US3109330A

US3109330A - Continuous mill control means

Info

Publication number: US3109330A
Application number: US51586A
Authority: US
Inventors: Richard W Barnitz; John F Mccarthy
Original assignee: Jones and Laughlin Steel Corp
Current assignee: Jones and Laughlin Steel Corp
Priority date: 1960-08-24
Filing date: 1960-08-24
Publication date: 1963-11-05
Anticipated expiration: 1980-11-05

Description

1963 R. w. BARNITZ ETAL 3,109,330

CONTINUOUS MILL CONTROL MEANS Filed Aug. 2.4, 1960 INVENTORS Richard W. Bornitz 8 John F. McC'Orthy B Ma ATTORNEY 000 0 Ooomooo .l l 1 ooooooo Nu mm #0 no 8. 3.2.0

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United States Patent 3,109,330 CONTINUOUS MILL CONTROL MEAN Richard W. Barnitz and John F. McCarthy, Pittsburgh, Pa., assignors to Jones & Laughlin Steel Corporation, Pittsburgh, Pa a corporation of Pennsylvania Filed Aug. 24, 1960, Ser. No. 51,586 4 Claims. (Cl. 8tl-35) This invention relates to apparatus for rolling hot metal slabs and the like at high speed to minimize gage variations between the leading and trailing portions of the rolled product. More particularly, the invention relates to a rolling procedure wherein the rolling mill is initially operated at a relatively low speed to permit the forward end of the rolled product to pass over a run-out table and become attached to a coiler, followed by an increase in the speed of the mill to minimize the required rolling time.

Although not limited thereto, the present invention is particularly adapted for use with continuous hot strip mills. In such mills, a steel slab or the like is first heated to the proper rolling temperature and thereafter conveyed through one or more scalebreakers and roughing stands to a plurality of tandem finishing stands where the metal is progressively rolled to the final gage. As the rolled strip proceeds from the last tandem finishing stand, it is carried over a long table, called the run-out table, which consists of individually driven rollers having a plurality of water sprays positioned overhead to cool the strip as it passes thereby. From'the run-out table, the strip is fed to a coiler where it is wound into coils for shipment or further processing.

In a continuous hot strip mill of the type described above, gage variations normally occur between the leading and trailing portions of the rolled product. That is to say, the gage will usually be greater at the trailing portion of the strip. One of the primary causes of gage variation is the temperature dillerential along the length oi the strip. As the slab is rolled, it continuously cools, meaning that the trailing portion of the strip to be rolled will be cooler and less ductile than the forward portion. This, of course, results in a gradual increase in gage along the length of the strip.

Gage variations due to the aforesaid temperature differential may be minimized by increasing the speed of the rolling mill. Previous to this invention, however, continuous hot mills were normally operated at a constant speed throughout the rolling operation; and this speed was limited primarily by the permissible entry speed of the strip into the coiler. As was mentioned above, the forward end of the rolled strip, after leaving the last finishing stand, passes over a run-out table before being directed into a coiler which automatically grips the end of the strip and places it under tension. As the strip passes over the run-outtable before being attached to the coiler, it is efiect-ivelypushed from behind by the rolling mill while its forward end is tree, the result being that if the speed of the mill istoo great the-strip'will buckle and possibly run off the table before being attached to the coiler. This problem is particularly acute in thecase of strip of narrow width such as skelp used in the manufacture of seam welded tubular products. j

Thus, the speed of prior art rolling mills, being constant during the entire rolling procedure, was determined by the maximum permissible coiler entry speed, notwithstanding the fact that this speed might be below the maximum speedof the mill where the gage variation referred to above could be minimized.

As a primary object, the present invention provides apparatus for continuously rolling hot strip wherein temperature and gage variations between the leading and trailing portions of the strip are minimized.

3,109,339 Patented Nov. 5, 1963 Another object of the invention is to provide a system of the type described above in which the speed of the rolling mill is initially maintained at a relatively low value to facilitate entry of the end of the strip into the coiler and thereafter increased to minimize the required rolling time.

In accordance with the invention, hereafter described, the rolling mill is initially operated at a low speed until the forward end of the strip passes over the run out table and is fed into the coiler. Thereafter, when the forward end of the product is attached to the coiler and the problem of guiding the free end of the strip is no longer present, the mill speed is increased to decrease the amount of time required to roll an entire slab and thereby minimize any gage variations along the length of the strip. As will be understood, this procedure also allows larger and heavier slabs to be rolled since the cooling time is reduced.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying single FIGURE drawing which schematically illustrates the operation of the invention.

Referring now to the drawing, which is for the purpose of illustrating an embodiment of the invention and not for the purpose of limiting the same, a heated steel slab 10 on conveyor 12 is first passed through one or more roughing stands, schematically illustrated at 14, to a scalebreaker 16. From the scalebreake-r 16 the slab 10 is passed through a plurality of tandem finishing stands S1-S6, it being understood that only three stands S1S2 and S6 are shown herein. Each of the finishing stands 81-86 is provided with an individual direct current drive motor, the drive motor for stand S1 being indicated at M1 and the drive motor for stand S6 being indicated at M6. Motors M1 and M6, as well as the motors for the other stands, are provided with external control windings 18 which are connected to motor control circuits, generally indicated at 20. The motors M1 and M6 are also provided with series windings 22 and are connected to indi vidual direct current generators G1 and G6, respectively. As will be understood, the various drive motors for the other finishing stands are also provided with their direct current generators. Generators G1 and G6 are driven by three-phase alternating-current motors A1 and A6, respectively, substantially as shown. The generators G1 and G6 are also provided with field windings 24 which are connected to individual generator control circuits, indicated at 26. The generator control circuits 26 for each mill stand are, in turn, connected to a master pilot regulator circuit 28, the arrangement being such that the output of regulator 28 will control the fields produced by windings 24 and, hence, the output voltages or generators G1, G6 and the generators, not shown, associated with the other stands. The output of the master pilot regulator 28 is controlled by a potentiometer 3b which is connected through mechanical linkage 32 to a pilot motor 34. With this arrangement, when the motor 34 rotates, it will vary the position of the movable contact on the potentiometer 30 whereby the output voltages of the generators G1 and G6 will be varied to regulate the speed of motors M l M6. After the leading end of the rolled strip passes through the last finishing stand S6, it must travel over a run-out table 36 before being deflected by a deflector 38 into a coiler 40. Above the run-out table 36 are a plurality of water sprays 42 which cool the strip as it passes thereby. The coiler 40, well known in the art, automatically grasps the end of the strip and thereafter rotates to place the material in tension. However, when the forward end of the strip initially passes through stand S6, it must be pushed over the run-out table 36 by the metal following it until said end reaches the coiler 40 where it may be grasped to place the strip under tension. If the speed of the rolling mill is too great during the time that 3 v the forward end of the strip passes over run-out table 36, it may buckle or possibly run off the table. Consequently, during this time, the speed of the mill must be adjusted whereby the end of the strip may be successfiully guided onto coiler 40.

As was explained above, most prior art rolling mills were normally operated at a constant speed throughout the rolling operation. Since the slab 10 will cool down during rolling, the latter part of the slab which is rolled 'is cooler and less ductile than the first part to be rolled,

resulting in a gradual increase in gage along the length of the strip. This variation in gage may be minimized by increasing the speed of the mill, but if the mill is operated at a constant speed, in accordance with previous practice, this speed is limited by the maximum permissible entry speed of the strip into the coiler 40.

In accordance with the present invention, the rolling mill comprising stands S1, S6, etc., is initially operated at a relatively low speed until the end of the strip passes over the run-out table 36 and-is attached to the coiler 4t I of the circuit whereby the field produced by winding 76 is at a maximum. Output terminal82 of amplidyne 72 may be connected to one side of the pilot motor 34 through the normally closed contacts 84 of a mill down normally open contacts '92 of relay M'U. In parallel with relay MU is a holding coil MDH for relay MD; and, similarly, in parallel with relay MD is a holding coil MUH for relay MU. With this arrangement when relay MU is energized, for example, coil MDH will lock relay MD in its deenergized position wherein contacts 84 are closed and contacts 9% are open. Similarly, when relay MD is energized, holding coil MUH will hold relay MU in deenergized condition wherein contacts 86 are closed Thereafter, the speed of the mill is increased to minimize the time required for the slab 10 to pass through the'mill and thereby reduce any variation in gage between the leading and trailing portions of the strip. To effect this procedure, circuit means including load relays lLR and and 6LR are provided. Load relay lLR is connected in shunt with the series field winding 22 for motor M1 and will be energized when the load on this motor increases. That is, it will be energized when the leading end of the slab initially passes through stand S1. Similarly, a load relay 6LR in shunt with the series winding 22 for motor M6 will be energized when the load on motor M6 increases due to passage of the forward end of the strip through stand S6. Of course, when the trailing end of the strip passes through stands S1 and $6, the load relays lLR and 6LR, respectively, will become deenergized due to the decrease in the loads on motors M1 and M6.

' Load relay 1LR is provided with a pair of normally open contacts 44 which, when closed, will energize relay lLRX having a pair of normally open contacts 46 and a pair of normally closed contacts 48. When load relay 6LR is energized, it will close its normally open contacts 54) to energize the relay 6LRX having a pair of normally open contacts 52 and a pair of normally closed contacts 54. When relays 6LR and 6LRX are energized due to an increase in the load on motor M6 when the forward end of the strip passes through stand S6, contacts 52 will close to energize a time delay relay T after a predetermined amount of time has elapsed subsequent to the energization of relays 6LR and 6LRX. As will be seen, the time delay of relay T is such that the forward end of the strip will pass over run out table 36 'and become attached to coiler 40 before the relay T becomes energized to close its normally open contacts 58.

Connected across the output terminals of generator 66 is a magnetic amplifier 60 which will produce an output signal to trip relay 62 when the voltage of generator G6 exceeds a predetermined level. age or speed) at which the relay 62 will be energized to close its normally

open contacts

66 and 67 is determined by a manually adjustable potentiometer 64 coupled to the magnetic amplifier 60. Thus, the operator may manually adjust the point at which relay 62 will be energized to close contacts 66.

Referring now to the pilot motor 34, it is provided with an external field winding 68, as well as a series winding 70, and is connected to the output of an amplidyne regulator 72 having a winding 74 magnetically coupled to an external control winding 76. Winding 76, in turn, is connected. through resistor 78 to a manually adjustable potentiometer 30, the arrangement being such that the' operator may manually adjust the field produced by winding 76 and, hence, the output voltage of amplidyne 72. It will be noted that when contacts 48 of relay lLRX are closed, the potentiometer 80 is effectively shorted out The load (i.e., voltand contacts 92 are open. When relay M-U is energized, contacts 92 will close to complete a circuit betweenterm-inals 88 and 82 of amplidyne 72 through contacts 92 of relay MU, motor 34 and contacts 84 of relay M D. Un-

der these conditions, motor 34 will rotate the movable tap on potentiometer 3th in a clockwise direction as shown in the drawings to accelerate each of the motors M1, M6, etc., associated with the various finishing stands S1-S6. Similarly, when relay MD is energized, contacts 90 will be closed to complete a circuit. from terminal 88 of amplidyne 72, through motor 34 and contacts 86 of relay MU to terminal 82. Now, the movable tap on potentiometer 30 will be rotated in a counterclockwise direction as shown in the drawing to deceleratethe motors M1, M6, 7

etc. When the movable tap on potentiometer 30 rotates to its extreme clockwise position, it will open the normally closed contacts 93 of a limit switch 95. r

The system may be operated either automatically or semi-automatically. -Under automatic operation, the speeds of the stands Sl-S6 willLbe automatically increased when the end of the strip becomes attached to coiler 40. On the other hand, under semi-automatic operation, the point at which the acceleration starts may be controlled manually by the operator. If fully-automatic operation is desired, the switch 91 will be closed and potentiometer 89. As was explained above, the positioning of the tap on potentiometer 80 thus determines the rate of acceleration of the various motors M1, M6, etc.

When the leading edge of the rolled strip enters the roll pass of finishing stand S6, the load on motor M6 will increase to energize load relay 6LR and close contacts 50. Closure of contacts 54) energizes relay 6LRX to close its normally opencontacts 52 and open its normally closed contacts 54. Since contacts 56 are now closed, a circuit is completed to relay T. This relay will be energized to close its contacts 58 after a predetermined amount of time has elapsed subsequent to the energization of relay 6LRX. The time delay of relay T is'chosen'to coincide with the amount of time required for the leading edge of the strip to pass from stand S6 to the coiler 40..

Thus, relay T will not pick up until the end of the strip is in the coiler 40 and attache-d thereto.

When the end of the strip is attached to the coiler 40v and the contacts 58 of relay "T close, acircuit is completed through switch 91, contacts 58, contacts 106 of hold pushbutton switch H, contacts 46 of relay ILRX, which are now closed, and contacts 93 of limit switch 95 to the mill up relay MU, as well as the mill down holding coil MDH. Thus, since relays T and .ILRX are now both energized, relay MU will be energized to close contacts 92 whereby the output of amplidyne 72 is applied to motor 34 to rotate the movable contact on potentiometer 30 in a clockwise direction, the speed of rotation of this movable contact being determined by the position of the contact on potentiometer 80 to control the rate of acceleration of the mill. The mill will accelerate to full speed; whereupon the movable contact of potentiometer 30 reaches its extreme clockwise position to trip limit switch 95 and open contacts 93, thereby deenergizing the mill up relay MU and stopping the motor 34. When motor 34 thus stops, the acceleration of motors M1, M6, etc., is also stopped so that the mill is now operating at maximum speed, this speed being greater than the maximum permissible entry speed of the end of the strip into the coiler 40. Since, however, the speed was not increased until the end of the strip was attached to the coiler, the problem of coiler entry at the high speed is eliminated.

During the main portion of the rolling procedure, the mill will continue to operate at high speed. When the trailing edge of the rolled strip passes through stand 81, the load on motor M1 will fall to deenergize relays lLR and ILRX to open contacts 46 and close contacts 48. With contacts 48 closed, the maximum field will be produced in winding 76 on amplidyne 72 such that, when mill down relay MD is energized, the motor 34 will rotate the movable contact on potentiometer 31 in a counterclockwise d-irection at maximum'speed to produce a maximum rate of deceleration in the motors M1, M6, etc. After the trailing edge of the strip passes through stand S6, the load on motor M6 will fall, thereby deenergizing relays 6LR and 6LRX to open contacts 52 while closing contacts 54. of course, deenergized.

When the motor M6 is at its maximum speed, the relay 62 will be energized through magnetic amplifier 60 to close

contacts

66 and 67. Relay 62 will remain energized until the output of generator G6 falls to a predetermined level, this level being determined by the position of the movable contact on manually adjustable potentiometer 64. Thus, if it is assumed that the trailing end of the strip has just passed through stand 86, motor M6 will still be operating at a high speed so that relay 62 will be energized to close

contacts

66 and 67. Since switch 91 is now closed, a circuit will be completed through contacts 66, switch 91, contacts 54 of relay 6LRX, which is now deenergized, and contacts 104 of pushbutton hold switch H to the mill down relay MD and holding coil MUH. Energization of mill down relay MD then closes contacts 90 while opening contacts 84 to cause motor 34 to rotate the movable contact on potentiometer 3%) in a counterclockwise direction from its extreme clockwise direction where it trips limit switch 95. The movable contact on potentiometer 30 will continue to rotate in a counterclockwise direction until the speed of motors When contacts 52 open, the relay T is, I

opened by the movable contact on potentiometer 30. In this manner, it will be seen that by closing switch 94 the time at which the motors M1, M6, etc., begin accelerating may be delayed under the control of the operator- That is, the motors 'wil not accelerate until the operator has depressed the pushbutton switch 100, notwithstanding the fact that a considerable amount of time may have elapsed since the entry of the strip into the coiler 4%).

Similarly, the time at which deceleration of the motors M1, -M6, etc., occurs, may be controlled by pushbutton switch @102 when the semi-automatic switch 94 is closed. Thus, when switch .102 is momentarily closed, a circuit will be completed through switch 94, contacts 54 of relay 6L-RX, which is now deenergized, and contacts 104 of pushbutton switch H to the mill down relay MD which then closes contacts 90 to rotate motor 34 and the movable contact on potentiometer in a counterclockwise direction. In this latter case, the mill will continue to decelerate until contacts 67 are opened upon deenergization of relay 62 at the speed determined by the position of the contact on potentiometer 64.

The acceleration or deceleration of the mill may be stopped at any point by depressing the hold pushbutton switch H. Thus, during acceleration of the mill, opening of contacts 106 will stop the acceleration process until these contacts again close. Similarly, the deceleration process may be stopped for any period of time by depressing pushbutton switch H to open contacts 104.

It can thus be seen that the present invention provides a method and apparatus for rolling hot strip wherein the speed of the mill is initially maintained at a relatively low 3 value until the forward end of the strip is attached to a Nil-4M6 reaches a point where the relay 62 is deener- For semi-automatic operation of the system, switch 94 a will be closed while switch 91 remains open. Under these conditions, the pilot motor 34 will not he energized to rotate the movable tap on potentiometer '39 in a clockwise direction until the pushbutton switch 160 is closed. After the pushbutton switch 100'is closed and relay MU is energized, the contacts 96 provide a holding circuit which will persist until contacts 93 of limit switch 95 are coiler, and thereafter increased to a higher value to minimize the amount of time required for the strip to pass through the mill.

Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

We claim as our invention:

1. In a multi-stand tandem rolling mill of the type in which each stand is provided with a separate electrical drive motor and a separate generator for that motor together with a master pilot regulator for adjusting the output voltages of said generators and the speeds of said motors; the improvement which comprises first relay means actuable in response to an increase in the load on the drive motor for the first stand of the tandem rolling mill, second relay means actuable inresponse to an increase in the load on the drive motor for the last stand of the tandem rolling mill, third relay means operatively connected to said second relay means and adapted to be actuated when a predetermined amount of time has elapsed after actuation of the second relay means, a device responsive to actuation of said first and third relay means for causing said master pilot regulator to increase the output voltages of said generators and thereby accelerate the respective motors on each stand, fourth relay means actuable when the output voltage of the generator associated with the last tandem rolling mill stand increases above a predetermined level, and means actuable when second relay means is deenergized and the fourth relay means is energized to cause said master pilot regulator to decrease the output voltages of said generators and thereby decelerate the motors on the respective stands of the rolling mill.

2. in a multi-stand tandem rolling mill of the type in which each stand is provided with a separate electrical drive motor and a separate generator for that motor; the improvement which comprises means including an adjustable potentiometer for varying the output Voltages of said generators and the speeds of said motors, a pilot motor for driving said adjustable potentiometer, first relay means actuable in response to an increase in the load on the drive motor for the first stand of the rolling mill, second relay means actuable in response to an increase in the load on the drivemotor for the last stand of the rolling mill, third relay means operatively connected to said relay means and adapted to be actuated when a predetermined period of time has elapsed after actuation of the second relay means, and fourth relay means responsive to actuation of the first and third relay means for causing said pilot motor to adjust the potentiometer whereby the out,- put voltages of said generators and the speeds of said motors are increased.

3. In apparatus for controlling a multi-stand tandem rolling mill of the type in which each stand is provided with a separate electrical drive motor and a separate generator for that motor; the improvement which comprises means including an adjustable potentiometer for regulating the output voltages of said generators and the speeds 'of said motors, a pilot motor for driving said adjustable potentiometer, first relay means actuable in response to an increase in the load on the drive motor for the first stand of the rolling mill, second relay means actuable in response to an increase in the load on the drive motor for the last stand of the rolling mil], third relay means operatively connected to said second relay means and adapted to be actuated when a predetermined amount of time has elapsed after actuation of the second relay means, fourth relay means actuable when the output voltage of the generator associated with the last stand in said tandem rolling mill exceeds a predetermined value, fifth tentiometer whereby the output voltages of the generators and the speeds of the motors are increased, and sixth relay means actuable in response to deenergization of the second relay means and energization of the fourth relay means for causing said pilot motor to drive the potentiometer whereby the output voltages of the generators and the speeds of the drive motors are decreased.

4. In a rolling mill comprising a plurality of stands in tandem, a run-out table at the discharge end ofthe mill and a coiler at the discharge end of the run-out table, drive motors for the stands, and a master pilot regulator for varying the speeds of, the drive motors; the improvement comprising first means actuated when the work 4 enters the last stand, second means actuated in response to actuation of the first means and after the work enters the coiler, third means responsive to actuation of the second means adapted to cause the master pilot regulator to accelerate the drive motors, fourth means actuated when the trailing end of the work leaves the last stand, and fifth means responsive to deactuation of the first means and actuation of the fourth means for causing the master pilot regulator to decelerate the drive motors.

References Cited in the file of this patent UNITED STATES'PATENTS

Claims

1. IN A MULTI-STAND TANDEM ROLLING MILL OF THE TYPE IN WHICH EACH STAND IS PROVIDED WITH A SEPARATE ELECTRICAL DRIVE MOTOR AND A SEPARATE GENERATOR FOR THAT MOTOR TOGETHER WITH A MASTER PILOT REGULATOR FOR ADJUSTING THE OUTPUT VOLTAGES OF SAID GENERATORS AND THE SPEEDS OF SAID MOTORS; THE IMPROVEMENT WHICH COMPRISES FIRST RELAY MEANS ACTUABLE IN RESPONSE TO AN INCREASE IN THE LOAD ON THE DRIVE MOTOR FOR THE FIRST STAND OF THE TANDEM ROLLING MILL, SECOND RELAY MEANS ACTUABLE IN RESPONSE TO AN INCREASE IN THE LOAD ON THE DRIVE MOTOR FOR THE LAST STAND OF THE TANDEM ROLLING MILL, THIRD RELAY MEANS OPERATIVELY CONNECTED TO SAID SECOND RELAY MEANS AND ADAPTED TO BE ACTUATED WHEN A PREDETERMINED AMOUNT OF TIME HAS ELAPSED AFTER ACTUATION OF THE SECOND RELAY MEANS, A DEVICE RESPONSIVE TO ACTUATION OF SAID FIRST AND THIRD RELAY MEANS FOR CAUSING SAID MASTER PILOT REGULATOR TO INCREASE THE OUTPUT VOLTAGES OF SAID GENERATORS AND THEREBY ACCELERATE THE RESPECTIVE MOTORS ON EACH STAND, FOURTH RELAY MEANS ACTUABLE WHEN THE OUTPUT VOLTAGE OF THE GENERATOR ASSOCIATED WITH THE LAST TANDEM ROLLING MILL STAND INCREASES ABOVE A PREDETERMINED LEVEL, AND MEANS ACTUABLE WHEN SECOND RELAY MEANS IS DEENERGIZED AND THE FOURTH RELAY MEANS IS ENERGIZED TO CAUSE SAID MASTER PILOT REGULATOR TO DECREASE THE OUTPUT VOLTAGES OF SAID GENERATORS AND THEREBY DECELERATE THE MOTORS ON THE RESPECTIVE STANDS OF THE ROLLING MILL.