Patent Publication Number: US-2013233899-A1

Title: Discharge nozzle for installation inside the base of a metallurgical vessel

Description:
The invention relates to a discharge nozzle for installation inside or at the base (bottom) of a metallurgic vessel with an upper end, preferably for the connection to a metallurgic vessel or to a sliding valve of a metallurgic vessel, and a lower end, wherein a flow-through channel with at least one discharge opening at its lower end is arranged between the two ends, wherein the radially to the outside pointing wall of the flow-through channel is surrounded by a gas-proof casing (envelope). Furthermore, the invention relates to a technique for the operation of the bottom discharge nozzle. 
     Especially when steel is melted, the liquid metal is ultimately poured from a metallurgic vessel into a casting mould. Such a metallurgic vessel can especially be a casting ladle or a so called tundish (also called intermediate vessel). The liquid metal is poured from the ladle into the tundish and from the tundish into the casting mould of a strand casting apparatus. In doing so, it flows through a discharge nozzle which is located in the base of the ladle, or respectively in the base of the tundish. 
     The adherence of materials to the wall of the discharge nozzle, which accumulates while flowing through, is disadvantageous. Thereby the cross-section of the opening is reduced so that the stream properties and hence the quality of the steel are negatively affected, inter alia through turbulences. The accumulated material can break off and cause enclosures, which affect the quality of the steel. 
     In order to prevent the adherence of material to the wall, a noble gas like argon is often fed into the flow-through channel. Too large quantities of gas can also negatively affect the quality of the steel though, for example by the formation of hollow enclosures in the steel, which lead to damage on the surface when the steel is rolled out (milled). 
     A material for the discharge nozzle is described for example in WO 2004/035249 A1. A discharge nozzle within a metallurgic vessel is disclosed in KR 2003-0017154 A or in US 2003/0116893 A1. In the latter publication, the use of noble gases is displayed with the target of reducing the adherence of materials to the inner wall of the discharge nozzle (so called clogging), similar to the way as described in JP 2187239. A mechanism with a gas supply control is known relatively detailed from WO 01/56725 A1. According to the Japanese publication JP 8290250 nitrogen is supplied. JP 3193250 discloses a technique to monitor the adherence of materials with the aid of multiple temperature sensors which are arranged in series alongside the discharge nozzle. The supply of noble gas into the inner space of the discharge nozzle is further known from JP 2002210545, JP61206559, JP 58061954 and JP 7290422. 
     From some of these publications it is also known, additionally to the supply of noble gas, to prevent oxygen from entering by installing cases around a part of the discharge nozzle. To some extent, for example in JP 8290250, a noble gas high pressure is created inside such a casing. To prevent the entrance of oxygen a case around the sliding-gate of the discharge nozzle is disclosed in JP 11170033. According to the previously mentioned publications the flow of metal melt along the discharge nozzle is controlled by sliding-gates. These sliders glide perpendicular to the direction of flow of the metal melt and can hence close the discharge nozzle. Another method to regulate the flow is a so called stopper rod, for example as known from JP 2002143994. 
     The installation of an additional case around the valve of a discharge nozzle is described in the Korean publication KR 1020030054769 A. The gas that is within the case is extracted by suction via a vacuum pump. JP 4270042 describes a similar case. In this case a non-oxidising atmosphere is created within the case, as described in other aforementioned publications. The casing features an opening, through which the noble gas can be supplied. A further arrangement, wherein gas is extracted by suction from the casing that partially surrounds the discharge nozzle in order to create a vacuum inside the casing is known from JP 61003653. 
     Further discharge nozzles are for example known from DE 10 2004 057381. Here it is attempted to avoid the problem of adherence with the aid of a controlled noble gas supply or with the aid of an almost complete sealing of the whole coating-area of the discharge nozzle and the associated prevention of oxygen entering through the wall of the discharge nozzle into the steel melt. 
     The object of the present invention is to further improve the present technologies in order to minimize the adhesion of material inside the nozzle of a discharge device in a simple and reliable way without affecting the quality of the metal melt or the solidified metal respectively. 
     This task is solved by the characteristics of the independent claims. Preferred embodiments are disclosed in the sub-claims. 
     Surprisingly it has been found that good results for a discharge nozzle for the arrangement in the base (bottom) of a metallurgic vessel with an upper end, preferably for the connection to a metallurgic vessel or to a slide valve of a metallurgic vessel, and a lower end, wherein a flow-through channel with at least one discharge opening at its lower end is arranged between the two ends, wherein the radially to the outside pointing (fireproof) wall of the flow-through channel is surrounded by a gas-proof casing (envelope), can be achieved by the fact, that not only the circumference of the discharge nozzle, i.e. the radially to the outside pointing wall of the flow-through channel being surrounded by a gas-proof case, but by the fact that the casing of the discharge nozzles also encloses the lower end with the at least one discharge opening. The term gas-proof is not to be understood as absolute leakage-free, but rather that the entering of gas, especially atmospheric oxygen and nitrogen, is generally prevented or stopped respectively. 
     For an skilled person it is clearly understandable that the discharge nozzle, the sliding gate valve (or a stopper rod closure) and a further upper nozzle, which is surrounded by a case and arranged in the base of the metallurgic vessel above the sliding valve, are connected in a gas-tight manner and in this way represent a system of a completely sealed nozzle-arrangement. 
     A method according to the invention for the operation of a discharge nozzle, for example by using the discharge nozzle according to the invention as described above, is characterized by the fact that the discharge nozzle is arranged at a sliding gate (valve) or a stopper rod closure of a metallurgic vessel and that before the opening of the sliding gate or the stopper rod closure respectively either a vacuum is created or a noble gas flushing with a subsequent creation of a noble gas excess or high pressure taking place in the discharge nozzle and that the sliding gate valve or the stopper rod closure is opened afterwards. 
     For the noble gas, argon can preferably be used. In doing so, oxygen is at least partially removed from the discharge nozzle, so an oxygen deficit or low partial pressure of oxygen is created. The high pressure or rather the vacuum (low pressure) exists in the whole volume within the gas-proof case. The term “in the discharge nozzle” therefore means the space within the casing (envelope) or the outer-wall respectively and includes the internal volume and the pores of the whole discharge channel. 
     Before the entry of the steel melt, this low or high pressure also exists in the flow-through channel. At the entry of the steel melt into the discharge nozzle, or rather into its flow-through channel, after the opening of the slide valve or the stopper rod closure, the casing melts when it comes into contact with the steel melt in the area of the at least one discharge opening, so that the steel melt can flow into the vessel which is located underneath. After the opening, the discharge nozzle can be run either under a vacuum or under noble gases. 
     One type of discharge nozzle is the so called submerged entry nozzle, called SEN or SES (Submerged Entry Nozzle or Submerged Entry Shroud) among experts. With its lower end, it dips (penetrates) into the steel melt which is inside the subjacent metallurgic vessel, whereby the case (casing) melts when it comes into contact with the liquid steel, so that a free flow-through is possible. 
     It is advantageous that the case features multiple case parts that are connected with each other in a gas-proof manner and preferably arranged above each other. The case is preferably made of metal, like steel, so that it is resistant enough but also melts when it comes into contact with the steel melt. The metal of the case is depending on its purpose chosen in such a way that it melts by the metal inside the melt-receiving container. 
     It can also be advantageous that the case features a lower case part made of steel which surrounds at least the lower end with the at least one discharge opening in a gas-proof manner and that above that a gas-proof case part, designed as an integral part of the wall, being arranged, so that the discharge opening is enclosed by a kind of cap, while the circumferential wall of the discharge nozzle arranged above features a gas-proof layer, especially surface, which—according to the invention—is considered as part of the case. 
     It can also be advantageous that the case features a lower case part made of steel which is implemented in a gas-proof manner into the lower end with the at least one discharge opening and that a gas-proof case part designed as an integral part of the wall is arranged above, so that the discharge opening is closed by a kind of plug, whereby the outer circumference of the discharge nozzle, including the plug, features a gas-proof layer, especially surface, which, including the plug, may be considered—in accordance with the invention—as part of the casing. 
     Furthermore it can be advantageous to install a layer of a dividing (separating) material, like a paper coating, which is known to the skilled person, in order to prevent the adhesion of slag or scoria, which are typically present at the surface of the area of the metallic case which is to be dipped into, in order to accelerate the melting of this casing. 
     It is appropriate to arrange a getter material within the casing, preferably selected from at least one metal of the group comprising silicon, calcium, titanium, aluminium, magnesium or zirconium. By this remaining free oxygen in the casing can be bound. 
     The fireproof (refractory) material of the wall can feature a low porosity of 2 to 13%, preferably smaller than 10%. Such material, for example carbon impregnated alumina-graphite-material, can—in terms of the invention—create a sufficient impermeability (sealing). Standard fireproof material has a porosity of more than 16%. 
     It is furthermore advantageous that a heating is arranged inside the wall of the flow-through channel in order to be able to pre-heat the discharge nozzle before use in order to prevent or minimise temperature shocks. 
     Preferably, a layer of a dividing (separating) material, like paper, is arranged around the outer surface of the discharge nozzle. Furthermore is can be advantageous that the outer surface of the wall is surrounded by an insulating cement seal at its upper end, below the gas-proof case, whereby the cement seal preferably contains a castable heat-proof cement, preferably with at least one of the group alumina (Al2O3), aluminium-silicate, magnesia (MgO). Furthermore it is preferred that the outer circumference of the wall is surrounded by an isolating material at its lower end, below (under) the gas-proof case, especially a ceramic paper or a woven fabric of ceramic fibres. The insulating material can be arranged directly below (underneath) the cement seal. 
     It is also preferred that gas channels are arranged in the lengthwise direction of the nozzle, underneath the gas-proof casing, especially between the gas-proof casing and the wall. 
     A sliding gate valve, according to the invention, for use with a discharge nozzle and especially for use with a discharge nozzle as defined above, which comprises an outer gas-proof case, is characterized by the fact that the gas-proof case includes at least one gas inlet and at least one gas outlet. The at least one gas inlet can be used to pump noble gases like argon into the case and the at least one gas outlet can be used to create a vacuum within the case. 
     A method is advantageous whereby after the opening of the slide valve or the stopper rod closure respectively
         a) a noble gas high pressure is created if a low pressure (negative pressure) was present before said opening or   b) a low pressure is created if a high pressure (excess pressure) was present before said opening.       

     It is especially advantageous that the low pressure is 1 to 1013 mbar, especially 150 to 1013 mbar, and the high pressure is 1013 to 1500 mbar or more, i.e. high pressure being above atmospheric pressure. 
     Especially at a discharge nozzle of a casting ladle a vacuum (low pressure) can be created first and later, after the opening, a noble gas high pressure. At the discharge of a tundish it is advantageous to create a noble gas high pressure first and a vacuum after the opening. 
    
    
     
       In the following, the invention is explained in an exemplified manner with the aid of a drawing. In the drawing 
         FIG. 1  shows a discharge nozzle for a tundish 
         FIG. 2  shows a further discharge nozzle for a tundish 
         FIG. 3  shows a third variation of a discharge nozzle for a tundish 
         FIG. 4  shows a discharge nozzle for a casting ladle 
         FIG. 5  shows a further discharge nozzle for a casting ladle 
         FIG. 6  shows the arrangement of a discharge nozzle at a tundish and 
         FIG. 7  shows the arrangement of a discharge nozzle at a casting ladle. 
     
    
    
     The discharge nozzle displayed in  FIG. 1  features a flow-through channel  1  with multiple lateral discharge openings  2 . The wall  3  of the flow-through channel  1  is generally made out of a mixture of alumina and graphite. At its upper end a mounting sleeve  4  is arranged for the alignment to a sliding gate valve, which represents the main part of the completely sealed system. The outer circumference of the wall  3  is surrounded by an insulating cement seal  5  at its upper end; below an insulating material  6 , for example a ceramic paper or a fibre mat of ceramic fibres being arranged. On top of the cement seal  5  and the isolating material  6  a gas-proof case  7  is arranged. This encloses the whole discharge nozzle up to the mounting sleeve  4  and solely provides one opening  8  for feeding in a noble gas (Argon). The noble gas can be fed into a gap between the gas-proof case  7  and the insulating material  6  for the flushing action. A so called scoria belt (scoria layer)  9  made of zirconium-graphite is arranged above the discharge openings  2 . The discharge openings  2  are closed by the case  7 . 
     A similar discharge nozzle is displayed in  FIG. 2 . It features a cap  10 , for example made out of steel, at its lower end, which closes (encloses) the discharge openings  2 . At least the outer surface of the wall  3  is gas-proof at least above said cap  10 , thus forming a gas-proof part of the case. Along the outer surface of the cap  10  a layer of a separating material  10 ′, like for example paper, is arranged. This dividing layer  10 ′ can also cover the whole outer surface of the discharge nozzle. 
       FIG. 3  shows a similar arrangement to  FIG. 1 , whereby a circumferential slit  27  within the wall  3  is connected to the opening  8 . By this means Argon can be fed into the wall and an Argon high pressure can be achieved. 
     The discharge nozzle for a casting ladle ( FIG. 4 ) is, in principle, designed in a similar way, however it features a persistently straight flow-through channel  1 ′ and a discharge opening  2 ′ which is located centrically at the lower end. A similar arrangement is displayed in  FIG. 5 , wherein the discharge opening  2 ′ is closed by a gas-proof plug  28  and wherein at least the outer surface of the wall  3  is designed in a gas-proof manner. The plug  28  can be melted, burned or dissolved by the influence of the metal melt in the metallurgic vessel in order to clear the discharge opening  2 ′. It can for example consist of a metal like steel, stainless steel or copper. 
     In  FIG. 6  the arrangement of a discharge nozzle as a lower nozzle  11  at a tundish  12  is displayed. The tundish  12  features a multi-layered lining  13 , which protects the tundish wall  14 . An upper nozzle  15  in which electrodes  16  are embedded and which outer periphery  29  being gas-proof is arranged in the base of the tundish  12 . At the upper end the upper nozzle  15  is surrounded by a well nozzle  17  for its protection. At the lower face of the upper nozzle  15 , below the base of the tundish  12 , a sliding gate valve  18  is arranged, surrounded by a gas-proof slider-case  19 , which is connected in a gas proof manner at its upper end with the outside  29  of the upper nozzle  15  and with the gas-proof case  7  at its lower end. Inside the slider-case  19  an inlet  20  for noble gas and a connection  21  for a vacuum pump are provided. 
       FIG. 7  shows the arrangement of a discharge nozzle at a casting ladle  22  as well as the tundish  12  which is arranged underneath. The tundish comprises, besides its outlet opening  23 , so called impact pads  24  which are supposed to calm the steel melt mechanically, so to prevent turbulences that are too large. At the casting ladle opening (sliding valve)  25 , the discharge nozzle displayed in  FIG. 4  is arranged. The inlet for noble gas as well as the connection for a vacuum pump are, for reasons of simplicity, not displayed in  FIG. 7 . It is obvious for the skilled person that the general structural arrangement of the described components of the invention to pass the metal melt from the casting ladle into the tundish and from there into the casting mould is very similar and features a common design and function. The casting ladle  22  itself features a multilayered lining  26  along its inside. 
     Before the casting process starts, the sliding valve  25  is closed and a vacuum is created in the flow-through channel  1 ′,  FIG. 4 , of a casting ladle in order to remove any oxygen. Thereby a vacuum is also created in the flow-through channel  1 ′, in the wall of the discharge nozzle, so between the inside wall surrounding the flow-through channel  1 ′ and the outer case as well as inside the sliding valve  25  a low pressure (vacuum) is created. Upon flowing in of the steel melt into the flow-through channel  1 ′ the gas-proof case  7  melts in the area of the discharge opening  2 ′ when it comes into contact with the steel melt, so that the steel melt can flow into the subjacent container (tundish  12 ). The low pressure was, in an example, regulated within the area of 700 to 800 mbar, and the subsequent high pressure was adjusted to a maximum of 1500 mbar. 
     At the discharge of the tundish, a discharge nozzle is also located. Initially a high pressure with an argon pressure of a maximum of 1500 mbar is created inside said nozzle. At the flowing in of the steel melt into the flow-through channel  1 , the gas tight casing  7  melts in the area of the discharge opening  2 , so that the steel melt can flow into the subjacent vessel. The gas is pumped off the discharge nozzle, so that a vacuum is created.