US3213656A

US3213656A - Rolling mill motor speed control apparatus

Info

Publication number: US3213656A
Application number: US255260A
Authority: US
Inventors: John W Cook
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1963-01-31
Filing date: 1963-01-31
Publication date: 1965-10-26
Anticipated expiration: 1982-10-26
Also published as: GB1005058A; JPS4220487Y1

Description

Oct. 26, 1965 J. w. COOK ROLLING MILL MOTOR SPEED CONTROL APPARATUS 4 Sheets-Sheet 1 Filed Jan. 31, 1965 Oct. 26,

Filed Jan J. W. COOK 4 Sheets-Sheet 2 scREwDowN /26 scREwDowN '3 eo Q 24 l /loo /liz l 28 AMPLIFIER .'/26 AMPLIFIER @D30 9 (Wl [L /l24 SPEED SPEED REGULATOR REGULATOR THREAD BUS RUN BUS lNvENToR John W. Cook BYL/ AT'ToRNEwr Oct. 26, 1965 J. w. COOK ROLLING MILL MOTOR SPEED CONTROL APPARATUS Filed Jan. 5l, 1965 4 Sheets-Sheet 5 m. .32 s mmm ...mmm Qmmam STAND Fig. 3

RUN SPEED THREAD SPEED TIME Fig. 5

Oct. 26, 1965 J. w. cooK 3,213,656

ROLLING MILL MOTOR SPEED CONTROL APPARATUS United States Patent O 3,213,656 ROLLING MILL MTR SPEED CQNTRL APPARATUS .lohn W. Cook, Monroeville, Pa., assigner to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed dan. 31, 1963, Ser. No. 255,269 Claims. (Cl. 72-15) The present invention relates in general to motor speed control apparatus and more particularly to motor Speed control apparatus for varying the operative speed of one or more drive motors of a workpiece rolling mill such as the finishing train of a hot strip mill for steel rolling.

In the well known operation of a hot rolling mill having at least one drive' motor, up to the present time, all of the stands of the rolling mill had been threaded at running speeds up to two thousand feet per minute. The workpiece slabs have in the past been of such size that delivered strips about two thousand feet in length have required approximately sixty seconds of elapsed rolling time.

It has recently been contemplated to increase the incoming slab weights to obtain larger and longer coils of rolled strip without the necessity of providing welds between delivered strip portions. It a four thousand foot long strip is delivered from a rolling mill operating in the order of two thousand feet per minute, this would require about two minutes of time to complete the rolling operation. Such an elapsed time results in undesired temperature losses particularly, in the tail-end of the strip as compared to the leading-end of the strip. A higher rolling mill speed could reduce this elapsed rolling time but this presents threading problems for both the rolling mill and the subsequent coil winding equipment for winding the rolled strip into a coil.

Accordingly, it is an object of this invention to provide an improved motor speed control apparatus for the drive motors of a rolling mill such that a more suitable workpiece threading speed is provided and a more rapid acceleration of the rolling mill to a higher and desired running speed is effected to result in a better operation of the rolling mill and to increase the productivity of the rolling mill.

It is a different object to provide an improved motor speed control apparatus for the motors operative with a strip rolling mill such that undesired temperature effects are minimized relative to the rolling of any particular workpiece strip and permitting the rolling of strips having a greater length than was previously practical and in addition successive workpiece strips can be passed through the rolling mill with less time required between the respective rolling schedules.

In accordance with the teachings of the present invention, a speed control apparatus for a tandem type hot strip mill drive system is provided to be operative under a first threading speed and then accelerated to a higher running speed. Two, speed reference buses are provided for this purpose. One is the thread-speed bus and the other is the run-speed bus. The thread-speed bus is supplied by a separate, thread-exciter generator which controls the voltage of the thread-speed bus. The runspeed bus is energized by a combination of the same thread-exciter generator plus a run-exciter generator which are connected together such that the run-speed bus voltage is the sum of the output voltages of the two exciter generatorS. The thread-bus voltage is set by an adjustable reference working in the thread-exciter generator voltage regulator and the run-bus voltage is controlled at a maximum value by a voltage limiting device operative with a ramp function generator connected to control the output voltage of the run-exciter generator. The desired flexibility of operation is provided and protection against operation of the drive motors in excess' of ratedy speed is provided.

These and other objects and advantages of the present invention will become apparent in view ot the following description taken in conjunction with the drawings wherein:

FIGURE l is a diagrammatic showing of the control apparatus in accordance with the present invention;

FIGURE 2 is a schematic showing of the present control apparatus operative with two stands of a multiple stand rolling mill;

FIG. 3 is a graph showing the well known speed cone or relative operative speeds for the multiple stands of the rolling mill;

FIG. 4 is a schematic showing of the speed control apparatus for the strip winding apparatus in accordance with the present invention; and

FIG. 5 is a graph showing the speed changes effected by this control apparatus.

In FIGURE l there are shown six stands of the finishing train for a hot strip mill with the strip entering successively a first stand 10, a second stand i2, a third stand 14, a fourth stand 16, a fifth stand 18 and a sixth stand 2li from which it passes across a roll table 22 to a strip winding device 24.

Each of the stands is provided with a screwdown mechanism, such as the screwdown mechanism 26 operative with the first stand 10. Similarly, each of these stands includes a drive motor, such as the drive motor 28 operative with the first stand 10. Each of the drive motors is controlled in speed by the output voltage from a generator operative with the armature ot the drive motor. For the first stand 10 this voltage is provided by a stand generator 3i) shown operative with the drive motor 28. A speed regulator for each stand is provided to energize the field of the generator, such as the speed regulator 32 provided for the first stand 10 and operative with the field winding 34 of the generator 30.

There are provided a thread-voltage bus 40 and a runvoltage bus 42, operative with each of the rolling mill stands. The thread-bus 4i) is energized by a thread voltage exciter generator 44 connected between a common return conductor 46 and the thread voltage bus 4i). A run voltage exciter generator 48 is connected between the common-bus 46 and the run-voltage bus 42 in series with the thread voltage exciter generator 44, such that the output voltage from the run exciter 48 is added to the output voltage from the thread exciter generator 44 and provided between the run-voltage bus 42 and the common conductor 46.

The speed regulator for each stand includes a voltage sensing impedance member operative with a first contactor connected between the common conductor 46 and the thread-bus 4i) and a second contactor to connect this impedance member between the common conductor 46 and the run-bus 42. More specifically, the first stand speed regulator 32 operative with the first stand 1i) includes a voltage sensing impedance member Si) operative with a first contactor 52, which when closed connects the impedance member 5i) between the thread-bus 40 and the common conductor 46 such that the movable tap 54 provided with the impedance member Sil is adjustable to provide a predetermined and desired speed range for the motor 28 of the first stand Titi and is connected to energize the speed regulator 32 through a vernier resistor 56. A second contactor 58 is operative to energize the resistor 50 between the run-bus 42 and the common conductor 46.

A roll force sensing device 62 is operative with the first stand for providing an output signal to indicate the roll force loading of the first stand or when the workpiece strip 60 is passing through the rst stand 10. A similar roll force loading sensing device is provided for each of the stands of the rolling mill, with each of the respective roll force sensing devices being connected to a sequence control apparatus 64 operative to open and close the respective contactors for each of the stands, such as the

contactors

52 and 58 operative with the first stand 10 as will be later described.

The strip winding device 24 is provided with a drive motor 70 and a motor load sensing device 72 operative to sense the loading of the strip winding device 24 through the armature current of the motor 70. If desired a suitable sensing member may be provided such as a tension member operative with the strip entering the winding device to indicate when the winding device 24 is applying tension to the workpiece strip 60.

A first ramp signal providing generator 80 is operative with a field winding 82 of the thread exciter generator 44 for providing the desired ramp function pattern to the energization of the thread-bus 4t) relative to the common conductor 46. A run ramp signal providing generator 84 is operative with a field Winding 86 of the run exciter generator 48 for causing the voltage of the run-bus 42 to increase above the thread voltage of the thread-bus 40 in a ramp function pattern. This is done after closing the run contactors, such as the contact 58 for the first stand is closed, and after opening the thread contactors, such as the contactor 52 for the first stand 10, by the sequence control apparatus 64.

In FIG. 2 there is schematically shown a portion of the control apparatus of the present invention operative to sequence the opening and closing of the respective contactors to switch the operation of the stand drive motors from the thread-bus 40 to energization by the run-bus 42. In FIG. 2 there is shown the output signal from the roll force sensing device 62 being applied to a signal arnplifier 100 responsive to a minimum roll force signal to control the operation of a contactor 102 connected through a time delay 104 to energize the control winding 106 operative with the contactor 52. The contactor 102 also controls the energization of the control winding 108 operative with the contactor 58. The sixth stand is shown including a roll force sensing device 110 providing an output signal through a minimum signal responsive amplifier 112 to energize a control winding 114 operative with a contactor 116 which controls the energization from a suitable voltage source 118 of a control winding 120 through a time delay device 122, which control winding 120 is operative with a contactor 122 connected between the speed regulator 124 for the drive motor 126 of the sixth stand 20 and the thread-bus 40. The contactor 116 also controls the energization of a control winding 128 operative with a contactor 130 connected between the runebus 42 :and the speed regulator 124 for the drive motor 126. It should be understood in this regard that the

stands

12, 14, 16 and 18 are similarly provided with control circuitry such as shown for

stands

10 and 20.

The strip winding device 24 is provided with a motor load sensing device 72 which energizes a control winding 140 operative with a contactor 142 connected between the voltage source 118 and the respective control windings for each of the contactors connected between the thread-bus 40 and the run-bus 42 and the respective speed regulators for all of the

stands

10, 12, 14, 16, 18 and 20.

In FIG. 3 there -is shown a curve illustrating the speed cone for the respective stands of the rolling mill shown in FIG. l. The curve of FIG. 3 is plotted in terms of speed in feet per minute of the respective stands as a function of the stands. As illustrated in FIG. 3, for purpose of example only, the first stand 10 may be operative between a speed range of 300 feet per minute and 70() feet per minute. The second stand may be operative between a speed of 450 feet per minute and 1200 feet per minute. The third stand 14 may be operative between a speed of 700 feet per minute and a speed of 1750 feet per minute.

The fourth stand 16 may be operative between a speed of 900 feet per minute and a speed of 2250 feet per minute. The fifth stand 18 may be operative between a speed of 1300 feet per minute and 3200 feet per minute. The sixth stand 20 may be operative between a speed of 1500 feet per minute and 3750 feet per minute. It should be understood that the curve shown in FIG. 3 is for purpose of illustration only and any desired changes or variations in the relative speed ranges of the respective stands could be made in accordance with the present knowledge and skill of the rolling mill art.

In FIG. 4 there is shown an application of the present control apparatus for controlling the operative speed of the motor 70 of the strip winding device 24 through energization first by the thread-bus 40 and subsequently by the run-bus 42. As the workpiece strip 60 enters the strip winding device 24, it is desired to sense the resultant additional loading of the motor 70 to energize the control winding and close the contactor 142, such that the regulator operative to energize a field winding 152 of the generator 154 operative with the strip winding device motor 70 will change the operative speed of the strip winding device 24 from a threading speed as determined by the voltage of the thread-bus 40 to a run-speed as determined by the voltage of the run-bus 42. It should be understood that a current of tension regulator can be operative with the generator 154 and a counter E.M.F. regulator with the field winding of the motor 70, such that the counter regulator reference is held proportional to strip speed to provide a substantially constant strip tension. The closing of contactor 142 energizes a control winding 156 to open contactor 157 through a time delay device 158 and energizes a control winding 160 to close a contact member 162. Thusly, when the load sensing device 72 indicates that a strip has entered the strip winding device 24, the contactor 142 is closed resulting in closing of the contactor 162 and subsequently as determined by the time delay 158 the opening of the contactor 157 to change the energization of the speed regulator 150 from across the thread-bus 40 relative to the common conductor 46 and instead to be energized by the run-bus 42 relative to the common conductor 46. Thusly, as the voltage of the run-bus 42 is increased in a ramp or linear function such as shown in FIGURE 5 by the ramp generator 84, the operative speed of the motor 70 is in this manner caused to increase from the predetermined thread-speed to the desired and predetermined run-speed. The respective predetermined speeds are set by the maximum output voltages provided by the thread and the run exciter generators when the top of the ramp control signals are supplied to the respective generator field windings for those generators.

In FIGURE 5 there is shown a curve to illustrate the ramp function change of the thread signal to a .predetermined maximum value 200 to provide the desired thread speed pattern and the subsequent ramp function increase to a predetermined maximum value 201 to provide the desired operative run-speed pattern for the rolling mill. Each individual stand has a particularly desired operative speed in accordance with the curve shown in FIG- URE 3, with all of the stands being controlled to follow the thread-speed and run-speed pattern shown in FIG- URE 5.

In the operation of the control apparatus `shown in FIG. l the thread contactor for each of the

stands

10, 12, 14, 16, 18 and 20, and corresponding to the contact member 52 shown for stand 10, is normally closed to energize the speed regulator and thereby the stand generator to control the operation of the stand drive motor such that the first stand 10 and the other stands operate `at a thread-speed determined by the voltage of the threadbus 40 from the excitation generator 44. In this regard, it should be understood that the thread ramp generator 80 initially controlled the operation of the exciter generator 44 through the generator field 82 such that the voltage of the thread-bus 40 was caused to increase initially in a ramp function or linear manner to a predetermined maximum or thread run excitation voltage. This is shown by the curve of FlGURE 5. When the workpiece strip 60 has passed through each of the

stands

10, 12, 14, 16, 18 and 20 land passes the run-out table rollers 22 and enters the strip winding device 24, this changes the loading of the drive motor 7 0 operative with the strip winding device 24 such that the motor load sensing device 72 can provide an output signal to a sequence control apparatus 64. This causes the contactors connected between the run-bus 42 and the respective speed regulators for the stand drive motors to close and subsequently to open after a provided time delay the normally closed contactors connected between the thread-bus 40 and the speed regulators for the respective stands. In this regard, it should be noted that a voltage sensing device 45 is operative with the run-bus exciter generator 48 and provides an output control signal to the sequence control apparatus 64 such that only when the output voltage of the run exciter generator 48 is zero can the normally open contactors operative with run-bus 42, such as the contactor 58, be closed. When the control signal from the load sensing device is provided to the sequence control apparatus to indicate that the workpiece strip 60 has entered the strip winding device 24, it is now desired to increase the operating speed of each of the

stands

10, 12, 14, 16, 18 and 20 as well as to increase the operating speed of the strip winding device 24 from the thread-speed to the higher desired run-speed. To do this, the sequence control apparatus 64 closes the contactors connected between the run-bus 42 and each of the speed regulators for the respective stand motors. After a suitable time delay, the contactors open which are connected between the thread-bus 40 and the stand speed regulators. Now the run ramp generator 84 begins to increase the output voltage from the excitation generator 43 such that the operating speed of the drive motors for each of the respective stands is increased to a predetermined maximum running speed established by the adjustment potentiometer.

Thusly, as shown in FIG. 5, a typical stand will initially accelerate from a zero speed to a desired thread speed 200. When the workpiece strip 60 enters the strip winding device 24, the speed of that individual stand will increase in a ramp function or linear manner to a desired run speed 201 as determined by the maximum voltage energization of the run-bus 42. After the workpiece 60 passes through that particular stand, the operative speed `of the stand will then decrease in a predetermined manner by dynamic braking or the like back to the thread-speed 200 and it will remain at the threadspeed until a second workpiece strip has been threaded through all of the stands of the rolling mill and enters the strip winding device at which time the operative speed of that particular stand will again increase in a ramp function manner to the desired run speed 201.

As shown in FIGURE 1, each stand includes a roll force sensing device, such as the roll force sensing device 62 provided for the first stand 10. This provides an output signal to the sequence control apparatus 64 which causes the operating speed of that particular vstand to decrease from the run-speed 201 shown in FIGURE 5 back to the thread-speed 200 when the workpiece strip 60 has passed through that particular stand. In other words, when the workpiece strip 60 leaves, the operating speed of the lirst stand will change from the run-speed back to the thread-speed. Subsequently, as the tail end `of the workpiece strip passes through the second stand 12, it will then change from run-speed to thread-speed. This speed changing operation will successively move through the plurality of stands in conjunction with the tail-end of the workpiece strip 60 passing through the respective stands. rThis allows a succeeding workpiece strip to enter stand 10, for example, before the tail-end of the preced- 6 ing workpiece strip 60 has left stand 20. In theory, depending upon the time .period required to decelerate the first stand 10 from its run-speed to its thread-speed, the leading end of the succeeding workpiece strip could enter stand 10 before the tail-end of the preceding workpiece strip traveling at run-speed had left the second stand 12.

As shown in FIG. 2, the strip winding device 24 is provided with a motor load sensing device 72 to close the contactor 142 when the workpiece strip enters the strip winding device 24 which energizes the control winding 108 for the normally open contactor 58 and the corresponding control winding 128 for the normally open contactor 130, for the respective first stand 10 and last stand 20 of the rolling mill, from the voltage source 11S whenever the workpiece strip 60 enters the strip winding device 24. This simultaneously changes the operating speed of each of the stand drive motors from the thread-speed to the run-speed in accordance with the ramp function or linear increase in the voltage energization of the run-bus 42. On the other hand, the roll force sensing device 62 operative with the tirst stand 10 individually opens the normally closed contactor 102 operative only with the irst stand speed regulator 32 when the workpiece strip 60 leaves the irst stand 10. When contactor 102 opens, this opens the normally open contactor 5S and closes the normally closed contactor 52 to cause the speed regulator 32 to change the operative speed of the drive mot-or 28 for the rst stand 10 from its run-speed to its thread-speed as shown in FIG. 5. As the trailing end of the workpiece ystrip passes through the rolling mill and eventually passes through the sixth stand 20, the roll force sensing device similarly opens the normally closed contactor 116 to result in opening of the normally open contactor member and closing the normally closed contactor 122 to cause the speed regulator 124 for the drive motor 126 of the sixth stand 20 to change its operating speed from the run-speed to the threadspeed as shown in FIG. 5.

The apparatus shown in FIG. 4 is similarly operative to sense the increased load taken by the motor 70 when the workpiece strip 60 enters lthe strip winding device 24. This closes the normally open contactor 142 to result in closing the normally open contactor 162 and to open the normally closed contactor 157. This causes the tension regulator to energize the drive motor 70 through the generator 154 in accordance with the increased voltage of the run-bus 42 as compared to the previous thread-bus 40 energization of the tension regulator 150.

Thusly, it will be seen that when the tail-end of the workpiece strip 60 drops out of any particular stand of the rolling mill, that stand is reset to its thread-speed to be ready to accept the head-end of the next workpiece strip or bar t-o enter the rolling mill. This avoids the necessity of waiting until the tail-end :of a particular workpiece strip leaves the last stand of the whole rolling mill to then reset the entire rolling mill in a single operation to the thread-speed. In accordance with the teachings of the present invention, the successive workpiece strips are permitted thereby to enter the rolling mill on a more frequent time schedule and are closer together such that only a few seconds is required between the tail-end of a previous workpiece strip to leave a particular stand of the rolling mill and the entry of the head-end of the next and succeeding workpiece strip.

The two

reference exciter generators

44 and 48 as shown in FIG. 1 are provided to supply the desired speed reference signals to the stand speed regulators. The threadbus 40 is operative as 'a reference bus to set the threadspeed of the whole rolling mill. This reference threadbus 40 is regulated and adjustable over a nominal range of approximately 1,500 feet per minute to approximately 2,500 feet per minute. The run exciter generator 48 then supplies the additional required excitation voltage which is added directly to the output voltage of the thread exciter generator 44 such that the run-speed is set bythe sum or" the thread exciter output voltage and the output voltage from the run exciter generator 48. The voltage output of the generator 48 is adjusted by the speed operator to allow setting the running speed of the rolling mill in accordance with any desired work schedule. This in theory could vary over a range from the thread-speed operation to a value corresponding to the top speed of the rolling mill. The stand speed setting motor operated rheostat, such as the rheostat 50 for the stand 10 and the Vernier rheostat 56 are used to set the individual stand speeds for the various rolling schedules substantially in accordance with the conventional practice at the present time and the curve shown in FIGURE 3. The speed regulator, such as the speed regulator 32 `operative with the first stand 10, is operative with either the eld winding of the drive motor or could be operative with the power supply connected to energize the motor armature.

In a typical operation, the mill operator will set the thread-speed for the mill to `a value which he knows to be correct by setting the thread exciter output voltage from the exciter generator 44. In addition, the motor operated rheostat 51 of the last stand 20 is set to provide the desired speed operation for the last stand 20. The other stands will be set to their correct speed by operation of the individual stand motor operated rheostat. The operator will then set the top run-speed by adjusting a potentiometer S3 operative with the run ramp generator 84 to determine the maximum output voltage of the run exciter generator 48. However, the run exciter generator 48 will have a zero output voltage until it is properly sequenced to go to the increased output voltage value and which zero output voltage i-s provided when the sequence control apparatus 64 operates to close the run contactors corresponding to the contactor 58 operative with the first stand 10. A workpiece strip 60 is then threaded into the rolling mill at the set thread-speed. As soon as the headend of the workpiece strip 60 enters the down coiler or strip winding device 24, the mill acceleration will be initiated by the motor load sensing device 72. The run exciter generator 48 will then increase its output voltage in a ramp function buildup manner to a predetermined top speed value. The desired ramp function pattern can be controlled by any of the well known ramp function generator devices such las a motor operated rheostat or the like. The whole of the rolling mill will then accelerate from the threading-speed toward the running-speed in conjunction with the voltage increase of the run-bus 42.

When the tail-end of the workpiece strip leaves stand 10, the roll force sensing device 62 which could if desired be a Well known load relay or some other sensing device, will cause the contactor 58 to open and the contactor 52 to close. Stand 1 will then be decelerated back to thread-speed. In a similar manner, when the tail end of the workpiece strip leaves stand 12, the illustrated control apparatus will cause stand 12 to be reset to threadspeed. All other stands follow this pattern of operation in -a similar manner. When the tail end of the strip enters the winding device 24 the run reference exciter generator 48 will be returned to a zero output voltage value and all the contacts operative with the thread-bus 40 will then be closed and the contacts corresponding to contact 58 operative with the run-bus 42 will be open. The mill control apparatus will then be ready to accelerate the rolling mill from the thread-speed to the run-speed when a new workpiece strip has been threaded through the six stands of the rolling mill and has entered the strip winding device 24.

The operation of the present control apparatus is such that the head-end of a succeeding workpiece rstrip may actually have entered the iirst stand or iirst few stands of the rolling mill before `the tail-end of the preceding Workpiece strip has passed through the final stand 20. The practical limitation controlling the spacing between the successive workpieces is -how long it will take before the individual stand motors can be reset from their run-speed to the lower thread-speed.

The contactor for each stand corresponding to contactor 52 should remain closed for a short time after the contactor 5S for each of the stands is closed. Further the latter contactor 58 can close only at zero voltage output from the run exciter generator 48. Similarly it is mandatory when changing from the run-speed operation for a given stand to the thread-speed operation, that the contactor 58 open before the contactor 52 is closed. The roll force sensing device 62 for a particular stand such as stand 10 will initiate the opening of the contactor 58 when the workpiece leaves that stand. When the headend of the workpiece strip enters the strip Winding device 24, this will initiate the closing of the contactor 58 when it is desired to change to the higher run-speed.

It should be further noted that the last stand motor operated rheostat 51 will be c-alibrated in feet per minute at top desired mill speed. In other words, if the speed range of the last stand 20 is between 1,30() feet per minute and 3,750 feet per minute at rated output voltage from the run exciter generator 48, the preset rheostat 51 will be calibrated from 1,300 to 3,750 feet per minute. In addition, the energization of the run-bus 42 will be such that regardless of the actual operating speed of the rolling mill, the run-bus 42 will always go to the same voltage level during the normal run condition. The run excitation provided by the run-bus 42 is the sum of the output voltages provided by the thread exciter generator 44 and the run exciter generator 48. It should be further understood that further adjustment of the thread speed may be provided by an additional control eld winding for the thread exciter generator 44 to determine the actual output voltage supplied by the thread exciter generator 44 to the thread bus 40. The voltage sensing device 45 only allows the sequence control apparatus 64 to close the run-bus contactor 58 when the output voltage supplied by the run exciter generator 48 per se, is zero. The voltage limit circuit 47 is operative to limit the reference voltage of the run bus 42 to its correct desired maximum value. The operation of the voltage limit circuit 47 is such that the correct run reference voltage is provided by the run-bus 42, and this is not necessarily determined by the run exciter generator 48 voltage, depending upon the thread-speed selected, which in turn determines the thread exciter voltage provided by the generator 44. The voltage supplied by the run exciter generator 48 will have to cover a wide range of voltages to provide the desired run reference as a correct steady state value.

If the mill operator wants to deliver the next Workpiece schedule at 3,200 feet per minute and he wants -to thread at 1,600 feet per minute, he first sets his preset rheostat 51 for the last stand 20 at 3,200 feet per minute. He can also set the other stands at the correct run-speed in accordance with the speed cone curve shown in FIG. 3. As soon as the tailend of the last bar of the present schedule leaves the rolling mill, the operator can cause all of. the motor operated rheostats of the respective stands to change to their new desired positions for the succeeding schedule. However, the mill stands will have decelerated to thread-speed when the previous workpiece strip or bar left the succeeding stands. This means that the stands are all at the predetermined thread-speed but are running at approximately the correct speed ratios for the schedule selected. The operator now adjusts the rheostat 81 operative with the thread ramp generator 80 to obtain the correct thread-speed out of the last stand 20 by observing the speed indicator for that stand. The adjustment of rheostat 81 will cause all stands to change speed by the same percentage. If desired, the rheostat 81 can also have a preset feature such as do vthe mill stands. As soon as the speed of the last stand is correct the mill can then be threaded. It will also be possible to change thread-speed of the mill after a bar has started through the mill provided the rate of change of speed is slow.

the

The mill will then run at ...e 1,600 feet per minute until the strip enters the down coiler or strip winding device 24, which will cause the mill to be accelerated to the run-speed by the contactors corresponding to the contactor 58 being closed for each of the stands and the contactors connected to the thread-bus 40 corresponding to the contactor 52 being opened. The run exciter voltage is then raised until the desired reference value is provided for the run-bus 42. This reference voltage will have been determined in advance and the mill will have been set up for this value such that the speed range of the individual stand is correct for the involved particular motor design. When the run-bus voltage reaches this value, the limit circuit 4*.-7 will function to prevent the run exciter voltage from being raised further.

In the same manner, any delivery run-speed within the speed cone of the mill can be set and also any threadspeed within the range the mill was originally designed for can be set. The thread control is set so that the thread voltage can be lowered to a predetermined minimum value and the run reference can be raised to a predetermined maximum value. This allows the necessary flexibility for the mill operator and at the same time offers a maximum of protection preventing the operator from attempting to overspeed the stand motors.

in the operation of the apparatus shown in FIG. 4 the strip winding device 24 is controlled from the same thread-bus d!) and run-bus 42 as are the stands of the rolling mill. The previous practice was to control the strip winding device 24- speed from a pilot generator operative with the last stand of the rolling mill. This was suitable for rolling mills run at a substantially constant speed for a given schedule. The thread-speed of the strip winding device 24 is limited by the top speed at which the workpiece strip can enter the strip winding device 24 or down coller. When the tail-end of a given workpiece strip leaves the individual stands of the rolling mill, those stands are individually reset to thread-speed to accept the next succeeding bar. However, it might take in the order of fifteen seconds for the tail-end of a preceding strip to reach the strip winding device 24 after leaving the last stand 2i). It will not be desirable to attempt to slow down the strip winding device 2d during the resetting of the mill stand as this may adversely affect the wrapping of the coil. Since the head end of a given succeeding workpiece strip may be only a few seconds behind the tail-end of the previous workpiece strip, the stands must be reset to thread-speed immediately after the tail-end leaves. Therefore, it is not practical to use a pilot generator on the last mill stand 2@ as a speed reference to the down coilers. A load relay can be used to maintain the operative speed of the motor 7@ until 'the coil is completed, and when the strip winding device is not under load it can change its operative speed to a predetermined thread speed provided by the thread-bus di). it a plurality of alternative strip winding devices or down coilers are provided, the one which is actually winding strip should be maintained at run-speed and the other down coilers may change to thread-speed as provided by the thread-bus 40. ln this same manner only the strip winding device which is operative with a work strip should follow the mill as it increases speed from the thread-speed to the run-speed. Suitable interlocking of the provided selector switch can be provided to accomplish this function.

Although the present invention has been described with a certain degree of particularity, it should be understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to Without departing from the scope and spirit of the present invention.

i claim as my invention:

1. In apparatus for contro-lling the operating speed of at `least the drive motor 'for one stand of a strip rolling mill operative with la strip coil winding device, the com-v bination of first voltage means connected to energize said one drive moto-r to operate at a first predetermined speed, second voltage means for energizing said one drive motor to operate at 'a second predetermined speed greater than said `first speed, load sensing meians operative with said strip rolling mill for providing a iirst control signal when the iWork-piece ystrip enters said `strip winding device ,and for providing ya second control signal when the workpiece strip leaves said one stand, `and circuit connection means provided between the second voltage means and said one drive motor for connecting the second voltage means to energize said lone drive motor from the second voltage means in response to said rst control signal and for disconnecting the second voltage means to deenergize said one drive motor relative to the second voltage means in response to said second control signal.

2. In `apparatus ifor controlling the operating speed of a plurality of drive motors for the respective stands ozf a workpiece strip rolling mill operative with a workpiece strip coil winding device, the combination of lirst voltage means connected to energize simultaneously each of said drive motors to operate at a predetermined threading speed, second voltage means for energizing simultaneously each of said drive motors to operate :at -a predetermined running speed lgreater than said threading speed, load sensing means operative Witlh said strip IWinding [device for providing a first control signal when the workpiece strip ybecomes operative with said strip winding device land for providing a second control signal each time the work-piece strip successively leaves one of said respective stands, and circuit connection means provided between the second voltage means and said plurality of drive motors for connecting the second voltage means fro energize each of said drive mot-ors in response to said iirst control signal such that each drive motor of the rolling mill simultaneously increases its speed of operation from the threading speed to the running speed when `the workpiece strip becomes operative with said strip winding device 'and for disconnecting the second voltage means relative to each successive drive motor in response to each :respective second control signal as the fworkpiece strip successively leave the respective stands ofthe rolling mill.

3. In apparatus for controlling the operating speed of a plurality of drive motors of la multiple stand workpiece strip rolling mill operative 'with ia strip coil winding device, the combination of lirst voltage supply means for energizing said drive motors to operate at a first predetermined threading speed, second voltage supply means for energizing said drive motors to operate :at ia second predetermined running speed greater than said iirst speed, first load sensing means Ioperative with said workpiece strip for providing a lirst control signal when there occurs a predetermined positioning of the workpiece strip, circuit connection means provided between the second voltage supply means and said drive motors for connecting the second voltage supply means to energize said drive motors in response to said first control signal, and second load sensing means operative with each one of said multiple stands for providing `a second -controi signal when the workpiece strip leaves each said one stand, with said ycircuit connection means being responsive to each said second control signal for disconnecting the second voltage supply means from the drive motor operative with each said one stand after the workpiece strip has left that respective one stand.

4. In speed control apparatus for la plurality of drive motors operative respectively with the plurality of stands of a workpiece strip rolling mill including a strip fcoiling device, the combi-nation of first voltage supply means for providing a first predetermined speed of operation, second voltage supply means for providing :a second predetermined speed of operation greater than said iirst speed, first load .sensing means opera-tive with said strip coiling device for providing a first output control signal when a workpiece strip is :being coiled by said strip coiling device, second floa-d sensing means operative |with each of said stands for providing a second output control signal in accordance with the successive operation of each respective stand with the workpiece strip, rst -circuit means responsive to said rst output control signal and connected between the first and second voltage supply means and said drive motors for energizing said drive motors to operate at said first speed when a workpiece strip is not being coiled by said strip ooiling device and to operate ,at said second speed when a workpiece strip is being coiled Iby said strip coiling device, and second circuit means responsive successively to cach second output control signal and connected between the second voltage supply means and the drive motor for each of said stands tor controlling the energizlation of the respective drive motors Eby the second voltage supply means in accordance with the successive operation of said plurality tot stands with .the workpiece strip.

5. In speed control apparatus for a plurality of drive motors respectively operative with the multiple stands of a workpiece strip rolling mil-1 including Ia strip coiling device, the combina-tion of rst voltage supply means operative with said motors to provide a first predetermined speed `off operation, second voltage supply means operative with said motors to provide a second predetermined spced of operation greater than said first speed, first xload sensing means operative with said strip coiling device yfor providing a first output control signal when the leading-end of the work-piece strip is being coiled by said strip coiling device, second Iload sensing means operative rwith each of said stands to sense the passage of the tail-end of the workpiece strip through each of said stands, first circuit means connected between 4the first voltrage supply means and said drive motors for initially energizing a'll of said motors to opera-te at said first speed, second circuit means connected between the second voltage supply means and all of said drive motors and being responsive to said `iirst output control signal lfor energizing said motors -to operate at said second speed when a Workpiece strip is 'being coiled by said strip ooiling device, and third circuit means operative with the second lload sensing means :and operative with the second volt-age supply means for sequentially returning each o said motors to operati-on at said iirst speed las the tail-end of the workpiece strip Irespectively leaves each of said stands in passing through said workpiece strip rolling mill.

References Cited by the Examiner UNITED STATES PATENTS 2,342,767 2/44 Stoltz 80-351 3,109,330 11/63 Barnitz et al 80-35.1

FOREIGN PATENTS 214,663 4/58 Australia.

CHARLES W. LANHAM, Primary Examiner.

W'IILLIAM J. STEPHENSON, Examiner.

Claims

5. IN SPEED CONTROL APPARATUS FOR A PLURALITY OF DRIVE MOTORS RESPECTIVELY OPERATIVE WITH THE MULTIPLE STANDS OF A WORKPIECE STRIP ROLLING MILL INCLUDING A STRIP COILING DEVICE, THE COMBINATION OF FIRST VOLTAGE SUPPLY MEANS OPERATIVE WITH SAID MOTORS TO PROVIDE A FIRST PREDETERMINED SPEED OF OPERATION, SECOND VOLTAGE SUPPLY MEANS OPERATIVE WITH SAID MOTORS TO PROVIDE A SECOND PREDETERMINED SPEED OF OPERATION GREATER THAN SAID FIRST SPEED, FIRST LOAD SENSING MEANS OPERATIVE WITH SAID STRIP COILING DEVICE FOR PROVIDING A FIRST OUTPUT CONTROL SIGNAL WHEN THE LEADING-END OF THE WORKPIECE STRIP IS BEING COILED BY SAID STRIP COILING DEVICE, SECOND LOAD SENSING MEANS OPERATIVE WITH EACH OF SAID STANDS TO SENSE THE PASSAGE OF THE TAIL END OF THE WORKPIECE STRIP THROUGH EACH OF SAID STANDS, FIRST CIRCUIT MEANS CONNECTED BETWEEN THE FIRST VOLTAGE SUPPLY MEANS AND SAID DRIVE MOTORS FOR INITIALLY ENERGIZING ALL OF SAID MOTORS TO OPERATE AT SAID FIRST SPEED, SECOND CIRCUIT MEANS CONNECTED BETWEEN THE SECOND VOLTAGE SUPPLYMEANS AND ALL OF SAID DRIVE MOTORS AND BEING RESPONSIVE TO SAID FIRST OUTPUT CONTROL SIGNAL FOR ENERGIZING SAID MOTORS TO OPERATE AT SAID SECOND SPEED WHEN A WORKPIECE STRIP IS BEING COILED BY SAID STRIP COILING DEVICE, AND THIRD CIRCUIT MEANS OPERATIVE WITH THE SECOND VOLTAGE SUPPLY MEANS AND OPERATIVE WITH THE SECOND VOLTAGE SUPPLY MEANS FOR SEQUENTIALLY RETURNING EACH OF SAID MOTORS TO OPERATION AT SAID FIRST SPEED AS THE TAIL-END OF THE WORKPIECE STRIP RESPECTIVELY LEAVES EACH OF SAID STANDS IN PASSING THROUGH SAID WORKPIECE STRIP ROLLING MILL.