Abstract:
In an electric arc furnace system for making steel, a method and structure (1) for eliminating teeming hang-ups and ensuring temperature homogeneity in a ladle which teems into an ingot mold by gas purging at all possible steps under both atmospheric and vacuum conditions, and (2) for preventing non-metallic inclusions from appearing in the final product by deflecting the granular material in the teeming ladle well block away from the ingot mold by a heat resistant but combustible deflector just prior to entry of the teeming stream into the ingot mold.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application is a continuation-in-part of application Ser. No. 13/134,027 filed May 27, 2011, the disclosure in said application being incorporated herein by reference. 
         [0002]    The invention disclosed in that application relates to electric arc furnace steel making systems and specifically to such systems having a ladle metallurgical furnace therein, which systems have the advantage of requiring decreased energy input per unit of steel produced compared to prior art systems. It is particularly directed to making alloy steel at a rate limited only by the maximum melting capacity of the arc furnace. In addition the invention, without modification, is adaptable to nearly every end use found in the steel industry today and particularly to producing unique, one of a kind heats of widely varying compositions in a randomized production sequence. 
         [0003]    For example, the invention disclosed therein makes possible the production of up to four different types of steel (as distinct from grades of steel) in a single electric arc furnace system without slowdown or delay in the processing sequence of heats regardless of the number or randomized order of the different types of steel to be made in a campaign. Thus the system will produce at least non-vacuum arc remelt steel, vacuum arc remelt steel, vacuum oxygen decarburized non-vacuum arc remelt steel and vacuum oxygen decarburized vacuum arc remelt steel as well as vacuum treated ladle metallurgical furnace steel. 
         [0004]    Now, although the process time from the charging of the electric furnace to teeming in the invention disclosed in said application is considerably shorter than the charge to teem time in conventional electric furnace steel making, the time between furnace tap to teeming is not necessarily commensurably shortened because of the added step of ladle furnace treatment; indeed, the time span may equal or even somewhat exceed the time span in conventional electric furnace steel making due to the dwell time in the ladle metallurgical furnace. Although the ladle metallurgical furnace has heat input capacity, that capacity is considerably less than the heat input capacity of the electric arc furnace. As a consequence, and particularly in connection with the larger heat sizes experienced in the system of the aforesaid application, teeming problems may arise due to the tendency of the molten steel in the teeming vessel to cool an undesirable amount in the bottom of the teeming vessel. This cooling can adversely affect the teeming stream, as by forming a semi-solid plug or glob in or above and adjacent to the teeming nozzle which can restrict the flow rate of the teem stream. 
         [0005]    It is therefore highly desirable that the steel in the region of the teeming nozzle be just as fluid as the steel in the balance of the teeming vessel so that blockage or restricted flow through the teeming nozzle may be avoided. 
         [0006]    A drawback to teeming systems that utilize granular material in the teeming nozzle of the teeming vessel is the possibility that at the moment the teeming stream begins the granular material may find its way into the molten metal receiving teeming receptacle and, eventually, into the final solidified product thereby causing serious cleanliness problems in the final product. 
         [0007]    Accordingly a need exists to ensure that the teeming stream from the teeming vessel is as fluid as it can be, even in heats of over 100 tons; that is, the temperature of the molten steel in the region of the teeming nozzle should be as close to the temperature of the steel in the regions above the teeming nozzle as possible so that a restricted flow from the teeming nozzle (sometimes referred to as a hang-up) is avoided. 
         [0008]    And as the cleanliness specifications of the final product become tightened it is more and more incumbent on the steel maker to ensure that no steel is rejected due to an undesirably high inclusion content attributable to the insulating granular material present in the teeming nozzle region, often referred to as the well block or well block region. 
         [0009]    It is accordingly an object of the invention disclosed herein to provide, in a system having a single arc furnace, a single metallurgical furnace and a single vacuum treatment station means for ensuring that teeming stream difficulties, such as hang-ups, do not arise due to a temperature differential between the molten steel adjacent the well block in a teeming ladle and regions of the steel remote from the well block. 
         [0010]    Another object of the invention is to decrease or eliminate the presence of undesirable inclusions in the final, solidified product attributable to the presence of granular material in the passage in the nozzle of the teeming vessel. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0011]    The invention is illustrated more or less diagrammatically in the accompanying drawing in which 
           [0012]      FIG. 16 , consisting of sub-parts  16 A through  16 J, inclusive, is a schematic view of the system of the invention showing particularly the means for eliminating teeming nozzle hang-up with certain parts indicated schematically or by legend for ensuring the temperature uniformity of a heat of steel being tapped into a teeming receiving receptacle, such as an insert; 
           [0013]      FIG. 17  is a partial cross-section of the teeming set-up just prior to the commencement of teeming with parts broken away for clarity; 
           [0014]      FIG. 18  is a cross-section of the teeming set-up with parts broken away for clarity showing the condition of the elements just after the slide gate has been activated to release the disposable granular blocking material in the teeming mechanism and the initiation of the teeming stream; 
           [0015]      FIG. 19  is a cross-section with parts broken away similar to  FIG. 18  showing the condition of the elements a moment after the disposable granular blocking material has been deflected away from the flow path of the teeming stream and a protective chamber formed around the teeming stream; 
           [0016]      FIG. 20  is a perspective view of the pouring shroud used to form a partial seal about the pouring stream; 
           [0017]      FIG. 21  is a top plan view of the pouring shroud; 
           [0018]      FIG. 22  is a bottom plan view of the pouring shroud; 
           [0019]      FIG. 23  is a side view of the pouring shroud; 
           [0020]      FIG. 24  is a vertical section through the pouring shroud taken along line  24 - 24  of  FIG. 20 ; and 
           [0021]      FIG. 25  is a perspective of the cone of  FIGS. 17 and 18 . 
       
    
    
       [0022]    Like numerals will be used to refer to like or similar parts from Figure to Figure of the drawing. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    The system and method for insuring that the molten metal at the teeming station is as fluid as it can be within the limitations of time and available equipment, and teeming problems thereby reduced or entirely eliminated, is indicated at  300  in  FIG. 16  which consists of sub-Figures  16 A through  16 J inclusive. In the description of the elements and processing steps in  FIG. 16 , a familiarity with the disclosure in application Ser. No. 13/134,027 will be assumed, although for the sake of clarity of description herein certain elements in said application may be referenced by reference numerals different from those used in said application. 
         [0024]      FIG. 16A  shows a tapping ladle, indicated generally at  301  (which is similar or functionally equivalent to tapping vessel  72  of said application), said tapping ladle  301  being shown in its condition just prior to being moved into tapping position from the electric arc furnace  309  which is the melting unit of the system. In its  FIG. 16A  position, a source of inert gas under pressure, preferably argon, is indicated at  303 , the source being connected by line  304  to a connection, not shown for purposes of clarity, to tapping cart  302 . It will be understood that the argon connection on the tapping cart will be connected to the ladle  301  in a manner now well known in the art, an example of which is shown in the right portion of  FIGS. 17-19 . 
         [0025]    Following connection of the argon source  303  to the ladle  301  the ladle is moved to the position of  FIG. 16B  where the electric arc furnace  309  is schematically shown to be tapping into the ladle  301 . 
         [0026]    In  FIG. 16C  the ladle  301  now containing a heat of molten steel has been moved back to the position of  FIG. 1A , and the argon connection between the tapping cart and the ladle  301 , and between the source of inert gas  303  and the ladle  301  have been disconnected in order for the ladle to be subsequently moved by crane. The inert gas was bubbled upwardly through the heat of molten metal in the tapping cart  302  during all, or substantially all, of the time of tapping to promote temperature uniformity in the ladle at the end of tapping. 
         [0027]    In  FIG. 16D , the tapping ladle  301 , hereafter sometimes referred to merely as “the ladle”, is lifted by crane  305  and placed on a ladle metallurgical furnace cart  306  preparatory to undergoing treatment in the ladle metallurgical furnace, sometimes hereinafter referred to as the LMF. 
         [0028]    In  FIG. 16E  an argon hose  308  has been connected from an argon supply associated with the LMF cart  306  and then an argon connection is made between the cart  306  and ladle. 
         [0029]    In  FIG. 16F  the LMF cart  306  carrying ladle  301  is moved under the LMF electrodes  307  which provide heat input to the heat during the LMF processing which usually includes make-up alloy additions. Just prior to initiation of the processing in the LMF the ladle  301  will have been connected to a source of inert gas by a hose indicated at  309  so that inert gas can be bubbled through the heat in the ladle as heat is added by the electrodes  307  to maintain temperature homogeneity in the heat during LMF treatment. 
         [0030]    At the conclusion of LMF treatment the ladle  301  is disconnected from the inert gas line  309  in preparation for movement of the ladle to the next processing station. 
         [0031]    In  FIG. 16G  the ladle  301  is shown being crane lifted into a vacuum tank  310  which has an inert gas line  311  connected to a source of inert gas  312 , preferably argon. 
         [0032]    Referring now to  FIG. 16H , after the ladle  301  is lowered completely into vacuum tank  310 , argon hoses  313  are connected to ladle  301 . 
         [0033]    In  FIG. 161  the ladle  301  has been shown lowered into the vacuum tank  310  with the inert gas hoses connected to the source  312  of inert gas. The heat in the ladle  301  is purged with the inert gas which enters the heat at a location remote from the surface while the ladle is subjected to vacuum on the order of a few mm of Hg, and, if desired, in some cases at 0.5 torr. 
         [0034]    After the vacuum purging process in tank  310  is completed, the inert gas hose connections to the ladle are disconnected and the ladle lifted by crane  305  and transferred to the teeming station shown in  FIG. 16J . 
         [0035]    A bottom pour ingot system is shown more or less diagrammatically in  FIG. 16J , the system including ingot molds  314  and  315  which are connected to a generally centrally placed pouring trumpet system, indicated generally at  316 , by runners  317  and  318  in mold stool  319 , by which the molds  317  and  318  will be filled from the bottom up. 
         [0036]    A pouring shroud is indicated generally at  321 , the shroud being connected to a source  322  of inert gas by hose  323 . 
         [0037]    The pouring shroud system  321  and the pouring trumpet system  316 , and their mode of operation, are shown to a larger scale in  FIGS. 17 through 25 . 
         [0038]    In  FIG. 17  the ladle  301  is shown to have one or, preferably, more, purging plugs  326  in its bottom indicated generally at  330 , the plug or plugs  326  being connected by inert gas line  327  to a source of inert gas under pressure shown at  328 . 
         [0039]    A well block is indicated generally at  329  and located, here, in the center of the bottom  330 . The well block is preferably composed of a high heat resistant refractory, such as alumina or magnesia. Its upper end  333  is substantially flush with the upper refractory surface  332  of the bottom  330 . As the bubbles of inert gas exit from the upper surface of the purging plug  326  they will expand several hundred times in volume due to the Boyle and Charles laws of gas expansion since the temperature of the molten metal will be very high, and, in the case of steel, approximately 3000° F. at this stage of the process. The movement of the gas bubbles generates a circulation of the molten metal which is indicated by the arrows  334 . This circulation continually moves molten metal across the upper refractory surface  332  of the bottom  330  and the flush or substantially, flush, upper surface  333  of the well block  329 . 
         [0040]    As a result of the continuous circulation set up by the purging gas, there will be identity, or near identity, of the temperature of the molten metal across the entire bottom of the ladle  301 , including the upper surface  333  of the well block  329 . Thus, since the temperature will be uniform and the molten metal in constant movement as long as the purging gas is admitted to ladle  301 , the tendency of the molten metal in the region of the well block to form a semi-solid or even slushy glob over the well block will be eliminated. As a consequence, when teeming begins no obstruction of the pouring passage  334  of the well block  329  will occur, and hence there will be no degradation of the teeming stream, which obstructions have been referred to by the steel industry as “hang ups”, and hence the ladle  301  will be emptied in the shortest possible time with the teemed steel being only minimally cooled. 
         [0041]      FIGS. 17 through 25  also disclose a means and method for insuring that undesirable inclusions will not appear in the final solidified product. 
         [0042]    Referring first to  FIG. 17  it will be seen that the center line of the pouring passage  334  is vertically aligned with the vertical center line of the vertical refractory tube  336  which is centered by sand  337  inside the upper end portion  338  of the pouring trumpet system  316 . However downward passage of the molten metal  339  through the pouring passage  334  is precluded by the slide gate system indicated generally at  340 . The slide gate system includes an upper stationary plate  341  having a teeming passage  346  and a lower, slidable plate  342  which is connected by bolts to a slide gate activator  343  which is shown in its closed position in  FIG. 17 . Slidable plate  342  has secured thereto by any suitable means a nozzle  344  having a central passage  345 . 
         [0043]    When the slide gate activator  343  is retracted leftward as viewed in  FIG. 17 , the slidable plate  342  will be moved to the left so as to align lower slide gate passage  345  with upper slide gate teeming passage  346  thereby allowing molten metal in ladle  301  to move from the ladle into the pouring trumpet system  316 . 
         [0044]    In the slide gate closed position of  FIG. 17  the pouring passages  334  and  346  are shown filled with a heavy granular material having a specific gravity greater than the specific gravity of the molten metal. Since the upper, open end of pouring passage  334  is no higher than, and preferably slightly below the upper refractory surface  332  of bottom  330 , the granular material will not be washed away from its illustrated position by the moving current of molten metal in ladle  301  represented by arrows  334  caused by the upward passage of the purging gas. 
         [0045]    The contours of the components of the purging shroud system indicated generally at  321  and the physical operation of the pouring shroud system can be seen best in  FIGS. 17 ,  18  and  19 . 
         [0046]    In  FIGS. 17 ,  18  and  19  a pouring shroud indicated generally at  350  in an inoperative condition is shown in  FIGS. 17 and 18 , and in an operative condition in  FIG. 19 . 
         [0047]    In  FIG. 17  in particular the pouring shroud  350  is shown connected to the lower slide  342  of the slide gate system  340  by wedging clamps  351 . A cone shaped cover  352  of high heat resistant but combustible material is shown in section in  FIG. 17  and in perspective in  FIG. 25 . Although many suitable materials may be used so long as they possess the quality of physical integrity up to around 500° F. and combustibility at temperatures above that number, an industrial cardboard material available under the trademark has been found to be quite satisfactory. The circular bottom of the cone  352  rests on the upper mating surface of the top section  328  of the pouring trumpet system  316 . The vertical axis of the cone  352  is aligned with the central vertical axes of the upper slide gate teeming passage  346  and the lower slide gate nozzle passage  345 . 
         [0048]    The moment the lower slide gate  342  is moved to the left as shown in  FIG. 18 , the two passages  345  and  346  will be aligned with one another, and the granular material  335  will drop downward toward the pouring trumpet system  316  and this condition, which is almost instantaneous, is shown in  FIG. 18 . The granular material will hit the cone  352  at or near its center and deflect radially outwardly to fall harmlessly to the bottom of the teeming pit; i.e.: it will not enter the upper end portion  338  of the pouring trumpet. However the heat of the granular material soon exceeds the combustion point of the cone  352  and the cone quickly disintegrates, the cone  352  having done its task of deflecting the granular material away from the vertical refractory tube  336  of the pouring trumpet system. The beginning  355  of the teeming stream immediately follows the removal of the granular material as shown in  FIG. 18 , and within a fraction of a second the teeming stream is in full flow condition  356  as seen in  FIG. 19 . By the time the full flow condition  356  of  FIG. 19  is established, the cover  352 , or, more accurately, the remnants thereof, will have disappeared from the system. 
         [0049]    The pouring shroud  350 , which is shown in its non-operative positions in  17  and  18  and in its operative condition in  FIG. 19 , is shown in detail in  FIGS. 20 through 24 . 
         [0050]    Referring first to  FIG. 20  it will be seen that the shroud  350  takes roughly the shape of an inverted bowl having a substantially flat section  357  with a flange  358  extending downwardly therefrom. The lower circular edge  359 , see  FIG. 22 , of the flange  358  extends around the outside periphery of the upper end portion of the top section  353  of the pouring trumpet as seen in  FIG. 19 . The central area of the shroud  350  has an upwardly extending neck area indicated at  361  which includes, at its upper end, in this instance, three radically outwardly extending locking lugs  362 ,  363  and  364 , see  FIG. 20 , which lugs are contoured to mate in supporting contact with inwardly extending locking flanges  365 ,  366  as best seen in  FIG. 18 . The upper flat edge  368  of the neck portion  361  receives a ring of high temperature heat resistant fibrous ceramic material indicated at  369 . The fibrous ring  369  is shown in its uncompressed state in  FIGS. 18 ,  20  and  24 , and in its compressed state in  FIG. 19 . The ring  369  rests on the flat upper circular surface  368  of the neck portion  361  of the shroud. 
         [0051]    A source a inert gas, such as argon, under a pressure greater than atmospheric pressure, is indicated at  378 , the source of gas being connected to the interior of the shroud by a gas line  373  shown best in  FIG. 19 . 
         [0052]    Slide gate actuator  343  consists of a piston  375  actuated by cylinder  376  which moves the lower slide gate  342  from its blocking position of  FIG. 17  to its open position of  FIG. 18 . 
         [0053]    The use and operation of the invention is as follows. The tapping ladle  301  is preferably pre-heated to a temperature on the order of about 2000° F. and then placed on the tapping ladle cart  302 . After placement on the tapping cart an argon line  304  from a source  303  is connected to the cart and then a similar line is connected from the cart to the ladle. 
         [0054]    The cart and the tapping ladle  301 , with the argon hoses connected, are then moved under the tapping sprout of the electric arc furnace  309 , see  FIG. 16B , which may contain anywhere from 75 to 115 tons of metal or more. The molten metal in the furnace is then tapped into ladle  301 . As the molten metal goes into the ladle  301  the argon gas source  303  is actuated and argon bubbles upwardly through the rising level of metal in the ladle during tapping. The bubbling action performs the dual function of causing good mixing of the molten metal with whatever additions have been added to the ladle prior to and/or during tapping, and promoting temperature uniformity throughout the tapped heat. 
         [0055]    Upon conclusion of tapping the now filled ladle  301  of molten metal is moved back to its starting position and the argon hoses from the argon source  303  disconnected from the cart carrying the ladle. 
         [0056]    Thereafter ladle is lifted off the tapping cart and placed on a ladle metallurgical furnace cart  306  as best seen in  FIG. 16D . 
         [0057]    One or more argon hoses  308  from the supply of argon at the LMF are then connected to the LMF cart, and then argon hoses are connected from the LMF cart to the ladle as shown in  FIG. 16E . 
         [0058]    Thereafter the LMF cart and ladle  301  are treated at the LMF station for a desired period of time during which chemical adjustments are usually made and heat is added from the LMF electrodes sufficient to ensure that the molten metal will be at a desired temperature during tap. The heat in ladle  301  is purged with argon gas during the dwell time in the LMF to ensure good mixing of the added alloys and to promote uniformity of temperature within the heat. 
         [0059]    After treatment in the LMF the purging gas is disconnected and the ladle  301  moved to a vacuum degassing station as indicated in  FIG. 16  G. 
         [0060]    Preferably, before the ladle  301  is lowered into the vacuum tank  310  at the vacuum treatment station, a source of inert gas  312  is connected by lines  313  to the ladle  301  as best seen in  FIG. 16H . 
         [0061]    Thereafter the ladle  301  is lowered into the vacuum tank which completely envelops it as shown in  FIG. 161 , and the heat purged by argon as the heat is subjected to absolute pressures on the order of about as low as 0.5 torr. 
         [0062]    Following treatment at the vacuum station the ladle is moved to the teeming station of  FIG. 16J  and the heat in the ladle purged with argon during teeming into the pouring trumpet system  316  as best seen in  FIG. 17 . 
         [0063]    The molten metal forming the teeming stream is further treated in a manner shown in greater detail in  FIGS. 17 through 25 . 
         [0064]    Prior to teeming, and with the slide gate system  340  in the closed position of  FIG. 17 , a fibrous refractory high temperature resistant ceramic cone  352  is placed on the upper end portion  353  of the pouring trumpet system  321 , the cone having the ability to withstand temperatures up to about 500° F. or somewhat higher before completely disintegrating. 
         [0065]    At this time the well block  329  is filled with a granular material having a specific gravity greater than the molten metal so that said material will not be swept out of the upper slide gate teeming passage  346  by the generally horizontal current set-up within the metal  339  by the upward passage of purge gas bubbles entering the metal  339  through one or more purging plugs  326 . 
         [0066]    At this time the pouring shroud  350  is merely suspended from the clamp member  351  on the lower portion of the slide gate  342 . In this condition the high heat resistant fibrous ring  369  of the pouring shroud system will be uncompressed as shown in  FIG. 17 . 
         [0067]    When the ladle  301  is carefully lowered as in  FIG. 19  the underside  367  of the shroud  350  will contact the upper edge of the top section  353  of the pouring trumpet and thereafter, by a slight further downward movement of the ladle  301 , said underside  367  of shroud  350  will make a partial sealing contact with the upper edge of the top portion  353  of the pouring trumpet. At the same time, the non-compressed condition of the fibrous ring  369  in  FIG. 17  will be compressed to the condition shown in  FIG. 19 . 
         [0068]    The cone  352  shown in  FIGS. 17 and 18  performs, during its very short operational life, the very important task of preventing undesirable particles from showing up as inclusions in the final solidified product. Thus, the moment the slide gate actuator  343  moves the lower plate  342  in the slide gate system  340  into alignment with the upper plate  341 , the granular material  335  begins falling through the upper slide gate teeming passage  346  which is in alignment with the lower slide gate teeming passage  345 . When the granular material hits the apex of the cone  352  it is immediately deflected radially outwardly and downwardly away from the vertical refractory tube  336  in the upper end portion  353  of the pouring trumpet, and thus the granular material will not enter the pouring trumpet/ingot mold portion of the system. The contact is very brief because the temperature of the molten metal is on the order of about 3000° F. and as a consequence the cone  25  will burn up quickly having completed its task of preventing the granular material from entering in the system. 
         [0069]    The molten metal will immediately follow the granular material as indicated at  355  in  FIG. 18 . As soon as the granular material  335  leaves the system the teeming stream  356  will flow freely into the pouring trumpet, see  FIG. 19 . 
         [0070]    As soon as the under surface  367  of the flat section  357  makes contact with the top surface of the top section  353  of the pouring trumpet and the ring  369  is compressed as seen in  FIG. 19 , a closed chamber, in effect, is formed around the pouring stream  356 , the pouring stream being isolated from the ambient atmosphere. It will be understood that since there is refractory to refractory contact between the vertical refractory tube  353  and the shroud  350 , an absolutely gas tight seal is seldom, if ever, attained. However the inert gas from the argon supply  328 , which is under a pressure greater than atmospheric, will displace the ambient atmosphere containing oxygen from the chamber formed around the teeming stream so that the teeming stream  356  will move through a non-oxidizing atmosphere. 
         [0071]    Although a preferred embodiment of the invention has been disclosed, it will be apparent that the scope of the invention is not confined to the foregoing description, but only by the scope of the hereafter appended claims when interpreted in light of the relevant prior art.