Abstract:
The invention provides an apparatus for the continuous casting of metal sheets and bands, including two rotatable roll-crystallizers having parallel axes located in the horizontal plane and defining between them a gap of adjustable width, and means for supplying metal melt to fill the gap; characterized by means for generating at least three substantially horizontal magnetic fields producing electromagnetic pressures adapted to act to contain at least one end face of the melt within the gap.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to the casting of metal sheets and bands, and more particularly, to the continuous vertical casting of sheets between rotating roll-crystallizers.  
         BACKGROUND OF THE INVENTION  
         [0002]    The production of thin sheets from various metals and alloys, using traditional methods, is one of the most power-consuming technological processes in ferrous and non-ferrous metallurgy. Striving to reduce the high costs of such sheets, metallurgists reverted to the idea proposed by Bessemer as early as 1847. However, the application of this idea to high-temperature melts has become possible only during the last 30 years, after it was proposed to use electromagnetic methods for a sidewall containment of the melt in the working gap between rolls.  
           [0003]    There exist three U.S. Patents, largely based on the theoretical and experimental work of Kapusta, et al., carried out in the U.S.S.R. in the early 1970&#39;s: U.S. Pat. No. 4,936,374 (1990), which proposes the application of a horizontal, high-frequency magnetic field for metal containment in the working gap between rolls; U.S. Pat. No. 4,974,661 (1990), which suggests a vertical, high-frequency magnetic field, and U.S. Pat. No. 5,495,886 (1996), featuring three vertical magnetic fields— a DC field, an AC high-frequency field, and an AC low-frequency field.  
           [0004]    Analysis of the prior art, based on extensive experience in electromagnetic metal containment, leads to the following conclusions:  
           [0005]    The use of one horizontal or vertical, high-frequency magnetic field affords control of only one parameter and does not ensure the stable containment of metal, e.g., steel, at heavier liquid layer thicknesses for relatively thick layers.  
           [0006]    While, under certain conditions, the use of three vertical magnetic fields and a horizontal current density field is possibly able to ensure stable metal containment, this is conditional upon the simultaneous control of four electromagnetic parameters, which casts serious doubt on the practicability of such control. Moreover, the design of an apparatus for carrying out such a method is extremely complex.  
           [0007]    Also, all of the prior art patent refer to the apparatus used by inference only.  
         DISCLOSURE OF THE INVENTION  
         [0008]    It is thus one of the objects of the present invention to provide an apparatus for the continuous, vertical casting of metal sheets and bands that is mechanically relatively simple and that comprises an arrangement of coils for generating strategically located magnetic fields which ensure the sidewall containment of the gap between rolls that defines the thickness of the cast sheet or band and enhances the stability and smoothness of the surface of the sheet or band being cast.  
           [0009]    According to the invention, the above object is achieved by providing an apparatus for the continuous casting of metal sheets and bands, comprising two rotatable roll-crystallizers having parallel axes located in the horizontal plane and defining between them a gap of adjustable width, and means for supplying metal melt to fill said gap; characterized by means for generating at least three substantially horizontal magnetic fields producing electromagnetic pressures adapted to act to contain at least one end face of said melt within said gap. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood.  
         [0011]    With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.  
         [0012]    In the drawings:  
         [0013]    [0013]FIG. 1 is an elevational view of the apparatus according to the present invention, showing, on the left of the vertical center line, a cross-sectional view of one of the rolls, and, on the right, a view in the direction of arrows AA in FIG. 2;  
         [0014]    [0014]FIG. 2 is a side view of the apparatus as-seen in the direction of arrow B in FIG. 1;  
         [0015]    [0015]FIGS. 3 a - c  represent three variants of the jacket enveloping the core;  
         [0016]    [0016]FIG. 4 represents, to a larger scale, detail D of FIG. 5;  
         [0017]    [0017]FIG. 5 is a perspective view of the C-shaped, high-frequency electromagnet;  
         [0018]    [0018]FIG. 6 is a schematic top view of the apparatus, illustrating the arrangements of the magnetic fields and the connections of the various power supplies;  
         [0019]    [0019]FIG. 7 is a perspective view of one of the two supporting beams of the roll assembly, and  
         [0020]    [0020]FIG. 8 is a perspective view of the laminate arrangement of the expanding magnetic cores. 
     
    
     DETAILED DESCRIPTION  
       [0021]    Referring now to the drawings, there is shown in FIG. 1, on the left of the vertical center line, a cross-sectional view of one of two roll-crystallizers  2 , (hereinafter referred to as roll or rolls  2 ), having parallel axes lying in a horizontal plane. Each of the rolls  2  comprises a core  4  made of non-magnetic steel with ducts  6  for the circulation of a liquid coolant; two stub axles  8  made of magnetic carbon steel with a central bore  10  communicating with ducts  6 ; jacket  12 , made of a thermally highly conductive material, e.g., copper, and adapted to be cooled by the liquid coolant.  
         [0022]    Jacket  12  is shown to better effect in FIGS. 3 a - c , which represent three possible variants of the jacket. A basic jacket  12  is shown in FIG. 3 a , the inside surface of jacket  12  being provided with a plurality of equally spaced, axially directed grooves  13  which end in a manifold on both sides of roll  2  (FIG. 4). A similar cooling effect can also be achieved by helical grooves  13 . FIGS. 3 b  and  3   c  show variants in which the outer surface of jacket  12  is provided with U-profiled and trapezoidal grooves, respectively, into which are inserted electrically insulated copper bars  14 ,  14   a , having appropriate cross-sections. The purpose of these bars will become apparent further below.  
         [0023]    The connection between roll cores  4 , stub axles  8  and jacket  12  is shown to better effect in FIG. 4, where it is seen that cores  4  are connected to flanges  15  of stub axles  8  by means of screws  16 , with the interposition of sealing washers  18 . Jacket  12  is seated on a shoulder  20  of flanges  15  and is sealed off by a sealing ring  22 .  
         [0024]    Further seen is an electromagnet  24 , of which two are provided, one on each side of rolls  2  (see FIG. 6). Electromagnet  24  has a laminated, C-shaped core  26  and sloping pole faces  28 . Windings  30  are made of copper tubing. Each of the poles of core  26  faces a laminated, annular armature  32 , each armature being attached by means of screws  34  to flange  15  of the stub axle  8  of its roll  2 .  
         [0025]    Core  26  is slidably mounted on a bracket  35  (FIG. 1), which in turn is mounted on chassis  36 . As the angle of slope of annular armatures  32  and the angle of slope of pole faces are identical, gap a between rolls  2 , which determines the thickness of the cast sheet, can be altered without altering the air gap between armatures  32  and pole faces  28 , by shifting core  26  in either direction of double arrow C. Windings  30  of electromagnet  24  are connected to a high-frequency (2.5-10 kHz) source of a voltage  38  (FIG. 6).  
         [0026]    Returning to FIG. 1, there are seen coils  40 , surrounding, but not touching, stub axles  8 . Each of coils  40  has either one or two electrically separate windings. In the coil variant having only one winding, the DC and AC circuits are separated by a capacitor. When coils  40  are connected to sources of direct voltages  42  and low-frequency (5-100 Hz) alternating voltages  44  (FIG. 6), two magnetic fields are generated in annular magnetic circuits  32 , one field being a direct and the other, a low-frequency, alternating magnetic field.  
         [0027]    Magnetic core  46  is slipped over, but does not touch, two adjacent stub axles  8  and is fixedly attached to the coil former of coils  40 . In order to accommodate alterations in the center distance d between the two adjacent rolls  2  due to alterations of gap  a , core  46  is designed to be expanding. Expansibility is achieved by simply intercalating stacked laminations of core  46 , as is clearly seen in FIG. 8. Holes  50  serve to allow stub axles  8  to pass through.  
         [0028]    Stub axles  8  are mounted in bearings supported in bearing housings  52 , which also serve as inlet (left housing) and outlet (right housing).  
         [0029]    Rolls  2  are each connected, via coupling  54 , to a drive  55  comprising a worm reduction gear  56  and an electric motor  58 . Near the surface of rolls  2 , arcuate stators  60  are installed, as shown in FIG. 2. These stators are connected to an m-phase (m≧3) voltage source  62  (FIG. 6) of controllable frequency, voltage and sequence of phase switching. Bearing housing  52  and drive  55  are mounted on beams  64 , which are fitted with guides  66  consisting of female dovetails, guide rollers  68  freely rotating in bearing supports  70 , and bracket  72  fixed to the bottom of frame beam  64  to which bracket nut  74  is attached. These are parts of the displacement mechanism of beam  64  with respect to chassis  36 .  
         [0030]    Chassis  36  includes guide rails  76  in the form of male dovetails matching the female dovetails of guides  66  on which the beams  64  rest, as well as screws  78  with handles  80  serving for the displacement of beams  64 , and bracket  35  on which high-frequency electromagnets  24  are mounted. The working position of rolls  2  with respect to chassis  36 , which determines the thickness of a cast sheet, is fixed using bolted joint  82 .  
         [0031]    Liquid metal is fed to the apparatus by a vacuum- or MHD-pump  84 , through a thermally insulated metal conduit  86  and ceramic distribution box  88 . The cast band or thin sheet is wound down using a puller strip  90 , representing a steel band of a thickness corresponding to the thickness of the sheet to be case. Strip  90  has recesses at its upper end in which the crystallizing metal is caught; the strip serves as a leader for winder  92 .  
         [0032]    The continuous casting apparatus operates as follows: Using screws  78 , the required gap between rolls  2  is set, then the position of beams  64  is rigidly fixed using bolted joints  82 . Puller strip  90  is attached at its lower end to the drum of winder  92 , its upper end being inserted into the gap between rolls  2  and held in position by guide rollers  68 . Then, using voltages  38 ,  42 ,  44 , currents are applied to the electromagnet windings, which excite direct magnetic field B 3  and alternating magnetic fields B 1  and B 2  in the zone of the anticipated location of the liquid layer end faces.  
         [0033]    Then liquid metal is fed into the gap between rolls  2  by means of pump  84  via metal conduit  86  and distribution box  88  and, while the gap is being filled, rolls  2  are driven up by drive  55  to the nominal speed. The drum of winder  92  is driven up to a speed appropriate to the speed of rolls  2 . At the appearance of liquid metal in the gap, vertical currents J 1 , J 2  are induced at the edges of the liquid layer by alternating magnetic fields B 1 , B 2 . The interaction of these currents with these fields results in the appearance of electromagnetic body forces f 1 , f 2 , acting within a thin surface layer in the direction parallel to the axes of the rolls. These forces generate electromagnetic pressure, counterbalancing the hydrostatic pressure of the liquid column and thus preventing liquid metal overflow from the end faces of the liquid layer in the gap. However, these forces have an alternating component, which generates, together with the disturbing action of jets of liquid metal in the gap, wave disturbances on the free surface of the liquid layer. Free surface deviation in the direction perpendicular to the direct magnetic field B 3 , induces a vertical current J 3 , whose interaction with field B 3  leads to the appearance of electromagnetic body forces f 3 , which are always directed counter to the motion of surface points and thus suppress wave excitations of the surface, making it more stable.  
         [0034]    If the rate of liquid-metal feeding to rolls  2 , the rate of rotation of the rolls and the intensity of roll cooling are well coordinated, the technological process of thin sheet (band) production is sufficiently stable.  
         [0035]    The use of arcuate stators  60  together with jackets  12  (FIGS. 3 b ,  3   c ) can make the technological process even more controllable, in the following way: A travelling magnetic field B 4 , excited by arcuate stators  60 , induces a travelling field of currents J 4  in rods  14 ,  14   a . Since rods lying in the diametral plane of rolls  2  are connected pair-wise, forming frames, travelling magnetic fields B 5  are induced in the liquid metal filled working gap, with the direction of motion being determined by the sequence of phases of arcuate stators  60 . If the field B 5  moves in the direction opposite to that of the motion of the surface of rolls  2 , the area of the contact surface of the liquid metal with the rolls increases and the thickness of the liquid layer in the central portion decreases, which increases the reliability of the liquid metal containment in the gap and permits an increase in the speed of rolls  2 , i.e., the apparatus output. The use of arcuate stators  60 , together with jackets  12  of FIG. 3 b  or  3   c  as an additional electrical drive-enhancing electrical force, makes it possible to drastically reduce the power required by electrical drive  55 .  
         [0036]    It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrated embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.