The present invention relates to a method as stated in the introductory part of claim 1, for removal of elements dissolved in metal melts. Particularly it relates to removal of dissolved metals, such as magnesium, from aluminium melts. Further it comprises a device for removal of such elements, as stated in the introductory part of claim 4.
On treating metals, the need for cleansing of a metal for another metal arises. This relates particularly to remelting of metals with impurities of one or more other metals. An example is at remelting of aluminium containing magnesium, Mg. To provide sufficient purity, the magnesium remnants in most cases should be removed. Currently, this is done by
1 Adding Cl2(g), which is reacting with Mg according to the equation: Mg+Cl2=MgCl2
2 By adding active salts reducing the Mg content.
Common to both methods is the development of MgCl2, which is a salt depositing on the melt surface together with Al2O3 slag, which is removed periodically. Such slag is transferred to melting works recovering aluminium, while the rest containing oxides, chlorides etc. normally is stored on land or is dumped at sea. This is undesirable for environmental reasons.
The main object of the invention is to provide a method and a device for removal of undesirable metals from metal melts, reducing said problems. It is particularly an object to provide a method and a device for remelting aluminium containing magnesium, in which Mg is removed during the melting treatment. It is an object to provide a device being advantageously built, operated and maintained.
The invention should be integrated in a device according to Norwegian patent specification 318848, with the general scheme of operation: In a hollow rotating body being immersed in a melt, an electrode conducting gas is arranged. Between the electrode and the melt a flame arch is burning, from which the heat energy is transferred directly to the melt.
In the following, the method according to the invention is stated in claim 1 and the device is correspondingly stated in claim 4. Further features of the invention are stated in the remaining claims.
The invention may for example be used for removing of magnesium from aluminium melts.
The magnesium vapour is mixed with further gas which is added in the rotor. The gas mixture is led through a vacuum exit to a condenser for depositing of liquid magnesium. The exhaust gas from the condenser is fed through a vacuum pump into the atmosphere. The emission is without CO2 gas. If the aluminium melt contains other alkalis they will evaporate correspondingly.
The invention is described in more detail in the following and with reference to the figures, wherein
The vacuum pump 29 is connected to a series of three condensers 27 being connected to the container 1 by a tube 5. In the container 1, a rotor 6 is provided, powered by a motor 7 over a drive belt 8 or similar, to a pulley 9 attached to a tubular shaft connected to the rotor 6. The motor is attached to a bracket 11. The bracket 11 can be attached to the container 1 or to a separate rack. The sealing between the rotor shaft 10 and the container 1 is provided by a sealant 12. The bracket 11 has a bearing 16 journaling the rotor shaft 10. Centrally in the shaft an electrode 13 is arranged, the upper end of which is connected to a cable with a cable shoe 14. The electrical current, which can be DC or AC, is transferred to the device through the cable shoe 14 and through an electrode connection 28 on the container 1.
The metal melt of the example is heated to a temperature between 800 and 1200° C., preferably ca. 1000° C. by the electrode 13 and 26.
The electrode 13 has a central bore for supplying gas from a connection 15 at the outer end of the electrode 13. The gas supplied through the electrode 13 is preferably argon or nitrogen or a mixture thereof. Other gases may also be utilized. The gas over an upper melt level 21 will comprise of a mixture of gas supplied to the rotor and gas emitted from the melt. The gases emitted from the melt are hydrogen and the vapour of magnesium, zinc, sodium etc. The gases over the melt level 21 are extracted through the tube 5 to the condensers 27, in which magnesium, zinc and sodium etc. are condensed to melts. The residual gas is fed through the vacuum pump 29 to the environment, possibly through a purification device.
Between the rotor shaft 10 and the electrode 13 a ring 16 is arranged for acting as a sealant and an electrical insulation. The ring 16 has a passage for gas and particles through a tube 17 connected to a powder supply 18. The reservoir 24 has a dividing wall 20 and a gatevalve 19 (the operation of which is not illustrated), to allow continuous handling of the melt, but the reservoir may also be a melting pot filled with melt. At the lower end of the rotor 6, multiple holes 25 are arranged between the circumference and the melt level 23. The level 23 of the melt in the rotor is governed by the gas pressure of the rotor 6.
The plant is started with the gate valve 19 closed and the reservoir 24 is filled to a certain level. When the vacuum is provided by the vacuum pump 29 through the condensers 27 and the tube 5, gas is provided simultaneously through the electrode 13 and/or the ring 16 to the rotor 6. The melt is brought to the level 21. The rotor 5 is operated and the voltage from a rectifier or transformer is applied. The current is led through the cable shoe 14 to the electrode and through the contact 28, alternatively through the rotor shaft 10 via a collector ring (not shown). A flame arch 22 is created between the electrode 13 and the top level of the melt 23. The rotation of the rotor 6 will pump the heated melt in the rotor through the holes 25 and mix it into the melt of the container. Simultaneously gas bubbles are created at the outlet of the holes 25. The gas bubbles, containing gases emitted from the melt, hydrogen and vapours of magnesium, zinc, sodium, etc. The gas bubbles are rising in the melt, through the upper level 21 and are released through the tube 5 and to the condensers 27, wherein magnesium, zinc and sodium etc. are condensed to melts which can be drained through the valve connection 30. The holes 25 of the rotor 6 can be circular or polygonal, and be arranged at the lover end of the rotor, being notches therein. When the melt has reached a desirable temperature, the valve 19 is opened and the metal may exit from the container 1 for further processing. The invention is not restricted to the example of
Number | Date | Country | Kind |
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2006 5893 | Dec 2006 | NO | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/NO07/00437 | 12/12/2007 | WO | 00 | 3/1/2010 |