US3220232A - Hot rolling mill controls - Google Patents

Description

A. TIX

HOT ROLLING MILL CONTROLS Filed June 29, 1962 Nov. 30, 1965 AR THUR 77X United States Patent fice 322,232 Patented Nov. 30, i965 Filed .lune 29, 1962, Ser. No. 2fl7,i55 Claims priority, application Germany, .Italy 1, 1961,

3 115 s claims. ici. i2- 7) This invention relates to finishing mills of the continuous hot rolling type, and further relates to methods pertaining to such finishing mills.

In mills of the above-noted type, procedures are known which include controlling roller clearances at various stations in order to eliminate the undesirable effect of elastic deformation of the equipment at such stations when the rolling pressures thereat vary.

It is also known to correct roller clearances by reference to a detector which measures the gauge and/ or the width of the rolled material as it leaves the mill and in such a way that the trailing end of the stock, which has been subjected to a longer cooling due to its longer wait before entering the mill, will have the Isame finished gauge and/ or finished width as the leading end.

However, the complete elimination of a slight taper or variance in )both gauge and width, which arises when roller clearances are not controlled, is not satisfactorily achieved by known methods of control. This is due, at least in part, to the dependence of control upon feedback from a zone subsequent to the final station, which relationship causes a delayed corrective action which is too late. In fact, the final gauge and width tend to oscillate substantially between plus and minus -on either side of the desired gauge and width and it is extremely difficult to keep diviations of the final gauge and width within acceptably low limits. This result is also due, in part, to the fact that the regulating action of known controls oscillates between positive and negative correction and thereby introduces backlash or hunting errors.

An object of the invention is to provide for overcoming the defects of known techniques and, to this end, the invention proposes a continuo-us finishing mill which comprises feedback control means for individually controlling the clearance between the rollers of a plurality of stations and monitoring means for measuring the gauge and/or width of the rolled stock leaving the final station, and which differs from known types of mills in that at least one of the stations-exclusive of the final stationis associated with a regulator for regulating roller clearance at that station, the regulator functioning to reduce the clearance at a rate calculated to decrease the gauge and/ or width of the product leaving the final station progressively, contrary to the natural tendency to increase in gauge and width as rolling proceeds.

With regard to the continuous mill train and techniques proposed by the invention, it will be understood that only some of the roller stations may be asociated with regulators of the aforesaid kind.

According to one feature of the invention, as rolling proceeds, the clearance between the rollers associated with a given regulator is decreased below the basic clearance prescribed by conventional computation. The station asociated with this regulator generates a rolling taper in the gauge or thickness yof the product which is contrary to the natural rolling taper of gauge or thickness, and which is empirically chosen. Even if this opposing taper Ishould not completely compensate the natural rolling taper, it at least has the effect that the required corrections of the roller clearances in the controlled stations will tend to be in one direction only, as will be hereinafter more fully described. This eliminates the undesirable effect of backlash. Moreover, the magnitude of the required corrections will be smaller, as will be likewise discussed in greater detail.

In accordance with a preferred embodiment of the invention, it is preferred to associate the improved regulation with the second station of the mill since the first station is called upon to break down the cooler outer skin of the entering stock, a task which subjects this station to higher loads. Moreover, it may be advisable to distribute the generation of the negative rolling taper between several stations, especially in those situations where the additional load imposed upon a single station might be excessive. Such a distribution has incidental advantages from the point of view of control, as will also be described hereinafter. In such a case, the first and third, or if for the above-mentioned reason the first station is to be excepted, the second and the fourth stations may be associated with the regulator.

As a further development of the invention, it is proposed that a continuous strip mill be operated in conjunction with a primary mill train which rolls down ingots or slabs from thicknesses exceeding mm. without intermediate heating. Such a mill train is of par- -ticular advantage for hot rolling .strip to a final width of say 7 mm. from an unrolled ingot of say l0 tons or from a correspondingly heavy slab. When the strip is of considerable length, the difference in temperature between the leading end which first enters the mill and the trailing end which is the last to enter is particularly great.

According to yet another feature of the invention it is proposed to provide a gauge and/or width detector between thes station associated with the regulator or the last station associated with the regulator and the following station. A suitable device may be provided which determines the mean between the value measured by said detector and the value obtained from the gauge and/ or width detector behind the nal station.

In order to assist in a better understanding of the principles underlying the invention, reference will now be made to the accompanying drawing in which:

FIGURE 1 diagrammatically illustrates the general layout of a continuous strip mill comprising control means according to `the present invention;

FIGURE 2 is a graph including curves which represent values as measured by two gauge and/ or thickness detectors in a continuous rolling mill according to the invention; and

FIGURE 3 diagrammatically illustrates the structure of the rolling station.

The continuous rolling mill in FIG. 1 rolls down a slab 1 received from a primary =mill from an initial gauge so of, for example, 20 mrn. to a final gauge s of, for example, 2 mm. in seven roller stations I to VII respectively. After having left the final stand the strip is coiled on a reel not shown. The individual stations are diagrammatically indicated and are each of conventional structure as diagrammatically illustrated in FIG. 3. The reduction of the slab l is shown on an exaggerated scale and as if reduction were continuous. The roll stations III to VI are respectively associated with controls 2(a-d) for maintaining constant separation of the rollers in each station by continuous adjustment which compensates the elastic deformation of the mechanical structure of the station during rolling. Each control 2 comprises a controller 4, a measuring device 5 for measuring the rolling pressure and a clearance adjuster 6 for adjusting roller clearance (distance RC in FIG. 3). The devices 5 for measuring the pressure may each be of a conventional load cell or a conventional device for measuring the elastic elongation of the mechanical structure of the associated station. The roller adjusting means 6 may be conventional screw-type equipment which permits a relatively fine adjustment. Alternatively, special supplementary hydraulic devices may be included in and controlled by the controller.

All the controllers 4 are connecte-d in conventional manner to a computer 7 which is of known type and supplies the required input quantity (X) and causes the rollers in all of the stations (III-VI) of the continuous rolling mill to be set to an initial basic clearance before the stock enters. The computer is associated with a conventional mixer 8. This mixer is supplied a correcting feedback quantity (KVH) from a detector 9 located following the final station VII, and with a seco-nd correcting quantity (KH) derived from a detector 1li located between stations II and Ill. The detectors may be conventional gamma ray thickness gauges and, in any event, should be precision instruments capable of measuring thickness variations in terms of hundredths of a millirneter. The mixer 8 contains conventional lmeans for rescaling the correcting input (KH) as next explained. The scaling factor is predetermined by the fluctuation amplitudes at different points of the train. For instance, (KVK) may require evaluation in terms of tenths of a millimeter and (KH) in full millimeters for establishing equivalence. Since the measuring points are fixed, the scaling factor remains constant while stock of given gauge and width is rolled down. The roller clearance adjusting device 6 of station II is connected with a regulator 11 which may be `a computer. This regulator is a conventional computer which stores a program for all anticipated lengths of rolled stock. The stored program has been fed into regulator 1l. before the actual rolling operation, and the particular program for a specific length is preselected on the basis of such specific length. According to the magnitude of the quantity (ZT) which modifies the uniformity of gauge and width-that is to say according to the degree of cooling experienced by the rear end of the stock as a function of the time which elapses before this end of the stock enters the rst stand of the millthe stored program provides a specific characteristic controlling effect which might be described as the injection of an error compensating value or of a negative error quantity (-ZT).

The described arrangement functions as follows:

When stock of a gauge sO enters the continuous strip mill, the rollers in all of the stations have been adjusted to the basic roller clearance prescribed by computers 7 and corresponding to the curvilinear clearance taper of the rolling mill train. The rollers of stations I and VII remain in this basic position of adjustment during the entire rolling operation of the stock. Computer 7 may be part of the computer 7, but is not modified by the output from mixer 8. However, the control of the roller clearance in roller stations III-VI by the associated control devices Za-d is modified by correcting inputs received by the measuring devices Sa--d to increase the rolling pressure by further reduction of the roller clearance, when the pressure has already been raised by the passage of a harder section of stock. On the other hand, the roller clearance is slightly increased when a softer length of stock has already caused the rolling pressure of its own accord to fall. The stations therefore operate to maintain a rigidly constant product and thereby substantially compensate non-uniformities in working conditions. Immediately after the stock has entered the rolling gap of station II, the rollers of this station are controlled to produce a rolling taper contrary to the natural rolling taper of the product. In other words, the regulator reduces the separation of the rollers at a rate which may be constant or otherwise prescribed by the programsay from l2 mm. to a final l0 mm. This increased reduction of the rolled section beyond the basic reduction envisaged for station II generates a compensating rolling taper with the result that roller stations III to VII are fed with a progressively diminishing gauge stock per mitting them to roll down the progressively colder and therefore less easily deformable material to the required gauge. Instead of the roller clearance in stations III-VI being reduced by their control equipment 2, as was heretofore the case to compensate the rolling taper of the product, the separation of the rollers in these stations is gradually increased because of the reduction in rolling pressure. Now the programmed regulator 11 can only roughly compensate the natural rolling taper. Either the compensating taper is too accentuated and the final gauge s as the end of the strip is less than at its beginning or the compensating taper is insufficient and the gauge s at the end of the strip is slightly too thick. This error is now compensated with the help of the detector at 9, because the group of controllers associated with stations III to VI is itself controlled by a controller by reference to the feedback quantity (KVH). Computer 7 corrects the basic rolling pressure by reference to (KVH). However, since the input signal (KVH) arrives too late at the stations III to VI, namely not until a considerable length of faulty gauge has already left the rolling mill, the correcting quantity is mixed with the correcting quantity (KVK). The error detected by detector 10 may differ from the error detected by detector 9. However, statistical considerations show that the mean value derived from both these quantities (KVH) and (K11) will be smaller than the error caused by the belated arrival of (KVK). This error will be partly rather than wholly compensated. The remaining fluctuations of the quantity (KVK) in this form of control which includes programmed prediction will thus be less than they have been heretofore.

The length L of the abscissa of the graph of FIG. 2 represents the length of the rolled stock leaving roller station VII. As illustrated in the graph of FIG. 2 the values of (KVH) measured by detector 9, which represent the gauge of the outgoing strip, are on a line parallel with the abscissa. This is so because the desired finished gauge is independent of stock length. Deviations from the controlled gauge appear as oscillations about the straight dot-dash line. Detector 1t) measures a (KVK) which diminishes linearly towards the abscissa, but which is likewise subject to oscillating deviations. (KVH) diminishes because it is a function of both stock length and desired finished gauge.

In a test of a control system according to the prior art, the amplitude of the oscillations of (KIQ) was much larger than in FIG. 2. These positive and negative deviations induced positive and negative fluctuations of the roller clearances controlled by computer 7. The separation of the rollers therefore alternately increased and decreased and, apart from the greater amplitude of these fluctuations, they also introduced further irregularities into the actual value of s because of the backlash arising in a to-and-fro adjustment. In a continuous strip mill according to the invention, the generation of a compensating rolling taper along the length of the rolled stock substantially reduces the amplitude of oscillation. Moreover, since the fluctuations of (Kn) have no rising but only a decreasing tendency, the mixing of (KVK) and (KH) generally gives rise to a resultant which applies only negative corrections to computer 7. The gradual change in roller clearance therefore Varies only between zero and negative values and rarely, if ever, includes changes in the positive direction. The backlash in a toand-fro adjustment cannot therefore arise, because the separation of the rollers in the controlled stations III to VI varies only in the direction of a gradual increase.

If in addition to controlling the gauge of rolled stock it is also desired to control its width, then the entire apparatus shown in FIG. l is duplicated for the control and regulation of the vertical roller stations. However, generally, control of gauge is the more important.

If in modification of the described example the fourth station is likewise controlled by a programmed regulator 11, then the generation of the compensating rolling taper will be distributed between two points along the train. This has advantages in permitting better compensation in the controlled roller stations. It is desirable that a controlled station, namely station III, should intervene between the stations regulated by predicted programming. The controlled stations will then be the stations III, V and VI.

What is claimed is:

1. Apparatus comprising a sequence of rolling stations each comprising rollers having an adjustable clearance therebetween and being aligned to roll a metal body into a strip of determinable gauge, clearance adjusting means coupled to the rollers of each station, irst control means coupled to the clearance adjusting means of the first and last stations to provide constant roller clearances therein according to a predetermined program, first measuring means in selected of the stations between the first and last stations to measure rolling pressure in said selected stations, second control means in said selected stations and coupled to said first measuring means, second and third measuring means respectively positioned following the said last station and at a station between the first and last stations, said second and third measuring means measuring strip thickness variations at their respective positions, mixing means coupled to said second and third measuring means to combine the measurements received therefrom, and computer means coupled to said mixing means and to said second control means and controlling the latter according to a combination of the said predetermined program and the combined measurements, the second control means being also controlled by said first measuring means, said second control means being coupled to and controlling said clearance adjusting means whereby to compensate undesired variations in said gauge.

2. Apparatus as claimed in claim 1 wherein the clearance adjuster of the second of said stations is coupled to and controlled by said first control means.

3. Apparatus as claimed in claim 2 comprising a programmed regulator coupled to and controlling the clearance adjuster of the said second station.

4. Apparatus for hot rolling a metal strip comprising a multiple stand continuous finishing mill including a plurality of stands arranged in succession and including a first stand, a last stand and a plurality of stands between the first and last stand, each stand including a [pair of rolls through which the strip passes and is rolled, said strips being reduced in thickness as the strip is passed from the first stand to the last stand, said last stand having rolls with fixed adjustment to provide constant spacing between the rolls for the particular strip, means ,for measuring the thickness of the strip at the last stand and at one of the stands between the first and last -stands and proximate the rst stand, and means responsive to the thicknesses of the strip as measured by the last mentioned means for continuously varying the spacing between the rolls of at least one stand located between those stands at which the thicknesses of the strip are measured to produce a strip of substantially uniform thickness at the last stand despite the constant spacing of the rolls thereat and despite the increasing resistance to deformation of the trailing end of the strip as a result of cooling of the strip, the latter said means continuously adjusting the rolls of said one stand to an extent which exceeds the adjustment which would be required if the spacing between the rolls of the last stand were reduced during passage of the strip.

5. Alpparatus as claimed in claim 4 comprising a program control device coupled to the rolls of the stand proximate the iirst stand at which the thickness of the strip is measured.

6. Apparatus as claimed in claim 5 wherein the mill is constituted of seven stands, the second stand of the mill being coupled to the program control device, the third through sixth stands being continuously controlled by the means which continuously varies the spacing of the rolls.

7. Apparatus as claimed in claim 6 wherein the means for measuring thickness comprise thickness gages located at the outlet of the second stand and at the outlet of the seventh stand, said means for varying the spacing of the rolls comprising mixer means for receiving the thickness measurements from the thickness gages for correcting the spacing of the rolls in accordance therewith.

8. Apparatus as claimed in claim 4 wherein the apparatus further comprises rolls at each stand for controlling the width of the strip, the latter rolls corresponding to the rolls controlling the thickness of the strip but being operated in accordance with width measurements to produce strips of substantially uniform width.

References Cited by the Examiner UNITED STATES PATENTS 2,931,917 4/1960 Beelitz Sil-56.2 2,972,268 2/ 1961 Wallace et al 80-56.2 2,985,043 5/1961 Roberts 80-56.1 3,081,653 3/1963 Kincaid 80-56.8

OTHER REFERENCES Control Engineering, pages 116, 117, September CHARLES W. LANHAM, Primary Examiner.

WILLIAM I. STEPHENSON, Examiner.

Claims (1)

1. APPARATUS COMPRISING A SEQUENCE OF ROLLING STATIONS EACH COMPRISING ROLLERS HAVING AN ADJUSTABLE CLEARANCE THEREBETWEEN AND BEING ALIGNED TO ROLL A METAL BODY INTO A STRIP OF DETERMINABLE GAUGE, CLEARANCE ADJUSTING MEANS COUPLED TO THE ROLLERS OF EACH STATION, FIRST CONTROL MEANS COUPLED TO THE CLEARANCE ADJUSTING MEANS OF THE FIRST AND LAST STATIONS TOI PROVIDE CONSTANT ROLLER CLEARANCES THEREIN ACCORDING TO A PREDETERMINED PROGRAM, FIRST MEASURING MEANS IN SELECTED OF THE STATIONS BETWEEN THE FIRST AND LAST STATIONS TO MEASURE ROLLING PRESSURE IN SAID SELECTED STATIONS, SECOND CONTROL MEANS IN SAID SELECTED STATIONS AND COUPLED TO SAID FIRST MEASURING MEANS, SECOND AND THIRD MEASURING MEANS RESPECTIVELY POSITIONED FOLLOWING THE SAID LAST STATION AND AT A STATION BETWEEN THE FIRST AND LAST STATIONS, SAID SECOND AND THIRD MEASURING MEANS MEASURING STRIP THICKNESS VARIATIONS AT THEIR RESPECTIVE POSITIONS, MIXING MEANS COUPLED TO SAID SECOND AND THIRD MEASURING MEANS TO COMBINE THE MEASUREMENTS RECEIVED THEREFROM, AND COMPUTER MEANS COUPLED TO SAID MIXING MEANS AND TO SAID SECOND CONTROL MEANS AND CONTROLLING THE LATTER ACCORDING TO A COMBINATION OF THE SAID PREDETERMINED PROGRAM AND THE COMBINED MEASUREMENTS, THE SECOND CONTROL MEANS BEING ALSO CONTROLLED BY SAID FIRST MEASURING MEANS, SAID SECOND CONTROL MEANS BEING COUPLED TO AND CONTROLLING SAID CLEARANCE ADJUSTING MEANS WHEREBY TO COMPENSATE UNDESIRED VARIATIONS IN SAID GAUGE.

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