EP2861360B1 - Method for processing milled goods in a rolling mill - Google Patents

Description

The invention relates to a method for processing rolling stock in a rolling mill with at least one rolling mill having a drive.

In the processing of rolling stock, e.g. Steel or various metals in the form of so-called slabs or billets, the rolling stock passes through a rolling train with one or more rolling stands. The individual rolling stands each have a drive for rollers, with which the rolling stock is rolled into sheets or wires with a desired geometry, such as thickness or cross section.

To achieve this, the rollers must be controlled to a certain speed with the aid of the drives of the individual rolling stands. It is also important that during the entire operation of the rolling mill and the predetermined ratio of rotational speeds of the rollers of the individual rolling stands remains constant, otherwise tensile and compressive loads on the rolling occur, which in turn lead to an undesirable rolling result or even tearing or can cause a looping of the rolling stock.

From the DE 197 26 586 D1 a method for rolling of rolling stock is to be taken in a rolling mill, wherein a roll torque feed forward control of a rolling mill drive is proposed to reduce a speed drop by a foreseeable load torque.

In order to ensure this mechanically, in particular at high rolling speeds, for example, some rolls located in a long-product rolling mill are rigidly coupled together in a multi-stand wire block via a mechanical transfer case and driven by a common motor. A big disadvantage here, however, is that the unit due to the fixed speed ratios for more Products can not be adjusted and that, for example, wear of individual rolls of the complete set of rolls must be reground, otherwise it can lead to the above effects.

These disadvantages can be overcome by having each rolling stand with a separate drive for the rolls. In this case, the individual drives each have a separate speed control, so that they can be controlled individually.

A major challenge of such a drive solution, however, is the speed control of the rollers or drives of the individual rolling stands during the processing of rolling stock. This is especially true when different load moments act on the individual rolling stands, which for example when tapping, i. when striking the rolling stock on the rollers is the case. In such an action of a load torque on the drive, the rollers are braked, which thus leads to a collapse of the rotational speed of the rollers or of the drive to the relevant rolling stand. The rollers of other rolling stands, however, on the time of tapping no or a deviant, z. B. acts a smaller load torque, have an unchanged or only slightly changed speed. This has the consequence that the rotational speeds of the individual drives or rollers are no longer synchronous, so no longer work in a predetermined speed ratio to each other. This leads to errors in the material thickness and can lead to tearing of the wire or looping of the rolling stock between the individual rolling stands in case of unacceptable tensile or compressive load.

In addition, the behavior of the overall system, that is to say the individual drives or rollers of the rolling stands and thus their effects on the rolling result, was not always predictable with the previous speed controls with partially overlaid correction setups, so that the quality of the rolling stock did not always meet the requirements.

It is therefore an object of the invention to provide a method for processing rolling stock in a rolling mill, in which the above-mentioned disadvantages are avoided.

The object is achieved by a method for processing rolling stock in a rolling mill with the features of claim 1. In this case, a rolling mill has at least one rolling mill having a drive in which, in order to reduce a speed drop of the drive caused by a foreseeable load torque acting on the drive, a rolling moment pilot control of the drive takes place by the torque-generating current supplied to the drive.

In the method according to the invention, therefore, the occurrence of a foreseeable load torque, as is the case, for example, when piercing, the resulting reduction in speed is reduced by a rolling torque pilot control of the torque-generating current supplied to the drive. For the predictability of the load torque suitable parameters such as roll gap geometry, position and characteristics of material sensors, distance of the individual rolling stands or roller and material speeds are used, with which it can be determined when the load torque and at what level it acts on the relevant drive. The corresponding values including the amount of the foreseeable load torque can be determined, for example, by means of a model of the rolling mill. Depending on this prediction, the current supplied to the drive can then be selectively controlled in such a way that a reduction in the rotational speed of the drive associated with the occurrence of the load torque is reduced. Thus, a controlled operation of the drives or the rollers of the individual rolling stands and thus the entire system is guaranteed. It is therefore no longer to individual tensile or compressive loads due to strong speed fluctuations of the individual drives or rollers of different rolling stands. Thus, variations in the thickness are reduced and cracking of the rolling or looping largely avoided. This is especially true when the rolling mill has several rolling stands with separate drives and each drive is individually pre-controlled.

The foreseeable load torque is corrected by evaluating the actual values, in particular torque, speed, and derived actual accelerations. This results in a dynamic correction in the position of the tape head. By means of observer models, the height of the load torque can be corrected dynamically. In the case of repetitive processes with the same material, an evaluation is made by evaluating the deviation between the precontrol values for the foreseeable load torque and the actual load torque, an iterative optimization for correcting the Aufschaltzeitpunktes and an iterative correction of the height of the predictable load torque.

In a preferred embodiment of the invention, the feedforward control is material-based. This means that material parameters such as hardness or influencing factors such as temperature and type of material are initially taken into account, how high the foreseeable load torque acts on the drive in question, so that depending on the drive, the drive is accordingly pre-controlled and thus the supplied current is changed.

If, in order to pre-control the drive, the current is suddenly increased when a load torque occurs, the system reacts briefly to the occurrence of the load torque. The disadvantage here, however, is that in such sudden changes in the supplied torque-generating current in addition to the properties of the mechanism and the behavior of the power converter in each operating point has an influence on the response of the overall system.

To avoid this, the current is not leaps and bounds, but increasing, within a time window continuously, in particular increases ramped for pre-control of the drive. Thus, the corresponding torque of the drive is changed only relatively slowly, so ramped. Alternatively, the ramp can also be preset in a staircase.

The slope of the ramp for the torque is dimensioned such that the drive train remains in a defined and reproducible state at any time. Thus, the overall system is better controlled and it shows a much improved timing of the individual drives and in particular the overall system. Thus, a reproducibility of the behavior of the entire system is ensured. The limitation of the increase of the current takes place with a corresponding ramp-shaped increase of the current setpoint value and can take place indirectly via a torque or also speed precontrol.

The steepness of the ramp depends on the dynamics of the power converter. In this case, type of converter, operating point and the design of the power converter, in particular the amount of current to be impressed, the speed and the voltage reserve play a role. With high reproducibility, the slope corresponds to an average value that can be achieved at the specified operating points. For complete reproducibility, the slope of the ramp or staircase must be smaller than the possible maximum slope that the power converter can provide over all specified operating points. The setpoint increase then does not exceed the achievable dynamics of the converter at the voltage limit at nominal motor voltage and maximum power. This eliminates deviations of the converter behavior in different operating points. This allows extremely accurate and predictable feedforward control at high speeds. The reproducible operation allows a very precise analysis of the inertia by interpolation, in addition a dynamic statement about the occurring load torque for the dynamic correction of the material position and the load height.

In order to obtain a pre-control without speed deviation before and after the connection, the ramp is designed such that the increase in torque of the drive achieved by the current increase causes a symmetrically acting deviation, so that the speed increase to the occurrence of the load and the delay after the occurrence of the load cancel until the complete build-up of the torque. In the event of a sudden load and a constant ramp, the torque input is thus realized halfway before and the other half after the load torque has occurred.

Pre-control is completed before the material enters the scaffold when the rise time between the occurrence of the load until complete torque application does not exceed the scaffold spacing divided by material velocity. In the case of a symmetrically acting deviation, this corresponds to twice the time required for the material to pass between two scaffolds.

The above-described characteristics, features, and advantages of this invention, as well as the manner in which they will be achieved, will become clearer and more clearly understood in connection with the following description of the embodiments, which will be described in connection with the drawings.

FIG 1

einen Ausschnitt einer Walzstraße mit aufeinanderfolgenden Walzgerüsten und mit einem separaten Antrieb für jedes Walzgerüst,

FIG 2

eine Diagramm, bei dem jeweils auf Antriebe von Walzgerüsten wirkende Lastmomente sowie der diesen Antrieben zugeführte Strom im zeitlichen Verlauf dargestellt ist,

FIG 3

ein Diagramm, bei dem der entsprechende Drehzahlverlauf der Antriebe bei Einwirkung der in FIG 2 dargestellten Größen im zeitlichen Verlauf dargestellt ist

For a further description of the invention reference is made to the embodiments of the drawings. In a schematic schematic diagram:

FIG. 1

a section of a rolling train with successive rolling stands and with a separate drive for each roll stand,

FIG. 2

a diagram in which in each case acting on drives of rolling stands load moments and the power supplied to these drives is shown over time,

FIG. 3

a diagram in which the corresponding speed curve of the drives under the action of in FIG. 2 shown sizes over time is shown

FIG. 1 shows a section of a rolling train 2 with successive rolling stands 4 for processing a rolling stock 6. In FIG. 1 By way of example, eight consecutive rolling stands 4 are shown which pass through the rolling stock 6, eg a billet, which is rolled into wire.

Each mill stand 4 is a separate drive 8, comprising a motor 10 and a gear 12 associated with, wherein in the figure for clarity, only one drive 8 is indicated. The drive is supplied by means of a power converter 14 with a control unit 16, a desired current I. Each roll stand 4 further comprises at least one roller 13, which is driven by the respective drive 8 at a predetermined speed n, which is taken for example from a pass schedule.

If rolling stock 6 now encounters the roll 4 of a roll stand 13, then a load moment M _{L is} exerted on the drive 8 of the corresponding roll stand 13. This load torque M _L now causes the speed n of the relevant drive 8 to break down. In rolling mills 2 according to the prior art, a corresponding correction of the rotational speed n then takes place upward, so that after a certain delay time the drive 8 of the respective rolling stand 4 again has the desired rotational speed n. However, the behavior of the drive 8, in particular immediately after the occurrence of the load torque M _{L is} not always reproducible. Due to the resulting speed deviations with associated tension fluctuations, the quality of the rolling result does not always meet the requirements. In other words: The dynamic behavior of the drives depends on the occurring load torque M _L and the behavior of the controller. However, this behavior is not always sufficiently predictable and due to the dependence on the operating point only partially reproducible.

According to the present invention, the speed of rotation caused by a load torque M _L acting on the drive 8 is reduced by the drive 8 with the aid of the control device 16 and the power converter 14 is precontrolled with respect to its supplied current I.

To achieve this goal, it is first necessary that the load torque M _L can be known or estimated, that is, a predictable size. For example, based on models of the rolling mill 2 as well as known sizes of the rolling stock 6 to be rolled, a corresponding expected value of the load moment M _L acting on a drive 8 of a rolling stand 4 can be determined. This expectation value is determined over time so that the load moment M _L for a particular drive 8 of a roll stand 4 is predicted over time. Depending on the foreseeable load torque M _L , the rolling torque precontrol of the drive 8 is then effected by the torque-generating current I supplied to the drive such that a fall in the rotational speed of the drive 8 is compensated. For drives which, unlike the preferred solution, drive more than one rolling stand 4, the motor-related load torque M _L determined over time reflects the sum of the individual motor-related rolling moments.

In FIG. 2 is now exemplified for two rolling stands 4, each with a drive assigned to this 8, the time course of impinging on them load moments M _L and these drives 8 supplied current I with the corresponding control variable, namely the current setpoint shown over time. Curve 18 represents a sudden change of the load torque M _L on the drive 8 of the first stand 4 at time t ₂ , while curve 20 represents a jump of the load moment M _L on the drive 8 of the second stand 4 at time t7.

In order to reduce the speed of rotation of the drive 8, which is caused by acting on the drive 8 load torque M _L , there is a targeted feedforward control of the drive 8 by the drive I supplied current I by means of the control unit 16 and the power converter 14. This is already for Time t ₀ , ie before the occurrence of the load torque M _L of Set point for the current I ramped increases, as shown in curve 22. The current I then follows with a slight time delay from the time t ₁ , which is also before the time t _{2 of} the occurrence of the load torque M _L , as shown in curve 24. The ramp for the current setpoint and for the current I is dimensioned such that the drive 8 remains in a stable state, which is also reproducible, that is, the increase of the current setpoint and the current I is so slow that the drive. 8 has a defined operating behavior. In particular, the ramp of the current I is designed such that the torque increase of the drive 8 achieved by the increase in current is realized to one half before and the other half after the occurrence of the load torque M _L. This means that the time span from t ₁ to t ₂ equals the period from t ₃ to t ₄ . When the time t ₄ is reached, the amount of the load torque M _L then corresponds to the amount of the torque M of the drive 8.

After a certain period of time, for example, during threading of the rolling stock 6, it encounters the second rolling stand 4, where it causes a jump of the load moment M _L at a different height, as shown in curve 20. The corresponding load torque M _L is again predictable by known sizes. Here again, in order to reduce a speed drop of the drive 8 caused by the load torque M _L , a precontrol of the drive 8 takes place by means of the current setpoint, which is ramped between the times t ₅ and t ₈ , as shown in curve 26. Again, after appropriate delay time, the current I according to curve 28 in the interval between t ₆ and t ₉ increases ramped such that the drive 8 remains in a stable state and the increase in torque achieved by the torque increase of the drive 8 to one half before and the other Half after the occurrence of the load torque M _{L is} realized.

In FIG. 3 now the speed curve of the two drives 8 is shown on the corresponding rolling stands 4. The lower curve 30 shows the time course of the rotational speed n of the drive 8 of the first rolling stand 4. By the precontrol of the drive 8 supplied current I, the torque M is first increased from the time t ₁ as described above and thus also increases the speed n , This happens up to the time t ₂ at which the load torque M _L acts on the drive 8, which now has a speed drop below the desired speed n result. By further increasing the current I and thus the torque M between the times t ₂ and t ₄ , the speed n is then brought to the desired value.

A corresponding course is shown in curve 32 for the drive 8 of the second roll stand 4.

On the basis of the curves of the rotational speeds n, it can be seen that a fall in the rotational speed of the drives 8 is compensated by the corresponding precontrol. Superimposed decaying torsional vibrations are not shown for the sake of simplicity. By the precontrol of the current I and the associated predefined increase in the current I, here in ramp form, it is also ensured during the dynamic operation of the drive that this is always operated in a defined and reproducible state, so that a looping or even a Tearing of the rolling stock is prevented during the rolling process. Thus, the system behavior by the pilot control is better influenced to compensate for a load torque occurring M _L.

Although the invention has been further illustrated and described in detail by the preferred embodiment, 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.

Claims (8)

1. Method for processing rolling stock (6) in a rolling mill (2) having at least one rolling stand (4) which has a drive (8), wherein, in order to reduce a rotational speed dip of the drive (8) caused by a predictable load torque (M_L) which acts on the drive (8), a rolling torque pilot control of the drive (8) is carried out by the torque-forming current (I) which is fed to the drive (8), characterised in that a curve over time for the load torque M_L acting on the drive (8) of the rolling stand (4) is anticipated as an expected value using models of the rolling mill (2) and known values of the rolling stock (6) to be rolled and, as a function thereof, the rolling torque pilot control of the drive (8) is carried out by the torque-forming current (I) which is fed to the drive and a dip in the rotational speed of the drive (8) is compensated.
2. Method according to claim 1, wherein the rolling mill (2) is a long product rolling mill and has a plurality of rolling stands (4) each with a separate drive (8) for high rolling speeds and the load torque (M_L) caused by the rolling process is individually pilot controlled in the case of each drive (8).
3. Method according to claim 1 or 2, wherein the pilot control is material-based.
4. Method according to one of the preceding claims, wherein the current (I) is increased suddenly for pilot control of the drive (8).
5. Method according to one of claims 1 to 3, wherein the current (I) is increased in a ramp- or step-like manner for pilot control of the drive (8).
6. Method according to claim 5, wherein the steepness in the course of the ramp due to the reduction in dynamics as a function of converter properties is dimensioned in such a way that the drive (8) provides high or completely reproducible performance.
7. Method according to claim 5 or 6, wherein the ramp is designed in terms of time for elimination of a residual difference in rotational speed in such a way that the difference between load torque (M_L) and the increase in the torque of the drive (8) attained by the pilot control after the occurrence of the load until complete establishment of the load torque (M_L) compensates the difference in rotational speed until the occurrence of the load torque (M_L).
8. Method according to claim 6 or 7, wherein the predictable load torque (M_L) is corrected by evaluating the actual rotational speed or torque values resulting on the form of the pilot control.

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