Method and device for cooling the copper plates of a continuous casting ingot mould for liquid metals, especially liquid steel

Abstract

The invention relates to a device for cooling the copper plates (1.1) of a continuous casting ingot mould (1) for liquid metals, especially liquid steel, comprising an ingot mould coolant (2) which is guided in cooling channels. During the initial temperature rise to achieve a set casting speed or when said casting speed is exceeded for a deviating copper plate skin temperature (8), the copper plate skin temperature (8) is influenced, even when the casting speed is higher, in such a way that surface errors in the casting shell and/or cracks in the surface of the copper plates are prevented from occurring or occur in a significantly reduced manner by adjusting the copper plate skin temperature (8) at alternating casting speeds (6) of between 1 m/min and a maximum 12 m/min by means of quantitative correction of the amount of ingot mould coolant (4) and/or ingot mould coolant inflow temperature (5) according to the casting speed (6) and according to the thickness of the copper plates (9), to a desired constant value.

Description

[0001] The invention concerns a method and a device for cooling the copper plates of a continuous casting ingot mold for molten metals, especially molten steel, with an ingot mold coolant conveyed in cooling channels and with a copper plate nominal skin temperature that deviates during the ramping up to the set casting rate or when the set casting rate is exceeded.

[0002] DE 41 27 333 C2 describes a method for conveying the coolant at the maximum rate in the region of the highest thermal stress. This improves heat dissipation and lowers the temperature of the ingot mold plate. Another goal is the reduction of the temperature differences over the height of the ingot mold and the attendant stress reduction and prolongation of the service life of the ingot mold walls. However, this method does not take into account a changed, especially an increased, very high casting rate.

[0003] Continuous casting ingot molds of this type for casting molten steel are cooled in widely used and well-known processes by maintaining the amount and the temperature of the ingot mold coolant flowing into the continuous casting ingot mold at constant levels, independently of the casting rate. The result of this method of operation is that the thermal load, measured in W/m2, and thus the copper plate skin temperature increase sharply with increasing casting rate, especially during casting at casting rates above 4 m/min. When flux powder slag is used between the strand shell and the ingot mold copper plate, this temperature rise at a given copper plate thickness of, for example, 20 mm between the ingot mold coolant and the hot side results, for one thing, in variable lubricating behavior and variable thermal loads, and, for another, in shortened service lives of the ingot mold copperplates due to the recrystallization temperature of cold-rolled copper being exceeded.

[0004] These disadvantages, which arise not only with increasing casting rate, but also with increasing thickness of the copper plate, lead to disturbances in the casting process and/or to surface defects in the strand shell and cracks in the surface of the copper plates.

[0005] The disturbances arise with water flowing in the continuous casting ingot mold both from bottom to top and from top to bottom. However, it can be stated that a lower copper plate skin temperature develops when the water flows from top to bottom than when it flows from bottom to top.

[0006] The objective of the invention is to influence the copper plate skin temperature in such a way that, even with a varied, especially a higher casting rate, surface defects in the strand shell and/or cracks in the surface of the copper plate do not occur or occur to a much lesser extent.

[0007] In accordance with the invention, this objective is achieved by adjusting the copper plate skin temperature at varying casting rates between 1 m/min and a maximum of 12 m/min by means of a quantitative correction of the amount of ingot mold coolant and/or the intake temperature of the ingot mold coolant to a desired, constant value, depending on the present casting rate and depending on the thickness of the copper plates. In this way, the copper plate skin temperature can be advantageously selected and held constant, depending on the casting rate, even at different copper plate thicknesses. In addition, constant conditions are present for the lubricating behavior of the flux powder slag, which is melted on the liquid metal level from the flux powder that is used (if flux powder is used). Furthermore, advantages can result from ingot mold copper plates that are no longer stressed to the point that recrystallization of the copper occurs and therefore do not become cracked. Additional advantages are an improved strand surface quality and casting reliability, independently of the casting rate and the thickness of the copper plate, for selected “working windows”. This also increases output.

[0008] It is advantageous that this also makes it possible to adjust the desired constant copper plate skin temperature in the region of the liquid metal level to a constant value.

[0009] The effects that have been explained above can also be achieved either completely or partially when the ingot mold coolant is conveyed through the cooling channels from top to bottom or from bottom to top.

[0010] In accordance with additional features of the invention, the continuous casting ingot mold is oscillated.

[0011] Additional advantages result from the fact that the cast strand is cast together with the flux powder slag that forms.

[0012] The method is further designed in such a way that, to control the amount of ingot mold coolant and the intake temperature of the ingot mold coolant, process data and plant data are introduced, which are processed into controlled variables in an online simulation model.

[0013] The accuracy of the method can be further increased by using a direct determination of the copper plate skin temperature in the region of the liquid metal level in addition to or alternatively to the online simulation model.

[0014] In accordance with the invention, a device for cooling the copper plates of a continuous casting ingot mold, especially for molten steel, with cooling channels through which ingot mold coolant flows, achieves the objective of selecting the copper plate skin temperature and maintaining it at a constant value on the basis of the present casting rate, even at different copper plate thicknesses, by providing controlled variables for controlling the intake temperature of the ingot mold coolant and/or the amount of ingot mold coolant at casting rates between 1 m/min and a maximum of 12 m/min and at copper plate thicknesses of 4 mm to about 50 mm. In this way, the copper plate skin temperature on the hot side can be maintained at a significantly lower level than before, even at the beginning of casting, and the copper plate can be protected in a way that prevents the temperature from coming even close to the recrystallization temperature of copper. This advantage is obtained over a large range of casting rates.

[0015] In accordance with another design, the ingot mold coolant intake can be located some distance above the liquid metal level.

[0016] It is also advantageous if the continuous casting ingot mold can be oscillated by an oscillation device.

[0017] In addition, with respect to protecting the strand shell of the cast strand, it is useful to be able to supply flux powder to the cast strand during casting.

[0018] In addition, the amount and temperature of the ingot mold cooling water are controlled in such a way that a process-control computer, which is supplied with process data and plant data for an online simulation model for controlled variables for controlling the intake temperature of the ingot mold coolant and/or the amount of ingot mold coolant, controls a three-way valve and a control valve as well as a speed-controlled pump in the ingot mold coolant circulation.

[0019] Furthermore, in accordance with another refinement, this control can be carried out in such a way that, in addition to or instead of the process-control computer, a device for determining the copper plate skin temperature in the region of the liquid metal level can be used to control the intake temperature of the ingot mold coolant and/or the amount of ingot mold coolant.

[0020] The drawings show an embodiment of the invention, which is explained in greater detail below.

[0021] FIG. 1A shows a functional block diagram of the coolant circulation of a conventional ingot mold.

[0022] FIG. 1B shows the corresponding functional block diagram of the coolant circulation of a so-called ISO ingot mold in accordance with the invention.

[0023] FIG. 2A shows a casting rate profile with heat flow as a function of time.

[0024] FIG. 2B shows the heat behavior as a function of time with conventional cooling

[0025] FIG. 2C shows the desired heat behavior as a function of time in accordance with the invention.

[0026] FIG. 2D shows the desired heat behavior as a function of time with adjusted copper plate skin temperature.

[0027] FIG. 3 shows a comparison of the state of the art with the invention on the basis of the temperature curves as a function of the casting rate, taking into consideration the flow of the coolant from top to bottom and from bottom to top in the continuous casting ingot mold.

[0028] In accordance with the state of the art (FIG. 1A), a continuous casting ingot mold 1, into which molten steel is cast, is cooled in such a way that the ingot mold coolant 2 at the ingot mold coolant intake 3 into the continuous casting ingot mold 1 is maintained at constant values with respect to the amount 4 of ingot mold coolant and the intake temperature 5 of the ingot mold coolant, independently of the casting rate 6.

[0029] This method of operation means that, with increasing casting rate 6, the thermal load 7 in W/m2 (see FIG. 2A) and thus the copper plate skin temperature 8 rise sharply, especially during casting at an increasing casting rate 6 of up to 12 m/min. The temperature rise at a given copper plate thickness 9, e.g., 20 mm, between the coolant and the hot side leads, in the presence of flux powder slag 10 between the strand shell of the cast strand 11 and the ingot mold copper plate 1.1, for one thing, to variable lubricating behavior and thermal load 7 and, for another, to reduced services lives of the ingot mold copper plates 1.1, which is caused by the recrystallization temperature 12 of cold-rolled copper being exceeded (see FIG. 3).

[0030] These disadvantages, which arise with increasing casting rate 6 and/or with increasing copper plate thickness 9, lead to disturbances of the casting process or to surface defects in the strand shell and cracks in the surface of the copper plates.

[0031] The disturbances occur both with water flow 13.1 of the ingot mold water 13 in the continuous casting ingot mold 1 from bottom to top and with water flow 13.2 from top to bottom (see FIG. 3). However, it can be stated that a lower copperplate skin temperature 8 develops when the water flow 13.2 occurs from top to bottom than when the water flow 13.1 occurs from bottom to top.

[0032] In FIG. 1A (state of the art), the continuous casting ingot mold 1 is cooled by an internal coolant circulation 19 and an external coolant circulation 20. The external coolant circulation 20, which passes through a heat exchanger 21, serves to cool the ingot mold coolant 2 in the internal coolant circulation 19.

[0033] The internal coolant circulation 19 is conveyed through the heat exchanger 21 in such a way that the ingot mold coolant 2, which is adjusted to a constant amount 4 by a pump 22, is likewise held constant with respect to its intake temperature 23 (Tin), independently of the casting rate 6.

[0034] This is accomplished by means of a three-way valve 24, a bypass 25, and a controlled system 26 between a Tin measuring device for the intake temperature 23 (Tin) and the three-way, valve 24. As a rule, the ingot mold coolant 2 is conveyed as water flow 13.1 from bottom to top, although in the case of thin-strand plants, it is also conveyed as water flow 13.2 from top to bottom.

[0035] Like FIG. 1A, FIG. 1B shows the coolant circulation in a functional block diagram, but in this case, with increasing casting rate from 1 m/min to a maximum of 12 m/min, the copper plate skin temperature 8 is adjusted to a desired constant value by a quantitative correction of the amount 4 of ingot mold coolant and/or of the intake temperature 5 of the ingot mold coolant, independently of the casting rate 6 and independently of the thickness 9 of the copper plates at a constantly adjusted intake temperature 5 of the ingot mold coolant. The amount 4 of ingot mold coolant and the intake temperature 5 of the ingot mold coolant can be controlled by a process-control computer 27 for an online simulation model 27.4 and process data 27.1 of the continuous casting ingot mold 1 at constant copper plate skin temperature 8 by means of a run-in rate window 6.2 (see FIG. 3). To this end, the process-control computer 27 needs process data 27.1 and plant data 27.2 to control the amount 4 of ingot mold coolant via a pump station 22.1 and/or control valves 29 and to control the intake temperature 5 of the ingot mold coolant by the three-way valve 24 via controlled variables 27.3. A surge tank 30 is located in front of the pump station 22.1

[0036] The process-engineering relationships are explained in FIGS. 2A to 2D.

[0037] FIG. 2A shows a heat flow 17 and a profile 16 of the casting rate 6 as a function of the casting time 18. The graph describes the course of casting from the start over a constant run-in rate window 6.2 with subsequent acceleration to a high rate level.

[0038] FIG. 2B shows the state of the art. The actual copper plate skin temperature 8, denoted TCu-actual, increases with increasing casting rate 6 and deviates from the desired copper plate skin temperature 8, denoted the copper plate target temperature 8.1 (TCu-target), since the amount 4 of ingot mold coolant and the intake temperature 5 of the ingot mold coolant for cooling the continuous casting ingot mold 1 are held constant.

[0039] In FIG. 3C, the actual copper plate skin temperature 8 (TCu-actual) is caused to coincide with the desired copper plate skin temperature 8, i.e., the copper plate target temperature 8.1 (TCu-target) by a suitable quantitative correction of the amount 4 of ingot mold coolant, independently of the casting rate 6, at constant intake temperature 5 of the ingot mold coolant.

[0040] In FIG. 2D, the copper plate skin temperature 8 (TCu-actual) is caused to coincide with the copper plate target temperature 8.1 (TCu-target) by suitable quantitative adjustment of the amount 4 of ingot mold coolant and of the intake temperature 5 of the ingot mold coolant as a function of the profile 16 of the casting rate over casting time 18. When both influencing variables are varied, such as the amount 4 of ingot mold coolant or its flow rate, which increases the heat transfer, and the intake temperature 5 of the ingot mold coolant, which increases the potential and thus the heat flow, the run-in rate windows 6.2 with respect to the casting rate 6 are greater for a desired, actual copper plate skin temperature 8 at a given copper plate thickness 9 than is the case when only one of the two influencing variables is varied.

[0041] The difference between the previously known method and the method of the invention is clearly shown in FIG. 3. The ingot mold plate skin temperature 8 as a function of the rising casting rate 6, which is a maximum of 12 m/min, is used as the basis of this comparison. A horizontal straight line of the recrystallization temperature 12 represents the end of the thermal load of the copper plate made of cold-rolled copper, at which the copper loses its strength and/or its cold-rolled structure and thus its properties which are important for the casting of molten steel. The temperature behavior 14 in the state of the art is described by the curve 14.1 (water flow from bottom to top) and the curve 14.2 (water flow from top to bottom). Both curves 14.1 and 14.2 increase steadily to higher copper plate skin temperatures 8 in the region of the liquid metal level with increasing casting rate, and the copper plate skin temperature 8 intersects the recrystallization temperature 12 at a critical casting rate 6.1 in the case of water flow 14.1 of the ingot mold coolant 13 from bottom to top sooner than in the case of water flow 14.2 from top to bottom.

[0042] The rapid increase in the copper plate skin temperature 8 in the region of the liquid metal level with increasing casting rate 6 and increasing copper plate thickness 9 can be attributed to the constant amount 4 of ingot mold coolant and the constant intake temperature 5 of the ingot mold coolant at the ingot mold coolant intake 3 during casting by the state-of-the-art method.

[0043] The control and constancy of the copper plate skin temperature 8 as a function of the casting rate is represented with the curve 15. It is clear here that, with increasing copper plate thickness 9, the copper plate skin temperature 8 rises under the same cooling conditions, expressed by the coolant flow rate or the amount 4 of ingot mold coolant and by the intake temperature 5 of the ingot mold coolant. The same is also true of the previously known method (see curve 13.1—water flow from bottom to top—and curve 13.2—water flow from top to bottom).

[0044] The principle of the invention can also be applied to strip-casting machines operated at casting rates of up to 100 m/min. In this case, all measures applied at the height of the continuous casting ingot mold 1 are applied at the circumference of the twin rolls.

List of Reference Numbers

[0045] 1 continuous casting ingot mold

[0046] 1 .1 ingot mold copper plate

[0047] 2 ingot mold coolant

[0048] 3 ingot mold coolant intake

[0049] 4 amount of ingot mold coolant

[0050] 5 ingot mold coolant intake temperature

[0051] 6 casting rate

[0052] 6 .1 critical casting rate

[0053] 6 .2 run-in rate window (with equal copper plate temperature)

[0054] 7 thermal load (W/m2)

[0055] 8 copper plate skin temperature

[0056] 9 copper plate thickness

[0057] 10 flux powder slag

[0058] 11 cast strand

[0059] 12 recrystallization temperature

[0060] 13 ingot mold coolant

[0061] 13 .1 water flow from bottom to top

[0062] 13 .2 water flow from top to bottom

[0063] 14 temperature behavior in the state of the art

[0064] 14 .1 curve of ingot mold coolant from bottom to top

[0065] 14 .2 curve of ingot mold coolant from top to bottom

[0066] 15 curve

[0067] 16 profile of the casting rate over the casting time

[0068] 17 heat flow

[0069] 18 casting time

[0070] 19 internal coolant circulation

[0071] 20 external coolant circulation

[0072] 21 heat exchanger

[0073] 22 pump

[0074] 22 .1 pump station

[0075] 23 intake temperature Tin

[0076] 24 three-way valve

[0077] 25 bypass

[0078] 26 controlled system

[0079] 27 process-control computer

[0080] 27 .1 process data

[0081] 27 .2 plant data

[0082] 27 .3 controlled variable

[0083] 27 .4 online simulation model

[0084] 28 temperature measurement

[0085] 29 control valve

[0086] 30 surge tank

Claims

1. Method of cooling the copper plates (1.1) of a continuous casting ingot mold (1) for molten metals, especially molten steel, with ingot mold coolant (2) conveyed in cooling channels and with a copper plate nominal skin temperature (8) that deviates during the ramping up to the set casting rate or when the set casting rate is exceeded, wherein the copper plate skin temperature (8) is adjusted at varying casting rates (6) between 1 m/min and a maximum of 12 m/min by means of a quantitative correction of the amount (4) of ingot mold coolant and/or the intake temperature (5) of the ingot mold coolant to a desired, constant value, depending on the present casting rate and depending on the thickness (9) of the copper plates.

2. Method in accordance with claim 1, wherein the desired, constant copper plate skin temperature (8) in the region of the liquid metal level is constantly adjusted.

3. Method in accordance with claim 1, wherein the ingot mold coolant (2) is conveyed through the cooling channels from top to bottom or from bottom to top.

4. Method in accordance with claim 1, wherein the continuous casting ingot mold (1) is oscillated.

5. Method in accordance with claim 1, wherein the cast strand (11) is cast together with the flux powder slag (10) that forms.

6. Method in accordance with claim 1, wherein, to control the amount (4) of ingot mold coolant and the intake temperature (5) of the ingot mold coolant, process data and plant data are introduced, which are processed into controlled variables in an online simulation model (27.4).

7. Method in accordance with claim 1, wherein a direct determination of the copper plate skin temperature (8) in the region of the liquid metal level is used in addition to or alternatively to the online simulation model (27.4).

8. Device for cooling the copper plates (1.1) of a continuous casting ingot mold (1), especially for molten steel, with cooling channels through which ingot mold coolant (2) flows, wherein controlled variables (27.3) are provided for controlling the intake temperature (5) of the ingot mold coolant and/or the amount (4) of ingot mold coolant at casting rates (6) between 1 m/min and a maximum of 12 m/min and at copper plate thicknesses (9) of 4 mm to about 50 mm.

9. Device in accordance with claim 8, wherein the ingot mold coolant intake (3) is located some distance above the liquid metal level.

10. Device in accordance with claim 8, wherein the continuous casting ingot mold (1) is oscillated by an oscillation device.

11. Device in accordance with claim 8, wherein flux powder is supplied to the cast strand (11) during casting.

12. Device in accordance with claim 7, wherein a process-control computer (27), which is supplied with process data (27.1) and plant data (27.2) for an online simulation model (27.4) for controlled variables (27.3) for controlling the intake temperature (5) of the ingot mold coolant and/or the amount (4) of ingot mold coolant, controls a three-way valve (24) and a control valve (29) as well as a speed-controlled pump (22) in the ingot mold coolant circulation.

13. Device in accordance with claim 8, wherein, in addition to or instead of the process-control computer (27), a device for determining the copper plate skin temperature (8) in the region of the liquid metal level is used to control the intake temperature (5) of the ingot mold coolant and/or the amount (4) of ingot mold coolant.