Abstract:
The reliable sealing of a gap ( 10 ), between a roller front face ( 7 ) and a side seal ( 3 ) on a roller-strip-casting machine is achieved by the generation of an electrical eddy field in the region of the gap ( 10 ), such as to produce a local gradient field ( 13 ). The eddy currents generated in the metal melt for casting prevent the ingress of the metal into the gap ( 10 ) or eject the metal from the gap ( 10 ). The risk of escape of liquid metal is essentially eliminated and the formation of ridges on the narrow edge of the metal strip avoided.

Description:
BACKGROUND OF THE INVENTION 
     The invention concerns a method for sealing a gap between an end face of a roll and a side seal of a roll strip-casting machine and a device for carrying out this method. 
     It is well known that, in a twin-roll strip-casting machine for casting metal strip, especially steel strip, side seals, preferably in the form of ceramic plates, can be installed in the region of the end faces of the casting rolls. A sealing gap, whose capillary action is used to produce the seal, is formed between the given end face of the roll and the given side seal. However, extremely small fluctuations in the capillary gap can cause the low-viscosity, molten steel to penetrate the gap, which results in the formation of flash on the narrow edge of the steel strip, which gives rise to the risk of unacceptable wear of the casting rolls and/or the side seals and may also damage the rolls of a downstream rolling stand. Damage may also be caused by the potential emergence of the molten steel. The irregularities on the narrow edge of the strip must be removed by cutting off the edges, which results in both extra work and reduced output. 
     SUMMARY OF THE INVENTION 
     The objective of the present invention is to propose a method of the aforementioned type and a device for carrying out this method, by which the risk of emergence of molten metal is largely eliminated, and the formation of flash on the narrow edge of the metal strip is avoided. 
     In accordance with the invention, as a result of the fact that a rotational electric field is generated in the region of the gap in such a way that a local gradient field is produced, and the eddy currents generated in the molten metal to be cast prevent the molten metal from penetrating the gap or force the molten metal out of the gap, the capillary action in the sealing gap is effectively supported, a reliable seal is ensured, and thus better quality of the edges of the cast strip and a reduction of the scrap are achieved. A special advantage here is the relatively small power consumption for generating the local rotational field. 
     Preferred refinements of the method and device are the objects of the dependent claims. 
     The invention is explained in greater detail below with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a schematic representation of the principle of the invention for sealing a gap between the end face of a roll and a side seal. 
         FIG. 2  is a schematic representation of the arrangement of a number of magnetic elements for inducing a rotational electric field, which are arranged along the end faces of the rolls in the region of the mold of a strip-casting machine. 
         FIG. 3  shows a first embodiment of one of the magnetic elements in  FIG. 2  in the cross section along line A. 
         FIG. 4  shows a second embodiment of one of the magnetic elements in  FIG. 2  in the cross section along line A. 
         FIG. 5  shows a third embodiment of one of the magnetic elements in  FIG. 2  in the cross section along line A. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a partial section of a casting roll  1  of a twin-roll strip-casting machine for casting a metal strip, especially a steel strip. This casting roll  1  is also schematically indicated in  FIG. 2 , along with a second casting roll  2 . A mold space (labeled  5  in  FIG. 2 ) for the molten metal is bounded by the two casting rolls  1 ,  2 , on the one hand, and by two side seals  3  installed in the region of the end faces of the rolls  1 ,  2 , on the other hand. A through-gap  4  ( FIG. 2 ), through which the metal strip that has been produced is carried away, is present between the two rolls  1 ,  2 , which can be rotated about horizontal axes of rotation D ( FIG. 1 ). 
     As shown in  FIG. 1 , each of the rolls  1 ,  2  consists of a basis material  5 , preferably copper, and is provided with a surface layer  6 , which consists of a wear-resistant material. The side seals  3  are generally composed of a ceramic material. 
     As  FIG. 1  shows on an enlarged scale, a sealing gap  10  is present between an annular end face  7  of the roll  1  and the corresponding side seal  3 . To prevent molten metal from penetrating this sealing gap  10  (thereby producing flash on the narrow edge of the metal strip) or even escaping through this sealing gap  10 , not only is the capillary action in this sealing gap  10  utilized, but also, in accordance with the invention, a rotational electric field is induced in such a way that a local gradient field is produced in the region of the sealing gap  10 . This local gradient field is schematically indicated in  FIG. 1  and is labeled with reference number  13 . It results in a force that opposes the penetration of the molten metal into the sealing gap  10 . 
     To induce the local rotational electric field, several magnetic elements  15  are arranged in succession along the circumference of the roll in the region of the mold space  5  and the associated sealing gap between each end face  7  of a roll and the associated side seal  3 . The magnetic elements  15  are permanently arranged and are preferably mounted on the side seals  3 , so that, during a roll change, they can be easily removed, together with the side seals  3 , by means of a manipulator, which is not shown in the drawing. The design of the individual magnetic elements  15  is shown in  FIGS. 3 to 5 . Of course, other designs of the magnetic element would be possible in addition to the three embodiments shown here. 
     In accordance with the invention, it is advantageous to arrange the individual magnetic elements  15  in a row as modules distributed along the particular roll circumference from top to bottom as far as the through-gap  4 . They cover approximately the entire length of the side seal  3 , which runs along the given casting roll  1 ,  2 . 
     In the embodiment shown in  FIG. 2 , the two lowermost sets of magnetic elements  15 ′,  15 ″ of the two rolls  1 ,  2 , which are located in the immediate vicinity of the through-gap  4 , are combined into single magnetic elements. The individual magnetic elements  15 , which are suitably designed accordingly, are preferably provided with independently controllable power supplies, and they are independently controlled according to process requirements and pressure level. Preferably, opposing magnetic elements  15  located at the same height (i.e., the same distance from the through-gap  4 ) in front of the end face of the two rolls  1 ,  2  are controlled together in each case. 
     As is apparent from  FIGS. 3 to 5 , each magnetic element  15  comprises a laminated iron body  16  composed of essentially L-shaped plates or an iron body  16  produced by a sintering process and an associated coil  17 . These are used to produce an alternating magnetic field in the frequency range of 300 to 3,000 kHz. This alternating field induces the formation of electric eddy currents, which flow through the molten steel (or other electrically conductive metal) and, as has already been mentioned, locally opposes the penetration of the molten metal into the sealing gap  10 . The magnetic elements  15  distributed along the circumference of the given roll from top to bottom immediately adjoin each other. In a preferred design, the given iron body  16  has half the length in the coil region  16   s , as viewed in the circumferential direction of the roll  1  or  2 , and the L-shaped plates are layered in an overlapping fashion in the coil region, so that the same cross section is formed over the entire length in the field direction of the iron body  16  as inside the coil  17 . 
     The upper region  16   o  of the iron body  16  is supported from the outside on the side seal  3  and mounted by means that are not shown. A lower region  16   u  is joined with a forward region  16   v  of the iron body that extends upward to the sealing gap  10 . To intensify the gradient formation of the rotational electric field in the active air gap between the parts  16   o ,  16   v  of the iron body and in the sealing gap  10 , a “field guide” ( 20 ) is built into the end face  7  of the roll. The field guide is formed by a ferromagnetic, laminated, or sintered ring or by one or more ring segments. An upper surface  18  of the region  16   v  of the iron body runs parallel to a surface  19  of the field guide  20  and the roll end face  7 , which results, for example, in the formation of an obliquely running part  10 ′ of the sealing gap  10 . 
     Copper plates  22 ,  23 , which likewise influence the gradient formation of the rotational electric field  13  and force the stray field in the direction of the sealing gap  10 , are preferably installed inside the iron body  16 . If necessary, two copper plates  22 ,  23  are present. They simultaneously serve as cooling elements. 
     As a comparison of  FIGS. 3 to 5  shows, the iron bodies  16 , the side seals  3 , the field guides  20 , and the copper plates  22 ,  23  may have different cross-sectional shapes and dimensions. Suitable field guides could also be installed in side seals  3  (instead of on the end face  7  of the roll or in addition to this).  FIG. 5  shows that the gradient formation in the region of the sealing gap can also be optimized by modifying the air gap by installing other, additional oblique surfaces  24  and  25  on the iron body  16 . 
     The invention is sufficiently defined with the embodiments explained above. However, it could also be illustrated in other variants. For example, the number of magnetic elements  15  provided per row could be varied, i.e., in principle, it would be possible to provide only one magnetic element or to provide more than eleven (as shown). 
     The particular gap  10  between the end face  7  of the roll and the side seal  3  may be formed either by mutual positioning or by arrangement of the two some distance apart.