US3237071A - Motor load distributing system for metal rolling mill - Google Patents

Description

Ww w @di 26d@ .QW d@ P QN mw M Feb. 22, 1966 P. l.. MCMATH ETAL MOTOR LOAD DISTRIBUTING SYSTEM FOR METAL ROLLING MILL Filed April 5, 1963 um m ww n m ST W United States Patent() 3,237,071 MTR LOAD DlS'ERlBUTWG SYSTEM FR METAL ROLLING Mill.

Paul li... Meh/latin, Hales Corners, Wis., and Ralph E.

Perrault, Monrovia, Ealif., assignors, by mesne assignments, to Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

Filed Apr. S, i963, Ser. No. 271,025 4 Claims. (Cl. S18-99) This linvention relates to a control for distributing the load on a group of electric motors. More specifically, this invention relates to a control for distributing the load on the motors that drive the work rolls in a metal rolling mill with automatic gauge control.

Some automatic gauge controls for metal rolling mills measure the thickness of the strip being rolled, compare the measured thickness with a reference thickness, and order any appropriate changes in the force of the work rolls on the strip. The reference thickness decreases from stand to stand in the direction of rolling to cause each stand to contribute part of the total reduction in the strip thickness. Since the load on a work roll drive motor depends on the reduction at its stand, the drive motors share the mill load according to the relative values of the reference thicknesses. The automatic gauge control at each stand varies the work r-oll force as various factors cause the gauge to differ from the reference, and it gradually increases the work roll force during the rolling process as the strip cools and Ibecomes harder. This invention is particularly concerned with the problem of keeping a `satisfactory distribution of the load on the Work roll drive motors.

One object of this invention is to sense when the load on the work roll drive motor of one reducing stand is at a predetermined high level and to operate the reducing stand to shift some of this load to the next stand. Another object of the invention is to sense when the next stand is loaded at a predetermined high level and to prevent shifting the load forward to the next stand in this situation.

Another object of this invention is to sense the load on the last stand with automatic gauge control and to perate the preceding reducing stands to shift the load backward before the last stand reaches a preset high load level. Another object of the invention is to prevent shifting the load backwards to stands that are already heavily loaded.

Another object of the invention is to provide a warning to the mill operator whenever all of the stands with automatic gauge control -have reached a level at which it is undesirable to shift the load backward from stand to stand and to prevent further forward shift.

Another object of the invention is to provide a warning to the mill operator when none of the stands can accept additional load `from the last stand, and the load on the last stand has increased to a second preset high level.

The drawing and the detailed description of the invention will suggest other objects and advantages of this control.

The control of this invention senses two load conditions at each mill stand that has automatic gauge control. The rst level warns that the load is becoming high but the motors still have capacity to drive the rolls as the roll force is increased. The second level indicates that the load should not be increased farther. For example, the second level may be set just below the level that protective devices would trip out the work roll drive motor. In response to a signal indicating the second level, the control operates the work roll positioning mechanisrn to reduce the roll force until the load falls to the ice rst level. The reduction in load-at this stand must be made up at the following stands if the material is to have the desired thickness, and the automatic gauge controls cause the load to be shifted aheadv from the stand that is partially unloaded. When the vload on the mill increases so much that the last stand reaches the first load level, the control shifts the load backwards, in a preset sequence, to any stand that is not already operating at the lirst level. ln this way the control keeps any stand from becoming overloaded, and it assures that every stand will be highly loaded before the last stand is operated by its automatic gauge control above the first load level.

ln the drawing, the single figure is a schematic of a rolling mill with automatic gauge control and the control of this invention.

The mill and the automatic gauge control The mill that the drawing illustrates has three reducing stands lo which have automatic gauge control. Stands l@ are suilixed a, b and c in the direction of rolling, and these sumxes are used to distinguish between equivalent components used at more than one reducing stand. Stands iti represent the iirst, next to the last, and last stands and illustrate intervening stands with automatic gauge control. Other stands with or without gauge control (not shown) may be located in any position. Each stand i0 has Work rolls and backup rolls ll. that are driven -by a motor l2 to pull a strip 13 through the mill. A device ld `for each stand is controlled to position the work rolls il. and apply force through the work rolls on strip 1.3. Each stand l@ has a thickness measuring device (not shown) that produces a thickness signal l5. The automatic gauge control of each stand has a means ld that compares gauge signal 15 with a reference 17 (combined with a reference biasing signal that will be described later) and produces a thickness error signal 18.

In response to signal 18, roll positioning device 14 varies the ywork ro-ll force to maintain the reference gauge. As will be explained later, the control of this invention biases the reference i7 to adjust the load on motors.

The components of the mill and the automatic gauge control that have been described are well known and they have been described -suiciently to suggest the `application of the control of this invention to various types of mills and automatic controls.

The forward load shift The control of this invention includes for each stand lila, Mb, and lite, a load sensing relay 2@ that produces a preset rst load level signal 2l and a load sensing relay 22 that produces a preset second level signal 23. Preferably, the relays 2t), 22 are adjustable by the mill operator so that signals 2l, 23 correspond to the characteristics of the associated stand lil. As will be explained, the signals 21, 23 are used toindicate whether a stand should shift some of its load to the other stands and whether the stand could accept part of the load from other stands. Stands lila and ltlb have identical coniponents that operate in response to signals 2l, 23 to shift the load forward. These components are shown in detail inside the dotted lines for stand ltlb and shown by a 'box for stand lila. (Since the last stand ltc cannot shift its 'load forward, its control is different from t-he control of the preceding stands lila, 10b.)

As the controls for stand 10b iilustrates, the `second level signal 23 sets a device 25 such as a iiip-iiop to produce a signal 2d that indicates that the motor has reached the second level. Device 25 maintains output 26 until it is reset even though the load falls below the second level and signal 23 is removed. A reset signal .AND gate 29 from energizing its output 32.

27 (the complement of signal 2l) is developed from first level signal 2l by means of a NOT gate 28 and is applied to the reset input of device 25 to reset device 25 when the load falls below the first level. Preferably, signal 26 is applied to reduce the load on the stand only if the next stand is not at the second level. An AND gate 29 receives signal 25, and it receives a signal 3th: that is derived from the second level signal 23 of the last stand with automatic gauge control, ltlc, by a NOT gate 31 to indicate when the load of stand lldc is below the second level. AND gate 29 produces an `output 32 when the load on stand llfib should be reduced to the first level and this action will not excessively load the last stand c. The complementary output of device provides a suitable signal 30h for controlling a corresponding AND gate in the box representmg part of the control of the preceding stand lila.

Signal 32 is transmitted to a device 33 that combines signal 32 and a signal that will be d-escribed later and produces a signal 34 that indicates that the load on the stand should be changed. An integrator 35 receives signal 34 and produces an output 36 that is combined with reference signal 17 in automatic gauge control device I6. Device 33` may comprise the input circuitry of integrator 35. So long as device 25 is set and the Stand 10c is below its second level, signal 34 operates integrator 35 to change the reference bias signal 36.

Suppose that stand 10b is operating below the first level and that the load on its motor l2 increases sufficiently to actuate load sensing relay 22 to set device 25 and energize output 26. If the last stand ltlc is -at level two, the absence of a signal at input 36C to AND gate 29 prevents In this situation device 25 would maintain its output 26 energized until the load on stand 10c is reduced below level two or until some other factor causes the load on stand 10b to fall below the first level. When both inputs 2d and C are energized, AND gate 29 energizes output 32 and input 34]) of integrator 35b is energized in a polarity for integrator 35h to begin increasing reference bias signal Sb. In response to the increase in reference bias signal 36h, roll positioner I4b opens the work rolls lll of stand lltlb and thereby reduces the load on motor I2. When the load has been reduced below the first level, load sensing relay Ztb cooperates with NOI` gate 2S to energize reset input 27 of device 25 and thereby deenergize input 34b of integrator 35h. Integrator 351; then maintains its output 36h at the level that reduced the load on the stand 1Gb to below the first level. After device 25 is reset, the automatic gauge control of stand 10b is free to increase or decrease the Work roll force in response to variations in thickness signal l5.

Preferably as the drawing indicates, components Ztl, Z2, 25, 28, 29, 33 and 35 are well known static logic elements. If desired these components may be made up of electromechanical load sensing relays 20, 22, a third relay in device 25, and their contacts. Device 25 may comprise the third relay with its coil connected to be energized by a pair of normally open contacts on relay 22 (represented by signal 23) in parallel with the series combination of a pair of normally closed contacts on relay 2t) (represented by NOT ga-te 28) and a normally open pair of contacts on the relay of device 25. The relay of device 25 also operates a pair of normally open contacts represented by output 26 and a pair of normally closed contacts represented by output Stb. AND gate 29 may comprise the s-eries combination of a pair of normally open contacts already mentioned on the relay of device 25 and a pair of normally closed contacts (represented by NOT gate 3l) on the second level relay 22C of the last stand 10c. Integrator 35 may comprise, for example, a reversible motor connected to drive a potentiometer, an integrating amplifier, or a digital counter. Device 3.3 may comprise the input to integrator 35.

The backward shift of the load The control that has been described for opening the work rolls to shift the load forward from stands 10a' and 10b is not applied to the stand 10c because the strip I3 would leave the mill over gauge. The control for the last stand ltlc responds to the first level signal 21C from load sensing relay Ztlc to operate other components to shift the load backwards. These components are illustrated in the drawing by AND gates. The arrangement of these gates is intended to present the functional relationship of the components in a verbal form and to suggest connections of contacts on the relays 2d, 22. Variations of this specific logic network will be apparent from well known design techniques.

An AND gate 4t) receives a first level signal Zic from the stand fdc and the complement first level signal Zlb from stand ltlb and produces a signal 41 whenever the stand 10c is loaded to the first level and stand 10b is not loaded to the first level. Signal 41 energizes input 34b of integrator 35b in a polarity to reduce reference bias signal 36b and cause work roll positioning device 14h to increase the roll force at stand 10b. Output 41 of AND gate 4d will remain energized until the Work roll force at stand 10b has increased sufficiently to bring the load on the stand 10c below the first level or until the load on stand 10b has increased sufficiently to actuate load sensing relay Zflb and thereby deenergize input 271) to AND gate 40.

When both the stand 10c and stand lub are at the first level, the control tries to increase the load on stand lfm. An AND gate 43 receives ythe first level signals 2lb and 21C from stands 10b and 10c and energizes an output 44 whenever both stand 10b and stand libc' are at the first level. Output 44 energizes one input of an AND gate 45 and a complement first level signal 27a from stand lila energizes another input of AND gate 45. When both stand 10b and stand we are at the first level and stand 10a is below the first level, AND gate 45 energizes its output 46 in a polarity to reduce reference bias signal 36a and thereby increase the load on stand lila.

An AND gate 48 receives a first level signal 21a from stand 1Gb and signal 44 from AND gate 43 and energizes an output 49 whenever the stands 10a, 10b, an-d 10C are at level one. Output 49 operates an alarm that tells the mill operator that each stand is operating at the first level. The mill operator may consider some corrective action not provided by this control, or he may allow the mill to operate without change since the motors l2 still have capacity for increased load up to the second level.

Preferably, gates 40, 43, 45 and 48 comprise static logic devices. If desired, the gates may comprise contacts on electromechanical relays 20, 22. AND gate 4U may comprise the series combination of a pair of normally open contacts on the relay 20c of stand lfc and a pair of normally closed contacts (indicated by NOT gate 28) on the relay 2Gb of stand llflb. AND gate 43 m-ay comprise a pair of normally open contacts on each first level relay 24M), Zflc, of stands 10b, llttc. AND' gate 45 may comprise the series combination of a pair of normally closed contacts on the relay 20a of stand lila, a pair of normally open contacts on relay Ztlb of stand 10b, and a pair of normally open contacts on the relay 20c of the stand lila'. AND gate 4S may comprise the series cornbination of a pair of normally open contacts on each relay 20 of stands 10a, 10b, llflc.

The control of this invention and the automatic gauge control will maintain the desired gauge without overloading any of the motors until the load on the last stand in the Aautomatic gauge control reaches the second level. Output 23 of the second level sensing relay 22 of the last gauge controlling stand operates an alarm that tells the mill operator that this stand is operating near its maximum load. The operator may elect to let the mill run and to rely on safety devices to protect the motor, or he may elect other procedures not provided by this control.

The sequence that thas been described of shifting the load backwards in the reverse order of the reducing stands is somewhat arbitrary and the AND gates 4), 43, 45 and 48 may be connected to shift the load backwards in any desired sequence.

As the control has been described so far, the tirst level s-ignal is used for the two independent lfunctions of estabylishing the portion of the load that Jche control shifts forward .and establishing the level at which the stand is isolated from the backward shift of the load. If desired, a stand (except the last stand with automatic gauge control) may be provided with two load responsive relays where the single relay l is illustrated. One would provide reset input signal 27 to limit the forward shift of the load and one would provide the complementary signals 21 and Z7 to control the backward shift of the load.

This description of the invention will suggest to those skilled lin the art a variety of devices that rare suitable for the functional boxes shown in the drawing and variations in the relation of the components within the spirit of the invention and the scope of the claims.

Having now particularly described and ascertained the nature of our said invention and the manner in which it is to be performed, we declare that what we claim is:

1. A control for a selected -last stand and a plurality of preceding stands, all with automatic gauge control, in a metal rolling mill, comprising,

means connected to sense the work roll drive motor load of each of said stands to produce a first signal for each of said preceding stands when the motor load is at or above a preset irst level and to produce a second signal for each of said stands when the load is at or above .a preset second level,

flip-Hop means for each of said preceding stands connected to be set by said second signal 'and to be reset by the complement of said rst signal of the associated stand, means for each of said preceding stands connected to respond to the output of the flip-op of the associated stand and the complement of the second signal of the next stand in the direction of rolling to produce a binary control signal, and

integrator means for each of said preceding stands connected to respond to the control signal of the associated stand and to operate on the automatic gauge control to reduce the motor load -at the associated stand to below said `first level after the load rises to the second level. y2. A control for a selected last reducing stand and a plurality of preceding stands, all with automatic gauge control, in a metal rolling mill, comprising,

means for each lof said stands connected to sense the load -on the -work roll drive motors and to produce a signal when the motor load at the associated stand reaches a preset level, said load sensing means on each of said preceding stands having a ip-ilop connected to Ibe set when the motor load reaches a preset relatively higher level and to be reset when the load reaches a relatively lower level, means for each of said preceding stands connected to respond to the signal of the associated stand .and the complement of the signal from the next stand -in the direction of rolling to produce a control signal, and

means responsive to said control signal to operate on the automatic gauge control of the -associated stand to reduce the load on the Iassociated stand by a preset amount.

3. A control for -a selected last reducing stand and a plurality of preceding stands, all with automatic gauge control, in .a metal rolling mill, comprising,

load sensing means for each of said stands connected to sense the work roll drive motor load and to produce a iirst signal when the load rises to a rst preset level,

each said load sensing means for said preceding stands produces a second signal when the motor at the associated stand reaches a second level that is higher than the associated rst level,

means responsive to said first level signal .from said last stand and to the complement of said :first level signal from a irst of said preceding stand when said last stand is at or above its rst level and said rst preceding stand is below its yfirst level, and

means responsive to the complement of said iirst signal of a second of said preceding stands and said rst signals of said rst and last stands to shi-ft part of the load on said last stand to said second preceding stand when said -irst preceding stand and said last stand are at or above said iirst level Iand said second preceding stand is below said first level,

means for each said preceding stand for operating on the automatic gauge control of the associated stand to shift the load forward from the associated stand when its load reaches its second level, said means -for shifting the load forward comprising a flip-flop that is connected to be set by `the associated second signal and to be reset by the comple- -ment of the .associated first signal, and

an integrator connected to receive Ian output of said flip-flop to increase the reference thickness at the associated stand until the load at the associated stand has fallen below its rst level.

4. A control according to claim 3 in which said means that operates to shift the load forward includes -a logic gate for each of said preceding stands, each gate being connected to receive an output from the Hip-flop of the associated stand and each except the next to said last being connected to receive a complementary signal from the flip-flop of the next preceding stand in the direction of rolling, the flip-flop 4of said next to the last stand being connected to receive the complement of the second level signal of said last stand, whereby each said gate energizes the associated integrator only when the associated stand is at or above its second level and the next stand in the direction of rolling is not at its second level or operating to shift the load forward.

References Cited by the Examiner UNITED STATES PATENTS 1,969,536 8/1934 Winnie. 2,752,545 `6/ 1956 Halter 3118-7 2,933,626 4/1960 Giboney et al. 318-6 X 2,972,268 2/1961 Wallace et al 318-6 X `2,972,269 2/ 1961 Wallace et al. 3118-6 X 3,078,746 2/1963 Dirth et al. '318-6 X 3,160,802 12/1964 Obell 318-7 FOREIGN PATENTS 1,222,878 6/ 1960 France.

438,690 111/ 1935 Great Britain. 716,488 l-2/ 1941 Germany.

ORI'S L. RADER, Primary Examiner.

Claims (1)

1. A CONTROL FOR A SELECTED LAST STAND AND A PLURALITY OF PRECEDING STANDS, ALL WITH AUTOMATIC GAUGE CONTROL, IN A METAL ROLLING MILL, COMPRISING, MEANS CONNECTED TO SENSE THE WORK ROLL DRIVE MOTOR LOAD OF EACH OF SAID STANDS TO PRODUCE A FIRST SIGNAL FOR EACH OF SAID PRECEDING STANDS WHEN THE MOTOR LOAD IS AT OR ABOVE A PRESET FIRST LEVEL AND TO PRODUCE A SECOND SIGNAL FOR EACH OF SAID STANDS WHEN THE LOAD IS AT OR ABOVE A PRESET SECOND LEVEL, FLIP-FLOP MEANS FOR EACH OF SAID PRECEDING STANDS CONNECTED TO BE SET BY SAID SECOND SIGNAL AND TO BE RESET BY THE COMPLEMENT OF SAID FIRST SIGNAL OF THE ASSOCIATED STAND, MEANS FOR EACH OF SAID PERCEDING STANDS CONNECTED TO RESPOND TO THE OUPUT OF THE FLIP-FLOP OF THE ASSOCIATED STAND AND THE COMPLEMENT OF THE SECOND SIGNAL OF THE NEXT STAND IN THE DIRECTION OF ROLLING TO PRODUCE A BINARY CONTROL SIGNAL, AND INTEGRATOR MEANS FOR EACH OF SAID PRECEDING STANDS CONNECTED TO RESPOND TO THE CONTROL SIGNAL OF THE ASSOCIATED STAND AND TO OPERATE ON THE AUTOMATIC GAUGE CONTROL TO REDUCE THE MOTOR LOAD AT THE ASSOCIATED STAND TO BELOW SAID FIRST LEVEL AFTER THE LOAD RISES TO THE SECOND LEVEL.

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