Patent Publication Number: US-6216769-B1

Title: Process for guiding a slab and slab-guide

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 371 of PCT/DE97/06342 filed Jun. 23, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to a process for guiding a strand in a continuous casting plant with a soft reduction zone in which hydraulic servo units continuously adjust the gap between oppositely located strand guide rollers, and to the corresponding strand guide for performing this process. 
     2. Description of the Prior Art 
     Continuous casting plants, especially continuous casting plants for steel, use rollers to guide the strand; these rollers limit the thickness of the strand which is not yet completely solidified and prevent bulging of the strand shell due to ferrostatic internal pressure. 
     Usually, groups of at least 4 pairs of rollers are combined in guide matter segments. The strand guide rollers arranged above the strand are fastened to a movable upper part, of the segment, while the strand guide rollers located below the strand are arranged at a fixed lower part, of the segment. The fixed part and movable part of the individual segment are connected with one another via 4 tension cylinders. These clamping cylinders, as they are called, pull the movable top part of the segment on spacers, so that the desired gap width results between the oppositely located rollers. This gap width of a segment of this type corresponds to the strand thickness. 
     A strand guide of the type mentioned above is known from DE 40 22 871 C2, wherein frame parts which carry the strand guide rollers that are located opposite to one another can be clamped relative to one another by means of a displacement device on one part of the segment until support devices contact counter-support devices which are provided with supporting surfaces located at different height positions and with counter-supporting surfaces, on the other part of the segment. The individual support disks are adjustable by means of rotation. 
     A device of this kind can only adjust a fixed gap width which cannot be readjusted during casting. 
     However, modern process technologies for improving product quality require that the gap width for a segment is changed during the casting process. In particular, soft reduction in the region of the lowest point of the liquid pool requires a wedge-shaped adjustment of the strand and a variable change in gap width of the corresponding segment. 
     A simple possibility for changing the gap width of segments with 4 clamping cylinders can be achieved in that the cylinders are constructed with position regulation as servo-hydraulic axles. In a solution of this type, the spacers, as they are called, can be dispensed with. The gap width of the segment is predetermined by a corresponding preset reference value for the 4 position-regulated piston-cylinder units. In so doing, the two servo units at the run-in end of the segment and the two servo units at the run-out end of the segment are regulated so as to be synchronized. Due to the use of a total of 4 servo units, this system is statically redundant. 
     DE 41 38 740 A1 discloses a process for the continuous casting of slabs or ingots in a continuous casting plant with a soft reduction zone which has rollers which can be continuously adjusted individually or as segments relative to one another by means of hydraulic cylinders and, with respect to their gap width, by means of spindles. The spindles can be moved to a desired gap spacing such that load is reduced. The movable part of the segment which is held in its position by four hydraulic cylinders is also statically redundant. 
     SUMMARY OF THE INVENTION 
     Therefore, it is the object of the invention to provide a process and a corresponding device for guiding a strand in a continuous casting plant in which the static redundancy brought about by the four-point support of the strand segment is eliminated and the tensioning of the movable parts of the segment brought about in this way is reduced. 
     This object is achieved by a process for guiding a strand having a soft reduction zone in a strand guiding segment of a continuous casting machine, the strand guiding segment having four servo piston cylinder units for adjusting a gap between oppositely arranged guide rollers of the strand guiding segment. In the process, two adjacent ones of the four servo piston-cylinder units are hydraulically linked and adjusted to the strand as a unit and the remaining servo piston-cylinder units are independently adjusted to the strand. The objects of the invention are also met by a strand guide for use in a continuous casting plant including a strand guide segment having oppositely arranged strand guide rollers defining a gap through which the strand is guidable. The strand guide segment includes four servo piston-cylinder units operatively connected for continuously adjusting the gap, wherein two of the servo piston-cylinder units are adjustable as a unit by a shared servo valve and the other of the four servo piston-cylinder units are independently adjustable by separate servo valves. 
     The subclaims indicate advantageous further developments of the invention. 
     According to the invention, in a strand guiding segment with 4 servo units, two adjacent servo units are linked with one another hydraulically and the rest of the servo units remain independently adjustable. As a result of the parallel connection of two cylinders to form a unit corresponding to communicating pipes with only one position regulator, the plane maintained by four cylinders is statically determinate and is transformed into three-point support. 
     The pair of cylinders connected with only one servo valve has one position transmitter per cylinder. A mean value is taken from the signals of the individual position transmitters of the servo piston-cylinder units which are combined with one another and this means value is supplied, as a position adjustment value, to the shared position regulator acting on both cylinders. 
     In an advantageous construction, the servo piston-cylinder units of the run-in or run-out of the strand guide segments are linked with one another. Each of the strand guide segments for a strand guide is preferably linked in the same way as the others; for example, all servo units connected at the run-in end are connected to a position regulator and all servo units connected at the run-out end are driven independently. 
     When a defined path value, for example, a distance that can be predetermined, is exceeded when determining the average value or other technical data pertaining to continuous casting, another pair of servo piston-cylinder units can be linked with one another. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An example of the invention is shown in the accompanying drawing. 
     FIG. 1 is a schematic view of a strand guide with servo units of a segment according to an embodiment of the present invention; and 
     FIG. 2 is a schematic view of a segment of a strand guide with servo units linked at a strand run-in end and strand end of the segment. 
    
    
     FIGS. 1 and 2 show a strand guide segment  81  with strand guide rollers  82  to  87 . The strand guide direction is indicated by an arrow A. 
     The upper part and the lower part (not shown in the drawing) of the strand guide frame  81  are linked with one another by four servo piston-cylinder units  11 ,  15 ,  21 ,  25 . 
     Referring to FIG. 1, the servo piston-cylinder units  11 ,  15 ,  21 ,  25  have position transmitters  12 ,  16 ,  22  and  26  which are connected with position regulators  71  and  72  by measurement lines  75  to  78 . 
     In FIG. 1, the piston surface ends of the servo piston-cylinder units  11 ,  15 ,  21  and  25  are connected via hydraulic lines  31  to  38  and the other ends of the servo piston-cylinder units  11 ,  15 ,  21  and  25  are connected via hydraulic lines  41  to  48 . The hydraulic lines  31  to  38  for the piston surfaces can be blocked by locking elements  51  to  58  and the hydraulic lines  41  to  48  of the ring surfaces can be blocked by locking elements  61  to  68 . 
     In the present schematic circuit, servo piston-cylinder unit  11  can be driven individually by servo valve  13  and servo piston-cylinder unit  15  can be driven individually by servo valve  17 , while, in the run-out, servo cylinder units  21  and  25  are linked jointly with servo valve  27  because locking elements  53 ,  57 ,  58 ,  63 ,  67  and  68  are closed and locking elements  56  and  66  are open. 
     In FIG. 2, servo piston-cylinder units of the run-in end of a segment  11 ,  15  are linked via hydraulic lines  31 ,  41  and servo piston cylinder units of  21 ,  25  of the run out end of the segment are linked via hydraulic lines  32 ,  42 . 
     In the run-in region, servo valves  13 ,  17  can be linked with a servo piston-cylinder unit  11  and  15 , respectively when the locking elements  53 ,  63  are closed, or each can be linked with both servo units  11  and  15  when the locking elements  53 ,  63  are open. In order to connect a servo valve  13  or  17  to the servo piston-cylinder units  11  and  15 , the locking elements  53 ,  63  are opened and the servo valve which is not in operation is blocked by suitable hydraulic units. 
     When connecting a servo valve  13  or  17  to both servo piston-cylinder units  11 ,  25 , this servo valve  13  or  17  is connected with position regulators  73  or  74  and, when connected jointly with the two position transmitters  12  and  16 , the individual position regulators  73  or  74  are linked by measurement techniques via the measuring lines  75  or  76 . 
     In the run-out end of the segment of the strand guide frame  81  in FIG. 2, only an individual servo valve  24  is provided for the servo piston-cylinder unit  21  and  25 . This servo valve  24  is linked with a position regulator  72  which communicates via measurement technique with the position transmitters  22  and  26  via measurement lines  77  and  78 .