AT522073B1 - Hot rolling with flexible roll stand configuration - Google Patents

Abstract

A hot rolling train has at least a first and a last roll stand (1a, 1d). A first and a second metal strip (2, 5) are rolled one after the other in the hot rolling mill. Sections of the metal strips (2, 5) first pass through the first and only then the last roll stand (1a, 1d) of the hot rolling mill. The last roll stand (1d) is converted between the rolling of the first metal strip (2) and the rolling of the second metal strip (5) from a four-high stand to a six-high stand or vice versa, so that the last roll stand (1d) is converted during the rolling of the first metal strip ( 2) is configured as a four-high stand with work rolls (3) and back-up rolls (4) and during the rolling of the second metal strip (5) as a six-high stand with work rolls (6), intermediate rolls (7) and back-up rolls (4).

Description

description

NAME OF THE INVENTION Hot rolling with flexible configuration of the rolling stands

TECHNICAL FIELD

The present invention is based on an operating method for a hot rolling

road, which has at least a first and a last roll stand,

- a first and a second metal strip being rolled one after the other in the hot rolling mill,

- whereby sections of the metal strips first pass through the first and only then the last roll stand of the hot rolling mill,

- The last roll stand is converted between the rolling of the first metal strip and the rolling of the second metal strip.

The present invention is also based on a hot rolling mill, which has at least a first and a last roll stand, so that sections of metal strips rolled in the hot rolling mill first pass through the first and only then the last roll stand, the first roll stand being a four-high stand configured with work rolls and backup rolls.

STATE OF THE ART

The above-mentioned objects are generally known. In particular, finishing trains for rolling metal strips (in particular made of steel) are usually operated in this way and finishing trains for rolling metal strips (in particular made of steel) are usually designed in this way. The last roll stand (and, as a rule, also the other roll stands of the finishing train) is retooled in order to replace worn work rolls and, if necessary, worn back-up rolls. The configuration of the roll stands is not changed. There is only a 1: 1 exchange of pairs of rollers.

The roll stands of hot rolling mills are usually equipped with so-called four-high stands. Four-high stands are roll stands that, in addition to the work rolls, have back-up rolls on which the work rolls are supported. In the English-speaking world, such roll stands are often referred to as 4-high.

In hot rolling, the trend is towards ever lower final thicknesses, especially for materials with high strength. For example, in modern casting and rolling mills, a strip thickness of well below 1 mm can be produced for soft grades, sometimes even as low as 0.6 mm. Such final thicknesses cannot be achieved with stronger materials. In practice, this requires work rolls with a very small diameter. The diameter of the work rolls used today, however, limits the final thicknesses. In particular, as the work roll diameter decreases, the torque that can be transmitted also decreases. Furthermore, it must be possible to apply a sufficient amount of coolant to the work rolls so that the hot rolling mill can be operated in endless operation.

The problem is usually solved by using work rolls with the smallest possible diameter. The smaller the diameter of the work rolls, however, the lower the torque with which the work rolls can be driven without the risk of breaking the roll neck. The torque is higher with harder materials. This results in the problem that, on the one hand, the diameter of the work rolls should be as small as possible in order to be able to achieve the smallest possible final thickness, but on the other hand it must not become too small, since otherwise the required torque cannot be transmitted.

In cold rolling, the problem is solved by roll stands that have a plurality of rolls

have, for example so-called 12-roll mill stands or 20-roll mill stands. Roll stands of this type cannot be used in hot rolling because they take up too much space and do not allow adequate cooling of the rolls - especially the work rolls.

From US 2006/0 010 952 A1 it is known to design individual roll stands in a cold rolling mill so that they can be converted so that they can be configured as four-high stands or as six-high stands as required. Six-high stands are roll stands which, in addition to the work rolls and the back-up rolls, also have intermediate rolls, the work rolls being supported on the intermediate rolls and the intermediate rolls being supported on the back-up rolls. In the English-speaking world, such roll stands are often referred to as 6-high.

From US 2006/0 196 243 A1 it is also known to design a roll stand so that it can be converted so that it can be configured as a four-high stand or as a six-high stand as required. The roll stand of US 2006/0 196 243 A1 also appears to be a cold roll stand.

From JP 63 013 603 A it is known to design a roll stand so that it can be converted so that it can be configured as a four-high stand or as a six-high stand as required.

SUMMARY OF THE INVENTION

The object of the present invention is to create ways of being able to produce materials with higher strength with low final thicknesses in a hot rolling train.

[0013] The object is achieved by an operating method for a hot rolling mill with the features of claim 1. Advantageous refinements of the operating method are the subject matter of the dependent claims 2 to 7.

According to the invention, an operating method of the type mentioned is designed in that, as part of the conversion of the last roll stand, the last roll stand between the rolling of the first metal strip and the rolling of the second metal strip is converted from a four-high stand to a six-high stand or vice versa, so that the last roll stand is configured as a four-high stand with work rolls and backup rolls during the rolling of the first metal strip and is configured as a six-high stand with work rolls, intermediate rolls and backup rolls during the rolling of the second metal strip.

This conversion makes it possible to roll a metal strip from a softer material or to roll a metal strip to a greater final thickness, while the last roll stand is configured as a four-high stand as in the prior art. If, however, a metal strip made of a harder material is to be rolled to a small final thickness, according to the invention the last roll stand can be converted to a six-high stand.

It is possible to create the rolling plan (ie the sequence of the metal strips to be rolled one after the other) in such a way that the conversion of the last roll stand takes place at a time when the work rolls are expanded anyway due to the wear and tear of the work rolls currently in the last roll stand would have to be. This approach leads to optimized productivity. In principle, however, the changeover can also be carried out independently of the state of wear of the work rolls and therefore independent of any wear-related replacement of the work rolls (in the case of a four-high stand) or the work rolls and possibly also the backup rolls (in the case of a six-high stand).

Preferably, the sum of the diameter of the work rolls and intermediate rolls of the last roll stand configured as a six-high stand corresponds at least approximately - usually to 20%, better to 10% - the diameter of the work rolls of the last roll stand configured as a four-high stand. As a result, the adjustment range of the last roll stand can be optimally used both in the configuration as a four-high stand and in the configuration as a six-high stand.

Preferably, when converting the last roll stand from a four-high stand

to a six-high stand or vice versa, the work rolls and the intermediate rolls of the last roll stand configured as a six-high stand installed or removed as a unit. This means that the conversion can be carried out particularly quickly.

The first roll stand is preferably configured as a four-high stand both during the rolling of the first metal strip and during the rolling of the second metal strip. As a result, the construction of the first roll stand remains simple.

Preferably, the metal strips are cast in a continuous casting plant upstream of the first roll stand before rolling in the hot rolling mill and are fed to the first roll stand from the casting heat. As a result, the operation of the hot rolling mill can be optimized in terms of energy.

[0021] The hot rolling mill is preferably operated in endless operation. Thereby, the productivity of the hot rolling mill can be maximized.

In the minimal configuration, the hot rolling mill has only the first and the last roll stand, that is, a total of two roll stands. Often, however, the hot rolling mill has a number of further roll stands between the first and the last roll stand, for example two further roll stands, three further roll stands or four further roll stands, so that - including the first roll stand and the last roll stand - a total of four, five or six Roll stands are available. While the first metal strip is being rolled, the other roll stands are configured as four-high stands. During the rolling of the second metal strip, the further roll stands can be configured either as four-high stands or as six-high stands. Seen in the sequence of the roll stands - i.e. from the first roll stand to the second roll stand, on to the third roll stand, etc. to the last roll stand - there is preferably only one change from rolling in a four-high stand to rolling in a six-high stand. If a specific one of the further roll stands is configured as a four-high stand, all further roll stands that are arranged between this roll stand and the first roll stand are also configured as four-high stands. Conversely, if a specific one of the further roll stands is configured as a six-high stand, all further roll stands that are arranged between this roll stand and the last roll stand are also configured as four-high stands.

[0023] The object is also achieved by a hot rolling mill having the features of claim 8. Advantageous refinements of the hot rolling train are the subject of dependent claims 9 to 12.

According to the invention a hot rolling mill of the type mentioned is designed such that the last roll stand - at least temporarily - is configured as a six-high stand with work rolls, intermediate rolls and backup rolls.

Preferably, the work rolls and the intermediate rolls of the last roll stand configured as a six-high stand are arranged in a cassette that can be installed and removed as a unit. As a result, both a change of the work rolls and the intermediate rolls due to wear and a changeover to a four-high stand or a six-high stand or vice versa can take place particularly quickly.

Preferably, the first roll stand is preceded by a continuous caster in which the metal strips are cast before rolling in the hot rolling train, so that the metal strips can be fed to the first roll stand from the casting heat. As a result, the operation of the hot rolling mill can be optimized in terms of energy.

Preferably, the hot rolling mill can be operated in endless operation. Thereby, the productivity of the hot rolling mill can be maximized.

As a rule, the hot rolling train has a number of further roll stands between the first and the last roll stand. The further roll stands can be configured as four-high stands or as six-high stands. Viewed in the sequence of the roll stands - that is, from the first to the second roll stand, etc. - however, it is preferably only carried out once

Change from a four-high stand to a six-high stand.

BRIEF DESCRIPTION OF THE DRAWINGS

The properties, features and advantages of this invention described above and the manner in which they are achieved will become clearer and more clearly understood in connection with the following description of the exemplary embodiments, which are explained in more detail in connection with the drawings. Here show in a schematic representation:

1 shows a hot rolling train during the rolling of a first metal strip, [0031] FIG. 2 shows the hot rolling train from FIG. 1 during the rolling of a second metal strip,

FIG 3 shows the expansion of work rolls from a last roll stand of the hot rolling mill,

FIG 4 shows the installation of work rolls and intermediate rolls in the last roll stand of the hot rolling mill,

FIG. 5 shows the last roll stand of the hot rolling mill in two different configurations and

FIG. 6 shows a modification of the hot rolling train from FIG. 1.

DESCRIPTION OF THE EMBODIMENTS

According to FIG. 1, a hot rolling train has a plurality of roll stands 1a to 1d. The hot rolling train can in particular be designed as a finishing train.

According to FIG. 1, there are four roll stands 1a to 1d. The number of roll stands 1a to 1d could, however, also be greater, for example five, six or seven. Alternatively, it could be smaller, for example two or three. At least two roll stands 1a to 1d are available. If there are more than two roll stands 1a to 1d, a number of further roll stands 1b, 1c are arranged between the first roll stand 1a and the last roll stand 1d.

In the hot rolling mill, a first metal strip 2 is hot rolled at a certain point in time. The first metal strip 2 can in particular be a steel strip. The first metal strip 2 runs through the hot rolling mill without stopping and without a direction reversal in a transport direction x. The individual sections of the first metal strip 2 thus first pass through the first roll stand 1a, then the second roll stand 1b, then the third roll stand 1c and finally the last roll stand 1d. Before rolling in the first roll stand 1a, the first metal strip 2 can be heated to the required rolling temperature, for example in an oven (not shown). The rolling temperature for a steel strip is usually between 900 ° C and 1200 ° C. After rolling in the last roll stand 1a, the first metal strip 2 can be wound up, for example, into a coil (not shown).

In the state shown in Figure 1, that is, during the rolling of the first metal strip 2, all roll stands 1a to 1d of the hot rolling mill are configured as four-high stands. The roll stands 1a to 1d thus each have work rolls 3 and backup rolls 4, but no further rolls. This also applies in particular to the first and the last roll stands 1a, 1d of the hot rolling mill.

2 shows the same hot rolling mill with the same roll stands 1a to 1d during the rolling of a second metal strip 5. As shown in FIG. 2, the first roll stand 1a is still configured as a four-high stand at this point in time, that is, during the rolling of the second metal strip 5 . At least the last roll stand 1d is configured as a six-high stand. It therefore has, in addition to the backup rolls 4, work rolls 6 and intermediate rolls 7. The intermediate rolls 7 are arranged between the backup rolls 4 and the work rolls 6.

The further roll stands 1b, 1c can according to the illustration in FIG 2 during

the rolling of the second metal strip 5 can be configured either as four-high stands or as six-high stands. Regardless of which of the further roll stands 1b, 1c are configured as four-high stands and which of the further roll stands 1b, 1c are configured as six-high stands, there is only one change from a four-high stand to a six-high stand in the sequence of the roll stands 1a to 1d . In the specific configuration of the rolling train according to the illustration in FIGS. 1 and 2 with a total of four roll stands 1a to 1d, it is therefore possible for both further roll stands 1b, 1c to be configured as four-high stands. It is also possible that the two further roll stands 1b, 1c are configured as six-high stands. However, if one of the two further roll stands 1b, 1c is configured as a four-high stand and the other of the two further roll stands 1b, 1c is configured as a six-high stand, the further roll stand 1b - that is, the roll stand adjoining the first roll stand 1a - is configured as a four-high stand and the further roll stand 1c - that is, the roll stand adjoining the last roll stand 1d - as a six-high stand.

In a four-high stand, the work rolls 3 are usually driven. In the case of a six-high stand, the work rolls 6 are also usually driven. Additionally or alternatively - as a rule alternatively - the intermediate rolls 7 can also be driven in the case of a six-high stand. In the case of the respective configuration, these statements also apply to the last roll stand 1d of the hot rolling mill.

In the following it is assumed that first the first metal strip 2 is rolled in the hot rolling train and only then is the second metal strip 5 rolled. In principle, however, the reverse procedure is also possible.

In order to be able to roll both the first metal strip 2 and the second metal strip 5 in the same hot rolling mill, at least the last roll stand 1d (and possibly also at least one of the others) is placed between the rolling of the first metal strip 2 and the rolling of the second metal strip 5 Roll stands 1b, 1c) converted from a four-high stand to a six-high stand. Thus, in accordance with the illustration in FIG. 3, starting from the configuration of the last roll stand 1d as a four-high stand, the work rolls 3 of the four-high stand are removed. The expansion takes place, as is generally customary and indicated in FIG. 3 by an arrow A, in the axial direction of the work rolls 3 through the window of the service-side stand. The dismantled work rolls 3 are shown in dashed lines in FIG.

After the work rolls 3 have been removed, the work rolls 6 and the intermediate rolls 7 of the six-high stand are installed as shown in FIG. The installation takes place, as is generally customary in the approach and indicated in FIG. 4 by an arrow B, in the axial direction of the work rolls 6 and the intermediate rolls 7 through the window of the service-side stand.

As a result, the last roll stand 1d is configured either as a four-high stand - see left in FIG. 5 - or as a six-high stand - see right in FIG. 5 - configured.

The backup rolls 4 are not changed when the last roll stand 1d is converted. The backup rolls 4 are therefore the same backup rolls 4 both in the configuration of the last roll stand 1d as a four-high stand and in the configuration of the last roll stand 1d as a six-high stand.

Preferably, as shown in FIG. 4, the work rolls 6 and the intermediate rolls 7 of the six-high stand are arranged in a cassette 8. This makes it possible to install the cassette 8 as such, that is to say as a unit. The work rolls 6 and the intermediate rolls 7 of the six-high stand can also be used as a unit, i.e. especially simultaneously.

In order to keep the adjustment range of the last roll stand 1d - that is, the roll gaps that can be formed between the work rolls 3 or between the work rolls 6 - as large as possible both in the configuration as a four-high stand and in the configuration as a six-high stand, the Diameters D, D 'and D "of the work rolls 3, the work rolls 6 and the intermediate rolls 7 should preferably be coordinated with one another in such a way that the sum of the

Diameter D ", D" of work rolls 6 and intermediate rolls 7 of the six-high stand corresponds at least approximately to the diameter of the work rolls 3 of the four-high stand. Smaller deviations of a maximum of 20%, better of a maximum of 10%, can, however, be tolerated.

The diameters D ', D "of the work rolls 6 and the intermediate rolls 7 in the configuration of the last roll stand 1d as a six-high stand should furthermore be determined taking into account whether the work rolls 6 or the intermediate rolls 7 are driven the diameter D 'of the work rolls 6 must be as large as the diameter D "of the intermediate rolls 7, possibly even greater than the diameter D" of the intermediate rolls 7. In the latter case, the diameter D' of the work rolls 6 is preferably significantly smaller than the diameter D " of the intermediate rolls 7. For example, the diameter D ′ of the work rolls 6 can be between 50% and 70% of the diameter D ″ of the intermediate rolls 7.

The conversion of the last roll stand 1d from a configuration as a four-high stand to a configuration as a six-high stand was explained above. However, the reverse procedure, i.e. converting from a six-high stand to a four-high stand, is also possible. Only the reverse procedure has to be taken. Furthermore, the explanations relating to FIGS. 3 to 5 also apply to each further roll stand 1b, 1c that is to be converted from a configuration as a four-high stand to a configuration as a six-high stand.

As shown in FIG. 6, the hot rolling train can have a continuous casting plant 9. The continuous caster 9 is arranged upstream of the first roll stand 1a. In the continuous caster, the metal strips 2, 5 are cast before rolling in the hot rolling mill. It is therefore possible to feed the metal strips 2, 5 to the first roll stand 1a from the casting heat. In this case, the hot rolling mill has been expanded to form a composite casting and rolling plant. Due to the presence of the continuous caster 9, it is particularly possible to operate the hot rolling mill in endless operation. Alternatively, batch operation is also possible. Furthermore, it is possible that the hot rolling mill - as an alternative or in addition to the continuous caster 9 - has a furnace (not shown in the figures). The furnace, if it is present, is arranged upstream of the first roll stand 1a. If necessary, roll stands 10 arranged upstream of the first roll stand 1a can also be arranged upstream, in particular roughing stands of a roughing train. The upstream roll stands 10, if they are present, are arranged downstream of the continuous caster 9 and / or the furnace.

FIG. 6 shows a state in which the roll stands 1a to 1d are all configured as four-high stands. The continuous caster 9 and possibly also the upstream roll stands 10 are also present when the last roll stand 1d and possibly also at least one of the further roll stands 1b, 1c is or are configured as a six-high stand.

Further configurations of the roll stands 1a to 1d can be made as required. In particular - both in the configuration as a four-high stand and in the configuration as a six-high stand - the work rolls 3, 6 can be axially displaceable. In the configuration as a six-high stand, the intermediate rolls 7 can also be displaceable as an alternative or in addition to the work rolls 6. The bending of the work rolls 3, 6 and possibly also the intermediate rolls 7 can also be the same as in the prior art. Furthermore, viewed in the transport direction x of the metal strips 2, 5 in the configuration of the roll stands 1a to 1d as a four-high stand, the work rolls 3 can be arranged slightly offset relative to the support rolls 4. In the configuration of the last roll stand 1d as a six-high stand, viewed in the transport direction x of the metal strips 2, 5, the work rolls 6 can be arranged slightly offset with respect to the intermediate rolls 7. Likewise, viewed in the transport direction x of the metal strips 2, 5 in the configuration of the last roll stand 1d as a six-high stand, the intermediate rolls 7 can be arranged slightly offset relative to the support rolls 4. The offset of the work rolls 6 relative to the intermediate rolls 7 and the offset of the intermediate rolls 7 relative to the backup rolls 4 are preferably in the same direction. If necessary, any shear forces can be absorbed by support rollers. If they are present, the support rollers are arranged on the inlet side and / or outlet side of the work rolls 6. If possible, however, such support rollers should be avoided.

In the last roll stand 1d, the work rolls 3, 6 are generally cooled both in the configuration as a four-high stand and in the configuration as a six-high stand. Appropriate cooling bars are available for cooling. For the cooling of the work rolls 6 in the configuration as a six-high stand, the cooling beams can optionally be arranged on the inlet side and / or on the outlet side of the cassette 8. Alternatively, the cooling beams can be a component of the last roll stand 1d as such, so that they are not installed and removed when the configuration of the last roll stand 1d is changed over.

The present invention has many advantages. Because of the smaller diameter D 'of the work rolls 6 compared to the diameter D of the work rolls 3, for example, not only metal strips 2, 5 made of softer materials, but also metal strips 2, 5, made of harder materials, can be rolled to small final thicknesses. Subsequent cold rolling can be omitted or it can begin with a thinner input product, which in turn means that the output product of the cold rolling can have a smaller thickness. Nevertheless, the product range that can be manufactured is not impaired, and is often even expanded. In particular, for greater final thicknesses, the necessary flexural rigidity during rolling can be achieved by configuring the last roll stand 1d as a four-high stand. The pass decrease in the last roll stand 1d can be maximized in the configuration as a six-high stand, although the rolling forces and rolling torques required for this can be reduced. In this way, improved material properties of the second metal strip 5 can also be achieved at the same time. In particular, the microstructure of the second metal strip 5 can be homogenized and so-called shear strips can be prevented. Finally, ferritic rolling is possible in the hot rolling mill. As a result, the so-called r-value, which characterizes the planar anisotropy and is important for the deep-drawing ability of the rolled metal strips 2, 5, can be positively influenced. In the prior art, this requires cold rolling with subsequent annealing. With the present invention, cold rolling and annealing can be eliminated.

Although the invention has been illustrated and described in more detail by the preferred exemplary embodiment, the invention is not restricted by the disclosed examples and other variants can be derived therefrom by the person skilled in the art without departing from the scope of protection of the invention.

REFERENCE LIST

1a to 1d roll stands

2.5 metal bands

3.6 work rolls

4 support rollers

7 intermediate rollers 8 cassette

9 Continuous caster 10 upstream roll stands A, B arrows

D, D ', D "diameter

X transport direction

Claims (12)

Claims 1. Operating method for a hot rolling mill that has at least a first and a last rolling mill has framework (1a, 1d), - A first and a second metal strip (2, 5) being rolled one after the other in the hot rolling mill, - wherein sections of the metal strips (2, 5) first pass through the first and only then the last roll stand (1a, 1d) of the hot rolling mill, characterized, that the last roll stand (1d) between the rolling of the first metal strip (2) and the Rolling the second metal strip (5) from a four-high stand to a six-high stand or reversed is converted, so that the last roll stand (1d) during the rolling of the first metal strip (2) as a four-high stand with work rolls (3) and back-up rolls (4) configurable is ured and during the rolling of the second metal strip (5) as a six-high stand with working rolls (6), intermediate rolls (7) and backup rolls (4) is configured. 2, operating method according to claim 1, characterized in that the sum of the diameters (D ', D ") of work rolls (6) and intermediate rolls (7) of the last roll stand (1d) configured as a six-high stand is at least approximately the diameter (D) of the Corresponds to work rolls (3) of the last roll stand (1d) configured as a four-high stand. 3. Operating method according to claim 1 or 2, characterized in that when converting the last roll stand (1d) from a four-high stand to a six-high stand or vice versa, the work rolls (6) and the intermediate rolls (7) of the last roll stand configured as a six-high stand (1d) as Unit can be installed or removed. 4. Operating method according to claim 1, 2 or 3, characterized in that the first roll stand (1a) is configured as a four-high stand both during the rolling of the first metal strip (2) and during the rolling of the second metal strip (5). 5. Operating method according to one of the above claims, characterized in that the metal strips (2, 5) are cast in a continuous caster (9) upstream of the first roll stand (1a) before rolling in the hot rolling mill and that the metal strips (2, 5) the first roll stand (1a) are fed out of the casting heat. 6. Operating method according to claim 5, characterized in that the hot rolling mill is operated in endless operation. 7. Operating method according to one of the above claims, characterized, - That the hot rolling train between the first and the last roll stand (1a, 1d) has a number of further roll stands (1b, 1c), - that during the rolling of the first metal strip (2) the further roll stands (1b, 1c) are configured as four-high stands, - That during the rolling of the second metal strip (5) the further roll stands (1b, 1c) are configured either as four-high stands or as six-high stands, and - That seen in the sequence of the roll stands (1a to 1d) during the rolling of the second metal strip (5) there is only one change from rolling in a four-high stand to rolling in a six-high stand. 8. Hot rolling mill, which has at least a first and a last roll stand (1a, 1d), so that sections of metal strips (2, 5) rolled in the hot rolling mill first pass through the first and only then the last roll stand (1a, 1d), wherein the first roll stand (1a) is configured as a four-high stand with work rolls (3) and backup rolls (4), characterized in that the last roll stand (1d) is configured as a six-high stand with work rolls (6), intermediate rolls (7) and backup rolls (4) is. 9. Hot rolling mill according to claim 8, characterized in that the work rolls (6) and the intermediate rolls (7) of the last roll stand (1d) configured as a six-high stand are arranged in a cassette (8) which can be installed and removed as a unit. 10. Hot rolling mill according to claim 8 or 9, characterized in that the first roll stand (1a) is preceded by a continuous caster (9) in which the metal strips (2, 5) are cast before rolling in the hot rolling mill, so that the metal strips ( 2, 5) can be fed to the first roll stand (1a) from the casting heat. 11. Hot rolling mill according to claim 10, characterized in that the hot rolling mill can be operated in endless operation. 12. hot rolling mill according to one of claims 8 to 11, characterized, - That the hot rolling mill has a number of further rolling stands (1b, 1c) between the first and the last rolling stand (1a, 1d), - That the further roll stands (1b, 1c) are configured as four-high stands or as six-high stands, and - That in the sequence of the roll stands (1a to 1d) there is only one change from a four-high stand to a six-high stand. In addition 3 sheets of drawings