US 3848443 A
A method and apparatus for adjusting the respective roll openings of the roll stands of a cold rolling mill during the workstrip threading operation so that the rolling mill can be accelerated and to maintain the workstrip on-gauge without undesired waste of material before acceleration. The interstand tensions are maintained at the desired value and tension disturbance is eliminated by workstand adjustment in relation to roll speed and by roll opening adjustment of either the same stand or an adjacent workstand.
Description (OCR text may contain errors)
United States Patent Peterson et al.
1451 Nov. 19,1974
[ AUTOMATIC CONTROL METHOD AND 3,212,310 10/1965 Brys 72/12 APPARATUS FOR A ROLLING MILL 1440346 4/1969 S 3,507,l34 4/1970 Silva Inventors: Robert Peterson; John W. Cook, 3,768,286 10 1973 Peterson 72 9 both of Williamsville, NY.
 Assignee: Westinghouse Electric Corporation, Primary ExaminerMilton Mehr Pittsburgh p Attorney, Agent, or F1rm-C. M. Lorin  Filed: May 31, 1973 ABSTRACT ] Appl' 365668 A method and apparatus for adjusting the respective roll openings of the roll stands of a cold rolling mill 52 US. Cl 72/8, 72/17, 72/205 during the Workstrip threading operation to that the 51 Int. Cl B2lb 37/06 rolling mill can be accelerated and to maintain the  Field of Search 72/8, 17, 9-12, workstrip on-gaoge without undesired waste f m e- 72/205 rial before acceleration. The interstand tensions are maintained at the desired value and tension distur- 56 References Cited bance is eliminated by workstand adjustment in rela- UNITED STATES PATENTS tion to roll speed and by roll opening adjustment of either the same stand or an adjacent workstand. 3,170,344 2/1965 Marrs 72/11 3,196,646 7/1965 Brys .1 72/9 14 Claims, 6 Drawing Figures so, l 50 SCREWDOWN SCREWDOWN CONTROLLER CONTROLLER )M l I 5 V 5 V I 2 Q D/ I l2 2 E) 30 e 40 I 40' SPEED SPEED REGULATOR REGULATOR 2OI MASTER ERRORV SPEED REFERENCE z SPEED ERROR Q- CORRECTION CONTROLLER L ERROR N I3 E TENSION TENSION CONTROLLER REFERENCE 3 PATENTELNUVJ 9 14 SHEET 10F 3 FIGAZ STRESS STRAIN SENSED TENSION AT I CORRECT TENSION l 3 SITAND SPEED I CORRECT SPEED SPEED ERRORV ZERO ERROR ROLL OPENING BEFORE CORRECTION CORRECTED ROLL OPENING H t2 t3 III I 9M4 I PATENH sum 2 or s '4- SCREWDOWN I SCREWDOWN CONTROLLER CONTROLLER g m M M M 40 I 4 2 [@1 SRI SR2 SPEED SPEED REGULATOR REGULATOR MASTER 24 SPEED REFERENCE I L SPEED ERROR CORRECTION CONTROLLER ERROR l3 LIMIT TENSION TENSION CONTROLLER REFERENCE DB AUTOMATIC CONTROL METHOD AND APPARATUS FOR A ROLLING MILL CROSS REFERENCES TO RELATED APPLICATION The invention here described is related to the invention in copending patent application Ser. No. 230,300 filed Feb. 29, 1972 and entitled lnterstand Tension Regulator for A Multistand Rolling Mill, by R. D. Peterson and assigned to the same assignee.
BACKGROUND OF THE INVENTION In a multistand roll mill, it is the usual practice for a workstrip to be reduced in gauge by passing through a plurality of tandem roll stands each having a progressively smaller opening and driven at a speed which is increased in the direction of workstrip movement from the entry stand to the final delivery stand. As the workstrip is reduced, the product of the roll gap and the workroll speed for each roll stand is kept substantially constant in order to maintain a constant mass flow for the metal plastically deformed by the roll stands. The settings of the rolls, as determined by speed controlled motors, are maintained automatically by a master speed and roll opening reference control system during the entire operation of the rolling mill. Once the roll stands are at normal run speed there is a desired controlled tension in the metal between stands and this tension depends upon the relative speeds of the adjacent stands, as well as upon the roll gaps of those stands. Therefore, automatic gauge control for a rolling mill often uses the tension condition existing between stands as an additional parameter for controlling the gauge. In the latter respect, it is known that the interstand tension is of greater importance in cold mill operation than in a hot mill operation, because the hot metal has a much higher degree of plasticity, and also because in a cold mill smaller delivery gauges are achieved and soft metals such as copper and the like, are more often the kind of product there processed. Thus, at the operating speed of a tandem rolling mill, which for providing increased product throughput is a high speed, for instance 5000 feet per minute, the metal strip is automatically maintained on-gauge by suitable adjustments of the workroll settings, of the speed thereof and, particularly in a cold mill, this is often done in response to interstand tension variations, in addition to variations in other parameters sensed at different locations along the workpiece pass line. While such adjustments and corrections can be made more accurately at run speed, thereby to assure at the output the desired product delivery gauge, manual or automatic control has not received sufficient attention in the past to adequately provide the same quality of control at lower speeds of operation, particularly during start up of the mill operation. Once the head end of the workpiece has been entered through one stand, the strip of material is threaded successively through all the stands, and a certain number of wraps are taken on the windup reel before the rolling mill is accelerated to run speed. Industrial practice sometimes allows for an intermediate speed, somewhat above thread speed before proceeding to desired final run speed. If the run speed of a rolling mill is in the order of 5000 feet per minute, thread speed is typically in the order of 5 percent of run speed, eg 250 feet per minute. At such low speeds,
workstrip gauge control by roll gap adjustment generally loses some of its effectiveness. One reason for this is that the metal does not flow as well between the rolls until the speed of the rolls has reached a sufficient level. Also, any precise gauge correction attempted by varying the work roll gaps is too slow to be effective to keep the strip on gauge. On the other hand, at low speed the amplitude of a gauge correction by roll gap adjustment can be objectionally large which might cause undesired markings on the workstrip due to pinch effect, or even break the workstrip. Nevertheless, it is most desirable to extend the advantages of gauge control, manual or automatic, down to thread speed operation of the'rolling mill in order to avoid the very appreciable waste of material otherwise taking place at thread speed in the operation of many multistand rolling mills today. The present invention provides a solution to this problem, which is best carried out in relation to a multistand tandem cold mill.
Therefore, it is an object of the present invention to operate a tandem rolling mill with more effective gauge control so as to produce more on-gauge product at all speeds, including thread speed of operation.
Another object of the present invention is to automatically and concurrently control the speeds of the respective work stands in a multistand rolling mill and the roll gaps of the workstands before acceleration of the mill in order to provide more on-gauge material being rolled.
A-further object of the present invention is to provide an improved cold mill operation in which relatively soft material is effectively kept under correct tension during thread speed operation and better maintained ongauge, manually or automatically.
It is still another object of the present invention to provide, in the operation of a rolling mill, a more effective gauge correction by screwdown action of the work rolls at a roll speed which is much lower thanthe normal operative speed of the mill.
SUMMARY OF THE INVENTlON According to the present invention a method and apparatus are provided for controlling the delivery gauge of work strip material issuing from a tandem rolling mill, by providing a substantially constant mass flow condition in relation to adjacent roll stands through desired tension operation, sensing a deviation from said desired tension, translating said tension deviation into a speed change at a selected one of said stands thereby to cancel said tension deviation and maintain said desired tension, and changing the stand roll gap of the subsequent one of said stands to reduce said change in roll speed of said selected stand to zero.
DESCRIPTION OF THE PRIOR ART It is known from US. Pat. No. 3,170,344 of Marrs to maintain a constant tension condition between adjacent mill stands working under constant mass flow condition, by screwdown adjustments of the second of said stands along the workpiece pass line. It is also known to adjust the speed of the stand preceding the last stand of the mill in order to maintain a constant tension condition before the last stand. However, the Marrs patent contemplates tension control at the normal run speed of operation of the mill, and therefore does not teach effective tension control at thread speed.
It is known from US. Pat. No. 3,440,846 of Scott to maintain constant the tension of a strip between adjacent stands through the use of a tension regulator operative at thread speed and run speed. The Scott patent does not provide roll gap adjustment in relation to changes in the tension between adjacent roll stands.
The prior art US. Pat. No. 3,049,036 of Wallace teaches the combination of fast control by roll stand speed control for small gauge corrections and slower control by roll-gap adjustment for larger gauge corrections. Such strip tension control in the Wallace patent does not call for any sensing of tension between stands, but rather operates in response to measured gauge error.
US. Pat. No. 3,507,134 of Silva is another teaching in the prior art of speed and screwdown control in response to interstand tension, and provides for a change from one type of control to the other in order to accommodate for the difference between thread and run mill speed.
The above referenced copending application discloses a fast control loop for correcting changes in interstand tension by controlling a selected stand speed through operation of a tension control loop including an adaptive tension regulator having a transfer function interposed to compensate for strip cross section area and for the adjacent stands relative speeds. This adaptive tension regulator also includes a control loop effective at thread speed operation of the rolling mill, but no provision is made for tension control by roll gap adjustment at thread speed.
In order that the invention may be more clearly understood and readily carried into effect reference will now be made to the accompanying drawings, in which:
FIG. I is a schematic diagram of the work rolls of two adjacent stands in a rolling mill illustrating metal flow under the rolls at each stand;
FIG. 2 is a representation of the stress-strain curve typical of a metal under stress;
FIG. 3 is a schematic diagram of a two-stand tandem rolling mill accordding to the invention;
FIG. 4 comprises waveforms illustrating the operation of the embodiment of the invention shown in FIG.
FIG. 5 is a schematic diagram of a multistand cold mill embodying the invention in the preferred form.
FIG. 6 illustrates in greater detail part of the circuit shown in FIG. 5.
With reference now to the drawing, and particularly to FIG. 1, a strip of material entering a stand S, with a thickness H is reduced under the rolls to a thickness H,. By the same process when the strip enters the next stand 8, the thickness is further reduced from H, to H If the speeds of the rolls are V, at stand S, and V, at stand 5,, the law of constant volume of the plastically deformed metal is expressed by the relation H,V, H V Thus metal enters the stand 8, with a velocity V, and the metal delivered by stand 8, flows at a velocity V, which is larger than V,. Metal cohesion in the workstrip is expressed by a tension developed between roll stands. In a cold mill the interstand tension is expressed by T K(\ V,), where K is a coefficient of proportionality between tension and the difference between the speeds of adjacent roll stands. The tension of the metal remains the same all along between stands. A metallurgical characteristic of metal under tension is the stress-strain curve. A typical curve is shown on FIG. 2. This curve exhibits a linear portion 0A corresponding to elastic stretch of the metal under load which is the effective portion during mill operation. Tensile stress is a physical property of the metal. The stress of a metal under the work rolls of a cold mill satisfies the following empirical equation:
PSI PSI =l.15 PSI in which PSI- is the tension (per square inch) under the rolls along the axis of flow (see FIG. 1), PSI,.- is the transversal force component due to the action of the work rolls exerted in the spacing between work rolls, and PSI is the resultant representing yield tensile stress. The latter thus is a constant. From equation (I) it appears that, should the roll gap be narrowed by screwdown, PSI will increase and therefore PSI, must decrease to keep the sum constant. The converse is true if the roll gap is increased. In other words decreasing the roll opening of stand 8, will decrease the tension between roll stands S, and 8, while increasing the roll opening of stand 8, will increase the interstand tension. assuming the roll opening H, of stand S, remains the same.
It is known in the prior art to use screwdown positioning for modifying the delivery gauge. It is also known to control the roll opening of a work stand in response to workstrip tension changes ahead of such work stand in order to stay on-gauge, whenever such changes in tension are indicative of a misadjustment in the setting of the work stands. However, while such roll opening adjustment is effective at the relatively high operating speed of the mill, this mode of controlling the gauge is not satisfactory at much lower speeds and has not up to now been successively achieved. Typical of a low speed operation in a rolling mill is the thread speed. First the head end of the work strip is pinched, then pulled through all the workstands and rolled at moderate speed until passed on the windup reel and anchored thereon. Prior to threading, manually, or automatically, each of the roll stands has been given proper speed and roll opening settings. Then the mill is run at thread speed. If the gauge of the strip is not well controlled during this first phase of the mill operation an appreciable length of the workstrip will be wasted and this can be very costly on the overall production.
While tension control is desirable in order to avoid such waste, at thread speed the tension loop has to be very slow in order that the work rolls do not pinch the strip. The present invention provides a solution to overcome this difficulty, and thus affords full advantage of interstand tension control which in a cold mill is best indicated. The invention combines with a tension loop which has a slow response for the reasons just given, a fast response loop responsive to interstand tension changes for adjusting the speed of one of the adjacent roll stands, the operations of the two loops being coordinated as will now be explained with particularity by reference to FIGS. 3 and 4.
As shown on FIG. 3 work strip 10 is passed through a two-stand tandem rolling mill. The work rolls of stand S, and the work rolls of stand 8, have been initially set by their respective screwdown controllers 8D,, SD, and by the respective speed controllers SR,, SR to predetermined roll openings H H and roll speeds V V respectively. The screwdowncontrollers SD,, SD, actually control the screw positioning motors M which move the screwdown mechanisms. A signal indicative of the screw position is fed back by a tachometer T for each stand. The speed controllers SR,, SR determine the speed of drive motors M, and M respectively. Tachometers 40, 40' feedback to the corresponding speed controller signals indicative of the work roll speed. Each speed controller, SR,, SR has a setpoint provided by a master reference adjusting the rolling mill automatically for a desired constant mass flow and a predetermined delivery gauge. All this is conventional. A tensiometer 30 senses a tension T, existing in the work strip between the two stands 8,, S The output signal of tensiometer 30 is applied over lead 11 to a ten sion regulator 130, but not directly. The tension signal from lead 11 is compared at 14 with a tension reference and the error signal so derived is applied over lead 15 to a tension controller 13, which is part of the tension regulator 130.
At the output of the tension controller 13 a signal is derived representing an error in tension, ERROR which over lead 200 is applied as input to a speed error correction controller 13'. The latter circuit is also part operation of the rolling mill has increased beyond a transition level, e.g. at 10% of the normal speed ofop- Y eration. Such disabling of the tension regulator 130 may be manual, or automatic, for instance in response to the count of tachometer 40.
The control signal derived at the output of the speederror correction controller 13' is-used as input, over" lead 12, for the screwdown controller SD 'of stand S,
and as input, over lead 201, the speed regulator SR, of stand 8,. This control signal represents relative to speed regulator SR,, an error condition ERROR requiring a change in speed for the work rolls of stand 8,. When such error condition appears over lead 201, which signal prevails over the master speed reference on lead 24, motor M, is controlled accordingly. Similarly, over lead 12, a control signal will cause the screwdown controller SD to move the screws and change the roll gap of stand 5,. It is important to note here that while the speed regulator has a fast response to any change in ERROR, on line 201, the circuit of the speed error correction controller 13' includes a ramp function which integrates any variation in the tension error signal ER- ROR, derived over 200 from tension controller 13. As a result any change in tension sensed by tensiometer will not be immediately felt at the output of the-speed error correction controller.
The operation of the embodiment of FIG. 3 will now be described by way of reference to FIG. 4 which shows with curves A to D respectively, cumulative effects of speed correction and roll opening adjustment which in I given instant t tensiometer 30 senses a tension which;
as shown (curve A) is in excess by AT over the desired interstandtension T As a result a speed error AE appearsat the output of the speed error correction controller 13'. As shown by curves A and B of FIG. 4 speed regulator SR, increases the speed V, of stand S, in re sponse to AE (it would be adecrease in speed if AE were below desired tension) and such response is fast enough to immediately effect a decrease in tension T,, as shown from time t to time t,, to a point where T,, is giventhe desired tension. At time r,, as shown on curve C, the speed error, ERROR is still present at the output of the speed error correction controller because of the integrator-present in this circuit. It is assumed that at that time the screwdown controller SD begins to respond. As a result the roll opening of stand S, begins to decrease. The effect of such narrowing of the roll gap is to increase-the transversal force exerted by therolls on the metal'in the gap itself (see FIG. 1). It appears from equation (I) that whenever PSI increases, PSI, must decrease in order to have a constant as the sum thereof. Therefore the effect of the screwdown controller SD, on stand S, is to decrease the tension. It is observed that the screwdown response has been made to be slow, asexplained hereabove, in order to prevent pinching of the workstrip. Curves C and D show between time t, and time t, thecorrective effect. Asa result of aprogressive reduction of the speed error ERROR' the-'speedof work stand S, is now reduced from V, AV, with the same. gradual action as the roll opening change, on: stand 8,. The cumulative effect of roll openingcorrection (curve D) and. speed change (curve B) is translated into a change in tension, which passes by a maximum at time t,, as shown by curve A, which changealso affects the output of speed error correction controller l3' (curve C). Finally at time t, the correctspeed'V, and a zero error exist and are perfectly matched. Atthis-time the correct roll opening I-I, exists on stand 5,.- If before screwdown correction the unknown misadjusted roll opening of stand S had been H, instead of H the volumetric flow equation would have been at time t,: H, (V, +AV,) H V whereas we Should have H,V, H V Then, HX= H1(V1+ It thus appears that, according to the present invention, AV, is reached to zero in orderto bring H X to the correct value H Such reduction of AV, to zero is effected by adjusting theroll opening of work stand S in a direction to slowly drive the output of the tension regulator to zero. This in turn causes AV, to be reduced to zero so that H,V, H V is finallysatisfied.
Theexplanation just given regarding the corrective process according to the invention is valid in another context than the two roll stand tandem mill of FIG. 3. For instance, while screwdown correction must be made on a roll stand with respect to the entry side of the stand, fast tension control byroll speed can be effected on either one of the adjacent stands. Indeed when change in roll speed is effected on the subsequent one of two adjacent roll stands, speed changes must occur in;a direction opposite to what they would be if made on the prior roll stand.
It is also conceivable that adjustment by roll speed be done concurrently on the two adjacent roll stands, since interstand tension is responsive to a change in speed relationship between adjacent roll stands. In such acase, tension error AT would be shared by certain amounts of changes AV, and AV, in the roll speeds of the two roll stands.
Also, the invention is not limited to control of two roll stands only. Preferably it is applicable to a multistand rolling mill. The roll opening of the first stand of the mill is generally known because an X-ray gauge is commonly used at such stand. Knowing the roll opening H of the first stand, the invention offers a method of adjusting the roll opening H of the second stand as has been explained hereabove. H being correctly adjusted, by the same technique the roll opening of stand 8;, is in turn adjusted. All the stands are by this method successively brought to the right screwdown position. It is clear that this method of adjusting screwdown during thread speed operation can be conducted manually by an operator instead of using automatic control. The stand screwdown settings are changed until the correct speed is achieved on all stands. Thus, while the correct speed can be easily known and fixed, the settings of the stand screws cannot be easily calculated as explained hereabove. This difficulty is readily overcome when the method and apparatus according to the present invention are used.
THE PREFERRED EMBODIMENT FIG. shows a cold mill including four stands S S S and 5,. A work strip of material is threaded through the work rolls onto a winding reel 43 after being passed and pulled through the rolls of each of the work stands. Motors M M M M drive the rolls of the respective stands at a speed determined by speed regulators 51, 52, 53, 54, respectively, the latter responding to a master speed reference signal derived over lead 29 and respective summing points 1, 2 and 3, from a master mill speed controller, not shown. The gauge issuing from stand 1 is measured by an X-ray gauge, or the like, producing a signal on lead 95 which is proportional to actual gauge error of the work strip delivered by stand 8,. Similarly, the gauge issuing from stand 4 is measured by an X-ray gauge 6, producing a signal on lead 96 which is proportional to the delivery gauge error of the work strip wound on the reel 43. Between each pair of adjacent stand interstand tension sensing devices 111, 112 and 113 provide an actual tension signal applied to respective tension regulators 41, 42 and 44 over leads 55, 56 and 57, respectively. Each tension regulator is operative to respond to a tension error signal obtained by comparison of an interstand tension signal received from respective leads 55, 56, 57,with a tension reference signal received from the lead lines 18. Tension regulator 41 has its output 65 connected through a summing point 5, to speed regulator 51 of stand S Similarly, the output 66 of tension regulator 42 is connected through a summing point 6 to speed regulator 52 of stand 8 For reasons explained later no tension regulator is associated with the speed regulator 53 of stand S Tension regulator 44 has its output 67 connected through a summing point 7 to speed regulator 54 of stand 5,. Each of these tension regulators is simi-v lar to the tension regulator 130 of FIG. 3. Therefore each includes a tension controller such as tension controller 13 of FIG. 3 and a speed error correction controller such as shown by 13 on FIG. 3. Conventional automatic gauge control circuits 55 and 56 are provided at the entry and at the delivery end of the rolling mill which are responsive to X-ray gauges G and G respectively, as generally known. Each work stand has a screwdown system. Screwdown controllers 81, 82, 83,84 control the positions of screws 101, 102, 103,
104 of the respective stands S S S and S Screwdown controller 81 of stand S, receives a control signal from the entry automatic gauge control circuit 56. The output of tension regulator 41 of stand S, is applied to the screwdown controller 82 of stand S but not directly. The output of circuit 82 is applied to screwdown error correction controller 92 and the output of circuit 92 is applied to a circuit 72 having a transfer function which is a certain function of the velocity of the metal strip 10 between stands S and S The output from circuit 72 is in turn corrected by a circuit 62 having a transfer function representing the cross-section area of the work strip of material 10 between stand 8, and S The output of circuit 62 is applied to screwdown controller 82. Similarly, the output 66 of tension controller 42 of stand S is applied over lead 116 to screwdown 83 of stand 8:, in a loop comprising a screwdown error correction controller 93, circuit 73 introducing a transfer function of the velocity of the workstrip between stands S and S and an area compensating circuit 63, velocity and area being taken from the strip between stands S and S For reasons explained hereinafter, the output 67 from tension regulator 44 is applied over lead 117 to screwdown controller 84 of the last stand S in a loop including screwdown error correction controller 94, a correcting circuit as function of velocity between stands 8:, and S4 74 and an area compensating circuit 64, velocity and area being taken from the strip between stands S3 and S4. Circuits 92, 93 and 94 of the screwdown error correction controllers are shown in more detail on FIG. 6. Various limiters are provided in order to disable those circuits when the speed of the mill is above a given minimum speed of operation since they should be operable only at thread speed or somewhat above thread speed. These disabled circuits are tension regulators 41, 42 and 44 respectively disabled by signals on leads 75, 76 and 77, and screwdown error correction controllers 92, 93 and 94 respectively disabled by signals appearing on leads 85, 86 and 87. Those circuits as explained herebelow, cease to be effective when the mill is accelerated to full speed of operation. The disabling signals thus, may be generated in response to the tachometers 400, 500 or 700.
When the mill is to be started, the head end of a work strip of material 10 is passed through the successive work rolls of the successive stands 8, to S, and led to the reel 43 where it takes a few wraps. After each stand is threaded the operator, digital computer, or screw adjustment controller changes the screwdown settings from stand S to stand S, until the output signal of each tension regulator 41, 42, 44 of those stands, read zero. At this moment the stand screwdown setting is correct and the mill can be accelerated. The installation shown in FIG. 4 provides for an automatic adjustment of the stands to such condition necessary to proper acceleration of the strip and this is conducted so that no calculation of the right screwdown position is necessary after stand S The operation of the four-stand tandem mill of FIG. 5 will now be explained in order to more fully describe the essential features of the present invention. Each of the tension regulators 41, 42, 44 has been described in full detail in the abovementioned copending application, and a similar regulator has been more completely shown on FIG. 3. It is sufficient to indicate here that the response of the corresponding speed regulators 51, 52 and 54 of stands 8,, S and S is fast for a given tension error appearing at the input, whereas with screwdown adjustment in response to such tension error the response is slow. In this respect the explanation given by reference to FIGS. 3 and 4, should suffice. It is observed also that as shown on FIG. 5, S is a pivot stand, e.g. correction of tension is effected on either side of this stand. Thus, the speed of stand S, is modified by speed regulator 51 in order to correct the tension detected by tensiometer 111, and in the same fashion subsequent stand S has its speed modified so as to correct the tension sensed by tensiometer 112. However, after stand S it is stand 8., following the sensing device 113 which is adjusted in speed to correct the intertension. In the latter case, roll speed changes having an opposite effect on the interstand tension, the speed regulator 54 must be adapted to change roll speed in the opposite direction as compared to front stands S, or S Considering now roll gap changes, it appears from FIG. 5 that the outputs of the tension regulators 41, 42 and 44 are all applied over leads 115, 116 and 117, respectively, to the screwdown system of the next subsequent stand. Therefore, should a disturbance be sensed by the sensing device 111, for instance, the tension regulator 41 will respond to a difference between the signal on lead 55 and the tension reference signal 18. As a result at point 5 a voltage will appear indicating a tension error condition. If the tension error corresponds to an excess of tension relative to the tension reference, speed regulator 51 will increase the speed of the rolls at stand S thus above the initial speed setting. Since such roll speed response is fast, the roll speed is readily adjusted, and tension between stands S and S returns to normal. As explained above, in response to such tension error the screwdown controller 82 will narrow the gap between the rolls of stand S which in effect will reduce tension between stands 8, and S and cause the speed regulator 51 in turn to reduce the speed of stand 8,. While the response of the roll gap loop is relatively slow, the speed of stand S will progressively return to the initial setting set by the master speed reference while the tension between stands will be maintained substantially at the level indicated by the tension reference.
Should the disturbance be a decrease in tension, corrections of speed and roll gap will occur in the opposite direction, as can be easily understood. The same can be said of any disturbance sensed by tension device 112 or the tension device 113. In the latter instance, however since the interstand tension error is corrected by the speed regulator of the subsequent stand the speed of the rolls is acted upon in the reverse direction. .Roll gap adjustment, though is the same relative to tension as in the previous stands S and S In contrast, to FIG. 3, the screwdown system of stands 5 S or 8,, includes a screw error correction controller 92, 93 or 94 and two transfer functions 72, 62 or 73, 63, or 74, 64 which will be now considered with particularity. To this effect, reference is made first to FIG. 6 representing in detail the circuit of block 92, 93 or 94.
FIG. 6 typically shows the circuitry of screw error correction controller 92 of FIG. 4. The same circuit is used for the other two controllers 93 and 94 of FIG. 5.
Referring to FIG. 6, the error signal derived over lead 115 from the output of tension regulator 44 (FIG. 5) is applied, through contacts CR1 ofa relay CR, to a potentiometer 200. Between contacts CR1 and potentiometer 200 a derivation path to ground is provided from junction 210 through contacts CR2 of the same relay CR. FIG. 6 shows that relay CR is energized by a source V-through contacts SC of a limiter circuit 214 controlled by a signal over lead 85. When the mill is to be started the control signal on lead 85 causes the limiter circuit 214 to close contacts SC and energize relay CR. As a result, contacts CR1 are closed while contacts CR2 are open, and the signal on lead 115 is being applied as an input to the potentiometer 200. When the mill is accelerated above a predetermined level the signal over lead 85 is suppressed and the limiter circuit 214 opens its contacts SC thereby to deenergize relay CR. Consequently the screwdown error correction controller 92 no longer is operative. At this time, the conventional control system of the rolling mill takes over. Potentiometer 200 is connected at its other end to ground and the slider is connected to a resistor 201 which at its other end connects with one input of an operational amplifier 215. The second input of the amplifier is to ground through a resistor 204. Also at the junction 211 with resistor 201, there is a connection to ground through a resistor 202. A feedback path is provided from output junction point 213 to input point 212 over a resistor 203. At the output of amplifier 215, point 213 is connected to ground via a resistor 205. The output lead to circuit 72 of FIG. 5 goes through contacts CR3, which, for the sake of simplicity, are also contacts of relay CR. Contacts CR3 concur with contacts CR1 in disabling controller 92 when the rolling mill is accelerated above thread speed. In operation, the signal over lead is amplified by the high gain amplifier 215, the gain being varied by adjusting potentiometer 200, thereby to derive a proper control signal for the screwdown position motor.
Referring again to FIG. 5, it is shown there that additional circuits such as 72, 62, 73, 63 and 74, 64 are in terposed in the loop of the corresponding screwdown system. These are features which have been described inthe abovementioned copending application. However, these features are valuable also when embodied in the circuit according to the invention. Considering only circuits 72 and 62 for the purpose of explanation, these have been interposed at the output of the screwdown error correction controller 92 in order to compensate for the velocity of the strip of material before stand S and for the cross-section area of the work strip, also before it reaches the stand operated on by controller 92. Compensation by circuit 72 may be proportional to velocity, but not necessarily. Any function of velocity may be selected as the transfer characteristic of circuit 72. All the necessary teachings can be found in the earlier mentioned copending application.
We claim as our invention:
1. In the method of controlling the gauge of work strip material passing through a tandem rolling mill having a plurality of roll stands, with each of said roll stands being initially adjusted in speed and roll opening for maintaining a desired relatively constant mass flow passage of said material through the roll stands with a desired tension condition between at least one pair of said roll stands, said method including the steps of: sensing a tension deviation from said desired tension condition, changing the speed of a selected one of said pair of roll stands in response'to said tension deviation to correct said tension and adjusting the roll opening of the latter of said pair of roll stands in relation to the direction of the passage of said work strip material in response to the change of speed in said selected one roll stand and concurrently changing the speed of said selected one roll stand in response to resulting change in tension, for restoring said desired mass flow condition.
2. The method of claim 1 including the steps of: providing initial settings for the speeds and the roll openings of at least said pair of stands for said desired mass flow condition when the rolling mill operation is thread speed operation and threading the work strip material through said roll stands with said tension deviation sensing and speed adjustment steps being conducted during said thread speed operation of the rolling mill.
3. The method of claim 2, wherein said speed and roll opening adjusting steps are effected concurrently and with the speed adjusting step being performed with a faster response than the roll opening adjusting step.
4. In the method of controlling the gauge of work strip material passing through a tandem rolling mill having a plurality of roll stands adjustable in speed and roll opening, with the speeds and roll openings of the roll stands being initially adjusted to provide a desired mass flow of the strip material through the roll stands and such initial adjustment being effected at thread speed before the rolling mill is accelerated to normal run speed, said method including the steps of: sensing the tension of said work strip material between at least one pair of adjacent stands to determine a tension error in relation to a desired tension; controlling the speed relationship between the work rolls of said pair of stands in response to said tension error; controlling the opening between the rolls of the subsequent one of said adjacent roll stands in the direction of flow of the workstrip material in response to said tension error; with said speed and roll opening steps being coordinated to establish said desired mass flow condition at said thread speed while maintaining the tension between said adjacent stands substantially in accordance with said desired tension.
5. A method of correcting the roll opening of the work rolls of a correction roll stand of a multi-stand cold mill running at thread speed, said method comprising the steps of: detecting an error in the tension of the material being rolled ahead of said correction roll stand, with said tension error being representative of an error in roll opening between the work rolls of said correction roll stand; changing the roll speed ofa selected roll stand adjacent the location of said detection tension error, changing the roll opening of said correction roll stand in response to said tension error; changing the roll speed of said selected roll stand in relation to said correction roll stand roll opening change for achieving the desired roll opening of said correction roll stand.
6. A method of rolling a strip of soft metal in a cold mill having a plurality of roll stands initially adjusted in speed and roll opening for maintaining a desired relatively constant mass flow passage of said metal with desired tension condition between a selected pair of adjaquent roll stand of said pair of roll stands in response to said tension error condition and concurrently changing in a second direction opposite to said first direction the speed of said one roll stand in relation to said roll opening control.
7. The method of claim 6 including repeating the above recited steps for any pair of adjacent stands successively; the roll opening of the first of all the roll stands being accurately adjusted initially.
8. The method of claim 7 with the above recited steps being conducted at thread speed and including the further step of accelerating the mill to normal run speed after all tension errors between roll stands have been successively eliminated.
9. ln apparatus for controlling the passage of a strip of material through a plurality of tandem roll stands with each said roll stands being adjustable in roll speed and roll opening to maintain a relatively constant mass flow condition for the material passing through said plurality of roll stands with a desired tension condition between said stands, the. combination of: means for sensing a tension error between a selected two adjacent roll stands; means for converting said tension error into a speed correction signal; faster response means for controlling the speed of one of said two adjacent roll stands in response to said speed error correction signal; and slower response means for controlling the roll opening of the subsequent one of said two adjacent roll stands in response to said speed error correction signal.
10. The apparatus of claim 9 with said faster response means being operative with a speed reference signal.
11. The apparatus of claim 9 with said means for sensing a tension error including a ramp function.
12. The apparatus of claim 9 wherein each pair of said roll stands is provided with such said means for sensing a tension error relative to adjacent roll stands, means for converting said tension error, faster response means and slower response means, and including means responsive to the speed of at least one of said work stands exceeding a predetermined transition speed level for disabling at least one of said faster response means and said slower response means to prevent operation thereof, said transition speed level corresponding to acceleration of the rolling mill to normal run speed.
13. The apparatus of claim 9 including means for providing a signal corresponding to the area of the work'strip of material for modifying the operation of said slower response means.
14. The apparatus of claim 9 including means for providing a signal corresponding to the velocity of said work strip material for modifying the operation of said SlOWGI' response means.