirring device is used, achieving a higher solid particle content necessarily involves an increase in the weight of the cast metal pieces. As mentioned above, this is undesirable. Therefore, a higher solid particle content can be produced in a shorter time by providing at least two stirring devices with cast metal pieces attached, each having a smaller diameter than if only a single stirring device was used to provide a corresponding weight of cast solid metal.

[0009] In certain embodiments of the present disclosure, rotating the at least two agitation devices further comprises rotating the at least two agitation devices about a common axis.

[0010] Rotation of the individual mixing devices both about their own axes and about a common axis increases mixing and shear, which is advantageous for the reasons discussed above.

[0011] In certain embodiments of the present disclosure, the rotation of the at least two stirring devices about their respective central axes is in the same direction.

[0012] In one embodiment of the present disclosure, the rotation of one of the at least two stirring devices about its respective central axis is in a first direction, and the rotation of another of the at least two stirring devices about its respective central axis is in a second direction opposite to the first direction.

[0013] The rotation scheme of the at least two stirring devices can be optimized to provide optimal stirring and therefore optimal slurry properties, which is an advantage compared to having only one stirring device.

[0014] In one embodiment of the present disclosure, the method includes controlling the temperature of the cast metal pieces to have a temperature range of 80 to 200° C. prior to the step of inserting at least two stirring devices into the liquid metal bath.

[0015] The temperature of the cast pieces is one of the parameters that determines the amount of cooling provided to the liquid metal bath, affecting both the properties of the slurry and the melting time of the cast pieces. When at least two stirring devices are used, the size of each cast piece can be smaller than if only one stirring device was provided, thereby allowing for lower temperature cast pieces.

[0016] In certain embodiments of the present disclosure, the step of providing at least two stirring devices includes casting a piece of cast metal on a first end of each stirring device.

[0017] In certain embodiments of the present disclosure, casting is performed simultaneously for each of the cast metal pieces through the same casting inlet.

[0018] By using the same injection port, also known as a feeder, the process is made more efficient. Additionally, simultaneous casting results in equal degrees of solidification, temperatures, and other properties of the cast metal pieces.

[0019] In certain embodiments of the present disclosure, after casting in each stirring device, a cooling step is provided which includes cooling the cast pieces to a temperature corresponding to the temperature at which the cast pieces will be inserted into the liquid metal bath.

[0020] After casting, the cast metal pieces are brought directly to temperature for insertion into the liquid metal bath, eliminating the need to reheat the cast metal pieces.

[0021] In one embodiment of the present disclosure, casting is carried out in a mold adapted so that the cast metal piece acquires the shape of a cylinder, and the radial thickness of the cylinder is 40 mm or less, preferably 35 mm or less, and more preferably 30 mm or less.

[0022] When at least two stirring devices are used, the size of each cast metal piece can be smaller than if only one stirring device were provided, which can shorten the melting time. The size and shape of the cast metal pieces are generally adapted to each slurry making process. However, it can be said that in general they must be large enough to provide adequate cooling to the liquid metal bath to form a semi-molten slurry, and at the same time small enough so that the entire cast metal piece is melted when the slurry is ready to be cast. It is important to avoid the need to remove the stirring devices from the slurry bath before the cast metal pieces are melted, and therefore the need to provide separate processes for the removal of residues on the stirring devices, as well as the disposal of unused material.

[0023] In another aspect of the present disclosure, there is provided an arrangement for producing a semi-molten metal slurry, comprising: at least two stirring devices, each having a first end and an opposite second end defining a central axis therebetween, each of the at least two stirring devices having a cast metal piece attached to each first end; and a stirring apparatus arranged to insert the first ends of each of the at least two stirring devices into a liquid metal bath such that each cast metal piece is submerged in the liquid metal bath, and to simultaneously rotate the at least two stirring devices having the cast metal pieces attached thereto about their respective central axes following insertion of the at least two stirring devices into the liquid metal bath, thereby rotating said cast metal pieces in the liquid metal bath, wherein the rotation is continued until at least a majority of the cast metal pieces are melted to produce a semi-molten metal slurry.

[0024] In one embodiment of the present disclosure, the at least two stirring devices are between 2 and 4 in number, each having a cast metal piece attached to a first end thereof.

[0025] In an embodiment of the present disclosure, the arrangement is further arranged to cast in a mold adapted to cause the cast metal piece to acquire the shape of a cylinder, and the radial thickness of the cylinder is 40 mm or less, preferably 35 mm or less, and more preferably 30 mm or less.

[0026] BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described, by way of example, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0027] [Figure 1a] 1 illustrates an embodiment of the present invention that includes two stirring devices. [Figure 1b] 1 illustrates an embodiment of the present invention that includes two stirring devices. [Figure 2a] 1 illustrates an embodiment of the present invention that includes three stirring devices. [Figure 2b] 1 illustrates an embodiment of the present invention that includes three stirring devices. [Diagram 3] 1 illustrates an embodiment of a stirring device. [Figure 4] 1 illustrates one possible rotation pattern for an arrangement according to the present disclosure. [Diagram 5] 1 illustrates a method for producing a semi-molten slurry according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Description of the embodiments In the following, a detailed description of a method for producing a semi-molten metal slurry and an arrangement for carrying out the same is disclosed. The disclosed embodiments should be considered as illustrative examples, and not as limitations on the scope of the present invention.

[0029] 1a and 1b generally illustrate one embodiment of an arrangement 1 according to the present disclosure including first and second stirring devices 111, 112 having first ends 111a, 112a and opposing second ends 111b, 112b, where first and second cast metal pieces 121, 122 are attached to the first ends 111a, 112a of the first and second stirring devices 111, 112, respectively. The arrangement 1 further includes an agitator 14. The agitator 14 is positioned to simultaneously hold the second ends 111b, 112b of the first and second stirring devices 111, 112, respectively. The agitator 14 is further positioned to rotate the first and second stirring devices 111, 112. When the first ends 111a, 112a of the first and second stirring devices 111, 112, respectively, are inserted into the liquid metal bath, rotation by the stirring device 14 provides stirring in the melt. Rotation and stirring are described in more detail in relation to FIG.

[0030] The present disclosure is based on the insight that by simultaneously providing at least two stirring devices, each having a cast metal piece attached to a first end thereof, during the process of producing a semi-molten slurry, it becomes possible to scale up the process, i.e. to produce more semi-molten metal slurry, without compromising production time, quality or cost.

[0031] The insight arose from the need to optimize the slurry making process and achieve desired properties in the finished semi-molten slurry. To this end, the inventors discovered that not only could the number of stirring devices be increased, but the dimensions of the cast metal pieces could also be optimized.

[0032] The inventors have found that below a certain radius (melting radius R1 in FIG. 3), the melting time of the cast metal pieces is optimal, leading to reduced lead times during the production of semi-molten slurry. This is contrary to the common practice of needing to increase the size of the cast metal pieces to increase the shot weight. On the contrary, the inventors have found that when the melting radius of the cast metal pieces is greater than 40 mm, suboptimal process conditions are achieved. This is explained in more detail in relation to FIG. 3. Thus, when a larger shot weight is desired, according to the present disclosure, at least two stirring devices with attached cast metal pieces are provided, each cast metal piece having a smaller radius than if only a single stirring device were used to provide the corresponding weight of solid metal. According to the present disclosure, a larger desired shot weight instead entails providing a larger number of stirring devices.

[0033] In Figures 1a and 1b, the first and second stirring devices 111, 112 each include an elongated shaft extending between a first end 111a, 112a and a second end 111b, 112b. The first and second stirring devices 111, 112 have a circular cross section. In one embodiment, the circular cross section has a diameter of 14 mm. In other embodiments, other diameters are possible. As mentioned above, the first and second stirring devices 111, 112 have first and second cast metal pieces 121, 122 attached to the first ends 111a, 112a of the first and second stirring devices 111, 112, respectively. In the embodiment shown in Figures 1a and 1b, the first and second cast metal pieces 121, 122 have a cylindrical shape and are preferably essentially equal in shape and size. The second ends 111b, 112b each include at their tip a first and a second rotation transmission member 131, 132 in the shape of a cylinder, which may also appear as a disk having a certain thickness. The first and second rotation transmission members 131, 132 are disposed in a plane essentially perpendicular to the elongated shaft.

[0034] In Fig. 1a and Fig. 1b, the stirring device 14 is shown. The stirring device 14 includes a first rear wall 141, a first guiding unit 142 arranged on the first rear wall 141, and a central shaft 143 that is held in an upright and / or essentially vertical position by the first guiding unit 142 and includes a first bottom end 143a and a second upper end 143b. A third rotation transmission member 144 is arranged on the second upper end 143b. The stirring device further includes a second rear wall 145 and a second guiding unit 146 arranged on the second rear wall 145 and arranged to keep the first and second stirring devices 111, 112 in an upright and / or essentially vertical position.

[0035] A motor-driven rotating spindle (not shown) is arranged in contact with the third rotation transmission member 144 to rotate the central shaft 143. When the rotating spindle comes into contact with the third rotation transmission member 144, the rotation is transmitted to the central shaft 143. The rotation of the central shaft 143 is transformed into the rotation of the first and second stirring devices 111, 112 by the first and second rotation transmission members 131, 132 of the first and second stirring devices 111, 112, which come into contact with the central shaft 143 at the position of the first bottom end 143a of the central shaft 143. For this purpose, a fourth rotation transmission member 147 is arranged at this position.

[0036] In an alternative embodiment, the first and second rotational transmission members of the stirrer are both in direct contact with the motor-driven rotating spindle, in which case no central shaft is required since the rotational motion is transmitted directly from the spindle to the stirrer.

[0037] The stirrer 14 allows at least two types of rotation: first, individual rotation of each of the first and second stirrers 111, 112 about their respective central axes, defined here as an axis extending through the elongated shaft of each respective stirrer extending between its first end 111a, 112a and its second end 111b, 112b; and second, relative rotation about an axis common to the first and second stirrers 111, 112, which will be described in more detail in connection with FIG. 4. The stirrer 14 may hold the first and second stirrers 111, 112 when inserted into the liquid metal bath during the production of the semi-molten slurry. Preferably, the stirrer 14 further holds the first and second stirrers 111, 112 during the casting and cooling steps, as described below.

[0038] In Figures 1a and 1b, a feeder 148 is also visible between the first and second cast metal pieces. The feeder is a remnant from casting that is placed to compensate for solidification shrinkage. The feeder 148 is removed from the cast metal pieces 121, 122 before being inserted into the liquid metal bath. Removal of the feeder 148 may be by any suitable method, in one embodiment the feeder 148 is removed by plasma cutting. As shown in the figures, the feeder connects the first and second cast metal pieces 121, 122. This is due to how they are cast. The first and second cast metal pieces 121, 122 are produced by simultaneous casting, where liquid metal is poured into both moulds at the same time by a common feeder 148. Additionally, the first and second stirring devices 111, 112 are also placed in the mold during casting so that the first and second cast metal pieces 121, 122 are cast therein and thereby attached to the first and second stirring devices 111, 112.

[0039] 2a and 2b show an embodiment of the arrangement 2 of the present disclosure, which includes first, second and third stirring devices 211, 212, 213. The first, second and third stirring devices 211, 212, 213 are preferably positioned equidistant from each other, thus having a triangular arrangement. Other arrangements are possible.

[0040] Each of the first, second and third stirring devices 211, 212, 213 includes an elongated shaft having a first end 211a, 212a, 213a and a second end 211b, 212b, 213b. The first, second and third stirring devices 211, 212, 213 have first, second and third cast metal pieces 221, 222, 223 attached to the first end 211a, 212a, 213a of each of the first, second and third stirring devices 211, 212, 213. In the embodiment of Figures 2a and 2b, the first, second and third cast metal pieces 221, 222, 223 have a cylindrical shape and are preferably essentially equal in shape and size. The second ends 211b, 212b, 213b each include at their tip a first, second and third rotation transmission member 231, 232, 233 in the shape of a cylinder, which also appears as a disk having a certain thickness. The first, second and third rotation transmission members 231, 232, 233 are disposed in a plane essentially perpendicular to the elongated shaft.

[0041] 2a and 2b further show an embodiment of the agitator 24. The agitator 24 includes a rear wall 241 and a first guiding unit 242 arranged on the first rear wall 241. In this embodiment, the first guiding unit 242 includes an upper part and a bottom part. The agitator further includes a central shaft 243 that is held in an upright and / or essentially vertical position by the first guiding unit 242 and includes a first bottom end 243a and a second upper end 243b. A fourth rotation transmission member 244 is arranged on the second upper end 243b. Two side shafts are also arranged on the first guiding unit 242 to enhance stability. A second guiding unit 245 is further arranged on the first bottom end 243a of the central shaft 243 and on the bottom ends of the two side shafts, and is arranged to keep the first, second and third agitators 211, 212, 213 in an upright and / or essentially vertical position.

[0042] In another embodiment of the present disclosure, an arrangement is provided having a first, second, third and fourth agitation device, while in other embodiments, five or more agitation devices are provided.

[0043] A motor-driven rotating spindle (not shown) is arranged to come into contact with the fourth rotation transmission member 244 in order to rotate the central shaft 243. When the rotating spindle comes into contact with the fourth rotation transmission member 244, the rotation is transmitted to the central shaft 243. The rotation of the central shaft 243 is transformed into the rotation of the first, second and third agitator devices 211, 212, 213 by the first, second and third rotation transmission members 231, 232, 233 of the agitator devices, which come into contact with the central shaft 243. In this embodiment, the first, second and third rotation transmission members 231, 232, 233 come into contact with the central shaft 243 at a position above the first bottom end 243a of the shaft. For this purpose, a fifth rotation transmission member 246 is arranged at this position.

[0044] In the following the invention will be described with reference to Figures 3 to 5. Reference numerals correspond to the embodiment shown in Figures 1a and 1b, but it will be understood that the same applies, where applicable, to the embodiment of Figures 2a and 2b, as well as all other embodiments of the invention.

[0045] FIG. 3 shows the first end 111a of the stirring device 111. As mentioned above, the cast metal piece 121 is attached at the first end 111a. The cast metal piece 121 preferably has a cylindrical shape. In FIG. 3, the melting radius R1 is shown. Here, the melting radius is defined as the thickness of the cast metal piece 121 outside the stirring device 111, and as such, determines the melting time of the cast metal piece. The melting time is the time it takes for the cast metal piece 121 to essentially completely melt. Therefore, a larger melting radius entails a longer melting time. The melting radius is measured from a point on the circumference of the elongated shaft of the stirring device 111 to a point on the circumference of the cast metal piece that is positioned radially outward from the point on the stirring device. The melting radius R1 may also be considered as the radius to the center of the cylinder minus the radius R2 of the stirring device. Therefore, the melting radius can be increased or decreased by changing the radius of the shaft of the stirring device 111. Preferably, the melt radius R1 is less than 40 mm, preferably less than 35 mm, and even more preferably less than 30 mm. Therefore, in accordance with the present disclosure, a higher total weight of the cast metal pieces 121 is preferably achieved by increasing the number of stirring devices 111, rather than increasing the melt radius R1 of each cast metal piece 121 so as to exceed the preferred melt radius.

[0046] Figure 4 shows a rotation scheme for the rotation of stirring devices 111, 112 by a stirring device 14 in a liquid metal bath. In Figure 4, two stirring devices 111, 112 with respective cast metal pieces 121, 122 are shown, but it will be understood that the same applies when three, four or more stirring devices are provided.

[0047] The rotation scheme shows the rotation of the individual stirring devices 111, 112 around their respective central axes (axis XX in FIG. 3) as well as the rotation of all stirring devices 111, 112 around a common axis.

[0048] The rotation of the individual stirrers 111, 112 may be in the same or opposite directions. In some embodiments where more than two stirrers are provided, one or more of the stirrers may rotate in a first direction and one or more of the remaining stirrers may rotate in a second, opposite direction.

[0049] The common axis is an axis parallel to at least one of the central axes of the stirring devices 111, 112. The common axis may be equidistant from the stirring devices 111, 112 or may be offset and therefore closer to each other. The common axis may, for example, coincide with an extension of the central shaft 143 of the stirring device 14. The rotation around the common axis may or may not coincide with the direction of the individual stirring devices 111, 112. The rotation may be at different speeds. Furthermore, the rotation speeds of the individual stirring devices 111, 112 may be the same or different from each other. Furthermore, the rotation speeds of the individual stirring devices 111, 112 may be the same or different from each other about the common axis.

[0050] Since two or more stirring devices are provided in all embodiments of the present disclosure, better stirring of the semi-molten slurry is achieved. Better stirring can mean, for example, higher shear during stirring, as the slurry is sheared between the cast metal pieces 121, 122, as well as between the cast metal pieces 121, 122 and the walls of the ladle containing the slurry. Higher shear can result in finer solid particles in the semi-molten slurry. Better stirring can also result in a better distribution of the solid particles in the melt. Better stirring can also mean a higher removal rate of solid particles from the vicinity of the cast metal pieces 121, 122, and thus a faster melting of the cast metal pieces 121, 122. Better stirring can also mean a better and faster homogenization of the chemical composition variations. Better stirring can also mean a more even temperature distribution.

[0051] The stirring may be combined with additional stirring from an external stirring means.

[0052] The method of the present disclosure will now be described with reference to Figure 5. The method of the present disclosure provides an efficient way of producing semi-molten slurries, including the process generally described below. Reference numerals correspond to the embodiment shown in Figure 1, however, it will be understood that the same applies to the embodiment of Figure 2, where applicable, as well as all other embodiments of the present invention.

[0053] The first step involves casting S1 the cast metal pieces 121, 122. A liquid metal melt is provided to at least two moulds together with the first ends 111a, 112a of the respective stirring devices, so that the liquid metal in each mould solidifies into the cast metal pieces 121, 122, which are then attached to the first ends 111a, 112a of the respective stirring devices 111, 112 for casting. The casting of the cast metal pieces 121, 122 is preferably performed simultaneously and even more preferably through the same inlet, also known as the feeder 148. The moulds preferably have an inner shape such that the cast metal pieces 121, 122 obtained have a cylindrical shape. The moulds even more preferably have an inner diameter such that the cast metal pieces 121, 122 obtained have a radius corresponding to the desired melting radius R1 mentioned above. The first and second stirring devices 111, 112 are then removed from the mold together with the attached cast metal pieces 121, 122. Each second end 111b, 112b is preferably held by the stirring device 14 during the casting step S1.

[0054] Casting is preferably followed by a temperature control step S2. The temperature of the cast pieces 121, 122 is preferably controlled to have a temperature range of 80-200°C, more preferably 80-140°C. This temperature corresponds to the temperature at which the cast pieces 121, 122 are inserted into the liquid metal bath. The temperature of the cast pieces 121, 122 is of great importance. The temperature may not be too high, since the cast pieces 121, 122 need to bring sufficient cooling to the liquid metal bath to form a semi-molten slurry. The temperature may not be too low, since the cast pieces 121, 122 must not freeze the liquid metal bath. Furthermore, the cast pieces 121, 122 should preferably not be cooled below the temperature at which they are inserted into the melt (in the next step), since this requires reheating of the cast pieces 121, 122 before insertion, thus making the slurry making process less energy and more time efficient. In a preferred embodiment, controlling the temperature S2 includes cooling the cast metal pieces 121, 122, preferably to a temperature at which the cast metal pieces 121, 122 are inserted into a liquid metal bath. During the temperature control step S2, each second end 111b, 112b is preferably held by a stirring device 14.

[0055] By means of the stirring device 14, the first ends 111a, 112a of the first and second stirring instruments 111, 112 are inserted S3 into a ladle containing the liquid metal bath. The insertion S3 of the first and second stirring instruments 111, 112 is preferably performed simultaneously. In other words, the first and second stirring instruments 111, 112 are preferably inserted S3 together. The first and second stirring instruments 111, 112 are preferably inserted S3 such that each cast metal piece 121, 122 is submerged in the liquid metal bath, and preferably such that each cast metal piece 121, 122 is submerged simultaneously. The insertion S3 of the first and second stirring instruments 111, 112 is preferably performed before the start of stirring.

[0056] The casting step S1, the temperature control step S2 and the insertion into the melt step S3 are preferably a continuous process, in which unnecessary reheating and therefore the waste of time and energy are avoided.

[0057] After insertion S3, the first and second stirring devices 111, 112 are rotated S4 to stir the liquid metal bath. The rotation S4 of the first and second stirring devices 111, 112 is preferably performed simultaneously. By rotating the first and second stirring devices 111, 112 simultaneously, it should be understood that the first and second stirring devices 111, 112 are rotated simultaneously for most of the melting of the cast metal pieces 121, 122. The rotation S4 of the first and second stirring devices 111, 112 may begin or stop at the same time or at different times. The first and second stirring devices 111, 112 are kept in the liquid metal bath until a semi-molten slurry is formed and / or until most of the cast metal pieces 121, 122 are melted. Preferably, the cast metal pieces 121, 122 are essentially completely melted when the stirring devices 111, 112 are withdrawn from the ladle, avoiding unnecessary subsequent cleaning of the stirring devices 111, 112. Preferably, the slurry preparation process is optimized to achieve the desired properties of the semi-molten slurry essentially at the same time that the cast metal pieces 121, 122 are melted from their respective stirring devices. This optimization process is facilitated by providing at least two stirring devices, as compared to using only one.

[0058] Subsequently, the stirring devices 111, 112 are removed from the finished semi-molten slurry, and the semi-molten slurry is provided to a casting process S5.

[0059] As mentioned above, the temperature of the cast metal pieces, together with other parameters, influences the amount of cooling provided from the cast metal pieces to the liquid metal bath. Furthermore, in this disclosure, it has been revealed that the size of the cast metal pieces influences the cooling, with larger pieces providing more cooling. If only one stirring device is provided (as in the prior art), one degree of freedom is lost since the dimensions may not be changed - a larger shot weight necessarily requires a larger cast metal piece. However, by proposing at least two stirring devices, and therefore having the possibility to optimize both dimensions and temperatures, high control and quality of the process parameters as well as the slurry properties can be achieved.

[0060] Preferred embodiments of the method and arrangement have been disclosed. However, those skilled in the art realize that this may be modified within the scope of the appended claims without departing from the inventive idea.

[0061] All or parts of the alternative embodiments described above can be freely combined with each other or used separately, as long as the combination is not contradictory, without departing from the idea of ​​the present invention.

Claims

1. A method for producing a semi-molten metal slurry, comprising: - providing at least two stirring devices (111, 112; 211, 212, 213) each having a first end (111a, 112a; 211a, 212a, 213a) and a second end (111b, 112b; 211b, 212b, 213b) on the opposite side, and defining a central axis therebetween, wherein casting metal pieces (121, 122; 221, 222, 223) are attached to each first end (111a, 112a; 211a, 212a, 213a), and the casting of the casting metal pieces (121, 122; 221, 222, 223) is carried out in a mold adapted such that the casting metal pieces acquire the shape of a cylinder, and the radial thickness (R1) of the cylinder is 40 mm or less; - inserting each first end (111a, 112a; 211a, 212a, 213a) of the at least two stirring devices (111, 112; 211, 212, 213) into a liquid metal bath (step S3), such that each casting metal piece (121, 122; 221, 222, 223) is simultaneously submerged in the liquid metal bath; - after inserting the at least two stirring devices (111, 112; 211, 212, 213) into the liquid metal bath, simultaneously rotating the at least two stirring devices (111, 112; 211, 212, 213) about their respective central axes (step S4), thereby rotating the casting metal pieces (121, 122; 221, 222, 223) in the liquid metal bath; The rotation is continued until at least the casting metal pieces (121, 122; 221, 222, 223) are essentially completely melted to produce a semi-molten metal slurry.

2. The rotation (S4) of the at least two stirring devices (111, 112; 211, 212, 213) further comprises rotating the at least two stirring devices about a common axis. The method according to claim 1.

3. The rotation (S4) of the at least two stirring devices (111, 112; 211, 212, 213) about their respective central axes is in the same direction. The method according to claim 1 or 2. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

4. For the method according to claim 1 or 2, the rotation (S4) of one of the at least two stirring devices (111, 112; 211, 212, 213) about its central axis is in a first direction, and the rotation of the other of the at least two stirring devices (111, 112; 211, 212, 213) about its central axis is in a second direction opposite to the first direction.

5. Furthermore, before the step of inserting the at least two stirring devices (111, 112; 211, 212, 213) into the liquid metal bath, the temperature of the casting metal pieces (121, 122; 221, 222, 223) is controlled to have a temperature range of 80 to 200 °C (S2), The method according to any one of claims 1 to 4, comprising this.

6. Furthermore, before the step of providing at least two stirring devices (111, 112; 211, 212, 213), casting the casting metal pieces (121, 122; 221, 222, 223) on the first end (111a, 112a; 211a, 212a, 213a) of each stirring device (S1 The method according to any one of claims 1 to 5, comprising this.

7. ） The method according to claim 6, wherein the casting is carried out simultaneously for each of the casting metal pieces (121, 122; 221, 222, 223) through the same inlet (158).

8. Furthermore, after the casting (S1) on each stirring device, the casting metal pieces (121, 122; 221, 222, 223) are cooled to a temperature corresponding to the temperature at which the casting metal pieces (121, 122; 221, 222, 223) are to be inserted into the liquid metal bath, wherein the temperature is within the range of 80 to 200 °C, step The method according to claim 6 or 7, comprising this.

9. An arrangement (1; 2) for producing a semi-molten metal slurry, at least two stirring devices (111, 112; 211, 212, 213) each having a first end (111a, 112a; 211a, 212a, 213a) and an opposite second end (111b, 112b; 211b, 212b, 213b), and defining a central axis therebetween, wherein each of the at least two stirring devices (111, 112; 211, 212, 213) has a respective first end (111a, 112a; 211a, 212a, 2 ​ ​ ​ ​ ​ ​ ​ having cast metal pieces (121, 122; 221, 222, 223) attached to 13a) configured to do so, and the casting of the cast metal pieces (121, 122; 221, 222, 223) is carried out in a mold adapted such that the cast metal pieces acquire the shape of a cylinder wherein the radial thickness (R1) of the cylinder is 40 mm or less, at least two stirring devices; and a stirring device (14; 24), - inserting respective said first ends (111a, 112a; 211a, 212a, 213a) of said at least two stirring devices (111, 112; 211, 212, 213) into a liquid metal bath so that the cast metal pieces (121, 122; 221, 222, 223) attached to said first ends (111a, 112a; 211a, 212a, 213 a) are simultaneously submerged in the liquid metal bath, - after inserting said at least two stirring devices into the liquid metal bath, rotating said at least two stirring devices (111, 112; 211, 212, 213) to which the cast metal pieces (121, 122; 221, 222, 223) are attached simultaneously around their respective central axes thereby rotating the cast metal pieces (121, 122; 221, 222, 223) in the liquid metal bath a stirring device configured as including wherein the rotation continues until at least the cast metal pieces (121, 122; 221, 222, 223) are essentially completely melted to produce a semi-molten metal slurry, arrangement configuration

10. Said at least two stirring devices (111, 112; 211, 212, 213) are two to four in number, and each has a cast metal piece (121, 122; 221, 222, 223) attached to its first end (111a, 112a; 211a, 212a, 213a), the arrangement configuration (1; 2) according to Claim 9. ​ ​ ​ ​ ​

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