Abstract:
Continuous strip casting device comprises a pair of parallel casting rolls onto which molten metal is supplied by metal supply means. Casting rolls are enclosed by a casting chamber into which hot strip is delivered downwardly from the casting rolls. Strip passes downwardly into a cooling chamber where it can either fall into a moveable scrap box at the bottom of chamber or be guided by operation of moveable apron through an exit door from chamber into a heat exchange chamber provided with heaters. A pair of seal rolls are moveable in a seal chamber to form a seal between chambers and are provided with respective gas inlets to admit oxidation inhibiting gas into those chambers. Scrap box is moveable into and out of the bottom of chamber via a scrap box exchange chamber fitted with an airtight door.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to a continuous strip casting device and to a method for the use thereof.  
         PRIOR ART  
         [0002]    [0002]FIG. 5 illustrates the continuous strip casting device revealed by JP 8-300108 (and also U.S. Pat. Nos. 5,590,701 and 5,960,856), such continuous strip casting device being provided with a pair of casting rolls  101   a  and  101   b  that are rotatably supported in such a manner as to be juxtaposed horizontally parallel to each other and as to form roll gap G, with the outer circumferential surfaces of the casting rolls facing the said roll gap G. A molten metal supply means  102  of the casting device supplies molten metal to and between the casting rolls  111   a  and  101   b , and a strip guide means  112  guides sideways the strip  103  that emerges from the roll gap G through the rotation of the casting rolls  101   a  and  101   b.  A pinch roll stand  105  grips the strip  103  that has passed from the strip guide means  112 . An enclosure wall  107  provides a chamber  106  that is positioned below the casting rolls  101   a  and  101   b  and encloses the moving path for the strip  103  from the roll gap G to the pinch roll stand  105 , with a scrap box  108  whose upper edge is in contact from below with the edge of the chamber  106  of the enclosure wall  107 .  
           [0003]    The outer circumferential surfaces of the casting rolls  101   a  and  101   b  are cooled by means of the cooling water that flows through the interiors of the casting rolls and the solidification of the molten metal on the surfaces of the casting rolls  101   a  and  101   b  is accelerated thereby.  
           [0004]    Moreover, an actuator (not shown) that holds in close proximity the rotational axes of the casting rolls  101   a  and  101   b  is attached in order to regulate the roll gap G, and in turn the gauge of the strip  103  that is to be manufactured.  
           [0005]    The molten metal supply system  102  also possesses a tundish  109  that receives the molten metal, and a nozzle  110  that pours the molten metal from the said tundish  109  to and between the casting rolls  101   a  and  101   b.    
           [0006]    The strip guide means  112  is comprised of a support shaft  111  that is disposed below the casting roll  101   b  and that is pivoted parallel to the said casting roll  101   b , and a plurality of guide rolls  113  that are dispose laterally and that support the strip  103  that is transported sideways by the movable apron  112 A.  
           [0007]    The pinch roll stand  105  possesses a housing  114  through which the strip  103  passes, and a pressure roll  115   a  that is so mounted in the housing  114  as to come into contact with the lower surface of the strip  103 , and a pressure roll  115   b  that is so mounted in the housing  114  as to come into contact with the upper surface of the strip  103 .  
           [0008]    The enclosure wall  107  is comprised of a steel outer shell  116  which is intended to impart support to an interior refractory lining  117  which extends across the entire inner surface of the outer shell  116 .  
           [0009]    A scrap box  108  is formed of refractory materials, and a seal member  118  is mounted in the top of the scrap box  10 . The scrap box  108  is mounted on the car  121  that has wheels  120  that are able to move over the rails  119 , and has a cylinder  122  that is able to raise the scrap box  108  as provided on the said car  121 .  
           [0010]    When strip  103  is manufactured by means of the continuous strip casting device illustrated in FIG. 5, the cylinder  122  attached to the car  121  raises the scrap box  108  bringing the upper edge of the scrap box  108  through the seal member  118  into contact with the edge of the chamber  106  of the enclosure wall  107 . The leading edge of the movable apron  112 A is so set as to be positioned below the support shaft  111 . The distance between the rotational axes of the casting rolls  101   a  and  101   b  is set so that a roll gap G corresponds to the gauge of the strip  103  that is to be cast, and the casting rolls  101   a  and  101   b  are rotated in such a manner that their outer circumferential surfaces move from above towards the roll gap G.  
           [0011]    Next, molten steel is supplied to the tundish  109 , and when the molten steel is poured through the nozzle  110  to and between the casting rolls  101   a  and  101   b , a solidified shell forms on the outer circumferential surfaces of the rolls, and as the casting rolls  101   a  and  101   b  rotate, the strip  103  is transported into chamber  106 .  
           [0012]    After the strip  103  has been presented in a laterally uniform state, the rotational axis of the casting rolls  111 a and  101   b  rebounds in a very short time (approximately from 0.1 to 0.5 seconds) such that the roll gap G becomes approximately 1.5 to 3 times the thickness of strip  103 , and then the roll gap G reverts to its original state. The expansion in the roll gap G causes the casting rolls  101   a  and  101   b  to produce areas of imperfect cooling, so that the strip  103  melts again through reheating effectively acting as a hot shear.  
           [0013]    In this way, the strip  103  that is transported before the expansion of the roll gap G is broken off in a straight line from the strip  103  that is transported after the roll gap G has reverted to its original state, with the portion of the strip  103  that was remelted through the expansion of the roll gap G forming the boundary of the strip  103  to be transported to the coilers.  
           [0014]    Moreover, the movable apron  112 A is disposed laterally, and the strip  103  that is transported from the roll gap G after the break is led by the guide rolls  113  to the pinch roll stand  105 .  
           [0015]    The problem addressed by the present invention is that in the continuous strip casting device shown in FIG. 5, the space formed by the enclosure wall  107  that encloses the moving path for the strip  103  from the roll gap G to the pinch roll stand  105 , and the scrap box  108  that comes into contact with the lower edge of the of the chamber  106  of the enclosure wall  107 , is not filled with a non-oxidizing or weakly reducing atmospheric gas, and hence scale caused by oxidation develops on the strip  103 .  
           [0016]    Moreover, no means is provided for control of the flow of the atmospheric gas (air) between the casting rolls  101   a  and  101   b  and the movable apron  112 A, and between the movable apron  112 A and the guide rolls  113 . The high temperature air that has been heated by the strip  103  blows in a concentrated manner onto the casting rolls  101   a  and  101   b , while the insulating effect of the refractory lining  117  of the enclosure wall  107  impedes the cooling of the air within the chamber  106 . This causes reheating of the strip  103  immediately after transport from the roll gap G and breakout and instability in casting. The high temperature strip  103  (not less than 1250° C.) is transported to the pinch roll stand with scale, leading to embedded scale damage, and a likely reduction in yield.  
           [0017]    Moreover, because the seal member  118  of the scrap box  108  is in contact with the edge of the enclosure wall  107  forming chamber  106 , when an attempt is made to exchange the scrap box  108  during casting, a large amount of air flows into the chamber  106  causing severe strip oxidation. As a result, for practical purposes, it is not possible to exchange the scrap box  108  during the operation of the continuous strip casting device.  
           [0018]    Moreover, splashes of molten metal and slag fall onto and accumulate on the seal member  118  between the enclosure wall  107  and the scrap box  108 . As a result, the seal member  118  is deformed and damaged by the raising of the cylinder  122  of the scrap box  108  so that, each time the scrap box  108  is exchanged, the seal member  118  must be cleaned or replaced. Furthermore, it is difficult to restrict the inflow of external air and to maintain a low oxygen content inside the enclosing wall  107 .  
           [0019]    The present invention takes account of such deficiencies of the prior art, and enables the efficient manufacture of strip from molten steel with substantially reduced scale.  
         SUMMARY OF THE INVENTION  
         [0020]    According to the invention there is provided apparatus for continuously casting metal strip comprising:  
           [0021]    a pair of parallel casting rolls forming a nip between them;  
           [0022]    a molten metal delivery system to delivery molten metal into the nip between the rolls to form a casting pool of molten metal supported on the casting roll surfaces immediately above the nip;  
           [0023]    roll drive mechanism to drive the casting rolls in counter-rotational directions to produce a solidified strip of metal delivered downwardly from the nip between the casting rolls;  
           [0024]    a casting chamber to enclose strip delivered downwardly from the nip;  
           [0025]    a cooling chamber disposed below the casting chamber to receive the strip passing through the casting chamber from the nip through a transfer opening between the casting chamber and cooling chamber located beneath the nip between the casting rolls;  
           [0026]    interchamber sealing system disposed at said transfer opening and having an open condition in which the opening is dilated and a closed condition in which the opening is contracted about the strip to enhance sealing between the casting and cooling chambers.  
           [0027]    The apparatus may further comprise casting chamber gas inlet means to admit an oxidation inhibiting gas into the casting chamber. The oxidation inhibiting gas may be an inert gas or a weakly reducing gas.  
           [0028]    There may be cooling chamber gas inlet to admit an oxidation inhibiting gas into the cooling chamber.  
           [0029]    The interchamber sealing system may comprise a pair of seal rolls disposed on to either side of said transfer opening and a roll moving mechanism operable to move the sealing rolls between retracted positions and extended positions in which they contract the transfer opening.  
           [0030]    The apparatus may further comprise a moveable scrap box to receive scrap strip at the bottom of the cooling chamber and a scrap box exchange chamber communicating with the bottom part of cooling chamber through an exchange opening closable by a moveable air tight door through which the scrap box can be moved in and out of its scrap receiving position at the bottom of the cooling chamber. The scrap box exchange chamber is provided with a moveable air sealing entry door through which the scrap box can pass into the exchange chamber, and with exchange chamber gas inlet through which to supply an oxidation inhibiting gas to the scrap box exchange chamber.  
           [0031]    The apparatus may be further possess a heat exchange chamber with radiant tubes that are disposed in the heat exchange chamber. Guide rolls are disposed in the heat exchange chamber and transport laterally the strip that is sent from the cooling chamber. The heat exchange chamber is also provided with an atmospheric gas inlet.  
           [0032]    The apparatus may also have a pinch roll chamber that communicates with the exit of the heat exchange chamber and that is able to receive the strip from the heat exchange chamber, and a partition door that is able to expand and contract in cross section the opening of the exit of the pinch roll chamber, and pinch rolls that are disposed in the pinch roll chamber and are capable of gripping the strip.  
           [0033]    The apparatus may also have a rolling mill that is disposed in the downstream strip travel direction from the pinch roll chamber, and a strip pass line that runs from the exit of the pinch roll chamber to the rolling mill being typically so set as to lower the strip by between 10 mm and 150 mm for every 1 m distance of travel.  
           [0034]    The invention further may provide a continuous strip casting device having a pair of casting rolls that form a roll gap and that are disposed parallel to each other in diametrical juxtaposition, and a molten metal supply system that supplies molten metal from above to and between the casting rolls, and a casting chamber that encloses the strip emerging from between the two casting rolls and in some embodiments the two casting rolls themselves, and an inter-chamber sealing system having a pair of seal rolls that permit the passage of the strip that is emerging from between the casting rolls downwards. A seal roll chamber may enclose the pair of seal rolls and communicate with or be within the casting chamber. A seal member slides the seal guide that is disposed in the seal roll chamber and positions the seal rolls in the path of and on either side of the strip in such a manner as to cause the movement of the seal rolls. A movable apron is so disposed as to guide sideways the strip that is transported downwards from between the seal rolls or alternatively to lower the said strip to a scrap box. The scrap box is disposed below the movable apron. A cooling chamber communicates with the inter-chamber sealing system and possesses an exit that is able to transport the strip that has been guided by the movable apron and that encloses the movable apron. An exit door is able to increase and decrease the cross section of the opening of the exit from the cooling chamber, and a scrap chamber possesses an air sealing door that is able to move the scrap box in and out of the cooling chamber and that encloses the scrap box that communicates with the cooling chamber, and in which the said casting chamber, cooling chamber and scrap chamber each possesses an atmospheric gas inlet.  
           [0035]    The invention also provides a method of use of the continuous strip casting device, such method supplying an oxidation inhibiting gas such as a non-oxidizing or alternatively weakly reducing atmospheric gas, to the said casting chamber, cooling chamber and scrap chamber when strip is being continuously cast. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0036]    In order that the invention may be more fully explained, specific embodiments will be described with reference to the accompanying drawings in which:  
         [0037]    [0037]FIG. 1 is a vertical cross-section through part of a continuous strip casting installation constructed in accordance with the invention;  
         [0038]    [0038]FIG. 2 is a vertical cross-section through a further part of the installation of FIG. 1;  
         [0039]    [0039]FIG. 3 is a detail view of part of the installation;  
         [0040]    [0040]FIG. 4 is a transverse cross-section through part of the installation;  
         [0041]    [0041]FIG. 5 illustrates part of a prior art installation;  
         [0042]    [0042]FIG. 6 is a vertical cross-section through part of an alternative continuous casting installation in accordance with the present invention;  
         [0043]    [0043]FIG. 7 is a top view of part of the installation of FIG. 6; and  
         [0044]    [0044]FIG. 8 is a front view of the installation components illustrated in FIG. 7. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0045]    FIGS.  1  to  4  are an embodiment of the continuous strip casting device envisaged by the present invention.  
         [0046]    The molten metal supply system has tundish  1  that supplies molten metal down from above through the nozzle  2  to between the casting rolls  3   a  and  3   b . The molten metal supply system may have insulated sealing material  23  positioned between the tundish  1  and the casting chamber  4 , and nozzle  2  inserted into the pool of molten steel that is formed between the casting rolls  3   a  and  3   b.    
         [0047]    The outer circumferential surfaces of the casting rolls  3   a  and  3   b  are cooled by cooling water that flows through them, which accelerates the solidification of the molten steel.  
         [0048]    Moreover, the casting rolls  3   a  and  3   b  are juxtaposed horizontally in order to form the roll gap G, and the casting rolls  3   a  and  3   b  are so supported that their outer circumferential surfaces revolved from the top towards the roll gap G.  
         [0049]    When the molten steel that flows down between the casting rolls  3   a  and  3   b  passes through the roll gap G, the molten steel forms a solidified shell on the outer circumferential surfaces of the casting rolls  3   a  and  3   b , and strip  10  emerges downwards from the roll gap G.  
         [0050]    Immediately after the strip  10  is separated from the outer circumferential surfaces of the casting rolls  3   a  and  3   b , the strip may not be solidified through to the center of its thickness, but from 30% to 50% of the central portion of the strip may be still molten steel.  
         [0051]    In the continuous strip casting device illustrated in FIGS.  1  to  4 , any non-solidified center portion of the strip  10  is solidified after it has separated from the casting rolls  3   a  and  3   b . However, the leading edge of the strip  10  that is transported from the roll gap G is irregular.  
         [0052]    At this time, the seal rolls  6   a  and  6   b  are moved by the cylinders  9   a  and  9   b  to positions as indicated by the double dotted lines in FIG. 1, so that they are not affected by splash of molten metal from the roll gap G, and expand the gap between the seal rolls  6   a  and  6   b  to its largest extent. The movable apron  14  is at this time positioned facing downwards as indicated by the unbroken lines in FIG. 1.  
         [0053]    The strip  10  that has initially been transported from the roll gap G passes through the seal rolls  6   a  and  6   b  and faces downwards and enters the scrap box  17  that is disposed inside the scrap chamber  16 .  
         [0054]    Next, after the distance between the rotational axes of the casting rolls  3   a  and  3   b  has widened in a very short period of time (typically 0.1 to 0.5 seconds), the roll gap G reverts to its original position. The expansion of the roll gap G causes liquid steel to be admitted between the strip shells and thus cause a portion of a portion of the incompletely cooled strip  10  to reheat and remelt forming a new head end suitable for transportation of the strip to the coilers.  
         [0055]    The alignment of the movable apron  14  is then set laterally as indicated by the double dotted lines in FIG. 1. The strip  10  is thus guided onto the upper surface of the movable apron  14 , onto the guide rolls  18  and passes through the exit door  20 , in an open state, to the heat exchange chamber  19 . The strip  10  moves through the heat exchange chamber  19  to the exit door  21 , in open state, of the heat exchange chamber  20 , and is then gripped by the pinch rolls  22  in the pinch roll chamber  65  so that the desired tension is then imparted to the strip  10 .  
         [0056]    The strip  10  is gripped by the pinch rolls  22  and is prevented from falling into the scrap box  17 . Hence the alignment of the movable apron  14  is set in the direction indicated by the unbroken line in FIG. 1 forming a gently curving moving path for the strip  10  in the cooling chamber  15 , whereby the continuous strip casting device is shifted from activation state to normal continuous casting operation.  
         [0057]    At this time, the cylinders  9   a  and  9   b  move the pinch rolls  6   a  and  6   b  closer together, as indicated in FIG. 1, and the gap between the seal rolls  6   a  and  6   b  is reduced to a value set by the seal guide  8 , and the exit door  20  of the cooling chamber  15  and the exit doors of the heat exchange chamber  21  are lowered to their lowest positions at which they do not come into contact with the strip  10 .  
         [0058]    Thus, in the continuous strip casting device illustrated in FIGS.  1  to  4  through the combination of the gap between the casting rolls  3   a  and  3   b  instantly expanding and reverting to its original state and the appropriate setting of the alignment of the movable apron  14 , operation may be readily repeated, and the casting of the strip  10  may be started and stopped readily, without the necessity for the use of a dummy bar.  
         [0059]    During continuous casting operations, the casting chamber  4  is sealed by reducing the gap between the seal rolls  6   a  and  6   b  and the strip  10 . The exhaust control valve  27 , apart from the exhaust vent  26 , permits control of the volume of exhaust gas from casting chamber  4 . Casting chamber  4  may be filled with a mixed non-oxidizing gas such as 99.99% nitrogen or argon or weakly reducing gas such as mixture from 2% to 10% hydrogen with the balance nitrogen. The gas is introduced through the atmospheric gas intake vent  24  and the atmospheric gas is exhausted through the gap between the seal rolls  6   a  and  6   b  to the cooling chamber  15 , thus preventing the surface oxidation of the strip  10  that is at a temperature of between 1300° C. and 1400° C. immediately after casting in the casting chamber  4 .  
         [0060]    The casting chamber  4  consists of water cooled panels with cooling water flowing between dual outer and inner plates. The strip  10  that moves through the casting chamber  4  radiates heat to the cooling panels and is continuously cooled.  
         [0061]    The seal roll chamber  5  communicates with both the casting chamber  4  and the cooling chamber  15 , and encloses the seal rolls  6   a  and  6   b  is disposed between the casting chamber  4  and the cooling chamber  15 . The seal roll chamber  5  is also constructed of water cooled panels after the fashion of the casting chamber  4 , and continues cooling of the strip  10  as the strip moves from the casting chamber  4  to the cooling chamber  15 .  
         [0062]    The outer circumferential surfaces of the seal rolls  6   a  and  6   b  are cooled by cooling water that flows through the interiors of the seal rolls  6   a  and  6   b  and this accelerates the cooling of the strip  10 .  
         [0063]    The inter-chamber sealing system with seal rolls  6   a  and  6   b  is intended to reduce and may minimize the atmospheric gas that is communicated from the cooling chamber  15  to the casting chamber  4  and to minimize the movement of the gas in the casting chamber  4  in order to stabilize the casting operation. However, the gap between the seal rolls  6   a  and  6   b  can be extended at the start and finish of casting operations because splashes of molten metal may fall from the roll gap G and strip of indeterminate shape may collide with the seal rolls  6   a  and  6   b  and become entangled with them.  
         [0064]    The sealing system with the seal rolls  6   a  and  6   b  may be comprised of sealing members  7  that are positioned on the path traversed by the strip, and which moves with the seal rolls  6   a  and  6   b . Seal guides  8  may be disposed in the seal roll chamber  5  and extend along the entire circumference of the sealing members  7 .  
         [0065]    Sealing members  7  are formed of blocks of materials that are softer than the cast iron, ceramic or polymer resin and the like, which is employed for the seal rolls  6   a  and  6   b , and are supported in frames sideways to the seal rolls  6   a  and  6   b.    
         [0066]    Moreover, the gap between the sealing members  7  and the seal rolls  6   a  and  6   b  may be set at not more than 1 mm.  
         [0067]    Furthermore, an electric motor may also appropriately be employed in place of the oil, air or gas fluid hydraulically powered cylinders  9   a  and  9   b  as the means of moving the seal rolls  6   a  and  6   b.    
         [0068]    The seal guides  8  performs a sealing function for the sealing members  7  and also sets the magnitude of the gap between the seal rolls  6   a  and  6   b.    
         [0069]    The gap between the seal rolls  6   a  and  6   b  and the strip  10  may be set at a maximum of between 1 mm and 20 mm greater than the gauge of the strip  10 , which is to be cast, in order to minimize the ingress of atmospheric gas into the casting chamber  4 , while avoiding rupture of the strip  10  caused by gripping by the seal rolls  6   a  and  6   b.    
         [0070]    Moreover, because the gauge of the strip  10  emerging from the roll gap G normally ranges between 1 mm and 5 mm, the seal rolls  6   a  and  6   b  are also capable of being driven by the drive mechanism, for example by a electric motor, in a range of up to 20 mm.  
         [0071]    The cooling chamber  15  is also constituted of water cooled panels after the fashion of the casting chamber  4 , and the cooling of the moving strip  10  is continued in the cooling chamber  15  by means of radiant cooling.  
         [0072]    Moreover, the outer circumferential surfaces of the movable apron  14  are cooled by cooling water that flows through the interior of the movable apron  14  and thus accelerates the cooling of the strip  10 .  
         [0073]    An atmospheric gas intake vent  29 , an exhaust vent  30 , a chamber internal pressure gauge  31 , a gas analyzer  32  and a strip temperature gauge  33  are disposed in the cooling chamber  15 , with the signals indicating the pressure by the chamber internal pressure gauge  31 , indicating the gas composition by the gas analyzer  32  and indicating the temperature by a strip temperature gauge  33  being sent to a control computer that controls the internal pressure, gas composition and temperature of the cooling chamber  15 .  
         [0074]    A door roll  38  that passes cooling water into the exit door  20  of the cooling chamber  15  is attached rotatably to the bottom end of the exit door  20 .  
         [0075]    The exit door  20  of the cooling chamber  15  is set to an open state, until the leading edge of the strip  10  passes, by a drive mechanism of a door opening and closing device  37  that is powered by a fluid hydraulic or electric drive motor, and the exit door  20  of the cooling chamber  15  is set to an opening sufficient to leave a gap of between 2 mm and 10 mm to the strip  10  during continuous casting operations.  
         [0076]    The exit door  20  of the cooling chamber  15  is constituted of insulation material, and is intended to provide insulation against radiant heat or cold from the heat exchange chamber  19 .  
         [0077]    The scrap chamber  16  is composed of water cooled panels after the fashion of the casting chamber  4  in such a manner as to communicate with the cooling chamber  15 .. The strip  10  is received in the scrap box  17  immediately after the start of continuous casting operations, and immediately before the conclusion of continuous casting operations.  
         [0078]    The scrap chamber  16  is provided with an airtight door  42  to allow the insertion and removal of the scrap box  17 , and a door seal  43  that is attached to the airtight door  42 .  
         [0079]    The door seal  43  preferably consists of an  0  ring that is formed of a heat resistant rubber material such as Viton, and an inflatable seal that expands on contact and which is provided internally with water pressure or gas pressure. The scrap chamber  16  also has an atmospheric gas intake vent  44 .  
         [0080]    Moreover, transport rollers  40  support the base of the scrap box  17 . A jack  41  that raises the scrap box  17  is also provided in the base of the scrap chamber  16 . The gap between the upper edge of the scrap box  17  and the edge of the opening at the bottom end of the cooling chamber  15  should be as narrow as possible when the scrap box  17  is raised by means of the jack  41 , in order to prevent air leakage into the scrap box  17  from the exterior.  
         [0081]    The scrap box  17  possess refractory materials mounted on the inside surfaces of the outer steel plates, such refractory materials providing buffers against collision when the strip  10  falls and providing insulation around the perimeter of the scrap box  17 .  
         [0082]    Moreover, the portion in which the airtight door  42  of the scrap chamber  16  is disposed communicates with the exchange chamber  45  for the placement of the scrap box  17 .  
         [0083]    The exchange chamber  45  contains an airtight door  48  for the insertion and removal of the scrap box  17 , a door seal  49  for the airtight door  48 , an exchange gas intake vent  50 , and a gas exhaust vent  51 .  
         [0084]    The door seal  49  preferably consists of an O ring that is formed of a heat resistant rubber material such as Viton, and an inflatable seal that expands on contact and which is provided internally with water pressure or gas pressure.  
         [0085]    Moreover, transport rollers  46  and  47  that support the base of the scrap box  17  are disposed in the bottom of the exchange chamber  45  and outside the airtight door  48 .  
         [0086]    When the scrap box  17  is to be removed from within the scrap chamber  16 , the jack  41  is retracted, and the scrap box  17  is supported on the transport rollers  40 .  
         [0087]    Next, the airtight door  42  is opened, and the scrap box  17  is moved by means of the transport rollers  40  and  46  to the exchange chamber  45 , whereupon the airtight door  42  is closed, and the airtight door  48  is opened. The scrap box  17  is then moved by means of the transport rollers  46  and  47  to outside the exchange chamber  45 .  
         [0088]    When the scrap box  17  is to be sent into the interior of the scrap chamber  16 , the airtight door  48  is opened and the scrap box  17  is moved by means of the transport rollers  46  and  47  into the exchange chamber  45 , and the airtight door  48  is closed.  
         [0089]    Next, the gas exhaust vent  51  is opened, the air within the exchange chamber  45  is exhausted to the exterior, and non-oxidizing or weakly reducing atmospheric gas is supplied through the exchange gas inlet vent  50  into the exchange chamber  45 . The interior of the exchange chamber  45  is thus filled with atmospheric gas, and then the gas exhaust vent  51  and the exchange gas inlet vent  50  are closed.  
         [0090]    Then the air sealing door  42  is opened, the scrap box  17  is moved by means of the transport rollers  46  and  40  into the scrap chamber  16 , and the airtight door  42  is closed, whereupon the scrap box  17  is raised by means of the jack  41 .  
         [0091]    Consequently, the scrap box  17  can be exchanged during the operation of continuously casting the strip  10 , without permitting the invasion of the external air, and avoiding oxidation of the strip  10 .  
         [0092]    Moreover, by providing an exhaust vacuum pump in the gas exhaust vent  51 , the time required in order to replace the air with the atmospheric gas can be reduced.  
         [0093]    If the scrap box  17  is replaced only at the conclusion of the continuous casting operation, there is no need to provide an exchange chamber  45 , and the scrap box  17  can be inserted and removed simply by the opening and closing of the airtight door  42 .  
         [0094]    Moreover, wheels may be provided on the scrap box  17  in place of the transport rollers  40 ,  46  and  47 , whereby the scrap box  17  may be moved.  
         [0095]    When the strip  10  passes through the cooling chamber  15 , the strip  10  is cooled through radiant conduction, but the strip  10  can be cooled down to not more than 1000° C. if the continuous casting velocity is low (between 30 m and 100 m/minute according to strip gauge). On the other hand, if the continuous casting velocity is high, the temperature of the strip  10  is not less than 1250° C., and temperature differences are produced laterally across the strip.  
         [0096]    A plurality of radiant tubes  53 , which may be formed of heat resistant steel or ceramic, are disposed in the interior of the heat exchange chamber  19 , and insulating material is disposed on the inner surfaces of the heat exchange chamber  19 . The heat exchange chamber  19  provides for correction of such differences in temperature and also controls the temperature of the strip  10  at a desired temperature within the range of from 950° C. to 1200° C., which is suitable for rolling when the strip  10  reaches the entrance to the rolling mill  76  downstream in the movement of the strip  10 .  
         [0097]    A temperature gauge  54  for measuring the temperature within the heat exchange chamber  19 , a gas analyzer  55  for measuring the composition of the gas, and a pressure gauge for measuring the pressure are positioned within the heat exchange chamber  19 . An atmospheric gas inlet vent  57  is also disposed within the heat exchange chamber  19 , with the signals from the chamber temperature gauge being sent to the control computer. Accordingly, the fuel  59  and the combustion air  60  mixture that is sent to the burners  58  that may be attached to the radiant tubes  53  is adjusted, and the temperature within the heat exchange chamber  19  is regulated and maintained.  
         [0098]    Alternatively, if the temperature of the strip  10  that is transported into the heat exchange chamber  19  is low, the amounts of fuel  59  and combustion air  60  that are supplied to the burners  58  that are attached to the radiant tubes  53  are increased in order to raise and again control the temperature of the strip  10 .  
         [0099]    Moreover, if the temperature of the strip  10  that is transported into the heat exchange chamber  19  is high, the supply of fuel  59  to the burners  58  is stopped, and combustion air  60  only is supplied to the burners  58  that are attached to the radiant tubes  53 , in order to cool the strip  10  through the radiant tubes  53 .  
         [0100]    Heat-resistant steel rolls, and internally water cooled rolls or internally water cooled rolls to the outer circumferential surfaces of which refractory materials are attached are employed for the guide rolls  18  that are disposed in the heat exchange chamber  19 .  
         [0101]    Moreover, the output signals from the gas analyzer  55  and the chamber pressure gauge  56  are sent to the control computer which adjusts the atmospheric gas that is supplied through the atmospheric gas intake vent  57  into the heat exchange chamber  19  in order to prevent the oxidation of the strip  10 .  
         [0102]    Door rolls  61  through the interiors of which cooling water passes are rotatably mounted at the lower end of the exit door  21  of the heat exchange chamber  19 .  
         [0103]    Until the leading end of the strip  10  has passed through, the exit door  21  of the heat exchange chamber  19  is set to open by means of the door opening and closing device  64  which is operated either by a fluid hydraulic drive or by an electric motor, and the opening of the exit door  21  is so set as to provide a minimum gap in relation to the strip  10  of from 2 mm to 10 mm during the operation to continuously cast the strip  10 .  
         [0104]    The exit door  21  of the heat exchange chamber  19  is formed of steel plate to which insulating material is attached, and thus the escape of the radiant heat from the heat exchange chamber  19  is inhibited.  
         [0105]    Moreover, a seal trough  63  that holds water may be disposed in a fixed position in relation to the heat exchange chamber  19 , over the exit door  21  to the heat exchange chamber, and a seal plate  62 , whose upper part is linked to the rising and falling part of the door opening and closing device  64 , and whose lower end is always immersed in the seal trough  63 , is also disposed over the exit door  21  of the heat exchange chamber  19 . Such seal trough  63  and seal plate  64  minimize the outflow of the atmospheric gas from the heat exchange chamber  19  to the exterior.  
         [0106]    Referring to FIG. 2, the pinch roll chamber  65  is also constructed of water cooled panels after the fashion of the casting chamber  4 . The cooling of the strip  10  that is continued as it is moved into the pinch roll chamber  65 .  
         [0107]    The outer circumferential surfaces of the pinch rolls  22  are cooled by cooling water that flows through the interiors of the pinch rolls  22 , whereby the cooling of the strip  10  may be accelerated.  
         [0108]    Disposed in the pinch roll chamber  65  are transport rolls  66  supporting the strip  10  from below, and plate guides  67  permit accurate insertion of the strip  10  into the pinch rolls  22 .  
         [0109]    Also disposed in the pinch roll chamber  65  are atmospheric gas intake vent  68  that supplies atmospheric gas into the interior of the pinch roll chamber  65 , and a drain  69  that drains off to the exterior lubricating oil that is sprayed onto the pinch rolls  22  and drips onto the base of the pinch roll chamber  65 .  
         [0110]    Moreover, the pass line for the strip  10  that is supported by the guide rolls  18  and the transport rolls  66  may be lowered by d 1  only from the exit portion of the heat retention chamber  19  to immediately before the pinch rolls  22  in order to prevent the invasion of the heat exchange chamber by the lubricating oil.  
         [0111]    The appropriate extent of the dip in the pass line may be between 10 mm and 100 mm per 1 m of distance travelled by the strip  10 .  
         [0112]    The path of movement of the strip  10  between the pinch roll chamber  65  and the entrance portion of the rolling mill  76  is enclosed by the pre-rolling mill chamber  72 . Transport rolls  73  support the strip  10  from below are provided before and after the rolling mill  76 .  
         [0113]    The strip  10  that is transported from the pinch rolls  22  passes below the partition door  70  and enters the pre-rolling mill chamber  72 , and after the strip  10  has been rolled in the rolling mill  76 , the strip  10  is passed on to the downstream units.  
         [0114]    The pre-rolling mill chamber  72  is also constructed of water cooled panels after the fashion of the casting chamber  4 . The cooling of the strip  10  is continued as the strip is moved into the pre-rolling mill chamber  72 .  
         [0115]    The pre-rolling mill chamber  72  is provided with an atmospheric gas intake vent  74  in order to supply atmospheric gas to the interior of the pre-rolling mill chamber  72 . a water tank  77  collects the cooling water that drips down to the base of the pre-rolling mill chamber  72  after being sprayed onto the rolls of the rolling mill  76 , and a waste water drain is provided in order to drain to the exterior the cooling water from within the water tank  77 . The oxidation of the strip  10  in the pre-rolling mill chamber  72  is prevented by filling the pre-rolling mill chamber  72  with atmospheric gas.  
         [0116]    The partition door  70  is so constructed as to be internally water cooled. Hence a door roll  71  that causes the cooling water to flow inwardly is mounted rotatably in the lower end of the partition door  70 .  
         [0117]    The partition door  70  is set to an open state by a drive mechanism such as a fluid hydraulic device or an electric motor until the leading end of the strip  10  has passed, and the partition door  70  is set to a minimum opening sufficient to leave a gap of between 2 mm and 10 mm to the strip  10  during continuous casting operations.  
         [0118]    Moreover, the pass line for the strip  10  that is supported by the transport rolls  66  and  73  may be lowered by d 2  only from the partition door  70  to the entrance portion of the rolling mill  76 , in order to prevent the backflow of the cooling water after it has been sprayed onto the rolls of the rolling mill  76  into the pinch roll chamber  65 .  
         [0119]    The appropriate extent of the dip in the pass line may be between 10 mm and 150 mm per 1 m of distance travelled by the strip  10 .  
         [0120]    Moreover, disposed over the partition door  70  is a seal trough  80 , which holds water, is disposed in a fixed position in relation to the pre-rolling mill chamber  72 , and a seal plate  79  whose upper part is linked to the rising and falling part of the door opening and closing device  78  and whose lower end is always immersed in the seal trough  80 . Such seal trough  80  and seal plate  79  minimize the outflow of the atmospheric gas from the pre-rolling mill chamber  72  to the exterior.  
         [0121]    Moreover, Table 1 shows the changes over time in each portion when nitrogen gas is supplied at a rate of 500 Nm 3 /hr to a continuous strip casting device illustrated in FIGS.  1  to  4 , and when nitrogen gas is supplied at a rate of 2000 Nm 3 /hr and when nitrogen gas is not supplied to the device revealed by JP 8-300108.  
                                                                                                                                                                                               TABLE 1                                       JP 8-300108                            After 6                       hours                       from           Present invention           com-                After 1   After 6   After 1   After 6   mence-           hour   hours   hour   hours   ment of           from   from   from   from   casting,           com-   com-   com-   com-   with            mence-   mence   mence-   mence-   nitrogen           ment of   ment of   ment of   ment of   gas in-       Item   casting   casting   casting   casting   jection                    internal   10   Pa   10   Pa   2 Pa   1 Pa   5 Pa       pressure       (strip pass line)            Amount of   500   500   0   0   2000       atmospheric       gas injected       into casting        chamber and       cooling       chamber       (Nm 3 /hr)            Amount of   ≦100   ppm   ≦100   ppm   10%   18%   6%       oxygen in       casting       chamber            Temperature of   ≦200   ≦200    500   1000   1000       gas in casting       chamber (° C.)       Temperature of   ≦800   ≦800   1300   1100   1200       gas in cooling       chamber or       enclosure       (° C.)       Thickness of   ≦0.02   ≦0.02   20-30   30-50   8-20       oxidized scale       on strip at       cooling       chamber or exit       from enclosure       (μm)       Yield of cast   95   95   85   80   87       strip (%)                  
 
         [0122]    The device envisaged by the present invention and illustrated in FIGS.  1  to  4  possesses seal rolls  6   a  and  6   b  and is therefore able to maintain a low level of oxygen in the casting chamber, such that it is possible to restrict the formation of scale on the strip  10  due to oxidation to not more than 0.02 microns. It is also possible to provide the temperature within the casting chamber  4  to not more than 700° C.  
         [0123]    Thus in the present invention, the path of movement of the strip  10  that is transported from the casting rolls  3   a  and  3   b  is filled with a non-oxidizing or weakly reducing atmospheric gas, such as to enable an increase in the yield of the strip  10 .  
         [0124]    FIGS.  6  to  8  illustrate a modified embodiment of the invention in which the inter-chamber sealing system between the casting and cooling chambers has a pair of pivoting closures rather than sliding closures as in the previous embodiment. Moreover, in this modified construction, the casting chamber  4  does not enclose the casting rolls  3   a  and  3   b , but is sealed against the underside of those rolls so as to enclose the strip  19  as the strip emerges from the gap between the casting rolls  3   a  and  3   b.    
         [0125]    In the modified caster illustrated in FIGS.  6  to  8 , the casting chamber  4  is substantially sealed against the underside of those rolls by seal plates  81 . Further, in this modified construction the seal rolls  6   a  and  6   b  are mounted on a pair of pivoting flaps  82  hanging from horizontal pivots  83  about which they are pivotable from positions below the casting chamber  4  and open to the positions shown in FIG. 6 in which their lower parts are swung inwardly toward the strip  10  to close the transfer opening  84  through which the strip passes from the casting chamber  4  to the cooling chamber  15 .  
         [0126]    As shown in FIGS. 7 and 8, the pivot shafts  83  for flaps  82  extend to one side of the chambers  4  and  15 , where they are fitted with actuator links  85  by which they can be actuated by a pair of actuating cylinder units  86  to swing the flaps  82  between their retracted positions and the positions in which they tend to close the opening between the casting chamber  4  and cooling chamber  15 . In all other respects the casting installation may be generally in accordance with the previous embodiment as illustrated in FIGS.  1  to  4 .