DE1527612B2 - DEVICE FOR REGULATING THE THICKNESS AND SECTIONAL SHAPE OR FLATNESS OF SHEET METALS AND STRIPS IN ROLLING MILLS - Google Patents

Description

Js =

-s +

N -M

ΔΕ

wired or programmed, where As is the. required change of the roll gap setting, N is a constant and AE is the difference between the signal representing the actual flatness and the signal representing the target flatness.

45

The invention relates to a device for regulating the thickness and cross-sectional shape or flatness of Sheets and strips in rolling mills with a control circuit in which roll adjustment devices the roll gap and, via hydraulic pressure pistons arranged between the roll necks, the roll crown as a function of the cross-sectional shape or flatness detected by a measuring device of the sheet is affected.

A control device of this type is described in US Pat. No. 13,655, in which the cross-sectional profile or flatness of the sheet rolled in a roll stand is controlled. A good cross-sectional profile represents an important parameter for the rolled sheet, but another parameter is which has at least the same meaning, the waviness of the rolled sheet.

The following definitions can be used for the waviness of a sheet metal within the scope of the present invention: a completely flat sheet has the waviness £ = 0, a sheet with wavy edges has a positive waviness £> 0 and a sheet with a wavy center has a negative one Ripple £ <0. If, in practical cases, a rolling mill is initially set in such a way that the sheet rolls to a nominal thickness ti * and a waviness £ * = 0, then unavoidable changes in the rolling conditions result in thickness errors Ah = h-ti * and waviness errors AE = EE *. The results of experiments and theoretical considerations show that both errors occur together and have the same sign. It is evident that the waviness of the rolled sheet is a completely different parameter than the cross-sectional shape or flatness and has no relation to the thickness of the sheet. The waviness of the sheet is namely the extent to which a section across the width of the sheet has experienced a greater reduction in thickness than another part. This can then manifest itself in different distributions of internal stresses in the interior of the sheet or it can occur in the form of a greater elongation of a part across the width of the sheet, for example in the middle in comparison with the edges. f

It is thus evident that it is possible to produce a sheet metal with a perpendicular rectangular cross-section or profile produce, which at the same time, however, has insufficient waviness properties. This can be done in a typical situation occur when the workpiece entering a roll stand is not exactly rectangular is in its cross-sectional profile, on the other hand, however, the sheet leaving the roll stand is accurate Has a rectangular cross-sectional profile. In this situation there must be a different reduction the sheet thickness and consequently also a different elongation across the sheet width. If the sheet leaving the roll stand is under the tensile stress of a strip reel, the different elongation nods in appearance, but with a different tensile stress pattern in the sheet is present across its width. The insufficient waviness properties of the sheet are only then obviously when the sheet is free of tension, d. H. when it is cut into bars. Sheet the are not completely flat due to waviness, but are not suitable for many press processes, \ where sheet steel is commonly used, such. B. in the manufacture of motor vehicle bodies.

The above-mentioned US-PS 32 13 655 does not describe a method for measuring and controlling the waviness of rolled sheet metal, so that the expert in this field is faced with the task of a control system for to create a sheet rolling mill which is suitable for the production of sheet metal with good waviness properties is, can not draw any suggestion from this known method.

In the OE-PS 2 40 481 a type of automatic thickness control is also described in which the Sheet thickness is measured by a recording instrument and the resulting thickness error in is fed into a tension control loop of the rolling mill. The control system described in this patent specification is able to ensure an improved form of sheet thickness control in the longitudinal direction of the strip, however, no provision is made to in any way affect the cross-sectional profile, i.e. H. the Control sheet thickness via the width of the strip or the waviness. That using a Such a control system rolled sheet can consequently

be completely inadequate either in terms of cross-sectional profile or waviness.

It is also known (Iron and Steel Engineer, August 1965, pp. 83, 84) that the waviness of the rolled sheet depends on many different factors including the cross-sectional profile of the incoming strip and that, as will be explained in more detail below, corrective measures with regard to the Thickness and / or the cross-sectional profile or flatness of the rolled sheet simultaneously influences the waviness of the finished rolled sheet. Since this connection is given, it is recognized by experts that both conditions, namely strength, profile or flatness and waviness can only be achieved at the same time with considerable difficulty. In order to achieve a completely rectangular cross-sectional profile or flatness, the setting of the roll stand must be constantly changed so that this rectangular profile is retained regardless of changes in the incoming strip profile, hardness, thickness, etc. in the sheet emerging from the roll gap. In contrast, in order to achieve a sheet with a waviness E = 0, the roll stand must be controlled in a completely different way, namely in such a way that the percentage difference between the incoming strip profile and the outgoing strip profile is kept constant and is equal to the desired reduction. This means that in the ideal case, each infinitesimally small section over the width of the sheet should be reduced in height by exactly the same fraction and stretched. In all known rolling processes, the greatest difficulties arise when one tries to regulate the waviness of the rolled sheet to zero, while at the same time maintaining a constant sheet thickness over the entire length, since any corrective measures with regard to the waviness have an effect on the sheet thickness and vice versa, whereby both corrections can compete with each other. This fact is discussed in more detail below with regard to the tolerability and incompatibility of various types of corrective measures.

A proposal that does not belong to the state of the art has already been made for controlling the ripple has been, in which a device for detecting the waviness of the sheet is described. Such a device can be designed in a wide variety of ways. For example, the device can have a variety of roles, which are in engagement with the sheet metal from below at various points across the width of the sheet. If that Bleoh has poor waviness properties, then the rollers take up different height positions and an electrical signal representing these height differences can be used to generate the to represent corresponding waviness errors. Though other means of displaying ripple errors as well can be used, the device of the type described above is preferred because it is not only detects waviness errors that are recognizable on the surface as local transverse corrugations of the strip, but also hidden ripples caused by longitudinal stresses that change with respect to the width of the tape arise. The above-described device for detecting the ripple errors can also easily be used in Robust shape can be produced and does not require a very precise type to accurately detect the waviness of signal generation.

As with the thickness control, a ripple signal can be used for the present problem of ripple generated according to the ripple error and used to set a control parameter of the To form the rolling process, for example to adjust the roll gap to regulate the sheet tension or the Roll bending to thereby control the rolling with regard to the desired waviness properties.

Starting from a device of the type mentioned at the outset, the object of the invention is

ίο based on creating a control system in which Sheet thickness and cross-sectional shape or flatness at the same time as the waviness of the sheet in the relaxed State can be influenced in the sense of a setpoint without causing harmful mutual influence the controlled variable comes.

In the case of a control device of the type mentioned at the outset, this object is essentially achieved by that a second control circuit is assigned through which, as is known, the belt tension as a function of the is influenced by a measuring device detected rolling force.

In comparison with the prior art, the present invention therefore provides a control system for a Strip or sheet rolling mill created in which both the sheet thickness and the waviness are measured will. The sheet thickness error signal is sent to a tension control loop of the rolling mill and the waviness error signal fed into a roll gap adjustment device. The roll gap adjusting device can either be formed by the spindle adjustment or alternatively by hydraulic pressure pistons, which the Press the roll ends of the work rolls and the backup rolls away from each other in a Quatro stand. on In this way, both the waviness and the sheet thickness can be influenced.

Further advantageous details according to the invention are characterized in the subclaims

It is of particular importance to point out at this point that the present invention is not only consists of an automatic thickness control system and an automatic waviness control system summarize. This is best illustrated using examples with reference to compatible control systems and incompatible control systems explained with reference to the drawings

In Fig. 1 of the drawing shows the effects of thickness control by adjusting the spindle or sheet tension on the waviness of the sheet. The vertical axis represents the rolling force F and also the shape value E corresponding to the waviness and the roll gap setting, the input thickness H of the sheet and the output thickness h of the sheet are plotted on the horizontal axis. Point A represents the rolling conditions at a certain moment when the input thickness is H and the roll gap setting has the value s.The point A is determined as the intersection of the straight line sA, which represents the effect of the spring forces of the roll stand on the roll gap, with the deformation curve AH, which relates the rolling force F to the initial thickness h.

Assuming that the rolling conditions at this time are such that the target thickness h * and the waviness E * = 0 are obtained, it is to be examined what happens if the input thickness subsequently changes to the value H ' and what for changes in the rolling conditions result from the various correction options. as

First, the changes in the rolling conditions are to be examined: The new situation is represented by point B , which represents a positive thickness error and a positive waviness error, the latter occurring for the following reason: As the rolling force increases and thus the rolls are subjected to increased bending, there is a tendency towards a convex roll gap. Second, possible corrections are to be discussed: If the adjusting spindles are tightened in order to reduce the thickness error, then this corresponds to a shift of the spring characteristic sA of the roll stand to the left by -As, and point B moves along the new deformation curve H'B ' until it coincides with a point C , which in turn corresponds to the desired thickness h * . Obviously, the effect of this process consists in an increase in the already existing positive waviness error AK

If instead a belt tension adjustment is carried out to change the roll separation force in order to thereby reduce the thickness error, then this corresponds to a movement of the curve H'B until point B coincides with A , where the thickness error is reduced to zero. It can be seen that in this way the ripple error also goes back to zero.

The above discussion with reference to FIGS. 1 is idealized to a certain extent, but nevertheless shows that different forms of thickness control have very different effects on the influence of waviness to have. This is due to the fact that the roll gap is generally reduced by adjusting the spindle causes the intersection of the spring characteristics of the roll stand and the deformation curve to be on the Deformation curve moves while a tension adjustment marks the intersection point on the spring characteristic can be moved

It follows that a correction of thickness errors by regulating the strip tension, namely either by regulating the strip tension on the incoming strip or the strip tension on the outgoing strip tends to correct for those waviness errors caused by the same process were like the thickness errors. Trying to correct the thickness error by reducing the Bringing the roll gap by means of the adjusting spindles, however, results in a control system which, with the Controlling the ripple using the automatic ripple control is incompatible because in this way, already existing waviness errors are enlarged.

Another aspect of the invention is the use of devices for bending the Rollers, as these are indicated generally in Figure 2 of the drawing, in which printing devices in Form of hydraulic cylinders between the ends of the work rolls and the associated backup rolls are arranged. When the waviness is controlled, the forces on the spindles and the roll stand elongation change not, but the mutual flattening of the backup roll and the work roll is reduced, whereby the roll gap becomes narrower and there is a negative thickness error. However, this error is much smaller sls in the case of strip tension control for the purpose of ripple control and one can use this Basically, a combination of automatic thickness control by belt tension and automatic roll gap control using hydraulic piston and cylinder arrangements between the backup roll and the work roll to control the waviness.

When considering the use of an automatic ripple control system, which one the piston and cylinder assemblies are located between the journals of the work rolls one can easily show from a consideration of the direction and magnitude of the forces that a correction of a positive waviness error, the elongation of the roll stand and the mutual flattening of the backup rolls enlarged, resulting in a positive thickness error. After waviness and thickness errors usually occur in the same sense, interfere with the ripple control via pressure pistons between the Axes of the work rolls the automatic thickness control.

Another possible method of influencing the waviness is to regulate the longitudinal tension of the strip across the belt by tiltable tension rollers, which on the other hand result in a corresponding change the framework expansion occurs. This would correct a positive ripple error with the Introduction of a positive thickness error.

The consideration shows that when using separate control systems for the thickness and the waviness of the Tape compatibility, d. H. technical compatibility of the two systems can only be achieved if the knowledge on which the invention is based is used and then the appropriate systems are used accordingly the invention chooses. Even if highly compatible systems are used, a Mutual influence cannot be completely ruled out, resulting in a buildup due to the detrimental differences between the response speeds of the two systems can arise. These differences arise from the nature of the measurement of ripple and a feedback control system The waviness causes a time delay in the signal transport, which changes with the rolling speed changes, while there is no such delay in the thickness measurement

Another possibility is to use two control systems which are linked in such a way that the secondary windings of one control system are then corrected by the second control system will.

In such a system, the tape tension for controlling the thickness is advantageously regulated and the Adjusted spindle adjustment to regulate the ripple. This could be an automatic thickness control by pulling the tape by using the inlet or outlet tension z. B. in a first control loop and an error signal representing an error in the waviness is allowed to move the spindle Operate in a similar way to the automatic thickness control via spindle adjustment the case is.

In Figure 3 of the drawings, a control system is shown schematically, wherein the thickness control over the strip tension and the Welligkeitsregelung via the spindle appointment is made, the thickness control is effected by a signal AF which is proportional to the deviation of the respective rolling force of that force at which the The respective roll gap setting delivers sheet metal of the target thickness. This signal is calculated electronically from: A signal corresponding to the respective rolling force F, which comes from a load cell

1, a load cell and the like; a signal representing the roll gap setting s which comes from the detectors 2 which detect the spindle position; and a signal Λ *, which represents the nominal thickness. This calculation is carried out by a computer 4 in accordance with the equation AF = FM (h * - s) , where M represents the spring constant of the roll stand. The signal calculated in this way is used via a torque controller 5 to control one or more drive motors 6 of the take-up reel or the supply reel 7.

The waviness is corrected by using a signal which represents the waviness E just present and is detected by a device 8 which detects the waviness. The signal E is used via a computer 9 to control the spindle adjusting motors 10, whereby the roll gap setting s is determined. The computer 9 controls the adjusting motors 10 in a predetermined manner as a function of the signal E such that the roll gap size s is reduced or enlarged depending on whether E is greater than or less than zero.

During operation, a ripple error signal changes the spindle position and thereby in turn the forces on the rolls, whereby the separation of the rolls in the nip is also changed. This will in turn, the thickness control system for regulating the tape tension put into operation that it the helps reduce original waviness errors and maintains proper thickness. The mode of operation of the thickness control system is inevitably faster than that of the waviness control system, so that the Thickness is corrected at the same time, while the rolling mill is adjusted for waviness correction. It there is therefore no risk of looking up.

In a further embodiment of such a combined thickness and waviness control system, as can be used, for example, in the case of discontinuous adjustment of the spindle adjustment the calculator for the ripple control in addition to the ripple f on the respective rolling force Fund the Address spindle position S as an additional variable. Such a system is shown schematically in FIG Drawing shown. The thickness control system provided in this plant is the same as that according to F i g. 3, but the ripple control is based on the following consideration:

First, a measure of the waviness of the rolled sheet can be represented by the following expression will:

E = a

Je_-Jc_
w ■ Ic

U)

Volume, i.e. if the relationship hl = HL is valid, which results in:

he j he he / he '

Since the associated thickness control system is irn ^ generally works on the basis of an average thickness Λ, equation (3) in rewritten as follows:

1 +

where b · w is the distance from the center line of the ribbon to the point where h = h and the approximation is good if £ is not excessively large.

From equation (4) it follows that a waviness error AE can be corrected by changing the value of the roll gap in the center line, the rolls being adjusted in such a way that the following applies:

whereby

is and the value - = -
H

for this purpose a constant

Value is close to the unit.

From the theory of loaded girders it can also be deduced that hc = d · ^ Fist, where your is a constant dependent on the bandwidth and the various mechanical constants of the rolling mill. Under the above conditions, a change in the rolling force - * - - - - ■ ^h

corresponds to, where N
the changing factor is.
Consequently, the
Control equation

required a yourself

with

the AF = jj -AE of the bandwidth

mean thickness Λ by the

h = s +

certainly. If one now assumes that a roll stand is designed with automatic thickness control, the Λ holds essentially constant, it follows that the required change in the spindle position by the the following equation is given:

where a is a constant, Ic is the length of the outgoing strip measured along the center line, Ie is the corresponding length at the edge of the sheet and w is half the width of the sheet.

If the incoming sheet has a perfect nominal waviness E = O, which is expressed by Le = Lc, then equation (1) can also be written in the following form:

(2)

and without lateral spreading, the input thickness H and the output thickness Λ can be based on constant

NM

\ E

In of the in F i g. 3 and 4, the computer 4 can be designed so that it calculates the straight rolled thickness according to equation (5) above and subtracts the target thickness Λ * so that the signal given to the torque controller 5 has the value s + F / Mh * represents.

The systems according to FIG. 3 and 4 can also be equipped, for example, with an X-ray thickness measuring device in order to obtain a direct measure of the thickness h which is just coming out, such devices preferably being close to

709 514/145

the waviness detecting device are arranged. The signal coming from the thickness measuring device can then be compared with the signal h * , as a result of which the resulting thickness error signal (h-h *) can be applied to the torque controller 5; in the case of FIG. 3 the detectors indicating the load cells and the position of the spindles can then be dispensed with.

In summary it can be said: The invention shows that an automatic control of both the Thickness as well as the waviness in a single sheet roll stand not by combining any independent systems can be obtained, but rather a certain degree of compatibility must be found between the systems. The combination of a thickness control system via belt tension appear with a ripple control system via pressure pistons between back-up and work rolls expedient from this point of view. Consideration has also shown that various forms of thickness and waviness regulations via belt tension and spindle adjustment are appropriate.

Ultimately, it is advantageous if the automatic thickness and waviness control system has a lead or negative feedback thickness control system is connected upstream, so that the control according to the invention

ίο not having to deal with mistakes that are too big. Obviously this is compatible; H. compatible with the predominantly common factor of automatic Thickness control systems via the strip tension according to the above proposals, since such a control is normally is used on the last stand of a multi-stand rolling mill.

For this purpose 2 sheets of drawings

Claims (4)

Patent claims: 1. Device for regulating the thickness and cross-sectional shape or flatness of sheets and Belts in rolling mills, with a control loop in which the Roll gap and the roll crowning via hydraulic pressure pistons arranged between the roll necks depending on the cross-sectional shape or flatness of the detected by a measuring device Sheet is influenced, characterized by the assignment of a second control loop, by which, as is known, the belt tension as a function of that recorded by a measuring device Rolling force is influenced. 2. Device according to claim 1, characterized in that hydraulic pressure pistons between the journals of the backup rolls and the journals of the work rolls are arranged. 3. Control device according to claim 1 or 2, characterized in that a computer is provided in the second control loop (4,5) which wired or for calculating a change in the roll separation force AF according to the formula AF = FM (ti * -s) is programmed, where F is the current rolling force, M is the spring constant of the roll stand, ti * is the nominal value of the sheet thickness and s is the size of the roll gap setting. 4. Control device according to one of the preceding claims, characterized in that in the first control circuit, a computer is switched on, which is used to control the spindle adjustment of the rollers according to the equation 35