Abstract:
An apparatus for starting the casting of a continuous casting system has a mold ( 2 ) and a strand guide ( 10; 10′ ) comprising drive and guide rollers ( 11, 12; 11′, 12′ ). Moreover, a dummy bar ( 22 ) that can be introduced into the mold ( 2 ) by the strand guide ( 10; 10′ ) and be withdrawn from said mold is provided. A safety device ( 20; 20′ ) for the dummy bar ( 22 ) has an element ( 25 ) that can be engaged, with form fit, with the dummy bar ( 22 ) and limiting the speed of the cold bar ( 22 ). It is thus guaranteed that a predetermined maximum strand speed can not be exceeded and that the dummy bar does not slide through.

Description:
FIELD OF THE INVENTION 
     The invention relates to an apparatus for starting the casting of a continuous casting system which has a mould and a strand guide comprising drive and guide rollers, with a dummy bar that can be introduced into the mould via the strand guide and be withdrawn from the mould. 
     BACKGROUND OF THE INVENTION 
     It is known for starting the casting of a continuous casting system to tightly close off the lower mould opening before and during the casting start-up process with a dummy bar in order to prevent steel poured into the mould from flowing out. The dummy bar is introduced into the mould via the strand guide provided for the casting strand and which comprises the drive and guide rollers. The steel poured into the mould is partially solidified so that a strand with a solidified edge zone and a liquid core is produced. As soon as this edge zone is of a sufficient thickness, the dummy bar (and after the latter the hot strand, additional steel then being poured into the mould) is drawn out of the mould, once again by means of the strand guide. 
     The movement of the dummy bar is determined by the drive torque generated by the drive rollers and by the contact force and friction coefficients between the drive and guide rollers and the dummy bar. Interruptions, such as for example with a power failure, can lead to an uncontrollable movement of the dummy bar. This can lead to damage to the system, both when running in and when starting the casting. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     The object forming the basis of the present invention is to provide an apparatus of the type specified at the start wherein the risk of the dummy bar sliding through is largely eliminated. 
     This object is achieved according to the invention by an arrangement including a dummy bar adapted to be introduced into and withdrawn from the mould and a safety device for the dummy bar which includes a toothed wheel operatively connected to the dummy bar in the manner of a rack and pinion or toothed wheel drive and which is configured to apply a braking force when a predetermined speed generated by the drive rollers for the dummy bar is exceeded. 
     Further preferred embodiments of the apparatus according to the invention form the subject matter of the dependent claims. 
     Since according to the invention a safety device is provided for the dummy bar which has an element which can be engaged, with form fit, with the dummy bar and limiting the speed of the dummy bar, it is guaranteed that a predetermined maximum strand speed can not be exceeded and the dummy bar will not slide through. The “form fit” engagement of the element of the safety device with the dummy bar means that the element of the safety device fits the form of, e.g., has a corresponding form as or shape to, a part of the dummy bar so that the element of the safety device can engage with the dummy bar. An example of a form fit is when the element of the safety device has the form of a toothed wheel that engages with teeth of the dummy bar in the manner of a rack and pinion or toothed wheel drive. 
     The element that can be engaged with the dummy bar is preferably in the form of a toothed wheel that is operatively connected to the dummy bar in the manner of a rack and pinion or toothed wheel drive. Upon exceeding the predetermined speed generated by the drive rollers for the dummy bar the toothed wheel element applies a braking force or a rotary resistance to the dummy bar. 
     Here the safety device advantageously comprises an autonomous, hydraulic circuit system with a pump, for example a toothed wheel pump (which is operatively connected to the toothed wheel element) and to a throttle. The practically resistance-free rotary resistance of the toothed wheel element during normal operation can be increased over the circuit system and over a transmission gearing when the dummy bar exceeds the speed due to sliding. 
     The safety device advantageously constitutes an autonomous system, for example independent of the roller drive, with which it is ensured that e.g. during a power failure and the loss of drive torque or contact force caused by the latter, no sliding through of the dummy bar takes place. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following the invention is described in greater detail by means of the drawings. These show as follows: 
         FIG. 1  shows a continuous casting system in diagrammatic form; 
         FIG. 2  is a perspective illustration of an exemplary embodiment of an apparatus according to the invention for starting the casting of a continuous casting system; 
         FIG. 3  shows the apparatus according to  FIG. 2  as a vertical cross-section; and 
         FIG. 4  is the top view of an apparatus according to  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows diagrammatically the structure of a continuous casting system  1  comprising a mould  2  cooled with water which is filled with liquid metal, in particular steel. A casting strand  3  is taken out of the mould  2  such as to form a shell which is a pre-profile. The casting strand  3  is conveyed away by means of rollers  11 ,  12  of a curved guide  10  and bent into the horizontal. As indicated by dashes in  FIG. 1 , the casting strand  3 ′ could also be led away vertically by means of a vertical strand guide  10 ′. 
     Whereas the rollers  11  disposed on the outside of the curved strand guide  10  and of the strand produced in the curved strand guide  10  are fixed guide rollers, the rollers  12  located on the inside of the curved strand guide  10  form the drive rollers and can be adjusted radially to the casting curve. 
     To one side the vertical strand guide  10 ′ also has guide rollers  11 ′ positioned securely, and to the other side perpendicular to the vertical casting direction adjustable drive rollers  12 ′. 
     As is known, a dummy bar is also moved and held over the strand guides  10 ,  10 ′, and this is used for starting the casting of the corresponding continuous casting system  1 ,  1 ′ and is used to tightly close off the lower mould opening  15  before and during the casting start-up process in order to prevent steel poured into the mould  2  from flowing out. After the steel poured into the mould  2  has partially solidified so that a strand with a sufficiently thick solidified edge zone and liquid core has been produced—the dummy bar introduced into the mould  2  by means of the strand guide  10  and  10 ′ is also drawn out again by means of the strand guide  10  and  10 ′ Here the movement of the dummy bar while introducing and while drawing out is determined by the drive torque generated by the drive rollers  12 ,  12 ′ and by the contact force and friction coefficients between the drive and guide rollers  11 ,  11 ′;  12 ,  12 ′ and the dummy bar. 
     Both for the continuous casting system  1  with the curved strand guide  10  and for the vertical strand guide  10 ′ a rigid dummy bar or a chain dummy bar can be used in a conventional manner. 
     According to the invention, both for the chain dummy bar conveyed through the curved strand guide  10  and for the rigid dummy bar conveyed through the vertical strand guide  10 ′ a safety device  20  and  20 ′ is provided which ensures that with a decline or loss of the contact force or the friction coefficient and with a decline or loss of the drive torque the dummy bar does not slide through, as this would inevitably lead to the continuous casting system  1  or  1 ′ being damaged. 
     The safety devices  20 ,  20 ′ indicated in  FIG. 1  are designed on the same principle. With the continuous casting system  1  provided with the curved strand guide  10  the safety device  20  is disposed on the inside of the strand guide  10 , in the same way as the drive rollers  12 . With the continuous casting system  1 ′ provided with the vertical strand guide  10 ′ the safety device  20 ′ is preferably disposed on the same side as the postionable rollers  12 ′. 
     In  FIGS. 2 to 4  the safety device  20 ′ provided for the vertical continuous casting system  1 ′ and co-operating with the rigid dummy bar  22  is shown, and is described in greater detail in the following: 
     The safety device  20 ′ according to the invention disposed on the same side as the drive rollers  12 ′ has an element  25  in the form of a toothed wheel which can be engaged, with form fit, with teeth  26  of the dummy bar  22  in the manner of a rack and pinion or toothed wheel drive. With the exemplary embodiment shown the teeth  26  are formed by a plurality of transverse pins. (When using the chain dummy bar moved within the curved strand guide  10  the element can be engaged, with form fit, with the individual links of the chain dummy bar). The toothed wheel element  25  is coupled into the teeth perpendicularly to the direction of casting (with the curved strand guide  10  radial to the casting curve) and when drawn out must be uncoupled again in good time from the upper end of the dummy bar  22  or from the dummy bar head so that the subsequent hot strand is not damaged. This takes place automatically, for example with the aid of controllable a knee lever system, not shown in the drawings. 
     The safety device  20 ′ further comprises an autonomous, hydraulic circuit system  40  having a hydraulic pump (which is operatively connected to the toothed wheel element  25 ) and a throttle (the circuit system is shown schematically in  FIG. 3  and its operative connection to the toothed wheel element  25  is depicted by the dotted line). If a speed generated by the drive rollers  12 ′ for the dummy bar  22  is exceeded due to sliding, the rotary resistance of the toothed wheel element  25  is increased by means of the hydraulic circuit system and by means of transmission gearing comprising further toothed wheels  27 ,  28 ,  29 ,  30  or rack and pinion teeth  31 , and so applies a braking effect to the dummy bar  22  in quadratic speed/rotary resistance dependency. 
     Since the safety apparatus constitutes an autonomous system, for example independent of the roller drive, it is ensured that the dummy bar  22  does not slide through for example with a power failure and loss of the drive torque or the contact force caused by the latter. 
     As already mentioned, the toothed wheel element  25  (and also the transmission gearing  27 ,  28 ,  29 ,  30 ,  31 ) can be positioned for the purpose of coupling and uncoupling perpendicularly to the casting direction (or radially to the casting arch). Independently of this, the whole safety device  20 ′ and  20  can be positioned in this direction—depending on the format of the casting strand  3  to be produced and of the corresponding blank bar, preferably together with the drive rollers  12 ′ and  12  positionable in relation to the securely positioned guide rollers  11 ′ and  11 . 
     Furthermore, in  FIG. 3  two pivotable protective caps  41 ,  42  are indicated which are illustrated in the open position in the engaged state of the toothed wheel element  25 . If this toothed wheel element  25  is drawn back with the safety device  20 ′, these protective caps  41 ,  42  are pivoted against the strand by a mechanism (not shown), and they then serve as a closed heat shield for the gear mechanism in this safety apparatus.