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 precise, high-quality components are required. Semi-molten metal slurries contain a mixture of solid and liquid metals, which gives the slurries a higher viscosity than fully liquid melts. Furthermore, they often exhibit thixotropic properties, meaning they flow more easily when under stress, such as during a pressure casting process. The use of semi-molten slurries is beneficial for many reasons compared to fully liquid metal melts. Semi-molten slurries solidify more slowly, allowing all cavities in the tool to fill before solidification. Furthermore, because nucleation points in the form of solid grains are already present in the slurry, a greater degree of control over the resulting microstructure can be achieved. Due to these and other beneficial properties, semi-molten slurries have attracted increasing attention from large-scale industries, such as 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 presents a challenge for companies offering solutions for semi-molten slurry production.

[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 cast 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. Therefore, the shot weight includes both the weight of the liquid metal in the liquid metal bath and the weight of the strand 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 strand on the stirrer must be increased to achieve the same amount of cooling from the strand to the liquid metal bath. However, increasing the weight of the strand on the stirrer presents many problems. For example, the melting time of the strand in the liquid melt increases, so even an increase in lead time of only a few seconds can lead to high costs. Furthermore, the strand generally has a cylindrical shape, and increasing the weight of the strand, and therefore the volume of the cylinder, results in a strand with a larger surface area. Therefore, it becomes more difficult to break down 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 strand, 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-mentioned problems. Therefore, there is provided a method for producing a semi-molten metal slurry, the method comprising the steps of: providing at least two stirring devices, each having a first end and an opposite second end and defining a central axis therebetween, wherein a piece of cast metal is attached to each first end; inserting the first end of each of the at least two stirring devices into a liquid metal bath so that each piece of cast metal is submerged in the liquid metal bath; and after inserting the at least two stirring devices into the liquid metal bath, simultaneously rotating the at least two stirring devices with the attached piece of cast metal about their respective central axes, thereby rotating the cast metal pieces in the liquid metal bath, wherein the rotation continues until at least a majority of the cast metal pieces are melted to produce a semi-molten metal slurry.

[0007] Providing at least two stirring devices has many advantages. Mixing can be improved, at least due to the increased shear of the slurry provided by having at least two stirring devices rotating simultaneously. Improved mixing results in finer solid particles and faster and more even distribution of the solid particles throughout the slurry. Furthermore, for example, when the cast metal pieces do not have the same chemical composition as the liquid metal bath, stirring enhances and / or improves homogenization of the components. More efficient homogenization can also be related to temperature distribution within the slurry. Improved mixing can result from the stirring devices attached to the cast metal pieces, which causes cooling. Therefore, high mixing / shear is essentially provided at the same location where solidified material forms on the surface of the cast metal pieces, thereby efficiently breaking down and distributing the solidified material throughout the melt. Furthermore, having at least two stirring devices provides the possibility of varying the size of the cast metal pieces. That is, the injection 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 result in a smaller surface area for each piece and therefore reduced melting time, avoiding problems associated with excessive initial cooling and increased shear between the cast metal pieces. Therefore, 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 a semi-molten slurry. That is, the solid particle share of the finished semi-molten slurry. The desired solid particle content can 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 affects the solid particle content. Generally, a higher solids weight relative to the liquid weight is said to provide 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 must 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 discussed 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 attached cast metal pieces, each having a smaller diameter than would be possible if only a single stirring device were used to provide the 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 stirring devices both about their own axes and about a common axis increases stirring 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, one of the at least two stirring devices rotates about its respective central axis in a first direction, and another of the at least two stirring devices rotates about its respective central axis in a second direction opposite to the first direction.

[0013] The rotation scheme of 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 slurry properties 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 were 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 metal pieces to a temperature corresponding to the temperature at which the cast metal pieces are inserted into the liquid metal bath.

[0020] After casting, the cast metal pieces are brought directly to the temperature at which they are inserted into the liquid metal bath, eliminating the need to reheat the cast metal pieces.

[0021] In certain embodiments 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, thereby shortening the melting time. The size and shape of the cast metal pieces are generally adapted to each slurry preparation process. However, it can generally be said that they need to be large enough to provide adequate cooling for 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 device from the slurry bath before the cast metal pieces are melted, and therefore the need to provide separate processes for removing residue on the stirring device and disposing of unused material.

[0023] In another aspect of the present disclosure, there is provided an arrangement for producing a semi-molten metal slurry, the arrangement including: at least two stirring devices, each having a first end and an opposite second end and defining a central axis therebetween, each of the at least two stirring devices having a cast metal piece attached to its respective first end; and a stirring apparatus configured to insert the first end of each of the at least two stirring devices into a liquid metal bath so 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 after insertion of the at least two stirring devices into the liquid metal bath, thereby rotating the cast metal pieces in the liquid metal bath, wherein the rotation continues until at least a majority of the cast metal pieces are melted to produce a semi-molten metal slurry.

[0024] In some embodiments of the present disclosure, the at least two stirring devices are 2 to 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 explanation 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 shows an embodiment of the present invention including three stirring devices. [Figure 2b] 1 shows an embodiment of the present invention including three stirring devices. [Figure 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. [Figure 5] 1 illustrates a method for producing a semi-molten slurry according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

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

[0029] 1a and 1b generally illustrate one embodiment of arrangement 1 according to the present disclosure, including first and second agitators 111, 112 having first ends 111a, 112a and opposite 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 agitators 111, 112, respectively. Arrangement 1 further includes an agitator 14, which is positioned to simultaneously hold the second ends 111b, 112b of the first and second agitators 111, 112, respectively. The agitator 14 is further positioned to rotate the first and second agitators 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, stirring is provided in the melt by rotation by the stirring device 14. Rotation and stirring are described in more detail in connection with 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 (e.g., 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 common practice, which requires increasing the size of the cast metal pieces to increase the shot weight. Instead, the inventors have found that when the melting radius of the cast metal pieces exceeds 40 mm, suboptimal process conditions are achieved. This is explained in more detail in connection with FIG. 3 . Therefore, when a larger shot weight is desired, in accordance with the present disclosure, at least two stirring devices with attached cast metal pieces are provided, each having a smaller radius than if only a single stirring device were used to deliver the corresponding weight of solid metal. In accordance with the present disclosure, a larger desired shot weight instead necessitates the provision of a larger number of stirring devices.

[0033] In FIGS. 1a and 1b, the first and second agitators 111, 112 each include an elongated shaft extending between a first end 111a, 112a and a second end 111b, 112b. The first and second agitators 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 noted above, the first and second agitators 111, 112 have first and second cast metal pieces 121, 122 attached to the first ends 111a, 112a of the first and second agitators 111, 112, respectively. In the embodiment shown in FIGS. 1a and 1b, the first and second cast metal pieces 121, 122 are cylindrical and preferably have essentially equal shapes and sizes. The second ends 111b, 112b each include at their tip first and second rotation transmission members 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 arranged in a plane essentially perpendicular to the elongated shaft.

[0034] 1a and 1b, the agitator 14 is shown. The agitator 14 includes a first rear wall 141, a first guide unit 142 disposed on the first rear wall 141, and a central shaft 143 that is maintained in an upright and / or essentially vertical position by the first guide unit 142 and includes a first bottom end 143a and a second upper end 143b. A third rotation transmission member 144 is disposed on the second upper end 143b. The agitator further includes a second rear wall 145 and a second guide unit 146 disposed on the second rear wall 145 and configured to maintain the first and second agitators 111, 112 in an upright and / or essentially vertical position.

[0035] A motor-driven rotating spindle (not shown) is arranged to contact the third rotation transmission member 144 to rotate the central shaft 143. When the rotating spindle contacts the third rotation transmission member 144, the rotation is transmitted to the central shaft 143. The rotation of the central shaft 143 is converted into rotation of the first and second agitators 111, 112 by first and second rotation transmission members 131, 132 of the first and second agitators 111, 112, which contact 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 agitator are both in direct contact with the motor-driven rotating spindle, in which case no central shaft is required since rotational motion is transmitted directly from the spindle to the agitator.

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

[0038] 1a and 1b also show a feeder 148 between the first and second cast metal pieces. The feeder is a remnant from casting that is placed there to compensate for solidification shrinkage. The feeder 148 is removed from the cast metal pieces 121, 122 before they are 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 drawings, 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 simultaneously by a common feeder 148. Furthermore, 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 one embodiment of arrangement 2 of the present disclosure, which includes first, second, and third agitation devices 211, 212, 213. The first, second, and third agitation devices 211, 212, 213 are preferably positioned equidistant from each other, thus forming a triangular arrangement. Other arrangements are possible.

[0040] Each of the first, second, and third agitators 211, 212, and 213 includes an elongated shaft having a first end 211 a, 212 a, and 213 a and a second end 211 b, 212 b, and 213 b. The first, second, and third agitators 211, 212, and 213 have first, second, and third cast metal pieces 221, 222, and 223 attached to the first end 211 a, 212 a, and 213 a of the first, second, and third agitators 211, 212, and 213, respectively. In the embodiment of Figures 2a and 2b, the first, second, and third cast metal pieces 221, 222, and 223 are cylindrical in shape and preferably have essentially equal shapes and sizes. 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 arranged in a plane essentially perpendicular to the elongated shaft.

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

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

[0043] A motor-driven rotating spindle (not shown) is arranged to contact the fourth rotation transmission member 244 to rotate the central shaft 243. When the rotating spindle contacts the fourth rotation transmission member 244, the rotation is transmitted to the central shaft 243. The rotation of the central shaft 243 is converted into rotation of the first, second, and third agitators 211, 212, 213 by the first, second, and third rotation transmission members 231, 232, 233 of the agitators, which contact the central shaft 243. In this embodiment, the first, second, and third rotation transmission members 231, 232, 233 contact 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] The present invention will now 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 described above, the cast metal piece 121 is attached at the first end 111a. The cast metal piece 121 preferably has a cylindrical shape. FIG. 3 also shows a melting radius R1. 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 positioned radially outward from the point on the stirring device. The melting radius R1 may also be considered the radius to the center of the cylinder minus the stirrer radius R2. 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 in a liquid metal bath by a stirring device 14. Although Figure 4 shows two stirring devices 111, 112 with respective cast metal pieces 121, 122, 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 agitators 111, 112 may be in the same direction or in opposite directions. In some embodiments where three or more agitators are provided, one or more of the agitators may rotate in a first direction and one or more of the remaining agitators 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 agitators 111, 112. The common axis may be equidistant from the agitators 111, 112 or may be offset so that they are closer to each other. The common axis may, for example, coincide with an extension of the central shaft 143 of the agitator 14. Rotation around the common axis may or may not coincide with the direction of the individual agitators 111, 112. Rotation may be at various speeds. Furthermore, the rotation speeds of the individual agitators 111, 112 may be the same or different from each other. Furthermore, the rotation speeds of the individual agitators 111, 112 may be the same or different from each other around the common axis.

[0050] Because 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 and 122 and between the cast metal pieces 121, 122 and the wall 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 better distribution of 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 thereby faster melting of the cast metal pieces 121, 122. Better stirring can also mean better and faster homogenization of chemical composition variations. Better stirring can also mean 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 methods generally described below. Reference numerals correspond to the embodiment shown in Figure 1, but 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 molds together with the first ends 111a, 112a of the respective stirring devices, and the liquid metal in each mold solidifies into a cast metal piece 121, 122, which is 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 preferably occurs simultaneously, and even more preferably through the same injection port, also known as a feeder 148. The molds preferably have an internal shape such that the resulting cast metal pieces 121, 122 have a cylindrical shape. Even more preferably, the molds have an internal diameter such that the resulting cast metal pieces 121, 122 have a radius corresponding to the desired melt radius R1 described above. The first and second stirring devices 111, 112 are then removed from the mold together with the attached cast metal pieces 121, 122. During the casting step S1, each second end 111b, 112b is preferably held by the stirring device 14.

[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 important. The temperature may not be too high, since the cast pieces 121, 122 need to provide 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), as this would require reheating of the cast pieces 121, 122 before insertion, thereby making the slurry preparation process less energy-intensive 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] The first ends 111a, 112a of the first and second stirring devices 111, 112 are inserted (S3) into a ladle containing a liquid metal bath by the stirring device 14. The insertion (S3) of the first and second stirring devices 111, 112 is preferably performed simultaneously. In other words, the first and second stirring devices 111, 112 are preferably inserted (S3) together. The first and second stirring devices 111, 112 are preferably inserted (S3) so that each cast metal piece 121, 122 is submerged in the liquid metal bath, and preferably so that each cast metal piece 121, 122 is submerged simultaneously. The insertion (S3) of the first and second stirring devices 111, 112 is preferably performed before stirring begins.

[0056] The casting step S1, the temperature control step S2 and the insertion into the melt step S3 are preferably continuous processes, in which unnecessary reheating and therefore wasting time and energy is 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 relative to the majority of the melted 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 maintained in the liquid metal bath until a semi-molten slurry is formed and / or until the majority 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, thereby avoiding subsequent unnecessary 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 simultaneously as 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 opposed to using only one.

[0058] Subsequently, the stirring devices 111, 112 are removed from the semi-molten slurry of the finished product, and the semi-molten slurry is provided to the 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—larger shot weights necessarily require larger cast metal pieces. 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 and slurry properties can be achieved.

[0060] Preferred embodiments of the method and arrangement have been disclosed, however, those skilled in the art will recognize 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. 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 an opposite second end (111b, 112b; 211b, 212b, 213b), defining a central axis therebetween, wherein a cast metal piece (121, 122; 221, 222, 223) is attached to each first end (111a, 112a; 211a, 212a, 213a), the casting of said cast metal piece (121, 122; 221, 222, 223) being carried out in a mold adapted so that said cast metal piece acquires the shape of a cylinder, the radial thickness (R1) of said cylinder being equal to or less than 40 mm; - a step (S3) of inserting the first ends (111a, 112a; 211a, 212a, 213a) of each of the at least two stirring devices (111, 112; 211, 212, 213) into a liquid metal bath, so that each cast metal piece (121, 122; 221, 222, 223) is simultaneously submerged in the liquid metal bath; - after insertion of 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) to which the cast metal pieces (121, 122; 221, 222, 223) are attached around their respective central axes (S4), thereby rotating the cast metal pieces (121, 122; 221, 222, 223) in the liquid metal bath; Including, The method wherein the rotation continues at least until the cast metal pieces (121, 122; 221, 222, 223) are essentially completely melted to produce a semi-molten metal slurry.

2. 2. The method of claim 1, wherein the rotations (S4) of the at least two stirring devices (111, 112; 211, 212, 213) about their respective central axes are in the same direction.

3. 2. The method according to claim 1, wherein the rotation (S4) of one of the at least two stirring devices (111, 112; 211, 212, 213) around its central axis is in a first direction, and the rotation of another of the at least two stirring devices (111, 112; 211, 212, 213) around its central axis is in a second direction opposite to the first direction.

4. 2. The method of claim 1, further comprising controlling (S2) the temperature of the cast metal pieces (121, 122; 221, 222, 223) to have a temperature range of 80 to 200°C before the step of inserting the at least two stirring devices (111, 112; 211, 212, 213) into the liquid metal bath.

5. Furthermore, before the step of providing at least two stirring devices (111, 112; 211, 212, 213), Casting the cast metal pieces (121, 122; 221, 222, 223) on the first ends (111a, 112a; 211a, 212a, 213a) of each stirring device (S1). The method according to any one of claims 1 to 4, comprising:

6. 6. The method of claim 5, wherein the casting is performed simultaneously for each of the cast metal pieces (121, 122; 221, 222, 223) through the same inlet (158).

7. moreover, After the casting (S1) on each stirring device, the cast metal pieces (121, 122; 221, 222, 223) are cooled to a temperature corresponding to the temperature at which they will be inserted into the liquid metal bath, said temperature being in the range of 80 to 200°C. The method of claim 5 , comprising:

8. Furthermore, After the casting (S1) on each stirring device, the cast metal pieces (121, 122; 221, 222, 223) are cooled to a temperature corresponding to the temperature at which they will be inserted into the liquid metal bath, said temperature being in the range of 80 to 200°C. The method of claim 6, comprising:

9. 1. An arrangement (1; 2) for producing a semi-molten metal slurry, comprising: 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, each of said at least two stirring devices (111, 112; 211, 212, 213) having a respective first end (111a, 112a; 211a, 212a, 213a) and an opposite second end (111b, 112b; 211b, 212b, 213b), at least two stirring devices, each having a cast metal piece (121, 122; 221, 222, 223) attached to a corresponding one of the stirring devices (112a; 211a, 212a, 213a), the casting of the cast metal piece (121, 122; 221, 222, 223) being carried out in a mold adapted so that the cast metal piece acquires the shape of a cylinder, the radial thickness (R1) of the cylinder being equal to or less than 40 mm; and A stirring device (14; 24) comprising: - inserting the first ends (111a, 112a; 211a, 212a, 213a) of each of the at least two stirring devices (111, 112; 211, 212, 213) into the liquid metal bath so that the cast metal pieces (121, 122; 221, 222, 223) attached to the first ends (111a, 112a; 211a, 212a, 213a) are simultaneously submerged in the liquid metal bath; - after inserting the at least two stirring devices into the liquid metal bath, 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 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 follows: Including, An arrangement wherein the rotation continues at least until the cast metal pieces (121, 122; 221, 222, 223) are essentially completely melted to produce a semi-molten metal slurry.

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

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