System and method for adding molten lithium to a molten aluminium melt

Abstract

A system for adding molten lithium and inert gas in a molten aluminium or aluminium alloy melt including, a crucible defining a chamber for melting and storing molten metal, in particular molten lithium; the crucible having a sealed lid; an inert gas delivery system for maintaining chamber overpressure using inert gas; a conduit for withdrawing a portion of the molten metal from the crucible. The conduit arranged with respect to the crucible or the sealed lid so the conduit inlet can be moved below and above the molten metal surface level and arranged for feeding molten metal from the crucible to a separate holding furnace with the help of overpressure when the conduit inlet is below the molten metal surface level and arranged for feeding inert gas from the crucible to the separate holding furnace when the conduit inlet is above the molten metal surface level.

Claims

1. A dual-use system for alternately adding molten lithium or an inert gas to a melt of molten aluminium or aluminium alloy in a separate molten metal holding furnace, the system comprising: a crucible without a refractory on the inside thereof, defining a chamber for melting and storage of molten lithium, the crucible being equipped with a sealed lid; an inert gas delivery system arranged for maintaining an overpressure in the chamber of the crucible using an inert gas; and a conduit, having a conduit inlet and a conduit outlet, for withdrawing a portion of the molten lithium from the crucible, and the conduit being movably arranged with respect to the crucible or the sealed lid such that the conduit inlet is controllably moveable to a first position below a surface level of the molten lithium in the crucible and a second position above the surface level of the molten lithium in the crucible, and wherein the conduit is arranged for feeding of the molten lithium from the crucible to the separate molten metal holding furnace with the help of the overpressure when the conduit inlet is in the first position below the surface level of the molten lithium in the crucible, and wherein the conduit is further arranged for feeding of the inert gas from the crucible to the separate molten metal holding furnace when the conduit inlet is in the second position above the surface level of the molten lithium in the crucible further comprising at least one heating unit and at least one temperature measurement and control unit.

2. The system according to claim 1, further comprising: a supply tank of pressurised inert gas, the supply tank being interconnected to the chamber of the crucible through a gas delivery system that includes a pressure regulator and at least one valve mounted on a supply tube for the crucible.

3. The system according to claim 1, wherein the crucible is formed by a steel vessel or container.

4. The system according to claim 1, wherein the feeding of the molten lithium from the crucible to the separate molten metal holding furnace with the help of the overpressure is controllable via the inert gas delivery system.

5. The system according to claim 1, wherein overpressure is in a range of up to 200 mbar.

6. The system according to claim 1, wherein the conduit is adapted for feeding the molten lithium at a temperature in a range of up to 260 C.

7. The system according to claim 1, wherein at least a part of the conduit, or the conduit joined to a further conduit, has an upward inclination.

8. The system according to claim 1, wherein the overpressure is in a range of up to 80 mbar.

9. The system according to claim 1, wherein the overpressure is in a range of up to 200 mbar.

10. The system according to claim 1, the overpressure is in a range of up to 80 mbar.

11. The system according to claim 1, wherein the conduit outlet is adapted and configured to be communication with the separate molten metal holding furnace in the first position and the second position.

12. The system according to claim 1, wherein the metal holding furnace is an induction melting furnace.

13. The system according to claim 1, wherein the conduit is made from stainless steel with a BN coating.

14. The system according to claim 1, wherein the conduit outlet is in communication with the separate molten metal holding furnace when the conduit inlet is in the first position and when the conduit inlet is in the second position.

15. The system according to claim 14, wherein the crucible is airtight, and wherein the inert gas delivery system is in communication with the chamber of the crucible; wherein the inert gas delivery system for maintaining the overpressure comprises an inert gas supply tube having an inert gas supply tube outlet located in an upper portion of the crucible for discharging the inert gas directly into the upper portion of the crucible over the surface level of the molten lithium in the crucible when the conduit inlet is in both the first and second positions.

16. The system according to claim 15, wherein the conduit comprises an upstream conduit segment in communication with the crucible, a downstream conduit segment in communication with the separate molten metal holding furnace, and optionally an intermediate conduit segment; wherein: (a) the upstream conduit segment is coupled to the downstream segment, or (b) the upstream conduit segment is coupled to a first end of the intermediate conduit segment and the downstream conduit segment is coupled to a second end of the intermediate conduit segment.

17. The system according to claim 16, further comprising a second inert gas delivery system in communication with the downstream conduit segment.

Description

DESCRIPTION OF THE DRAWINGS

(1) Some preferred embodiments of the invention shall now be described with reference to the appended drawing, in which:

(2) FIG. 1 is a partial cross-sectional schematic representation of the system and the apparatus.

(3) FIG. 2 is a partial cross-sectional schematic representation of an insulated heated conduit.

(4) For the system, method and apparatus according to this invention there is provided a crucible or vessel (10) being airtight sealable with a lid (11) and defining a chamber (13) for storing molten lithium (50) and an inert gas. The lid (11) can be removed for maintenance and cleaning of the vessel and the seals. The vessel is for a part filled with molten lithium having a surface level. There is provided a conduit (12), having a conduit inlet and a conduit outlet, for withdrawing a portion of the molten lithium (50) from the vessel (10). In this embodiment the conduit (12) is movably arranged with respect to lid (11) using one or more seals known in the art (not shown) such that in operation the conduit inlet can be controllably moved, e.g. using mechanical means (100), below and above the surface level of the molten metal. Also, the conduit (12) is arranged for feeding of the molten metal from the crucible to a separate molten metal holding furnace (not shown) with the help of an overpressure when the conduit inlet is below the surface level of the molten lithium, or submerged in the molten lithium, and the conduit is further arranged for feeding of the inert gas from the crucible to the separate molten metal holding furnace (not shown) when the conduit inlet is above the surface level of the molten lithium. The mechanical means for raising and lowering can be any suitable means, for example a hydraulic or pneumatic activated piston.

(5) Appropriate seals for between the conduit and the vessel or vessel lid and that can withstand an operating temperature of up to about 260 C. and an overpressure of up to 200 mbar, and preferably up to about 80 mbar, are readily available.

(6) The conduit and the vessel can be moved with respect to each other, e.g. by maintaining the conduit in a fixed position and lowering the vessel or alternatively by actively raising or lowering the conduit while maintaining the vessel in a fixed position. Although on a less preferred basis, but for the skilled person it will be immediately apparent that the conduit can also be swung into a position below or above the surface level of the molten lithium.

(7) In operation the molten lithium or inert gas as the case may be, is fed to the molten aluminium alloy in the separate holding furnace (not shown) via a system of coupled conduits comprising a first conduit (12), second conduit (14) and third conduit (15). The second conduit (15) may have an upward angle of inclination (a), typically 5 to 45 degrees, to facilitate a back flow of molten lithium from the conduit(s) when the over-pressure is reduced when the required amount of molten lithium has been transferred to the molten aluminium in the holding furnace. The first conduit (12) and second conduit (14) may also form one conduit by taking a single conduit or tube and bending at least the end section to provide a curved conduit section that can be coupled to the third conduit (15). The curved section also facilitates a back flow of molten lithium when the over-pressure is reduced.

(8) The third conduit (15) can be connected to a separate additional pressurised inert gas delivery system (not shown) for fluxing of the molten aluminium. By opening a valve (not shown) this may provide additional inert gas to the inert gas flowing from through the conduit system from the vessel (10). By closing valve (25) after the transfer of molten lithium and some initial inert gas for cooling down of the conduit system, it may form the only source of purging gas to flux the molten aluminium.

(9) For alloying an about 6 tonnes aluminium alloy melt in the separate holding furnace about 50 kg to 200 kg of molten lithium needs to be transferred from the crucible or vessel in order to obtain the required AlLi alloy composition. Correspondingly the crucible or vessel requires an inner volume in the range of about 120 to 800 litres, preferably up to about 500 litres.

(10) The system further comprising a supply tank (43) of pressurised inert gas, the supply tank is interconnected to the chamber of the vessel through a gas delivery system (40) that includes a pressure regulator (42) and at least one valve (44) mounted on a supply tube (45) for the crucible. A pressure and/or temperature sensor (41) may also be provided. To bring molten lithium of a temperature of about 210 C. up by 20 mm an overpressure of about 1 mbar is required. In an industrial scale arrangement a working range for the overpressure would be in the range of about 20 to 200 mbar, and preferably in the range of about 40 to 80 mbar, e.g. 50 mbar.

(11) As mentioned above, in an embodiment one or more of the conduits are provided with thermal insulation material to avoid solidification of the molten lithium present in the conduit when being feed from the crucible to the molten aluminium in the holding furnace.

(12) As also mentioned above, in a further embodiment next to the thermal insulation material a heating assembly is disposed about parts of one or more of the conduits located outside the crucible to avoid solidification of the molten lithium present in the conduit when being feed from the crucible to the molten aluminium in the holding furnace. For example electrical resistance heating is annularly disposed about at least a part of the conduit located outside the crucible. For example, FIG. 2 shows a portion of second conduit (14) with thermal insulation (24) and coils (14) which may be an electrical resistance heater.

(13) Furthermore, the system may comprise different equipment (not shown) for the process, such as control cabinet for gas and associated valves in the system, a gas flow meter, for example, a rotameter, pipes and hoses, and an electricity supply. A pressure sensor (21) may be provided to measure pressure in the atmosphere of the chamber (13). A weight scale (37) may be provided to measure the weight of the crucible and thus weigh the lithium therein. Safety valves for a too high over-pressure can be provided. Also, a valve (25) may be provided on second conduit (14). Furthermore, one or more temperature measurement and control devices (23) can be provided for measuring the temperature of the molten lithium, and at least another temperature measurement and control device (33) to control the temperature of the heating device (27). In addition, control of the molten metal and gas transfer may be achieved by a controller (not shown) which may be equipped with a central processing unit (CPU), and content-addressable memory (for example, in the form of read-only memory (ROM) for storing a program which controls the operation of the overall apparatus and system, and a random-access memory (RAM) having a data storage area). The CPU is connected to an input/output interface (which may perform one or both of discrete and analog input and output), while additional signal-processing apparatus, such an an analog-to-digital (A/D) converter and one or more filter circuits. Such a controller may function as a digital signal processor, an application specific integrated circuit, a field programmable gate array, any suitable programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof.

(14) The heating device (27) may be any of the above mentioned heating devices. Moreover, the heating device (27) may be provided with thermal insulation (47).

(15) The methodology according to this invention is useful for producing lithium containing aluminium alloys having a Li-content in the range of at least about 0.2 wt. % Li, and preferably at least about 0.6 wt. %, and which may contain up to about 10 wt. % of Li, and preferably up to about 4 wt. %. In particular alloys of the 2XXX, 5XXX, 7XXX, and 8XXX-series families, such as, but not limited to, AA2050, AA2055, AA2060, AA2065, AA2076, AA2090, AA2091, AA2094, AA2095, AA2195, AA2196, AA2097, AA2197, AA2297, AA2397, AA2098, AA2198, AA2099, AA2199, AA8024, AA8090, AA8091, AA8093, and modifications thereof, can be produced. As will be appreciated herein, the aluminium alloy designations refer to the Aluminum Association designations in Aluminum Standards and Data and the Registration Records as published by the Aluminum Association in 2013 and are well known to the person skilled in the art.

(16) While various embodiments of the technology described herein have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the presently disclosed technology.