US2342767A - Control system - Google Patents

Description

Feb. 29, 1944. G. a sToLTz CONTROL SYSTEM Filed Feb. 21, 1942 INVENTOR GZen/zEStoZZz.

Patented Feb. 29, 1944 CONTROL SYSTEM- Glenn E. Stoltz, Pittsburgh, Pa.,

assignor to Westinghouse Electric Manufacturing Company,

a corporation of Pennsyl- East Pittsburgh, PL,

vania Application February 21, 1942, Serial No. 431,886

14 Claims.

My invention relates, generally, to control systems and, more particularly, to systems Ior controlling steel strip rolling mills.

In the operation of steel strip rolling mills, it is necessary that the mill speed be reduced very considerably when the end of a new coil of strip is threacied through the mill ln order to enable the strip to be properly threaded into the mill rolls. In the operation of tandem strip rolling mills, it has been the practice to slowthe mill down to such a speed that the rolls of the last roll stand are rotating at the desired threading speed. Since the speeds o: all of the roll stands are varied simultaneously and since the speeds of th stands ahead of the last roll stand decrease progressively toward the nrst roll stand. when the speed of the mill is so decreased as to produce the desiredthreading speed on the last roll stand, the speeds of the preceding roll stands are very low and the time, required for threading the end of strip through the several roll stands is very long.

It is an object of my invention to provide a control system for a tandem strip rolling "mill which shall function to so control the mill as to permit threading of the mill in a minimum length of time.

Another object of the invention is to provide a control system for a tandem strip rolling mill which shall function automatically to provide the desired threading speed for each succeeding roll stand as the end of a strip which is being threaded through the mill approaches each of, the stands.

' These and other objects and advantages will be apparent from the following detailed description taken in connection with the accompanying drawing, the single figure of which isa diagrammatic representation of a tandem strip rolling mill contro1 system embodying the principal features of the invention.

In practicing the invention, a main generator 2 is connected to energize a main bus comprising conductors 4 and 6 from which the armatures of the motors 0, I0, I2, and 14 receive their energization. The motors 8, l0, I2, and H drive reducing roll stands ls, I8, 20, and 22 of a continuous strip rolling mill. The excitation of the main generator 2 may be varied by a Variable resistor 24 driven by a motor 20 tc thereby vary the speeds of the motors 8, I0, I2, and I4 simultaneously. lZhe motor 26 is controlled by a. reversing circuit contro1 device 28, which, in turn, is controlled by load responsive relays 30, 32, and 34, and speed responsive pilot generators 36, 30, 40, and 42 under the control of a. circuit control device 44.

Considering the invention more in detail, the reversing circuit control device 20 may be controlled by the selective operation of a pair of potential responsive relays 46 and 48 through their contact elements' and 52, respectively. When the relay 46 is actuated and its contact element b0 is in th upper circuit closing position, an energizing circuit for the rheostat motor 26 is completed extending from positive potential through conductors 54 and 56, the contact element 50, conductors 58 and 60, the armature of the rheostat motor 26, conductors 62 and 64, the contact element 52, and conductors 66 and 68 to negative potential. When the relay 46 is released and the relay 40 is actuated, an energizing circuit of reversed pciarity is completed for the rheostat motor ru extending from positive potential through conductors 54 and 56, the contact element 52 in the upper circuit closing position, the conductor bz, the armature of the rheostat motor 26, tne conductor 60, the contact element w, and the conductors 66 and 68 to negative potential.

The energizing circuit for the rheostat motor 25 which is completed by the actuation of the relay 46 will cause the rheostat motor to drive the rheostat 24 in such a direction as to decrease the energization of the eld winding 69 of the main generator 2,to thereby decrease the energization r and decelerate the motors 8, l0, 12, and l4'. When the relay 48 is actuated, the energizing circuit for the rheostat motor 26 controlled thereby will cause the rheostat motor to actuate the rheostat 24 in such a direction as to increase the energization of the held winding 69 of the main generator 2 to thereby accelerate the motors 8, l0, l2, and l4.

The relays 30, 32, and 34 are potential responsive relays connected to respond to the potential drops across shunt members '10, '12, and 14 which areconnected in the energizing circuits of the motors 0, l0, and lz, respectively. Time-delayed pickup relays "u, 13, and 15 are disposed to be connected in an energizing circuit by the actuation of the relays 30, 32, and 34. When the contact element lb of the relay ll is inthe lower circuit closing position and the contact elements '18, 80, and 82 of the circuit contro1 device 44' are in the left-hand position opposite to the position shown in the drawing, the pilot generator 36 will be connected to energize the relay 46. in a circuit extending irom one terminal of the generator 36 through conductor 84, a resistor 85, a conductor 86, the contact element 16 of the relay "H, conductors 81 and 88, the contact element 18, a conductor 90, a Variable resistor 92, a conductor 94, the winding of the relay 46, conductors 96 and 98, and a conductor 100 to the other terminal of the generator 36. The Variable resistor 92 may be adjusted so that its effective resistance value will be such as to cause the relay 46 to pick up when the speed of the mill motor 8 is above the desired threading speed, and to be released when 4 the rheostat 24 has caused the motor 8 to be decelerated to the desired threading speed.

When the end of a strip of material ll which is being threaded through the mill enters the roll stand IG, there will be a very considerable increase in the load current of the motor 8, and this will cause the relay 30 to pick up to, in turn, cnergize the relay H. After the time delay for which the relay H is calibrated or adjusted, the contact element 16 of the relay 'Il will be moved from the lower circuit closing position to the upper circuit closing position to disconnect the relay 46 from the pilot generator 36 and to connect the relay 46 to be energized by the pilot generator 38 ln a circuit which extends from one terminal of the pilot generator 38 through a conductor l02, a resistor l03, a conductor l04, a contact element l of the relay 13 in the lower circuit closing position, conductors l06 and'l08, the contact element 16, the conductor 88, the contact element '18, the conductor 90, the Variable resistor 92, the conductor 94, the winding of the relay 46, and conductors 96, 98, and ll0 to the other terminal of the pilot generator 38.

When the relay 46 is energized by the pilot generator 36, it will cause the rheostat 24 to further decrease the excitation and, therefore, the output potential of the main generator 2 to decelerate the motors 8, l0, I2, and I4 until the speed of the motor l0 has decreased to the desired threading speed. at which time the output potential of the pilot generator 38 will nave been decreased to where it is insuiilcient to further maintain the relay 46 actuated. When the end of the strip l0l enters the roll stand I8, the additional load on the motor l0 will cause the relay 32 to pick up and, in turn, energize the relay 13. After the interval of time for which the relay 13 is calibrated or adjusted, its contact element l05 will be picked up to disconnect the relay 46 from the pilot generator 38 and connect it to be energized by the pilot generator 40 in a circuit Which extends from one terminal of the generator 40 through a conductor M2, a resistor ll3, a conductor Il4, a contact element M5 of the, relay 15, conductors M6 and 8, the contact-element l05, the conductor ios, the contact element 16, the conductor 68, the contact element 18, the conductor 90, the Variable resistor 92, the conductor 94,'the winding of the relay 46, and conductors 96, 98, and l20 to the other terminal of the generator 40. The actuation of the relay 46 will again cause the motors 8, l0, l2, and l4 to be decelerated until the speed of the motor l2 is such as to provide the desired threading speed of the roll stand 20, at which time the decreased potential of the pilot generator 40 will permit the relay 46 to be released.

When the end of the strip l0l enters the roll stand 20, the relay 34 will pick up to energize the time delay relay 15. After the time interval for which the relay 75, is calibrated, its contact element l I5 will be moved to the upper circuit closing position to connect the pilot generator 42 to energize the relay 46 in a circuit which extends from one terminal' of the generator' 42, a conductor i22, a resistor l23, a conductor I24, the contact element IIS, the conductor M8, the contact element l05, the conductor l08, the contact element 16, the conductor 86, the contact element 18, the conductor 00, the Variable resistor 92, the conductor 94, the winding'of the relay 46 az i conductors 96 and 98 to the other terminal of the generator 42. The relay 46 will thus pick up to cause the deceleration of the motors 8, l0, l2,

and M until the motor 14 is running at such a speed as to provide the desired threading speed r of the reducing rolls of the roll stand 22, at which time the pilot generator 42 will no longer maintain the relay 46 actuated, and the relay 46 will be permitted to drop.

After the strip loi has been threaded through the mill, the motors 8, l0, l2, and l4 may be accelerated to the normal running "speed of the mill by moving "the contact elements 18, 80, and 82 of the circuit control device 44 to the right-hand position shown in the drawing. When in the circuit closing position, the contact element 82 will close an energizing circuit for the lower winding of the relay 48 extending from positive potential through a conductor l25, the contact element 82, a conductor l26, a lower winding of the relay 40, a conductor l28, a calibrating resistor l30, and a conductor i32 to negative potential. The relay 48 will thus be actuated to cause the rheostat motor 26 to actuate the rheostat 24 in such a direction as to increase the output potential of the main generator 2 and thereby accelerate the motors 8, I0, 12, and I4. The upper winding of the relay 48 is connected to oppose the lower winding and is energized by the pilot generator 36 when the contact element 80 is moved to circuit closing position in a circuit which extends from one terminal of the generator 36, through conductors 84 and 86', the contact element 80, a conductor l34, a calibrating resistor [36, a conductor l38, the upper winding of the relay 48, and conductors 96, 98, and (00 to the other terminal of the generator 36. When the mill hasbeen accelerated to the desired normal running speed, the output potential of the pilot generator 36 will have increased to such a degree that its energization of the upper winding of the relay 48 will be sumcient to counteract the energization of the lower winding of the relay 48 and cause this relay to be released, thus deenergizing the rheostat motor 26 and discontinuing the acceleration of the mill.

It is to be understood that the upper winding of the relay 40 may be connected by the circuit control device 44 to be energized by any of the pilot generators 38, 40 and 42 instead of the generator 36 as described hereinbefore, to thereby control the speed of the mill in accordance with the speed of any desired one of the roll stands.

It is to be understood that limit switches or other equivalent devices Which will respond to the position of the end of the strip which is being threaded through the mill, may be used iu the place of the load relays 30, 32, and 34 andtheir associated time-delayed relays H, 13 and 15 to connect succeeding ones of the pilot generators 38, 40 and 42 to control the decelerating relay 46.

It is also to be understood that the Variable resistor 92 may be adjusted so as to make the relay 46 responsive to any desired threading speed at the several roll stands. It is also to be understood that the calibrating resistors [30 and l36 may be so adjusted as to cause the mill to be acceierated to any desired normal running speed. The time-delayed-release relays H, 13 and 15 'may be adjusted to pick up at a suii'icient interval of time after the entry of the end of the strip i0l into the roll stands with which each of these relays are, associated to permit the system to decelerate the mill until the next roll stand into which the end of the strip is to be threaded-has been decelerated to the desired threading speed. The Variable resistors 85, l03, 3, and l23 are provided as calibrating resistors so that dierent prcvided at each of the erated until the rolls of the roll stand l8 are running at the desired threading speed. At a predetermined interval after the strip has entered the roll stand IB, the mill will be decelerated until the rolls of the roll stand are running at the desired threading speed. At a predetermined interval after the strip has entered the roll stand 20, the mill will be decelerated until, the rolls of the roll stand 22 are rotating at the desired threading speed. With the mill thus threaded. it may be accelerated to the normai running speed by moving the circuit control device to the right-hand position shown in the drawing, and the system will automatically accelerate the mill to normai running speed, as explained hereinbefore.

Thus, a considerable saving inthe time required to thread a strip rolling mill is made by the system sincenone of the reducing rolls are decelerated below their desired threading speed until the end of the strip which is being threaded through the mill has passed through the preceding roll stand and it is necessary to decelerate the next roll stand to the desired threading speed.

Thus, it will be seen that I have provided a control system for a tandem strip rolling mill which shall function to automatically provide the desired threading speed for each succeeding roll stand as the end of a strip which is being threaded through the mill approaches each of the stands and which will thus function to permit threading of the mill in a minimumlength of time.

In compliance with the requirements of the patent statutes, I have shown and described herein a preferred embodiment of my invention. It is to be understood, however, that the invention is not limited to the precise construction shown and. described but is capable of modification by one skilled in the art, the-embodiment herein shown being merely illustrative of the principles of my invention.

I claim as my'invention:

l. In a control system fora motor driven strip rolling mill, a main generator to which the mill motors are connected for energization, and means responsive to the speeds of the successive motors and theposition of the end of the strip with respect to successive roll stands for automatically controlling the potential of the'generator to provide the desired threading speed at each succeeding roll stand as the end of a strip which is being threaded through the mill approaches each succeeding roll stand.

2. In a control system for the drive motors of a delayed relay means responsive to the entry of the end of a strip which is being threaded through the mill into one roll stand, means responsive to the speed of the drive motor for the next succeeding roll stand, and means responsive to said relay means and said speed responsive means for varying the speeds of the drive motors.

4. In a control system for the drive motors of a motor driven tandem strip rolling mill, time delayed relay means responsive to the entry of the end of a strip which is being threaded through the mill into one roll stand, means responsive to the speed of the drive motor for the next succeeding roll stand, and means responsive to said relay means and said speed responsive means for reducing'the speeds of the drive motors sufficiently by the time the end of the strip reaches the said succeeding roll stand to provide the desired threading speed for the v said succeeding roll stand.

motor driven tandem strip rolling mill, means for varying the speed of the drive motors, and means 1 responsive to the speed of the drive motor associated with one roll stand and the entry of the end of a strip which is being threaded through the mill into the preceding roll stand for varying the speeds of the drive motors associated with the roll stands.

3. In a control system for the drive motors of a motor driven tandem strip rolling mill, time 5. In a control system for the drive motors oi a motor driven tandem strip rolling mill, relay means associated with each roll stand beyond which there is a succeeding .roll stand in the direction of travel of a strip which is being threaded through the mill and responsive to the entry of the strip into the associated roll stand, speed responsive means associated with each of the roll stands succeeding the fini; rc-ll stand, and means responsive to each relay means and the speed responsive device associated with the succeeding roll stand for reducing the speeds of the drive motors sumciently to provide the desired ihre-riding speed for the said succeeding roll stand.

6. In a control system for the drive motors cf a motor driven tandem strip rolling mill, time delayed relay means associated with each roll stand beyond which there is a succeeding roll stand in the direction of travel of a strip which is being threaded through the mill and responsive to the entry of the strip into its associated roll stand. means responsive to the roll speed of each of the roll stands succeeding the first roll stand, and means responsive to said time delayed relay means and the speed responsive device associated with the succeeding roll stand for reducing the speeds of the drive motors sufficiently by the time the end of the strip reaches the said succeeding roll stand to provide the desired threading speed for the said succeeding roll stand.

7. In a control system for the drive motors of a tandem strip rolling mill, means for controlling the speeds of the drive motors simultaneously, means responsive to speed of the rolls of each of the roll stands, means whereby each speed responsive means controls the speed controlling means when connected for such control, means for connecting the speed responsive means associated with the first roll stand to control the speed control means, and means responsive to the entry of the end of a strip which is being threaded through the mill into actuating said decelerating means until the speed of the first roll stand has been reduced to the desired threading speed for that roll stand, means responsive to the entry of the strip into any roll stand which has a succeeding roll stand and the speed of the succeeding roll stand for actuating the mill decelerating means until the speed of the said succeeding roll stand has been reduced to the desired threading speed for that roll stand, and control means responsive to the speed of one of the roll stands for causing said accelerating means to accelerate the mill to normal running speed.

9. A control system for a tandem rolling mill having a plurality of motor-driven roll stands disposed to operate upon a strip of material, means for collectively varying the speeds of the motor-driven roll stands over a predetermined speed range between threading and normal running speeds, and electro-responsive control means operatively associated 'with the motordriven roll stands for controlling the operation of the speed varying means, said electro-responsive means being operable to effect successive reductions in the speeds of the roll stands in response to the entry of the end of the strip of material into a preceding roll stand and the speed of the next succeeding roll stand, thereby to provide for progressively reducing the speeds of the roll stands during a threading operation.

10. A control system for a tandem rolling mill having a plurality of motor-driven roll stands disposed to operate upon a strip of material, a main generator to which the driving motors are connected, means for varying the voltage of the main generator to simultaneously Vary the speeds of the motors, and control means jointly responsive to a predetermined increase in the load of one motor and the speed of the next succeeding motor for controlling the operation of the voltage varying means, thereby to eiect successive reductions in the speeds of the roll stands as the leading end of the strip of material approaches each succeeding roll stand.

11. In a control system for the driving motors of a tandem rolling mill having a plurality of roll stands disposed to operate on a strip of material, a source of- Variable-voltage power for the motors, means operable to Vary the voltage of the power source to simultaneously vary the speeds of the motors between threading to normal running speeds, control means associated with each roll stand operable when connected to the voltage control means to reduce the speed of its associated roll stand to a desired threading speed and to eifect a corresponding reduction in the speeds of the other roll stands, manually operable means for connecting the voltage control means to the control means of the rst roll stand, and additional control means associated with each roll stand except the last roll stand operable in response tc tne entry of the leading end of the strip into the associated roll stand to transfer the connection of the voltage control means 'to the next succeeding control means, thereby to provide for reducing the speeds of the roll stands to the desired threading speed at each succeeding roll stand.

12. In a control system for the driving motors of a tandem rolling mill having a plurality of roll stands disposed tc operate on a strip of material, a source of Variable voltage power for the motors, means for controlling the voltage of the power source to simultaneously Vary the speeds of the motors, a pilot generator driven in accordance with the speed of each roll stand and operable when connectzd to the voltage control means tc cause said means to reduce the speed of all the roll driving motors a predetermined amount from their normal running speeds, switch means operable to connect the pilot generator of the first roll stand to the voltage control means to effect a predetermined reduction in the speed of the nrst roll stand 'to a desired threading speed and corresponding reductions of the speeds of the succeeding roll stands, and means associated with each roll stand except the last roll stand operable in response to theentry of the strip of material therein to connect the voltage control means to be responsive to the pilot generator of the next succeeding roll stand, thereby to effect successive reductions in the speeds of the roll stands as the end of the strip approaches each succeeding roll stand during a threading operation.

13. In a control system for the driving motors of a tandem rolling mill having a plurality of roll stands disposed to operate on a strip of material, a source of variablevoltage power for the motors, means for controlling the voltage of the power source to simultaneously Vary the speeds of the motors, a pilot generator driven in accordance with the speed of each roll stand and operable when connected to the voltage control means to cause said means to reduce the speed of all the roll driving motors a predetermined amount from their normai running speeds, switch means operable to connect the pilot generator of the first roll stand to the voltage control means to'.

eifect a predetermined reduction in the speed of the ilrst roll stand to a desired threading speed and corresponding reductions of the speeds of the succeeding roll stands, and load-responsive relay means associated with each drive motor except the last drive motor operable in response to the entry of the end of the strip into its associated roll stand to transfer the connection of the voltage control means to the pilot generator of the next succeeding roll stand, thereby to eiect successive reductions in the speeds of the motors as a group as the end of the strip approaches each succeeding roll stand during a threading operation. v

14. In a control system for a tandem rolling mill or the like, having a plurality of roll stands disposed to operate upon a. strip of material and a motor connected to drive each roll stand, a main generatorfor supplying Variable voltage power to the motors, a motor-operated rheostat operable to Vary the voltage of the main generator, relay means selectively operable to control the operation of the motor-operated rheostat, a pilot generator connected tc each roll stand operable to develop a voltage in accordance with the speed of the associated roll stand, a load responsive relay connected to each drive motor except the drive motor of the last roll stand, a timedelay relay controlled by each load-responsive relay, said load-responsive relays, timerdelay relays and pilot generators being electrically interconnected and connected to the relay means for controlling the operation of the motor-operated rheostat to eect a progressive reduction in the speeds of the roll stands as the leading end of the strip of material passes through the mill, whereby the desired threading speed at each roll stand is obtained before theleading end of the strip enters the rolls.

GLENN E. STOLTZ.

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