Abstract:
The invention relates to a strip-casting machine ( 20 ) for producing a metal strip. Said strip-casting machine consists of a pair of casting rolls ( 22, 24 ) arranged in side-by-side parallel relation of lateral sealing elements ( 25 ) that are provided with respective sealing plates ( 61 ) at both sides of the casting rolls ( 22, 24 ) and that adjoin the casting rolls. The contact pressure of the sealing plate ( 61 ) against the casting rolls ( 22, 24 ) and/or the frictional conditions between them can be measured. The sealing plates ( 61 ) at the front faces ( 22′, 24′ ) of the casting rolls ( 22, 24 ) are positioned at a distance of a few tenth of millimeters or so as to closely fit the front faces ( 22′, 24′ ) in the operational state, with our without contact pressure. The sealing plates are positioned in such a manner that also in the heated operational state the desired positions of the sealing plates relative to the front faces of the casting rolls are kept very precise.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention pertains to a process for operating a strip-casting machine for the production of a metal strip, with two casting rolls set up next to each other to form a casting gap and with lateral sealing elements, which comprise sealing plates on each side of and in close proximity to the casting rolls, where the pressure which the sealing plate applies to the casting rolls and/or the frictional conditions between these components are measured, and where the sealing plates are positioned with respect to the end surfaces of the casting rolls in such a way that the nominal position of the sealing plates with respect to the end surfaces of the casting rolls can be maintained with a very high degree of precision, even at the high temperatures of the casting operation. The invention also pertains to a strip-casting machine for implementing the method. 
     2. Description of the Related Art 
     In a strip-casting machine of the type in question according to EP-A 0,714,716, the device for sealing the sides of the casting rolls consists of refractory sealing plates, which are pressed against the end surfaces of the two casting rolls on each side to prevent the steel melt which has been poured in between the casting rolls from escaping toward the sides. Thus a metal bath is formed instead, as in a conventional mold. As pressure is exerted on these sealing plates, they are subjected to frictional wear as a result of the rotation of the casting rolls, this wear being accompanied by large thermal load caused by the molten metal. One of the main problems in a casting machine of this type is therefore to ensure that the lateral sealing elements offer a reliable seal during the entire duration of the casting operation. 
     In the case of casting rolls with small diameters in the range of approximately 500-800 mm, the seals to be provided for the narrow sides are proportionately smaller. Because of the small volume of the metal bath, however, the surface of the molten bath is unsteady. In the case of the large casting rolls with diameters of, for example, approximately 1,500 mm, the surface of the molten bath is calmer because of its larger volume. Although this is advantageous, larger and more complicated lateral sealing elements become necessary. As a result of manufacturing and installation tolerances, irregular wear, and differences in the degrees to which casting rolls are heated as a result of deposits, it is possible that the sealing edges or sealing surfaces of the rolls are not precisely aligned with each other. 
     In EP-A 0,692,330, the contact conditions between the sealing walls and the casting rolls are detected by measuring the applied pressure and the frictional conditions, and after these values have been compared with the nominal values, at least one of the casting parameters is adjusted as required. So that such adjustment can be made, each of the sealing walls is held by an arrangement consisting of a main carrier, which can shift in the axial direction of the rolls, and a carrier which is guided horizontally on the main carrier. With this arrangement and with this system for controlling the sealing walls, however, optimal conditions for a long-lasting, satisfactory seal between these sealing walls and the casting rolls cannot be created, especially when work is being conducted with casting rolls with diameters of 1 meter or more. 
     There is also another document, namely, Patent Abstracts of Japan, Vol. 016, No. 576 (M-13 45), Dec. 16, 1992 &amp; JP 4[1992]-224,052 A, which deals with the measurement of the friction between the end surfaces of the casting rolls of a strip-casting machine and with the appropriate adjustment of the applied pressure as a function of those measurements. To obtain the desired seal between the sealing plates and the end surfaces of the casting rolls, adjustable piston-cylinder units with a pressure control system for the pistons and with a distance sensor for the positioning of the pressure plates are provided. The seal of the end surfaces of the casting rolls by means of the sealing plates is no longer guaranteed by the control of the applied pressure, however, when the end surfaces of the casting rolls are no longer aligned with each other. 
     SUMMARY OF THE INVENTION 
     Proceeding from these known solutions, the present invention is based on the task of creating a method for operating a strip-casting machine of the general type indicated above, so that, by means of such a method, leak-proof conditions can be ensured at the lateral sealing elements throughout the entire duration of the casting operation even when casting rolls of the optimum diameter are used. 
     The task is accomplished according to the invention in that the positions of the sealing plates are measured in the direction of the casting roll axis, and in that at least one of the casting rolls can be adjusted, especially in the axial direction, so that the end surfaces of the casting rolls can be aligned with each other on the same plane as accurately as possible. 
     For a strip-casting machine, the task according to the invention is accomplished in that distance sensors are provided to measure the position of the end surfaces of the casting rolls in the axial direction of the rolls, and in that these distance sensors are in working connection with a device for axially displacing the casting rolls and for aligning the end surfaces of the casting rolls to be sealed with respect to each other. 
     With this strip-casting machine according to the invention, optimal lateral sealing of the casting rolls is achieved, which sealing function remains intact throughout the entire casting time even in the case of large casting rolls with diameters of more than 1 meter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     An exemplary embodiment of the invention and additional advantages of same are explained in greater detail below on the basis of the drawing: 
     FIG. 1 shows a section through a strip-casting machine with the lateral sealing elements according to the invention; 
     FIG. 2 shows a longitudinal section through a lateral sealing element according to FIG. 1; 
     FIG. 3 shows a section through the lateral sealing element along line III—III of FIG. 2; 
     FIG. 4 shows a block diagram of a monitoring system for the lateral sealing elements, including a schematic view and a top view of the lateral sealing element; and 
     FIG. 5 shows a partial longitudinal section through a casting roll. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a strip-casting machine  20  for producing a metal strip  15 , especially a steel strip, in a continuous casting process. This strip-casting machine  20  stands on a suggested steel structure  12  and is supplied with molten metal by a tundish vessel mounted above it, as known from conventional continuous-casting machines. It is advisable here for the discharge opening of the tundish vessel, through which the melt flows out, to have a stopper or the like which can seal the opening. 
     This strip-casting machine  20  consists primarily of two casting rolls  22 ,  24 , which are set up essentially parallel to each other with their rotational axes approximately on a horizontal plane. A lateral sealing element  25  can be pressed against each of the two end surfaces, as a result of: which an enclosed space is created with an open casting gap at the bottom. The casting rolls  22 ,  24  are supported rotatably at each end on a standard  32 , and each is driven in a controlled manner by a motor. The strip-casting machine  20  mounted on the suggested steel structure  12 ′ or the like is enclosed in this case by a housing  30 , so that the strip-casting operation can proceed under an inert gas, sealed off from the air. On the top of the housing  30 , sliding doors  35  are provided so that the housing can be opened and closed. 
     Each of these lateral sealing elements  25  has a sealing plate  61 , which can be pressed by a pressing means against the end surfaces of the casting rolls  22 ,  24  to produce a mechanical seal. These triangular sealing plates  61 , made of a refractory material, cover approximately the upper part of the end surfaces  22 ′,  24 ′ of the casting rolls. 
     According to FIGS. 2 and 3, each sealing plate  61  is mounted so that it can be shifted by the pressing means against the end surfaces  22 ′,  24 ′ of the casting rolls and is also supported in a floating manner by an articulation means—in the present case by a ball joint  81 —so that the position can be kept constant and the sealing surface  61 ′ can always be kept exactly parallel to the two end surfaces of the casting rolls, which lie on the same plane. 
     Three cylinders  71 , each with a piston  72 , which can be shifted in a direction approximately perpendicular to the sealing plate  61 , are preferably provided, which exert an approximately constant, controllable pressure on the sealing plate  61  by way of a support frame  64 ,  65  in the manner of a three-point support, where each of these cylinders  71  advisably exerts its force at one of the three corner areas of the sealing plate  61 , which, because of the arrangement of the casting rolls, is approximately triangular. 
     According to the invention, the sealing plates  61  are positioned to be less than a few tenths of a millimeter away from the end surfaces  22 ′,  24 ′ of the casting rolls  22 ,  24  or actually to rest against these end surfaces  22 ′,  24 ′, either with or without an applied pressure, so that, even at the high temperatures of the casting operation, the nominal position of the sealing plate in question with respect to the end surfaces of the casting rolls can be maintained with a very high degree of precision. 
     By positioning the sealing plates  61  according to the invention with respect to the end surfaces  22 ′ of the casting rolls  22 ,  24  in this way, the two components can be adjusted optimally to each other, regardless of whether the sealing plates are positioned without contact with the casting rolls or whether they advantageously rest against them, with or without applied pressure. Thus an optimum sealing effect can be achieved, and in addition the wear of the sealing plates as well as that of the adjacent end surface areas of the casting rolls is reduced to a minimum. 
     The support frame  64 ,  65  holding the sealing plate  61  is supported on a butt plate  80  by way of articulated connections  66 ,  67 . The butt plate is supported in turn in a floating manner on the carrier element  41  by the ball joint  81 ; the support frame  64 ,  65  is pressed at all times against the pistons  72  of the pressing means by an elastic connection, namely, an adjustable tension spring  68  with anchor, located between the frame and the butt plate  80 . Each of the articulated connections is formed by an approximately horizontal articulated lever  66  and a vertical articulated lever  67 , these articulated levers  66 ,  67  also being spherically supported at one end on the support frame  64  and at the other end on the butt plate  80 , so that the sealing plate  61  can be moved both horizontally and vertically in a plane parallel to the butt plate  80 . With this optimum support system for the sealing plate  61 , it is possible permanently to exclude the possibility that the sealing plate can become jammed or locked even after the entire lateral sealing assembly has become hot. 
     A projecting centering pin  82 , furthermore, is provided on the ball joint  81 , by means of which the carrier element  41  can be centered with respect to the device  85 . A cam  83  or the like makes it possible to center the lateral sealing element  25  vertically with respect to the carrier element  41 . A flexible retaining element  84  is provided between the butt plate  80  and the top part  41 ′ of the carrier element  41 . A stop screw  86  on this top part  41 ′ limits the range over which the plate  80  can swing. 
     FIG. 1 also clearly shows that the carrier element  41  holding the lateral sealing elements  25  is associated with a manipulator  40 , by means of which the lateral sealing element in question can be moved laterally away from the casting rolls  22 ,  24  and returned. After the lateral sealing elements  25  have been brought laterally up into position next to the casting rolls  22 ,  24 , they are centered by a device  85  mounted on the standard  32  of the casting rolls, and their cylinders  71  are connected to their respective drive elements. Conversely, after the device  85  has been disconnected, the lateral sealing elements  25  can be moved away by the manipulator for maintenance. The device  85  is mounted on the standard  32 , but it could also be mounted on the manipulator. 
     A monitoring and control system according to FIG. 4 for these lateral sealing elements  25  makes it possible to adjust the sealing plates  61  with respect to the casting rolls  22 ,  24  in optimum fashion and also to monitor the system for problems, leaks, etc., both for the sake of prevention and for the sake of early detection in conjunction with an on-line error correction system, especially in regard to the sealing plate. 
     The strokes of the pistons of the cylinders  71  are measured by the measuring elements  151 ,  152 ,  153 , and the positions of the end surfaces of the casting rolls are measured by the distance sensors  127 ,  128 ,  129 . These measurements are transmitted to a receiver  150 , and from there they are sent to an evaluation unit  100 . The distance sensors  127 ,  128 ,  129  make it possible to detect the extent to which the casting rolls have worn down or expanded. On the basis of the stroke measurements of the pistons, it is possible to determine the position of the sealing plate  61  and, in cases where the plate is held under pressure, to determine the extent of its wear, which occurs in a controlled manner during the casting operation as a result of the rotating casting rolls and the resulting sliding friction. If the plate is wearing down too quickly, it is advantageous to lower the pressure being applied to it and vice versa. 
     This monitoring and control system also comprises three temperature probes  111 ,  112 ,  113 , by means of which the temperatures at the contact points of the sealing plate  61  with the casting rolls  22 ,  24  in the end areas of the sealing plates  61  can be measured. These temperatures are then recorded by a receiver  110  and preferably compared with a nominal process in a central evaluation unit  100 . As long as the temperatures at these contact points are below those of the melt, it can be assumed that operations are proceeding normally. But as soon as only one of the these temperatures rises disproportionately, it must be assumed that there is a leak between the sealing plate  61  and at least one of the casting rolls  22 ,  24 . 
     The computer  100  then immediately issues a command via line  101  to close the stopper on the tundish vessel, and the flow of molten metal between the casting rolls is thus stopped. 
     Another temperature probe  114  is installed approximately at the center of the holding frame  65  of the sealing plate  61 . The temperature measured here makes it possible to draw conclusions concerning the functionality of this holding frame  65  and especially concerning any deformations it may have undergone. 
     Three pressure cells  121 ,  122 ,  123  for the cylinders  71  are also provided in this monitoring system. In conjunction with an appropriate receiver  120 , these pressures, which it is also advantageous to measure continuously, can be compared in an evaluation unit with a nominal trend of the cylinder pressures and thus used to regulate these pressures. 
     Strain gauges  131 ,  141  on the articulated levers  66 ,  67  are also provided within the scope of the invention, which, together with the receivers  130 ,  140 , can be used to determine the change in the forces and thus in the frictional conditions between the sealing plate  61  and the casting rolls  22 ,  24 . An increase in the coefficient of friction without any change in the applied pressure can indicate an increase in the wear of the sealing plate  61 , whereas a decrease logically suggests a decrease in the perpendicular force component, on the basis of which a correction must be made in the form of an increase in the applied pressure. 
     By measuring the extension of the horizontal articulated lever  66 , it is possible in particular to determine when the frictional force between the one casting roll  22  and the sealing plate  61  is different from that between the other casting roll and the sealing plate. When the frictional forces are balanced, the force at this articulated lever  66  is approximately zero. When these frictional forces are out of balance, the one or the other cylinder  71  can be actuated via the evaluation unit and a control valve  105 , the pressure being thus adjusted to bring the horizontal force back to zero again. 
     In another variant, the sealing plates  61  of refractory material are pressed by the cylinders against the end surfaces  22 ′,  24 ′ and thus ground in before casting begins. By means of these strain gauges  131 ,  141 , the frictional forces between the casting rolls and the sealing plate can be determined and adjusted to a defined value. 
     Another measuring instrument which can be used to advantage is a vibrometer  161 , which can be installed between the sealing plate  61  and the holding frame  65  to measure the vibrations which occur during the casting operation. With this vibrometer  161  and the signal pickup  160 , an operating problem can be quickly detected on the basis of a deviation between the actual vibrations and the nominal ones, such deviation occurring, for example, when there is a leak between one of the casting rolls and the casting plate, which necessarily changes the intensity of the vibrations produced between them. In the case a vibration slowly changing to, for example, a level approximately 50% below the normal vibration level, a correction of the applied pressure can bring the measurement back toward the nominal value. In principle, this vibration measurement leads to the improved utilization or to a longer life-span of the refractory sealing plate  61 . 
     The values are stored in this monitoring and control system, and they can therefore be kept in long-term memory by the evaluation unit  100 . Statistical values can be derived from them, which can be advantageously used on-line. 
     It is also conceivable that the automatic temperature control  110 ,  100  can be used to adjust the control  106  of the heating devices  155  (shown in FIG. 4) for the lateral sealing elements which are standing by to serve as replacements. 
     FIG. 5 shows a device for the axial displacement and alignment with respect to each other of the end surfaces  22 ′ of the casting rolls  22  to be sealed. The casting roll  22  consists of a stationary axle  1  with axle journals  2 , which are supported on a stand  3 . The casting roll  22  comprises a ring-shaped support element  4 , which is connected to the cylindrical jacket  5  by means of a wedge-type clamping device  6 . The jacket  5  is provided around its circumference with axially oriented cooling bores  7 , which are connected to additional bores  9 ,  10 ,  11  in the support element  4 , in the axle  1 , and in the stand  3 , which supply and carry away a coolant. The jacket  5  and the support element  4  are driven by a motor/transmission device (not shown). So that the end surfaces  22 ′ of the casting roll  22  can be aligned on the same plane with the end surfaces of the other casting roll (not shown), the jacket  5  is mounted on the stationary axle  1  with freedom to shift position together with the support element  4 . The displacement is accomplished with a ring-shaped, double-acting piston-cylinder unit  13 , which is connected to both the support element  4  and the axle  1  and is mounted at the end of the casting roll  22 . A piston ring  14  on the support element  4  engages with clearance in a circumferential groove  16  in the axle  1 , so that cylindrical chambers  17  are formed on both sides of the piston ring  14 . Pressure can be built up in either of these chambers by a pressure medium via pressure lines p 1  and p 2 . As a result of the difference in pressure between the chambers, the support element  4  and thus the end surface  22 ′ of the casting roll  22  are shifted by a maximum value of, for example, 8 mm toward one side or the other. 
     In an automatic control process carried out by means of the evaluation unit  100 , the positions of the casting rolls in the axial direction are measured by the distance sensors  127 ,  128 ,  129 , and, if there is a deviation between the two casting rolls  22 ,  24 , a correction is made so that the end surfaces  22 ′,  24 ′ lie on the same plane again on the one or on the other side of the casting rolls. This is accomplished by actuation of the piston-cylinder unit  13  by means of a valve (not shown). 
     If one of the casting rolls, by reason of wear, manufacturing tolerances, or some other reason, is shorter than the other roll by an amount of, for example, 0.3 mm, it is highly advantageous to position these casting rolls so that half of the total difference in length (e.g., 0.15 mm) between them is present on each side. This provides another effective means of avoiding leaks. 
     The invention has been sufficiently described on the basis of the exemplary embodiments described above, it could also be embodied in other variants. Thus, for example, a lateral sealing element  25  comprising a mechanical and/or a magnetic seal could be provided. To simplify the design of the monitoring system, it would be possible to provide only one or two measuring elements instead of three.