US3926024A

US3926024A - Method and device for regulating the thickness of rolled products

Info

Publication number: US3926024A
Application number: US084299A
Authority: US
Inventors: Jean Philippe Mornas
Original assignee: Compagnie des Ateliers et Forges de la Loire SA
Current assignee: Compagnie des Ateliers et Forges de la Loire SA
Priority date: 1969-10-31
Filing date: 1970-10-27
Publication date: 1975-12-16
Anticipated expiration: 1992-12-16
Also published as: GB1319327A; JPS4937623B1; BE757563A; DE2052487A1; FR2063781A5

Abstract

A method of regulating the thickness of a product such as a metal strip processed in a rolling-mill, which mill comprises a position corrected under-load clamping system. The method being characterized in that the rolling mill, within a certain range of positions, is rendered elastic by causing the rolling effort to be responsive to a given preset reference value, and outside said range, the rolling mill recovers at least its natural rigidity or, better still, is made rigid, by properly monitoring said reference value of said effort responsiveness.

Description

United States Patent [191 Mornas Dec. 16, 1975 [541' METHOD AND DEVICE FOR REGULATING 3,527,074 9/1970 Guillot 72/8 THE THICKNESS 0F ROLLED PRODUCTS 1538117 11/1970 72/8 3,543,549 12/1970 72/8 [75] Inventor: Jean Philippe Mornas, St. Etienne, 3 55Q413 13/1970 73 France 3,580,022 5/1971 Waltz 72/8 [73] Assignee: Compagnie des Ateliers et Forges de la L i S Chamond, Firminy9 St Primary E.\-aminer-Milton S. Mehr E i J bJ-i lt Paris, Attorney, Agent, or Firm-Wenderoth, Lind & Ponack France [22] Filedz. Oct. 27, 1970 [5 ABSTRACT [21] App]. No; 84,299 A method of regulating the thickness of a product such as a metal strip processed in a rolling-mill, which 30 mill comprises a position corrected under-load clamp- 1 Forelg Appllcanon Pnomy Data ing system. The method being characterized in that Oct. 31. 1969 ran 69-37440 the rolling mill, within a certain range of positions, is

rendered elastic by causing the rolling effort to be re- [52] U.S. u 72/19 pongive to a given preset reference value and utside [5 i] Cl. B2113 said range the rolling recovers at least its natural Fleld 0f Search l9, or better tu] is made rigid by propgrly monitoring said reference value of said effort responsive- [56] References Cited ness,

UNITED STATES PATENTS 7 Claims, 1 Drawing Figure 3,416,341 12/1968 Dey et al. 72/8 24 r16 va ider-6n) 20 f- "'1 2 26 I9 23 U.S. Patant Dec. 16, 1975 3,926,024

- JEAN PHILIPPE MORNAS,

Inventor Attorneys METHOD AND DEVICE FOR REGULATING THE THICKNESS OF ROLLED PRODUCTS This invention relates in general to the continuous regulation of rolled products during the processing thereof, and has particular reference to methods and means for regulating the thickness of a product processed in a rolling mill.

It is known that the thickness of a rolling-mill product, for example a metal strip varies considerably due to the influence exerted by various parameters which do not remain strictly constant during the entire rolling operation, or even during a single pass. These parameters are related:

either to the product itself, such as resistance to distortion, conditions prevailing during the distortion (mainly the lubrication between the strip surface and the rolls), thickness and width of the mill inlet,

or to the rolling-mill proper of which the opening varies on the one hand on account of its elastic distortion (yield), on the other hand on account of various defects such as the eccentricity of the rolls (out-of-true), or also of the irregular play in the oil-film bearings.

Regulation methods are already known for correcting the defects of one or the other types set forth hereinabove, but these methods are objectionable in that the adjustments thus accomplished cancel one another; in other words, if the defects due to the irregular properties of the incoming products are corrected, those resulting from rolling-mill defects are increased, and vice-versa.

It is the essential object of the present invention to provide a method capable of overcoming this difficulty by correcting both the defects due to irregularities in the product to be rolled and the defects due to rollingmill defects, mainly its out-of-true or out-of-round.

To this end, the present invention consists essentially of a method of continuously regulating, adjusting and readjusting the thickness of a product processed in a rolling mill, equipped with a position-corrected underload clamping system. According to this method, the rolling mill, within a certain range of positions, is rendered elastic by causing the rolling effort to be responsive to a given preset reference value, and outside said range, the rolling mill recovers at least its natural rigidity or, better still, is made rigid, by properly monitoring said reference value of the effort responsiveness.

This invention is also concerned with a regulating device for carrying out the method set forth hereinabove, this device being characterized in that it comprises:

a. a primary correcting circuit adapted to set the value of the clamping position correction in such a manner that the measured rolling effort be constantly very substantially equal to a reference magnitude called the effort reference value;

b. a secondary correcting circuit adapted to determine the magnitude of the effort reference value, this chain comprising;

a dead zone device having the property of transmitting in magnitude and sign of the signal applied to the input of this device, only the fraction lying outside a predetermined range, the limits of this range being disposed symmetrically on either side of a predetermined magnitude called a position reference,

a device having integrating and memory functions, which is responsive to said dead zone device in such a manner that its output signal is the integral of the signal delivered by said dead zone device, this output signal constituting the effort reference and being fed as such to the reference inlet of said primary circuit;

c. means for displaying the position reference, adjusting the width of the dead zone and putting the regulating system into its operative and inoperative conditions, as required.

The invention will now be described in detail with reference to a typical embodiment thereof in the case of a strip rolling mill equipped with hydraulic means for clamping the product under load. Of course, this example should not be construed as limiting the scope of the invention.

In the following description reference will be made to the attached drawing of which the single FIGURE illustrates the wiring diagram of the regulating device of this invention, associated with the strip rolling mill.

In the drawing, a roll stand 1 is equipped with a hydraulic device 2 for clamping the product being processes under load. In this example this hydraulic device comprises, as shown diagrammatically: a main hydraulic cylinder and piston unit 2 disposed between the lower plummer-block and the stand bottom; a plunger rod 5 actuated by a control cylinder and piston unit 3, said rod penetrating into the chamber of the first unit 2 and being responsive to a servo-valve 4. Any movement of plunger 5 is accurately reproduced, except for a dividing factor, by the piston 6 of the main hydraulic unit, so as to change the clamping action exerted by the mill 1.

The main hydraulic unit further comprises a pressure detector 7 for measuring the effort (rolling effort) exerted by the rolling mill on the product. Finally, the position of plunger 5 is also measured by a displacement detector 8 displaying the degree of clamping movement performed by the device.

A comparator 27 is provided for comparing this clamping-movement measure with a reference signal e3 transmitted by wire 9. The resultant signal actuates a corrector amplifier 10 so that the position of plunger 5 and therefore the clamping effort produced by the clamping device proper is proportional to said reference signal e3.

The use of this hydroelectric device for regulating the clamping force is described herein only because its very valuable properties, i.e., its rapidity, precision and reliability, make the device highly adaptable to features characterizing the device of the present invention to be described hereafter. However, it should be emphasized that this choice does not constitute a limiting factor as far as the present invention is concerned, since the invention relates more particularly to the method of determining the reference signal e3.

This reference signal e3 is produced by an effort regulating circuit causing the rolling effort (measured by detector 7) to be constantly responsive to a reference value ef in wire 11.

To this end, the information received from detector 7 can be added at 12 to a corrector signal C cancelling the error due to roll bending, if the mill comprises means for detecting this bending. Thus, a signal ep corresponding to the actual rolling effort is obtained in wire 13. This signal ep is compared at 28 with the reference signal ef existing and the difference is applied to wire 11, in a correcting amplifier 14. The latter delivers an output signal e3 which, as already explained hereinabove, constitutes a reference signal for regulating the position of plunger 5.

It is clear that this regulating circuit is adapted to constantly keep the rolling effort, except for extremely short transitory time periods, at a value equal to a reference value represented by said signal ef.

The function of this first regulating circuit is to reduce to zero the variations in thickness of the rolled product which are caused by variations in the clamping pressure as a consequence of the out-of-true of one or more rolls in the stand. Under these conditions it is obvious that a clamping device having a high degree of dynamic performance must be used for the frequency of the correcting movements is relatively high, i.e., of the order of several Hertz as far as the fundamental component is concerned.

However, so far as described this circuit cannot correct any defects due to irregularities in the product itself. Therefore, the amplitude of the movements controlled by the clamping effort corrector is kept within the limits of a certain range.

To this end, according to this invention, the signal e3 is also fed to a comparator 15 receiving on the other hand a reference signal em transmitted via a wire 16. A signal corresponding to the difference (em e3) is delivered to the input terminal of a threshold device 17. This device is adapted to deliver a zero signal when the difference eme3 is less in absolute value than a certain constant K, and a signal proportional in absolute value to the quantity I em e3 I K, and of the same sign as (em e3) when (em-e3) is greater in absolute value than K. The constant K is adjustable; its value must correspond exactly to the peak-to-peak amplitude of the out-of-true.

An exemplary form of an embodiment of this aspect of the invention is shown diagrammatically in the FIG- URE.

The output signal of the threshold device 17 is fed to an integrator 18 whose output signal is the ef signal corresponding to the reference value of the rolling effort.

The function of this second circuit may be described as follows: as long as the characteristics of the product remain nearly constant, the rolling effort necessary for obtaining the final thickness also remains constant, and this value is memorized by the integrator 18.

The effort regulating circuit produces movements of the plunger 5 and therefore of piston 6 for compensating very exactly the variations in the clamping efforts which are caused by the out-of-true. The amplitude of these movements is such that the reference signal e3 varies exactly within the above-defined range em: K. Thus, the threshold device 17 delivers a zero signal and the output voltage of integrator 18 remains constant.

Now let us assume that the thickness of the incoming product increases. This will tend to increase the rolling effort by an amount ep. The effort regulating means react accordingly by causing a reduction in the clamping reference value e3; under these conditions, this value e3 will fall below the limit of the range emi K. Obviously, this will increase the signal ef and therefore e3 until the latter signal e3 is returned to the abovementioned range.

As it is, this arrangement will cancel the out-of-true effect while maintaining the natural rigidity of the rolling mill with respect to the irregularities of the product being processed therein. The defects due to this lastmentioned cause are corrected by a third circuit according to the present invention.

To this end, the reference signal cf of the rolling effort is not only fed to the effort corrector but also to one input of comparator 19. The other input of this comparator receives at 23 a reference voltage eo corresponding to a given, constant effort F0. The difference (ef eo) is amplified k times by an amplifier 20 whose output is fed to.an adder 21. This adder is an optional component of the third circuit and if provided it receives various correcting signals whose functions will be explained presently. The output of this adder is the reference signal em of the second circuit which limits the amplitude of the action exerted by the effort corrector.

This third circuit operates as follows: when the characteristics of the product vary, and assuming for example that the input thickness increases, as explained in the foregoing, the clamping reference e3 tends to overstep the limits of the range em i K imposed thereto, and this is attended by an increase in the reference effort value ef. More exactly, in the selected example concerning an increase in the input thickness e3 decreases and tends to become lower than em K.

As a consequence of the increase of ef, the third circuit described hereinabove will cause em to increase, thus further increasing the quantity (em e3) K and also the reference value ef.

This second increase of ef is attended bya clamping effect since e3 must increase in order to maintain the quantity em e3 at least equal to K.

It can be seen that this third circuit operates somewhat like a well-known thickness regulator. These devices operate by compensating. the yield in proportion to the effort or to the effort variation. More particularly, if the coefficient of amplification k2 of amplifier 20 is equal (with due consideration for the sensitivity of the position and pressure detectors) to the coefficient of elasticity kl of the rolling mill, it will be proved that the yield compensation is complete and the output thickness constant.

Therefore, these three circuits operatively linked in the manner described hereinabove impart to the rolling mill:

an infinite flexibility, within a certain range of adjustable amplitude. If care is taken to adjust this range within limits corresponding to the peak-to-peak amplitude of the out-of-true, the latter becomes inoperative as far as the thickness of the product is concerned, an infinite rigidity outside said range, so that the out-put thickness is independent of variations in the characteristics of the incoming product.

It may also be noted that both the adjustment of constant K and that of coefficient k2, as well as the yield compensation, depend only on the rolling mill, not on the rolled product.

Now the manner in which this arrangement is particularly adapted for making secondary corrections, such as those likely to be derived from information supplied by thickness gauges disposed on the incoming and/or outgoing product, will be described in detail.

Anticipated correction:

A thickness gauge may be disposed upstream of the rolling mill so as to detect any variation in thickness of the incoming product before it is engaged between the rolls. In this case it is extremely difficult to utilize this information, even with a suitable time-lag for taking account of the travel time betweenthe gauge and the roll stand, and at the same time the system for compensating the yield proportional to the effort variation. In fact, in this case two independent regulating circuits are involved and the correction orders issuing therefrom are added to each other instead of substituting the order of the second circuit for that of the first.

However. it is perfectly possible to obtain this substitution by feeding via a terminal 24 to the input 22 of integrator 18, through the medium of a differentiation capacitor, the error signal delivered by the upstream thickness gauge. This may cause, for example, an increase in ef. Now let us assume that the gain of this correction is so adjusted that the increase in the reference value ef corresponds to the increase in the rolling effort to be created, by increasing the clamping force, for maintaining the output thickness constant. In this case:

the increase in the clamping force must be: k1 A F, where A F denotes the increase in the rolling effort, and k1 is the coefficient of elasticity of the rolling mill, as explained hereinabove.

except for the sensitivity of the pressure and position detector, the reference value em increases by the same quantity k1 A F since it was adjusted as explained in the foregoing k2 Id, (k2 being the coefficient of amplification of 20, as already mentioned hereinabove).

therefore, since the variation of e3 was simultaneous with an equal variation of em, the charge of integrator 18 is not modified.

If on the contrary the correction gain is inaccurate it will be seen that when clearing one of the end or utmost points of the out-of-true the charge of this integrator will be corrected, as a consequence of the presence of the third circuit defined hereinabove.

In other words, the correction by upstream measurement provides a pre-adjustment of the clamping force, which is subsequently and possibly modified by the yield compensation chain.

Other secondary corrections can be applied to the regulation through the medium of adder 21, so as to cause a shift of the above-mentioned range. Therefore, the clamping-action modification will take place only when, as a consequence of the out-of-true, the quantity (em e3) has attained its limit value K. Therefore, when an immediate correction is desired, there will be fed at the same time, to point 22 via a differentiation circuit, a signal of such amplitude that it will produce substantially the effort variation corresponding to the signal fed to 21. It should be noted that in all cases the amplitude of the signal thus fed to 21 must correspond to the variation in thickness which it is desired to obtain at the output, and not to a variation in the clamping effort which is necessary to this end. In fact, the third yield compensation circuit adds its action to that of the signal fed to 21 so that the output thickness variation will correspond to the amplitude of this signal.

As a consequence, it is possible to feed to 21 and 22 a correction signal obtained from information supplied by a thickness gauge located downstream of the rolling mm. It is also possible to introduce at these point any necessary manual corrections. These inputs are shown diagrammatically in the form of a terminal 25.

Eventually, it will also be possible to introduce (but only into adder 21) the signal for correcting the thickness variation resulting from oil-film bearing play, or

any other correction of which an immediate application is not strictly necessary (through inputs shown diagrammatically in the form of a terminal 26).

In the above description it is obvious that certain technological choices have been made for illustrating the method and device of the present invention. However, it will readily occur to those skilled in the art that these choices should not be construed as limiting the scope of the invention. Thus, more particularly, numerical techniques may be substituted for the analogical solutions described.

On the other hand, the results and modes of opera tion described qualitatively can be justified mathematically and given quantitatively. More particularly, the stability of the various circuits has been proved and described. Therefore, these mathematical developments, which would only burden unduly the specification without appreciably improving the understanding thereof, are omitted herein.

What I claim is:

1. In a rolling mill having a position-corrected under load clamping system, a means for accurately regulating the thickness of the rolled product, comprising:

a. means to measure the rolling effort of the rolling mill;

b. a primary correcting circuit connected to said measuring means and adapted to set the value of a clamping position correction in such a manner that the measured rolling effort is constantly very sub stantially equal to a first reference magnitude called an effort reference value;

c. a second correcting circuit connected to said first circuit and to said measuring means and adapted to determine the magnitude of the said effort refer ence value, said second circuit comprising:

a dead zone device having the property of transmitting, in magnitude and sign, of the signal applied to the input of this device, only the fraction lying outside of a predetermined range, the limits of this range being disposed symmetrically on either side of a predetermined magnitude called a position reference,

a device having integrating and memory functions responsive to said dead zone device in such a manner that its output signal is the integral of the signal delivered by said dead zone device, this output signal constitutes the effort reference value and is connected to a reference inlet of said primary circuit; and

d. means for adjusting the width of the dead zone.

2. A device for controlling the thickness of a rolled product according to claim 1 wherein the position reference is determined by a third circuit comprising a multiplying device for multiplying the effort reference magnitude, the coefficient of said multiplying device is substantially equal to the coefficient of elasticity or yield of the rolling mill and the output magnitude of said multiplying device is fed to a position reference input of said dead zone device.

3. A device for regulating the thickness of a rolled product according to claim 2 further including a thickness gauge located near the input to said rolling mill for measuring the thickness of the product fed to said mill; said gauge having an output connected to the input of said device having integrating and memory functions.

4. A device for regulating the thickness of a rolled product according to claim 3 further including a second thickness gauge for measuring the thickness of the product emerging from the mill; said second gauge having an output also connected to the input of said device having integrating and memory functions, the output of said second gauge further being added to the output of said multiplying device of said third circuit.

5. A device for regulating the thickness of :1 rolled product according to claim 3 further including a time delay device connected between the output of said gauge and the input of said device having integrating and memory functions for delaying the signal fed to said input a time equal to the time needed for the measured product to reach the mill.

6. A device for regulating the thickness of a rolled product according to claim 1 further including a thickmagnitude of the dead zone device.

Claims

1. In a rolling mill having a position-corrected under load clamping system, a means for accurately regulating the thickness of the rolled product, comprising: a. means to measure the rolling effort of the rolling mill; b. a primary correcting circuit connected to said measuring means and adapted to set the value of a clamping position correction in such a manner that the measured rolling effort is constantly very substaNtially equal to a first reference magnitude called an effort reference value; c. a second correcting circuit connected to said first circuit and to said measuring means and adapted to determine the magnitude of the said effort reference value, said second circuit comprising: a dead zone device having the property of transmitting, in magnitude and sign, of the signal applied to the input of this device, only the fraction lying outside of a predetermined range, the limits of this range being disposed symmetrically on either side of a predetermined magnitude called a position reference, a device having integrating and memory functions responsive to said dead zone device in such a manner that its output signal is the integral of the signal delivered by said dead zone device, this output signal constitutes the effort reference value and is connected to a reference inlet of said primary circuit; and d. means for adjusting the width of the dead zone.

5. A device for regulating the thickness of a rolled product according to claim 3 further including a time delay device connected between the output of said gauge and the input of said device having integrating and memory functions for delaying the signal fed to said input a time equal to the time needed for the measured product to reach the mill.

6. A device for regulating the thickness of a rolled product according to claim 1 further including a thickness gauge for measuring the thickness of the product emerging from the mill; the output of said gauge being connected to the input of said integrating and memory device and also being added to the position reference magnitude of the dead zone device.

7. A device for regulating the thickness of a rolled product according to claim 2 further including a thickness gauge for measuring the thickness of the product emerging from the mill; the output of said gauge being connected to the input of said integrating and memory device and also being added to the position reference magnitude of the dead zone device.