Method for the continuous casting of a metal strand in a continuous casting installation and a continuous casting installation

Abstract

A method for the continuous casting of a metal strand in a continuous casting installation, in which, in a casting machine, the metal formed into a slab, with a still molten core, is brought out vertically from a mold, wherein, downstream of the mold in the conveying direction, the slab is made to move along a casting bow, through a number of casting bow segments, and is deflected into the horizontal, wherein each casting bow segment has a number of segment rollers, which are designed for coming into contact with the surface of the slab. In the region before the end of the casting machine, a number of segment rollers are lifted off from the surface of the slab, or are not installed in receptacles provided, and so the contact between the slab and the segment roller is interrupted or there is no contact.

Claims

1. A method for continuous casting of a metal strand in a continuous casting installation, comprising the steps of: bringing a metal, which has been formed into a slab with a still-molten core in a casting machine, vertically out of a mold; guiding the slab downstream of a mold in a conveying direction through a number of segments and deflecting the slab into a horizontal plane, wherein each segment comprises a number of rollers on each side of the slab, which rollers are configured to make contact with a surface of the slab; raising a number of the rollers from the surface of the slab on the side of the slab that faces upward when the slab is in the horizontal plane or not installing the rollers in mountings provided in an area upstream of an end of the casting machine, so that contact between the slab and the raised rollers is interrupted or is not present; and introducing a thermal insulating element between the surface of the slab and a surface of the raised or not installed rollers, which roller surface is closest to the slab surface.

2. The method according to claim 1, wherein, downstream of the mold in the conveying direction, the slab is guided along a curved apron through a number of curved apron segments and deflected into a horizontal plane, wherein each curved apron segment comprises a number of segment rollers, which are configured to make contact with the surface of the slab, wherein, along the curved apron in the area upstream of the end of the casting machine, a number of segment rollers are raised from the surface of the slab or not installed in the mountings provided.

3. The method according to claim 2, further including carrying out a numerical simulation pursuant to a mathematical model, wherein a location of a tip of the molten core is determined at least based on casting speed and slab geometry, wherein raising of the segment rollers is carried out on the basis of the numerical simulation so that the raising is carried out for a defined section along the segments.

4. The method according to claim 3, wherein the raising is carried out along the curved apron.

5. The method according to claim 1, wherein introduction of the insulating element is accomplished by inserting the insulating element horizontally from a side of the slab.

6. The method according to claim 1, wherein the thermal insulating element is permanently installed between support rollers or drive rollers, which are spaced a certain distance apart in front of one or both sides or edges of the slab.

7. The method according to claim 1, further including providing the segments with coolant to cool the slab, wherein cooling action is reduced or decreased to zero at least in a number of segments.

8. The method according to claim 1, wherein the slab is supported by support rollers at least in an area of the segments with raised segment rollers.

9. The method according to claim 1, wherein the raised segment rollers and/or support rollers exposed to radiant heat of the slab are driven in rotation.

10. The method according to claim 1, including arranging a furnace downstream from the casting machine, and arranging at least one thermal insulating element for thermally insulating the slab in an area between the end of the casting machine and the furnace entrance.

11. The method according to claim 10, wherein the at least one thermal insulating element is moved only temporarily into the area of the slab to thermally insulate the slab.

12. The method according to claim 11, wherein the at least one thermal insulating element is moved into an area of a shears and/or into an area of an in-line stand and/or into an area of a cold strand removal unit.

13. A continuous casting installation for continuous casting of a metal strand, comprising: a casting machine, in which a metal which has been formed into a slab with a still molten core is brought vertically out of a mold; a number of segments arranged downstream from the mold in a conveying direction to deflect the slab into a horizontal plane, wherein each segment comprises a number of rollers on each side of the slab, which rollers are configured to make contact with a surface of the slab, wherein in an area upstream of an end of the casting machine, a number of the rollers are provided with positioning means to allow the rollers to be raised from the surface of the slab on the side of the slab that faces upward when the slab is in the horizontal plane; and, at least one movable thermal insulating element placeable in a passive position outside the segment and in an active position inside the segment and between the slab surface and a surface, which is closest to the slab surface, of the raised rollers.

14. The continuous casting installation according to claim 13, wherein, downstream from the mold in the conveying direction, a curved apron with a number of apron segments is arranged, by which the slab is deflected into a horizontal plane, wherein a number of the segment rollers extending along the curved apron in the area upstream of the end of the casting machine are provided with the positioning means to allow the segment rollers to be raised from the surface of the slab.

15. The continuous casting installation according to claim 13, wherein the at least one movable thermal insulating element is adjustably arranged so as to be positionable horizontally and transversely to the conveying direction of the slab.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows a side view of a casting machine forming a component of a continuous casting installation according to the prior art;

(2) FIG. 2 shows the change in temperature according to the prior art between the mold and a furnace installed downstream from the casting machine, wherein a first, high casting speed is being used;

(3) FIG. 3 shows the change in temperature according to the prior art between the mold and the downstream furnace, wherein a second, reduced casting speed is being used;

(4) FIG. 4 shows a side view of the casting machine, which is now equipped and operating according to the invention;

(5) FIG. 5 shows the area of the continuous casting installation between the end of the casting machine and the furnace, which is equipped and operating according to the invention;

(6) FIG. 6 shows the change in temperature between the mold and the downstream furnace, wherein the second, reduced casting speed and the method according to the invention is being used.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 4 represents a continuous casting installation 1, wherein the casting machine 2 is shown. Concerning the structure and manner of operation of the machine, reference is made to the above discussion of FIG. 1, which applies analogously here. The new element here is that work is carried out at a casting speed which has been reduced to such an extent that, unless additional measures are taken, the tip of the molten crater is no longer situated in the area of the end 14 of the casting machine but rather—as illustrated in FIG. 3—in the middle area of the casting machine. This would have negative consequences, as discussed above in conjunction with FIG. 3.

(8) To prevent this, it is now provided according to the invention that, along the curved apron 3, a number of segment rolls 12 and 13 are raised from the surface of the slab. The contact between the segment rolls and the slab is thus interrupted. This has the effect per se that the cooling action produced by the surface contact between the segment rolls and the slab is no longer present, and the slab therefore cools down to a lesser extent as it travels toward the end 14 of the casting machine.

(9) The segment rolls, furthermore, are raised or lowered in the direction perpendicular to the surface of the slab to such an extent that a thermal insulating element 15, 16 can be introduced between the slab surface and the segment rolls 12, 13 which have been raised from the slab. Said insulating elements 15, 16 have been pushed laterally, in the horizontal direction, into the intermediate space created between the slab and the segment rolls 12, 13.

(10) The result is that the slab now cools down to a much lesser extent that it would in the absence of the measure just described.

(11) To continue to provide the slab with adequate guidance in spite of the raising or lowering of the segment rolls 12, 13, preferably driven support rolls 17 are arranged in the segments of the curved apron. The strand will therefore be supported by only a few support rolls 17. In the exemplary embodiment according to FIG. 4, the last three or four curved apron segments 8, 9, 10, 11 have been set up in this way.

(12) In the present case, as will be seen again later in conjunction with FIG. 6, the cast strand has already solidified completely in the area of the curved apron segment 7. The following curved apron segments 8, 9, 10, and 11, therefore, are opened up and provided with insulating elements 15, 16. These measures can be carried out above and below the slab, but it is also possible to carry them out on only one side.

(13) Lateral insulation along the edges of the slab is also provided. This insulation can be attached to the insulating elements 15, 16, or it can have its own positioning mechanisms. This lateral insulation is not, however, shown in FIG. 4.

(14) The increased extent to which the segment rolls are raised or lowered can be carried out by means of, for example, long-stroke hydraulic cylinders 27, which, in the exemplary embodiment according to FIG. 4, are mounted on the frames 28. It is also possible to use mechanical adjusting devices or pneumatic cylinders as positioning elements.

(15) When the casting conditions are set up so that one or more casting segments or segment areas are not being used for a considerable period of time, it can be advantageous, as an option, to prepare these casting segments in such a way that the insulating elements are mounted permanently in position. Here, too, as shown in FIG. 4, the cast strand is supported by support or drive rolls spaced a certain distance apart, and stationary insulation is built into the areas in between, at the top and/or at the bottom, and possibly also along the side edges. In this case, therefore, there is no longer any need to move the insulation in and out. In addition, there is no need to move the segment rolls a considerable distance away from or back toward the slab, or the segment rolls can simply not be installed in the insulated area from the very beginning.

(16) In FIG. 5 it can be seen that thermal insulation measures are also implemented in the area between the end 14 of the casting machine and the entrance 19 to the following furnace 18 in order to keep the slab hot on its way to the furnace. Thermal insulating elements 20, 21, and 22 are provided, which, like the thermal insulating elements 15 and 16, block the transfer of heat from the slab to the surroundings and thus ensure that the slab remains hot.

(17) In the area of the slab cleaning unit 24, a swingable insulating hood 20 is provided. The hood can be swung into position when the spray beam of the slab cleaning unit 24 is not active and has been swung up and out of the away.

(18) Thermal insulating elements 21 are also present in the area of the shears 25. The arrows at the insulating elements 21 show the directions in which the insulating elements 21 are swung, either into their active position (in which they insulate) or into their passive position (to allow the slab to be cut).

(19) A thermal insulating element 22 is also present in the area of the cold strand removal unit, directly in front of the furnace 18. The boom 26 for removing the cold strand is indicated. After the cold strand has been removed, the upper insulating element 22 can be swung into the position shown. The lower thermal insulating elements are, in the present case, configured as permanent insulation.

(20) These measures supplement the insulating effect in the continuous casting installation. Without insulating elements downstream from the continuous casting installation, some of the temperature effect generated by the continuous casting installation would be lost.

(21) In FIG. 6 it can be seen how the temperature of the slab changes when the configuration and operating method according to the invention are used.

(22) The resulting temperature curves for the core temperature T.sub.K, the mean temperature of the slab T.sub.M, and the mean surface temperature T.sub.O on the bottom of the slab are again indicated, wherein, in addition, for the purpose of comparison, the mean value of the temperature T.sub.M* is entered in dotted line, which shows the change which would have occurred without the measures according to the invention. That the curve T.sub.M on a higher temperature level is obtained instead of the curve T.sub.M* is therefore the result of the circumstance that the previously described thermal insulation measures were carried out in the area labeled D.

(23) Accordingly, even though no additional energy has been consumed, the slab has a higher temperature at the entrance to the furnace 18.

(24) In the proposed continuous casting installation in which the segment rolls are raised to an increased extent, the support lengths (frames) and the strokes of the positioning elements, etc., are increased as well. To optimize the accuracy with which the segment rolls are adjusted, a mathematical model and/or a control algorithm is used, which describes the stiffness of the segment and of the segment frame and the influence of the positioning elements (e.g., oil columns) as a function of the contact pressure and the thermal changes in the mechanical components (rolls, frames). Alternatively or in addition, it would also be possible to use force and position sensors.

(25) In the continuous casting installation according to the invention, furthermore, some of the segments do not have one fixed and one loose side; instead, both sides are adjustable. When the segments are opened and closed, the sides are positioned by means of position sensors or optionally moved by the positioning elements against stops (distance limits, simulating a fixed side), which thus define the position setting.

(26) The modified structure of the segments can also have an effect on the procedure for replacing the segments. When segment replacement is called for, the segments can be replaced together with the frames 28 and the positioning elements 27; or the frame 28 can represent a permanent structure, and, after removal of the transverse beams, the segment rolls are removed for replacement.

(27) For replacement, the segments or parts of segments can be removed laterally through the frame, transversely to the slab transport direction, or they can be raised vertically, perpendicular to the slab transport direction.

LIST OF REFERENCE SYMBOLS

(28) 1 continuous casting installation 2 casting machine 3 curved apron 4 segment/curved apron segment 5 segment/curved apron segment 6 segment/curved apron segment 7 segment/curved apron segment 8 segment/curved apron segment 9 segment/curved apron segment 10 segment/curved apron segment 11 segment/curved apron segment 12 segment roll 13 segment roll 14 end of the casting machine 15 thermal insulating element 16 thermal insulating element 17 support roll 18 furnace 19 furnace entrance 20 thermal insulating element 21 thermal insulating element 22 thermal insulating element 23 point of complete solidification 24 slab cleaner 25 shears 26 cold strand removal boom 27 positioning element (hydraulic cylinder) 28 frame V vertical H horizontal F conveying direction T.sub.K core temperature T.sub.O surface temperature (on bottom of the slab) T.sub.M mean value of the temperature T.sub.M* mean value of the temperature without thermal insulation measures D area of the thermal insulation measures