Abstract:
For a further development a device for continuous casting of metal, in particular steel, with a metal mold with mold walls ( 1,18 ) and a mold cooling device and which can remove high thermal flows and can be subjected to thermal loads and, thereble, is suitable for use at high speeds, at least one mold wall ( 1,18 ) of the mold of this device should include a steel wall ( 2 ) and a support mesh ( 3 ) for this wall and the device further should be provided with magnetic field generator ( 3.2 ) for generating a magnetic field ( 3.1 ) acting on the mold steel wall ( 2 ) via the support mesh ( 3 ) for attracting the mold steel wall ( 2 ) to the support mesh ( 3 ), with the mold cooling device comprising spray cooling means.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a device for continuous casting of metal, in particular steel, and including a metal mold with mold walls and a mold cooling device. Such a device serves for casting strands of different sizes, e.g., slabs, thin slabs, blooms, or beam blanks (dog bones). Here, the mold itself or the strand can oscillate, as during horizontal continuous casting. The mold itself, however, is arranged at a predetermined location and, therefore, can be called a continuous casting mold. 
     2. Description of the Prior Art 
     Such a mold, as a casting mold for continuous casting plants, consists either of mold plates, namely, of two plates for the mold broad sides and two plates for the mold narrow sides, or of mold tubes. 
     Such mold plates or mold tubes are formed of copper and have, as a rule, a thickness from 10 to 50 mm between the water cooling side and a side adjacent to the steel melt. 
     The selection of the copper plate thickness depends on the thermal load or the thermal flow measured in MWh/m 2  or MW/m 2 . Thus, continuous casting plants with a mold for slab sizes with a thickness greater than 150 mm and width 3 m, with a casting speed of maximum about 2.5 m/min, have a thermal flow of maximum 2 MW/m 2 . The thickness of the copper plates of the mold lies between 25 and 50 mm. In comparison, the thin slabs, which are cast with a casting speed up to 10 and in the future up to 15 m/min, have a thermal flow of maximum 4-5 MW/m 2  and copper plate thicknesses from 10 to 25 mm. 
     In order to match the increased thermal flow with the increased casting speed, the copper wall must always be thinner with the intensification of water cooling. This is difficult because a thinner mold wall always withstands worse high water pressures of 5-15 bar, which are necessary for a corresponding water velocity of 5-15 m/sec, without being deformed. An additional drawback consists in that the thin copper plates lose their rigidity when the recrystallization temperature exceeds its threshold at a too high thermal load of the cold-rolled copper. Besides, there is a problem of mounting of very thin copper plates on the mold frame. Usually, the mold plates are secured on a water box or a mold frame with bolts which are secured into the plates with their threaded section. This is not possible with very thin plates; in this case, the bolts must be welded to the copper plates. 
     An object of the invention is to so improve the devices of the above-described type so that the above-mentioned drawbacks are eliminated despite the increase of the casting speeds. In particular, a device for continuous casting with a mold should be provided which is capable of leading away of high thermal flows and can, therefore, be subjected to high thermal loads. Also the assembly should be improved. 
     SUMMARY OF THE INVENTION 
     This object is achieved by a device with the features of claim  1 . Advantageous further developments are described in the sub-claims. 
     According to the invention, it is proposed that at least one mold wall includes a steel wall and a support mesh for the steel wall, that a magnetic field generator for generating a magnetic field is provided, which acts on the steel wall via the support mesh, and that the mold cooling device includes a spray cooling device. 
     The foregoing features permit to provide a mold having a thin mold wall with a high and controllable heat dissipation characteristics even at high casting speeds. The mold wall is formed, on one hand, of a steel wall facing the metal melt and, on the other hand, of a support mesh for stabilizing the steel wall. Because of magnetic attraction forces, the steel mold wall can be easily mounted. In addition, such a mold has a particular advantage consisting in that the steel mold wall, which is wearable because of its exposure to the metal melt, if needed, can be, contrary to an expensive copper wall, rapidly and simply replaced without a high-quality treatment, while the used one is “thrown away”, i.e., is subject to a steel-recycling process. With the contemplated double wall, which consists of a thin steel wall and a support mesh, a simple and relatively inexpensive mold spray cooling can be used. In order to avoid high mold cooling water pressures, e.g., of 15-20 bar, the spray cooling takes place in open chambers or passages left by the support mesh, i.e., the thin steel wall is directly cooled, while being provided, despite this, with a relatively high support. With the spray cooling, the use of splash water becomes possible. Overall, along with a high efficiency of heat dissipation, a simple mold construction and, therefore, a relatively inexpensive mold is obtained. The inventive solution provides a mold that has a thermal conduction which otherwise would have required a copper plate thickness of 10 mm or more, and that can be easily mounted on a base frame, while permitting water cooling and being, at the same time, very economical. 
     The steel mold wall according to the present invention has preferably a thickness between 0.5 and 5 mm and corresponds, in its effectiveness, to a copper plate having a thickness of 10 mm, while having a definite constructional and economical advantage. 
     Preferably, the support mesh has a support wall with chambers formed therein, so that separate chambers or passages of the mesh are surrounded by wall webs of the support wall, with the magnetic field being introduced in the mold wall via the support wall. 
     The spray-cooling for cooling the mold wall includes, preferably, spray nozzles extending in the chambers of the support mesh at a side of the support mesh remote from the steel wall, i.e., through the freely accessible chamber regions or openings in the mesh. These spray nozzles for mold spray-cooling and the conduits for the cooling medium, in particular water, are integrated, completely or partially, in the support walls of the support mesh. 
     The advantage of the proposed spray cooling consists in that the intensity of the spray cooling is functionally adjusted in accordance with energy flow in the mold wall over the mold height. The energy flow has a thermal maximum somewhat in the upper third of the mold. With the spray cooling with separate, arranged one above the other, nozzles, the intensity of cooling can be adjusted in a controlled manner and, thereby, to be adapted to an energy flow with energy maximum or to an energy unit, as it is in this point a more intensive cooling takes place. 
     According to a further development of the device, it is contemplated to provide a device for controlling the surface temperature of the side of the steel mold wall adjacent to the liquid metal in order, when necessary, to adapt the spray cooling, by using a regulating mechanism, to fluctuation of the surface temperatures. 
     In addition to the proposed, according to the invention, attachment of the steel mold plate to the support mesh, the mold plate can be additionally secured mechanically. To this end, it is proposed to use a fixation device for securing the steel mold wall, e.g., a broad side in the middle of the broad side with respect to the mold height. In addition, the steel mold wall can be horizontally secured at the mold inlet or mold outlet. In addition to the broad sides, if necessary, the narrow sides can be secured in case they are likewise stabilized by a support mesh. 
     According to a particularly advantageous embodiment, the support walls of the support mesh are provided, at their ends facing the steel mold wall, i.e., in their fore-side or their head with a ball that serves as a (ball) bearing for a free, heat-dependent, movement of the steel mold plate. In order to form a fluid bearing, the balls are filled with fluid medium, e.g., water or gas. To this end, conduits are formed in the support walls which extend transverse to the steel mold wall and which supply the balls or the ball cages with water at the end sides of the support walls. 
     In order to prevent an uncontrolled flow of the spray water away after it has been sprayed on the free rear wall regions of the steel mold wall, according to the further development of the present invention, the support mesh includes an outer frame with a sealing surrounding the mesh. 
     Backward, i.e., toward the side remote from the steel melt, the used cooling medium can either flow freely away, i.e., flow to the atmosphere, or flow directly along. In the second case, preferably, a collection chamber is provided at the lower portion of the mold wall which opens into a drain for bringing the cooling water, if necessary, to a processing plant. In the collection chamber, the cooling medium, which flows along the support mesh wall, in particular along a wall portion of the support mesh located below a respective spray nozzle, is collected and is evacuated through the drain. 
     Further features and advantages of the invention follow from the sub-claims and from the following description that explains in detail embodiments of the invention shown in the drawings which include the above-described combination of features, separate features alone, or other essential combinations. The drawings show: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  a side view of a mold wall of a mold, here, a broad side of a mold for casting rectangular strands viewed from the side of steel melt; 
     FIG. 1 b  a transverse elevational view of the mold wall of FIG. 1 a;    
     FIG. 2 a  a transverse elevational view of a mold wall with spray cooling adapted to the energy flow distribution over the mold height; 
     FIG. 2 b  a diagram showing a thermal flow profile over the mold height; 
     FIG. 3 a  a cross-sectional view of a mold with a narrow side wall and with a small side section with a width and conicity change; 
     FIG. 3 b  a detail with a ball bearing in the fore-side end of the support wall for supporting the steel mold wall on the support mesh. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a broad side  1  of a mold having two broad and two narrow sides and suitable for casting a rectangular stock such as slabs or thin slabs. The mold broad side is formed by a steel mold wall  2  having a thickness of 2 mm. The steel mold wall  2  is a portion of an entire mold wall and is pulled toward a support mesh  3  by a magnetic field  3 . 1  which is generated by a magnetic field generator  3 . 2  and which acts on the steel mold wall  2  via the support mesh  3  having support walls  11 . The steel mold wall  2  is formed preferably as a layered steel mold wall  2 . 1  which consists of layers steel/copper or copper/steel/copper or other metals instead of copper. The magnetic field generator can be formed preferably as a permanent magnet  3 . 4 . 
     The steel mold wall  2  having a thickness of 2 mm has a specific thermal conductivity corresponding to a copper wall having a thickness 14 mm. For additional fixation, a device  4 . 1  (shown schematically) is provided and which secures the broad side with a width  17  and a height  16  along a transverse center line  4 , whereby the thermal expansion can take place symmetrically in both horizontal directions (shown with arrows and reference characters  5 ). 
     Further, the steel mold plate is likewise secured at its upper edge  6  or a lower edge  7  of the mold in order to be able to uniformly expand in the vertical direction (shown with an arrow and a reference character  6 ). In the shown embodiment, one deals with a bar-shaped element rotatable about its longitudinal axis. 
     In order to avoid high mold cooling water pressures of up to 15 or 20 bar, the back side of the steel mold wall  2  is cooled, as shown in Fig. 1 b , with a mold spray-cooling device  10  with spray nozzles extending into chambers  9  of the support mesh  3 , or the openings, or the passages. The heated cooling water or the falling splash water  10 . 2  can flow away along the support mesh wall  11  or support wall webs. The splash water can be collected in a closed space or a collection chamber  12  and be evacuated through a drain  12 . 1  or be evacuated into open atmosphere  13  (see FIG. 3 a ). 
     The outer frame of the rectangular magnetic support mesh  3 . 1  is surrounded with a rubber seal  3 . 3  to prevent an uncontrolled evacuation of the mold splash water  10 . 
     The support wall  11  of the support mesh  3  is provided in the fore-regions  11 . 1  with balls  11 . 2  that serve as standard bearings or fluid bearings for a free, thermally-dependent, movement of the mold steel wall  2 . Examples of support points or the balls  11 . 2  can be seen in FIG. 1 a . Instead of balls, the support mesh heads  11 . 1  can be formed of rounded graphite heads  11 . 1  which should provide for a thermally-dependent sliding movement. 
     A detailed view of an embodiment of a ball support is shown is FIG. 3 b . It shows a section of a support wall  11  with the support wall head  11 . 1  with the ball  11 . 2  received in the head for supporting the steel mold wall  2  or  2 . 1 . The ball cage is supplied with fluid  11 . 3 , such as water or gas, through a conduit, and which serves for forming a fluid bearing or a hydraulic bearing. Also shown are spray nozzles  10 . 1  provided between the support walls  11  or the webs of the mesh  3 . 
     FIG. 2 a  shows the use of the inventive device for continuous casting or a mold with a submerged nozzle  23 . 2  that projects into the mold. The reference character  24  designates a casting slag, and the reference character  24 . 1  designates powder. The liquid steel  23 . 1  is provided into the mold through the submerged nozzle  23 . 2 , and solidification starts, with formation of a strand skin  23  on the mold walls. The casting speed Vc is shown with a reference character  25 . The magnetic field  3 . 1 , which is generated by a magnetic field generator  3 . 2  or  3 . 4 , can be so formed that it would influence the steel flow in the mold as an electromagnetic brake  3 . 1 . 1 . 
     In FIG. 2 a , the reference character  15  represents the mold wall temperature of the mold side adjacent to the liquid steel. For measurement of the temperature, a corresponding measuring or control device is provided. FIG. 2 a  also shows the embodiments of the support with balls  11 . 2  integrated with the head of the support wall  3  or with a rounded head, preferably, of graphite  11 . 1 . 1 . Preferably, only one type of support is used, however, it is within the scope of the invention to provide the support wall with both types of the support. In the mold with the spray cooling shown in FIG. 2, the back-flowing splash water  10 . 2  does not hang as a screen but rather flows often downward, whereby it hangs then beneath the mold. 
     An advantageous feature of the invention consists in that the spray cooling or the parameters of separate spray nozzles are adapted to a respective required cooling of the mold. Contrary to FIG. 2 a , FIG. 2 b  shows occurring energy values  14  over the mold height, i.e., a maximum released heat in the upper third of the mold. For controlling the mold wall, temperature  15  is measured, and the spray cooling is correspondingly adapted over the mold height. 
     FIG. 3 a  shows a narrow side  18  of a mold. In this embodiment of the mold, the broad sides are formed according to the invention, whereas the narrow sides are formed of steel but without any support mesh. However, it is within the scope of the invention to form both the broad sides and the narrow sides or only the narrower sides according to the invention. In the embodiment shown, the narrow side is formed of steel. The narrow side has a high stability due to a slight concavity and/or inner convexity  18 . 1 . It is mounted on its own narrow side body  19  which provides for width adjustment  20  and conicity adjustment  21  of the mold. This construction allows a water pressure of up to  20  bar in the region of a conventional small side water cooling, here shown with a reference character  22 . A reference character  22 . 1  designates a water-displacement body. In another embodiment, the small sides of a mold can consist of water-cooled copper plates according to the state of the art. The components, which have been discussed with reference to other embodiments, have in FIG. 3 a  the same reference characters. 
     Returning to the proposed, according to the invention, wall construction of a casting mold for continuous casting and the corresponding cooling, the chambers  9  or openings of the support mesh  3  can have any arbitrary shape, with a rectangular shape being shown. Preferably, the chambers  9  have a honeycomb shape, with the chambers  9  or  12  extending between the support walls  11 . 
     Altogether, there is provided a mold for a continuous casting that provides for a high regulation of thermal conductivity and a simple assembly, in particular, for assembly of a steel mold wall. The control of the mold temperature can be effected in both casting (vertical) direction and in the transverse to the casting direction (horizontal) direction. The steel mold wall can be a disposable wall, which makes a high quality an expensive maintenance, which is necessitated by wear, superfluous. A relatively simple mold spray cooling can be used that can be adjusted functionally with respect to its effect or intensity. A conventional spraying water can be used. The mold has a simple construction and is relatively inexpensive. 
     Reference Numerals 
       1 . Broad side of a slab mold 
       2 . Steel mold wall, e.g., the broad side of a slab 
       21  Layered steel mold wall, e.g., of steel/Cu, Cu/Steel/Cu, or Me/Steel/Me 
       3  Support mesh, grid 
       3 . 1  Magnetic field 
       3 . 1 . 1  Electromagnetic brake for killing the steel flow in the mold, EMBR 
       3 . 2  Magnetic field generator 
       3 . 3  Sealing, e.g., a rubber sealing 
       3 . 4  Permanent magnet 
       4  Transverse Central line of broad side 
       4 . 1  Device for securing the steel mold wall ( 2 ) 
       5  Horizontal direction 
       6  Upper mold edge, mold inlet 
       7  Lower mold edge, mold outlet 
       9  Vertical direction, casting direction of a slab plant 
       10  Mold spray cooling 
       10 . 1  Spray nozzles, nozzle head 
       10 . 2  Return flow of splash water 
       11  Support wall of the support mesh ( 3 ) with chambers ( 4 ) 
       11 . 1  Head of the support wall 
       11 . 1 . 1  Graphite head of the support wall 
       11 . 2  Balls which serve as bearings for free, thermally caused movement of the steel mold wall ( 2 ) 
       11 . 3  Fluid such as, e.g., gas or water that serves for flowing a fluid bearing or hydro-bearing 
       12  Closed space, chamber of the mold spray cooling means ( 10 ) 
       12 . 1  Splash water removal 
       13  Open atmosphere of the mold spray cooling means 
       14  Energy value 
       15  Mold wall temperature on a side adjacent to liquid steel 
       16  Mold Height 
       17  Mold width 
       18  Narrow side 
       18 . 1  Concave and/or convex shape of the heat-removing narrow side 
       19  Narrow side body 
       20  Width adjustment 
       21  Conicity adjustment 
       22  Conventional narrow side mold water cooling with water pressure maximum 20 bar 
       22 . 1  Water displacement body 
       23  Strand skin 
       23 . 1  Liquid steel 
       24  Casting slag 
       24 . 1  Casting powder 
       25  Casting speed, Vc 
       26  Honeycomb shape of the support mesh.