US3820366A - Rolling mill gauge control method and apparatus including temperatureand hardness correction - Google Patents

Abstract

The roll openings of the respective roll stands of a tandem hot steel strip rolling mill are controlled in relation to the measured temperature of an approaching present workpiece, which is similar to a previous workpiece, and which measured temperature of the present workpiece is compared to the weighted average temperature of previous similar workpieces. In addition the workpiece hardness as indicated by the measured lock on roll force for the present workpiece and compared to the weighted average of the lock on roll forces of previous similar workpieces is used for control purposes. The automatic gauge control system calculates the screwdown movement correction required for correction of the roll opening of each roll stand in relation to the expected per unit change in stand roll force for at least one of these comparisons. The control system operates the mill screwdowns in accordance with these calculated screwdown movement corrections.

Description

United States Patent [191 Smith, Jr.

[ ROLLING MILL GAUGE CONTROL METHOD AND APPARATUS INCLUDING TEMPERATURE AND HARDNESS CORRECTION 1 [75] Inventor: Andrew W. Smith, Jr., Pittsburgh,

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Nov. 6, 1972 [2]] Appl. No.: 303,723

I [52] US. Cl. 72/9, 72/13 [51] Int. Cl B2lb 37/10 [58] Field of Search 72/8, 6, 13

[56] 7 References Cited UNITED STATES PATENTS 3.111.046 11/1963 Koss et a1. 72/15 X 3,186,201 6/1965 Ludbrook ct al. 3,253,438 5/1966 Stringer 3.568.637 3/1971 Smith, Jr 3,628.358 12/1971 Fapiano 3,691,801 9/1972 Gillstrom 72/9 i 3,820,366 ].June 28,1974

Primary ExaminerMilton S. Mehr Attorney, Agent, or Firm-R. G. Brodahl [5 7] ABSTRACT The roll openings of the respective roll stands of a tandem hot steel strip rolling mill are controlled in relation to the measured temperature of an approaching present workpiece, which is similar to a previous workpiece, andwhich measured temperature of the presentworkpiece is compared to the weighted average temperature of previous similar workpieces. In addition the workpiece hardness as indicated by the measured lock on roll force for the present workpiece and compared to the weighted average of the lock on roll forces of previous similar workpieces is used for control purposes. The automatic gauge control system calculates the screwdown movement correction required for correction of the roll opening of each roll stand in relation to the expected per unit change in stand roll force for at least oneof these comparisons;

The control system operates'the mill screwdowns in accordance with these calculated screwdown movement corrections.

15 Claims, 5 Drawing Figures SCR EWDOWN POSITIONING CONTROL 2 SCREWDOWN POSITION DE TECTOR SCREWDOWN POSITIONING CONTROL s l'c POSITION DETECTOR CF OP H SH :AR

I MILL ENTRY SIDE L SIDE TEMPERATURE iGUARDS 1 GUARDS] nsrecroa 37 @T 53 SI spar-:0

B TENSION B TENSION CONTROL CONTROL INFORMATION .11

lNPUT AUTOMATIC 1 DEVICES GAUGE CONTROL SYSTEM OPERATOR STATION DISPLAY ururs.

CONTROL PANEL E %E I ROLLING MILL GAUGE CONTROL METHOD AND APPARATUS INCLUDING TEMPERATURE AND I-IARDNESS CORRECTION CROSS REFERENCE TO RELATED APPLICATIONS Reference is made to the following previously filed and related patent applications which are assigned to the present assignee:

Ser. No. 215,747, filed Jan. 6, 1972 and entitled Gauge Control Method And Apparatus Including Workpiece Plasticity Determination For Metal Rolling Mills, by A. W. Smith and R. Q. Fox.

Ser. No. 215,749, filed Jan. 6, 1972 and entitled Gauge Control Method And Apparatus Including Workpiece Gauge Deviation Correction for Metal Rolling Mills, by A. W. Smith and R. 0. Fox.

Ser. No. 215,743, filed Jan. 6, 1972 and entitled Gauge Control Method And Apparatus For Metal Rolling Mills, by A. W. Smith and R. Q. Fox.

Ser. No. 031,842, filedApr. 30, 1970 and entitled Gage Control System For I-Iot Rolling Mills, by R. B. Gillstrom.

Reference is made to the following concurrently filed and related patent applications which are assigned to the present assignee:

Ser. No. 303,721, filed Nov. 6, 1972 entitled Rolling Mill Gauge Control Including Entry Gauge Correction, and filed by A. W. Smith and R. Q. Fox.

Ser. No. 303,725, filed Nov. 6, 1972 entitled Rolling Mill Gauge Control Including Speed Correction, and filed by R. Q. Fox. 1

Ser. No. 303,724, filed Nov. 6, 1972 entitled Rolling Mill Gauge Control Including X-ray Correction, and filed by R. Q. Fox.

Ser. No. 303,722, filed Nov.v 6, 1972 entitled Rolling Mill Gauge Control Including Feedback Correction, and filed by R. Q. Fox and D. J. Emberg.

Ser. No. 303,723, filed Nov. 6, 1972 entitled Rolling Mill Gauge Control Including Plasticity Determination and filed by R. Q. Fox.

BACKGROUND OF THE INVENTION The present invention relates to workpiece strip metal tandem rolling mills and more particularly to roll force gauge or thickness control systems and methods used in operating such rolling mills.

In the operation of a metal or steel reversing or tandem rolling mill, the unloaded roll opening and the speed at each tandem mill stand or for each reversing mill pass can be set up by the operator to produce successive workpiece (strip or plate) reductions resulting in delivered work product at the desired thickness or gauge. 1

Since the operator provided initial setup conditions, or the initialroll opening settings provided by an associated computer control system operative with model equation information to calculate the setup screwdown schedules for the rolling mill, can be in error and since in any event certain mill parameters affect each stand loaded roll opening during rolling and after setup conditions have been established, a stand automatic gauge control system is desired if it is necessary that the stand delivery gauge be closely controlled. Thus, at the present state of the rolling mill art, and particularly the steel rolling mill art, a stand gauge control system is normally used for a reversing mill stand and for predetermined stands in tandem rolling mills.

More particularly, the well known gaugemeter or roll force system has been widely used to produce stand gauge control in metal rolling mills and particularly in tandem hot steel strip rolling mills and reversing plate mills where experience has demonstrated that roll force control is particularly effective. Earlier publications and patents, such as an article entitled Installation and Operating Experience with Computer and Programmed Mill Controls by M. D. McMahon and M. A. Davis in the 1963 Iron and Steel Engineer Year Book at pages 726 to 733, an article entitled Automatic Gage Control for Modern Hot Strip Mills by J. W. Wallace in the Dec. 1967 Iron and Steel Engineer at pages to 86', US. Pat. No. 3,561,237 issued Feb. 9, 1971 to Eggers et al. and US. Pat. No. 2,726,541, issued Dec. 13, 1955 to R. B. Sims, describe the theory upon which operation of the roll force and related gauge control a systems is based. Attention is also called to US. Pat. No. 3,568,637 issued Mar. 9, 1971, US. Pat. Nos.

3,574,279 and 3,574,280 issued Apr. 13, 1971, and I US. Pat. No. 3,600,920 issued Aug. 24, 1971 to A. W. Smith which relate to roll force automatic gauge control systems. In referencing prior art publications or patents as background herein, no representation is made that the cited subject matter is the best prior art.

Briefly, the roll force gauge control system uses Hookes law in controlling the screwdown position at a rolling stand,i.e. the loaded roll opening under workpiece rolling conditions equals the unloaded roll opening or screwdown position plus the mill spring stretch caused by the separating force applied to the rolls by the workpiece. To embody this rolling principle in the roll force gauge control system, a load cell or other force detector measures the roll separating force at each controlled roll stand and the screwdown position is controlled to balance roll force changes from a reference value and thereby hold the loaded roll opening at a substantially constant value. The following well known formula expresses the basic roll force gauge control relationship:

h=S0+F.K.

position signals to control the screwdown position and hold the following equality:

AS -AF-K where AF measured change in roll force from an initial force AS =controlled change in screwdown position from an initial screwdown position. Afterthe unloaded roll opening setup and the stand speed setup are determined such as by the mill operator for a particular workpiece pass or series of passes, the rolling operation of an actual workpiece is begun and the screw-downs are controlled to regulate the workpiece delivery gauge from the reversing mill stand or from each roll force controlled tandem mill stand. By satisfying Equation (2), and the assumptions implicit in Equation l the loaded roll opening h in Equation (1) is maintained constant or nearly constant. 2 As the head end of the workpiece strip enters each roll stand of the mill, the lock-on screwdown position and the lock-on roll separating force are measured to establish what strip gauge should be maintained out of that roll stand. As the strip rolling operation proceeds, the roll stand separating force and the roll stand screwdown position values are monitored and any undesired change in roll separating force is detected and compensated for by a corresponding correction change in screwdown position. The lock-on gauge LOG is equal to the lock-on screwdown LOSD plus the lock-on force LOF multiplied by the mill stand spring modulus K. The workpiece strip delivery gauge G leaving the roll stand at any time during the rolling operation is in accordance with above equation (1) and is equal to the unloaded screwdown position SD plus the roll separating force F multiplied by the mill spring modulus K. The gauge error is derived by subtracting the lock-on gauge from the delivery gauge. The following .Equa: tions 3, 4 and 5 set forth these relationships.

(4) G LOG GAUGE ERROR SD LOSD (FLOF)*K (5) One mill condition which can cause gauge error is the rolling of a present workpiece having a different temperature or hardness when compared to a previous workpiece of similar grade and/or gauge classification.

There are cited several prior art publications and patents in the prosecution file of the above-referenced Gillstrom patent application that are. related to the measurement or workpiece temperature for the improvement of the workpiece rolling operation.

A digital computer system can be employed to make the screwdown correction movement determinations as well as to perform other mill control functions. The digital computer employs a programming system including an automatic roll force gauge control program or AGC program which is executed at predetermined intervals to calculate the desired screwdown movement required at each roll force gauge controlled stand for gauge error correction including that related to roll force error detection at that stand. Screwdown movement for correcting roll force error is made on the basis of calculations which use selected workpiece plasticity and mill spring constant values stored in data tables in the computer system memory or otherwise determined by the digital computer system.

' There is disclosed in the above-referenced previously filed patent application Ser. No. 215,743 the logic flow chart of an illustrative automatic gauge control suitable for operation with the temperature and force correction operation of the present invention. It should be readily understood by persons skilled in this art that the present invention is also suitable for operation with other well known automatic gauge control systems for controlling the delivery gauge of a workpiece strip passed through the roll stands of a rolling mill.

A background teaching of stored program digital computer system operation can be found in a book entitled Electronic Digital Systems by R. K. Richards and published in l966 by John Wiley and Sons.

Amore detailed description of computer programming techniques in relation to the control of metal rolling mills can be found in an article in the Iron and Steel Engineer Yearbook for 1966 at pages 328 through 334 entitled Computer Program Organization for an Automatically Controlled RollingMill by John S. Deliyannides and A. H. Green, and in another article in the Westinghouse Engineer for Jan. 1965 at pages 13 through 19 and entitled Programming for Process Control by P. E. Lego.

SUMMARY OF THE lNVENTlON At least one of a different workpiece temperature or a different workpiece hardness is detected in relation to the established pattern of previously rolled similar workpieces. This is done in relation to temperature by comparing the measured head end temperature CST of each new workpiece as measured at the crop shear ahead of the finishing mill stands, with the measured and average value of the head end temperature ACST of the previously rolled similar workpieces. A new workpiece, similar in gauge class and grade class to previously rolled workpieces, that is hotter or colder than the previously established average crop shear temperature ACST, will require an adjustment to be made in the operator scheduled roll opening before the new workpiece enters the mill stands.

This is done in relation to hardness by measuring the head end or lock on roll force LOF(I) of this same new workpiece, as measured in the first operating stand of the rolling mill, and ratio comparing this with the established average ALOF(I) for lock on roll force measurements for similar previous workpieces. A new present workpiece that is harder or softer than the average hardness of these previous workpieces, as indicated by the measured lock on roll force at stand one, requires an adjustment in the roll opening of each subsequent stand in the rolling mill, perhaps not adjusting the sec ond stand because of available time for moving the screws to make the change in the second stand roll opening setting.

The initial roll opening for each stand is provided as an operator input within a provided schedule of these roll openings to establish the roll opening setting for each stand.

The determined correction is in the form of a per unit change in roll force for each stand, so the adjustment for the screwdown or roll opening setting for each stand is calculated by taking the product of either one of a temperature or force correction, TCF for temperature difference determined correction factor or FCF for the hardness difference determined correction factor, times the normal or average lock on force ALOF (N) for that stand (N) times the known stand mill spring constant K(N) to determine how much the change or the adjustment should be in relation to the operator scheduled stand (N) roll opening SDREF(N) to compensate for the expected per unit change in roll force at stand (N), due to either one or both of the sensed temperature difference of the new workpiece and the sensed different hardness in relation to the new workpiece.

In both the operation of the temperature determined correction TCF and the force determined correction FCF, the actual correction established is in the form of the expected per unit change in the stand roll force. Thusly, the corrected screwdown CSD(N) for each stand (N) roll opening is calculated using the proper one of the following equation relationships:

CSD(N) SDREF(N) ALOF(N) TCF K(N) 6 CSD(N) SDREF(N) e ALOF(N) FCF K(N) 7) where equation (6) is used to determine the temperature difference determined correction and where equation (7) is used to determine the hardness difference determined correction. The average or normal lock on force ALOF(N) for each stand (N) as used in the above equations is determined by the following relationship ALOI-(N) =[ALOF(N) WF+ LOF(N)]/WF+1 s) ,where the new averagelock on force ALOF(N) for each of the roll stands is determined each time that the head end of a new workpiece, having a similar grade class and similar gauge class to previous rolled workpieces, enters the first operating roll stand (I). This new average lock on force ALOF( N) is determined for each roll stand by equation (8) in relation to the previous value of this average lock on force multiplied by a predetermined weighting factor WF plus the measured lock on roll force LOF(N) for the head end of the present workpiece and divided by the weighting factor WF plus one. The weighting factor WF used in equation (8) is determined each time the stands of the rolling mill are preset with a schedule of roll opening settings for the respective stands of the rolling mill, such as would occur prior to the entry of another workpiece as compared to the last workpiece to pass through the stands of the rolling mill. This weighting factor isdetermined by the following equation relationship:

where the new weighting factor for the next workpiece is equal to the old weighting factor, for a given operator determined schedule in relation to the number of workpieces similar to the next workpiece in relation to grade class and gauge class that have previously passed through the stands of the rolling mill in accordance with this same operators schedule for the roll opening settings of the respective stands, plus one. This new weighting factor may then be limit checked, with a TCF (ACST- CST) TK where this temperature correction factor is determined each time the head end of a workpiece passes by the temperature measurement device, for example a pyrometer located adjacent the position of the crop shear, ahead of the finishing mill stands. The temperature correction factor TCF is determined in relation to the difference between the average of the measured temperatures ACST of the respective previous workpieces passing by the temperature sensing position and the measured temperature CST the present workpiece at the sensing position location, with that temperature difference then being multiplied by a provided constant TK which may have a typical value of 0.002 per unit correction per degree F. This temperature correction factor TCF is then limited to a value between +0.10 and 0.05 before'it is utilized.

The hardness related force correction factor FCF utilized in equation (7) is determined by the following relationship:

FCF= [LOF(I)]/ALOF(I) l where this force correction factor is determined each time a present workpiece strip enters the first operating stand (I), and if desired this operation may be limited to stand (I), being the first stand; The force correction factor FCF is determined in relation to the lock on roll force LOF(I) at stand (I) for the present workpiece being divided by the average lock on roll force ALOF(I) at stand (I) for the previous similar workpieces, with that quotient then being reduced by one. The force correction factor may then be limited to a value between +0.10 and 0.05 before it is utilized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. lshows a schematic diagram of a tandem hot steel striprolling mill and an automatic gauge control therefor arranged for operation in accordance with the present invention;

FIG. 2 shows an illustrative logic flow chart of the weighting factor WF determination in accordance with the present invention;

FIG. 3 shows an illustrative logic flow chart of the stand average lock-on roll force ALOF( N) determination program;

FIG. 4 shows an illustrative logic flow chart of the temperature difference corrected screwdown reference determination and the average lock on rollforce determination; and

FIG. 5 shows an illustrative logic flow chart of the hardness, corrected screwdown reference determination.

GENERAL DESCRIPTION OF THE GAUGE CONTROL SYSTEM AND ITS OPERATION There is shown in FIG. 1 a tandem hot strip steel finishing mill 11 operated with improved gauge control performance by a process control System13 in accordance with the principles of the invention. Generally, however, the invention is applicable to various types of mills in which roll force gauge control is employed. Thus, the invention can be suitably adapted for application in hot steel plate reversing and other rolling mills.

The tandem mill 11 includes a series of reduction rolling stands with only two of the stands S1 and S6 shown. A workpiece 15 enters the mill 11 at the entry end in the form of a bar and it is elongated as it is transported through the successive stands to the delivery end of the mill where it is coiled as a strip of a downcoiler 17. The entry bar would be of known steel grade classification and it typically would have a thickness of about 1 inch and a width within some limited range such as inches to 80 inches. The delivered strip would have approximately the same width and a delivery gauge or thickness classification based upon the production order for which it is intended.

In the reduction rolling process, the successive stands operate at successively higher speeds to maintain proper workpiece mass flow. Each stand produces a predetermined reduction or draft such that the total mill draft reduces the entry bar to strip with the desired gauge or thickness.

Each stand is conventionally provided with a pair of backup rolls 19 and 21 and a pair of work rolls 23 and 25 between which the workpiece 15 is passed. A large DC drive motor 27 is controllably energized at each stand to drive the corresponding work rolls at a controlled speed.

As previously described, for a given stand the sum of the unloaded work roll opening and the mill stretch substantially defines the workpiece gauge delivered from any particular stand in accordance with Hookes law. To vary the unloaded work roll opening at each stand, a pair of screwdown motors 29 (only one shown 'at each stand) position respective screwdowns 31 (only one shown at each stand) which clamp against opposite ends of the backup rolls and thereby apply pressure to the work rolls. Normally, the two screwdowns 31 at a particular stand would be in identical positions, but they can be located in different positions for strip guidance during threading, for flatness or other strip shape control purposes or possibly for other purposes.

A conventional screwdown position detector or encoder provides an electrical representation of screwdown position at each stand. To provide an absolute correspondence between the screwdown position and the unloaded roll opening between the associated work rolls, a screwdown position detection system which includes the screwdown position detector 33 can be calibrated from time to time.

Roll force detection is provided at each of predetermined stands by a conventional load cell 35 which generates an electrical analog signal. At the very least, each roll force controlled stand is provided with a load cell 35 and in many cases stands without roll force gauge control would also be equipped with load cells. The number of stands to which roll force gauge control is applied is predetermined during the mill design in accordance' with cost-performance standards, and increasingly there is a tendency to apply roll force gauge control to all of the stands in a tandem hot strip steel. mill. In the present case, a roll force gauge control system is, assumed to be employed at each of the stands.

Conventional motorized sideguards 37 arelocated at predetermined points along the mill length. The sideguards 37 are operated during mill setup on the basis of the widths of the upcoming workpiece 15 thereby .ance PUI'POSCS.

The process control system 13 provides automatic control for the operation of the tandem mill 1] as well as may be desired for associated production processes (not indicated) such as the operation of a roughing mill. Preferably, the process control system 13 comprises an automatic gauge control system 39 which can include a programmed process control digital computer, and which is interfaced with the various mill sensors and the various mill control devices to provide control over many of the various functions involved in operating the tandem mil] 11. According to user preference, the control system 13 .can also include conventional manual and/or automatic analog controls for backup operation in performing preselected mill functions.

The automatic gauge control system 39 can include a finishing mill on-line roll-force gauge control digital computer system, such as a Prodac 2000(P2000) sold by Westinghouse Electric Corporation. A descriptive book entitled Prodac 2000 Computer Systems Reference Manual has been published in 1970 by Westinghouse Electric Corporation and made available for the purpose of describing in greater detail this digital computer system and its operation.

A digital computer processor can be associated with well known predetermined input systems typically including a conventional contact closure input system which scans contact or other signals representing the status of various process conditions, a conventional analog input system which scans and converts process analog signals, and operator controlled and other information input devices and systems such as paper tape teletypewriter and dial input systems. It is noted that suitable information input devices 41 are generally indicated by a single blockv in FIG. 1 although different input devices can and typically would be associated with the automatic gauge control system 39. Various kinds of information are entered into the gauge control system through the input devices including, for example, desired strip delivery gauge and temperature, strip entry gauge and width and temperature (by entry detectors if desired), grade of steel being roller, plasticity tables, suitable hardware oriented programs and control programs for the programming system, and so forth.

The contact closure input'systems and the analog input systems interface the automatic gauge control or AGC system 39 with'the process through the medium of measured or detected .variables. The present invention is largely involved in the functioning of an automatic gauge control system, which in one typical invention application, various mill signals are applied to the AGC input systems. These mill signals include the following: v i

l. A roll force signal from the load cell 35 at each stand proportional to stand roll separating force for use in roll force gauge control.

2. Screwdown position signals generated by the respective detectors 33 at thestands for use in roll force gauge control.

3. Screwdown motor speed signals generated by respective tachometers 49 at the stands for use in programmed regulation.

4. Stand speed signals generated by respective tachometers 43, with the speed signal used for calculation of acceleration compensation and for calculation of time delays in monitor operation. I

5. A gauge deviation signal from an X-ray gauge 47 at the delivery end of the mill for programmed monitor gauge control through the roll force control. 1

6. An entry temperature signal from a mill entry temperature detector or pyrometer 45; the mill entry temperature for the head end of each workpiecelS is stored.

- 7. Width signals supplied by sideguard follow potentiometers for mill spring constant calculations, etc.

It is noted at this point in the description, that the measured head end roll force is. stored and used as a reference for roll force gauge control functioning at the respective stands if the AGC system is in the lock-on mode of roll force operation.

A contact closure output system would normally be associated with a digital computer,-and inthe operation of the AGC output system, various control devices are operated in response to control actions calculated or determined by the AGC system 39.

To effect determined control actions, controlled devices are operated directly by means of output system contact closure or by means of analog signals derived from output system contact closures through a digital be associated with the outputs of the AGC system 39- in order to keep the mill operator generally informed about the mill operation and in order to signal the operator regarding an event or alarm condition which may require some action on his part. The printout systems are also used to log mill data.

' Generally, the AGC system 39 uses Hookes law to determine the total amount of screwdown movement required at each roll force controlled stand at the calculating point in time for roll force and gauge error correction, i.e. for loaded roll opening and stand delivery gauge correction to the desired value. The calculation defines the total change in the unloaded roll opening required to compensate for a new mill stretch value or other roll force and gauge error causing condition. The predicted corrective screwdown position change value is employed by the AGC system to define the screwdown motor position-time profile to be followed in making the corrective screwdown movement.

During rolling operation, the on line gauge control system operates the stands to produce strip product having desired gauge. On line gauge control is produced by the roll force gauge control loops at the stands and the previously noted screwdown monitor gauge control system.

In the monitor system, the X-ray gauge 47 produces the previously indicated X-ray deviation signal which indicates the difference between actual strip delivery thickness and desired or target strip delivery thickness. in other cases, it may be desirable to employ an absolute thickness measurement X-ray gauge signal to form a basis for monitor control actions or, more generally, for screw-down position offset control actions. I

To effect on line gauge control in the closed loops, the AGC system operates on the screwdown position detector and load cell signals from each stand as well as the X-ray gauge deviation signal to determine the control actions required for producing desired strip delivery gauge. Screwdown motor speed is in this invention also applied to the AGC system 39 in order to provide for desired screw-down positioning control. In effecting control operations, the AGC system can employ a digital computer including an AGC programming system which forms a part of the total programming system for the AGC system 39. The AGC programming system could include programs oriented to controlling the AGC system hardware and programs oriented to developing the desired control actions.

It is generally known and understood by persons skilled in this particular art of applying a digital computer control system that a combined hardware and software process control system comprises a special purpose extended control computer machine, and is provided when a general purpose computer is operated under the control of one or more software instruction programs. Such a process control system can be built if desired using hardware or wired logic programming in relation to the functional steps set forth in the flow charts, in view of the recognized general equivalence of a software programming-embodiment and a hardware programming embodiment and a hardware programming embodiment of substantially the same control system. However, when an involved industrial application such as here described becomes somewhat complex, the economics tend to favor the software approach due to the greater expense and lack of flexibility when hardware logic circuits, such as well known NOR logic circuits, are wired together to provide the desired circuit arrangement built up of such logic circuits to perform the sequential program steps set forth in the illustrated flow charts.

DESCRIPTION OF PREFERRED EMBODIMENT The AGC system is operative to detect present workpieces that are a different temperature or a different hardness in relation to previous similar workpieces and to adjust the roll opening of each stand as desired. This is done by comparing the temperature of the head end of the present workpiece as it passes the crop shear and approaches the mill with the temperature measurements on previous similar workpieces. A present work piece causes adjustments in the roll openings on the subsequent roll stands (excluding the second roll stand because of a lack of available time to make the desired correction). This gauge control method does not require a force prediction for each roll standsince the normal roll force is established from roll force measurements from preceding similar workpieces. No roll opening. correction is made in relation to either roll force or present workpiece temperature measurements on the first workpiece of a new schedule.

In both the temperature'correction operation and the force feed forward hardness correction operation, the roll opening correction is in the form of an expected per unit change in the stand roll force so the correction for each roll opening is calculated by taking the product of the correction, the normal roll force for that stand and the known mill spring constant to find how much the roll opening for a given stand should be changed to compensate for the expected change in roll force in relation to the present workpiece.

The required change or correction to be made in relation to the operation provided roll opening or screwdown setting for each roll stand (N) which it is desired be corrected can be determined in relation to the temperature difference by the relationship:

ASDUV) =ALOF(N) TCF K(N) weighting factor WF is set equal to zero and the program operation ends. lf at step 100 a new schedule is not provided, then at step 104 the weighting factor for the present workpiece is set equal to the previous weighting factor plus one. Atstep 106 a determination is made to see if the weighting factor. is greater than five, and if so, at step 108 the weighting factor is limited to five.

In FIG. 3 there is shown a flowchart to illustrate the determination of the average lock-on roll force for a given roll stand N, for N equal to stand one through N equal to the last stand. Thusly, if the mill setup is for a new schedule for this present workpiece, the weighting factor WF is set to zero; otherwise, the weighting factor is increased by one but limited to five. Each time a present workpiece strip enters a roll stand N, the lockon roll force of that stand N is measured for use in the roll force gauge control system. At step 120'there is determined for each roll stand (N) the weighted average lock-on roll force ALOF(N) for each stand N. For the first workpiece of a new schedule, the weighting factor WF is zero and the average lock-on force ALOF is then set equal to the actual lock-on force LOF measured on the particular first workpiece. On subsequent similar workpieces, the weighting factor'WF increases in value up to a maximum of five and a weighted average or normal lock-on roll force level ALDF N) is establishedfor each stand N in accordance with the formula relationship shown at step 120.

In FIG. 4 there is shown a flowchart to illustrate the determination of the weighted average crop shear temperature ACST in relation to previous similar workpieces. At step a check is made to see if the weighting factor WF is now set at zero. If so, the program advances to step where a determination is made of the average crop shear temperature ACST as being equal to the measured crop shear temperature CST for the present workpiece, since the weighting factor WF is now equal to zero to indicate that a new rolling schedule is underway and the present -workpiece is the first workpiece of a given grade classification and gauge classification to be rolled under that new schedtile. The asterisk indicates a multiplication function. If the weighting factor for the present workpiece is not zero, at step 132 the difference in temperature between the average crop shear temperature ACST and the present workpiece temperature CST is converted into an expected per unit change in roll force through multiplying by the predetermined temperature constant TK, which has a preselected value of about 0.002 per unit force change per degree Fahrenheit. The temperature correction factor TCF is limited to a range between positive 0.1 and negative 0.05 in steps 134 through 140. At step 142 the stand (N) screwdown reference SDREFis modified to compensate for an expected change in roll force that is established in relation to the average roll force ALOF and the temperature correction factor TCF. This change in roll force is converted into an adjustment in the operator provided roll opening setting SDREF(N) by multiplying by the stand (N) mill spring modulus K(N). The corrected screwdown setting CSD(N), is then used as a new position setting reference value for the stand (N) roll opening position regulator. The program then goes to step 135 where the determination is made of the average crop shear temperature ACST in relation to all the similar workpieces now considered, up to a maximum of the last five such workpieces.

In FIG. 5 there is shown a flowchart to illustrate an operation that occurs when the head end of the present workpiece enters the first operative roll stand Al, such as stand one, to determine the hardness corrected screwdown setting CSD(N) for stand (N). This determination is done in relation to each of the operative roll stands after the first operative roll stand, such that N equals I 2 to N equals the last stand; because of the time requirements for effecting the desired correction in the screwdown setting of the roll stand next following the first operative roll stand, it may be desired not to attempt to make a correction in relation to that next following roll stand, and for this reason N has been selected as -N equals 1 2, where stand I is the first operative roll stand. At step a check is made to see if the weighting factor WF is now'set at zero, to indicate that a new operator provided schedule is beginning with the present workpiece. If so, the program ends.

. If the weighting factor WF is not now set at zero, at step 152 a roll hardness correction factor FCF is determined as the ratio of the measured lock-on force CSD(N), for each of the subsequent roll stands N equals I 2 through N equals TI-IE the last stand, is determined in accordance with the relationship of the above equation (8). 7

If desired, the calculation of the force correction factor FCF by the operation illustrated by the flowchart of FIG. does not have to be limited to the lock-on force relationship for the first operating roll stand, but instead this calculation can be performed using the lockon force relationship for one or more other subsequent stands to establish a correction for one or more stands subsequent to that other stand.

When the head end of the present workpiece passes under the temperature measuring device, such as a pyrometer located adjacent the crop shear, the operation illustrated by FIG. 5 can take place to determine the temperature related corrected screwdown setting CSD(N) for each of roll stands one to the last stand. When the present workpiece subsequently enters the first operative stand I, the operation illustrated by FIG. 5 can take place to determine a subsequent and further hardness related screwdown setting correction CSD(N) for each of roll stands I 2 to the last stand.

Either one or both of these program operations may be used as desired by the operator. The temperature difference correction factor TCF has the advantage of making the screwdowncorrection of all the stands of the rolling mill before the present workpiece enters, but an accurate present workpiece temperature measurement is not easy to maintain. Since a change in similar workpiece temperature measurements is being used for the temperature difference related correction, it is more reliable than a control system operation that would require an absolute temperature measurement ability. The hardness related force feed forward correction factor FCF is easier to establish, and it can be used alone or in conjunction with the temperature related correction.

The routine gauge controlling improvement of the mill roll stand screwdown setups to accommodate the normal pieces within the normal temperature and hardness patterns is done by other systems, such as a conventional roll force AGC or the schedule calculation adaptive control system utilizing process model equations. Such improvements would be reflected in modified values of the roll opening reference, SDREF, for each stand. The here described control operation is provided to detect the temperature and hardness differences between a particular present piece and the normal patterns as established by the rollingof previous workpieces. The most common cause for such differences is an interruption in the movement of a given workpiece through the roughing mill and across the transfer table to the finishing mill. Such a time delay results in a loss of heat, so most screwdown setting corrections of any magnitude will more likely be in the dithe pyrometer located in front of the shear, and in accordance with FIG. 3,the control system determines the deviation of the temperature of the present workpiece from the temperature of the workpieces preceding it. This temperature deviation is used to calculate the expected change in rolling force for each stand of the rolling mill.

The expected hardness related change in rolling force is used, in conjunction with the mill spring constant, in accordance with FIG. 4, to calculate the required corrective change in roll opening for each stand that is necessary to produce on-gauge strip. As the previous strip falls out of each stand. the screws for that stand are positioned to correct for any hardness correction and any temperature correction.

If the operator chooses to input the temperature deviation manually, the roll opening correction can be obtained from a predetermined table of values. This procedure ensures that the manual input produces a predictable response each time it is used.

The temperature correction operation is initiated by a hot metal detector located near the shear. If automatic temperature correction operation is selected, the temperature is read on the first scan after the present workpiece passes under the pyrometer at the shear. If this workpiece is for a different gauge class of product than the last workpiece, the program exits without taking action. Otherwise, the program calculates how much the temperature of the present workpiece differs from the temperature of the previous workpiece in the similar gauge class and then uses this deviation in temperature-to predict the change in roll force which can be expected. This calculation assumes that the roll force is a'linear function of temperature. The operator should determine empirically the actual slope of the relationship between roll force and temperature.

The program limits the predicted force change to no more than +20 percent or lO percent. It then corrects the set-up of each stand roll opening to handle the offtemperature present workpiece. The correction to the set-up is calculated as a change to the previous set screw position. The change in screwdown is calculated by multiplying the expected change in roll force by the mill spring constant.

If there is a strip in the stand, the program sets flags to signal the AGC program to include temperature compensation with the head end correction. Otherwise, it bids for the screwdown positioning operation to correct the set-up immediately.

GENERAL DESCRIPTION OF INSTRUCTION PROGRAM LISTING In the Apendix there is included an instruction program listing that has been prepared to control the roll force automatic gauge control operation of a tandem rolling mill in accordance with the here-disclosed con trol system and method. The instruction program listing is written in the machine language of the PRODAC P2000 digital computer system, which is sold by Westinghouse Electric Corporation for real time process control computer applications. Many of these digital computer systems have already been supplied to customers, including customer instruction books and descriptive documentation to explain to persons skilled in this art the operation of the hardware logic and the executive software of this digital computer system. This instruction program listing is included to provide an illustration of one suitable embodiment of the present control system and method that has actually been prepared. This instruction program listing at the present time has been generally debugged through the course of practical operation for the real time automatic gauge control of a tandem rolling mill. It is well known by persons skilled in this art that most real time process control application programs contain some bugs or minor errors, and it is within the skill of such persons and takes varying periods of actual operation time to identify and correct the more critical of these bugs.

A person skilled in the art of writing computer instruction program listings, particularly for an invention such as thepresent roll force automatic gauge control system and method for a tandem rolling mill must generally go through the following determinative steps:

Step One Study the workpiece rolling mill and its operation to be controlled, and then establish the desired controlsystem and method concepts.

Step Two Develop an understanding of the control system logic analysis, regarding both hardware and software.

Step Three Prepare the system flowcharts and/or the more detailed programmers flowcharts.

Step Four Prepare the actual computer instruction program listings from the system flowcharts or from the programmers flowcharts. This instruction program listing included in the Appendix was prepared in relation to the system flowcharts shown in FIGS; 2 through 5.

What we claim is:

l. A gauge control system for a rolling mill having at least one roll stand operative to reduce the gauge of a plurality of similar workpieces passed through said rolling mill, said system comprising.

means for determining a difference in the temperature of a present one of said workpieces in relation to the average temperature of previous similar workpieces already passed through said rolling mill,

means operative in relation to said difference for determining a temperature correction factor in relation to a predetermined per .unit change in roll force multiplier,

means for determining ,a predetermined roll force measurement for said one roll stand during the passage of said previous similar workpieces through said one roll stand, and I a means for determining a corrected operation of said one roll stand in relation to said present one of said workpieces in accordance with a predetermined relationship between said correction factor and said roll force measurement.

2. The gauge control system of claim 1, with said rolling mill having a plurality of roll stands,

said means for determining the predetermined roll force measurement being operative'to determine the average roll force for said one roll stand, and

said means for determining a corrected operation where SDREF(N) is the initial provided roll opening setting for said one roll stand, where ALDF(N) is the predetermined roll force measurement of said one roll stand, 5 where TCF is the determined correction factor, and

where K(N) is the mill spring modulus for said one rollstand.

4. The gauge control system of claim 1, with said corl0 rected operation being determined in accordance with the relationship:

ASD(N) =ALOF(N) TCF K(N) relationship:

where TCF is said temperature related correction factor, I where ACST is the average temperature of said previous similar workpieces, where CST is the temperature of said present one of said workpieces, and v I I where TK is the predetermined per unit change in roll force multiplier. I l 6. A gauge control system for a rolling mill having a plurality of roll stands operative to reduce the gauge of each of a plurality of similar workpieces passed through said rolling mill, said system comprising;

means for determining a first predetermined relation- 40 ship between the roll force of a selected roll stand during the passage of a present one of said workpieces through said selected roll stand and a first average roll force of said selected roll stand during the passage of previous similar workpieces through said selected roll stand, means for determining a hardness correction factor in accordance with said first predetermined relationship, means for determining a second average roll force of one of said roll stands during the passage of said plurality of workpieces through said one roll stand, and means for determining a corrected operation of said one roll stand in accordance with a second prede-. termined relationship between said hardness correction factor and said second average roll force.

7. The gauge control system of claim 6 with said first predetermined relationship being [LOF(I)/ALOF(I)] where LOF (I) is the initial roll force of said selected 8. The gauge control system of claim 6, with said first predetermined relationship being between the roll force LOF(l) of a selected roll stand (l) during the passage of said present one of said workpieces through said selected roll stand (I) and a first average roll force ALOF(l) of said selected roll stand (1) during the passage of previous similar workpieces through said selected roll stand (I), with said hardness correction factor FCF being determined in accordance with said first predetermined relationship, and with said corrected operation CSD(N) of said one roll stand (N) being in accordance with a second predetermined relationship between said hardness correction factor PCP and a second average roll force ALOF(N). 9. The gauge control system of claim 6, with said hardness correction factor FCF being determined by the relationship where LOF(l) is the initial roll force of said selected roll stand (I) in relation to said present one workpiece, and

where ALOF(I) is the average roll force of said selected roll stand (I) in relation to said previous similar workpieces.

10. A method of controlling the gauge of a plurality of similar workpieces passed through a rolling mill having at least one roll stand, the steps of said method comprising:

determining a temperature change between the temperature of a present workpiece and the average temperature of the previous similar workpieces passed through said one roll stand,

determining a temperature correction in relation to said change and a predetermined roll-force relationship to said temperature change,

determining the average roll force of said one roll stand during the passage of said previous workpieces through that one roll stand, and

deterrning a corrected operation of said one roll stand during the passage of said present workpiece in accordance with said temperature correction and said average roll force.

11. The method of claim 10, with said determination of said temperature correction being in accordance with TCF= [ACST-CST] TK where TCF is said temperature correction,

where ACST is said average temperature,

where CST is said temperature of a present workpiece, and t where TK is said predetermined roll force relationship to the temperature change.

12. The method of controlling the gauge of a plurality of similar workpieces of claim 10,

with said temperature change (ACST-CST) being determined between the temperature CST of a present workpiece and the average temperature ACST of the previous similar workpieces passed through said one roll stand,

with said temperature correction TCF being determined in relation to said change (ACST-CST) and a predetemiined roll force relationship TK to said temperature change, and

where TCF is said temperature correction,

where ACST is said average temperature, I

where CST is said temperature of the present workpiece, and

where TK is said predetermined force relationship to the temperature change,

and with said corrected operation being in accordance with CSD(N) SDREF(N) ALOF(N) TCF K(N) where CSD(N) is said corrected operation,

SDREF(N) is the inital provided setting of said roll stand (N),

ALOF( N) is a predetermined roll force relationship of said one roll stand (N), and K(N) is the mill spring modulus for said one roll stand (N).

14. A method of controlling the workpiece gauge leaving a rolling mill having at least one roll stand operative to reduce the gauge of each of a plurality of similar workpieces passed through said rolling mill, the steps of said method comprising:

establishing a first predetermined relationship between the roll force of a selected roll stand during the passage of a present workpiece and the average roll force of said selected roll stand during the passage of previous similar workpieces through said selected roll stand,

establishing a hardness correction in relation to said first predetermined relationship,

establishing the average roll force of at least one roll stand during the passage of said previous workpieces through said one roll stand, I establishing a corrected operation of said one roll stand in accordance with said hardness correction and said average roll force, and controlling the operation of said one roll stand in accordance with said corrected operation.

15. The method of claim 14 for controlling the workpiece gauge leaving a rolling mill having a plurality of roll stands,

with said first predetermined relationship being established between the roll force LOF(l) of a selected roll stand (I) during the passage of said present workpiece and the average roll force ALOF(I) of said selected roll stand (1) during the passage of previous similar workpieces through said selected roll stand,

with the average roll force ALOF(N) being established for at least one roll stand (N) during the passage of said previous workpieces through said one roll stand,

with said corrected operation CSD(N) of at least said

Claims (15)

1. A gauge control system for a rolling mill having at least one roll stand operative to reduce the gauge of a plurality of similar workpieces passed through said rolling mill, said system comprising. means for determining a difference in the temperature of a present one of said workpieces in relation to the average temperature of previous similar workpieces already passed through said rolling mill, means operative in relation to said difference for determining a temperature correction factor in relation to a predetermined per unit change in roll force multiplier, means for determining a predetermined roll force measurement for said one roll stand during the passage of said previous similar workpieces through said one roll stand, and means for determining a corrected operation of said one roll stand in relation to said present one of said workpieces in accordance with a predetermined relationship between said correction factor and said roll force measurement.

2. The gauge control system of claim 1, with said rolling mill having a plurality of roll stands, said means for determining the predetermined roll force measurement being operative to determine the average roll force for said one roll stand, and said means for determining a corrected operation being operative to determine a corrected operation for said one roll stand in relation to the respective average roll force of that roll stand.

3. The gauge control system of claim 1, with said corrected operation being determined in accordance with the relationship: CSD(N) SDREF(N)-(ALOF(N) * TCF * K(N)) where CSD(N) is the corrected roll opening setting for said one roll stand, where SDREF(N) is the initial provided roll opening setting for said one roll stand, where ALDF(N) is the predetermined roll force mEasurement of said one roll stand, where TCF is the determined correction factor, and where K(N) is the mill spring modulus for said one roll stand.

4. The gauge control system of claim 1, with said corrected operation being determined in accordance with the relationship: Delta SD(N) ALOF(N) * TCF * K(N) where -SD(N) is the correction to the roll opening setting for said one roll stand, where ALOF(N) is the predetermined roll force measurement of said one roll stand, where TCF is the determined temperature correction factor, and where K(N) is the mill spring modulus for said one roll stand.

5. The gauge control system of claim 1, with said correction factor being determined in accordance with the relationship: TCF (ACST-CST) * TK where TCF is said temperature related correction factor, where ACST is the average temperature of said previous similar workpieces, where CST is the temperature of said present one of said workpieces, and where TK is the predetermined per unit change in roll force multiplier.

6. A gauge control system for a rolling mill having a plurality of roll stands operative to reduce the gauge of each of a plurality of similar workpieces passed through said rolling mill, said system comprising: means for determining a first predetermined relationship between the roll force of a selected roll stand during the passage of a present one of said workpieces through said selected roll stand and a first average roll force of said selected roll stand during the passage of previous similar workpieces through said selected roll stand, means for determining a hardness correction factor in accordance with said first predetermined relationship, means for determining a second average roll force of one of said roll stands during the passage of said plurality of workpieces through said one roll stand, and means for determining a corrected operation of said one roll stand in accordance with a second predetermined relationship between said hardness correction factor and said second average roll force.

7. The gauge control system of claim 6 with said first predetermined relationship being (LOF(I)/ALOF(I)) where LOF(I) is the initial roll force of said selected roll stand (I) in relation to said present one workpiece, and where ALOF(I) is the average roll force of said selected roll stand (I) in relation to said previous similar workpieces.

8. The gauge control system of claim 6, with said first predetermined relationship being between the roll force LOF(I) of a selected roll stand (I) during the passage of said present one of said workpieces through said selected roll stand (I) and a first average roll force ALOF(I) of said selected roll stand (I) during the passage of previous similar workpieces through said selected roll stand (I), with said hardness correction factor FCF being determined in accordance with said first predetermined relationship, and with said corrected operation CSD(N) of said one roll stand (N) being in accordance with a second predetermined relationship between said hardness correction factor FCF and a second average roll force ALOF(N).

9. The gauge control system of claim 6, with said hardness correction factor FCF being determined by the relationship FCF (LOF(I)/ALOF(I))-1 where LOF(I) is the initial roll force of said selected roll stand (I) in relation to said present one workpiece, and where ALOF(I) is the average roll force of said selected roll stand (I) in relation to said previous similar workpieces.

10. A method of controlling the gauge of a plurality of similar workpieces passed through a rolling mill having at least one roll stand, the steps of said method comprising: determining a temperature change between the temperature of a present workPiece and the average temperature of the previous similar workpieces passed through said one roll stand, determining a temperature correction in relation to said change and a predetermined roll force relationship to said temperature change, determining the average roll force of said one roll stand during the passage of said previous workpieces through that one roll stand, and determing a corrected operation of said one roll stand during the passage of said present workpiece in accordance with said temperature correction and said average roll force.

11. The method of claim 10, with said determination of said temperature correction being in accordance with TCF (ACST-CST) * TK where TCF is said temperature correction, where ACST is said average temperature, where CST is said temperature of a present workpiece, and where TK is said predetermined roll force relationship to the temperature change.

12. The method of controlling the gauge of a plurality of similar workpieces of claim 10, with said temperature change (ACST-CST) being determined between the temperature CST of a present workpiece and the average temperature ACST of the previous similar workpieces passed through said one roll stand, with said temperature correction TCF being determined in relation to said change (ACST-CST) and a predetermined roll force relationship TK to said temperature change, and with said corrected operation CSD(N) of said one roll stand (N) being determined during the passage of said present workpiece in accordance with said temperature correction TCF and said average roll force ALOF(N).

13. The method of claim 10, with said determination of said temperature correction being in accordance with TCF ( ACST-CST) * TK where TCF is said temperature correction, where ACST is said average temperature, where CST is said temperature of the present workpiece, and where TK is said predetermined force relationship to the temperature change, and with said corrected operation being in accordance with CSD(N) SDREF(N) - ALOF(N) * TCF * K(N) where CSD(N) is said corrected operation, SDREF(N) is the inital provided setting of said roll stand (N), ALOF(N) is a predetermined roll force relationship of said one roll stand (N), and K(N) is the mill spring modulus for said one roll stand (N).

14. A method of controlling the workpiece gauge leaving a rolling mill having at least one roll stand operative to reduce the gauge of each of a plurality of similar workpieces passed through said rolling mill, the steps of said method comprising: establishing a first predetermined relationship between the roll force of a selected roll stand during the passage of a present workpiece and the average roll force of said selected roll stand during the passage of previous similar workpieces through said selected roll stand, establishing a hardness correction in relation to said first predetermined relationship, establishing the average roll force of at least one roll stand during the passage of said previous workpieces through said one roll stand, establishing a corrected operation of said one roll stand in accordance with said hardness correction and said average roll force, and controlling the operation of said one roll stand in accordance with said corrected operation.

15. The method of claim 14 for controlling the workpiece gauge leaving a rolling mill having a plurality of roll stands, with said first predetermined relationship being established between the roll force LOF(I) of a selected roll stand (I) during the passage of said present workpiece and the average roll force ALOF(I) of said selected roll stand (I) during the passage of previous similar workpieces through said selected roll stand, with the average roll force ALOF(N) being established for at least one roll stand (N) during the passage of said previous workpieces through said one roll stand, with said corrected operation CSD(N) of at least said one roll stand (N) being established in accordance with the hardness correction FCF and said average roll force ALOF(N), and with the operation of at least said one roll stand (N) being controlled in accordance with the respective corrected operation CSD(N) of that roll stand.

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