AT520084B1 - Method for operating a cast-rolled composite plant and cast-rolled composite plant - Google Patents

Abstract

The invention relates to a method for operating a cast-rolled composite plant and a cast-rolling composite plant. The invention is intended to reduce the adhesion of scale to the strand (30), so that the strand (30) can either be finish rolled completely without descaling or at least the number of descaling steps or the intensity of the descaling can be reduced. This object is achieved in that the two broad sides of the strand (30) either in the continuous casting machine (1) or after leaving the continuous casting machine (1) are coated with a coating material, wherein the strand (30) in the coating a surface temperature TSurf of 1150 ° C.> Turf> 900 ° C. and the coating material hinders the diffusion of oxygen (O 2) into the strand (30) or reduces the reactivity of the hot broad sides, and wherein the coated strand (30) is uncentered into the roughing train (6) entry.

Description

description

METHOD OF OPERATING A GATE-ROLL COMPOSER AND GAS-WALZ ASSEMBLY

FIELD OF TECHNOLOGY

The present invention relates to the technical field of cast-rolling composite plants and the production of flat, metallic steel products on a casting-Walz-Ver-bundanlage.

Specifically, the invention relates to a method for operating a cast-rolling Verbundanla-ge, wherein in a continuous casting machine molten steel is poured into an endless strand with slab cross section, preferably thin slab cross section, the strand in a roughing mill to a pre-strip pre-rolled, the pre-strip finish-rolled in a finishing train to a finished strip, and the finished strip is discharged after cooling as a plate or reel.

Moreover, the invention relates to a cast-rolling composite plant for carrying out the method according to the invention, comprising [0004] - a continuous casting machine for casting molten steel into an endless strand of slab cross-section, preferably thin slab cross-section, [0005] - a roughing mill for pre-rolling the strand into a pre-strip, - a finishing train for finish-rolling the pre-strip into a finished strip, - a cooling section for cooling the finished strip, and [0008] - a discharge device for conveying the cooled finishing strip as a plate or reel.

STATE OF THE ART

Cast-rolling compound plants, such as an Arvedi-ESP plant, a CSP plant or a QSP-DUE plant, have become established for the production of flat steel products on the market.

Due to the typically relatively high surface temperatures of the cast strand when leaving the continuous casting or by the use of a tunnel furnace after the continuous casting of the strand within a short time scaled relatively strong. Although the use of inert furnaces is known from the literature, their high operating costs are currently not yet economical. By descaling the scaled surfaces, the temperature of the strand or pre-strip is also greatly reduced, whereby an energy-intensive heating of the pre-strip before finish rolling is necessary. As a result, the energy efficiency of the cast-rolling composite system drops and the operating costs increase.

From EP 916 414 the application of a so-called reactant on a pre-strip in a cast-rolling composite system is known. As examples of the reactant, metal powder, carbon but also metal oxides are mentioned.

From the publication M. Sartor et al. "Reducing Material Loss from Scale on Reheating with Coatings", Stahl and Eisen, 136, No. 2, 2016 discloses the use of a silicon-based inorganic compound as a coating material. By coating, the scale-related loss of material is to be reduced.

SUMMARY OF THE INVENTION

The invention is based on the object, not the formation of scale to the but to reduce the adhesion of the scale to the strand or the thin slab, so that the scale either finished without descaling or at least the number of descaling and / or the intensity of the descaling can be reduced.

In particular, the use of energy in the operation of the descaling devices over the prior art should be able to be significantly reduced, without this having a negative effect on the quality of the finish strip.

This object is solved by the subject matter of claim 1. Advantageous embodiments are the subject of the dependent claims.

Specifically, the solution is carried out by a generic method, wherein the two broad sides of the strand or the slab are either already coated in the continuous casting machine or after leaving the continuous casting machine with a coating material. However, the coating takes place before any possible intermediate heating of the strand or the slab and before roughing. The strand or slab has a surface temperature TSurf of 1150 ° C.> TSurf> 900 ° C. during the coating. The applied coating material hinders the diffusion of oxygen O 2 into the strand or reduces the reactivity of the hot broadsides. Subsequently, the coated strand or the slab enters the roughing train without being descaled. Thus, the invention is suitable both for continuous cast-rolling compound systems as well as for batch or semi-continuous operation.

By impregnating the hot broad sides of the strand in the continuous casting or preferably after leaving the continuous casting machine with a coating material, an intimate connection between the strand and the coating material is achieved. By the coating material, e.g. a powdery borate, the diffusion of oxygen into the strand is hindered or reduced the reactivity of hot broadsides. By direct pre-rolling of the coated strand in the roughing mill, i. without being descaled beforehand, the energy efficiency of the cast-rolling process is significantly increased.

The coating material may be either in solid form, e.g. as a powder, in liquid form, or as an emulsion, e.g. as a powder dissolved in a carrier (e.g., water).

In particular, the coating material can be sprayed onto the broad sides together with a liquid or gaseous carrier, in particular water or air, or the coating material can be rolled or brushed.

A particularly low adhesion of the scale is achieved when the coating material is a borate, in particular a salt of boric acid, more preferably a sodium salt of boric acid, most preferably borax with or without water of crystallization, such as Anhydrous borax (Ν32Β4Ο7), Boraxpentahydrate ( Na2B4O7 5H2O) or borax decahydrate (Na2B4O7-10H2O), or the coating material contains at least one of these compounds.

For homogenization of the temperature profile in the strand or to compensate for a drop in temperature, it is advantageous if the coated strand is heated before entering the roughing mill in a tunnel furnace, whereby the temperature of the strand or the slab homogenized either over the thickness and / or a temperature drop is compensated. The tunnel kiln can, for example, also be operated with an oxidizing or reducing atmosphere.

Particularly in the case of thin finished strip thicknesses, it is advantageous if the strand, the pre-strip and the finished strip pass through uncut through the continuous casting machine, the roughing train and the finishing train.

In order to prevent the rolling of the scale in the roughing or finish rolling, it is advantageous if the scale has a high ductility. This is achieved if, for example, the scale consists of the phase fractions 4-6% FeO, 30-40% Fe3O4 and 55-65% Fe2O3.

Depending on the steel quality or surface requirements, it may be appropriate to descalate the broad sides of the pre-rolled pre-strip before, preferably immediately before, the entry into the finishing train.

In most cases, however, it will be sufficient for the pre-strip to enter the finishing train without being descaled and for the finished strip to be pickled after leaving the cast-rolled composite plant.

The object of the invention is also achieved by a casting-rolling compound according to claim 15, wherein in the strand guide of the continuous casting machine or after the continuous casting machine and before Vorwalzstraße a coating machine for coating the two broad sides of the strand is arranged with a coating material, and the coated strand enters the roughing train without being descaled.

Preferably, the coating machine comprises a mixer for intimately mixing the solid or liquid coating material with a liquid or gaseous carrier, wherein the coating material is sprayed by spray nozzles on the broad sides of the strand.

Alternatively, the coating machine may comprise a roller for rolling the coating material or brushes for brushing the coating material on the broad sides of the strand.

To protect people from contact with the coating material, it is advantageous if the coating is carried out under a suppression, wherein the non-adhering to the broad sides of the coating material is sucked through a suction device.

As already stated above, it may be expedient if a tunnel oven is arranged in the transport direction after the coating machine and before the rough rolling mill.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and features of the present invention will become apparent from the description of non-limiting embodiments. 1 shows a cast-rolling composite installation according to the prior art FIG. 2 shows a cast-rolled composite installation according to the invention [0034] FIG. 3 shows a first variant with a cast-rolled installation according to the invention. 4 shows an illustration of a water circulation system for a coating device FIG. 5 shows an illustration of a coating device with extraction system [0037] FIG. 6 shows a second variant with a cast-rolled composite plant according to the invention in FIG

DESCRIPTION OF THE EMBODIMENTS

1 shows a casting-rolling compound with a continuous casting machine 1, a tunnel kiln 4, a roughing mill 6, a finishing train 8, a cooling section 9 and at least one coiler 10 according to the prior art. In the mold 2 of the continuous casting machine 1, a teilerstarrter strand 30 forms with the cross section of a thin slab 16. Optionally, the endless strand 30 can be cut by scissors 3 into slabs. The strand 30 or the thin slab 16 is then heated in the tunnel kiln 4, whereby the temperature profile is evened out or temperature losses are compensated. Before the rough rolling in the rough rolling 6, the strand 30 and the thin slab 16 is descaled by a descaling 5, whereby the surface temperature drops by about 50 to 100 ° C. After pre-rolling, the so-called. Vorband on an induction furnace 7

Rolling temperature heated. In order to prevent the rolling of scale in the finishing train 8, the pre-strip is descaled by a further descaler 5, whereby the surface temperature in turn drops by about 50 to 100 ° C. After finish rolling, the finished strip in the cooling section 9 is cooled to reel temperature and wound up by a coiler 10. Optionally, the finished strip is cut by a pair of scissors 3 on bundle length.

The two-time descaling decreases the energy efficiency of the cast-rolling composite plant. Since the finish rolling typically has to take place at a predetermined temperature or austenitic grades in the so-called austenitic temperature range, temperature drops must be compensated by the induction furnace 7.

FIG. 2 shows a first cast-rolled composite plant according to the invention. In contrast to FIG. 1, the broad sides of the strand 30 are either already coated in the continuous casting machine 1 or after the continuous casting machine 1 by a coating machine 11 with a coating material.

In this case, the strand 30 with thin slab cross section or the thin slab 16 has a surface temperature between 900 and 1150 ° C. As the coating material, e.g. Borax with or without water of crystallization, such as Anhydrous borax (Na2B4O7), borax pentahydrate (Na2B4O7 5H2O) or borax decahydrate (Na2B4O7-10H2O). The powdered coating material is used in the coating machine 11 either together with a carrier, e.g. Water or air sprayed or brushed on the broadsides.

Due to the high surface temperature, the coating material adheres to the broad sides and ensures that the diffusion of oxygen into the strand or the thin slab hindered or the reactivity of hot broadsides is reduced. After coating, the undentescended strand 30 is pre-rolled in the roughing train 6. Subsequently, the pre-strip is heated by the induction furnace 7 to rolling temperature. Depending on the quality requirements of the finished strip, the heated pre-strip is descaled by the descaling 5 or not. Since the Entzunderer 5 is optional, it was shown by dashed lines. After finish rolling in the finishing train 8, the finished strip is cooled and rewound as in the prior art.

For medium demands on the surface quality of the finished belt has been found that the descaling before finish rolling can often be dispensed with, especially if the finished strip is pickled after being coiled. Especially in this case, but also in the case of one-time descaling before finish rolling, the energy efficiency of the casting-rolling process is significantly increased.

In Fig 3, a second cast-rolling composite plant according to the invention is shown. In contrast to FIG. 2, the strand 30 or the thin slab 16 is heated after being coated in a tunnel kiln 4. By heating, the temperature of the strand 30 or the thin slab 16 is increased, the temperature profile is uniformed and a temperature drop compensated. Despite the coating, a scale layer is formed, in particular in the tunnel kiln 4. On the coated strand or the coated thin slab, an extremely ductile primary scale with the phase proportions 4-6% FeO, 30-40% Fe3O4 and 55-65% Fe2O3 forms, whereby the rolling of the primary scale in the pre-6 and the finishing train 8 is prevented. The intermediate heating, cooling and coiling takes place analogously to FIG. 2.

Finally, FIG. 6 shows a very advantageous embodiment of the cast-rolled composite plant according to the invention, wherein the rolling takes place not only completely without descaling but also on the division of the rolling stands between pre-rolling and finishing rolling. In contrast to FIG. 3, the coated, preferably endless, strand 30, after being preheated in the tunnel kiln 4, descents into the seven-stand rolling mill 8a and is finish-rolled there to form a finished strip. The cooling and coiling takes place analogously to FIG. 2. This mode of operation is very advantageous in continuous operation when the continuous casting machine 1 is operated at high casting speeds vc, e.g. vc> 6 m / min, can be operated. in the

Batch or semiendless operation, the strand 30 is cut by the scissors 3 in thin slabs 16 and then finish-rolled without intermediate heating or descaling. Preferably, the thin slabs 16 are accelerated on the roller table between the shears 3 and the rolling train 8a, so that the time that the thin slab is exposed to the oxygen in the air, is reduced. By coating the strand with a coating material, the diffusion of oxygen into the strand or the thin slab is hindered or the reactivity of the hot broadsides is reduced. The measures described not only improve the energy efficiency of the casting-rolling process but also drastically reduce the complexity of the cast-rolling composite plant. Both measures allow a cost-effective production of high quality finished strip.

4 shows a cross section through a coating machine 11 for spraying a coating material with a liquid carrier. For this purpose, a pump 14 sucks a carrier material from a tank 19, in this case water. To prevent damage to the pump 14, the water is filtered before pumping. The coating material 12, here powdered borax (would also be possible an emulsion of water and borax) is sucked by a Venturi mixer 13 from the container 12 and mixed with the pressurized water and then by spray nozzles 17 on the broad sides of the thin slab strand 30 and Thin slab 16 sprayed on.

The superfluous emulsion of water and borax is fed back to the tank 19 at the lowest point of the coating machine 11 via a return line 18.

In contrast to Figure 4, Figure 5 shows a cross section through a coating machine 11 for spraying a coating material with a gaseous carrier. For this purpose, a compressor sucks 20 air. The coating material 12, here again powdered borax, is sucked out of the container 12 by a Venturi mixer 13, mixed with the compressed air and then sprayed by spray nozzles 17 onto the broad sides of the thin slab strand or the thin slab 16. In order to prevent borax vapors, the interior of the coating machine 11 is held by the fan 21 under a suppression, so that there can be no contact between the operators of the cast-rolling composite plant and the borax.

Although the invention has been further illustrated and described in detail by the preferred embodiments, the invention is not limited by the disclosed examples, and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

REFERENCE LIST 1 Continuous Caster 2 Mold 3 Scissors 4 Tunnel Furnace 5 Descalator 6 Pre-Rolling Line 7 Induction Furnace 8 Finish Rolling Line 8a Rolling Line 9 Cooling Section 10 Coiling Line 11 Coating Machine 12 Coating Material Containers 13 Venturi Mixer 14 Pump 15 Filter 16 Slab or Thin Slab 17 Spray Nozzles 18 Return Line 19 Tank 20 Compressor 21 Fan 30 strand

Claims (18)

claims 1. A method for operating a cast-rolled composite plant, wherein in a continuous casting machine (1) molten steel to an endless strand (30) with slab cross section, preferably thin slab cross section, the strand (30) in a roughing mill (6) pre-rolled to a pre-strip, the pre-strip finish-rolled in a finishing train (8) to a finished strip, and the finished strip is discharged after cooling as a plate or reel, characterized in that the two broad sides of the strand (30) either in the continuous casting or after Leaving the continuous casting machine (1) are coated with a coating material, wherein the strand in the coating has a surface temperature Tsurf of 1150 ° C> Tsurf> 900 ° C and the coating material obstructs the diffusion of oxygen (O2) in the strand or the reactivity of the reduced hot broadsides, and wherein the coated strand (30) uncentered in the Vorwalzstra ße (6) enters. 2. The method according to claim 1, characterized in that the coating material is solid or liquid. 3. The method according to claim 2, characterized in that the coating material and by a liquid or gaseous carrier, in particular water or air, is sprayed onto the broadsides, or the coating material is rolled or brushed. 4. The method according to claim 3, characterized in that the coating material is a borate, in particular a salt of boric acid, more preferably a sodium salt of boric acid, most preferably borax with or without water of crystallization, such as anhydrous borax (Na2B4O7), borax pentahydrate (Na2B4O7 5H2O) or borax decahydrate (Na2B4O7-10H2O), or the coating material contains at least one of these compounds. 5. The method according to any one of the preceding claims, characterized in that the coated strand (30) before entering the Vorwalzstraße (6) is heated in a tunnel furnace (4), whereby the temperature of the strand (30) is homogenized either over the thickness and / or a temperature drop is compensated. 6. The method according to claim 5, characterized in that the tunnel furnace (4) has an oxidizing atmosphere. 7. The method according to claim 5, characterized in that the tunnel furnace (4) has a reducing atmosphere. 8. The method according to any one of the preceding claims, characterized in that the strand (30), the pre-strip and the finished strip uncut the continuous casting machine (1), the roughing train (6) and the finishing train (8) passes through. 9. The method according to any one of the preceding claims, characterized in that the scale when entering the strand (30) in the roughing train (6) has a high ductility, so that the scale in the roughing train (6) is not rolled. 10. The method according to claim 9, characterized in that the scale of the phase portions 4 - 6% FeO, 30 - 40% Fe3O4 and 55 - makes up 65% Fe2O3. 11. The method according to any one of the preceding claims, characterized in that the broad sides of the pre-strip are descaled before, preferably immediately before, the entry into the finishing train. 12. The method according to any one of claims 1 to 10, characterized in that the scale when entering the Vorstreifens in the finishing train (8) has a high ductility, so that the scale in the finishing train (8) is not rolled. 13. The method according to claim 12, characterized in that the scale of the phase portions 4 - 6% FeO, 30 - 40% Fe3O4 and 55 - makes up 65% Fe2O3. 14. The method according to claim 12 or 13, characterized in that the pre-strip enters the finishing train (8) without descaling and the finished strip is pickled after leaving the casting-rolling compound. 15. Cast-rolling composite plant for carrying out the method according to one of the preceding claims, comprising - a continuous casting machine (1) for casting molten steel to an endless strand (30) with slab cross section, preferably thin slab cross section; - A pre-rolling line (6) for pre-rolling of the strand (30) to a pre-strip; - A finishing train (8) for finish rolling the Vorstreifens to a finished strip; - A cooling line (9) for cooling the finished strip; and - a discharge device (10) for discharging the cooled finished strip as a plate or reel; characterized in that in the strand guide of the continuous casting machine (1) or after the continuous casting machine (1) and before the rough rolling mill (6) a coating machine (11) for coating the two broad sides of the strand (30) is arranged with a coating material, and that coated strand (30) enters the pre-rolling line (6) without descaling. 16. Cast-rolling composite plant according to claim 15, characterized in that the coating machine (11) comprises a mixer (13) for intimately mixing the solid or liquid coating material with a liquid or gaseous carrier, and the coating material by spray nozzles (17) the broad sides of the strand (30) is sprayed. 17. Cast-rolling composite plant according to claim 15, characterized in that the coating machine has a roller for rolling the coating material or brushes for brushing the coating material on the broad sides of the strand. 18. Cast-rolling composite plant according to claim 16 or 17, characterized in that the coating takes place under a suppression, wherein the non-adhering to the broad sides of the coating material is sucked through a suction device (21).