Rotating equipment for processing molten metal

Abstract

A rotor (11) for use in processing molten metal. The rotor (11) has a central axis (A) and includes a roof (12) including a plurality of peripheral notches (18). An intermediate plate (13) extends axially from the roof (12) and includes a plurality of side surfaces having arcuate portions (14). A plurality of blades (15) extend axially from the intermediate plate (13). The rotor is intended for use in casting processes, particularly for processing non-ferrous metals.

Description

[Technical Field]

[0001] The present invention relates to a rotary device for treating molten metal, and more particularly to a rotary device for removing unwanted impurities, such as dissolved gases and solid inclusions, from molten metal. [Background technology]

[0002] In casting applications, particularly the casting of non-ferrous metals such as aluminum or aluminum alloys, the molten metal must be treated before casting, and is usually treated by one or more of the following processes:

[0003] i) Degassing and inclusion removal - The presence of dissolved gases in molten metal can cause defects in the solidified product and adversely affect its mechanical properties. Hydrogen has a high solubility in liquid aluminum. While its solubility increases with increasing melting temperature, its solubility in solid aluminum is very low, which can lead to porosity in the solidified casting. Also, during the production of castings or other products made from aluminum or aluminum alloys, the diffusion of gases into voids or discontinuities (e.g., oxide inclusions) can lead to the formation of porosity or blisters.

[0004] ii) Grain refinement - The mechanical properties of the castings can be improved by controlling the grain size of the solidified metal.

[0005] iii) Modification - The microstructure and properties of metal alloys can be improved by the addition of small amounts of certain "modifying" elements such as sodium and strontium. Modifications can increase the high temperature tear resistance, improve the feeding properties of the alloy, and reduce the occurrence of shrinkage cavities.

[0006] iv) Cleaning and Alkali Removal - Significant concentrations of alkali elements have a detrimental effect on alloy properties and therefore these alkali elements must be removed or reduced.

[0007] The above treatment processes can be carried out individually or simultaneously using a variety of methods and equipment.

[0008] Degassing of molten metal is typically performed using a rotary degasser. This device injects fine bubbles of dry gas into the molten metal. The gas can be an inert gas, such as argon or nitrogen, or a reactive gas, such as chlorine or hydrogen, or a mixture of these. A rotary degasser typically includes a hollow shaft to which a rotor is attached. In use, the shaft and rotor rotate, and gas descends through the shaft and is dispersed into the molten metal via the rotor. As gas bubbles rise through the molten metal, hydrogen diffuses into the bubbles and is vented to the atmosphere when they reach the surface. The rising bubbles collect solid inclusions and transport them to the top of the melt, where they can be skimmed off. In addition to introducing gas to remove hydrogen (and oxide inclusions), rotary degassers can also be used to inject metal treating agents into the melt along with the inert gas through the shaft or through a tube adjacent to the shaft. Examples of rotary devices used in rotary degassing devices include the "XSR rotor" described in WO2004 / 057045 and the "FDR rotor" described in WO2009 / 004283 and DE202013102823.

[0009] Rotor geometry is important because it directly affects the time required to complete metal processing. Existing products have complex structures and intricate shapes to achieve the desired metal processing rate.

[0010] Rotors for handling molten metals, such as aluminum, magnesium, copper, and related alloys, have traditionally been manufactured by machining a solid block of graphite into a predetermined shape. However, machining is a difficult and costly process that is not suitable for manufacturing complex shapes, especially the interior surfaces of rotors, because line-of-sight access is required for drilling tools. Machining also limits the selection of materials that can be used to manufacture the rotor, as drill tools may not be able to drill through more durable or more abrasive ceramic materials. Additionally, such machining is relatively expensive and / or time-consuming, affecting unit costs.

[0011] Rotors used in molten metal processing are typically consumables. The harsh conditions of molten metal limit the number of times a rotor can be reused before replacement is required. Extending rotor life reduces rotor consumption, resulting in cost savings for the end user. Extending rotor life also has a positive impact on cost and productivity by minimizing downtime for maintenance and replacement.

[0012] The present invention is directed to overcoming or mitigating one or more of the above problems with rotors used in molten metal processing. Summary of the Invention

[0013] In a first aspect of the present invention, there is provided a rotor for use in processing molten metal. The rotor may have a roof. The roof may have a central axis. The roof may include a plurality of cut-outs around its periphery. The rotor may have an intermediate plate. The intermediate plate may extend axially from the roof. The intermediate plate may include a plurality of sides having arcuate portions. The rotor may include a plurality of blades extending axially from the intermediate plate. The intermediate plate may be directly adjacent to the roof or may be continuous with the roof.

[0014] In use, the rotor may be oriented so that the roof is above the intermediate plate and blades, although it will be appreciated that the rotor may be used at other angles.

[0015] The sides can define a boundary, e.g., a radial boundary, of the intermediate plate. The arcuate portions of the sides can be concave in shape. In this context, an arcuate portion is concave if the center of the arcuate portion is closer to the central axis of the rotor (e.g., compared to the ends of the arcuate portion or the straight sides).

[0016] The roof and / or plates may extend radially from the central axis and have an axial thickness. The roof may be generally disk-shaped. The roof may be configured to extend radially beyond the ends of the intermediate plate and / or blades. For example, the roof may have a radius (i.e., as measured from the axis) greater than or equal to the dimensions of the intermediate plate and / or blades. In some embodiments, the roof may also have a radius equal to the radius or length of the intermediate plate and / or blade at its maximum position. It will be understood that the radius of the roof refers to the distance between the axis and the outermost edge of the roof, not the distance between the peripheral cutout. When the plates and / or blades have a non-circular cross-section, the term "radius" refers to the distance from the axis to a location on the plate and / or the distance from the axis to a location on the blade that is furthest from the axis. For example, the intermediate plate and / or blades may extend to the edge (i.e., the radially outer edge) of the roof. In a preferred embodiment, the intermediate plate and blades have the same radius at their maximum positions. The diameter of the roof may be 100 to 300 mm, 125 to 275 mm, 150 to 250 mm, or approximately 200 mm. The axial thickness of the roof may be 20 to 50 mm, 25 to 45 mm, 30 to 40 mm, or approximately 35 mm. It will be understood that the end points of ranges herein may be combined in any combination. The top and bottom surfaces of the roof are separated by the thickness. The top surface of the roof may be flat or nearly flat. The top surface may be curved or may include a curved region adjacent to the central shaft. The bottom surface of the roof may be flat.

[0017] The plurality of peripheral notches can include at least six notches, preferably at least eight notches, and more preferably at least nine notches. The number of notches is preferably a multiple of the number of blades. The number of notches is preferably at least twice the number of blades and / or at most six times the number of blades. For example, if the rotor includes three blades, the number of notches is preferably 6, 9, 12, 16, or 18.

[0018] The peripheral cutouts can have an arcuate or semicircular shape in horizontal cross section. Horizontal cross section means that the plane is parallel to the base, in other words, the "cut" plane is perpendicular to the axial direction. The peripheral cutouts can extend in the thickness direction (e.g., axial direction) of the roof. The peripheral cutouts may extend through the entire thickness of the roof. The peripheral cutouts may be spaced apart around the periphery of the roof. The peripheral cutouts may be evenly spaced around the periphery of the roof, or a group of notches may be provided around the roof. In some embodiments, the notches are provided around the entire periphery of the roof, for example to form a continuously corrugated outer surface.

[0019] The intermediate plate may be disposed between the roof and the blades. In such an embodiment, the roof may be disposed between the shaft and the intermediate plate. The intermediate plate may extend directly from the roof. The intermediate plate may be continuous with the roof. The intermediate plate may be formed to extend axially from the roof such that there is no separation or gap between the roof and the intermediate plate. The roof and the intermediate plate may be formed integrally. The bottom surface of the intermediate plate may be flat. The top surface of the intermediate plate may be entirely continuous with the bottom surface of the roof.

[0020] The roof and intermediate plate may include a central opening, for example for fluid communication with a fluid supply.

[0021] In some embodiments, the rotor does not include a radial hole or radial opening. As used herein, a radial hole or opening is defined as a hole or opening through the rotor, for example, by being surrounded or substantially surrounded on all sides by portions of the rotor, and including an opening on the radially outer surface. In particular, the roof and intermediate plate may be free of radial holes or openings. The intermediate plate and / or roof may be configured such that there are no radial holes or openings between the intermediate plate and the roof.

[0022] The rotor may include a chamber defined by (at least) the intermediate plate and the inner surfaces of the blades. For example, the chamber may be axially defined by the intermediate plate and radially defined by the inner surfaces of the blades. The chamber may be axially bounded by the intermediate plate in one direction and open in the opposite direction. For example, the lower surface of the intermediate plate may form the upper surface of the chamber. The chamber may be radially bounded by the blades and open in part of the radial direction. For example, the blades may be positioned radially outside the chamber, and the radially innermost surface of the blade may define the chamber. In some embodiments, the chamber does not extend beyond the blades and / or between the blades. A central hole may open into the central chamber. At least one inner surface of the blades may be curved, for example, to define a nominally cylindrical chamber. The nominal radius of the chamber may be 20 to 60 mm, 25 to 55 mm, 30 to 50 mm, or 35 to 45 mm. For the purposes of this context, the nominal radius is measured from the central axis to the inner surface of the blade. The central chamber can have a width or nominal radius that is greater than the width or radius of the central opening. For example, the nominal radius of the central chamber can be at least 2, 2.5, 3 (or more) times the nominal radius of the central opening. The cross-sectional area of ​​the chamber can be greater than the cross-sectional area of ​​the central opening. In such embodiments, the blades do not extend inward to the central opening. Preferably, the rotor includes a single chamber. In this specification, a chamber is not considered a radial hole or opening because its main opening is axial and it has no physical boundary at its bottom.

[0023] In one set of embodiments, the intermediate plate includes three sides connected by three corners or ends. The corners can define sharp ends or edges, or the ends can be flat or rounded. The intermediate plate can have a generally triangular or truncated triangular cross-sectional shape (e.g., when viewed axially). Preferably, each corner or end includes one of the blades, although in some embodiments, each corner or end can include at least one of the blades. The rotor can have C3 rotational symmetry. In other embodiments, the intermediate plate can include four, five, six, or more sides and corners or ends.

[0024] Each of the sides of the intermediate plate can include a pair of straight sections separated by one of the arcuate sections. The pair of straight sections can be coplanar. In some embodiments, the corners or edges have an internal angle of 60°. In embodiments where the edges are flat or rounded, the internal angle of adjacent sides (i.e., straight sections) of the intermediate plate can be 60°. In some embodiments, the internal angle of the corners or edges can be between 40° and 80° or between 50° and 70°, and the straight sections can be at an angle to each other.

[0025] The cross-sectional shape of the blades may be the same as the adjacent portion of the intermediate plate. The height of the blades may be 10-50 mm, 15-45 mm, 20-40 mm, 25-35 mm, or 30 mm. In some embodiments, the blades do not extend radially beyond the intermediate plate and / or roof.

[0026] The peripheral edges of the blades may be tapered and may form pointed, flat, or rounded edges or ends. In some embodiments, the flat or rounded edges or ends may form a generally trapezoidal shape (when viewed axially). They may be axially disposed between notches in the roof. They may extend radially to the sides of the roof (e.g., the peripheral or outer edge or surface of the roof).

[0027] In some embodiments, the roof may be provided with one or more vanes that may extend axially from the roof toward the shaft and away from the intermediate plate.

[0028] In some embodiments, the roof, intermediate plate, and blades are integrally formed, and the rotor is continuous. In some embodiments, the rotor is formed from an isostatically pressed refractory material. In some embodiments, the rotor is formed from a moldable refractory material. As used herein, molding is intended to include a casting process. Any refractory material suitable for isostatic pressing can be used, such as a refractory mixture containing a metal oxide, carbide, or nitride. In some embodiments, the rotor is manufactured from graphite, alumina, alumina silicate, carbon-bonded alumina, carbon-bonded ceramics, clay-bonded graphite, silicon alumina nitride, fused silica, silicon carbide, zirconia, or any mixture thereof.

[0029] In a second aspect of the present invention, there is provided a rotating device including a rotor and a shaft as described herein. The rotor may be disposed at one end of the shaft. The shaft and rotor may be integrally formed so as to be continuous.

[0030] In some embodiments, the roof of the rotor is provided with an engagement means for attaching to the shaft of the rotating device. The engagement means can include a wall having threads that allow the rotor to be threadedly engaged with complementary threads on the end of the shaft. Alternatively, the engagement means can include a recess in the roof of the rotor, configured to have a size and shape complementary to the end of the shaft, allowing the rotor to be attached to the shaft by a push-fit mechanism or using a suitable fire-resistant adhesive, such as an expanding fire-resistant adhesive (e.g., Cera Foam, manufactured by ZYP Coatings, Inc.). Alternatively, the engagement means can include a locking mechanism. In one set of embodiments, the engagement means includes bayonet connectors.

[0031] The roof may be configured to have an upper surface that is angled obliquely relative to the shaft. The roof may be configured to have a greater thickness in a region immediately adjacent to the shaft. The roof may be tapered so that its thickness decreases toward its periphery.

[0032] The shaft may be hollow and / or tubular. The shaft may be configured to be in fluid communication with the roof and the central opening in the middle plate.

[0033] The rotor or rotating device of the above-described aspects can be formed from an isostatically pressed refractory material. Alternatively, the rotor or rotating device can be formed from a molded refractory material. In some embodiments, the rotor or rotating device can be formed from a combination of isostatically pressed and molded parts.

[0034] In a third aspect of the present invention, a method for treating molten metal is provided. The method can include immersing a rotor and optional portions of a shaft of a rotating device in molten metal. The method can include rotating the rotor. The method can include passing one or more molten metal treatments through the rotating device and introducing them into the molten metal via the rotor. The molten metal can include molten aluminum, magnesium, copper, or alloys thereof.

[0035] The method can include rotating a shaft to rotate a rotor. The method can include rotating the rotor at 100-500 rpm, 150-450 rpm, 200-400 rpm, 250-350 rpm, 300 rpm, or any combination thereof. In a preferred embodiment, the method includes rotating the rotor at 250-450 rpm. The method can include stirring the molten metal for 1-10 minutes, 2-8 minutes, 3-6 minutes, or 4-5 minutes.

[0036] The treatment of the molten metal can include passing a gas through a rotor and / or rotating device. The gas can include an inert gas, such as argon and / or nitrogen, or a reactive gas, such as hydrogen and / or chlorine. In some embodiments, a mixture of gases can be used. The gas can be supplied at a flow rate of 5 to 50 liters / minute, or preferably 10 to 30 liters / minute. The gas can be supplied at a flow rate of about 20 liters / minute.

[0037] In some embodiments, the molten metal process can include powder or granular metal processes. Powder or granular processes can be any chemical process used to degas liquid metal. The rotor can be used for mixing applications, such as stirring chips in a melting furnace. [Brief explanation of the drawings]

[0038] Embodiments of the present invention will now be described with reference to the following drawings. [Figure 1]FIG. 1 is a perspective view of a rotating device. [Figure 2] FIG. 2 is a perspective view of the rotating device of FIG. [Figure 3] FIG. 3 is a side view of the rotating device of FIGS. [Figure 4] Figure 4 is a graph comparing the torque of the two rotor designs. [Figure 5] Figure 5 is a graph comparing the degassing efficiency of the two rotor designs. DETAILED DESCRIPTION OF THE INVENTION

[0039] 1-3 illustrate a first embodiment of a rotating device 10. The rotating device 10 includes a rotor 11 connected to a shaft 20. The shaft 20 is tubular and has a central passageway 16A extending its length. The rotating device 10 defines an axis A extending centrally through the length of the central passageway 16A of the shaft 20 and the rotor 11. The shaft 20 has a flared end where it connects with the rotor 11, with a curved surface providing a smooth transition between the outer surface of the shaft 20 and the rotor 11.

[0040] The rotor 11 is formed in approximately three layers: a roof 12 adjacent the shaft 20, an intermediate plate 13 extending axially from the roof 12, and three blades extending axially from the intermediate plate 13. The roof 12 is approximately disk-shaped (i.e., has an approximately circular shape in horizontal cross-section) and has a thickness in the direction of the axis A. The outer (i.e., peripheral) surface of the roof 12 is formed with a series of notches 18 extending axially through the thickness of the roof 12. The notches 18 are arcuate, have a curved cross-section when viewed axially, and have a depth radially relative to the axis A. In other words, the notches 18 are arcuate, have a curved shape in horizontal cross-section, and have a depth radially relative to the axis A.

[0041] As best shown in FIG. 2 , the intermediate plate 13 has a generally triangular cross-section formed from a series of side surfaces 13a joined by corners 13b. Each of the side surfaces 13a has a pair of straight sections 13c separated by an arcuate section 14 extending radially into the side surfaces 13a. The peripheral edges (i.e., radially outermost edges) of the blades 15 and intermediate plate 13 are tapered to sharply pointed edges or corners 13b. In the illustrated embodiment, the intermediate plate 13 is sized so that the corners of the plate 13b are positioned at the peripheral edges of the roof 12. However, in other embodiments, the corners can be positioned away from the peripheral edges of the roof 12. A central opening 16 opens toward the center of the intermediate plate 13, providing a continuous passageway from the shaft 20 through the rotor 11.

[0042] A blade 15 is formed from each corner 13b of the intermediate plate 13, extending axially away from the intermediate plate 13 and the roof 12. The cross-sectional area of ​​the blade 15 (in horizontal section) is equal to the area of ​​the immediately adjacent intermediate plate 13, and the blade 15 extends continuously from the intermediate plate 13. The shape of the blade 15 is therefore defined by the corners 13b, the straight portions 13c, and part of the arcuate portions 14 of the intermediate plate 13. The surface of the blade 15 closest to the central axis A is curved, partially forming a circular chamber 17 between the three blades 15 below the intermediate plate 13. The chamber 17 opens through the space between each blade 15.

[0043] The corner portions 13b and leading edge of the blade 15 are angled at 60°, and the straight portions 13c are coplanar. In another embodiment (not shown), the angles of the corner portions may be different, such that each pair of straight portions 13c are angled relative to one another. Similarly, the size of the arcuate portions 14 can be set within the length and depth (i.e., radially).

[0044] The rotor 11 and shaft 20 are manufactured from a refractory material and formed by isostatic pressing or molding (including casting). The rotating device 10 shown in Figures 1-3 is formed as a single, integrally molded part. In an alternative embodiment, the rotor 11 and shaft 20 are formed as separate parts and connected together. The shaft 20 can be provided with a connection, such as a threaded or push-fit connection. In such an embodiment, the rotor 11 can be provided with a socket with a corresponding connection, for example a corresponding threaded or push-fit socket.

[0045] In use, the rotating device 10 is secured to a rotary degassing unit having a motor and gas supply and can be inserted into a vessel of molten metal. Gas travels down the hollow shaft, through the rotor 11 and central opening 16, and into the chamber 17. During this operation, the rotating device 10, which can be driven by a motor, rotates about axis A. Gas injected into the chamber 17 by the rotation of the rotor 11 is dispersed as it rises through the molten metal. While not intending to be bound by theory, it is believed that the peripheral notches 18 in the roof 12 act on gas bubbles rising through the molten metal. In particular, the peripheral notches 18 collect gas bubbles rising from the chamber 17, and the rotation of the rotor 11 causes the gas bubbles to be released radially from the rotor 11. This results in particularly effective distribution of the gas bubbles throughout the molten metal. Furthermore, it has been found that the chamber increases the residence time of the gas bubbles below the rotor, for example on the inner surface of the blades, thereby slowing the radial scattering of the gas bubbles due to the rotation of the rotor and preventing some of the gas bubbles from being scattered radially, which increases the mixing of the gas with the molten metal and therefore improves the purging effect of the gas on the molten metal.

[0046] <Water modeling results> The performance of various rotor designs was tested using water modeling in a full-scale crucible equipped with a baffle plate. The crucible was filled with 220 liters of water at 16°C, and the rotor was immersed 190 mm from the bottom of the vessel. Water has similar viscosity characteristics to molten aluminum, making it a useful surrogate for rotor performance in molten metal.

[0047] Two rotor structures were compared: (A) the rotor of the present invention shown in Figures 1 to 3; and (B) a rotor described in WO2004 / 057045 and a commercially available rotor (XSR (trade name) rotor) by the applicant.

[0048] stirring power Torque measurements were performed at different rotation speeds to compare the relative stirring power of each rotor design. The experiments were repeated at least three times in total, and the average values ​​were calculated.

[0049] The torque measurement results are shown in Figure 4, which is a graph of torque (N·m) versus rotational speed (rpm). At all rotational speeds, rotor configuration A exhibited greater torque than the comparative configuration B. It was confirmed that as torque increased, the size of the bubbles introduced through the rotating device decreased. Smaller bubble size increases the bubble surface area and reduces the bubble ascent velocity, thereby increasing the gas residence time in the melt and improving degassing of the liquid metal during use.

[0050] Degassing efficiency The oxygen meter was immersed in the water, facing the top of the crucible. Rotor Configuration A and Rotor Configuration B were rotated at 300 rpm and 400 rpm, respectively, and the time required for the oxygen concentration to reach a minimum plateau was measured. Because oxygen dissolved in water behaves similarly to hydrogen dissolved in molten aluminum, this test provides a useful measure of degassing efficiency in molten metal.

[0051] The degassing results are shown in Figure 5, which is a graph of oxygen concentration (mg / L) versus time. The rotor design according to the present invention (Example A) demonstrated significantly faster oxygen removal from water than the comparative Example B at both 300 rpm and 400 rpm. Increasing degassing rates is desirable in foundries to reduce processing time and improve productivity. Furthermore, increasing degassing rates at lower rotational speeds is particularly desirable to minimize wear on the rotor as well as other parts of the rotary degasser, thereby minimizing maintenance costs and downtime.

[0052] <Aluminum melting test results> Visual observation The rotator was immersed in 400 kg of liquid aluminum at 720°C to a depth of 200 mm from the bottom of the vessel. A baffle was attached to the degasser adjacent to the shaft of the rotator. Gas was supplied at different flow rates through the rotator. The rotor was rotated at different speeds. Visual observations of the melt surface were recorded in Table 1 to determine the acceptable operating conditions of the rotator.

[0053] [Table 1]

[0054] Visual observations determined that the working window for the rotor was 250–450 rpm with a gas flow rate of 10–20 liters / min through the rotor. Generally, a relatively calm melt surface is desirable to avoid negative effects. Large bubbles indicate poor mixing and a small bubble surface area, and therefore poor gas efficiency. A turbulent surface is likely to redissolve impurities that have been lifted from the melt. Small vortices result in faster degassing and improved mixing efficiency, but large vortices increase the entrainment of air and oxides, so a proper balance must be struck to achieve maximum efficiency.

[0055] The rotary equipment's operating window utilizes lower rotational speeds and lower gas consumption compared to existing commercially available rotary equipment. Lower rotational speeds are desirable because they reduce wear on the Rotary Degassing Unit (RDU) and the rotor itself, thereby extending the operating life of the rotary equipment.

[0056] Degassing efficiency Reduced pressure testing (RPT) can be used to determine the density index (DI) of metal samples. RPT is an inexpensive and effective method for determining the hydrogen concentration in aluminum and controlling gas porosity. The aluminum sample was removed from the melt and immediately placed in the vacuum dome of the reduced pressure testing machine. The sample was allowed to solidify under vacuum (i.e., a pressure of 8 kPa) for approximately 4 minutes. Solidification under vacuum increases the volume of hydrogen gas by approximately 10 times compared to solidification under atmospheric pressure, allowing for measurement and evaluation of the gas concentration in the melt.

[0057] A series of tests were conducted to investigate the hydrogen degassing efficiency of the rotor in liquid aluminum. The rotor was immersed in 400 kg of liquid aluminum at 720 °C to a depth of 200 mm from the bottom of the vessel. As a baseline, the liquid aluminum was first upgassed for 4 minutes at a rotation speed of 400 rpm with a combination of a 15 L / min mixture of 30% hydrogen and 5 L / min of inert gas. The aluminum was then degassed using the rotor according to the rotation speed and gas flow rate shown in Table 2. The sample was removed, the density index (DI) was calculated, and the process was repeated under new degassing parameters. The test was repeated using a new aluminum sample, and the average is recorded in Table 2. The DI of the upgassed aluminum was measured periodically, and the average was calculated to be 12.6%.

[0058] [Table 2]

[0059] The density index (%) is calculated using the formula: DI = (ρ atm -ρ 8kPa ) / ρ atm where ρ atm is the density of the sample solidified under air, and ρ 8kPa are the densities of the samples solidified under 8 kPa, and the units are g.cm -3 is.

[0060] The data shows that the rotor is very effective in degassing the aluminum melt, even at low rotational speeds and low gas flow rates.

[0061] The inventors have found that the rotor of the present invention is as effective or more effective than commercially available rotors, but at lower rotational speeds and / or lower gas consumption. While not intending to be bound by theory, it is believed that the arcuate portion of the middle plate increases the plate area, promoting melt acceleration and improving distribution of the gas-melt mixture. The notches in the blades and roof also increase the torque transmitted by the rotor. As previously mentioned, increased torque is believed to create smaller bubbles with a larger surface area, improving degassing efficiency. This combination provides the rotor with high torque, creating bubbles with longer residence times, which are highly effective at mixing the melt.

[0062] Furthermore, the rotor of the present invention is easy to manufacture, compared to commercially available rotors that require three-axis machining and are limited to materials such as synthetic graphite. Because of its simple design and the ability to be manufactured by, for example, isostatic pressing or die casting, the rotor of the present invention does not require complex machining processes and, in some embodiments, can be manufactured using two-axis machining. This allows for the use of alternative materials, such as clay graphite and castable refractory materials, which are much more durable than synthetic graphite. This results in longer rotor life, reduced maintenance costs, and increased productivity.

Claims

1. A rotor (11) for use in processing molten metal, comprising: a roof (12) having a central axis (A) and including a plurality of peripheral notches (18); an intermediate plate (13) extending axially from the roof (12) and including a plurality of side surfaces having arcuate portions (14); a plurality of blades (15) extending axially from the intermediate plate (13); A rotor (11) characterized in that said intermediate plate is directly adjacent to and continuous with said roof.

2. 2. The rotor (11) of claim 1, wherein the arc-shaped portions (14) on the sides are concave in shape, and the center of each arc-shaped portion is located closer to the central axis of the rotor than the ends of the arc-shaped portion.

3. A rotor (11) according to any one of the preceding claims, wherein the plurality of peripheral notches (18) comprises at least six notches (18).

4. A rotor (11) according to any one of the preceding claims, wherein the intermediate plate (13) is arranged between the roof (12) and the blades (15).

5. A rotor (11) according to any one of the preceding claims, wherein the intermediate plate and / or the blades extend to the edge of the roof.

6. 10. A rotor (11) according to any one of the preceding claims, wherein the roof (12) and the intermediate plate (13) include a central opening (16) through the roof (12) and the intermediate plate (13) for fluid communication with a fluid supply.

7. 7. The rotor (11) of claim 6, wherein the rotor (11) includes a chamber (17), the chamber being axially defined by the intermediate plate and radially defined by the inner surfaces of the blades, and the central opening opening into the chamber (17).

8. A rotor (11) according to claim 7, wherein the chamber has a width or nominal radius greater than the width or radius of the central opening.

9. 10. A rotor (11) according to any one of the preceding claims, wherein the intermediate plate (13) includes three side surfaces (13a) connected by three end or corner portions (13b), each end or corner portion including at least one of the plurality of blades (15).

10. 10. A rotor (11) according to any one of the preceding claims, wherein the plurality of side surfaces (13a) of the intermediate plate (13) each include a pair of straight portions (13c) separated by one of the arc-shaped portions (14).

11. A rotor (11) according to any one of the preceding claims, wherein the blades (15) have the same cross-sectional shape as the adjacent portions of the intermediate plate (13).

12. A rotor (11) according to any one of the preceding claims, wherein the peripheral edges of the blades are tapered to form pointed, flat or rounded edges.

13. A rotor (11) according to any one of the preceding claims, wherein the rotor (11) has C3 rotational symmetry.

14. 10. A rotor (11) according to any one of the preceding claims, wherein the roof (12), the intermediate plate (13) and the plurality of blades (15) are integrally formed and the rotor (11) is continuous.

15. A rotating device (10) comprising a rotor (11) according to any one of the preceding claims and a shaft (20), said rotor (11) being arranged at one end of said shaft (20).

16. The rotor (11) according to any one of claims 1 to 14 or the rotating device (10) according to claim 15, wherein the rotor (11) and / or the rotating device (10) is formed from an isostatically pressed refractory material.

17. 1. A method for treating molten metal, comprising: Immersing the rotor (11) of the rotating device (10) according to claim 15 or 16 and optionally a part of the shaft (20) in molten metal; rotating the rotor (11); and passing one or more molten metal treatments through said rotating device (100) and through said rotor (11) into said molten metal.

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