Rotary Devices for Molten Metal Processing

Abstract

The present invention relates to a rotating device and method for treating molten metal, a tubular sleeve for the rotating device, and the use of the rotating device in treating molten metal. The rotating device comprises a tubular sleeve with a rotor head at one end, the rotor head comprising a gas outlet for dispersing gas into the molten metal, and a hollow shaft extending within the tubular sleeve such that at least a portion of the hollow shaft is surrounded by the tubular sleeve, the hollow shaft being in fluid communication with the gas outlet of the rotor head. The tubular sleeve is formed of a heat resistant material having corrosion and thermal shock resistance, the hollow shaft being formed of a material including graphite. A first method includes applying a layer of synthetic slag material to an exposed surface of the molten metal and stirring the molten metal with the rotating device with the rotor head such that the molten metal flows through the layer of synthetic slag material. A second method includes adding a metal treating agent to the molten metal, stirring the molten metal with the rotating device with the rotor head, and releasing a gas into the molten metal through the rotor head.

Description

[Technical field]

[0001] The present invention relates to a rotary device and method for treating molten metal, in particular for removing undesirable impurities such as sulfur, dissolved gases, solid inclusions, and for introducing metal treatment additives into the molten metal, and also to a tubular sleeve for the rotary device and the use of the rotary device in treating molten metal. [Background technology]

[0002] Undesirable impurities in molten metal can cause significant problems in the metal casting process, adversely affecting the quality of the finished casting. For example, solid inclusions (typically solid oxides such as alumina and silica) can cause defects and discontinuous surfaces in the metal and clog the nozzles used for casting, and dissolved gases (such as hydrogen gas) can cause undesirable porosity and / or brittleness. Ferrous metals, especially steels, can contain residual sulfur from the raw materials used in the melting process, which increases the brittleness of the casting. It is therefore important to remove as many impurities as possible from the molten metal in order to improve the quality of the finished casting.

[0003] Dissolved gas and solid inclusions are typically removed by purging the molten metal with a gas or gas mixture that is insoluble in the metal, such as argon, nitrogen and / or carbon monoxide. The purge gas bubbles pick up dissolved hydrogen and solid inclusions they encounter as they travel through the molten metal and lift them to the surface. Conventionally, such purging is accomplished by a porous plug in the bottom of the melting furnace or casting ladle, which bubbles the purge gas into the metal. Aluminum (which has a melting point of about 660°C and a density of about 2.4 g / cm when molten) is a highly volatile metal. 3Another method of purging cooler and less dense molten metals such as molten iron (e.g., argon) is by injecting gas into the metal through a hollow shaft with a rotor attached to the end, which rotates and disperses the injected gas into the molten metal. This method produces finer bubbles than using a porous plug, since the injected bubbles are broken up by the rotating rotor head, which improves stirring efficiency and allows finer inclusions to be removed from the molten metal. In this case, the process is sometimes called "degassing".

[0004] Degassing rotors have not traditionally been used with higher temperature and higher density metals such as iron and steel for a number of reasons. Both iron and steel have melting points of about 1150-1550°C and produce about 7 g / cm3 when molten. 3 Conventional heat-resistant ceramic materials, commonly used for aluminum rotors, require a gradual heating before immersion in molten iron or steel; otherwise, they will shatter due to thermal shock. Such priming is a laborious and time-consuming procedure. Also, the extreme temperature and density of molten iron / steel can rapidly warp and distort the rotor head during use, depending on the material from which the rotor is made, which reduces the rotor's stirring and purging efficiency. Molten steel can corrode some heat-resistant ceramic materials, especially the slag layer on the metal surface, but also the bulk metal itself, and some heat-resistant materials (e.g., graphite) used in the manufacture of molten aluminum rotors can dissolve in molten steel. This makes the use of conventional rotors difficult and prone to very short lifespans in metals such as iron and steel at high temperatures, and the use of porous plugs is generally preferred for such applications.

[0005] Desulfurization of ferrous metals can be accomplished in several different ways. In one method, molten metal is treated with a desulfurization additive in a Kanbara Reactor. This reactor is equipped with a very large vessel (usually with a capacity of at least 100 tons) and a cross-shaped impeller to agitate the molten metal. The desulfurization additive (typically calcium oxide powder) is mixed into the molten metal by the rotation of the impeller, where it reacts with the sulfur in the metal to form a solid product (e.g., calcium sulfide). The solid product eventually floats to the surface of the metal and forms a layer of slag, which can be removed by skimming. In Kanbara desulfurization, as mentioned above, the impeller must be gradually heated before being immersed in the molten metal to avoid cracking.

[0006] Another method for desulfurizing ferrous metals involves treating the molten metal with a desulfurizing additive in the form of a cored wire that is fed into the metal from a spool. The cored wire contains a core of desulfurizing additive (usually containing calcium and / or magnesium) surrounded by a sheath of high melting point material (e.g., steel). The sheath protects the additive core from immediate oxidation upon contact with the molten metal and also melts or dissolves gradually as the wire is fed into the metal, releasing the additive core at a predetermined depth below the surface to spread through the top of the molten metal. The feed rate of the wire into the molten metal is balanced with the melting / dissolving rate of the outer sheath to ensure that the additive is released at the desired depth. This method is usually combined with the use of a porous plug, which bubbles gas through the metal to help distribute the additive.

[0007] In addition to (or instead of) desulfurization, metal processing additives may be used to modify the composition, morphology, and / or distribution of inclusions remaining after purging. For example, calcium additives may be used to react with solid oxide inclusions (such as alumina and silica) in the molten steel to form low melting calcium aluminates or silicates that are liquid at the melting point of the steel and do not clog the casting nozzle. The additives also change the morphology of dendritic and plate-like inclusions that may form fault-lines in the cast metal that are prone to cracking, so that the inclusions do not form such fault-lines by becoming more spherical. For example, calcium additives can be used in steel to change the morphology of solid oxide inclusions, and magnesium additives can be used in iron to change the morphology of carbon inclusions.

[0008] It is difficult and dangerous to introduce elemental calcium or magnesium into molten ferrous metals because the boiling points of calcium and magnesium are below the melting points of steel and iron, respectively. Thus, elemental Ca / Mg can either explode or oxidize rapidly on contact with molten iron / steel if too much is added at once. As a result, the additives are usually added in stabilized forms such as calcium silicon (CaSi), calcium silicon barium (CaSiBa), etc., rather than in elemental form.

[0009] CN106435216 discloses a pumping rotor made of graphite.CN210560564 discloses a rotor having a graphite component.JPS6245464 and RU2247289 disclose rotors for metal processing.EA016954 discloses rotors for aluminum processing.

[0010] SUMMARY OF THE PRESENT EMBODIMENT The present invention seeks to provide an improved apparatus and method for processing molten metal, or at least to provide a useful alternative. Summary of the Invention

[0011] <Rotation device> According to a first aspect of the invention, there is provided a rotating device (also referred to herein as a "rotor") for treating molten ferrous metal with a gas. The device comprises a tubular sleeve having a rotor head at one end, a hollow shaft extending into the tubular sleeve such that at least a portion of the hollow shaft is surrounded by the tubular sleeve, and the hollow shaft comprises a locking portion configured to engage a complementary receiving portion in the tubular sleeve. The rotor head comprises a gas outlet for releasing the gas into the molten ferrous metal, the hollow shaft being in fluid communication with the gas outlet of the rotor head. The tubular sleeve and the rotor head are formed from a heat-resistant material that is resistant to corrosion and thermal shock. The hollow shaft is formed from graphite and the tubular sleeve is formed from a more resistant heat-resistant material.

[0012] The inventors have found that a two-piece rotor with an inner hollow shaft made from a material containing graphite and an outer tubular sleeve and rotor head made from a more resistant heat-resistant material has excellent durability and life in high-temperature molten metals such as steel. An embodiment of the present invention has achieved excellent stirring and purging efficiency while undergoing repeated testing in molten steel with little deformation. It has been found that the hollow shaft containing graphite has adequate resistance to the high temperatures of molten steel and does not melt or shatter, while being plastic enough to be attached to a motor without breaking during use. Without wishing to be bound by theory, it is believed that an inner shaft made from a metal would soften excessively under the temperatures experienced in molten iron / steel, and an inner shaft made from a ceramic material would be too brittle to be attached to a motor. Thus, the inventors have found that graphite is particularly suitable for use in the hollow shaft of the present invention. Although graphite is not normally considered suitable for use in molten steel because it can dissolve in molten steel, in the present invention the hollow shaft containing graphite is protected by the outer tubular sleeve.

[0013] In an embodiment, the tubular sleeve is formed from a refractory material including fused silica; silicon carbide; alumina; carbon-bonded alumina; carbon-bonded ceramic; clay graphite; silicon nitride alumina; isopressed refractory mixtures containing metal oxides, carbides, or nitrides; refractory substrates coated with alumina and / or magnesium zirconate or metal oxides, or combinations thereof. The rotor head may also be formed from a refractory material including fused silica; silicon carbide; alumina; carbon-bonded alumina; carbon-bonded ceramic; clay graphite; silicon nitride alumina; isopressed refractory mixtures containing metal oxides, carbides, or nitrides; refractory substrates coated with alumina and / or magnesium zirconate or metal oxides, or combinations thereof. In some embodiments, both the tubular sleeve and the rotor head are made from the same material. In other embodiments, the tubular sleeve and the rotor head are made from different materials.

[0014] High resistance refractory materials including fused silica; silicon carbide; alumina; carbon-bonded alumina; carbon-bonded ceramics; clay graphite; silicon nitride alumina; isopressed refractory mixtures including metal oxides, carbides, or nitrides; refractory substrates coated with alumina and / or magnesium zirconate or metal oxides, or combinations thereof, also have sufficient corrosion resistance and thermal shock resistance to be used in molten steel without the need for priming. However, these materials are very expensive. Furthermore, these materials are relatively brittle, and the inventors of the present invention have found that they do not have the necessary plasticity to be attached to a motor. Without wishing to be bound by theory, it is believed that a single-piece rotor made entirely from such high resistance materials would be vulnerable to vibrations in use and could crack near the attachment point with the motor, causing the rotor to become unstable and eventually break completely. The rotating device of the present invention includes only an outer sleeve made from such materials, addressing both of the above problems by reducing the amount of high temperature resistant material required, and by providing an inner shaft made from a more plastic refractory material (including graphite) that is less susceptible to cracking when attached to a motor.

[0015] In an embodiment, the tubular sleeve and / or rotor head are formed from a refractory material comprising isopressed carbon-bonded alumina, such as that manufactured under the trade name Viso™ by Vesuvius Plc. The present inventors have found that rotors made using isopressed carbon-bonded alumina are particularly durable, able to withstand up to 18 uses without deformation before slag buildup prevents further use of the rotor.

[0016] In embodiments, the rotor head is integrally formed with the tubular sleeve. In other embodiments, the rotor head is a separate component that is coupled to the end of the tubular sleeve. In such embodiments, the rotor head may be coupled to the end of the tubular sleeve by any suitable means, such as a threaded connection, a press fit, or the like.

[0017] In an embodiment, the hollow shaft has a first end and a second end, and the first end of the hollow shaft is surrounded by a tubular sleeve. In an embodiment, the second end of the hollow shaft is configured to be coupled to an apparatus (e.g., a motor) for rotating the rotating device. For example, the second end of the hollow shaft may include a pulley configured to be connected to the motor by a V-belt, or the second end of the hollow shaft may be configured to be directly attached to a motor shaft. In some embodiments, the second end of the hollow shaft may be configured to receive a collar that includes a pulley for a V-belt, or a collar that is configured to be coupled to the motor shaft using other means (e.g., by providing a flange with an opening for a bolt).

[0018] The length of the hollow shaft may be measured between the first end and the second end. In embodiments, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of the length of the hollow shaft is surrounded by the tubular sleeve. In embodiments, the hollow shaft is substantially completely surrounded by the tubular sleeve, although it will be understood that in such embodiments, the tubular sleeve is open near the second end of the hollow shaft, and the second end of the hollow shaft may still be coupled to an apparatus for rotating the rotation device.

[0019] In an embodiment, the first end of the hollow shaft (surrounded by the tubular sleeve) is provided with a locking portion configured to engage a complementary receiving portion within the tubular sleeve. The locking portion and receiving portion serve not only to securely fix the tubular sleeve to the hollow shaft, but may also lock the hollow shaft and the tubular sleeve to each other in rotation, preventing the hollow shaft from rotating independently of the tubular sleeve during use. The complementary receiving portion may be located at the end of the tubular sleeve that comprises the rotor head. During use, the tubular sleeve may soften and, although supported by the internal graphite hollow shaft, some twisting of the rotor may occur. By providing a receiving portion at the end of the tubular sleeve that comprises the rotor head, the tubular sleeve will twist less than if the tubular sleeve were driven from the end remote from the rotor head. It will be appreciated that the receiving portion does not necessarily have to be at the very end of the tubular sleeve, but may be located away from the very end.

[0020] In an embodiment, the locking portion and the receiving portion have a polygonal cross section. It will be appreciated that in such an embodiment, the locking portion and the receiving portion have the same polygonal cross section, with the locking portion being slightly smaller in diameter to fit snugly inside the receiving portion. The edges of the locking portion abut the edges of the receiving portion to prevent the locking portion from rotating within the receiving portion. In some embodiments, the polygonal cross section has at least 3, 4, 5, or 6 vertices. Preferably, the polygonal cross section has no more than 12, 11, or 10 vertices to ensure that the angles formed between the edges of the polygons are sufficiently sharp to inhibit the vertices of the locking portion from sliding between the vertices of adjacent receiving portions. In other embodiments, the locking portion and the receiving portion have a circular cross section with the chords removed.

[0021] The length of the tubular sleeve may be measured along its longitudinal axis. In some embodiments, the hollow shaft extends within the tubular sleeve along at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of the length of the tubular sleeve. As such, the hollow shaft may terminate beyond the rotor head rather than extending into the rotor head. In embodiments, the hollow shaft extends within the tubular sleeve along substantially the entire length of the tubular sleeve such that the first end of the hollow shaft is immediately adjacent to the rotor head. In embodiments in which the hollow shaft does not extend within the tubular sleeve along substantially the entire length of the tubular sleeve and the first end of the hollow shaft is not immediately adjacent to the rotor head, the tubular sleeve may include a conduit or bore that fluidly connects the hollow shaft to a gas outlet of the rotor head.

[0022] In some embodiments, the second end of the hollow shaft may be secured to the tubular sleeve by a clamping means.

[0023] The rotor head may have any suitable shape or configuration for stirring the molten metal.

[0024] In embodiments, the rotor head comprises a plane (i.e., a plate) extending in a direction perpendicular to the longitudinal axis of the tubular sleeve and a number of vanes projecting from the plane in a direction substantially parallel to the longitudinal axis of the tubular sleeve. In such embodiments, the gas outlet may comprise a bore in the plane. In embodiments, the bore is located at the center of the plane. In some embodiments, the rotor head comprises a second plane (i.e., a plate) located opposite the first plane and connected thereto by a number of vanes or pillars. Such embodiments may also comprise vanes projecting from a base of the second plate. The plate may be substantially circular or polygonal, for example rectangular. In embodiments, the plate may be a parallel square plate with concave edges and truncated corners.

[0025] Single plate rotor head designs have been found to be easier to manufacture by pressing techniques (e.g., using materials such as isopressed carbon-bonded alumina) than double plate designs. Although double plate rotor head designs can be manufactured by pressing techniques, it has been found that complete densification is not always achieved throughout the rotor head. Single plate rotor head designs may increase the amount of downward flow away from the rotor head, and double plate rotor head designs may increase the amount of sideways flow away from the rotor head.

[0026] The hollow shaft and tubular sleeve may be coupled via a friction fit, although other coupling means and mechanisms may also be used.

[0027] In a second aspect of the invention there is provided a tubular sleeve for use with a rotating device of the first aspect, the tubular sleeve having an internal complementary receiving portion and formed from a heat resistant material that is more resistant than graphite.

[0028] The tubular sleeve may be formed from refractory materials including fused silica; silicon carbide; alumina; carbon-bonded alumina; carbon-bonded ceramic; clay graphite; silicon nitride alumina; isopressed refractory mixtures including metal oxides, carbides, or nitrides; refractory substrates coated with alumina and / or magnesium zirconate or metal oxides, or combinations thereof.

[0029] In some embodiments, the tubular sleeve has an integrally formed rotor head at one end, the rotor head having a gas exhaust port, while in other embodiments, the tubular sleeve has a means for coupling to a separate rotor head at one end, such as a threaded coupling means.

[0030] The length of the tubular sleeve of the second aspect may be measured along its longitudinal axis. In an embodiment, the tubular sleeve comprises a bore for receiving the hollow shaft, the bore extending into the tubular sleeve along at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of the length of the tubular sleeve. In an embodiment, the bore for receiving the hollow shaft extends inside the tubular sleeve along substantially the entire length of the tubular sleeve. In an embodiment where the bore for receiving the hollow shaft does not extend inside the tubular sleeve along substantially the entire length of the tubular sleeve, the tubular sleeve may comprise a further conduit or bore for fluidly connecting the bore for receiving the hollow shaft to a gas outlet of the rotor head or a means for coupling to the rotor head.

[0031] In embodiments, the tubular sleeve includes a receiving portion configured to engage a complementary locking portion of the hollow shaft. In some embodiments, the receiving portion has a polygonal cross-section. In some embodiments, the polygonal cross-section has at least 3, 4, 5, or 6 vertices. In some embodiments, the polygonal cross-section has 12, 11, or 10 or fewer vertices. In other embodiments, the locking portion and receiving portion have a circular cross-section with a chord removed.

[0032] It will be appreciated that any of the features and embodiments described in relation to the first aspect may be equally applicable to the second aspect.

[0033] <Method of processing molten metal> According to a third aspect of the present invention there is provided a method of treating molten metal comprising the steps of: applying a layer of synthetic slag material to an exposed surface of the molten metal; agitating the molten metal using a rotating device comprising a rotor head to cause the molten metal to flow through a layer of synthetic slag material on the surface; Includes.

[0034] In an embodiment, the molten metal is stirred such that at least a portion of the layer of synthetic slag material remains on the surface during stirring.

[0035] In an embodiment, the method further comprises discharging a gas through the rotor head into the molten metal. In an embodiment, the gas comprises one or more gases that are not soluble in the molten metal. In an embodiment, the gas comprises argon, nitrogen, carbon monoxide, or a mixture thereof.

[0036] The inventors of the present invention have found that the combination of applying a layer of synthetic slag material (also called flux) to the metal and agitating the metal with a rotating device through the surface layer of the synthetic slag is very effective in removing sulfur from the molten metal. Without being bound by theory, it is believed that the use of a rotating device to agitate the metal improves the circulation of the metal flowing through the surface layer of the synthetic slag, allowing more sulfur to be captured by the synthetic slag. Furthermore, releasing gas into the molten metal through the rotor head improves the removal of solid inclusions and dissolved gases. Thus, the method of the present invention provides a very efficient and effective method for simultaneously removing inclusions, degassing, and desulfurizing the molten metal.

[0037] In an embodiment, the molten metal is an iron-based metal. In an embodiment, the molten metal is iron or steel.

[0038] In an embodiment the rotating device is a rotating device according to the first aspect and is particularly suitable for stirring hotter and denser molten metals such as iron and steel.

[0039] In embodiments, the composite slag material includes one or more of calcium oxide, alumina, silica, magnesia, sodium oxide, potassium oxide, iron (III) oxide, carbon dioxide, and fluorine. In some embodiments, the composite slag material includes 50-90 wt% calcium oxide. In embodiments, the composite slag material includes 5-30 wt% alumina. In embodiments, the composite slag material includes up to 5 wt% silica, magnesia, sodium oxide, potassium oxide, iron (III) oxide, carbon dioxide, and / or fluorine.

[0040] In an embodiment, the method further comprises providing a cored wire comprising a metal processing additive into the molten metal. In an embodiment, the cored wire comprises an outer sheath comprising a high melting point metal such as iron or steel and an inner core comprising the metal processing additive. In an embodiment, the metal processing additive comprises a desulfurization additive, an inclusion modification additive, or a mixture thereof. An inclusion modification additive is an additive for modifying the composition, morphology and / or distribution of solid inclusions in the molten metal, as previously described. In an embodiment, the metal processing additive comprises magnesium, ferrosilicon magnesium, calcium, calcium oxide, calcium carbide, barium, strontium, or a combination thereof, in elemental or compound form.

[0041] During use, the outer sheath protects the cored additive from immediate reaction or oxidation and gradually melts or dissolves, releasing the additive at a predefined depth below the surface of the molten metal. The combination of cored wire and treatment with synthetic slag can further improve the desulfurization and / or treatment and removal of inclusions in the molten metal.

[0042] In an embodiment, the method of the present invention includes discharging a solid metal treatment additive through or adjacent to the rotor head. In an embodiment, the additive is in the form of a wire or powder. In an embodiment, the additive is contained in a cored wire. Discharging the additive through or adjacent to the rotor head allows for rapid and efficient dispersion of the additive throughout the molten metal. The inventors of the present invention have found that this rapid dispersion allows for the use of elemental Ca / Mg as an additive and greatly reduces the hazards normally associated with using elemental Ca / Mg in the molten metal, since the Ca / Mg is rapidly dispersed throughout the metal before it evaporates or oxidizes. As a result, the amount of additive required to effectively treat the molten metal is reduced, and also reduces the buildup of excess additive that can lead to brittleness in the finished casting.

[0043] A protective coating is not necessarily required since releasing the additive through the rotor head, among other things, prevents the additive from being exposed to the molten metal while it is contained within the rotating device and allows the additive to be released into the molten metal at a depth corresponding to the depth of the rotor head, however, a cored wire including a protective coating may be used for convenience when other forms of metal treatment additives are not available or when the additive needs to reach a lower depth before being released into the molten metal.

[0044] In some embodiments, the rotating device rotates at a speed of at least 50, at least 100, at least 200, or at least 300 rpm to stir the molten metal. In some embodiments, the rotating device rotates at a speed of 600 rpm or less, 500 rpm or less, 400 rpm or less, or 300 rpm or less to stir the molten metal. In some embodiments, the rotating device rotates at a speed of 50 to 600 rpm, 100 to 300 rpm, or 100 to 200 rpm, for example 150 rpm. Higher rotation speeds increase the overall flow rate and amount of downward flow from the rotor head (i.e., increased bottom stirring), but also increase air entrainment into the molten metal. Increasing the rotation speed beyond 600 rpm can create vortices that can re-draw air into the melt with detrimental effects. In some embodiments, the rotation speed is changed during the method of the present invention. In some embodiments, the rotation speed may be decreased from a higher starting rotation speed during the method of the present invention. As the metal cools, the density of the molten metal increases, requiring more power to stir. For example, the rotational speed of the rotating device may start at 200 rpm and decrease to 120 rpm during the process of the present invention.

[0045] The method of the third aspect is suitable for use with any ladle or furnace, including a coreless induction furnace (CIF) or a ladle furnace (LF). In embodiments where the method of the invention is used with a ladle, the molten metal may be poured (tapped) into the ladle from an electric arc furnace (EAF) or a CIF. The method of the third aspect is particularly suitable for treating molten steel, but may also be used to treat other molten metals, such as iron, requiring desulphurization and / or inclusion removal.

[0046] According to a fourth aspect of the present invention there is provided a method of treating molten metal comprising the steps of: adding a metal treatment agent to the molten metal; Stirring the molten metal with a rotating device comprising a rotor head; Discharging a gas through the rotor head into the molten metal; Includes.

[0047] In embodiments, the molten metal is an iron-based metal, hi some embodiments, the molten metal is iron or steel.

[0048] In an embodiment, the metal treatment agent comprises at least one metal treatment additive selected from a desulfurization additive, an inclusion modification additive, or a mixture thereof. The inclusion modification additive, as previously described, is an additive for modifying the composition, morphology, and / or distribution of solid inclusions in the molten metal. In an embodiment, the at least one metal treatment additive comprises magnesium, ferrosilicon magnesium, calcium, calcium oxide, calcium carbide, barium, strontium, or combinations thereof, in elemental or compound form.

[0049] In embodiments, the metal treatment agent includes a desulfurization agent that is applied to the surface of the molten metal in the form of a synthetic slag material. In some such embodiments, the molten metal is agitated with a rotating device such that at least a portion of the synthetic slag material remains in a layer on the surface during agitation and the molten metal flows through the layer of synthetic slag material on the surface.

[0050] In embodiments, the synthetic slag material includes one or more of calcium oxide, alumina, silica, magnesia, sodium oxide, potassium oxide, iron (III) oxide, carbon dioxide, and fluorine. In some embodiments, the synthetic slag material includes 50-90 wt% calcium oxide. In embodiments, the synthetic slag material includes 5-30 wt% alumina. In embodiments, the synthetic slag material includes up to 5 wt% silica, magnesia, sodium oxide, potassium oxide, iron (III) oxide, carbon dioxide, and / or fluorine.

[0051] In embodiments, the metal treatment agent is applied to the surface of the molten metal in the form of a powder, and in some such embodiments, the molten metal is agitated with a rotating device so that the powder is drawn into and dispersed in the molten metal.

[0052] In an embodiment, the metal treatment agent is added in the form of a wire that is fed into the molten metal. In an embodiment, the wire is a cored wire with a protective outer sheath as described above in relation to the third embodiment. In an embodiment, the wire is fed into the molten metal in cooperation with a rotating device.

[0053] In some embodiments, the rotating device rotates at a speed of at least 50, at least 100, at least 200, or at least 300 rpm to stir the molten metal. In some embodiments, the rotating device rotates at a speed of 600 rpm or less, 500 rpm or less, 400 rpm or less, or 300 rpm or less to stir the molten metal. In some embodiments, the rotating device rotates at a speed of 50 to 600 rpm, 100 to 300 rpm, or 100 to 200 rpm, for example 150 rpm. Higher rotation speeds increase the overall flow rate and amount of downward flow from the rotor head (i.e., increased bottom stirring), but also increase air entrainment into the molten metal. Increasing the rotation speed beyond 600 rpm can create vortices that can re-draw air into the melt with detrimental effects. In some embodiments, the rotation speed is changed during the method of the present invention. In some embodiments, the rotation speed may be decreased from a higher starting rotation speed during the method of the present invention. As the metal cools, the density of the molten metal increases, requiring more power to stir. For example, the rotational speed of the rotating device may start at 200 rpm and decrease to 120 rpm during the process of the present invention.

[0054] The method of the fourth aspect is suitable for use with any ladle or furnace, including a coreless induction furnace (CIF) or a ladle furnace (LF). In embodiments where the method of the invention is used with a ladle, the molten metal may be poured (tapped) into the ladle from an electric arc furnace (EAF) or a CIF. The method of the third aspect is particularly suitable for treating molten steel, but may also be used to treat other molten metals, such as iron, requiring desulphurization and / or inclusion removal.

[0055] In an embodiment the rotation device is a rotation device according to the first aspect.

[0056] According to a fifth aspect of the present invention there is provided the use of a rotating device according to the first aspect of the present invention in the treatment of molten metal. Preferably the molten metal is molten steel.

[0057] It will be appreciated that any of the features and embodiments described in relation to the method of the third aspect may be equally applied to the method of the fourth aspect. [Brief description of the drawings]

[0058] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, in which:

[0059] [Figure 1] FIG. 1 shows a rotation device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view of the rotating device shown in FIG. [Diagram 3] FIG. 3 shows a hollow shaft for use in a rotation device according to an embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view of the hollow shaft shown in FIG. [Diagram 5] FIG. 5 illustrates a rotation device according to an embodiment of the present invention. [Figure 6] FIG. 6 is a cross-sectional view of the rotation device shown in FIG. [Figure 7] FIG. 7 is a schematic diagram of a rotation device according to an embodiment of the invention, in combination with a stirring apparatus for use in stirring and processing molten metal. [Figure 8] FIG. 8 shows velocity field simulation data for (a) the dual plate rotor head design and (b) the single plate rotor head design rotating at 600 rpm. [Figure 9] FIG. 9 shows scaled flow pattern simulation data that corresponds to the velocity field simulation data shown in FIG. [Figure 10]Figure 10 shows the simulation data of the velocity fields and scaled flow patterns for a single-plate rotor head rotating at (a) 100 rpm, (b) 200 rpm, and (c) 300 rpm. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0060] 1 and 2 show a rotation device 100 according to an embodiment of the present invention. The rotation device 100 comprises a tubular sleeve 1 and a hollow shaft 3 extending inside the tubular sleeve 1.

[0061] A rotor head 5 is integrally formed at one end of the tubular sleeve 1. The rotor head 5 is of a standard double-plate design comprising a first planar surface (or plate) 7 and a second plate 9, each extending perpendicular to the longitudinal axis of the tubular sleeve 1. The first plate 7 and the second plate 9 are connected to each other by a number of pillars 11. The rotor head 5 is further provided with gas outlets 13 in the form of bores extending through the first plate 7 for releasing gases into the molten metal.

[0062] The hollow shaft 3 has a first end 15 and a second end 17, with the first end 15 being received within the tubular sleeve 1. The hollow shaft 3 further includes a bore 19 extending therethrough (as shown in FIG. 3). The tubular sleeve 1 includes a conduit 21 fluidly connecting the bore 19 of the hollow shaft 3 to the gas outlet 13 of the rotor head 5 such that gas and / or solid metal processing additives may flow through the hollow shaft 3 and out through the rotor head 5 to the molten metal for use. In some embodiments (not shown), the hollow shaft 3 may include multiple bores extending therethrough that allow multiple gas and / or solid metal processing additives to be separately delivered through the hollow shaft 3.

[0063] The first end 15 of the hollow shaft 3 is provided with a locking portion 23 which engages with a complementary receiving portion 25 of the tubular sleeve 1. The locking portion 23 has a circular cross-sectional shape with six adjacent chords removed, i.e., the locking portion 23 has a generally hexagonal cross-section. The receiving portion 25 of the tubular sleeve 1 has a corresponding cross-sectional shape such that edges and apexes of the locking portion 23 abut against the receiving portion 25 to prevent independent rotation of the hollow shaft 3 within the tubular sleeve 1.

[0064] The second end 17 of the hollow shaft 3 protrudes from the tubular sleeve 1 and is configured to be coupled to an apparatus (e.g., as shown in FIG. 7) for rotating the rotating device 100. In the illustrated embodiment, the second end 17 of the hollow shaft is provided with a circumferential groove 25. The circumferential groove 25 may act as a pulley for connecting to a motor via a V-belt. Alternatively, the circumferential groove 25 may be configured to engage with a collar (e.g., as shown in FIG. 6), which may act as a pulley for connecting to a motor via a V-belt or as a flange for connecting to a motor shaft by other means, e.g., a nut and bolt. In the illustrated embodiment, the second end 17 of the hollow shaft 3 further comprises a recess 27 for engaging with a clamping means for fixing the hollow shaft 3 to the tubular sleeve 1 (e.g., as shown in FIG. 7).

[0065] The tubular sleeve 1 has a length LA measured along the longitudinal axis of the tubular sleeve 1. The hollow shaft 3 has a length LB measured along the longitudinal axis. The tubular sleeve 1 tapers inwardly along its length from a maximum diameter DA such that the diameter of the tubular sleeve decreases slightly towards the rotor head 5. The hollow shaft 3 also tapers inwardly along its length from a maximum diameter DB at the first end 17 to a minimum diameter at the second end 15 corresponding to the internal dimensions of the tubular sleeve 1. The rotor head has a diameter DC.

[0066] FIG. 5 shows a rotating device 200 according to another embodiment of the invention. The rotating device 200 comprises a tubular sleeve 31 and a hollow shaft 33. The tubular sleeve 31 and the hollow shaft 33 are generally the same as the tubular sleeve 1 and the hollow shaft 3 shown in FIGS. 1-4, except that the tubular sleeve 1 comprises a rotor head 35 having a single-plate design. The rotor head 35 comprises a flat surface (i.e., a plate) 37 extending perpendicular to the longitudinal axis A of the tubular sleeve 31, from whose base a vane 39 projects. The plate 37 is generally square, with a concave edge 41 and a truncated corner 43.

[0067] The rotation device 200 comprises clamping means 45 for fixing the tubular sleeve 31 to the hollow shaft 33. The rotation device 200 further comprises a collar 47 which fits around the second end of the hollow shaft 33. The collar presents a flange 49 which is configured to couple the rotation device 200 to a rotation apparatus (e.g. as shown in FIG. 7).

[0068] Figure 6 is a cross-sectional view of the rotation device 200 shown in Figure 5. A first end of the hollow shaft 33 is received within the tubular sleeve 31 and includes a locking portion 51 that engages a complementary receiving portion 53 of the tubular sleeve 31. A bore 55 extends through the hollow shaft 33 and is in fluid communication with a gas outlet 57 of the rotor head 35 by conduits 59, 61.

[0069] The second end of the hollow shaft 33 is formed with a circumferential groove 63 which engages the collar 47. A clamping means 45 cooperates with the collar 47 to secure the tubular sleeve 31 to the hollow shaft 33.

[0070] 7 shows a rotating device 300 according to an embodiment of the invention, in combination with an apparatus 302 for rotating the rotating device 300 and for injecting gas and / or metal treatment additives into the molten metal through the rotating device 300. In use, the rotating device 300 is lowered into a ladle 304 (or a furnace). The ladle 304 may be filled with molten metal either before or after the rotating device 300 is lowered. The rotating device 300 is then used to process the molten metal, for example in a manner according to the invention.

[0071] <Example 1> A rotating device according to an embodiment of the invention was made using a hollow shaft comprising graphite and a tubular sleeve comprising fused silica. The tubular sleeve had an integrally formed rotor head. The length of the tubular sleeve measured along the longitudinal axis was 123 cm (not including the rotor head). The graphite shaft extended within the tubular sleeve along 100 cm of the tubular sleeve's length. The maximum diameter of the graphite shaft was 7.6 cm. The maximum diameter of the tubular sleeve was 11.6 cm, with a wall thickness of 1.6 cm.

[0072] The rotor head had a standard double-plate design, including two parallel square plates with concave edges and truncated corners, connected by four pillars. The first plate had a centrally located bore for releasing gases into the molten metal. The plate diameter was 25 cm.

[0073] Rotating devices have been used successfully to process molten metals. Repeated use eventually led to some warping and distortion of the rotor head due to slight softening of the fused silica, which reduced stirring efficiency.

[0074] <Example 2> Another rotating device according to an embodiment of the present invention was made with a hollow shaft comprising graphite and a tubular sleeve comprising VISO™ isostatically pressed carbon-bonded alumina. The dimensions of the rotating device were the same as those of Example 1.

[0075] The dual plate rotor design of Example 1 was found to present some difficulties in isopressing manufacture since complete densification was not always achieved throughout the rotor head. Thus, the rotating device of Example 2 had a modified rotor head design with a single plate and vanes. The plate was generally square with concave edges and truncated corners, with four vanes extending from the base of the plate at each corner. The plate had a centrally located bore for releasing gases into the molten metal. The plate had a diameter of 25 cm.

[0076] The rotating device of Example 2 was successfully used to process molten metal 18 times with no signs of deformation and minimal signs of wear. However, as the rotating device accumulated a large amount of slag, the stirring efficiency began to decrease. Because the graphite shaft showed no signs of failure, it was possible for the graphite shaft to be used further with a replacement outer sleeve. It was found that the graphite shaft could be used at least 50 times without failure.

[0077] <Flow pattern simulation> Flow pattern simulations were performed using OpenFoam™ software to compare the flow velocity and direction of single plate and dual plate rotor designs in molten steel at different rotational speeds, and the results are shown in Figures 8-10.

[0078] Figure 8 shows the velocity field after 15 seconds of rotation at 600 rpm for the double-plate rotor (a) and the single-plate rotor (b), and Figure 9 shows the scaled flow patterns. The peak flow velocities achieved by both designs were similar. However, the flow direction was slightly different, with the exit flow from the double-plate rotor being almost horizontal, whereas the single-plate design showed more downward flow. Both rotor designs showed good stirring simulation performance in the molten steel, although the single-plate rotor showed slightly higher torque than the double-plate rotor (271 N.m for the single-plate rotor and 235 N.m for the double-plate rotor).

[0079] Figure 10 shows the velocity fields and scaled flow patterns after rotating a single-plate rotor at (a) 100 rpm, (b) 200 rpm, and (c) 300 rpm for 15 seconds. The mixing performance was shown to increase with increasing rotation speed.

[0080] <Removal of inclusions and desulfurization> A method according to one embodiment of the present invention was tested against a standard method of desulfurization.

[0081] In the standard method (method 1), molten steel was tapped into a pouring ladle from a coreless induction furnace (CIF), an electric arc furnace (EAF), or both. In both cases, the metal from the CIF was tapped before the metal from the EAF. An aluminum-containing cored wire and a SiCaBa-containing cored wire were fed into the molten steel. Argon gas was flushed into the molten steel using a porous plug for 5-20 minutes.

[0082] In the method of the present invention (Method 2), molten steel was tapped into a pouring ladle in the same manner as in Method 1. An aluminum-containing cored wire and a SiCa-containing cored wire were fed into the molten steel. The argon was vented using the rotating device of Example 2, and the metal was stirred at 200-240 rpm for 5-15 minutes.

[0083] Method 1 and Method 2 were run multiple times on different amounts of molten steel ranging from 2.5 tons to 18 tons. Samples of molten steel processed by each method were analyzed for their inclusion content using Spark-DAT analysis on a Thermo Scientific™ ARL 4460 spectrometer. The Spark-DAT analysis method involves striking the sample area with a single spark. If a solid inclusion is present at the location where the spark struck, a spectrometer peak is produced. This process is repeated throughout the sample area. The number of peaks produced can then be counted to determine the number of inclusions in the sample area. The average content for Method 1 and Method 2 was calculated by taking the average content from the multiple repeat procedure described above. The results are shown in Table 1.

[0084] [Table 1]

[0085] On average, the molten steel processed by Method 2 had 14-30% fewer small inclusions and 50-60% fewer large inclusions than the molten steel processed by Method 1 (standard purge plug treatment).

[0086] It was also found that the liquid steel processed by Method 2 had significantly lower sulfur content than the liquid steel processed by Method 1. Using Method 1, typical sulfur contents were about 100 ppm for EAF and about 70 ppm for CIF. Using Method 2, the sulfur content was reduced to about 20 ppm.

[0087] As a result of the improved inclusion removal achieved by Method 2, the pouring temperature of the molten metal was reduced by 20-30°C compared to standard methods, resulting in significant energy savings. The lower metal temperatures also reduce wear on the refractory materials (thereby extending their life), reduce liquid shrinkage as the casting solidifies, and reduce re-oxidation of the metal surface.

Claims

1. 1. A rotary device for treating molten metal with a gas, comprising: a tubular sleeve having a rotor head at one end, the rotor head having a gas outlet for dispersing gas into the molten metal; a hollow shaft extending within the tubular sleeve, at least a portion of the hollow shaft being surrounded by the tubular sleeve; and It is equipped with the hollow shaft is in fluid communication with the gas outlet of the rotor head; the tubular sleeve is formed of a heat-resistant material that is resistant to corrosion and thermal shock; The hollow shaft is formed of a material including graphite. Rotation device.

2. 10. The rotating device of claim 1, wherein the tubular sleeve is formed from a heat-resistant material including fused silica; alumina; silicon carbide; carbon-bonded alumina; carbon-bonded ceramic; clay graphite; silicon nitride alumina; an isopressed heat-resistant composite comprising a metal oxide, carbide, or nitride; isopressed carbon-bonded alumina; a heat-resistant substrate coated with alumina and / or magnesium zirconate or a metal oxide, or a combination thereof.

3. 3. A rotating device according to claim 1 or claim 2, wherein the rotor head is integrally formed with the tubular sleeve or the rotor head is coupled to an end of the tubular sleeve.

4. 4. A rotation device as described in any one of claims 1 to 3, wherein the hollow shaft has a first end and a second end, the first end being surrounded by the tubular sleeve, and optionally the second end of the hollow shaft being configured to be coupled to an apparatus for rotating the rotation device.

5. 5. The rotary device of claim 4, wherein the first end of the hollow shaft comprises a locking portion configured to engage a complementary receiving portion in the tubular sleeve, and optionally the complementary receiving portion is located at an end of the tubular sleeve that comprises the rotor head.

6. 6. The rotation device of claim 5, wherein the locking portion and the receiving portion have a polygonal or circular cross section with multiple chords removed, optionally with at least three, four, five, or six vertices.

7. A tubular sleeve for use with a rotation device according to any preceding claim.

8. 1. A method for treating molten metal, comprising: applying a layer of synthetic slag material to the exposed surface of the molten metal; agitating the molten metal using a rotating device comprising a rotor head so that the molten metal flows along the layer of synthetic slag material; A method comprising:

9. The method of claim 8 further comprising dispersing a gas into the molten metal through the rotor head.

10. 10. The method of claim 8 or claim 9, wherein the synthetic slag comprises calcium oxide.

11. 11. The method of any of claims 8-10, further comprising feeding a cored wire comprising a metal treatment additive into the molten metal, optionally the cored wire comprising an outer sheath comprising a refractory metal and an inner core comprising a metal treatment additive, optionally the metal treatment additive comprising magnesium, ferrosilicon magnesium, calcium, calcium oxide, calcium carbide, or a combination thereof.

12. 12. The method of any of claims 8 to 11, wherein the method includes discharging a metal processing additive, optionally a solid metal processing additive, through the rotor head.

13. 1. A method for treating molten metal, comprising: adding a metal treatment agent to the molten metal; stirring the molten metal with a rotating device comprising a rotor head; Discharging gas into the molten metal through the rotor head; A method comprising:

14. 14. A method according to any one of claims 8 to 13, wherein the molten metal is steel or iron.

15. Use of a rotating device according to any one of claims 1 to 6 in the treatment of molten metal.

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