Rotating devices for processing molten metals

Abstract

The present invention relates to a rotating device for processing molten metal and a rotor for use therewith, the rotating device comprising a hollow shaft and a rotor at one end of the hollow shaft, the rotor comprising spaced apart roof and base sections connected by a plurality of partitions, a central chamber defined between the roof and base sections, the plurality of partitions extending radially from a periphery of the central chamber, passages defined between each adjacent pair of partitions, each passage having an inlet located radially outward of the central chamber and an outlet at an outer circumferential surface of the rotor, and a flow path defined through the hollow shaft into the central chamber through the plurality of passage inlets and out through the plurality of passage outlets. The base portion includes a plurality of apertures in fluid communication with the central chamber, radial blades defined between each adjacent pair of apertures, a central aperture, and a plurality of radial vanes projecting outwardly from the base portion, the plurality of radial vanes being disposed about the central aperture, the plurality of radial vanes extending toward a center of the base portion across at least a portion of the central aperture, or the base portion includes a central aperture and a plurality of radial vanes projecting outwardly from the base portion and disposed about the central aperture, the base portion further includes a plurality of notches disposed between the plurality of radial vanes, the plurality of notches in the base portion extending inwardly from an outer periphery of the rotor.

Description

[Technical field]

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

[0002] For casting applications, particularly the casting of non-ferrous metals such as aluminum or aluminum alloys, the molten metal typically needs to be treated by one or more of the following processes before it can be cast:

[0003] i) Degassing - The presence of dissolved gases in the molten metal can cause defects in the solidified product and adversely affect its mechanical properties. For example, hydrogen has a high solubility in liquid aluminium, which increases with the melting temperature, but its solubility in solid aluminium is very low. As a result, hydrogen gas is released as the aluminium cools, which results in blowholes in the solidified casting. The solidification rate influences the amount and size of the bubbles. In some applications, pinhole porosity can seriously affect the mechanical strength and pressure resistance of the metal casting. Gases can also diffuse into voids and discontinuities (e.g. oxide inclusions), which can cause blister formation during the manufacture of plates, sheets and strips made from aluminium or aluminium alloys.

[0004] ii) Grain Refinement - By controlling the grain size of the solidifying metal, the mechanical properties of the casting can be improved. The grain size of the cast metal depends on the number of nuclei present in the liquid metal when it starts to solidify and the cooling rate. Faster cooling rates generally result in smaller grain sizes and the addition of certain elements to the melt can provide additional nuclei for grain growth.

[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 or strontium. Modifications increase hot tear resistance, improve alloy feeding properties, and reduce shrinkage porosity.

[0006] iv) Purification and Alkali Removal - High concentrations of alkali elements can adversely affect alloy properties and therefore need to be removed or reduced. For example, the presence of calcium in cast alloys can interfere with other treatment processes such as reforming, while excessive concentrations of sodium can adversely affect the ductility properties of wrought aluminum alloys. The presence of non-metallic inclusions such as oxides, carbides, borides in the solidified metal can also adversely affect the physical and mechanical properties of the metal and therefore need to be removed.

[0007] The above processes may be carried out individually or simultaneously by a variety of methods and devices.

[0008] Degassing of molten metal is typically accomplished using a rotary degassing unit ("RDU"), which flushes the molten metal with fine bubbles of a dry inert gas, such as chlorine, argon, nitrogen, or mixtures thereof. The RDU typically includes a hollow shaft to which a rotor is attached. In use, the shaft and rotor rotate, and gas is dispersed downward through the shaft and through the rotor into the molten metal. Introducing gas through the rotor creates a large number of very fine gas bubbles, which disperse to the bottom of the melt. As these bubbles rise through the melt, hydrogen diffuses into the bubbles and is released into the atmosphere when they reach the surface. The rising bubbles then collect solid inclusions and carry them to the top of the melt where they can be skimmed off. In addition to introducing gas to remove hydrogen (and oxide inclusions), the rotary degassing unit may be used to inject metal treating agents into the melt along with the inert gas through the shaft or through tubes adjacent to the shaft.

[0009] An example of a rotation device for use in a rotary degassing unit is the "XSR rotor" (prior art rotor 1) described in WO 2004 / 057045 and shown in FIG. 1 of the present application. The rotation device 2 comprises a hollow shaft 4 having a bore 4a therethrough, which is connected at one end to a rotor 6. The rotor 6 is generally disk-shaped and comprises an annular upper roof portion 8 spaced apart from an annular base portion 10. An open chamber 12 is provided in the centre of the base portion 10 and extends upwards to the roof portion 8. The roof portion 8 and the base portion 10 are connected by four partitions 14 which extend outwards from the periphery of the chamber 12 to the periphery of the rotor 6. A compartment 16 is defined between each pair of adjacent partitions 14, the roof portion 8 and the base portion 10. The peripheral edge 8a of the roof portion 8 is provided with a number of semicircular notches 18 (eight in this embodiment). Each notch 18 serves as a second outlet for its respective compartment 16 .

[0010] Rotors for processing molten metals such as aluminum have traditionally been manufactured by machining a solid block of graphite into the desired shape. However, machining can be a difficult and expensive process and is not well suited to producing complex shapes, especially on the rotor's inner surface, since line-of-sight access is required for the drilling tool. Machining also limits the choice of materials from which the rotor can be made, since the drilling tool may not be able to drill holes in more durable or more abrasive ceramic materials. Furthermore, machining defects can adversely affect the strength of the manufacturing material and, therefore, the life of the rotor.

[0011] The inventors of the present invention have found that by using isostatic forming to press the manufacturing material around a sacrificial core and then removing the core, very complex rotor designs can be realized, especially in the interior of the rotor since line of sight access is not required. Furthermore, this new manufacturing method allows the use of more durable materials for the rotor, such as alumina, carbon-bonded alumina, or other refractory metal oxides, carbides, or nitrides that are difficult to form by machining. By isostatically forming the rotor around a sacrificial core, the surface finish of the rotor is also greatly improved, resulting in a very smooth surface with a seamless transition between Gaussian and non-Gaussian surface curvatures.

[0012] The present invention therefore aims to provide an entirely new and improved rotor design that was previously impossible to manufacture by conventional methods such as machining, and which can be manufactured from more durable materials. Summary of the Invention

[0013] According to a first aspect of the present invention, there is provided a rotary device for processing molten metal comprising a hollow shaft and a rotor at one end of the hollow shaft, the rotor comprising spaced apart roof and base sections connected by a plurality of partitions, a central chamber defined between the roof and base sections, the plurality of partitions extending radially from a periphery of the central chamber, passages defined between adjacent pairs of partitions, each passage having an inlet located radially outside the central chamber and an outlet at an outer circumferential surface of the rotor, and a flow path defined through the hollow shaft into the central chamber through the plurality of passage inlets and out the plurality of passage outlets, the base section comprising a plurality of apertures in fluid communication with the central chamber and radial blades defined between adjacent pairs of apertures.

[0014] It will be understood that the device has a longitudinal axis extending along the length of the hollow shaft, and that the terms "radial" and "radially" as used herein mean extending in a direction perpendicular to the longitudinal axis between the center of the rotor and the periphery of the rotor. The rotor may be generally circular in cross section, with a radius extending between the center of the rotor and the periphery of the rotor. Typically, the roof and base of the rotor lie in planes that are perpendicular to the longitudinal axis and parallel to one another.

[0015] The rotor may be integrally formed with the hollow shaft, or it may be a separate component that is attached to the hollow shaft, for example, screwed, press-fit, or secured by a locking mechanism or adhesive.

[0016] In use, the radial blades help chop up the gas bubbles injected through the hollow shaft to produce smaller and more numerous bubbles. Reducing the size and increasing the number of bubbles improves the distribution of the bubbles throughout the melt and significantly increases the degassing and purging efficiency at a given rotation speed, thereby shortening the processing time, or maintaining the same degassing and purging efficiency at a lower rotation speed, thereby extending the life of the shaft and rotor. Furthermore, smaller bubbles have a slower upward velocity through the melt and thus may have a longer residence time in the melt before hydrogen diffuses into the bubbles.

[0017] The plurality of apertures may be centrally located in the base. The base may be annular. The plurality of apertures may be axially located in the hollow shaft and / or central chamber. In some embodiments, the rotor base comprises at least three apertures and at least three radial blades. In some embodiments, the rotor base comprises three, four, five, or six apertures and radial blades. In some embodiments, the radial blades are equally spaced and form a turbine-like configuration.

[0018] In some embodiments, the radial blades are located in the plane of the base and do not project outwardly from the plane of the base. In alternative embodiments, the radial blades project outwardly from the plane of the base. The radial blades may project to a height, measured in the longitudinal axis direction, that is equal to or less than the height of the base. The radial blades may extend from the base away from the central chamber. In some embodiments, the radial blades do not extend into the region between the base and the roof.

[0019] In some embodiments, the radial blades are connected to one another by a central hub located in the center of the base. The central hub may be circular in shape. The central hub may provide structural support to the radial blades.

[0020] In some embodiments, the radial blades are angled, e.g., inclined, with respect to a plane of the base and / or a plane perpendicular to the axis of rotation of the rotor. For example, the radial blades may form an impeller. The radial blades may have a blade angle α of 30°-90°, 40°-80°, 50°-70°, or about 60°.

[0021] In use, the rotating device may be configured to generate a fluid flow path (e.g., a liquid flow path for molten metal) through the rotor. The fluid flow path may be defined axially through the plurality of apertures to a central chamber and then radially from the central chamber through a passage between each adjacent pair of partitions. For example, the rotor may be configured to draw liquid through the base portion and push it radially outward. The radial blades may be angled at an angle to the fluid flow path.

[0022] In one set of embodiments, the radial blades are angled positively relative to the fluid flow path, i.e., angled such that rotation of the rotor increases fluid flow in the fluid flow path. This may be desirable to increase the flow rate, velocity, or volume of fluid through the rotor. In such embodiments, the portion of the radial blade closest to the central chamber forms the trailing edge. In other words, the blade is angled upwards.

[0023] In a further set of embodiments, the radial blades are configured to decelerate the fluid passing through the base, for example, to decelerate the fluid entering the central chamber through the base. The radial blades may be angled negatively with respect to the fluid flow path, i.e., angled such that the rotation of the rotor reduces the fluid flow in the fluid flow path. This may be desirable to increase the residence time of the fluid in the rotor and / or to increase the time for the rotor to break up or disperse bubbles, prolonging the shear forces exerted on the fluid (e.g., either the liquid metal or the gas therein). In such embodiments, the portion of the radial blade closest to the central chamber forms the leading edge. In other words, the blade is angled downwards.

[0024] It will be understood that whether the radial blades are positively angled (e.g., upward) or negatively angled (e.g., downward) depends on the direction of rotation of the rotor. In this context, positive and negative angles are intended to be viewed relative to the rest of the rotor and the intended direction of rotation of the rotor. For example, in embodiments where the radial blades are negatively angled, this is intended to mean that the radial blades may be angled in the opposite direction relative to the direction of rotation determined by the configuration of the rotor, e.g., relative to other components of the rotor, such as partitions and / or apertures. In some embodiments, it may be intended that the rotor can be rotatable in either direction.

[0025] According to a second aspect of the present invention, there is provided a rotary device for processing molten metal, the device comprising a hollow shaft and a rotor at one end of the hollow shaft, the rotor comprising spaced apart roof and base sections connected by a plurality of partitions, a central chamber defined between the roof and base sections, passages defined between adjacent pairs of partitions, each passage having an inlet located radially outward of the central chamber and an outlet at an outer circumferential surface of the rotor, and a flow path defined to pass through the hollow shaft into the central chamber, through the inlets of the plurality of passages, and out through the outlets of the plurality of passages. The base section of the rotor comprises a central aperture and a plurality of radial vanes projecting outwardly from the base section, the plurality of radial vanes being arranged around the central aperture. The radial vanes extend toward a center of the base section, at least partially across the central aperture.

[0026] It will be understood that "center of the base" is intended to mean the center point measured from the periphery of the rotor along the plane of the base, not along the longitudinal axis of the device. The outwardly extending vanes may extend axially and / or away from the base to the central chamber.

[0027] In use, the radial vanes extending at least partially across the central aperture achieve a similar effect to the radial blades of the rotor of the first embodiment, namely, chopping up bubbles injected through the hollow shaft. In addition, the protruding vanes may increase the torque and directional flow of bubbles achieved by the rotor.

[0028] In some embodiments, the rotor base comprises at least three apertures and at least three radial vanes. In some embodiments, the rotor base comprises three, four, five, six, seven, or eight radial vanes. It will be appreciated that increasing the number of vanes increases manufacturing complexity and reduces the cross-sectional area of ​​each vane, so these factors must be balanced against rotor performance.

[0029] According to a third aspect of the present invention, there is provided a rotary device for processing molten metal, the device comprising a hollow shaft and a rotor at one end of the hollow shaft, the rotor comprising spaced apart roof and base sections connected by a plurality of partitions, a central chamber defined between the roof and base sections, passages defined between adjacent pairs of partitions, each passage having an inlet located radially outward of the central chamber and an outlet at an outer circumferential surface of the rotor, and a flow path defined to pass through the hollow shaft into the central chamber, through the inlets of the plurality of passages, and out of the outlets of the plurality of passages. The base section of the rotor comprises a central aperture and a plurality of radial vanes projecting outwardly from the base section, the plurality of radial vanes being disposed about the central aperture. The base section further comprises a plurality of notches disposed between the plurality of radial vanes, the notches extending inwardly from the outer periphery of the rotor to a center of the base.

[0030] In use, the notches in the base achieve a similar effect as the radial blades of the rotor of the first embodiment, i.e., chopping up bubbles injected through the hollow shaft. The radial vanes may increase the torque and directional flow of bubbles achieved by the rotor. In addition, the notches in the base may increase the torque and directional flow of bubbles achieved by the rotor.

[0031] In some embodiments, the base portion comprises at least three notches, hi some embodiments, the base portion comprises three, four, five, or six notches.

[0032] In some embodiments, the edge of each notch in the base is inclined relative to the plane of the base and / or a plane perpendicular to the axis of rotation. In some embodiments, the edge of each notch in the base is inclined at an angle of 20° to 70° relative to the plane of the base. Sloping the edges of each notch relative to the intended direction of rotation helps to reduce the drag coefficient as the rotor rotates in the melt, reducing the amount of stirring power required for a given rotation speed. Sloping the edges of each notch may improve ease of manufacture by iso-pressing.

[0033] In some embodiments, the cross-section of the notches in the base (i.e., an axial cross-section through the notches) is part-circular or semicircular. The cross-section may be perpendicular to the axis of rotation. In some such embodiments, the edge of each notch is pitched at an angle relative to the plane of the base, and the pitch angle may vary along the length of the edge. In some embodiments, one end of the edge is pitched at an angle between 20° and 70°, and the other end of the edge is pitched at an angle between 110° and 160°.

[0034] The notch in the base portion extends inward from the outer periphery of the rotor toward the center of the base portion. In some embodiments, the notch extends inward at least 5%, at least 10%, at least 20%, at least 30%, or at least 40% of the radius of the rotor. In some embodiments, the notch extends inward no more than 50%, no more than 40%, no more than 30%, no more than 20%, or no more than 10% of the radius of the rotor. In some embodiments, the notch extends inward between 5 and 50% of the radius of the rotor.

[0035] In some embodiments, the radial vanes are an extension of the divider through the base.

[0036] In some embodiments, the radial vanes are tapered, with the width of each vane decreasing from the outer periphery of the rotor to the central aperture.

[0037] The following optional features may be equally applicable to any embodiment of the first, second or third aspect of the invention described above.

[0038] In some embodiments, the radial blades or vanes are symmetrically positioned, hi some embodiments, the radial blades or vanes are equally spaced from each other.

[0039] In some embodiments, the radial blades or vanes are inclined at an angle relative to the plane of the base. In some embodiments, the radial blades or vanes are inclined at an angle between 20° and 70° relative to the plane of the base. In some embodiments, the radial blades or vanes are curved. In some embodiments, the radial blades or vanes are curved and inclined at an angle relative to the plane of the base. Inclining the blades / vanes at an angle or curving the blades / vanes in the intended direction of rotation helps to reduce the drag coefficient as the rotor rotates in the melt, reducing the amount of stirring power required for a given rotation speed.

[0040] In some embodiments, the rotor includes at least four partitions and at least four passages defined therebetween, or at least six partitions and at least six passages defined therebetween, hi some embodiments, the rotor includes four partitions and four passages, five partitions and five passages, six partitions and six passages, seven partitions and seven passages, or eight partitions and eight passages.

[0041] In some embodiments, the dividers are oriented perpendicular to the plane of the base. Alternatively, the dividers may be oriented at an angle to the plane of the base. In some embodiments, the dividers are oriented at an angle between 20° and 70° to the plane of the base.

[0042] The divider may extend axially between the base and the roof. Optionally, the divider does not extend beyond the base. The divider may be spaced apart from the plurality of apertures and / or radial blades in the base. In embodiments including vanes extending from the base, the divider may extend from the base in an opposite direction to the vanes.

[0043] In some embodiments, each passageway is provided with a second outlet in the roof of the rotor, which may disperse the gas upwards from the rotor in use. A combination of laterally directed and upwardly directed outlets allows for the production of smaller and more numerous gas bubbles, which has been found to improve degassing and purification efficiency, as described in the applicant's previous patent EP1573077.

[0044] In some embodiments, each second outlet is a notch extending inwardly from the outer periphery of the roof portion. The notch may be part-circular or semi-circular in cross section. In some embodiments, the notch extends inwardly at least 5%, at least 10%, at least 20%, at least 30%, or at least 40% of the radius of the rotor. In some embodiments, the notch extends inwardly no more than 50%, no more than 40%, no more than 30%, no more than 20%, or no more than 10% of the radius of the rotor. In some embodiments, the notch extends inwardly between 5 and 50% of the radius of the rotor.

[0045] In some embodiments, the roof cutout extends through the roof portion perpendicular to the plane of the roof portion. In some embodiments, the roof cutout extends through the roof portion at an angle to the plane of the roof portion. In some embodiments, the roof cutout extends through the roof portion at an angle between 20° and 70° to the plane of the roof portion. In some embodiments, the roof cutout extends through the roof portion at an angle between 110° and 160° to the plane of the roof portion. In embodiments where the dividers and / or radial vanes / blades are oriented at an angle to the plane of the base portion, the cutout may extend through the roof portion at an angle equal to or opposite to either the divider angle and / or the radial vane / blade angle.

[0046] In some embodiments, the inner surface of the roof portion includes a groove extending between the central chamber and the at least one second outlet. The groove may allow a portion of the gas injected through the shaft to be more efficiently directed to the second outlet.

[0047] In some embodiments, the roof of the rotor is provided with a central bore through the rotor to allow gas to be injected from the hollow shaft into the central chamber of the rotor.

[0048] In some embodiments, the inner surface of the roof portion comprises an internal flow guide for directing bubbles in the roof portion downward into the central chamber and toward the base of the rotor. In some embodiments, the flow guide comprises an annular wall. In some embodiments, the annular wall extends around the circumference of the central bore of the roof portion. The annular wall may be tapered to be widest at the roof portion and narrow as it extends toward the base of the rotor. In some embodiments, the annular wall comprises a plurality of open channels extending generally in a direction between the roof portion and the base portion. The channels may be curved to impart a downward spiral flow pattern to bubbles from the roof portion.

[0049] In some embodiments, the roof and base of the rotor are generally disc-shaped.

[0050] In some embodiments, the rotor is made from an isostatically pressed refractory material. Any refractory material suitable for isostatic pressing can be used, such as a refractory mixture containing metal oxides, carbides, or nitrides. In some embodiments, the rotor is made from graphite, alumina, alumina silicate, carbon-bonded alumina, carbon-bonded ceramics, clay-bonded graphite, silicon nitride alumina, fused silica, silicon carbide, zirconia, or any mixture thereof.

[0051] According to a fourth aspect of the present invention there is provided a rotor for use in a rotational device of any of the embodiments of the first, second or third aspects. Any of the optional features described above in relation to the first, second or third aspects may be freely combined with the rotor of the fourth aspect, where applicable.

[0052] In some embodiments, the roof portion of the rotor comprises an engagement means for attachment to a hollow shaft of a rotating device. The engagement means may comprise a threaded wall that allows the rotor to be screwed onto complementary threads on one end of the hollow shaft. Alternatively, the engagement means may comprise a cavity in the roof portion of the rotor. The cavity is configured to have a complementary size and shape to one end of the hollow shaft such that the rotor may be attached to the hollow shaft by a push-fit mechanism or using a suitable heat resistant adhesive such as an expanding heat resistant foam adhesive (e.g., Cera Foam manufactured by ZYP Coatings, Inc.). Alternatively, the engagement means may comprise a locking mechanism.

[0053] It will be understood that the rotors disclosed herein are not limited to a particular manufacturing method and may be formed by any suitable method, such as, for example, isostatic pressing around a sacrificial core followed by removal of the core, additive manufacturing methods, etc. [Brief description of the drawings]

[0054] [Figure 1] FIG. 1 shows a prior art rotor as described in WO2004 / 057045. [Figure 2a] Figure 2a shows an embodiment of a rotor for use in the first aspect of the invention. [Figure 2b] Figure 2b shows an embodiment of a rotor for use in the first aspect of the invention. [Figure 2c] Figure 2c shows an embodiment of a rotor for use in the first aspect of the invention. [Diagram 3] FIG. 3 shows another embodiment of a rotor for use in the first aspect of the invention. [Figure 4] FIG. 4 shows an embodiment of a rotor for use in the second aspect of the invention. [Diagram 5] FIG. 5 shows an embodiment of a rotor for use in the third aspect of the invention. [Figure 6] FIG. 6 is a graph comparing the torque of three different rotor designs. [Figure 7] Figure 7 is a chart comparing water level changes. [Figure 8] FIG. 8 shows three graphs comparing the mixing efficiency of three different rotor designs. [Figure 9] FIG. 9 is a graph comparing degassing efficiencies. [Figure 10a] FIG. 10a is a graph comparing the effect of various different features on degassing efficiency. [Figure 10b] FIG. 10b is a graph comparing the effect of various different features on degassing efficiency. [Figure 10c] FIG. 10c is a graph comparing the effect of various different features on degassing efficiency. [Figure 11] FIG. 11 is a graph comparing bubble mass transfer of five different rotor designs. [Figure 12] FIG. 12 is a graph comparing the surface mass transfer of five different rotor designs. [Figure 13a]FIG. 13a shows a graph comparing the degassing efficiency of five different rotor designs. [Figure 13b] FIG. 13b shows a graph comparing the degassing efficiency of five different rotor designs. [Figure 14] FIG. 14 is a graph comparing the degassing efficiency of the two rotor designs. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] Figures 2a-c show three different perspective views of a rotor 100 for use in a first aspect of the invention. The rotor 100 comprises a roof portion 20 and a base portion 22 spaced apart by a number of partitions 24 (six partitions in the embodiment shown). The partitions 24 extend radially from the periphery of a central chamber 26 defined between the roof portion 20 and the base portion 22. The roof portion 20 and the base portion 22 are generally disc-shaped.

[0056] A passage is defined between each adjacent pair of partitions 24, with each passage having an inlet 28 located radially outward of the central chamber 26 and a first outlet 30 at the outer circumferential surface of the rotor 100. The first outlets direct flow laterally away from the rotor. Each passage also has a second outlet 32 ​​in the roof portion 20. The second outlets 32 direct flow upwardly away from the rotor. Each of the second outlets 32 is a part-circular cutout in the roof portion 20 that extends inwardly from the outer periphery of the rotor 100. The second outlets 32 are narrower than the first outlets 30.

[0057] The base portion 22 includes three apertures 34 that are in fluid communication with the central chamber 26. Each adjacent pair of apertures 34 defines a radial blade 36 therebetween. In the illustrated embodiment, the base portion 22 includes three radial blades 36 equally spaced apart in a turbine configuration, the radial blades 36 lying in a plane A of the base portion.

[0058] The edge 37 of each radial blade 36 is inclined at an angle α to the plane of the base. In the embodiment shown, the angle α is 60°. The partition 24 and the second outlet 32 ​​are also oriented at the same angle α to the plane A of the base.

[0059] The roof portion 20 of the rotor 100 includes a central bore 39 and engagement means for attachment to a hollow shaft. In the illustrated embodiment, the engagement means includes an internally threaded wall 38 for screwing onto a male threaded end of a hollow shaft. The inner surface of the roof portion 20 includes a flow guide for directing air bubbles within the roof portion 20 downwardly into the central chamber 26. In the illustrated embodiment, the flow guide includes an annular wall 41 that extends around the central bore 35. The annular wall 41 is tapered, being widest at the roof portion 20 and narrowing as it extends towards the base portion 22. The annular wall 41 includes a number of open channels 43 that extend generally in a direction between the roof portion 20 and the base portion 22 and are curved to impart a downward spiral flow pattern to air bubbles within the roof portion 20.

[0060] Figure 3 shows another embodiment of a rotor 200 for use in the first aspect of the invention. The rotor 200 is substantially similar to the rotor 100 shown in Figures 2a to 2c, but with some differences.

[0061] 3, the radial blades 36 project outwardly from the plane A of the base and are slightly curved. The radial blades 36 are connected to one another by a central hub 42 in the center of the base 22, which provides structural support to the blades 36.

[0062] The second outlet 32 ​​is inclined at an angle α of 60° to the plane A of the base, while the partition 24 and the radial blades 36 are inclined at an angle β of 150° to the plane A of the base.

[0063] Figure 4 shows an embodiment of a rotor 300 for use in the second aspect of the invention. Features of rotor 300 that are shared with rotors 100, 200 of Figures 2-3 are referenced with the same numerals.

[0064] The rotor 300 includes a roof portion 20 and a base portion 22 separated by a number of partitions 24 (four partitions in the illustrated embodiment) that extend radially from the periphery of a central chamber 26 defined between the roof portion 20 and the base portion 22. The roof portion 20 and the base portion 22 are generally disk-shaped.

[0065] A passage is defined between each adjacent pair of partitions 24, each having an inlet 28 located radially outside the central chamber 26 and a first outlet 30 at the outer circumferential surface of the rotor 100. The first outlets direct the flow laterally from the rotor. Each passage also has two second outlets 32 in the roof portion 20. The second outlets 32 direct the flow upwardly from the rotor. Thus, in the illustrated embodiment, the rotor 300 comprises four partitions 24, four passages, four first outlets 30 and eight second outlets 32. Each of the second outlets 32 is a part-circular cutout in the roof portion 20, extending inwardly from the outer periphery of the rotor 100. The partitions 24 and the second outlets 32 are oriented perpendicular to the plane of the roof portion (parallel to the plane A of the base portion).

[0066] The base portion 22 includes a central aperture 46 that is in fluid communication with the central chamber 26. The base portion 22 further includes a plurality of radial vanes 48 that project outwardly from the plane A of the base portion and are disposed about the central aperture 46. The radial vanes 48 extend toward the center of the base portion 22 and project partially beyond the central aperture 46. In the illustrated embodiment, the base portion 22 includes five radial blades 46 that are equally spaced about the central aperture 46. The radial vanes 48 are curved, but are not inclined at an angle relative to the plane A of the base portion.

[0067] The roof portion 20 comprises four alternating grooves 44 extending between the central chamber 26 and the four second outlets 32. The roof portion 20 also comprises a central bore 39 and engagement means in the form of a hexagonal cavity 40 adapted to fit over the end of a hollow shaft having a corresponding size and shape.

[0068] Figure 5 shows an embodiment of a rotor 400 for use in the third aspect of the invention. Features of rotor 400 that are shared with the rotors of Figures 2 to 4 are referenced with the same numerals.

[0069] The rotor 400 includes a roof portion 20 and a base portion 22 separated by a number of partitions 24 (four partitions in the illustrated embodiment) that are curved and extend radially from the periphery of a central chamber 26 defined between the roof portion 20 and the base portion 22. The roof portion 20 and the base portion 22 are generally disc-shaped.

[0070] A passage is defined between each adjacent pair of partitions 24, with each passage having an inlet 28 located radially outward of the central chamber 26 and a first outlet 30 at the outer circumferential surface of the rotor 100. The first outlets 30 direct flow laterally from the rotor. Each passage also has two second outlets 32 in the roof portion 20. The second outlets 32 direct flow upwardly from the rotor. In the illustrated embodiment, the rotor 300 includes four partitions 24, four passages, four first outlets 30, and eight second outlets 32. Each of the second outlets 32 is a partial circular cutout in the roof portion 20 and extends inwardly from the outer periphery of the rotor 400.

[0071] The base portion 22 includes a central aperture 46 that is in fluid communication with the central chamber 26. The base portion 22 further includes a plurality of radial vanes 48 that project outwardly from the plane A of the base portion and are disposed about the central aperture 46. The radial vanes 48 are curved and tapered, with the width of each vane decreasing from the outer periphery of the rotor 400 toward the central aperture 46. The radial vanes 48 are an extension of the partitions 24 that extend through the base portion 22, with the partitions 24 and the radial vanes 48 forming a continuous plane that extends through the base portion 22.

[0072] The roof portion 20 of the rotor 400 includes a central bore 39 and engagement means for attachment to a hollow shaft. In the illustrated embodiment, the engagement means includes a threaded wall 38 for screwing onto the end of the hollow shaft. The inner surface of the roof portion 20 includes a flow guide for directing air bubbles within the roof portion 20 downwardly into the central chamber 26. In the illustrated embodiment, the flow guide includes an annular wall 41 that extends around the central bore 35. The annular wall 41 is tapered, being widest at the roof portion 20 and narrowing as it extends toward the base portion 22. The annular wall 41 includes a number of open channels 43 that extend generally in a direction between the roof portion 20 and the base portion 22 and are curved to impart a downward spiral flow pattern to air bubbles within the roof portion 20.

[0073] The divider 24, radial vanes 48 and second outlet 32 ​​are oriented at an angle α of 60° with respect to the plane A of the base (or with the plane of the roof parallel to the plane A of the base).

[0074] The base portion 22 includes a plurality of notches 50 disposed between the radial vanes 48, the notches 50 extending inwardly from the outer periphery of the rotor 400. In the illustrated embodiment, the base portion 22 includes four radial vanes 48 and four notches 50. The notches 50 are formed in a semicircular shape. The notches 50 extend inwardly from the outer periphery of the rotor 400 to a depth R2 that is approximately 30% of the radius R1 of the rotor 400.

[0075] The edge 52 of each notch is inclined at an angle relative to the plane A of the base. The angle of the edge 52 varies such that at one end the edge 52 is inclined at an angle of 60° and at the other end the edge 52 is inclined at an angle of 150°.

[0076] <Results of full-scale water modeling> The performance of various rotor designs was tested by water modelling in a full-size crucible fitted with a baffle plate. 250 litres of room temperature water was filled into the crucible to a depth of 700mm. Water has similar viscosity characteristics to molten aluminium and is therefore a useful surrogate for indicating rotor performance in molten metal.

[0077] Three rotor designs were compared: (A) a prior art rotor design as shown in Figure 1, (B) a design according to the present invention as shown in Figure 4, and (C) a design according to the present invention as shown in Figures 2a-c.

[0078] [Mixing force and vortex height] Torque measurements were performed at different rotational speeds to compare the relative stirring power of each rotor design. The height of the water in the crucible from a baseline of 700 mm was also measured. Usually, a higher water level indicates the generation of a stronger vortex. The strength of the vortex needs to be balanced because a higher vortex can result in faster degassing and better mixing efficiency, but it also increases air entrainment in the melt.

[0079] The torque measurement results are shown in Figure 7, which is a graph of torque (N·m) versus rotational speed (rpm). At all rotational speeds, both rotor design B and rotor design C showed higher torque than comparison design A, with rotor design B showing the highest torque.

[0080] As shown in Figure 8, the increased torque for design B resulted in a significantly higher water surface level and stronger vortexes than either design A or design C. Design C showed slightly higher water surface levels and slightly stronger vortexes than comparative design A.

[0081] [Mixing efficiency] A series of thermocouples were placed at various locations within the crucible and on the baffle plate to measure the temperature of the water at these locations. The rotor was submerged in the water and equilibrated at a rotation speed of 600 rpm. A volume of 7 liters of hot water (80°C) was then poured into the crucible and the time it took for the temperature to restabilize across all the thermocouples (referred to as the "mixing time") was measured.

[0082] The results are shown graphically in Figure 8, which is a graph of temperature (°C) versus time (sec). Each line on the graph corresponds to the temperature measurement of a different thermocouple within the crucible.

[0083] The mixing time for rotor design A was 109 seconds - 88 seconds = 21 seconds. The mixing time for rotor design B was 280 sec-272 sec=8 sec. The mixing time for rotor design C was 280 sec-272 sec=8 sec.

[0084] Both rotor design B and rotor design C demonstrated mixing efficiencies that were more than twice as high as that of comparative design A.

[0085] [Degassing efficiency] Example 1: The oxygen meter was submerged in the water toward the top of the crucible. The rotor was rotated at 600 rpm and the time required for the oxygen level to reach a minimum was measured. Oxygen dissolved in water behaves similarly to hydrogen dissolved in molten aluminum, therefore this test gives a useful measure of the efficiency of degassing of the molten metal.

[0086] The degassing results are shown in Figure 9, which is a graph of oxygen level (mg / L) versus time (sec). First, both Rotor B and Rotor C showed significantly faster oxygen removal than the comparative design A. The maximum oxygen removal achieved with Rotor B was less than that achieved with Rotor A, likely due to the higher vortex generated by Rotor B resulting in air entrainment. However, it is noted that the vortex level can be reduced by adjusting the baffle depth or the number of baffle plates to counteract this adverse effect.

[0087] Rotor C performed best, exhibiting both the fastest oxygen removal and the highest maximum oxygen removal (lowest final level of oxygen).

[0088] The degassing efficiency of several other rotor designs was also measured to compare the effect of different individual features.

[0089] Example 2: First, rotor design A was compared to a new rotor design D to compare the effect of radial vanes projecting outward from the base. Rotor D had all the same features as rotor B except for the grooves in the roof, which were omitted in rotor D.

[0090] Rotor design A was then compared to a new rotor design, E, to compare the effect of roof grooves. Rotor E had all the same features as rotor A, but with the addition of roof grooves extending between the central chamber and the four secondary outlets.

[0091] Finally, rotor design B was compared with rotor design D to demonstrate the synergistic effect of radial vanes and grooves.

[0092] The results are shown in Figures 10a-c, which are graphs of oxygen level (mg / L) versus time (sec). As shown in Figure 10a, the radial vanes produced a significant increase in degassing efficiency, while Figure 10b shows that the roof grooves produced a moderate increase in degassing efficiency. Figure 10c shows that the rotor with both radial vanes and grooves achieved the best degassing efficiency.

[0093] <Results of small-scale water modeling> Further experiments with various rotor designs were carried out in a small scale setup using a 193 x 300 mm cylindrical tank filled with water at 20°C to a depth of 230 mm (6.73 liters). The rotors were fitted with a common diameter of 65 mm. Baffles in the form of 400 x 20 mm aluminium strips were fixed adjacent to the tank wall. The rotors were attached to a centrally located laboratory overhead stirrer at a depth of 70 mm above the bottom of the tank. Gas was supplied adjacent to the rotor at either 1.8 L / min (air) or 2 L / min (argon). Oxygen concentration in the water was measured by a YSI optical dissolved oxygen probe submerged in the water.

[0094] [Mass transfer analysis] Each experiment began by equilibrating the water in the tank. This involved purging the tank with air while stirring at high speed (600 rpm) until a stable oxygen concentration of approximately 10 mg / L was achieved. For each rotor design, degassing rates were measured at 400, 600, and 800 rpm with a constant argon flow of 2 L / min.

[0095] The oxygen concentration C(t) in the tank, which changes over time, is considered to follow the following equation (1).

number

[0096] The boundary layer at the free surface of the water maintains local equilibrium with the air above it, and has an equilibrium concentration C E Assume that the equilibrium concentration at the surface, C E and the bulk composition C(t), drives the flow of dissolved oxygen from the surface to the bulk. This also reduces the area of ​​the free surface A S and the surface mass transfer coefficient k S A population of bubbles in water has a local equilibrium concentration C at their surface. B The bulk compositions C(t) and C B This difference between the surface area A of the bubble drives the flow of dissolved oxygen to the bubble. B and the bubble mass transfer coefficient k B Analysis of the flux of dissolved oxygen from the surface to the bulk and from the bulk to the bubbles leads to the following equation (2), which describes the expected time dependence of the bulk oxygen concentration:

number

number

[0097] As mentioned above, the bubble mass transfer parameter k1 depends on the rotor's ability to generate a population of small bubbles, which will have a larger mass transfer and a larger total interfacial area with the water. Hence, the higher k1, the greater the rotor's contribution to the degassing rate can be. The surface mass transfer parameter k2 represents the extent to which the rotor generates near-surface flows that generate gas generation / release at the free surface, but also the reabsorption of air from the free surface.

[0098] Five rotor designs were compared: (A) a prior art rotor design as shown in Figure 1, (B) a design according to the present invention as shown in Figure 4, (C) a design according to the present invention as shown in Figures 2a-c, (F) a design according to the present invention as shown in Figure 3, and (G) a design according to the present invention as shown in Figure 5.

[0099] Bubble mass transfer parameter k1: The above analysis was applied to the outgassing curves of each rotor. The calculated k1 values ​​for each rotor are shown in Table 1 below and in Figure 11.

[0100] [Table 1]

[0101] Each of the rotor designs (B, C, F, and G) according to the invention exhibited higher k1 values ​​at stirring speeds of 400 rpm and 600 rpm, which are within the standard range of speeds for stirring aluminum, than prior art Example A. Rotor design F and rotor design G exhibited the highest k1 values ​​at all stirring speeds, indicating that these designs are capable of producing a greater population of microbubbles.

[0102] Surface mass transfer parameter k2: The calculated k2 values ​​for each rotor are shown in Table 2 below and in FIG.

[0103] [Table 2]

[0104] The general trend of the calculated k2 values ​​roughly mirrors that of the k1 values, indicating that greater surface mass transfer generally correlates with greater bubble mass transfer. However, at 400 rpm, each of the rotor designs according to the invention (B, C, F, and G) exhibited lower k2 values ​​than prior art Example A, indicating less gas uptake and less air reabsorption from the free surface at this agitation speed.

[0105] [Degassing efficiency] Using the miniaturized configuration described above, five rotor designs A, B, C, F, and G were rotated at 400 rpm (Figure 13a) and 600 rpm (Figure 13b). The time it took for the oxygen level to reach its lowest point was measured.

[0106] All four designs according to the invention (B, C, F and G) showed higher degassing efficiency at both 400 and 600 rpm than prior art design A. Designs F and G showed the best degassing performance at both 400 and 600 rpm, with significantly faster oxygen removal at 600 rpm (about 30-50% faster than prior art design A).

[0107] The improved degassing performance of the rotor design according to the invention means that a lower rotational speed can be used for a set degassing time to achieve the same level of oxygen removal as prior art design A, reducing the amount of power required by the rotating device.

[0108] <Aluminum melting test results> The performance of rotor design C (according to Figures 2a-c) was tested in a full size crucible using molten aluminum and compared to prior art rotor design A (shown in Figure 1).

[0109] [Inclusion removal] Rotor C was submerged in molten aluminum and spun at 35 rpm for a treatment time of 4 minutes. A Vmet analysis (Vesuvius metallurgical quality analysis) was performed using a scanning electron microscope, predefined selection rules, and image processing algorithms. The test was repeated once and the summarized results are recorded in Table 3a below. The test was then repeated two more times with rotor design A (Figure 1) at a higher speed of 500 rpm, and a Vmet analysis was performed and the summarized results are recorded in Table 3b.

[0110] [Table 3a]

[0111] [Table 3b]

[0112] The inventors have found that rotors according to the invention are surprisingly effective in removing inclusions from molten aluminum. In Examples 1 and 2, rotor C was found to result in a dramatic reduction in both the inclusion index (derived from the area percentage of defects present) and the total number of inclusions in the aluminum. As Examples 3 and 4 show, a reduction in the total inclusions is achievable, but this is not supported by a comparable reduction in the inclusion index. Of particular note is the almost complete removal of larger inclusions by rotor C. Table 3a shows that almost no inclusions, whether aluminum oxide or not, having a size greater than 15 microns remained after treatment. In contrast, in Examples 3 and 4, the number of large inclusions (>15 microns) increased. This test shows that rotor design C is as effective or more effective than prior art rotor design A, and that this is achieved at a lower rotational speed.

[0113] Lower rotational speeds are desirable because they reduce wear on the rotor and machinery, and they reduce the size of vortices formed on the surface, thus reducing gas entrainment in the molten metal. However, higher speeds usually provide more mixing and are more effective at degassing and inclusion removal. Thus, the speed selected for a processing operation is a balance between these two factors.

[0114] [Degassing efficiency] Rotor C was submerged in the aluminum and rotated at 350 rpm while monitoring the hydrogen content in the molten aluminum. Nitrogen gas was passed through the rotor to remove hydrogen from the melt. The test was then repeated using Rotor A at 350 and 500 rpm. The results are plotted in the graph of Figure 14.

[0115] The average time for the hydrogen concentration to decrease by 50% was as follows: - Rotor C-350rpm 160sec - Rotor A-350 rpm 350 seconds - Rotor A-500rpm 185sec The graph shows that Rotor C is more effective than Rotor A in removing hydrogen from the aluminum melt at the same rotational speed, and is still improved compared to Rotor A even at a higher rotational speed of 500 rpm.

Claims

1. A rotary device for treating molten metal, comprising: a hollow shaft; and a rotor at one end of the hollow shaft; The rotor is a roof portion and a base portion, the roof portion and the base portion being spaced apart and connected by a plurality of partition portions; a central chamber defined between the roof portion and the base portion, the plurality of partitions extending radially from a periphery of the central chamber; a passage defined between each pair of adjacent partitions, each passage having an inlet located radially outward of the central chamber and an outlet at an outer peripheral surface of the rotor; a flow path defined through the hollow shaft into the central chamber, through the inlets of the plurality of passages, and out the outlets of the plurality of passages; It is equipped with The base portion includes a plurality of apertures in fluid communication with the central chamber, and radial blades defined between each adjacent pair of apertures.

2. The rotation device of claim 1 , wherein the base portion comprises at least three apertures and at least three radial blades.

3. 3. A rotating device according to claim 1 or claim 2, wherein the radial blades project outwardly from the plane of the base.

4. 3. The rotation device of claim 1, wherein the radial blades are inclined obliquely relative to a plane perpendicular to the rotation axis, and the radial blades are configured to decelerate fluid passing through the base portion and entering the central chamber.

5. 1. A rotary device for processing molten metal, comprising: a hollow shaft; and a rotor at one end of the hollow shaft, the rotor comprising: a roof portion and a base portion, the roof portion and the base portion being spaced apart and connected by a plurality of partition portions; a central chamber defined between the roof portion and the base portion; a passage defined between each pair of adjacent partitions, each passage having an inlet located radially outward of the central chamber and an outlet at an outer peripheral surface of the rotor; a flow path defined through the hollow shaft into the central chamber, through the inlets of the plurality of passages, and out the outlets of the plurality of passages; It is equipped with the base portion includes a central aperture and a plurality of radial vanes projecting outwardly from the base portion, the plurality of radial vanes being disposed about the central aperture; The plurality of radial vanes extend across at least a portion of the central aperture toward a center of the base.

6. 1. A rotary device for processing molten metal, comprising: a hollow shaft; and a rotor at one end of the hollow shaft, the rotor comprising: a roof portion and a base portion, the roof portion and the base portion being spaced apart and connected by a plurality of partition portions; a central chamber defined between the roof portion and the base portion; a passage defined between each pair of adjacent partitions, each passage having an inlet located radially outward of the central chamber and an outlet at an outer peripheral surface of the rotor; a flow path defined through the hollow shaft into the central chamber, through the inlets of the plurality of passages, and out the outlets of the plurality of passages; It is equipped with the base portion includes a central aperture and a plurality of radial vanes projecting outwardly from the base portion, the plurality of radial vanes being disposed about the central aperture; A rotary device, wherein the base portion further comprises a plurality of notches disposed between the plurality of radial vanes, the plurality of notches in the base portion extending inward from an outer periphery of the rotor.

7. The rotation device of claim 6 , wherein the plurality of cutouts in the base portion are part-circular or semi-circular in cross section.

8. 8. A rotation device according to claim 6 or claim 7, wherein the base portion comprises at least four notches.

9. 7. A rotating device as claimed in any one of claims 1, 5 and 6, wherein the rotor comprises at least four partitions and at least four passages defined therebetween, or the rotor comprises at least six partitions and at least six passages defined therebetween.

10. 7. A rotary device as claimed in any one of claims 1, 5 and 6, wherein each passage has a second outlet in the roof portion of the rotor.

11. 11. A rotary device according to claim 10, wherein each second outlet is a notch extending inwardly from the outer periphery of the roof portion, optionally with a part-circular or semi-circular cross section.

12. The rotation device of claim 10 , wherein the inner surface of the roof portion includes a groove extending between the central chamber and the at least one second outlet.

13. 7. A rotary device as claimed in any one of claims 1, 5 and 6, wherein the inner surface of the roof portion is provided with flow guides for directing bubbles in the roof portion downward into the central chamber and towards the base portion of the rotor.

14. 7. A rotating device according to claim 1, 5 or 6, wherein the rotor is made from an isostatically formed heat resistant material.

15. A rotor for use in a rotating device according to any one of claims 1, 5 and 6.

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