EP4249141B1 - Operating method for a rolling train - Google Patents

Description

The invention relates to an operating method for a rolling mill which has several rolling stands through which a metal strip passes, wherein the metal strip is successively threaded into at least some of the rolling stands and the metal strip passes through the rolling mill with stepwise thickness reduction from an initial thickness to a target thickness.

The invention relates in particular to the automation of a rolling mill, wherein the operating method can be used for the operation of cold rolling mills for steel in discontinuous and continuous operation, for the operation of combined pickling and cold rolling mill plants in discontinuous and continuous operation, for the operation of continuous and discontinuous hot rolling mills for steel, for the control of casting rolling mills, billet rolling mills, aluminum hot rolling mills, aluminum cold rolling mills, and for the control of reversing rolling mills with two or more rolling stands. A generic operating method for a rolling mill is defined as follows: US 4 460 852 A known.

In methods for monitoring and controlling rolling mills for rolling flat metal products, it is generally desirable to increase the productivity of the mill without having to adjust the mechanical configuration of the mill.

Rolling mills are typically operated automatically using multi-stage control systems. These control systems usually include controllers that receive setpoints from a higher-level system. The setpoints can be current values or target value trends. Level 2 systems generally calculate the setpoints using online optimization algorithms. They in turn rely on online models of the system to be controlled. These online models are data-based or mathematical-physical models.

The present invention relates in particular to the Level 1 and Level 2 automation of a plant for rolling metal strips. As already mentioned, the plant can be configured as a hot rolling mill, a cold rolling mill, or a profile rolling mill.

A Level 2 automation level within the meaning of the present invention is understood to be a process control level, which may, for example, comprise a higher-level process control technology, and which may be provided directly above a control level (Level 1 automation) for the direct control and regulation of the units of a rolling mill.

In the operation of a rolling mill, metal pre-products or semi-finished products are usually rolled out into a finished strip and assembled into a coil.

In a hot strip mill, for example, slabs with initial thicknesses of 200-150 mm are heated to temperatures around 1250°C in a furnace. These are then rolled out in a roughing mill using roughing stands into strips with thicknesses of 25-45 mm and strip temperatures in the range of 950-1050°C. The strips are then fed into a finishing mill with finishing stands arranged in series and finished into strip with thicknesses of 1.25-25 mm and final rolling temperatures of 850-950°C.

The state of the art involves threading the semi-finished product/pre-product in and/or out at a constant speed relative to the exit speed of the rolling mill. It is common practice to operate the individual rolling stands at a constant speed. For hot rolling mills, this is particularly important with regard to the temperature profile of the metal strip. It is useful if, after threading the tape head, it should have a predetermined target temperature starting from the oven temperature.

Known concepts for increasing the productivity of rolling mills therefore aim not to change the duration of the actual rolling process for temperature control reasons, but to reduce the idle times of the strips, for example by accelerating the bundle removal, by accelerating the bundle preparation processes or by reducing the time between unthreading a strip foot of the leading strip in the first stand and threading in the new strip head.

Within the rolling mill, specifically during threading or threading, the speed of the strip foot or head is determined by the ratio of the thickness reduction from the initial thickness before the respective rolling stand to the thickness after the respective rolling stand. The speed increase of the strip head is proportional to the thickness reduction of the metal strip within the rolling stand.

Further state of the art can be found in the documents. EP 3 437 748 A1 and DE 197 26 586 A1 known.

The invention is based on the objective of providing an operating method for a rolling mill that enables an increase in the mill's productivity without changing its mechanical configuration. In particular, the operating method should enable an increase in production through appropriate adjustments to the process control.

The invention is solved by an operating method with the features of claim 1. Advantageous embodiments of the invention are set forth in the dependent claims.

According to one aspect of the invention, an operating method is provided for a rolling mill which has several rolling stands through which a metal strip passes, wherein the metal strip is successively threaded into at least some of the rolling stands and the metal strip passes through the rolling mill with stepwise thickness reduction from an initial thickness to a target thickness, wherein the method comprises speed control of the individual rolling stands by means of a higher-level process control and wherein at least the entry speed of the metal strip into the rolling mill and the speed of the rolling stands when threading a strip head and/or a strip foot or a planned section change of the metal strip into the rolling stands is controlled according to a speed specification for the metal strip or for parts of the metal strip such that the speed of the strip head for each rolling stand has a maximum possible threading speed before a first rolling stand and between each pair of rolling stands, and that a maximum possible threading speed before a first rolling stand and/or between two rolling stands is calculated as the speed specification, under the condition that a The calculated and/or specified maximum rolling speed is not exceeded after completion of the threading process, whereby the calculation of the speed specification for the entry and/or threading of the metal strip is carried out taking into account the technical limits and boundary conditions of the rolling mill units and taking into account specified process parameters for the rolling process. As a result, the speed of the rolling stands, especially during the threading process, is controlled in such a way that the mass flow of the metal strip is variable during entry and/or threading through all rolling stands.

A section change, i.e. a planned change in the geometry of the metal strip, can result, for example, from a product change during continuous rolling.

In state-of-the-art operating procedures, the rolling stands are operated at a constant speed during the threading and/or passing of the metal strip. This results in a constant mass flow rate of the metal strip, due to the fact that the strip head is accelerated proportionally to the thickness reduction in the respective rolling stand. In state-of-the-art procedures, the speed of all rolling stands is determined by a constant target speed of the strip head behind the last rolling stand.

The operating method according to the invention is characterized in particular by the fact that the speed of the individual rolling stands is not constant, Rather, the speed of the individual rolling stands is regulated according to a speed target calculated in a higher-level process control system, preferably in Level 2 automation. This results in a "speed cascade" or speed profile for the metal strip through the entry and/or threading process.

This approach has the advantage that the threading speed of the metal strip into the rolling stands can be significantly increased, resulting in considerable time savings and thus also an increase in productivity.

According to the invention, a maximum possible threading speed is calculated as a speed specification in front of a first rolling stand and/or between two rolling stands, under the condition that a calculated and/or specified maximum rolling speed for the entire rolling process is not exceeded after completion of the threading process.

Speed control such that the speed of the tape head, tape foot or tape transition in the respective intermediate stand area is no longer calculated in proportion to the total thickness reduction, but is generally as fast as possible without exceeding a calculated exit speed, has the advantage that a time saving of up to approximately 30% can be achieved during the threading process.

The calculation of the speed requirement for the entry and/or threading of the metal strip is preferably carried out taking into account the technical limits and boundary conditions of the rolling mill's equipment, as well as given process parameters for the rolling process. Technical limits and boundary conditions of the rolling mill's equipment include, for example, the maximum power of the drives for the rolling stands or their maximum possible penetrating force.

Specified process parameters include the temperature of the metal strip, the temperature profile of the metal strip along its length and/or width, the maximum possible and/or permissible strip tension, the flatness of the metal strip, the applicable forming energy, the strip geometry, in particular the strip preparation, the enthalpy conservation, the specific enthalpy, the surface quality of the finished metal strip, the microstructure and the yield strength of the metal strip.

In principle, it is advantageous if the speed of the metal strip during threading through all rolling stands can be variably parameterized in the process control.

The speed control can comprise a data-based and/or rule-based speed specification, for example, material- and/or dimension-related. A data-based specification within the meaning of the present invention means that, through an automated analysis of a large data set, the optimal speed for the strip head is determined over the entire path during threading and/or passing through the rolling mill, and the individual rolling stands are controlled accordingly via Level 1 automation.

Alternatively or additionally, a rule-based specification of the optimal speed, for example material- and/or dimension-related, can also be provided.

Advantageously, a distance monitoring system is provided between the strip head and the strip foot of a metal strip traveling downstream through the rolling mill, with the speed control taking a minimum distance to the strip foot of the downstream metal strip into account as a boundary condition. This is advantageous and sensible to ensure that the rolled strip does not run into the advancing strip foot.

When the operating method of the invention is applied for the process control of a hot strip mill, in which a hot strip is threaded as a pre-strip from a pre-strip mill into a finishing mill, this has the advantage that, due to the increased threading speed at the strip head, lower heat losses occur and a more homogeneous temperature profile can be achieved over the strip length.

In this case, it is advantageous if the method includes temperature control of the tape head. Such temperature control can, for example, be based on a target temperature of the tape head. The temperature profile of the metal tape is particularly dependent on its thickness. With thinner metal tapes, a reference temperature at the tape head can only be achieved through the operating method or control system according to the invention.

The temperature of the pre-strip can be regulated, for example, by multiple uses of a descaling device and/or via temperature control and/or regulation of a furnace upstream of the pre-strip and/or via a thickness profile introduced into the metal bath in the pre-strip.

Alternatively or additionally, it may be provided that the coolant volume flow of at least one intermediate stand cooling system is controlled and/or regulated depending on the speed of at least one rolling stand.

In order to influence the distance between two different products or two metal strips to be produced one after the other, it is advantageous if the winding speed of at least one reel for winding the finished rolled metal strip is controlled and/or regulated as a function of a speed cascade of the metal strip over several rolling stands.

The method according to the invention is explained below with reference to an embodiment shown in the drawings.

Figur 1

eine schematische Darstellung einer Stranggießanlage mit einer Walzstraße, auf welche das Betriebsverfahren gemäß der Erfindung anwendbar ist,

Figur 2

eine schematische Darstellung eines Regelungskonzepts für die Geschwindigkeitsregelung an einer Vielzahl von Walzgerüsten und

Figur 3

eine schematische Gegenüberstellung der Temperatursteuerung für ein Warmwalzverfahren mit einer Regelung gemäß der Erfindung, einerseits für dünne Metallbänder mit einer Dicke von weniger als 2 mm und andererseits für dickere Metallbändern mit einer Dicke von mehr als 2 mm.

They show:

Figure 1

a schematic representation of a continuous casting plant with a rolling mill to which the operating method according to the invention is applicable,

Figure 2

a schematic representation of a control concept for speed control on a large number of rolling mills and

Figure 3

a schematic comparison of the temperature control for a hot rolling process with a control system according to the invention, on the one hand for thin metal strips with a thickness of less than 2 mm and on the other hand for thicker metal strips with a thickness of more than 2 mm.

Figure 1 Figure 1 shows a schematic representation of a continuous casting plant with a continuous casting plant 1, followed by a roughing mill 2 and a finishing mill 3. The roughing mill 2 comprises a first furnace 4, two pre-stands 5, a second furnace 6, and a shear 7.

The finishing line 3 includes a scale washer 8 and a large number of rolling stands F1 to Fn, which are arranged one behind the other in a rolling line.

The method according to the invention is described based on the Figure 1 The schematic and simplified representation of the casting and rolling mill is explained. As already mentioned at the beginning, the operating method according to the invention is not limited to such a mill; rather, it relates to speed control. the rolling stands F1 to Fn, which in the described embodiment are arranged as finishing stands in a finishing mill 3.

In the process according to the exemplary embodiment, a casting strand produced with the continuous casting plant 1 is pre-rolled, for example, into a metal strip in the form of a thin slab by means of the pre-setting stands 5, which, after descaling in the descaler 8, is threaded into the rolling stands F1 to Fn of the finishing mill 3. The rolling stands F1 to Fn arranged in the finishing mill 3 are each controlled by a higher-level process control system (not shown), wherein the process control system comprises a Level 2 automation level and a Level 1 automation level arranged below it for the direct control and regulation of the rolling stands F1 to Fn.

The operating method according to the invention comprises a speed control and speed regulation of the rolling stands F1 to Fn such that the entry speed of the metal strip, in the present case the thin slabs, into the rolling stands F1 to Fn is regulated during threading so that the speed of the strip head for each rolling stand F1 to Fn has a maximum possible threading speed in front of a first rolling stand F1 and in each case between two rolling stands F1 to Fn, taking into account the respective technical limits and boundary conditions of the rolling stands F1 to Fn and taking into account the fact that a calculated and/or predetermined maximum rolling speed is not exceeded after completion of the threading process.

If and insofar as the embodiment described with reference to the figures relates to the speed of the strip head, the invention is nevertheless to be understood as relating to the speed of the strip foot, for example in a reversing operation of the rolling mill, and/or to the speed of a section change, i.e. a change in product geometry due to a planned product change.

A schematic representation of the control concept according to the operating method according to the invention is shown in Figure 2 As shown, the hot-rolled strip/roughing strip or slab is initially fed into the first rolling stand F1 at the maximum possible speed. The first rolling stand F1 is operated at maximum rotational speed. The limit of the entry speed of the metal strip into the first rolling stand F1 is determined by the maximum speed of the descaling process within the descaler 8, the maximum speed of the roller table, and the safety distance to the preceding metal strip. Furthermore, the maximum speed of the first rolling stand F1 is determined by its engine power and the maximum penetrating stroke. This results in an initial speed V0 before the first rolling stand F1.

At the moment of penetration at the rolling stand F2, i.e., when the strip head of the metal strip is threaded into the rolling stand F2, the rotational speed of the rolling stand may be higher than V0. Only at the point of penetration is the rolling stand F1 slowed down and the strip head brought up to the appropriate speed. This has the advantage that the strip tension between the rolling stands F1 and F2 is built up relatively quickly and reliably. The speed of the rolling stands F1 and F2 is increased as much as possible. If an increase is not possible, the resulting speed of the strip head in the stand section between the rolling stand F1 and the rolling stand F2 is equal to the speed resulting from the reduction in thickness of the metal strip.

The mass flow or volume flow through all rolling stands depends on the speed of the strip head, which according to the invention can be specified according to a higher-level control objective and is variable.

The speed of the strip head (V _{_striphead)} and/or the speed of the strip foot (V _{_stripfoot)} and/or the speed of a section change (V _{_{productchange})} can be freely specified to achieve a higher-level control objective, in the simplest case maximization. However, the technical boundary conditions and the specified process conditions of the rolling process must be observed.

• V_{maxWalzgerüste} für alle Walzgerüste 1 bis n
• V_{maxBandkopfTransport} für die Geschwindigkeit des Bandkopfes selbst
• mit:
  • V_{MaxWalzgerüstn}=MIN (physikalische Grenzen des Walzgerüstes; physikalische Grenzen des Walzprozesses; Prozessvorgaben und - grenzen (z.B. Temp. / Dicke, Voreilung...))
  • V_{maxBandkopfTransport} = MIN (maximal mögliche Bandkopf Transportgeschwindigkeit: maximal sinnvolle (prozessbedingt) Bandkopf Transportgeschwindigkeit

These are:

• V _{max rolling stands} for all rolling stands 1 to n
• V _{max tape head transport} for the speed of the tape head itself
• with:
  • V _{MaxRolling stand} =MIN (physical limits of the rolling stand; physical limits of the rolling process; process specifications and limits (e.g. temp. / thickness, lead...))
  • V _{max tape head transport} = MIN (maximum possible tape head transport speed: maximum useful (process-related) tape head transport speed)

The speed settings for V _{_{strip head}} , V _{_{strip foot}} , and/or V_{_{product change}} should ensure the correct mass flow control of the interaction between the various rolling stands at all times. This is achieved by precisely feeding the higher-level speed setting into the so-called speed cascade (see...). Figure 2 , [Lim Fn])

Where V = velocity
D = Thickness

The function Min (A; B) is a function that returns the smaller value from both values A and B.

The speed of the strip head, determined as described above, is compared with a given calculated final speed of the metal strip behind the last rolling stand, Fn. The minimum of these two values is then calculated. selected so that the metal band does not exceed the final speed intended after the threading process.

As already explained at the outset, the operating method according to the invention comprises a control of the temperature of the metal strip, in particular of the strip head.

The Figure 3 Figure 1 shows two diagrams plotting the temperature of the metal strip, the mass flow rate (or volume flow rate) of the material, and the coiling speed along the length of the rolling mill. The left diagram shows the relevant values for a metal strip thickness of less than 2 mm, and the right diagram shows the relevant values for a metal strip thickness of more than 2 mm. The diagrams illustrate the temperature and speed profiles for the operating process according to the invention. The line representing the mass flow initially illustrates the so-called speed cascade, which, for example, the head of the metal strip undergoes as it passes through the rolling stands F1 to F6. The speed profile decreases slightly in steps from rolling stand F1 to rolling stand Fn until a constant final speed is reached, and then increases again in steps as the metal strip is wound onto the coil. Above this, the actual temperature profile of the metal strip and the reference temperature of the metal strip are shown. The reference temperature is the temperature targeted to achieve specific microstructure properties of the finished product. The water consumption of an intermediate stand cooling system along the length of the rolling mill is also shown. In the left-hand diagram, the rolled material reaches the reference temperature at a temperature measuring point downstream of the rolling stand F6. However, this temperature drops again immediately downstream of the roughing mill due to a relatively high cooling rate of the rolled material. An intermediate stand cooling system operates with a minimal... The water quantity has been reached. The increase in water consumption towards the end of the rolling process is due to a cooling section provided there.

As can be seen from the right-hand illustration in Figure 3 As can be seen, the strip head remains at the intended reference temperature behind the last rolling stand F6 or behind a temperature measuring point. This results primarily from the increased threading speed into the rolling stands F1 to Fn. Since the cooling of the strip head does not decrease as rapidly due to the high threading speed and higher heat capacity, a larger quantity of water is initially required for intermediate stand cooling, but this quantity then decreases progressively.

Reference symbol list

1

Continuous casting plant

2

Forecourt

3

Finishing plant

4

first oven

5

Pre-frameworks

6

second oven

7

Scissors

8

Tinder washer

F1 to Fn

Rolling mills

Claims (11)

1. Operating method for a rolling train, which comprises a plurality of roll stands (F1 - Fn) to be run through by a metal strip, wherein the metal strip is threaded successively into at least some of the roll stands (F1 - Fn) and the metal strip runs through rolling train with stepped reduction in thickness from a starting thickness to a target thickness, wherein the method comprises speed regulation of the individual roll stands (F1 - Fn) by means of a superordinate process control, characterised in that

   at least the entry speed of the metal strip into the rolling train and the speed of the roll stands (F1 - Fn) in the case of threading-in of a strip head and/or a strip foot or a planned section change of the metal strip in the roll stands (F1 - Fn) is so regulated in correspondence with a speed preset for the metal strip or for parts of the metal strip that the speed of the strip head for each roll stand (F1 - Fn) has a maximum possible threading-in speed in front of a first roll stand (F1) and in each instance between two roll stands (F1); and

   a maximum possible threading-in speed in front of a first roll stand (F1) and/or between two roll stands (F1 - Fn) is calculated as speed preset under the condition that a calculated and/or predetermined maximum rolling speed is not exceeded after the conclusion of the threading-in process,

   wherein the calculation of the speed preset for the entry and/or threading-in of the metal strip is carried out with consideration of the technical limits and boundary conditions of the units of the rolling train and with consideration of predetermined process variables for the rolling process.
2. Operating method according to claim 1, characterised in that the predetermined process variables are selected from a group of process variables comprising the temperature of the metal strip, the temperature plot over the length and/or width of the metal strip, the maximum possible and/or permissible strip tension, the planarity, the deforming energy, the strip geometry, particularly the strip width, the maintenance of enthalpy, the specific enthalpy, the surface quality of the metal strip, the structural form and the yield point.
3. Operating method according to one of claims 1 and 2, characterised in that the speed of the metal strip during threading-in can be parameterised in variable manner over all roll stands (F1 - Fn) in the process control.
4. Operating method according to any one of claims 1 to 3, characterised in that the speed regulation comprises a data-based and/or rule-based speed preset.
5. Operating method according to any one of claims 1 to 4 as operating method for a hot-strip train, into which a hot strip as pre-strip from a roughing train (2) is threaded in.
6. Operating method according to any one of claims 1 to 5, characterised in that the method comprises monitoring of spacing of the strip head from a strip foot of a downstream metal strip running through the rolling train, wherein the speed regulation takes into consideration a minimum spacing from the strip foot of the downstream metal strip, which is running downstream through the rolling train, as boundary condition for the calculation of the speed preset.
7. Operating method according to any one of claims 1 to 6, characterised in that the method comprises control of the temperature of the metal strip, particularly of the strip head.
8. Operating method according to any one of claims 4 to 7, characterised in that the temperature of the pre-strip is controlled in dependence on a target temperature of the strip head behind the finishing train.
9. Operating method according to claim 7, characterised in that the temperature of the pre-strip is regulated by multiple use of a device for descaling and/or by way of temperature control and/or temperature regulation of a furnace upstream of the roughing train and/or by way of thickness profile imparted to the metal band in the roughing train.
10. Operating method according to any one of claims 1 to 9, characterised in that the coolant volume flow of at least an intermediate stand cooling is controlled and/or regulated in dependence on the speed of at least one roll stand.
11. Operating method according to any one of claims 1 to 10, characterised in that the winding speed of at least one coiler for winding up the metal strip rolled to finished state is controlled and/or regulated in dependence on a speed cascade of the metal strip over a plurality of roll stands.