EP1047510B1 - Method and installation for the continuous production of hot-rolled, thin flat products - Google Patents

Abstract

A method and an installation for the endless production of hot-rolled, flat products from thin cast strip. The installation includes a casting machine for producing cast strip, a device for cooling the cast strip under inert gas, a single-stand roughing train, a multi-stand finishing train, a device for cooling, heating or maintaining the temperature of the hot-rolled strip, according to choice, between the roughing train and the finishing train, shears for separating the hot-rolled strip from coil to coil, a delivery roller table with devices for cooling the hot-rolled strip and with coiling machines arranged downstream of the finishing train for coiling up the finished strip.

Description

The invention relates to a production method and a system for endless Production of hot rolled thin flat products from thin cast Band, consisting of a single-skid road, a multi-skid Finishing line, an outfeed roller table with facilities for cooling the hot strip and the cooling devices upstream and downstream winding machines for Winding up the hot strip.

To produce hot-rolled strips, slabs are used as the starting material a thickness greater than 120 mm or thin slabs with thicknesses between 40 and 120 mm used. In the case of individual slabs, the rolling mills generally consist of a single or multi-stand rough street in which the slabs in several Rolling passes are reduced in reverse operation, as well as a multi-stand Prefabricated street or a Steckel scaffold. The almost uniform temperature The hot strip length is either between a preliminary and a Finishing line, by speed-up in the finishing line or by coiler in front and reached behind the Steckel scaffold. In these cases it is a discontinuous process, i.e. Rough and finishing lines generally work decouples and roll the individual slabs.

In a system known from EP 753 359 A1, the system in the Vorstrasse rolled slabs of two slabs between the roughing and finishing lines at the head and The foot is welded using a heating and pressing device. The seam between the two pre-strips is then mechanically processed before the opening strip runs into the finishing train. Then it becomes endless in the finishing train rolled, while the rough road works discontinuously. Disadvantages are those with one Problems related to process stability and hot strip quality in the seam Area of the rolled piece of the seam. A ferritic or mixed Austenitic-ferritic rolling is only possible with the structural transformation in the Finished line possible with the disadvantages already mentioned.

In the case of thin slabs, a distinction must be made between rolling mills Thin slabs with a thickness of 40 to 65 mm or greater than 65 mm as Use raw material.

The former consist of a multi-stand finishing train with an outfeed roller table Devices for cooling the hot strip to winding temperature and Winding machines for winding up the hot strip.

The plants for thin slabs> 65 mm exist due to the same final thickness necessary larger deformation work from a single or multi-stand Vorstrasse with more than one roll pass and a multi-stand finishing train as well as an outfeed roller table with facilities for cooling the hot strip Winding temperature and winding machines for winding the hot strip. Between There are facilities for heating and / or winding in the front and finishing lines of the preliminary strip, which is the necessary entry temperature of the hot strip into the Ensure the finishing train over the length of the hot strip.

The rolling mills are generally designed and operated so that the Forming in the individual stitches fully austenitic or mixed austenitic-ferritic.

In austenitic rolling, the rolling temperature is above that in all passes GOS line of the iron-carbon diagram, with the finish rolling temperature in the last scaffolding of the finishing train to achieve a fine-grained structure should be above the GOS line.

When mixed austenitic-ferritic rolling of steels with one Carbon content greater than 0.015%, the rolling temperature is in the last Scaffolding of the finishing train below the GOS line in the range from approx. 810 to 890 ° C. This can be achieved with the same final thickness by lowering the Furnace outlet temperature of the slabs can be reached, which increases the proportion of in Solution micro-alloy elements is reduced and the quality of the Hot strip lowers. There is also a reduction in the rolling speed without a lowering of the furnace outlet temperature of the slabs is possible, whereby a the rolling stock is cooled more intensely. But that leads to the disadvantage of one reduced production. It is also possible to combine both measures with the disadvantages already mentioned.

With ferritic rolling, the final rolling temperature is reduced to a minimum 720 ° C through those already mentioned for mixed austenitic-ferritic rolling Measures including their disadvantages. The ferritic area is only in the Last two to three passes were achieved, causing the decrease in this area is low. The conversion point lies (in the middle) within the finishing street and shifts as a result of temperature influences between the scaffolds Rolling force drops due to the lower deformation resistance of the material in the leads ferritic temperature range. This is disadvantageous for the roll bending and Roller adjustment systems to ensure thickness, profile and contour as well Flatness of the hot strip, as these systems measure the rolling force as Use output signal.

DE 196 00 990 A1 proposes the hot strip between the stands of the Finishing line with a cooling rate of more than 30 ° K / s to Cool ferrite transformation. Since the structural transformation and the Temperature equilibrium between the core and surface takes time Compensating section from a few meters after the cooling section to the next scaffold required. However, this is disadvantageous for austenitic rolling with a Finish rolling temperature greater than 890 ° C; because an increase in the spacing between the scaffolding increases the temperature losses of the hot strip.

In EP 0 761 325 A1 is behind a multi-stand rolling mill Outfeed roller table, facilities for cooling the hot strip and downstream Winding machines for winding up the austenitic rolled hot strip second downstream single or multi-stand rolling mill for ferritic rolling proposed by hot strip. That in the first multi-stand rolling mill The hot strip is initially austentitically deformed with the help of the between the two Mills arranged devices for cooling in the ferritic Cooled temperature range. The downstream single or multi-stand rolling mill is used exclusively for ferritic rolling, which practically means two rolling trains are required, which represents a high investment in plant technology.

EP 0 761 326 A1 proposes a production plant consisting of a multi-stand rolling mill, an outfeed roller table with facilities for cooling of the hot strip and downstream winding machines, in which at least that the first scaffold is designed as a reversing scaffold with at least one coiler are upstream and downstream, between the upstream reel furnace and the following reversing frame a controllable cooling device is provided. After this Rolling the hot strip in the austenitic temperature range becomes the hot strip cooled in the ferritic temperature region by means of the controllable cooling device and wound up in the reel furnace. The structural transformation takes place in the reel furnace. Then it is reversed by the one downstream of the coiler Rolled mill in the ferritic temperature range. Austenitic rolling is not cooled. The hot strip can be between the Rolling mills are heated. Different arrangements of scaffolding and Coiler furnaces are proposed. The characteristic is in any case Reverse operation, making the proposed production facility not endless can roll continuously. Increase the additional reel furnace (s) required the plant engineering effort.

Production plants for rolling hot strip are also known Thin slabs in which a single or multi-stand rough road facilities for cooling and heating are subordinate. These facilities are one Multi-stand finishing train with an outfeed roller table, facilities for cooling and winding machines for winding the hot strip downstream. As a general rule At least two roll passes are made in austenitic in the Vorstrasse Temperature range, either in multiple stands in continuous operation or in a single stand in reverse operation. For ferritic or mixed austenitic-ferritic rolls, the hot strip is used in the facilities Cooling between the roughing and finishing lines to the temperature of the respective one Temperature range cooled and then ferritic or in the finishing train mixed austenitic-ferritic finish-rolled. In the case of austenitic rolling, this becomes Hot strip in heating facilities between roughing and finishing lines reheated or kept at the same temperature in order to also be austenitic in the Finished mill can be finished rolled. Individuals are rolled Thin slabs or a melt cast into a long thin slab, where the weight of the long thin slab is a multiple of a single Corresponds to thin slab, i.e. in both cases the Rolling process.

All known or proposed production systems is the run of the Starting material through a furnace or an inductive heating system for Purpose of heating or temperature compensation across thickness and width or the homogenization of the starting material before rolling together.

The known production plants need facilities for descaling the Starting material before the first stitch and before the finishing train. The need the descaling of the starting material before the first stitch results from the scaling of the surface of the starting material during this Pass through a heating, equalizing or homogenizing furnace or one inductive heating system. The need for descaling before The finishing mill results from the secondary scaling of the hot strip in the Area of the Vorstrasse and between the Vorstrasse and Fertigstrasse.

The production process in the known or proposed production facilities is discontinuous or in the case of welding hot strip after Vorstraße only continuously in the finishing train.

All known or proposed production facilities are due to the Discontinuity in the process of adverse load shocks during the piercing of the Starting material in the scaffolding of the roughing or finishing train and during the Tapping the hot strip rolled in the roughing mill into the finishing mill as well while the finished hot strip is being fed into the winding machine together, which increases the wear of the system parts and their service life is reduced.

Roll gap lubrication can be carried out in the scaffolding of the roughing and finishing train known production plants only after tapping the raw material or of the hot strip in the respective scaffolding, otherwise the Gripping condition is not guaranteed. The associated with the roll gap lubrication Reduction. The friction between the rolling stock and the roll leads to a reduction in the Resistance to deformation and thereby the rolling force, the rolling moment and the required drive power. The surface quality of the hot strip is elevated. However, these advantages do not arise for the tapping piece of the Hot strip, which after rolling out a considerable part of the length of the Makes up hot strip. In addition, the production facilities for the Load condition can be designed without roll gap lubrication.

Finally, all known or proposed production facilities are due the discontinuity of the process adversely affects the quality Length of the rolled hot strip common, since the production facilities according to adjusted every time a slab, thin slab or hot strip is tapped Need to become.

In this prior art, the object of the invention is to: Production plant for the austenitic, the mixed austenitic-ferritic and the ferritic rolling of thin hot strip in an endlessly fully continuous To create a process that eliminates the aforementioned drawbacks and problems and on which all three previously mentioned technologies can be realized

The task is solved with a production plant of the type mentioned at the beginning Art according to the invention in that the cast in a thickness of 5 - 18 mm Belt before reaching the single-deck forecourt under a protective gas atmosphere controlled cooled and the pre-rolled hot strip in one of the rough streets downstream device either controlled cooled, heated or on Temperature is maintained and the edges of the hot strip are reheated.

The production process is specially designed for rolling thin cast strip all three possible technologies, i.e. the austenitic, the austenitic-ferritic and the ferritic rolling. Can from the thin casting belt endless and fully continuous strip material with small thicknesses both austenitic and ferritic as well as mixed austenitic-ferritic with a total decrease of at least 65% based on the overall system.

All that is required is depending on the duo, quarto or sex scaffolding Work roll diameters from 300 to 900 mm as well as those for hot and Cold rolling processes usual actuators and control loops for targeted Temperature control and to ensure the required finished product tolerances for thickness, profile, flatness and material and mechanical properties.

According to the invention, the rolling temperature in the austenite region is in the single-stand forecourt by variably controlled cooling of the casting belt in front of the Vorstrasse set. With the targeted cooling of the solidified casting belt of the The thickness is 5 to 18 mm under an adjustable protective gas atmosphere required parameters temperature, austenite starting grain size, the degree of Scale and chemical composition of the scale before the first Roll stitch set.

It is preferably provided that carbon steels, low-alloy steels, are low Carbonized steels and microalloyed steels through a material-dependent acceptance from 45 to 70% in the single-armed Vorstrasse in connection with the in austenitic range of variably adjustable rolling temperature and which adapts to the Forming subsequent cooling, heating or maintaining the temperature until Recrystallize entry into the multi-stand finishing train and the initial grain size of the casting belt with one stitch greatly reduced, but at least halved becomes.

In a further embodiment of the invention it is provided that the Rolling temperature before the multi-stand finishing train through the behind the roughing train arranged device for controllable cooling, heating or holding the Hot strip temperature optionally in the austenite or ferrite area or in the Transition range from austenite to ferrite is selectively adjustable.

Through a material-dependent total decrease of more than 50% in the Multi-stand finishing train in connection with the selectively adjustable According to the invention, the rolling temperature in the hot strip becomes a fine-grained structure grain size classes 6 - 10 according to DIN 50601.

Due to the rolling temperature, which is variably adjustable by means of cooling, the material-dependent high decrease of 45 - 70% in the one-stand forelevel and the variably controllable cooling, heating or maintaining the temperature of the Hot strip is the recrystallized hot strip before it enters the finishing train and greatly reduced the starting grain size of the casting belt.

It is also provided that the ferritic is endless and the mixed austenitic-ferritic endless continuously rolled hot strip immediately after the exit from the last scaffolding of the multi-stand finishing train in heat-insulated Winding machines wound into a bundle and one homogeneous across the bundle width is subjected to slow cooling.

It turned out to be cheap, the austenitic endless fully continuous rolled hot strip after emerging from the last stand of the multi-stand First, force-cool the finishing train from above and then add the hot strip targeted structural transformation to cool to winding temperature.

Since, according to the invention, the thin casting belt is provided with a starting piece, suggested that the approach piece be the open scaffolding of the Vorstrasse and the Multi-stand finishing train passes undeformed in the rolling direction and with scissors is separated from the rest of the casting line.

It is beneficial if the open scaffolding of the forecourt and the multi-scaffold Finishing line after separating the approach piece of the thin casting belt by means of the shears to those intended for rolling the required final thickness Roll nips are closed, and that rolled during the closing process Piece of the hot strip either chopped with scissors or by means of Winding machines is wound up.

To reduce the friction between the rolling stock and the roll and thereby Reduction of the rolling forces, rolling moments and drive power and to increase the surface quality over the entire length of the rolled hot strip proposed according to another feature of the invention, the rollers already during the closing of the open scaffolding of the single scaffold road and the multi-stand finishing train to the final thickness required for rolling to lubricate the intended nip.

If according to the invention the roll gap lubrication during the entire rolling time takes place, the wear on the work rolls decreases, which means that the thickness and profile of the total hot strip length can be improved and the service life of the rollers is increased.

According to the invention, after the roll gap has been closed, the single-arm Vorstrasse and the multi-stand finishing train on the for rolling the required final thickness values provided and after chopping the while of the rolling process rolled hot strip by means of scissors the stationary Condition of fully continuous endless rolling of thin casting belt has been reached and the austenitic, mixed austenitic-ferritic or ferritically rolled Hot strip can be cut into bundle lengths using scissors.

It is favorable if to increase the edge quality and the profile accuracy of the Hot strip the edges of the thin casting belt in one of the single-skinned A vertical scaffold with a special compression caliber with a low flange Decrease before the horizontal stitch and deform the thin The casting belt runs into the center of the single-row forecourt.

The fact that the starting material or the hot strip due to the endless fully continuous production process is rolled non-reversing repeated punctures and the associated shock loads.

Because the production line due to the endless. fully continuous Production process is regulated once after starting up, one constant high quality of the hot strip can be achieved over its length.

Finally, the invention provides that the degree of scaling on the Surface of the raw material and the chemical composition of the Tinder by controllable cooling of the casting belt under a protective gas atmosphere is specifically set until the first roll pass.

The invention results in an overall system concept with which in an optimal manner a fully continuous endless rolling process can be realized, all three possible rolling technologies for the production of hot strip, i.e. the austenitic, which allows mixed austenitic-ferritic and ferritic rolling.

A production system with which continuous and continuous casting of thin casting tape Strip material with small thicknesses both austenitic and ferritic as well as mixed austenitic-ferritic with a total decrease of at least 65% based on the entire system can be manufactured is in the single drawing figure shown and will be described below. It consists of one Thin slab caster 12, a first device 2 for cooling the casting belt under protective gas, a single-stand Vorstrasse 3, a multi-stand finishing train 5, a second device 4 for optionally cooling, heating or holding the Temperature of the hot strip between roughing and finishing mill, a pair of scissors 6 for Cutting the hot strip from bundle to bundle, using a run-out roller table Means 8 for cooling the rolled hot strip and one of the finishing train 5 downstream winding machines 10 for winding the finished tape

The rolling process begins with the targeted cooling of the solidified Casting belt with a thickness of 5 to 18 mm under an adjustable protective gas atmosphere, whereby the technologically required parameters temperature, austenite starting grain size Degree of scaling and the chemical composition of the scale before first roll pass can be set

The approach piece of the thin casting belt passes through the open undeformed Scaffolding of the single-stand Vorstrasse 3 and the multi-stand finishing street 5 in Rolling direction 11 and with the scissors 6 downstream of the finishing train remaining casting belt separated with one or more cuts. After that, the Open scaffolding of the single-scaffold Vorstrasse 3 and the multi-scaffold Finishing line 5 on the intended for the required final thickness rolling Roll gap closed and the piece of the rolled during the closing process Hot strip chopped using scissors 6 or using winding machines 7 or 10 coiled with.

A roller gap lubrication can be applied to the stands while the stands are still being closed Roll gaps provided for rolling the required final thickness as the gripping condition is due to the continuous up to the nip position increasing decrease is guaranteed.

The source material is endless in the single-storey Vorstrasse 3 with a material-dependent decrease of 45 to 70% for carbon steels, low alloy Steels, low-carbon and micro-alloyed steels in a horizontal stitch in austenitic temperature range rolled.

The edges of the casting belt are in front of the horizontal stitch in a single-stand Vorstraße 3 flanged vertical frame using special compression calibers slightly deformed, which means that the casting belt is simultaneously centered in the single-arm Vorstrasse arrives.

After the Vorstrasse the hot strip passes through a device 4 for controllable Cooling, heating or maintaining the temperature, thereby reducing the temperature of the Hot strip before entering the multi-stand finishing train 5 targeted in the austenite or is adjustable in the ferrite area or in the transition area from austenite to ferrite

Due to the variably adjustable rolling temperature by means of the cooling device 2, the material-dependent high decrease of 45 - 70% in the single-storey Vorstrasse 3 and the means 4 for controllable cooling, heating or holding the Temperature adjustable temperature of the hot strip is the hot strip before its entry into the finishing train recrystallized and the starting grain size of the Casting belt greatly reduced.

In the multi-stand finishing train, the hot strip is processed with a total material-dependent decrease of more than 50% to thin hot strip rolled, which in connection with the specifically adjustable rolling temperature fine-grained structure after rolling.

The ferritic and the mixed austenitic-ferritic endless fully continuous Rolled hot strip is insulated immediately after the finishing train Winding machines 7 wound into a bundle.

The austenitic, endless, fully continuously rolled hot strip runs through Leaving the finishing train 5, a cooling section 8 with forced cooling of and then a device for cooling the hot strip Winding temperature with targeted structural transformation.

The production system is adjusted once after starting up, after which one constant high quality of the hot strip over its length in the endless fully continuous process is achieved.

Reference symbol overview:

1

Production line for rolling thin casting strip

2

Device for cooling the casting belt

3

single-scored forecourt with flanged vertical scaffold

4

Device for cooling, heating or maintaining the temperature of the hot strip

5

multi-stand finishing train

6

scissors

7

thermally insulated winding machine

8th

Forced cooling section

9

Device for cooling the hot strip

10

winder

11

rolling direction

12

thin strip casting

Claims (17)

1. Production method for the continuous production of hot-rolled flat products made from thinly cast strip on an installation comprising a single-stand blooming train (3), a multi-stand finishing train (5), a run-out roller table with devices (8, 9) for cooling the hot strip and pre- and post-arranged coiling machines (7, 10) for coiling up the hot strip,
   characterised in that
   the strip which is cast in a thickness of 5 - 18 mm is cooled in a controlled manner in a protective gas atmosphere prior to reaching the single-stand blooming train (3) and the rough-rolled hot strip is cooled, heated or maintained at temperature as desired in a controlled manner in a device (4) which is arranged after the blooming train (3) and the edges of the hot strip are reheated.
2. Production method according to claim 1,
   characterised in that
   the roller temperature which lies in the austenitic region is adjusted in the single-stand blooming train (3) by means of variably controlled cooling of the cast strip prior to the blooming train (3).
3. Production method according to claim 1 and claim 2,
   characterised in that
   carbon steels, low alloy steels, low carbon steels and micro-alloyed steels re-crystallise by means of a material-dependent decrease of 45 to 70% in the single-stand blooming train (3) in conjunction with the roller temperature, which is variably adjustable in the austenitic range, and with the cooling, heating or maintaining of the temperature (4) subsequent to conversion up to entry into the multi-stand finishing train (5) and the initial grain size of the cast strip is severely reduced, in only one roll pass, but at least halved.
4. Production method according to claim 1 and claim 2,
   characterised in that
   the roller temperature is adjustable in a specific manner prior to the multi-stand finishing train (5) by means of the device (4), which is disposed behind the blooming train (3), for controllable cooling, heating or maintaining of the temperature of the hot strip as desired in the austenite or in the ferrite range or in the transition range from austenite to ferrite.
5. Production method according to claim 1 to 4,
   characterised in that
   a fine-grained texture of the grain size classes 6 - 10 according to DIN 50601 is produced in the hot strip by means of a material-dependent total decrease of greater than 50% in the multi-stand finishing train (5) in conjunction with the roller temperature which is adjustable in a specific manner.
6. Production method according to claim 1 to 5,
   characterised in that
   the ferritically endlessly and the mixed austenitically-ferritically endlessly, fully continuously rolled hot strip is coiled up into a coil in heat-insulated coiling machines (7) immediately after exiting from the last stand of the multi-stand finishing train (5) and is subject to a homogenously slow cooling over the coil width.
7. Production method according to claim 1 to 5,
   characterised in that
   the austenitically endlessly fully continuously rolled hot strip is first forcibly cooled (8) from above after exiting from the last stand of the multi-stand finishing train (5) and the hot strip is thereafter cooled (9) to coiling temperature with a specific texture conversion.
8. Production method according to claim 1 to 5,
   characterised in that
   the thin cast strip is provided with a dummy bar, which passes unworked in the roller direction through the opened stands of the single-stand blooming train (3) and of the multi-stand finishing train (5) and is separated from the remaining cast strip by the shearing machine (6).
9. Production method according to claim 1 to 5 and 8,
   characterised in that
   the opened stands of the single-stand blooming train (3) and of the multi-stand finishing train (5) are closed after the separation of the dummy bar of the thin cast strip by means of the shearing machine (6) to the roller gap which is provided for rolling of the required end thickness and the piece of the hot strip, which is rolled during the closing process, is either chopped off by means of a shearing machine (6) or coiled up by means of coiling machines (7, 10).
10. Production method according to clam 1 to 9,
    characterised in that,
    in order to decrease the friction between rolled product and roller and consequently to reduce the roller powers, roller torques and to increase the surface quality over the entire length of the rolled hot strip, the rollers are already lubricated during closing of the opened stands of the single-stand blooming train (3) and of the multi-stand finishing train (5) to the roller gap which is provided for rolling of the required end thickness.
11. Production method according to claim 10,
    characterised in that
    the roller gap lubrication is effected during the entire rolling time.
12. Production method according to claim 1 to 5 and 8 to 11,
    characterised in that,
    after closing the roller gap of the single-stand blooming train (3) and of the multi-stand finishing train (5) to the values which are provided for rolling of the required end thickness and after chopping off the hot strip piece, which is rolled during the closing process, by the shearing machine (6), the steady-state condition of the fully continuous, endless rolling of thin strip is achieved and the austenitically, mixed austenitically-ferritically or ferritically rolled hot strip is separated by means of the shearing machine (6) into coil lengths.
13. Production method according to claim 1 to 3,
    characterised in that,
    in order to increase the edge quality and the profile accuracy of the hot strip, the edges of the thin cast strip are deformed before the horizontal roll pass with less reduction in a vertical stand with special edging pass, which vertical stand is flanged onto the single-stand blooming train (3), and at the same time the thin cast strip feeds centrally into the single-stand blooming train (3).
14. Production method according to claim 1 to 3,
    characterised in that
    the initial material or the hot strip is non-reversibly rolled as a result of the endlessly fully continuous production process.
15. Production method according to claim 1 to 14,
    characterised in that
    the production installation is stabilised on a once-through basis after start-up as a result of the endlessly fully continuous, production process, as a result of which a constant high quality of the hot strip over its length is achieved.
16. Production method according to claim 1 to 15,
    characterised in that
    the degree of the scaling on the surface of the initial material and the chemical composition of the scale is adjusted specifically by means of the controllable cooling of the cast strip in a protective gas atmosphere up to the first roll pass.
17. Production installation for implementation of the method according to the invention according to one or more of the claims 1 to 16, comprising a casting machine (12) for producing the cast strip with a thickness of 5 - 18 mm, a device for cooling the cast strip in protective gas (2), a single-stand blooming train (3), a multi-stand finishing train (5), a device (4) for cooling, heating or maintaining of the temperature of the cast strip as desired between the blooming and the finishing train (3, 5), a shearing machine (6) for separating the hot strip from coil to coil, a run-out roller table with devices for cooling (8, 9) the rolled hot strip and with coiling machines (7, 10) for coiling up the finished strip which are arranged after the finishing train.

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