(1) Field of the Invention
The present invention relates to structures used for containing and conveying molten metal, and to parts of such structures. More particularly, the invention relates to such structures having a refractory or ceramic vessel contained within an outer metal casing used to support, protect and, if necessary, align the refractory vessel.
(2) Description of the Related Art
Metal containment structures of this kind generally include a refractory vessel of some kind, e.g. a molten metal conveying vessel, held within an outer metal casing. The vessel may become extremely hot (e.g. to a temperature of 700° C. to 750° C.) as the molten metal is held within or conveyed through the vessel. If this heat is transferred to the outer metal casing of the containment structure, the metal casing may be subjected to expansion, warping and distortion and (if the vessel is made in sections) may cause gaps to form between the sections of the vessel, thereby allowing molten metal leakage. Additionally, the outer surface of the casing may assume an operating temperature that is unsafe for operators of the equipment. These disadvantages are made worse if additional heating is applied to the vessel to maintain a desired temperature for the molten metal. For example, temperatures of up to 900° C. may be present at the outside of the vessel when vessel heating is employed. Layers of insulation may be provided between the vessel and the interior of the casing, but such layers may not provide rigid support for the vessel and may not make it possible for a gap to be formed between the vessel and the casing for heat circulation when a heated vessel is required.
To overcome such problems, the vessel may be rigidly supported at various spaced positions within the interior of the metal casing, thereby permitting the formation of a thermal isolation gap between the vessel and the casing. Such a gap also allows for heat circulation in distribution systems that apply heat to the vessel. Layers of insulation may then be used to line the interior of the casing on the casing side of the gap to provide further thermal isolation for the metal casing. However, rigid supports cannot accommodate the thermal expansion and shrinkage that the vessel experiences during thermal cycling of the distribution system, and tend not to contain cracks that may form in the vessel.
There is, accordingly, a need for improved means of providing rigid support for a ceramic vessel within a metal casing of a metal distribution structure.
An exemplary embodiment of the invention provides a compressive rod assembly for applying force to a refractory vessel positioned within an outer metal casing, the assembly comprising a rigid elongated rod having first and second opposed ends, a threaded bolt adjacent to the first opposed end of the elongated rod, and a compressive structure positioned operationally between the elongated rod and the bolt, whereby force applied by the bolt to the elongated rod passes through the compressive structure which allows limited longitudinal movements of the elongated rod to be accommodated by the compressive structure without requiring corresponding longitudinal movements of the bolt.
Another exemplary embodiment provides a molten metal containment structure (e.g. a structure for holding, distributing or conveying molten metal), having a refractory vessel positioned within an outer metal casing, the vessel being spaced from internal surfaces of the casing and being subjected to compressive force from at least one compressive rod assembly, the assembly comprising: a rigid elongated rod having first and second opposed ends, with the second end in contact with the vessel within the casing, a threaded bolt adjacent to the first opposed end of the elongated rod and extending outside the casing, and a compressive structure positioned operationally between the elongated rod and the bolt, whereby force applied by the bolt to the elongated rod passes through the compressive structure which allows limited longitudinal movements of the elongated rod to be accommodated by the compressive structure without requiring corresponding longitudinal movements of the bolt.
The vessel may be, for example, an elongated vessel having a metal conveying channel extending from one longitudinal end of the vessel to an opposite longitudinal end, a vessel having an elongated channel for conveying molten metal, the channel containing a metal filter, a vessel having an interior volume for containing and temporarily holding molten metal, and at least one metal degassing unit extending into the interior volume, or vessel designed as a crucible having an interior volume adapted for containing reacting chemicals.
In the structure, each of the plurality of compressive isolation rod assemblies preferably applies a force in a range of 0 to 5,000 lb (0 to 2268 Kg) to the vessel. The vessel preferably has longitudinal side walls and a bottom wall, and some of the compressive isolation rod assemblies preferably contact the longitudinal side walls and/or bottom wall at positions along the vessel spaced by distances of 1.5 to 15 inches (3.8 to 38.1 cm). There is preferably an unfilled gap between the vessel and the casing, and the tubular metal reinforcement terminates short of the gap, e.g. by a distance of 0.0 to 2.0 inches (0 to 5 cm). Alternatively, the tubular metal reinforcement is preferably spaced from the one of the longitudinal ends of the body by a distance of 0.0 to 3.0 inches (0 to 7.6 cm).
The structure may contain a heater for heating the vessel or alternatively the vessel may be unheated, and thermal insulation material may be provided adjacent to an inner surface of the casing.
The rigid rod of the compressive assembly can withstand the high heat of the vessel. Since essentially the only contact between the vessel and the metal casing is via the rigid rod, heat conduction from the walls of the vessel is reduced. The rod thus thermally isolates the vessel from the metal casing. Additionally, the compressive force applied by the rod helps to prevent cracks from forming and tends to contain such cracks when they do form, thereby reducing instances of metal leakage from the vessel.
The vessel is primarily intended for containing or conveying molten aluminium or aluminium alloys, but may be applied for containing or conveying other molten metals and alloys, particularly those having melting points similar to molten aluminium, e.g. magnesium, lead, tin and zinc (which have melting points lower melting points than aluminium) and copper and gold (which have higher melting points). Iron and steel have much higher melting points, but the structures of the invention may also be designed for such metals, if desired.
Yet another exemplary embodiment provides a rod component for a compressive isolation rod assembly of the above kind, the rod component comprising an elongated rigid rod having first and second opposed ends, and the rod having a refractory heat insulating material adjacent the second opposed end of the rod.
The rod 22 and preferably the tubular metal support 26 form a replaceable component for the assembly that may require replacement if the rod 22 fails, e.g. by breakage or metal creep caused by exposure to high temperatures.
The parts of the assembly 10 are shown in assembled form in
As will be seen in
Although
The interior of the metal casing is lined with layers of refractory thermal insulation 45 to further reduce heat conduction to the metal casing. Such layers do not provide significant physical support to the vessel 42 and, indeed, do not touch the vessel, at least at the vertical sides of the vessel as shown where there is an air gap 46 to provide further thermal isolation of the vessel 42. Of course, if desired, the entire space between the metal casing and the vessel may be filled with refractory insulation and, in the embodiment of
Although the embodiment of
When vessel heaters are employed, it is preferable that the tubular metal supports 26 for the rod 12 not be directly exposed to the heated atmosphere within the air gap 46. In such cases, the metal supports should terminate within the layer of insulating material 45 (see
The lengths L of rods 12 may vary to fit metal distribution systems of different sizes. However, lengths often vary from 1.5 to 12 inches (3.8 cm to 30.5 cm) or longer, and more usually 3 to 5 inches (7.6 cm to 12.7 cm).
Heat conduction of the rod 12 is advantageously reduced as the diameter of the ceramic body 22 is reduced, but compressive strength is disadvantageously reduced and brittleness may be increased, so there is normally an optimum range of thickness that minimizes heat conduction while retaining sufficient strength. This optimum range depends on the material used for the refractory rod 22 but is preferably in the range of 0.25 to 3.0 inches (6 mm to 7.6 cm), and more preferably 0.5 to 1.25 inches (1.3 cm to 3.2 cm).
As noted previously, the bolt 18 is normally tightened so that the rod 12 exerts a compressive force against the vessel 42. Preferably, this compressive force is in the range of 0 to 5,000 lb (0 to 2668 Kg), and more preferably 800 to 1,200 lb (363 to 544 Kg). A zero force is included in the larger range because the rod still functions if it prevents the vessel from moving without actually applying a force until the vessel presses against the rod under thermal load or due to the development of a crack.
The rods carry the compressive load applied to the vessel and so the ceramic material of the rods 22 is chosen to work under such loads without shattering or breaking. As an example, a 1,200 lb (544 Kg) compressive design load on a rod having a diameter of 0.625 inch (1.6 cm) produces a pressure of almost 4,000 psi (27.6 MPa) and, in practice, the pressure may be as high as 5,000 lb (2268 Kg), which produces a pressure of 16.3 ksi (112.4 MPa) on the rod. Rods made of alumina are available with a compressive strength of 300 ksi (2068.4 MPa) and higher, and so are suitable for most or all such applications. Other ceramics may have compressive strengths as low as 50 ksi (344.7 MPa), and are thus still acceptable for many applications. It should be kept in mind that material strengths are typically given for materials at room temperature, and will be moderately to greatly reduced at elevated temperatures, so it is advisable to choose materials having strength values much greater than those likely to be encountered. Because of its very high compressive strength, alumina is preferred for most applications.
It should be noted that although the rod 22 is preferably a cylinder or column of refractory material, it may be tubular or hollow. This further minimizes the area of contact between the end 23 of the rod and the vessel wall, thereby further reducing heat conduction from the vessel. The high strength of alumina, in particular, makes this possible without significantly increased risk of rod breakage. The rod 22 may also be of any desirable cross-sectional shape, e.g. circular, oval, triangular, square, rectangular, polygonal, etc.
The supporting metal tube 26 is preferably long enough provide good support for the refractory rod, but should terminate a sufficient distance short of the vessel contacting end 23 to avoid providing an increase in heat conduction from the vessel. The tube should be thick enough to contain the rod, if the rod should shatter in use, with enough strength to still apply a compressive load. A preferred wall thickness of the tube is at least 0.1 inch (3 mm), with a more preferred range of 0.03 to 0.07 inch (1 mm to 2 mm). Steel or other strong metal may be used for the tube.
Unless the tube fits around the rod with minimal clearance, the rod is preferably bonded within the tube with a space-filling, heat resistant adhesive. Suitable adhesives include Cotronics ResBond® 989FS (available from Cotronics Corporation of Brooklyn, N.Y., USA), which is a high temperature ceramic adhesive, and high temperature epoxy resins. A portion of the epoxy resin may burn off at the end closest to the vessel, but the remote end will remain sufficiently cool that the adhesive will remain functional. To avoid the need for adhesives altogether, the tube and rod may be thermally shrink fit together.
As shown in
As a further alternative, the rod 12 may be made partly of refractory material and partly of metal, with the refractory part positioned adjacent to the vessel contacting end 23. The refractory part may be made long enough to act as a thermal insulator between the vessel and the metal part of the rod.
Although the use of a rod 22 made completely or partly of refractory ceramic material has been described above, it is possible to make the rod entirely of metal, e.g. stainless steel, titanium or inconel (a nickel-chromium based alloy). Clearly, the use of metal rods reduces the likelihood of breakage under compression, but increases loss of heat from the vessel. Furthermore, certain metals may be subject to loss of strength or high temperature creep, so it is advisable to use all-metal rods only in lower temperature applications, e.g. with lower temperature metals and without additional heating of the vessel. In contrast, rods containing or consisting of refractory ceramics are suitable for applications at all temperatures.
Although not specifically shown, the longitudinal ends of the vessel 42 may also be placed under compression from abutting end plates thrust against the vessel ends by bolts and cupped washer assemblies attached to end walls of the metal casing. Isolation rods such as those shown in the Figures are not, however, required at these end wall positions.
The vessel 42 itself may be made from any suitable known ceramic material, e.g. alumina or silicon carbide, and may be made of two or more vessel sections (e.g. 42A and 42B shown in
In the embodiment of
Molten metal distribution structures of the kind shown in
An alternative embodiment is illustrated in
As in the previous embodiment, the cupped washers 15 and plate 14 act as a compressive structure between the rods 12 and the bolt 14 that allows limited longitudinal movements of the rods to be accommodated by the compressive structure without requiring corresponding longitudinal movements of the bolt 18.
The rods 12 may be made of metal (e.g. stainless steel) when there is no active heating of the vessel 42, and may be made of refractory ceramic (e.g. alumina) when there is active heating of the vessel, e.g. by means of electrical elements (not shown) provided in the gap 46. As a further alternative, a composite rod having ceramic at one end (the vessel contacting end) and metal at the other may be employed to avoid the use of a long column of ceramic material, that might be brittle. Furthermore, as in the previous embodiment, a ceramic rod reinforced with a metal tube may be employed for the rods 12.
As noted, the rods 12 are provided in pairs to prevent tilting of the plate 14 as force is applied. Alternatively, a single central rod 12 may be employed, with bolts 18 at each end of the plate 14. The bolts would then be tightened at the same time and by the same amounts to avoid undue tilting of the plate.
This application claims the priority right of prior provisional patent application Ser. No. 61/283,905 filed on Dec. 10, 2009 by applicants herein. The entire content of application Ser. No. 61/283,905 is specifically incorporated herein for all purposes by this reference.
Number | Date | Country | |
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61283905 | Dec 2009 | US |