Deaerator shaft

Abstract

The present invention provides a degasifier shaft for treating molten metal with a gas, the shaft comprising: (a) a first end connectable to a drive for rotating the shaft about a longitudinal axis, the first end having a first end outer diameter; (b) a second end having a second end outer diameter and connectable to or integral with a rotor, the second end outer diameter being considered to be the smallest shaft outer diameter proximal to the rotor; and (c) a passageway through which gas travels from the first end to the second end, the degasifier shaft comprising: a passage defined by an inner diameter of the shaft, wherein the degassifier shaft has a first portion located at or toward the first end and including a first tapered segment that decreases in cross-sectional area toward the second end, and optionally a first constant cross-section segment extending from the first tapered segment toward the first end, wherein the first portion comprises 48% to 100% of the total length of the degassifier shaft, and at least the first tapered segment of the degassifier shaft is made of a ceramic composite material.

Description

[Technical Field]

[0001] The present invention relates to a degassing shaft and its use for degassing molten metal, in particular molten aluminum, magnesium and their alloys. [Background technology]

[0002] In the degassing process, an inert gas is pumped into the aluminum melt to remove hydrogen and subsequently prevent porosity in the cast part. In the rotary degassing method, an inert or chemically inert gas is purged through a rotating shaft and rotor. The energy of the rotating shaft and rotor causes the formation of numerous fine gas bubbles, which provide a very high surface area to volume ratio. The large surface area promotes fast and efficient diffusion of hydrogen into the gas bubbles, resulting in equal activity of hydrogen in the liquid and gas phases and rapid removal of hydrogen from the melt.

[0003] Various degassing procedures exist, many of which require the shaft to rotate at high speeds, which results in vibration and high-frequency cyclic bending loads and stresses on the shaft, concentrated at the ends toward the motor connections. Graphite and carbon composite shafts are preferred for these types of applications due to their lower density, higher stiffness, and superior bending strength compared to shafts made from ceramic composite materials. However, while graphite shafts have good mechanical properties for these applications, they are susceptible to oxidation corrosion and mechanical erosion from contact with air and molten metal, respectively, and must therefore be replaced periodically.

[0004] EP 3180455 in the name of Pyrotek Inc. addresses this problem by impregnating the carbon composite element with oxidation resistant chemicals such as the phosphate based oxidation retarders disclosed in US Pat. No. 4,439,491.

[0005] WO 2022 / 129612, filed in the name of Foseco International Limited, addresses the challenging problem of injecting metal additives into molten iron, using a gas to inject the metal in powder form into the molten iron, with the gas pressure preventing the iron from flowing back onto the rotor shaft. WO 2022 / 129612 describes a ceramic composite sleeve placed over a graphite shaft (or otherwise dissolved in the molten iron) that can provide good mechanical properties while the ceramic composite can provide improved oxidation, corrosion, and erosion resistance. The graphite shaft and ceramic composite sleeve are tapered to allow for an interference fit between them. However, mismatched thermal expansion coefficients between the graphite shaft and the ceramic composite sleeve can compromise the integrity of the seal between the shaft and sleeve, thereby shortening the operating life of the shaft / sleeve combination.

[0006] WO2004 / 029307(A1) discloses a deaerator shaft that tapers toward the rotor head. Therefore, the peripheral speed of the shaft in the molten metal decreases with increasing depth, allegedly minimizing undesirable vortices. WO2004 / 029307(A1) does not define the material of the shaft.

[0007] Despite these advances, a need remains for improved deaerator shafts that have a longer operating life, can be manufactured without material or process complexity, and can be used in high frequency cyclic loading or stress applications, also known as fatigue applications. Summary of the Invention

[0008] In a first aspect of the present invention there is provided a degasifier shaft for treating molten metal with a gas, the shaft comprising: (a) a first end connectable to a drive device for rotating the shaft about a longitudinal axis, the first end having a first end outer diameter; (b) a second end having a second end outer diameter; and connectable to the rotor, or a second end portion integral with the rotor, the second end portion outer diameter being considered to be the smallest shaft outer diameter proximal to the rotor; (c) a passageway through which the gas travels from the first end to the second end, the passageway being defined by an inner diameter of the deaerator shaft; A degasser shaft is provided having a first portion located at or toward a first end and including a first tapered segment that decreases in cross-sectional area toward a second end, and optionally a first constant cross-section segment (having a constant cross-sectional area) extending from the first tapered segment toward the first end, wherein the first portion comprises between 48% and 100% of the total length of the degasser shaft, and wherein at least the first tapered segment of the degasser shaft is made of a ceramic composite material.

[0009] "Tapered" means a decrease in cross-sectional area, which may be linear or smooth, e.g., diverging from a first cross-sectional area to a second cross-sectional area such that the first cross-sectional area and / or the second cross-sectional area are smoothly approached.

[0010] The tapered segment is preferably frustoconical, and the constant cross section segment is preferably cylindrical.

[0011] In some embodiments, the deaerator shaft comprises: a first constant cross-section segment (having a constant cross-sectional area) having a cross-sectional area greater than the minimum cross-sectional area of ​​the deaerator shaft and extending contiguously from the first tapered segment toward the first end; and a second constant cross-section segment (having a constant cross-sectional area) extending adjacently from the first tapered segment towards the second end.

[0012] In some embodiments, the shaft is comprised of a first portion and an optional second constant cross-section segment. The first portion may comprise a tapered segment (e.g., a first cylindrical segment and an intermediate cylindrical segment disposed between frusto-conical segments), including a tapered segment having an optional constant segment with a cross-sectional area greater than the minimum cross-sectional area of ​​the degasser shaft.

[0013] The degasser shaft of the present invention has a long operating life due to its resistance to both oxidative corrosion of the shaft, mechanical erosion by the melt, and premature mechanical failure. While the innovative design features can be applied to any material suitable for use as a degasser shaft, the degasser shaft is particularly advantageous when made from a ceramic composite. Counterintuitively, the goal of extended operating life can be improved by using composite materials that generally have lower bending fatigue strength than graphite-based compositions.

[0014] The tapered (e.g., frustoconical) portion may comprise one or more tapered segments that occupy at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90%, or 100% of the total length of the first portion. The tapered segments may comprise one or more tapered segments and intermediate constant cross-section segments (excluding the first or second constant cross-section segments) that occupy at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90%, or 100% of the total length of the degasser shaft. In some embodiments, the one or more tapered segments occupy no more than 90%, or no more than 80%, or no more than 70%, or no more than 60% of the total length of the degasser shaft. The longer the one or more tapered segments, the smaller the angle of incidence from the shaft axis, thereby avoiding localized stress concentrations when the tapered segments abut against optional constant cross-section segments of the degasser shaft.

[0015] For purposes of the present invention, a constant cross-section segment includes a cylinder and a polygonal prism, or any other suitable shaped portion having a constant cross-sectional area. In some embodiments, the constant cross-section segment includes a cylinder. In other embodiments, the constant cross-section segment includes a prismatic polygon, preferably including at least five sides, and preferably including at least seven or at least eight sides. In embodiments in which the constant segment includes a polygonal prism (e.g., a hexagonal prism), the constant cross-section segment may function in cooperation with a fastening tool (e.g., a wrench) to fasten the deaerator shaft to a motor or rotor or its connection. Preferably, the constant cross-section segment does not include any acute angles (e.g., less than 90° or less than 60°) to avoid any stress concentration points in the shaft (e.g., pentagonal or hexagonal). The constant portion is preferably symmetrical about the central axis of the deaerator shaft. In some embodiments, the constant cross-section segment comprises a cross-sectional area of ​​the deaerator shaft that is at least 5%, or at least 8%, or at least 10%, or at least 12%, or at least 15%, or at least 20% greater than the smallest cross-sectional area of ​​the deaerator shaft proximal to or at the second end.

[0016] The first portion may comprise at least 50%, or at least 52%, or at least 55%, or at least 58%, or at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%, or 100% of the total length of the deaerator shaft. In some embodiments, the first portion may be no more than 90%, or no more than 80%, or no more than 70%, or no more than 60% of the total length of the deaerator shaft. A larger first portion may help minimize localized stress concentration areas during operation and increase shaft stiffness, while a smaller first portion may allow for reduced shaft weight.

[0017] If present, the first constant segment may represent less than 0% to 50%, or 5% to 40%, or 10% to 30% of the total length of the shaft. Typically, the first constant segment is at least 5 mm, or at least 10 mm, or at least 20 mm. The first constant segment is typically no longer than 1000 mm, or no longer than 800 mm, or no longer than 600 mm, or no longer than 500 mm, or no longer than 400 mm. In some embodiments, the first constant segment comprises the melt line of the shaft.

[0018] If the first portion does not extend the entire length of the shaft, the remainder of the shaft that is not part of the first portion may comprise a second constant segment (cylindrical or prismatic segment) defined by a second end diameter and extending from the first portion to the second end. The second end outer diameter is typically the smallest diameter (or effective diameter) of the shaft.

[0019] If present, the second constant segment may represent less than 0% to 52% of the total length of the shaft. Typically, the second constant segment is at least 5 mm, or at least 10 mm, or at least 20 mm, or at least 40 mm, or at least 60 mm. The first constant segment is typically no more than 1000 mm, or no more than 800 mm, or no more than 600 mm, or no more than 500 mm, or no more than 400 mm.

[0020] The first shaft end outer diameter is typically the largest outer diameter of the shaft. In some embodiments, the first shaft end outer diameter defines a first constant shaft segment extending from the end of the tapered segment toward the first end of the shaft.

[0021] In other embodiments, the first portion comprises two or more tapered sections connecting the first shaft end diameter to the second shaft end outer diameter. The tapered sections may have gradually decreasing outer diameters as they progress toward the second end of the shaft. Each of the tapered sections may be separated by one or more constant segments. The benefit of this "step-down" configuration is that the shaft outer diameter (and therefore stiffness) of the sections of the shaft may be customized to counter localized vibrations and therefore stresses along the deaerator shaft under operating conditions.

[0022] In some embodiments, the first constant segment extends to the first end of the shaft.

[0023] A motor guard or housing associated with the motor may require the first shaft end to have an outer diameter smaller than the maximum outer diameter of the shaft to allow the first shaft end to fit within such an auxiliary component of the degasser system. In these embodiments, the first end outer diameter may be connected adjacent to the maximum outer diameter of the shaft by a tapered segment.

[0024] Connectors and seamless connections A first end of the shaft may be connectable to a motor and a second end of the shaft may be connectable to a rotor. The connections to the motor and / or rotor may be male connectors, female connectors, or any other suitable coupling mechanism.

[0025] In some embodiments, the first end is connectable to the motor by a female connector. The female connector may be a helically threaded coupling means (e.g., a helically threaded cavity). To reduce stress concentrations around the female connector, the female connector preferably includes an arcuate bridge connection to the passage. The arcuate bridge connection preferably has a radius of at least 5 mm or at least 10 mm. The arcuate bridge connection may be incorporated into the male connector.

[0026] If there is a seamless connection of the shaft to the rotor (or a flanged connection that increases the shaft diameter), the possible second end is considered to be the smallest diameter of the shaft proximal to the rotor. This ensures that the second end does not include any tapered expansion of the device towards the larger diameter of the rotor, typically a disk shape.

[0027] Deaerator shaft dimensions The deaerator shaft is preferably monolithic. In some embodiments, the deaerator shaft extends from an inner diameter that defines a passageway and extends to an outer diameter. The outer surface of the deaerator shaft is defined by the outer diameter of the shaft. During operation, the outer surface of the deaerator shaft contacts the molten metal in the submerged region and the high-temperature air atmosphere in the adjacent non-submerged region, and the thickness of the deaerator rotor (i.e., outer diameter of the shaft minus inner diameter of the shaft), along with or in combination with the oxidation-corrosion protective sleeve, provides superior oxidation-corrosion and erosion resistance compared to a graphite shaft of the same thickness. Superior oxidation-corrosion and erosion-corrosion resistance may also allow for thinner shaft walls, reducing the shaft weight while maintaining sufficient oxidation-corrosion and erosion resistance.

[0028] The length of a degasser shaft is measured along the central axis from the first end to the second end. The length does not include extensions due to connectors, such as male connectors. If the second end of the degasser shaft includes a rotor (i.e., the rotor is integral with or seamlessly connected to the shaft (e.g., monolithic)), the second end is considered to terminate where the smallest shaft diameter is located nearest the rotor. Therefore, any tapered flange components that increase in diameter toward the shaft tip to match the rotor diameter are not included in the shaft length calculation.

[0029] Deaerator shafts typically range in length from at least 250 mm to 2500 mm, typically 2200 mm or less, or 2000 mm or less. The length of the shaft can be determined by the requirements of the deaerator system. However, when shaft lengths extend up to 2000 mm and the specified rotational speed is exceeded, vibration-induced stress on the deaerator shaft increases significantly, shortening the useful life of the deaerator shaft.

[0030] As shown in Table 1 below, deaerator shafts can be divided into three categories. [Table 1]

[0031] As shown in Table 1, as the deaerator shaft becomes longer, the rotational speed at which the deaerator shaft operates decreases. This is at least partially related to the increased rotordynamic instability when increasing the rotational speed of a longer shaft, which translates into additional stresses on the longer deaerator shaft.

[0032] For long shafts, the maximum outer diameter of the shaft (D 最大 ) is typically between 125 mm and 200 mm. In some embodiments, the maximum outer diameter is at least 130 mm, or at least 140 mm, or at least 150 mm, or at least 160 mm. As the diameter increases for a given cross-sectional weight, the cross-sectional moment of inertia increases and the shaft becomes stiffer at that point. The minimum outer diameter (D 最小 ) is typically 60 mm to 150 mm. The difference between the maximum and minimum outer diameters of the shaft (D 最大 -D 最小 ) is typically at least 20 mm, or at least 25 mm, or at least 30 mm, or at least 35 mm, or at least 40 mm, or at least 45 mm, or at least 50 mm, or at least 55 mm, or at least 60 mm. 最大 -D 最小 is typically 150 or less, or 100 mm or less.

[0033] For intermediate length shafts, the maximum outer diameter of the shaft (D 最大 ) is typically between 100 mm and 150 mm. In some embodiments, the maximum outer diameter is at least 110 mm, or at least 115 mm, or at least 120 mm, or at least 125 mm. The minimum outer diameter (D 最小 ) is typically 60 mm to 120 mm. The difference between the maximum and minimum outer diameters of the shaft (D 最大 -D 最小 ) is typically at least 20 mm, or at least 25 mm, or at least 30 mm, or at least 35 mm, or at least 40 mm, or at least 45 mm, or at least 50 mm. In some embodiments, D 最大 -D 最小 is less than 90mm.

[0034] For short shafts, the maximum outer diameter of the shaft (D 最大 ) is typically 60 mm to 100 mm. In some embodiments, the maximum outer diameter is at least 65 mm, or at least 70 mm, or at least 75 mm, or at least 80 mm. The minimum outer diameter (D 最小 The difference between the maximum and minimum outer diameters of the shaft (D 最大 -D 最小 ) is typically at least 10 mm, or at least 15 mm, or at least 20 mm, or at least 25 mm, or at least 30 mm, or at least 35 mm, or at least 40 mm. 最大 -D 最小 is typically 60 mm or less.

[0035] In some embodiments, the outer diameter of the first end is D 最大 up to 100mm or up to 50mm smaller than

[0036] In some embodiments, D 最大 and D 最小is at least 1.1, or at least 1.2, or at least 1.3, or at least 1.4, or at least 1.5, or at least 1.6, or at least 1.7, or at least 1.8. 最大 and D 最小 The ratio of D to D is typically 5 or less, or 4 or less, or 3 or less, or 2 or less. 最大 and D 最小 The ratio of promotes weight distribution toward the top (i.e., first end) of the shaft, thereby reducing the tendency of the shaft to vibrate excessively during operation, reducing stresses, and increasing thickness at the melt line.

[0037] In some embodiments, the ratio of the minimum shaft outer diameter to the minimum wall thickness (D 最小 / wall 最小 ) was at least 2.7, or at least 2.9, or at least 3.1, or at least 3.3. A higher ratio promotes a stiffer, lighter shaft.

[0038] In some embodiments, the ratio of the maximum outer diameter to the minimum outer diameter of the deaerator shaft is in the range of 1.05:1 to 3.0:1, or in the range of 1.1:1 to 2.5:1, or in the range of 1.2:1 to 2.0:1.

[0039] The maximum shaft outer diameter is typically at or around the first end or melt line, and the minimum shaft outer diameter is typically at or around the second end of the shaft.

[0040] In some embodiments, the degassing shaft includes an angle of incidence between the tapered segment and the constant cross-section segment (or central axis) of 16° or less, or 15° or less, or 14° or less, or 13° or less, or 12° or less, or 10° or less. Larger angles of incidence can result in bending stress concentrations at the intersection, leading to potential mechanical failure. The angle of incidence is greater than 0°, typically at least 0.3°, or at least 0.5°, or at least 1.0°, or at least 2.0°, or at least 3.0°, or at least 4.0°, or at least 5.0°, to allow for necessary changes in shaft diameter to achieve stiffness and weight goals.

[0041] The inner diameter of the shaft (i.e., passageway) can range from 10 mm to 80 mm, or 12 mm to 70 mm, or 15 mm to 60 mm, or 18 mm to 50 mm, or 20 mm to 40 mm. In some embodiments, the inner diameter of the shaft is at least 25 mm, or at least 30 mm, or at least 40 mm. A larger inner diameter allows for one or both of a larger outer diameter and a thinner wall thickness. A larger outer diameter contributes to a stiffer shaft for a constant cross-sectional weight, while a thinner wall contributes to a lighter deaerator shaft weight. The inner diameter can be constant along the length of the shaft, or the inner diameter can vary, with the inner diameter decreasing along the length of the shaft from the first end to the second end. If the first or second end includes a female connector, the inner diameter is measured immediately adjacent to the cavity housing the female connector.

[0042] The minimum shaft wall thickness is typically at least 12 mm, or at least 15 mm, or at least 18 mm, or at least 20 mm, or at least 22 mm, or at least 25 mm, or at least 27 mm, or at least 30 mm, or at least 35 mm, or at least 40 mm. The minimum shaft wall thickness is typically located toward the second end of the deaerator shaft and typically corresponds to the minimum outer diameter of the deaerator shaft. For long shafts, the minimum wall thickness is typically in the range of 20 mm to 45 mm, or 22 mm to 42 mm, or 25 mm to 40 mm. For medium-length shafts, the minimum wall thickness is typically in the range of 14 mm to 25 mm, or 16 mm to 22 mm, or 17 mm to 21 mm. For short shafts, the minimum wall thickness is typically in the range of 10 mm to 17 mm, or 11 mm to 16 mm, or 12 mm to 15 mm.

[0043] The maximum shaft wall thickness is typically 80 mm or less, or 70 mm or less, or 60 mm or less. The maximum shaft wall thickness is typically located toward the first end of the degasser shaft and typically corresponds to where the melt line of the degasser shaft is located or around (e.g., ±50 mm). The melt line is typically located 40 mm to 500 mm from the first end of the degasser shaft and within the first portion, depending on the overall length of the shaft and degasser system configuration. When a female connector is used to connect the degasser shaft to the motor, the melt line is preferably located below the female connector, preferably at least 20 mm or at least 40 mm below the female connector. Both the melt line and the female connector are potentially vulnerable areas due to corrosive stress concentrations. Therefore, these areas are preferably separated.

[0044] In some embodiments, the wall thickness at the second end of the shaft is in the range of 12 to 60 mm, or 14 to 50 mm, or 16 to 40 mm, and the wall thickness at the first end or melt line is in the range of 20 to 80 mm, or 22 to 70 mm, or 24 to 60 mm. In some embodiments, the ratio of the minimum shaft thickness (at the second end) to the maximum shaft thickness (at the first end or melt line) is at least in the range of 0.3 to less than 1.0, or in the range of 0.4 to less than 0.95, or in the range of at least 0.5 to less than 0.90, or in the range of at least 0.6 to 0.85. In some embodiments, the maximum wall thickness (at the second end) of the deaerator shaft is at least in the range of 0.3 to less than 1.0, or in the range of 0.4 to less than 0.95, or in the range of at least 0.5 to less than 0.90, or in the range of at least 0.6 to 0.85. 最大 ) is located at or proximal to (e.g., within 10 mm of) the maximum outer diameter of the deaerator shaft and has a minimum wall thickness (wall 最小 ) is located at or proximal to (e.g., within 10 mm of) the second end and 最小 / wall 最大 The ratio is in the range of 0.75 to 1.0 or in the range of 0.80 to 0.95. By increasing the shaft diameter while maintaining a relatively similar wall thickness, weight can be reduced, while the oxidation and corrosion resistance of ceramic composites allows a relatively thin wall thickness to provide sufficient oxidation and corrosion resistance.

[0045] In some embodiments, D 最大 / D 最小 is greater than 1.3 and the wall 最小 / wall 最大 is in the range of 0.80 to 1.0.

[0046] In some embodiments, the wall thickness of the shaft varies along its length. In some embodiments, the wall thickness is thickest toward the first end and thinnest toward the second end. In some embodiments, the wall thickness is thickest at or around the melt line and thinnest toward the second end. The difference between the thinnest and thickest wall thicknesses is typically 10% to 300%, or 20% to 200%, or 30% to 100% of the thinnest wall. By varying the thickness of the shaft along its length, greater oxidation-corrosion and stress resistance (e.g., thicker walls) and vibration minimization can be applied where needed, without unnecessarily increasing the weight of the shaft.

[0047] In a preferred embodiment, the deaerator shaft comprises: a.250~2200mm in total length, b. A first constant segment having a length in the range of 0 to 600 mm (or 10 mm to 500 mm); c. a tapered segment abutting an optional further constant segment, the tapered segment comprising a diameter that decreases as the tapered segment extends towards the second end, and the tapered segment comprising an axial length in the range of 100 to 2200 mm; d. an optional second constant segment; e. a first shaft end diameter in the range of 60 to 180 mm; f. a second shaft end diameter in the range of 45 to 140 mm; g. Passage diameter in the range of 10 to 60 mm.

[0048] The deaerator shaft preferably comprises a ceramic composite.

[0049] In another preferred embodiment, the short deaerator shaft comprises: a. Total length of 250~600mm (or 280~500mm) and b. a first constant segment having a length in the range of 50 to 100 mm; c. a tapered segment abutting the first constant segment and including a diameter that decreases as the tapered segment extends toward the second end, and including an axial length in the range of 100 to 400 mm; d. an optional second constant segment; e. a first shaft end diameter in the range of 60 to 90 mm; f. a second shaft end diameter in the range of 45 to 70 mm; g. Passage diameter in the range of 10 to 25 mm.

[0050] The minimum wall thickness of the short deaerator shaft can range from 10 mm to 24 mm, or from 12 mm to 22 mm, or from 14 mm to 20 mm. The maximum wall thickness can range from 18 mm to 32 mm, or from 20 mm to 30 mm, or from 22 mm to 28 mm.

[0051] In a preferred embodiment, the intermediate length deaerator shaft comprises: a. Total length of 500~1500mm, b. an optional first constant segment extending from or proximal to the first end and comprising a length in the range of 0 to 400 mm; c. a tapered segment, if present, abutting the optional first constant segment, the tapered segment comprising a diameter that decreases as the tapered segment extends toward the second end, and the tapered segment comprising an axial length in the range of 500 to 1500 mm; d. an optional second constant segment extending from the tapered segment adjacent the second end; e. a first shaft end diameter in the range of 70 to 150 mm (or 80 to 140 mm); f. a second shaft end diameter in the range of 50 to 130 mm (or 60 to 120 mm); g. A passage diameter in the range of 10 to 50 mm (or 15 to 40 mm).

[0052] The minimum wall thickness of the medium length deaerator shaft can range from 20 mm to 34 mm, or from 22 mm to 32 mm, or from 24 mm to 30 mm. The maximum wall thickness can range from 27 mm to 42 mm, or from 29 mm to 40 mm, or from 31 mm to 38 mm.

[0053] In a preferred embodiment, the long deaerator shaft comprises: a. Total length of 1500~2200mm, b. a first constant segment extending from or proximal to the first end and including a length in the range of 100 to 600 mm (or 120 to 500 mm); c. a first tapered segment adjacent to and abutting the first constant segment, the first tapered segment including a diameter that decreases as the tapered segment extends toward the second end, and the first tapered segment including an axial length in the range of 400 to 2200 mm; d. an optional second constant segment extending from the tapered segment adjacent the second end; e. an optional second tapered segment abutting adjacent an end of the first constant segment and extending adjacent the first end, the optional second tapered segment comprising a length of 0 to 600 mm (or 10 to 500 mm, or 120 to 350 mm); f. a first shaft end diameter in the range of 80 mm to 200 mm (or 90 to 180 mm); g. A second shaft end diameter in the range of 80 to 140 mm; h. Passage diameter in the range of 10 to 60 mm.

[0054] The minimum wall thickness of the long deaerator shaft can range from 10 mm to 24 mm, or from 12 mm to 22 mm, or from 14 mm to 20 mm. The maximum wall thickness can range from 18 mm to 32 mm, or from 20 mm to 30 mm, or from 22 mm to 28 mm.

[0055] The inner diameter of the deaerator shaft defining the passages can be at least 12 mm, or at least 14 mm, or at least 16 mm, or at least 18 mm, or at least 20 mm, or at least 22 mm, or at least 24 mm, or at least 26 mm. The maximum inner diameter of the passages is typically 70 mm or less, or 65 mm or less, or 60 mm or less, or 55 mm or less, or 50 mm or less. The deaerator shaft preferably comprises or consists of a ceramic composite. In some embodiments, the deaerator shaft does not include any components or parts made significantly of graphite (e.g., at least 50 wt.%, or at least 80 wt.%, or at least 98 wt.%). Graphite components have good mechanical properties, such as stiffness, but poor oxidation and corrosion resistance.

[0056] The deaerator shaft of the present invention is compatible with a variety of deaerator systems, including Foseco FDU deaerators, STAS deaerators, Novelis ALPUR deaerators, and Hertwich deaerator systems. Advantageously, the shaft of the present invention not only provides mechanical durability under a variety of rotational speeds, but also has excellent oxidation and corrosion resistance to ensure a longer operational life.

[0057] Ceramic Composites Ceramic composites may include composites containing refractory particles and graphite flakes within an inorganic binder matrix (e.g., glass and / or mullite) or an organic binder matrix (e.g., ceramic carbon composites). The refractory particles may include any suitable refractory material having suitable mechanical strength, oxidation resistance, erosion resistance, thermal shock resistance, and impact resistance. Suitable particles may include carbides, including silicon carbide; nitrides, including silicon nitride; alumina, zirconia, and aluminosilicates. The refractory particles are preferably crystalline or partially crystalline. The function of the graphite flakes is primarily to provide strength to the material while enhancing machinability during manufacturing. In some embodiments, ceramic composites may include inorganic fibers, which may increase the flexural strength of the composite.

[0058] Ceramic composites can be formed from clay or resin-bonded ceramic composite precursor materials. Ceramic composites formed from clay-bonded composite precursors can include refractory particles embedded in an aluminosilicate matrix. The aluminosilicate matrix can be glassy and / or crystalline (e.g., mullite). An aluminosilicate matrix is ​​defined as a matrix containing at least 60% by weight, or at least 70% by weight, or at least 80% by weight alumina plus silica. Ceramic composites formed from resin-bonded ceramic composite precursors can include refractory particles embedded in a carbon matrix.

[0059] Examples of suitable ceramic composites are disclosed in WO2022 / 013523, which is incorporated herein by reference. Ceramic composites generally have superior oxidation and corrosion resistance compared to carbon composite or graphite-based shafts. However, ceramic composites cannot directly substitute for graphite and carbon composite materials due to their higher density and reduced mechanical properties, including lower stiffness and bending strength.

[0060] The ceramic composite may be coated or impregnated using compositions and methods known to those skilled in the art.

[0061] Composite properties Ceramic composites typically include densities of at least 1.90 g / cc, or at least 2.0 g / cc, or at least 2.1 g / cc, or at least 2.2 g / cc. The upper limit is generally limited by the refractory material used in the composite, but is generally less than 2.5 g / cc. Due to the lower density of carbon, ceramic composites including a carbon matrix generally have lower densities than clay / glass-bonded ceramic composites.

[0062] The stiffness of a material can be determined by its Young's modulus. The Young's modulus of composite materials is typically significantly lower than that of graphite-based materials, with Young's moduli ranging from about 10 to 20 GPa. In contrast, the Young's modulus of ceramic composites can vary depending on the addition of components and is generally between 0.5 (or 1.0, or 2.0) and 20 GPa, with many ceramic compositions having a Young's modulus of less than 10 GPa, or less than 8 GPa, or less than 6 GPa. In one embodiment, the Young's modulus of a ceramic composite ranges from 0.5 GPa to 10 GPa.

[0063] Tensile flexural strength, or flexural strength, is a measure of a material's ability to withstand repeated bending stresses before mechanical failure (i.e., a measure of flexural fatigue strength). In one embodiment, the flexural strength of a ceramic composite ranges from 5 MPa to 30 MPa. The flexural strength of a ceramic composite can be at least 8 MPa, or at least 10 MPa, or at least 12 MPa, or at least 14 MPa, with an upper limit of 30 MPa or less, or 25 MPa or less, or 20 MPa or less. The flexural strength, and more significantly, the flexural fatigue strength, of a ceramic composite can be increased to the upper end of the range by controlling the grain size and porosity of the composite, as known to those skilled in the art. The flexural strength of graphite materials is typically greater than that of ceramic composites, ranging from 18 MPa to 36 MPa, but their flexural fatigue strengths for a given number of cycles and under a given stress ratio show similar trends.

[0064] operation The natural frequency of a shaft is an important design consideration because the amplitude of vibration of the shaft increases significantly as the shaft's rotational speed approaches the shaft's natural frequency. This increase in vibration increases stress on the shaft, which can lead to premature mechanical failure of the shaft. Therefore, it is desirable for the shaft's natural frequency to exceed the target operating rotational speed, preferably by at least 30%.

[0065] There are a number of factors that can affect the natural frequency of the deaerator shaft, namely: Shaft length (shorter shaft = higher natural frequency) Shaft weight (more weight = lower natural frequency) · There is shaft stiffness (increased stiffness = higher natural frequency).

[0066] Shaft stiffness can be influenced by shaft design, including the moment of inertia of the shaft cross section; larger diameter shafts are stiffer. However, increasing shaft weight can result in a decrease in natural frequency. Material selection can also have a significant effect on the natural frequency of a shaft, with stiffer materials resulting in shafts with higher natural frequencies. Applicant has discovered that a combination of design changes and material selection can not only produce longer shafts (e.g., greater than 1.5 m) with sufficiently high natural frequencies to enable the shaft to operate at the target rotational speed for high-density (greater than 2 g / cc) and low-stiffness (less than 10 GPa) materials, but also with natural frequencies sufficiently lower than the natural frequency to avoid any vibration amplification. Furthermore, this objective can be met by ceramic composite materials, which allow for increased oxidation, corrosion, and erosion resistance of shafts, particularly compared to graphite-based shafts.

[0067] The natural frequency of a long deaerator shaft (ie, greater than 1500 mm in length) may be in the range of 150 to 500 rpm, or 200 to 480 rpm, or 250 to 450 rpm.

[0068] In a second aspect of the present invention, there is provided a process for degassing a molten metal melt, comprising immersing a degasser in the molten metal melt, the degasser comprising a degasser shaft according to the first aspect of the present invention, and wherein the rotational speed of the degasser shaft is lower than the natural frequency of the shaft.

[0069] The rotational speed of the degassing shaft is preferably at least 20 rpm, or at least 40 rpm, or at least 50 rpm, lower than the natural frequency of the shaft.

[0070] In one embodiment, the shaft length is in the range of 1.5 to 2.2 metres, or at least 1.8 to 2.2 metres, or 1.9 to 2.1 metres, and the natural frequency of the shaft is greater than 300 rpm, or greater than 350 rpm, or greater than 400 rpm.

[0071] If the cross section of the shaft is not circular, the reference to diameter includes the effective diameter, which is considered to be the diameter of a circle having the same cross-sectional area as the non-circular shape.

[0072] For purposes of the present invention, tapered segments include frustoconical segments and polygonal prisms that include a cross-sectional area that decreases from one end to the other. For example, a segment of a pyramid is considered a tapered segment. However, in some embodiments, a tapered segment does not include any flat surfaces.

[0073] Flexural strength and lateral bending strength are used interchangeably throughout the specification.

[0074] For the avoidance of doubt, it is noted herein that the term "comprise," as it relates to a composition, has the meaning of "include," "contain," or "embrace," and that other ingredients may be present. The terms "comprise" and "comprising" should be understood similarly. It is also noted that no claim is made that any composition exceeds 100% in total of its ingredients.

[0075] Furthermore, it should be understood that the use of compositions named as oxides (e.g., alumina and silica) does not imply that these materials are in a particular stoichiometric form, but rather refers to composite compositions in which the relevant elements are expressed as oxides. It will also be understood that elements may also exist in non-oxide forms.

[0076] For purposes of the present invention, the length of a tapered segment is considered to be the axial length.

[0077] For purposes of the present invention, the deaerator shaft is separate and distinct from the deaerator shaft sleeve.

[0078] The term portion is used to denote one or more segments.

[0079] Unless otherwise indicated or implied, references to diameters are references to outer diameters.

[0080] The determination of the minimum and maximum wall thickness of the shaft excludes any measurements around the connection point to the motor or rotor or any flange area immediately adjacent to the rotor. [Brief explanation of the drawings]

[0081] [Figure 1] 1 is a schematic diagram of a deaerator shaft design with a connectable rotor according to the present invention. FIG. [Figure 2] FIG. 2 is a cross-sectional view of the deaerator shaft design of FIG. 1 showing an exploded view of the cross section of the female connection without the rotor. [Figure 3] FIG. 1 is a schematic diagram of the deaerator shaft design of Comparative Example 1 (CE-1). [Figure 4] FIG. 1 is a schematic diagram of the deaerator shaft design of Example 2. [Figure 5] FIG. 1 is a schematic diagram of the deaerator shaft design of Examples 5 and 6. [Figure 6] FIG. 1 is a schematic diagram of the deaerator shaft design of Example 3. [Figure 7] 4 is a photograph of the deaerator shaft design of FIG. 3 that has been mechanically damaged. [Figure 8] FIG. 1 is a design diagram of Comparative Example 5 (CE-5). [Figure 9] FIG. 1 is a design diagram of Comparative Example 6 (CE-6). [Figure 10] FIG. 10 is a design drawing of Example 7. DETAILED DESCRIPTION OF THE INVENTION

[0082] Although the present invention is illustrated by reference to frustoconical tapered segments and optional cylindrical segments, the invention is not limited thereto.

[0083] The degasser shaft of the present invention is made using conventional techniques in which raw materials are mixed, dried, packed into a mold, pressed, and sintered or fired at high temperatures (e.g., above 1000°C) for a sufficient time to sinter or otherwise harden the binder and ceramic composite together. The degasser shaft preferably comprises one or both of a single material and a one-piece construction.

[0084] 1 and 2, a schematic diagram of a deaerator shaft 10 and its cross section 110 is illustrated. The shaft has a first end 20 connectable to a motor. The connection is a female connector 50, which may include a helically threaded section 50 suitable for receiving a complementary male connector (not shown) on the motor or a device connected to the motor. To avoid stress concentrations in the female connector during operation, the connector includes a radiused or arcuate transition segment 58 between the helically threaded section and the passageway 100. The deaerator shaft also has a second end 30, which may include a one-piece rotor 40, where the rotor is seamlessly connected to the shaft. Alternatively, as illustrated in FIG. 2, the second end of the deaerator shaft may include a male helically threaded section forming a connector 70 connectable to a complementary helically threaded female connector (not shown) on the rotor.

[0085] The first end 20 is the largest diameter of the shaft (D 第1 The second end 30 includes the smallest diameter (D 第2 ) is included.

[0086] The degasser shaft has an outer diameter 80 and an inner diameter 90, the inner diameter defining a passageway 100 extending from the first end 20 to the second end 30. The outer diameter of the degasser shaft defines the frustum of a right circular cone, and the overall length of the degasser shaft (L全長 ) (i.e., the length of the male connector is not included in the overall length of the deaerator shaft).

[0087] The inner diameter of the degasser tube may be defined by a cylindrical portion and / or a frustoconical portion. The outer diameter may be enlarged to increase the stiffness of the degasser shaft. The inner diameter may also be enlarged in at least some portions of the shaft to avoid an associated increase in shaft weight. The passages may be formed using one or more cylindrical or tapered (i.e., frustoconical) mandrels in cooperation with a mold that defines the outer diameter of the shaft. In some embodiments, the passages have a cross-sectional area that increases from a first end at a maximum diameter point (e.g., the melt line) of the degasser shaft. This allows for a minimum difference in wall thickness between the minimum and maximum wall thicknesses, helping to reduce the weight of the degasser shaft. In some embodiments, the wall thickness is thickest at the maximum diameter point of the degasser shaft.

[0088] During operation, the deaerator shaft is positioned within a vessel containing molten metal. Depending on the deaerator configuration, the deaerator shaft is submerged in the molten metal up to a level of the shaft referred to as the "melt line," which defines the interface between the melt level and the gaseous atmosphere above it. The melt line 60 of the shaft is exposed to the most oxidatively corrosive environment, and therefore weakening of the deaerator shaft due to oxidation corrosion makes it more susceptible to mechanical failure at that point. To mitigate the risk of mechanical failure of the deaerator shaft around the melt line, the wall thickness of this section of the deaerator shaft may be increased compared to other sections of the deaerator shaft.

[0089] 3 and 4 illustrate a variation of the frusto-conical deaerator shaft of Figures 1 and 2, where a first portion 310, 410 includes a cylindrical portion 320, 420 and a frusto-conical portion 330, 430. The frusto-conical portion abuts a cylindrical section 340, 440 that extends to a second end of the deaerator 450.

[0090] As illustrated in FIG. 4 , the shaft wall thickness is greatest at cylindrical portion 420, where the melt line is located, and is smallest at cylindrical portion 440 at the second end of deaerator shaft 450. This configuration provides the highest oxidation corrosion resistance where oxidation corrosion is greatest at the interface between the gaseous air and the molten metal. In other embodiments (e.g., somewhat shorter shafts), the melt line may be located in a first portion of the lower half or bottom third of the shaft. Preferably, the melt line is positioned at an outer diameter of the shaft that is greater than the minimum shaft outer diameter, and preferably, the melt line is positioned at a shaft wall thickness that is greater than the minimum shaft wall thickness.

[0091] The deaerator shaft design 300 of FIG. 3 is a comparative example, in which the first section 310 is the entire length of the deaerator shaft (L 全長 ) does not extend for the necessary portion of the deaerator shaft. As a result, (i) the deaerator shaft has a lower stiffness due to the relatively smaller outer diameter (SD) of the deaerator shaft at the lower cylindrical section 340, and (ii) there is a sharper junction angle 350 between the frustoconical and cylindrical sections 340 compared to the corresponding junction angle 460 in FIG. 4 . These differences are illustrated by the fact that the first section of the deaerator shaft in FIG. 4 is longer than that in FIG. 3 (P2 > P1), and the frustoconical section in FIG. 4 is longer than that in FIG. 3 (P2-C1 > P1-C1). The combination of these two design features can significantly reduce stress concentrations on sections of the deaerator shaft, depending on operating conditions, thereby reducing the frequency of mechanical failure of the shaft. FIG. 7 illustrates the location of mechanical failure for a short deaerator shaft category design similar to that of FIG. 3 , with failure points at and around the intersection of the frustoconical section 710 and the cylindrical section 720.

[0092] The radius R that defines the tapered shoulder of the rotor 360 determines the deemed end of the second end of the shaft 370 when the rotor is seamlessly connected to the deaerator shaft 300 .

[0093] The design configuration of FIG. 4 can maintain similar, if not better, performance to the designs of FIGS. 1 and 2 because the melt line is positioned within the cylindrical section 420 of the mid-length and longer shaft, thereby keeping the melt line at the largest diameter portion of the deaerator shaft. c ) is similar to the cylindrical portion 320 of FIG. 3, but the length of the tapered portion 430 (L t ) is significantly longer than tapered section 330 of FIG. 3, thereby contributing to higher stiffness.

[0094] Furthermore, the relatively small cylindrical section 440 adjacent the second end of the deaerator shaft 450 has been shown not to significantly degrade performance, which may be at least partially offset by the lower weight of this section compared to its frusto-conical counterpart.

[0095] Additionally, to reduce the weight of the degasser shaft, the inner diameter of the passageway at the first end ID1 that runs to the inner diameter of the second end ID2 can be widened. This is particularly advantageous in longer degasser shafts, where the total weight and weight distribution of the degasser shaft can affect the natural frequency of the degasser shaft during operation. The inner diameter of the passageway at the first end ID1 can be measured directly below any female connection cavity 470 that may be present. The passageway 480 can be cylindrical, in which case the wall thickness of the degasser shaft is greatest at the melt line, which is located within the cylindrical portion 420 for mid-length and longer shafts, thereby adding oxidation resistance to the shaft at the point where maximum protection is needed. The shaft can also have tapered passageways to reduce the total weight of the shaft, if desired.

[0096] Further design variations within the scope of the present invention are provided in Figures 5 and 6. The degasser shaft design of Figure 5 differs from that of Figure 4 in that the cylindrical portion 420 is partially replaced with a frustoconical portion 525 that tapers from the cylindrical portion to the first end of the degasser shaft. This results in the cylindrical section 520 being offset from the first end. This configuration may allow the first end of the degasser shaft to fit existing degassers, which may include safety guards and housing features, and may reduce the overall weight of the shaft. Furthermore, the maximum outer diameter of the shaft may be maintained around the melt line at or around the cylindrical portion for medium-length and long shafts. Alternatively, the melt line may be positioned at the top portion of the frustoconical portion 530. It will be understood that the degasser may be configured to accommodate conventional shafts, which may have smaller outer diameters.

[0097] 6 illustrates a shaft 600 with a different design that further includes a first portion 610 that includes a first cylindrical portion at the top of the shaft 620. The first portion further includes a frusto-conical portion that includes a cascade or step-down portion that includes a series of cylindrical portions 640, 660, 680 of decreasing diameter that separate a series of frusto-conical sections 630, 650, 670, 690 of decreasing diameter.

[0098] The specific design features of a deaerator shaft depend on the operating environment to which the deaerator shaft will be exposed and the corrosion- and erosion-resistant ceramic composite properties required to extend the operating life of the deaerator shaft. Short shafts (e.g., less than 600 mm in length) generally operate at high rotational speeds, and shaft design focuses on reducing stress concentrations due to shaft deflection, especially in shafts with relatively low stiffness (i.e., relatively low Young's modulus). Often, the design focus is on increasing the shaft diameter and minimizing stress concentration points. For longer shafts, avoiding excessive vibrations that result in elevated stress levels in the shaft often focuses on shaft weight and weight distribution as an additional design priority.

[0099] The scope of the present invention is not limited to the specific embodiments illustrated herein, and those skilled in the art can readily use the teachings herein to make numerous modifications and variations that fall within the scope of the present disclosure. [Example]

[0100] Numerous shaft designs were evaluated under the stimulation conditions. Note that for experimental purposes, the end of the short rotor shaft was considered to be the rotor's largest diameter, not the smallest diameter of the shaft proximal to the rotor. Given that the weight of this additional section was similar, the results are still considered valid for comparison purposes.

[0101] Short deaerator shaft The short deaerator shaft designs shown in Table 2 can be operated at 700-1000 rpm and were compared with respect to their maximum stress levels and maximum displacements when subjected to a 25 N load.

[0102] The shaft was fabricated from a ceramic carbon composite from Molten Metal Systems GmbH, containing approximately 65 wt.% refractory particles (the remainder being approximately 40 wt.% SiC with alumina and aluminosilicate particles as the majority) and approximately 35 wt.% carbon matrix and graphite flakes, with a density of 2.2 g / cc, a Young's modulus of 3 GPa, and a flexural strength of 11 MPa.

[0103] The geometries of different deaerator shaft designs are provided in Table 2 with reference to FIGS. [Table 2] [Table 3]

[0104] As shown in Tables 2 and 3, Designs 1-3 had the lowest maximum stress and the smallest maximum displacement when subjected to a load of 25 N. The Comparative Examples had higher maximum stress and displacement levels and were therefore more susceptible to mechanical failure. Despite these superior mechanical properties, the corrosion resistance of graphite is significantly lower than that of ceramic composites. CE-1 and CE-2 have a relatively large first section, but the relatively small frustoconical component of this section resulted in a relatively large angle of incidence, which may contribute to the high maximum stress levels achieved by these designs.

[0105] Long deaerator shaft The ceramic composite used had the same composition and properties as the short deaerator shaft, but its Young's modulus was 3 GPa. The ceramic composite properties are provided in Table 4. The natural frequency of the deaerator shaft was determined when the shaft was attached to the rotor. The rotor weight was 5.8 kg, while the rotor for sample CE-4 weighed 4.5 kg. This was because this rotor was made of graphite, not the ceramic composite from which the other rotors were made. The frequency response analysis of the shaft and rotor to determine the natural frequency was based on a 1 kg transverse excitation at the base of the rotor with 0% damping. Typically, damping caused by a liquid affects the amplitude of vibration but not the value of the natural frequency. With 0% damping, the shaft rotates in air.

[0106] As illustrated in Table 4, a conventional cylindrical shaft (CE-3) made from a ceramic composite had a low natural frequency that made it unsuitable for operation above 220 rpm without vibration amplification. In contrast, the natural frequency of a similarly sized deaerator shaft made from graphite was 550 rpm. The increase in natural frequency can be attributed to the harder (e.g., higher Young's modulus) and lighter (e.g., lower density) properties of graphite.

[0107] The tapered deaerator shaft (4) can reduce the weight of the deaerator shaft, increasing the natural frequency of the deaerator shaft to 260 rpm despite the reduced diameter of the shaft at the second end. In Examples 5 and 6, a further increase in the natural frequency of the deaerator shaft is achieved by increasing the diameter of the deaerator shaft at the first end, despite the increased weight of the deaerator shaft compared to Example 3. Examples 3-5 all had lower deaerator shaft weights compared to the ceramic composite deaerator shaft of Comparative Example 3 (CE-3). The larger diameters of Examples 3-5, combined with the thinner minimum wall thickness, achieved this lighter deaerator shaft weight. [Table 4]

[0108] Service life The service life of a graphite shaft is typically dominated by mechanical failure caused by corrosion, whereas the service life of a ceramic composite shaft is dominated by mechanical failure due to fatigue.

[0109] Fatigue testing was performed to establish how the design of the present invention can extend the useful life of a ceramic composite shaft through increased stiffness, targeted weight distribution, and avoidance of stress concentrations.

[0110] Fatigue Testing Equipment a. Configuration: The fatigue testing machine includes a fixture rig having a shaft assembly, the shaft being fixed to a top coupler and connected to the fixture rig, and having a horizontally moving bottom coupler that induces a deflection that simulates application conditions. b. Load: A set deflection is applied to the shaft through horizontal movement of the bottom coupler. The horizontal deflection is repeated without rotating the shaft.

[0111] Test procedure: a. Sample Preparation: Manufacture six test samples for each design variant. b. Determining the offset. Through the use of a frequency response chart, a value of 600 to 800 cycles per minute (cpm) was empirically confirmed with a laser measurement device. c. Cyclic Load Profile: Deflection is applied to the shaft at a given cyclic rate. Since the offset is already fixed, the rig cyclic rate only affects the test duration. d. Test duration: The fatigue test duration was not predetermined, and the test continued until the shaft broke. After 1 million (1M) cycles at a deflection of 1.8 mm, the shaft deflection was then increased to 3.0 mm to accelerate shaft breakage.

[0112] Test execution: a. Cyclic Load: The fatigue test was initiated and the specimen was subjected to cyclic loading at the specified CPM and the specified deflection. b. Data Collection: The proximity sensor records failure indication when the shaft breaks and records the number of cycles each specimen completed before failure.

[0113] Data Analysis: a. Fatigue Life Assessment: The number of cycles each specimen endured before failure was recorded and represented the fatigue life for each design variant. b. Criteria for failure: Specimens with visible cracks or complete fractures are considered to be damaged. c. Statistical Analysis: The number of cycles endured and percentage of shafts damaged for each design variant are calculated to assess the relative durability of the designs. d. Interpretation of Results: The design with the highest number of cycles was deemed the most resilient, capable of longer service life in operation, excluding factors such as shaft weight.

[0114] Design Variants: Three design variations using the ceramic composite of the previous example were subjected to fatigue testing.

[0115] Comparative Example 5 (FIG. 8) is a shaft including a first portion outside the scope of the present invention, in which the frustoconical portion includes a relatively sharp angle of incidence with the adjacent cylindrical portion. Comparative Example 6 (FIG. 9) is a shaft having a constant shaft diameter (as expected for a flange portion at the second end). Example 7 (FIG. 10) is a shaft within the scope of the present invention.

[0116] Fatigue test results As illustrated in Table 5, Comparative Example 5 was only able to withstand 20 cycles with a horizontal deflection of 3.0 mm at 600 cpm. The shaft design was able to withstand a smaller horizontal deflection (1.8 mm) and associated stresses significantly longer, but still achieved less than 20% of the (average) cyclic operating life of the conventional cylindrical shaft of Comparative Example 6. [Table 5]

[0117] The shaft design of the present invention (Example 7) had a slightly shorter work cycle life compared to Comparative Example 6 in Runs 9 and 11, but Run 10 exhibited premature failure, which may be characteristic of manufacturing variations (e.g., uneven material loading). However, this premature failure was still more than twice the average cyclic life of Comparative Example 5.

[0118] The notion that Run No. 10 is anomalous is supported by the fact that Run No. 10 failed approximately 50 mm below the threaded connection to the motor (i.e., approximately 105 mm from the first end), while Runs 6-8 (CE-6) and Runs 9 and 11 (Example 7) all failed at the threaded internal connection point (i.e., approximately 57 mm from the first end). The failure at a different location for Run No. 10 compared to other runs of the same design suggests a composite inconsistency rather than an inherent design flaw.

[0119] Experiments 1-5 all failed below the internal threaded section, at the intersection of the tapered section and the cylindrical section towards the first end (approximately 105 mm from the first end), suggesting that stress was concentrated in this area.

[0120] Note that Example 7 had an arcuate bridge connection with a radius of 2 mm. Therefore, increasing this radius by at least 5 mm is expected to further extend the useful life of the shaft, as increasing the radius is expected to reduce stress in this area.

[0121] While the designs of Example 7 (except for Run 10) had similar cyclic life to the cylindrical shaft of CE-6, the reduced weight of the design of Example 7 compared to CE-6 (17% reduction) has the advantage of placing less load on the motor, thereby significantly reducing motor maintenance (e.g., bearing replacement), while extending the shaft life before mechanical failure by more than five times compared to the shaft of CE-5. The shaft design of the present invention can reduce the total maintenance costs (repair and replacement) of the degassing system over the shaft's life cycle. The lighter shaft is also easier to install and consumes less energy.

Claims

1. 1. A degasifier shaft for treating molten metal with a gas, said shaft comprising: (d) a first end connectable to a drive for rotating the shaft about the longitudinal axis, the first end having a first end outer diameter; (e) a second end having a second end outer diameter; and connectable to the rotor, or a second end portion integral with the rotor, the second end portion outer diameter being considered to be the smallest shaft outer diameter proximal to the rotor; (f) a passageway through which the gas travels from the first end to the second end, the passageway being defined by an inner diameter of the deaerator shaft; 1. A degasifier shaft having a first portion located at or toward the first end and including a first tapered segment that decreases in cross-sectional area toward the second end, and optionally a first constant cross-section segment extending from the first tapered segment toward the first end, wherein the first portion comprises 48% to 100% of the overall length of the degasifier shaft, and wherein at least the first tapered segment of the degasifier shaft is made of a ceramic composite material.

2. The deaerator shaft a first constant cross-section segment having a cross-sectional area greater than a minimum cross-sectional area of ​​the deaerator shaft and extending contiguously from the first tapered segment toward the first end; and a second constant cross-section segment extending adjacently from the first tapered segment toward the second end.

3. The deaerator shaft of claim 2 , wherein the second constant cross-section segment has a cross-sectional area equal to the minimum cross-sectional area of ​​the deaerator shaft.

4. 2. The deaerator shaft of claim 1, wherein the first tapered segment extends from the minimum shaft outer diameter to a maximum shaft outer diameter, and the second tapered segment extends from the maximum shaft outer diameter and decreases in cross-sectional area toward the first end.

5. The deaerator shaft of claim 4 , wherein a constant cross-section segment is disposed between the first tapered segment and the second tapered segment.

6. 6. The deaerator shaft of claim 4 or 5, wherein the first tapered segment comprises two or more tapered segments separated by two or more constant cross-section segments.

7. The deaerator shaft of claim 6 , wherein the outer diameter of the two or more constant cross-section segments decreases as the first portion progresses toward the second end of the shaft.

8. 8. The deaerator shaft of claim 2, wherein the first portion comprises in the range of 50% to 90% of the total length of the deaerator shaft, and the second constant cross-section segment comprises in the range of 10% to 50% of the total length of the deaerator shaft.

9. The deaerator shaft of any one of claims 1 to 8, wherein the first portion comprises one or more tapered segments that occupy between 40% and 90% of the overall length of the deaerator shaft.

10. The deaerator shaft of claim 9 , wherein the one or more tapered segments occupy at least 50% of the overall length of the deaerator shaft.

11. The deaerator shaft of any one of claims 2 to 10, wherein an angle of incidence between the tapered segment and the second constant cross section segment is greater than 0° and less than or equal to 16°.

12. 12. The deaerator shaft of claim 11, wherein the angle of incidence between the tapered segment and the second constant cross section segment is greater than 2 degrees and less than or equal to 10 degrees.

13. The degasifier shaft of any one of claims 1 to 12, wherein the shaft further comprises a melt line, the melt line being located at the maximum outer diameter of the shaft.

14. A deaerator shaft according to any one of claims 1 to 13, wherein the ratio of the minimum shaft wall thickness to the maximum shaft wall thickness is in the range of at least 0.3 to less than 0.

90.

15. The deaerator shaft of claim 14, wherein the ratio of the minimum shaft wall thickness to the maximum shaft wall thickness is in the range of at least 0.5 to less than 0.

85.

16. The maximum outer diameter (D 最大 ) to the minimum outer diameter (D 最小 16. The deaerator shaft according to any one of claims 1 to 15, wherein the length of the shaft minus the length of the shaft is in the range of 10 to 100 mm.

17. D 最大 -D 最小 17. The deaerator shaft of claim 16, wherein is at least 30 mm.

18. D 最大 -D 最小 17. The deaerator shaft of claim 16, wherein is at least 40 mm.

19. A deaerator shaft according to any one of claims 1 to 18, wherein the length of the shaft is greater than 1500 mm.

20. The deaerator shaft - Total length of 250 to 2200 mm, an optional first constant cross-section segment comprising a length in the range of 0 to 600 mm; a tapered segment, if present, abutting the first constant cross-section segment, having an outer diameter that decreases as the tapered segment extends towards the second end, and having an axial length in the range of 100 to 2200 mm; an optional second constant cross-section segment; a first shaft end outer diameter in the range of 60 to 180 mm; a second shaft end outer diameter in the range of 45 to 140 mm; A deaerator shaft according to any one of the preceding claims, having a passage diameter in the range of 10 to 60 mm.

21. The deaerator shaft - Total length of 1500 to 2200 mm, the first constant cross-section segment comprising a length in the range of 100 to 600 mm; a first tapered segment adjacently abutting the first constant cross-section segment, the first tapered segment including an outer diameter that decreases as the tapered segment extends towards the second end, and the first tapered segment including an axial length in the range of 400 to 2200 mm; an optional second constant cross-section segment; an optional second tapered segment abutting adjacent an end of the first constant cross-section segment and extending adjacent the first end, the optional second tapered segment comprising a length of 0 to 500 mm; a first shaft end outer diameter in the range of 80 to 180 mm; a second shaft end outer diameter in the range of 80 to 150 mm; A deaerator shaft according to any one of the preceding claims, having a passage diameter in the range of 10 to 60 mm.

22. The deaerator shaft - Total length of 500 to 1500 mm, a first constant cross-section segment comprising a length in the range of 0 to 500 mm; a tapered segment, if present, abutting the first constant cross-section segment and comprising an outer diameter that decreases as the tapered segment extends towards the second end, and comprising an axial length in the range of 500 to 1500 mm; a first shaft end outer diameter in the range of 70 to 150 mm; a second shaft end outer diameter in the range of 50 to 130 mm; A deaerator shaft according to any one of the preceding claims, having a passage diameter in the range of 10 to 50 mm.

23. The deaerator shaft - Total length of 250 to 600 mm, a first constant cross-section segment comprising a length in the range of 50 to 100 mm; a tapered segment abutting the first constant cross-section segment, the tapered segment including an outer diameter that decreases as the tapered segment extends towards the second end, and the tapered segment including an axial length in the range of 100 to 400 mm; an optional second constant cross-section segment; a first shaft end outer diameter in the range of 60 to 90 mm; a second shaft end outer diameter in the range of 45 to 70 mm; A deaerator shaft according to any one of claims 1 to 18, comprising: a passage diameter in the range of 10 to 25 mm.

24. Maximum shaft diameter external (D 最大 ) and minimum shaft outer diameter (D 最小 24. The deaerator shaft of claim 20, wherein the ratio of .mu.m to .mu.m is at least 1.

2.

25. Maximum shaft outer diameter (D 最大 ) and minimum shaft outer diameter (D 最小 25. The deaerator shaft of claim 24, wherein the ratio of .mu.m to .mu.m is at least 1.

4.

26. A deaerator shaft according to any one of claims 1 to 23, wherein the first end is connectable to a motor via a female connection.

27. 27. The deaerator shaft of claim 26, wherein the female connection comprises a threaded coupling means in which the helical thread of the shaft and the passageway are connected via an arcuate bridge connection.

28. 28. The deaerator shaft of claim 27, wherein the arcuate bridge connection has a radius of at least 5 mm.

29. The maximum wall thickness of the deaerator shaft (wall 最大 ) is located at or towards the location where the deaerator shaft has the maximum outer diameter, and the minimum wall thickness (wall 最小 ) is located at or toward the second end, and the wall 最小 / wall 最大 A deaerator shaft according to any one of the preceding claims, wherein the ratio of is in the range of 0.75 to 1.

0.

30. said wall 最小 / wall 最大 30. The deaerator shaft of claim 29, wherein the ratio of is in the range of 0.80 to 0.

95.

31. D 最大 / D 最小 31. The deaerator shaft of claim 29 or 30, wherein is greater than 1.

3.

32. D 最大 / D 最小 32. The deaerator shaft of claim 31, wherein is greater than 1.

4.

33. A deaerator shaft according to any one of the preceding claims, wherein the density of the ceramic composite material is in the range of 1.9g / cc to 2.5g / cc.

34. A deaerator shaft according to any one of the preceding claims, wherein the ceramic composite has a Young's modulus in the range of 0.5 GPa to 10 GPa.

35. A deaerator shaft according to any one of the preceding claims, wherein the ceramic composite has a transverse bending strength (TBS) in the range of 5 MPa to 30 MPa.

36. A deaerator shaft according to any one of the preceding claims, comprising a shaft length of at least 1500 mm and a natural frequency in the range of 250 to 500 rpm.

37. 10. A process for degassing a molten metal melt, comprising immersing a degasser in the molten metal melt, the degasser comprising a degasser shaft according to any one of the preceding claims.

38. 38. The process of claim 37, wherein the rotational speed of the deaerator shaft is less than the natural frequency of the deaerator shaft.

39. 39. The process of claim 37 or 38, wherein the surface of the molten metal melt reaches the deaerator shaft at a melt line positioned at an outer diameter of the shaft that is greater than the minimum outer shaft diameter.

40. 40. The process of any one of claims 37 to 39, wherein the shaft wall thickness at the melt line is greater than the minimum shaft wall thickness below the melt line.

41. Use of a deaerator shaft according to any one of claims 1 to 36 for treating molten metal.

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