Abstract:
The invention relates to a device ( 8 ) which is used to inject a treatment gas into a molten metal contained in a tank ( 1 ) and which is designed to be fixed in one of the walls of said tank. The inventive device comprises at least one injection nozzle ( 18 ) which is equipped with an end hole ( 19 ). Said device is characterised in that it comprises a mobile means ( 14 ) which can be manoeuvred from outside of the injection device and which is used to unblock the aforementioned end hole of the nozzle.

Description:
This application is a filing under 35 USC 371 of PCT/FR2003/002591, filed Aug. 27, 2003. 
     BACKGROUND OF THE INVENTION 
     This invention relates firstly to a device for injecting a treatment gas into a molten metal contained in a tank, and secondly a tank used in metallurgy and comprising at least one such injection device. 
     It is known how to treat a molten metal flow before casting it in the form of a metallurgical product, the molten metal possibly consisting particularly of aluminium, an aluminium alloy, magnesium or a magnesium alloy. The molten metal treatment is generally aimed at eliminating dissolved gases, particularly hydrogen, and also dissolved impurities such as alkaline metals, and solid or liquid inclusions that could reduce the quality of cast products. 
     Conventionally, this treatment step is done by injecting a treatment gas within the molten metal contained in a tank. The treatment gas may consist of an inert gas insoluble in the molten metal such as argon, or a reactive gas such as chlorine, or a mix of these gases. 
     The inert and insoluble gas absorbs the dissolved gas by a dilution effect and transports it with it. The reactive gas reacts with some dissolved impurities and thus generates liquid or solid inclusions that, like those already present in the molten metal, can be eliminated by a filtration operation. 
     U.S. Pat. No. 5,846,479 describes an in line treatment tank for a molten metal flow comprising several nozzles fixed in one wall of the tank. Part of each nozzle is located outside the tank and another part of the nozzle comprises an end hole housed inside the tank. However, this end hole has a very small diameter that can get blocked by the molten metal and metal oxides. 
     This hole can be cleaned after stopping the installation and opening the tank, from inside the tank. However, this is a laborious operation that causes loss of time and interrupts the treatment process. 
     SUMMARY OF THE INVENTION 
     The purpose of the invention is to provide a device for removing obstruction in the hole of each nozzle during operation of the installation. 
     Consequently, the invention relates to a device for injection of a treatment gas into a molten metal contained in a tank, the said device being designed to be fixed in one of the tank walls and comprising at least one injection nozzle provided with an end hole, characterized in that it comprises a mobile means that can be manoeuvred from outside the injection device and that can unblock the said nozzle end hole. 
     Thus, regardless of whether the treatment gas used is an inert gas or a reactive gas, it is then possible to continue the molten metal treatment process without deteriorating the treatment quality by perforating and/or pushing through the deposits blocking the end hole of the nozzle using mobile means manoeuvred from outside the tank. 
     The said mobile means is advantageously capable of passing through the end hole, which makes it easy to remove the obstruction from this hole. 
     According to one preferred embodiment, the mobile means comprises a rod installed free to slide inside the nozzle, the said rod being capable of passing from a rest position in which it is set back from the end hole of the nozzle so as to enable passage of the treatment gas, to an advanced position in which it may unblock the end hole. 
     According to a first variant embodiment, the rod comprises an upstream part that is firstly capable of passing through one end of the nozzle opposite the end hole, while maintaining leak tightness, and secondly is equipped with a manual control device. This manual control device advantageously comprises a handle. 
     Advantageously, the device comprises an elastic element, typically a spring, which holds the rod in the rest position. 
     According to a second variant embodiment, an automated control device is attached to the rod. This control device may for example be made using an operating element acting on the sliding of the rod, such as a pneumatic, electric or electromechanic element. These automated devices may be controlled by an operator or a programmable system. If there are several injection devices, it is then advantageous to combine one or several operating elements, so as to make the different rods slide. 
     The nozzle preferably contains at least one rod guidance means. This may be composed of a ring presenting a central hole and peripheral holes. The rod then slides through the central hole of the ring and the injected gas passes through the peripheral holes. 
     Advantageously, the cross section or diameter of the rod decreases along the direction of the end hole of the nozzle. 
     This invention also relates to a molten metal treatment tank such as a treatment tank for a molten metal flow (called the “inline treatment tank”), characterised in that it comprises at least one gas injection device according to the invention. In the case in which such a tank comprises several injection devices, it is then advantageous to activate these devices with a time offset using an automated control device. For example, this can be done using a camshaft in which the cams are fixed at an angular offset. 
     The invention also relates to the use of the molten metal treatment tank defined above. The molten metal may be aluminium, an aluminium alloy, magnesium or a magnesium alloy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood after reading the detailed description given below with reference to the attached figures. 
         FIG. 1  is a cross sectional view of a tank comprising several injection devices according to the invention. 
         FIG. 2  shows a partial sectional view of the tank according to line II-II in  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a tank  1  according to an advantageous embodiment of the invention. This tank  1  comprises a sidewall  2  and a bottom  3  to define a treatment compartment  4 , a cover  5 , and molten metal inlet means  6  and outlet means  7 , and devices  8  for injection of a treatment gas according to the invention. 
     The injection device  8 , or each injection device  8  is typically fixed in the sidewall  2  of the tank  1  that is composed of an assembly of layers  9  to  11 , the outer layer  9  being made from metal (and usually called the “box”) and the other layers  10  and  11  being made from refractory materials. The function of the layer  10  that may be formed from several superposed layers, is usually to thermally insulate the tank. The layer  11  is more specifically designed to resist the molten metal. 
       FIG. 2  more specifically illustrates an advantageous embodiment of one of the injection devices  8 . 
     In this embodiment, the injection device  8  comprises a metallic rod  14  capable of sliding in an approximately tubular housing, which can be used for inlet of treatment gas within the treatment compartment  4  of the tank  1 . 
     More precisely, the injection device  8  is broken down firstly into an upstream part  15  located outside the tank  1 , this upstream part  15  being fixed at one of its ends in a hollow connection element  16  that communicates freely with a treatment gas reservoir (not shown), and secondly a downstream part  17  comprising a nozzle  18  fixed in the connection element  16 . The nozzle  18  has an end hole  19  located inside the treatment compartment  4  of the tank  1 . 
     The rod  14  has a first end located outside the tank  1  and the injection device  8  to which a handle  20  is connected, and a second end housed in the tank  1 . Apart from an annular shoulder  21  fixed to the rod  14  adjacent to its first end, the rod  14  has a diameter that typically decreases non-uniformly towards its second end. A spring  22  inserted through the second end of the rod  14  is placed around the rod and has a diameter slightly smaller than the diameter of the shoulder  21 . 
     The upstream part  15  is made from an approximately tubular body  24  with an upstream end, a central channel and a downstream end. The diameter of the central channel at the upstream end is approximately equal to the diameter of the projection  21  from the rod  14 . A first seal  25  is fixed in the body  24  and is designed to cooperate with the shoulder  21  when the rod  14  is inserted in the central channel. The central channel has an inner shoulder  26  at the downstream end, with a diameter equal to approximately the diameter of the rod  14 . A second seal  27  is fixed in this shoulder  26 . The sealing means  25 ,  27  are particularly advantageous when the treatment gas is reactive. 
     After inserting the rod  14 , the spring  22  which is not stressed, is in contact with the shoulder  21  and the inner shoulder  26 . A nut  28  with a central hole with a diameter equal to approximately the diameter of the rod  14 , and therefore less than the diameter of the shoulder  21 , is screwed around the upstream end of the body  24  so as to prevent accidental extraction of the rod  14 . 
     The connection element  16  is provided with a central channel in which the rod  14  can slide and a peripheral recess in which a duct  29  coming from the treatment gas reservoir can be inserted. 
     In the embodiment shown on the drawing, the nozzle  18  of the downstream part  17  is made more particularly from a metallic tube  30 , firstly with a first end fixed in the downstream end of the connection element  16 , and secondly a second end that clamps an approximately tubular metallic body  31 . 
     This body  31  has a chamfered end that bears in contact with the upstream end, made in the form of a chamfered outer shoulder  33 , a nozzle  34  made of a refractory material that also has a downstream end terminating in the end hole  19 . This nozzle  34  is stabilised using a nut  35  screwed into the body  31  and with a central hole with diameter equal to approximately the diameter of the said nozzle  34 . The second end of the nozzle  18  is finally inserted into a body  37  made of a refractory material that has a conical recess and that is fixed in the layer  11  of the sidewall  2  of the tank  1 . At rest, the second end of the rod  14  is then fixed set back from the end hole  19  of the nozzle  34 . 
     The injection device  8  is fixed in place using a support made from two metallic rods  38 ,  39  each of which has one end fixed to a notch in the metallic layer  9  of the sidewall  2  of the tank  1 . A plate  40  comprising a central perforation and two peripheral perforations is slipped and then fixed along the two rods  38 ,  39 . The injection device  8  is firstly slipped through the central perforation of the plate  40 , and then fixed when it is correctly positioned. 
     The treatment gas used may consist equally well of an inert and insoluble gas such as argon, or a reactive gas such as chlorine, or a mix of these gases. 
     During operation, this treatment gas is inserted into the connection element  16  and is brought through the downstream part  17  of the injection device  8 . It is finally ejected through the end hole  19  of the nozzle  34  into the treatment compartment  4  containing the molten metal. 
     When a manipulator wants to move impurities that have started to block the end hole  19  of the nozzle  34 , he picks up the handle  20  and slides the rod  14 . Under the effect of this translation, the second end of the rod  14  then passes through the end hole  19  and therefore perforates and/or pushes the residual deposits through, if any. When the manipulator releases the handle  20 , the spring  22  relaxes between the shoulder  21  and the inner shoulder  26 , and the rod  14  thus returns to its rest position. 
     Note that rod  14 , instead of being manually controlled by the handle  20 , may be activated by an automated control device (pneumatic, electromechanic or other), which avoids operator actions. One advantage then lies in the fact that this automated control device can be adjusted so that the different injection devices  8  are activated with a time shift. 
     A molten metal  41  may be treated using a process typically comprising:
         installation of a treatment tank  1  provided with at least one injection device  8  according to the invention,   circulation of the molten metal  41  so as to form a determined flow of the said metal inside the tank,   injection of a treatment gas using the injection device(s)  8 ,   possibly, activation of means  14  to clear the end hole  19  of the nozzle  18 , or each nozzle  18 .       

     The operation to put the treatment tank into place in line typically includes the connection of the treatment tank to at least one molten metal supply duct  12  and at least one molten metal evacuation duct  13 . 
     Although the invention has been described with relation to particular example embodiments, it is obvious that it is in no way limited and that it comprises all technical equivalents of the means described and combinations of them if they are covered by the scope of the invention. 
     LIST OF REFERENCE NUMERALS 
       1  Treatment tank 
       2  Tank sidewall 
       3  Tank bottom 
       4  Treatment compartment 
       5  Cover 
       6  Molten metal inlet means 
       7  Molten metal outlet means 
       8  Injection device 
       9  Outer layer 
       10  Refractory layer 
       11  Refractory layer 
       12  Supply duct 
       13  Evacuation duct 
       14  Rod 
       15  Upstream part of injection device 
       16  Connection element 
       17  Downstream part of injection device 
       18  Nozzle 
       19  End hole 
       20  Manual control device 
       21  Shoulder 
       22  Elastic element 
       24  Tubular body 
       25  Seal 
       26  Inner shoulder 
       27  Seal 
       28  Nut 
       29  Duct 
       30  Metallic tube 
       31  Metallic body 
       33  Outer shoulder 
       34  Nozzle 
       35  Nut 
       37  Refractory material body 
       38  Metallic rod 
       39  Metallic rod 
       40  Plate 
       41  Molten metal