A METHOD AND ARRANGEMENT FOR PURGING MOLTEN METAL IN A CONTAINER WITH THE AID OF A GAS

Abstract: In the purging and agitation of molten metal carried in a ladle by injecting a pressurized gas into the molten metal through the intermediary of a nozzle mounted on the wall or on the bottom of the container, there is proposed a method for clearing the nozzle of blockages that are caused by molten metal being drawn into the nozzle-throughtflow passage immediately the flow of pressurized gas is cut-off, and freezing on the walls of the nozzle to form a blockage. The inventive method is characterized by passing an electric current through at least part of the nozzle at the same as the supply of pressurized gas is switched on, such as to heat and therewith at least partially melt the metal blockage in the throughflow passage of the nozzle, this at least partially melted metal blockage being forced from the passage by the pressurized gas flowing therethrough.

Description: A Method and Arrangement for Purging Molten Metal in a Container with the aid of a Gas. The present invention is concerned with the delivery of ^ 5 a pressurized gas to a molten metal bath contained in a container, for the purpose of purging and/or agitating the molten metal, in accordance with the preamble of Claim 1, and relates to a method of clearing the throughflow passage of a gas-delivery nozzle from the 10 solid metal blockages that are liable to occur when the delivery of gas to the melt is stopped. The invention also relates to an arrangement according to the preamble of Claim 2 for carrying out the inventive method. 15 Ladles are used to transport and to treat molten metals in the steel, metal and ferroalloying industries. In order to the agitate and refine, or purge, the melt an inert gas, such as argon, is injected into the melt through the bottom of the ladle. Hitherto, this gas has 20 been supplied through the intermediary of so-called purging stones or porous plugs, such plugs either con¬ sisting of a ceramic porous body or a ceramic body which contains many very fine channels. The pores or channels are so disposed in the plugs that while gas is able to 25 pass through, the molten material is unable to penetrate the pores or channels. Such porous plugs are encumbered with several drawbacks. For example, it can be difficult to cause the plugs to 30 allow gas to pass therethrough while preventing molten metal or slag from entering the pores or channels and freezing on the walls thereof, so as to cause blockages. $ Furthermore, porous plugs place a limit on the gas- pressures that can be used, which in turn places a limit 35 on the volume of gas that can be injected into the melt. Because of the success obtained with the use of nozzles or like devices in converters, it has been desirable to use nozzles for the purpose of injecting purging gas into molten metal contained in ladles, instead of the aforesaid porous plugs. When attempting to replace porous plugs with nozzles, it was found that immediately the supply of purging gas was interrupted or terminated, molten metal was drawn into the nozzle and froze onto the walls of the gas-throughflow passage, therewith causing a blockage. Attempts to remove this frozen metal plug have generally failed, meaning that the gas was unable to flow through the nozzle. As a result of this problem, the use of nozzles in ladles for the aforesaid purpose has not been pursued. It should be mentioned that this problem does not occur in converters, because a converter can be tipped sideways when purging is not in progress, so that the nozzle opening or nozzle ori¬ fice is located above the surface of the metal bath. The object of the present invention is to eliminate the aforesaid problems encountered with the use of nozzles for injecting gases into ladles, so as to enable the porous plugs used hitherto to be replaced with nozzles. This object is achieved with the inventive method and the inventive arrangement, which have the characteristic features set forth in the characterizing clauses of respective method and apparatus claims. The invention will now be described in more detail with reference to two exemplifying embodiments of an inven¬ tive nozzle arrangement. The inventive nozzle may, for example, be mounted on the bottom of a molten metal container, such as a ladle, converter or the like. The nozzle is connected to a container which contains gas under high pressure, through the intermediary of a valve which functions to « control the gas flow and gas pressure. * 5 According to a first embodiment of the invention the nozzle, or a part of the nozzle, is comprised of an electrically conductive material of such electrical resistance as to generate heat when an electric current is passed therethrough. 10 According to a second embodiment the nozzle includes a heating wire which is connected to a source of electric current and which is wound around the nozzle tube or around the region of the gas throughflow passage, said 15 tube preferably being made of a ceramic material. Pro¬ vided on the bottom end of the nozzle is a screw-thread¬ ed tube for connection with a quick-coupling between the nozzle and the conduit or pipe leading to the gas-flow control valve. The nozzle is surrounded by a body of 20 ceramic material. When injecting gas into the bath of molten metal, the valve of the gas container is opened to allow gas to pass from the container while, at the same time causing an electric current to be applied to the nozzle, such as to heat at the nozzle and therewith 25 melt, or partially melt, the frozen metal plug in the nozzle tube or nozzle throughflow-passage. This molten, or semi-molten metal, will then be blown from the nozzle tube and into the metal bath by the pressurized gas entering the nozzle tube, and therewith 30 enable the gas to pass freely through the nozzle. Agita¬ tion and refinement of the molten metal can now take place. The cross-sectional area of the nozzle tube 2 orifice is suitably from 0.2 to 15mm , preferably from 2 1.0 to 5.0 mm . When the nozzle is clear, i.e. un- 35 blocked, the gas pressure will suitably lie in a range of from 5 to 250 bars, preferably from 10 to 50 bars. It will be understand from the aforegoing that when using nozzles to deliver a purging gas to molten metal contained in a ladle, the nozzle will become blocked by the molten metal which is drawn into the nozzle immedi- ately the supply of gas is cut-off, by closing the gas- flow control valve, this molten metal freezing on the nozzle walls and forming a solid plug. In accordance with the invention, when the valve is opened to allow pressurized gas to flow from the gas container an elec- trie current is, at the same time, supplied to the nozzle, which subsequently becomes hot enough to melt or at least partially melt the plug. The force of the gas entering the nozzle is then suffi¬ cient to push the plug from the nozzle and into the molten metal bath. The gas pressure and gas flow can then be adjusted to values appropriate to gas-purging purposes and also to the geometry of the container, i.e. the ladle or converter. The arrangement also includes a monitoring means which monitors the state of gas throughflow and which func¬ tions to switch off the supply of electric current to the nozzle when gas flows freely therethrough

Claims: C L A I S 1. In the injection of pressurized gas into a molten metal bath contained in a container through the interme¬ diary of a gas-delivery nozzle, for the purpose of agitating and purging the molten metal, said nozzle being mounted on the wall or on the bottom of said container, a method for clearing said nozzle of block¬ ages that are caused by molten metal being drawn into the nozzle-throughflow passage immediately the flow of pressurized gas is cut-off and freezing on the walls of said nozzle to form a blockage, c h a r a c¬ t e r i z e d by heating the nozzle with the aid of an electric current to a temperature at which the metal blockage will at least partially melt and therewith be removed from the nozzle throughflow passage by the gas which then passes through said nozzle. 2. An arrangement for carrying out the method accord¬ ing to Claim 1, comprising a container for gas under high pressure, a molten metal container, a nozzle, and a valve which is incorporated in a conduit extending between the nozzle and the gas container, c h a r a c¬ t e r i z e d in that the nozzle is connected to a source of electric current; and in that when current is applied to the nozzle the arrangement is such as to at least partially melt any metal that may have solidified in the nozzle throughflow passage. 3. An arrangement according to Claim 2, c h a r a c - t e r i z e d in that at least a part of the nozzle is comprised of an electrically conductive material of a kind which will be heated by the current passing there¬ through. 4. An arrangement according to Claim 2 or Claim 3, c h a r a c t e r i z e d in that the nozzle carries an electric heating wire, 5. An arrangement according to Claim 4, c h a r a c¬ t e r i z e d in that the heating wire is wound around the through-flow passage of the nozzle. 6. An arrangement according to any one of the preced¬ ing Claims, c h a r a c t e r i z e d by means for switching off the supply of electric current when the gas flows freely through the nozzle.

Inventors: FALK THOMAS, FALK, THOMAS
Applicants: STIFTELSEN METALLURG FORSK, MEFOS STIFTELSEN FOER METALLURGISK FORSKNING
Application year: 1992
Main classification: C22B9
IPC codes: B22D1, F27D3