US3762194A

US3762194A - Constant speed driven continuous rolling mill

Info

Publication number: US3762194A
Application number: US00266895A
Authority: US
Inventors: H Maxwell
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1972-06-28
Filing date: 1972-06-28
Publication date: 1973-10-02
Anticipated expiration: 1990-10-02
Also published as: FR2190537B3; IT989426B; BR7304500D0; DE2332570A1; JPS4956865A; GB1419814A; FR2190537A1

Abstract

A continuous rolling mill having tandem stands driven by constant speed motors is described wherein the pattern of roll gap of a downstream stand is adjusted as a function of the measured drive power of the adjacent upstream stand or stands. Prior to threading, all gaps are preset for the drafting schedule in a conventional manner, manually or automatically, with recognition of usual parameters such as stand temperatures, roll diameters, and the width, thickness, temperature and physical characteristics of the incoming metal. Each gap except that of the first stand is automatically adjusted, if necessary, an instant after its threading as a function of measured drive power change or changes at the preceding stand or stands caused by its threading. Adjustment maintains interstand tension or compression at near-zero value to inhibit reduction in metal width or mill cobble. Drive power measurement of each stand after the mill is completely threaded results in periodic vernier gap adjustments to maintain acceptable power distribution between stands. As applied to hot strip steel roughing mills, and particularly as applied to the last few stands, the system makes possible a combination of tandem arrangement and AC synchronous motor drive, matching conventional mill capability but using simpler electric equipment of substantially lower first cost which can be accommodated by a smaller mill building.

Description

Unite Maxwell States Patent 1 Oct. 2, 1973 l l CONSTANT SPEED DRIVEN CONTINUOUS ROLLING MILL Hugh S. Maxwell, Wichita, Kans.

Primary ExaminerMilton S. Mehr AttorneyJohn .l. Kissane et al.

[57] ABSTRACT A continuous rolling mill having tandem stands driven by constant speed motors is described wherein the pattern of roll gap of a downstream stand is adjusted as a To a: 61 R2 function of the measured drive power of the adjacent upstream stand or stands. Prior to threading, all gaps are preset for the drafting schedule in a conventional manner, manually or automatically, with recognition of usual parameters such as stand temperatures, roll diameters, and the width, thickness, temperature and physical characteristics of the incoming metal. Each gap except that of the first stand is automatically adjusted, if necessary, an instant after its threading as a function of measured drive power change or changes at the preceding stand or stands caused by its threading. Adjustment maintains interstand tension or compression at near-zero value to inhibit reduction in metal width or mill cobble. Drive power measurement of each stand after the mill is completely threaded results in periodic vernier gap adjustments to maintain acceptable power distribution between stands.

As applied to hot strip steel roughing mills, and particularly as applied to the last few stands, the system makes possible a combination of tandem arrangement and AC synchronous motor drive, matching conventional mill capability but using simpler electric equipment of substantially lower first cost which can be accommodated by a smaller mill building.

11 Claims, 4 Drawing Figures FROM 60 FROM 19 k PREDICTED ROLL FORCE lSwlTCHlNG FROM 29 l CKT FROM 26 onu TO 6l PR ED lCTED ROLL FORCE PAIENIEDHBH 3L7$2.194

SHEET 3 BF 3 MEASURE ROLL FORCE IS SLAB BETWEEN NO ROLLS YES CALCULATE ROLL FORCE 7 COMPARE ADJUST SCREW DRIVE OF NEXT 3 STAND MEASURE AND STORE DRIVE MOTOR POWER IS SLAB 1N NEXT NO STAND YES MEASURE DRIVE MOTOR POWER &

COP! PARE THIS MEASUREMENT WITH STORED VALUE DRIVE SCREWS OF IMMEDIATELY SUCCEEDiNG- STAND TO RETURN POWER TO STORED VALUE FiG. 4

CONSTANT SPEED DRIVEN CONTINUOUS ROLLING MILL This invention relates to a novel continuous tandem rolling mill and to a method of controlling the flow of material through such mill. In a more particular aspect, the invention relates to a continuous tandem rolling mill wherein variations in power to the constant speed drive motor of an upstream stand are utilized to adjust the roll position of the immediate downstream stand, if necessary, to obtain low tension in the strip being rolled following threading at the downstream stand.

Continuous tandem rolling mills, i.e., mills wherein a strip of material being rolled simultaneously extends through a plurality of rolling stands, typically are driven by adjustable speed DC motors to permit alteration of the drive motor speed at a stand upon a sensing of tension in the rolled metal between mill stands. Because of the significant cost of adjustable speed motor drives relative to constant speed motor drives, rolling mills often have attempted to utilize constant speed motor drives for the rolling stands wherever possible. Tension, however, can build up in the metal being rolled in a tandem constant speed mill resulting in an undesired reduction in metal width, or compression can increase tending to produce cobbles in the rolled metal. Tension or compression of thick material is difficult to measure. Constant speed motor drives for mill stands, therefore, normally have been utilized only in roughing mills wherein the mill stands can be spaced by a distance permitting one piece of metal to pass through only one stand at a time. Such spacing of the mill stands, however, occupies a large amount of factory floor space leading to proposals that adjustable speed drives be utilized for the penultimate stand in a constant speed roughing mill to permit close spacing of the last two stands by speed control of the DC drive motor for tension regulation. Hybrid AC-DC tandem mills of the foregoing type, however, are more expensive than a completely constant speed driven mill and significant floor space is required between the two-stand hybrid mill and the preceding AC single stand mill.

Although the general concept of adaptive threading, i.e., the adjustment of predetermined set-up parameters for a downstream rolling mill stand in view of measured variations from predicted values observed during threading of an upstream stand, is known (e.g., one system of adaptive threading is described in my US. Pat. No. Re 26,996, re-issued Dec. 8, 1970), previous mills employing adaptive threading techniques normally have employed DC drives for the rolling stands and loopers or tensiometers between stands to measure tension. Not only are DC drives relatively expensive (as was heretofore mentioned), but loopers sized to accommodate the stiffness and weight of an interstand length of slab are massive and also expensive with a requirement of considerable space between stands for looper installation and maintenance.

It is therefore an object of this invention to provide a continuous tandem rolling mill completely powered by constant speed drive motors, without loopers or tensiometers.

It is also an object of this invention to provide an inexpensive continuous tandem rolling mill occupying limited floor space.

It is a still further object of this invention to provide a novel adaptive threading roll gap control system for tandem stands of a continuous mill driven by constant speed drive motors.

It is a still further object of this invention to provide a novel method of rolling sheet material in a continuous tandem rolling mill powered by constant speed drive motors.

These and other objects of this invention generally are achieved utilizing a roll gap control system wherein the change in drive power to a substantially constant speed drive motor of a rolling mill stand as the next downstream stand is threaded is observed to adjust the roll position of the downstream stand to compensate for the observed power change. Thus, the method of reducing the thickness of a strip or slab of deformable material in accordance with this invention generally includes driving each of at least two consecutive stands in a multi-stand continuous rolling mill with subtantially constant speed motors and measuring power to the drive motor of the upstream stand of the consecutive stands to measure deviation from a given reference level in power to the motor upon threading of the strip material through the immediately adjacent downstream stand. The rolls of the downstream stand then are adjusted in response to the measured deviation in power to the upstream stand drive motor to maintain the power to the upstream motor at a predetermined relationship relative to the reference level. Preferably, the roll force at the upstream stand also is measured to permit an initial coarse adjustment of the rolls of the downstream stand in response to an observed deviation in the roll force at the upstream stand from a predicted value during threading of the upstream stand.

Although this invention is described with particularity in the appended claims, a more complete understanding of the invention may be obtained from the following detailed description of various specific embodiments of the invention when taken in conjunction with the appended drawings wherein:

FIG. 1 is a simplified illustration of a continuous tandem constant speed driven rolling mill in accordance with this invention,

FIG. 2 is a simplified illustration of a preferred continuous tandem rolling mill wherein a computer is utilized to supervise rolling in accordance with this invention,

FIG. 3 is a flow chart illustrating use of the roll force at an upstream stand to coarsely adjust the roll opening of the immediately downstream stand prior to threading of the strip through the downstream stand, and

FIG. 4 is a flow chart illustrating the use of drive motor power change at the upstream stand to precisely adjust the roll opening of the downstream stand subsequent to threading the strip through the downstream stand.

A continuous rolling mill 10 in accordance with this invention is illustrated in FIG. 1 and generally includes three tandem rolling stands R3, R4 and R5 which may form the last three stands of a roughing mill utilized to incrementally reduce the thickness of slab SL. Typically, rolling stands R3-R5 are preceded by a spaced out vertical scale breaker, a horizontal scale breaker and the first two stands of the roughing mill. However, since the length of slab SL in the scale breakers and first two stands of the mill normally is not excessive, these preceding stands generally are situated at conventionally spaced apart locations along the mill and only roughing stand R2 of the preceding stands therefore is shown in FIG. 1 for clarity. Each of tandem rolling stands R3, R4 and R are driven by substantially constant speed motors DM3, DM4 and DM5 with the mass flow of material through stand R4 being essentially matched to mass flow thru R3 following threading of R4 and with the mass flow of material through stand RS essentially matched to the mass flow thru R4 following threading of R5 by detecting a deviation from a reference level in power to the drive motor of the adjacent upstream stand and making an automatic roll gap adjustment. For example, upon measurement of change from the reference level of power to motor DM3 of stand R3 as the immediately adjacent downstream stand R4 is threaded with slab SL, the screws SC4 of downstream stand R4 are adjusted by an amount to produce the required change in gap to return power to drive motor DM3 to the reference level, within acceptable tolerance. It is apparent that constant mass flow from each stand of a tandem combination of stands imemployed. The substantially constant speed drive motors are geared to the work rolls through suitable reduction gearing GR3-GR5 to produce the roll surface speed necessary to roll slab SL at a desired rate. Typically, a gear ratio of approximately 16:1, :1 and 6:1 can be utilized to drive stands R3, R4 and R5, respectively.

To initiate rolling, the mill schedule required to produce the desired output gage in slab SL is calculated from the known dimensions of the slab'entering the mill, the temperature of the slab and the known metallurgy of the slab utilizing known mass flow principles such as are set forth in detail in my heretofore cited Reissue Pat., No. 26,996, issued Dec. 8, 1970. For exam- TABLE 1.-LAST 3 STANDS, CLOSE-COUPLED ROUGHER SCHEDULE Incoming tl1ickness=4.3"

wherein M is the mill spring modulus, and k is the mean yield stress of the material being rolled.

plies a constancy of interstand tension or compression. By providing roll gap adjustment insuring zero or nearzero interstand tension, the initial rolling operation will have essentially constant mass flow at each stand.

The mill configuration includes conventionally structured rolling stands with each tandem stand being formed of upper and lower work rolls WR and backup rolls BR to reduce the thickness of slab SL as the slab passes thru the gap between the confronting work rolls. Load cells LC3-LC5 are employed under the bottom backup roll checks of each rolling stand to measure the roll force at the stand while screw drives SD3-SD5, e.g., commercially available 200 hp, 1,030 rpm, 460 volt drives with an SCR supply and a magnetic clutch, are located at opposite ends of each roll to rotate screws SC3-SC5 through an angle required to position the work rolls of the respective stands at a location to reduce the slab by a predetermined amount in each stand. The continuous tandem rolling stands, R3-R5, are spaced relative to each other by a distance such that slab SL extends between at least two consecutive stands, e.g., between stands R3-R4, during a typical rolling schedule with the stands illustrated in FIG. 1 being spaced by a distance such that the slab simultaneously extends between the last three stands of the tandem mill.

Drive motors DM3-DM5, in accordance with this invention, are substantially constant speed drive motors, i.e., motors exhibiting less than 1 percent speed change over the load range anticipated after threading of slab SL. Preferably, each of the drive motors are synchronous motors in a horsepower rating, i.e., 10,000 hp, required to drive the work rolls although any AC motor exhibiting a limited speed drop with load also can be The screws of the stands then are adjusted to produce the desired thickness at each stand taking into consideration the stand stretch (as determined in conventional fashion from empirically derived curves depicting the variation of mill stretch with roll force).

Shortly after slab SL has entered stand R3, the roll force at the stand is measured by load cell LC3 and the measured roll force is compared in comparator circuit 25 with a signal from potentiometer circuit 15 corresponding to the predicted roll force as calculated for the stand (e.g., using techniques such as are described in my heretofore cited reissue patent or in US. Patent Application Serial No. 200,400 entitled Computer Controlled Rolling Mill filed November 19, 1971 in the name of L.W. Spradlin and assigned to the assignee of the instant invention), to determine the difference therebetween. This force difference signal then is utilized to adjust screws 8C4 at the next succeeding stand. Because only a single adjustment of screws 8C4 is required to compensate for variations between calculated force and actual force, inhibit circuit 26 is placed between comparator circuit 25 and the screw drive for the downstream stand. The inhibit circuit is triggered to pass a single screw adjust signal only after sensing or entry of the head end slab SL into stand R3 (as deter mined by differentiator circuit 27 and threshold detector 28) and a delay, e.g., for 0.3 seconds, in delay circuit 29 to give the synchronous motor oscillations and the mill mechanical vibrations which occur at the instant of threading an interval of time to attenuate and to assure that the portion of the slab passing the roll gap is sufficiently beyond the head end to be full width, to produce an accurate roll force reading. A bistable switching circuit 24 is situated between threshold detector 28 and delay circuit 29 to trigger inhibit circuit 26 only on alternate signals from the delay circuit thereby preventing adjustment of the screws as the tail of the slab leaves the stand (as will be more fully explained hereinafter).

Power to drive motor DM3 is measured by a power transducer PT3 which produces an output signal which is stored within power storage circuit 31 upon activation of the storage circuit a fixed interval after the slab hasentered the roll gap of stand R3. To accomplish this, the output signal from delay circuit 29 can be utilized to trigger storage circuit 31 to store a signal proportional to power to drive motor DM3 with slab SL between work rolls WR prior to threading the forward end of the slab through the work rolls of stand R4. The stored value of power to drive motor DM3 then is compared in comparator circuit 36 to the power to the drive motor after threading of stand R4 to produce a difference signal which is fed to screw drive SD4 (through bistable switching circuit 30 switched to a closed position by the output signal from delay circuit 29) to continuously adjust the screws at stand R4 by an amount necessary to return power to DM3 to the stored reference level, within acceptable tolerance. An amplifier cricuit 61 also is utilized in the power screwdown control circuit to adjust the amount of screw position change for a given power change. Because difference in the power to drive motor DM3 before and after threading of stand R4 results primarily from tension or compression in slab SL between the threaded stands, adjustment of the screws at the downstream stand to return the drive power at the upstream stand to, or nearly to, the power level prior to threading of the slab into the downstream stand assures return to substantially zero tension in the slab.

Similarly, the deviation between predicted roll force at stand R4 and the actually measured roll force at the stand a short interval after threading of stand R4 (and prior to threading of stand R5) is fed forward to screw drive SDS to adjust the screws at stand R5 prior to arrival of slab SL at stand R5. Power to drive motor DM4 also is measured by transducer PT4 and stored within storage circuit 41 to be subsequently compared with power to the drive motor after threading of stand R5 in comparator circuit 46 to obtain a difference signal which is applied to screw drive SDS to adjust the work rolls at stand R5 by an amount to return the power to drive motor DM4 to, or nearly to, the original level prior to threading of stand R5.

As the tail end of slab SL leaves stand R3, load cell LC3 will produce a rapidly decreasing output signal which is detected by differentiator 27 and threshold detector 28 to switch bistable switching circuit 24 to an alternate mode, negating triggering of inhibit circuit 26 to block further adjustment of the screw drives of stand R4. The output signal from threshhold detector 28 also serves to trigger bistable switching circuit 30 to an open position, negating further change in screw drive SD4 by comparator circuit 36. Similarly, the output signal from load cell LC4 upon passage of the tail end of slab SL from the stand is detected by differentiator 47 and threshhold detector 48 to activate switching circuit 40 preventing any further correction of the screw drives of stand R5.

Unexpected time delays in slab travel between R2 and R3, resulting in threading at lower slab temperature, requires some reduction of preset gaps to maintain the original drafting schedule, and because of the increased resistance of the slab to deformation, may require greater screw position change for a given amount of gap change after threading. Accordingly, the time required for the head end of slab to travel from rougher R2 to the initial tandem rougher stand R3 is measured, e.g., by thermal sensing devices Ti and T2 situated at longitudinally spaced locations along the path of the slab between roughing stands R2 and R3, to produce a time difference signal from timing circuit 60. This time.

difference signal is utilized to adjust the preset gap of R3 prior to its threading and is also utilized to adjust, if necessary, the amplification of the signals from

comparator circuits

36 and 46, e.g., by altering the amplification factor of

amplifier circuits

61 and 62, respectively, using empirically or mathematically determined relationships of elapsed time to temperature, temperature to yield stress, yield stress to roll force and roll force to screw position change per unit of gap change to establish the quantitative adjustments.

A particularly preferred embodiment of this invention is shown in FIG. 2 wherein computer C, e.g., a general purpose digital computer or a stored program computing device, is utilized both to calculate the initial rolling schedule for slab SL in the entire roughing mill and to adjust the screws at stands R3-R5 in accordance with this invention. Thus, the computer initially is fed information by the operator concerning the slab, such as the slab dimensions upon entering the roughing mill, the desired output thickness from stand R5 and the metallurgy of the slab. The computer then calculates a rolling schedule and signals are sent out from the computer to the screw drives to produce the desired reduction in the slab at each stand. As slab SL exits rolling stand R2, the temperature of the slab (as measured by pyrometer P) is fed to computer C to permit an adjustment of the screws at each downstream stand should the temperature of the slab vary from the predicted temperature for the slab. The output signals from thermal sensing devices T1 and T2 also are fed to computer C to permit the computer to calculate the transit time for the slab from stand R2 to stand R3, calculate resulting temperature rundown and calculate and send a signal to SD3 to reduce R3 gap in anticipation of threading the colder slab. Similarly, the roll force at each stand, as measured by load cells LC3LC5, and the powers to substantially constant speed AC drive motors DM3-DM5, as measured by PT3PT5, are fed to the computer to permit further adjustment of the roll gap of the first AC stand after threading if desired, adjustment of roll gaps of downstream stands during threading to obtain near-zero interstand tensions, and later minor adjustment of any or all gaps to maintain acceptable power distribution between the several stands.

As can be seen from the flow chart of FIG. 3, roll force at stand R3 is continuously measured by load cell LC3 and a determination is made by the computer whether the slab is between the rolls of the stand by, for example, detecting a large increase in the output signal from the load cell. When this increase in signal is observed, the measured roll force is compared to the calculated roll force for the stand. Any discrepancy between the actually measured roll force and the calculated roll force then is compensated for by adjustment of the screw drive SD4 at stand R4 in accordance with the equation:

A S k'Ah l/Mf(AF) wherein 'AS is the screw adjustment produced by the screw drive,

k is a scaling factor, greater than one,

A is the adjustment in the loaded roll gap to be produced by the screw adjustment, essentially equal to the adjustment in delivery thickness of material rolled,

M is the mill spring modulus, and p AF is the difference bitvefi'tfi measured and the calculated roll forces.

The power to drive motor DM3 of stand R3, as determined by transducer TR3, also is fed to computer C and the computer continuously iterates the measurements, as shown in FIG. 4, until the presence of slab between the rolls of the stand is observed, e.g., by a rapid change in the input power to the drive motor. After the initial observation of slab between the rolls and a delay of approximately 0.3 second to enable the slab to be completely within the gap without threading into stand R4, the measured drive motor power is stored within computer C. This stored power then is retained and compared with a measured power to DM3 after the slab threads through stand R4 to produce a difference signal which is employed to adjust the screws SC4 of stand R4 to return the measured power of motor DM3 to the stored level, within acceptable tolerance. Similarly, the power to the drive motor of stand R4 is measured prior to threading of the slab through stand R5 to provide a reference signal to which a measured power to drive motor DM4 after threading is compared to permit adjustment of screw SCS to maintain power to drive motor DM4 at the stored level, within acceptable tolerance.

If steady state interstand tension is represented as 1.0, the increase from zero at the instant of threading the second stand is exponential in pattern, in the order of wherein e is the natural logarithm,

! is elapsed time in seconds,

V is a variable, less than 1.0, dependent on many rolling parameters including draft and tension, and

T is slab transport time between stands.

Assuming a stand spacing of centerline to centerline, and (Table 1) a slab speed of 338 fpm between R3 and R4, the transport time is approximately 3 seconds. As an example of potential improvement in product rolled, if a constant value of 0.1 is assigned to V (for illustration), tension will increase to approximately 637. of final value in one time constant VT, which is 0.3 seconds, but requires approximately three time constants or 0.9 seconds to closely approach steady state value.

The computer anticipates the steady state value by receiving a number of time-based power measurements from PT3, e.g., one every 0.01 second, for as short an interval as found practical for a particular installation, thereby identifies the applicable (modified exponential) curve of a stored family of curves (or their mathematical equivalent), and then identifies its steady state value.

The computer then calculates and sends an appropriate signal for vernier adjustment of R4 gap. In practice, the gap adjustment is completed and tension is reduced to near zero value before the slab threads R5. The early cutoff of tension increase avoids reduction in slab width.

Assuming l5 spacing R4-R5 the transport time R4-R5 is approximately 2 seconds. It is desirable that the measurement and adjustment be completed within this time interval, prior to the threading of R5, so that R3 is undistrubed by the threading of R5.

0 While various specific embodiments of this invention have been disclosed, it will be apparent to those skilled in the art that many variations may be made in these embodiments without departing from the broad scope of the invention.

For example, the adaptive threading feature could be utilized by a specialized, inexpensive, three-stand cold rolling mill for sheet material equipped with induction motor drive and used for rolling sheet product to thinner gages. Although constant speed drive forces threading at run speed, such operation yields high tonnage and a range of output thickness is obtainable by using various combinations of stands, by changing draft in the first stand used, and by changing work roll diameters in combination with change in draft in one or more stands.

What I claim as new and desire to secure by Letters Patent of the U.S. is:

1. In a method of reducing the thickness of a strip of deformable material by passing said material through a plurality of tandem rolling stands forming a continuous rolling mill wherein said strip is incrementally reduced in thickness by pre-determined amounts from an initial entry thickness to a final desired thickness, the improvement comprising driving each of at least two consecutive stands in said mill with substantially constant speed motors, measuring power to the drive motor of the upstream stand of said consecutive stands, detecting a power deviation to the drive motor of said upstream stand from a given reference power level after threading said strip through the rolls of the immediate downstream stand and automatically adjusting the roll gap of the downstream stand in response to the detected power deviation from said reference level.

2. A method of reducing the thickness of strip according to claim 1 wherein the reference level of power to said upstream stand is the power to said stand with the strip between the upstream stand rolls immediately prior to threading of said strip into the downstream stand.

3. Arnethod of reducing the thickness of strip according to claim 2 further including inhibiting further adjustment of the roll gap of said downstream stand upon detection of the tail end of said strip leaving said upstream stand.

4. In a method of reducing the thickness of a strip of deformable material by passing said strip through a plurality of tandem rolling stands forming a rolling mill to incrementally reduce the strip thickness by predetermined amounts from an initial entry thickness to a pre-determined final desired thickness, the improvement comprising driving each of two consecutive stands of said mill with synchronous motors, detecting the power to the synchronous motor drive of the upstream stand with said strip in said stand prior to threading of said strip between the rollers of the downstream stand, measuring the change in drive power to said upstream stand motor upon threading of said strip through said succeeding stand and adjusting the roll gap of the succeeding stand by an amount which is a function of the measured change in power to the drive motor of said upstream stand.

5. In a method of reducing the thickness of a strip of deformable material by passing said strip through a plurality of tandem rolling stands forming a continuous rolling mill to incrementally reduce the strip thickness in pre-determined amounts from an initial entry thickness to a final desired thickness, the improvement comprising driving each of two consecutive stands of said mill with substantially constant speed drive motors, detecting the roll force at the upstream stand and the power to the substantially constant speed drive motor of said upstream stand, determining the difference between predicted and measured roll force at said upstream stand, initially adjusting the roll openings of the downstream stand by an amount which is a function of the detected difference in roll force at said upstream stand and subsequently adjusting the roll gap of the downstream stand by an amount which is a function of the measured change in power to the drive motor upon threading of said downstream stand with said strip.

6. A method of reducing the thickness of a strip of deformable material according to claim wherein said substantially constant speed drive motors are synchronous motors.

7. A continuous rolling mill for reducing the thickness of deformable material comprising a plurality of rolling stands, adjacent stands being spaced by an interval less than the length of strip to be rolled by the upstream stand, substantially constant speed drive motors driving each of said adjacent stands, means for measuring power to the drive motor of the upstream stand of said adjacent stands, means for detecting a deviation in power to the drive motor of the upstream stand from a predetermined reference level upon threading of said strip through the downstream stand, and means for adjusting the screws of the downstream stand of the adjacent stands in response to a detected deviation from said reference level in power to said upstream drive motor to obtain low interstand tension or compression in the material.

8. A continuous rolling mill according to claim 7 wherein said reference level is power to the upstream stand with the strip between the upstream stand rolls prior to threading of said strip into the downstream stand.

9. A continuous rolling mill according to claim 7 wherein said constant speed drive motors are AC synchronous motors.

10. A continuous rolling mill according to claim 7 wherein the only monitoring of the rolling operation for maintaining acceptable levels of tension or compression of metal between stands subsequent to threading is provided by AC power transducer measuring AC motor input power, the output of said transducers being fed to a digital computer controlling screw position regulators for roll gap adjustment.

11. A continuous mill according to claim 7 with an anticipatory gap adjustment feature wherein a computer repeatedly samples the drive power of a stand motor as the next downstream stand threads, predicts the magnitude of steady state interstand tension during initial change from zero value, calculates the change in gap at the downstream stand required to restore nearzero tension, and initiates Vernier screw position change of required magnitude prior to threading of the next standv PC4050 United States Patent Office CERTIFICATE OF CORRECTION PatentNo. 6 Dated October 2, 1973 Inventor(s) Huqh S. Maxwell It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 1, cancel "Each of" and substitute --The. Column 3, line 2, after "driven" insert respectively,-. Column 3, line 65, cancel "are" and substitute --is a--. Column 3, line 66, cancel "motors" and substitute --motor--. Column 3, line 67, after "rolls" insert a comma Column 4, line 5, cancel "a" Column 4, line 5, cancel "ratio" and substitute -ratios.

Column 4, line 47, cancel "Application Serial No. 200,400"

and substitute -3,7l3,3l3--.

Column 4, line 48, cancel "filed November 19 1971" and substitute -issued January 30, l973--.

Column 4, line 55, after "force," (second occurrence) insert --an--.

Signed and sealed this 23rd day of April 1971+.

(SEAL) Attest: v

EDWARD I I.FLETCE1UR,JR. G. MARSHALL DANE Attesting Officer Commissioner of Patents

Claims

1. In a method of reducing the thickness of a strip of deformable material by passing said material through a plurality of tandem rolling stands forming a continuous rolling mill wherein said strip is incrementally reduced in thickness by predetermined amounts from an initial entry thickness to a final desired thickness, the improvement comprising driving each of at least two consecutive stands in said mill with substantially constant speed motors, measuring power to the drive motor of the upstream stand of said consecutive stands, detecting a power deviation to the drive motor of said upstream stand from a given reference power level after threading said strip through the rolls of the immediate downstream stand and automatically adjusting the roll gap of the downstream stand in response to the detected power deviation from said reference level.

3. A method of reducing the thickness of strip according to claim 2 further including inhibiting further adjustment of the roll gap of said downstream stand upon detection of the tail end of said strip leaving said upstream stand.

4. In a method of reducing the thickness of a strip of deformable material by passing said strip through a plurality of tandem rolling stands forming a rolling mill to incrementally reduce the strip thickness by pre-determined amounts from an initial entry thickness to a pre-determined final desired thickness, the improvement comprising driving each of two consecutive stands of said mill with synchronous motors, detectiNg the power to the synchronous motor drive of the upstream stand with said strip in said stand prior to threading of said strip between the rollers of the downstream stand, measuring the change in drive power to said upstream stand motor upon threading of said strip through said succeeding stand and adjusting the roll gap of the succeeding stand by an amount which is a function of the measured change in power to the drive motor of said upstream stand.

6. A method of reducing the thickness of a strip of deformable material according to claim 5 wherein said substantially constant speed drive motors are synchronous motors.

11. A continuous mill according to claim 7 with an anticipatory gap adjustment feature wherein a computer repeatedly samples the drive power of a stand motor as the next downstream stand threads, predicts the magnitude of steady state interstand tension during initial change from zero value, calculates the change in gap at the downstream stand required to restore nezr-zero tension, and initiates vernier screw position change of required magnitude prior to threading of the next stand.