US2275509A

US2275509A - Control for rolling mills

Info

Publication number: US2275509A
Application number: US226047A
Authority: US
Inventors: Frank P Dahlstrom
Original assignee: Aetna Standard Engineering Co
Current assignee: Aetna Standard Engineering Co
Priority date: 1938-08-22
Filing date: 1938-08-22
Publication date: 1942-03-10
Anticipated expiration: 1959-03-10

Description

March 10, 1942.` F. P. DAHLsTRoM CONTROL FOR ROLLING MILLS Filed Aug. 22, 1938 Patented' Mn.' 1o,` 1942 CONTROL Fon ROLLING MILLs `Frank-P. pamstrom, Parana, ohio, assignor to" AThe Aetna-Standard Engineering Company,

Youngstown, Ohio, a corporation of Ohio Application August 22,1938, Serial No. 226,047

8 Claims.

This invention relates to rolling mills such as are employed for rolling strips or sheets of steel, although it will be understood that the inventionv may be employed inlconjunction with mills adapted to operate on other materials. More i particularly the invention relatesto 4a method and apparatus for automatically controlling the setting of the rolls of rolling mills in such a manneras to produce a stripor sheet of material of substantially uniform thickness.

In modern strip mills used in the production of steel sheets and strips, the material is passed I between;` the rolls at high speed in long lengths. The operator attempts to produce material of uniform thickness by raising and lowering the screW-downs of the mill` in accordance with variationsin the thicknessin the finished product. `Frequently in modern mills, a continuously` reading micrometer disposed in engagement with the strip after the stripleaves the mill is provided. By watching the changes in gage of the strip, as indicated by the micrometer, the operator attempts to correct thesetting oi the mill rolls to produce avstrip of substantially uniform thickness. Necessarily, he is unable to even attempt `to correct the setting until after some material` of incorrect thickness has passed through the mill. In modern mills operating at speeds of say 500 or 600 feet per minute, even the most skilled operator with the best equipment must produce a considerable proportion of material which varies noticeably from the standard gage desired. i

Many of thesevariationsare caused by variations in the thickness of the strip entering the mill. Because of the elasticity `of the mill', a

thick strip entering the mill `will result in the production of nishedmaterial above the standard gage unless the mill setting is adjusted before the thickened portion reaches the mill, and similarly if the strip being fed has a `portion thinner than standard the finished strip will be rolled to a thinner gage than desired. In accordance `with the present methods of operation wherein the operator adjusts the screw-downsinV for this is that the large present day mills require powerful motors for operating screw-downs and an appreciable length of time elapses between the time when the operator presses the buttonto start the screw-down motor and the time when the motor gets up to speed and is able appreciably to move the screw-down mechanism.

Furthermore, the operator himself can not act instantaneously but must note the kind` and extent of error occurring in the finished strip and decide how to correct it, and then proceed` With making the correction in the roll setting. Thus in the ordinary operation of mills, there are three l cumulative delays between the time the error accordance with the indications on a gage disposed on the strip after the strip leaves the mill, it frequently may occur that the changes 'inthickness in the entering strip will be so closely spaced `as to make it impossible for the operator to adjust the roll setting in time to produce strip of correct thickness, and in fact the changes may occur in such a manner that the operators actions will accentuate the differences in thickness in the finished strip. One reason occurs and the time when the mill setting is corrected kto 'compensate for the error. The rst is due to the fact that the` strip is not gaged` until it has passed through the mill, the second is occasioned by the time required for theoperator to note the error and take steps to correct it, and the third is caused by the relatively slow response of the screw-down mechanism of the mill. While the total delay may be very small,

lnevertheless the mills are operated at such speeds that a considerable quantity of material may pass through the mill before the error is corl rected.

According to a preferred form of my invention, I eliminate the delays noted vabove and automatically and accurately correct the setting of the mill to insure the production of material of substantially uniform thickness by automatically adjusting the mill in accordance withvariations in thickness of the material entering the mill. My mechanism is preferably controlled by gages engaging the strip before it passes through the` niill as well as after it has passed through the mill. I thus provide an anticipating control which detects Variations in thickness of material entering the mill and corrects thejsetting of the mill rolls as the material of changed thickness reaches the roll stand so as to insure' the delivery of material of proper gage. Further, I preferably provide in conjunction with the anticipating control apparatus a gaging and contolling mechanism actuated by a gagemeasuring the thickness of the `strip after it leaves the roll stand automatically to adjust or calit brate the anticipating control mechanism to insure the production of material of correct thickness and to correct the mill setting to compensate for variations in thickness of the finished str-ip which may occur even though no substantial changes in the thickness` of the entering strip have taken place. In combination with the foregoing mechanism I preferably provide man-` from operating when there is no strip in the mill.

It is ,arnong,-.the., objects of .my invention. provide'a method andapparatus" for fcontrollig the setting of the rolls of a rolling mill to insure fthe production of material of substantially uniqcelerating l c'fonijactor 14 Ythe connections" being form thickness throughout its length It v isa further object of my invention to* provide'aimethod and apparatus for varying thepercen-, tage of reduction taken in a rolling mill Iin accordance with variations in thickness of material entering the mill. It is a further object to provide such a method and apparatus in which the gage of the finished productv is employed to calibrate the mechanism to compensate for any errors which' may occur in the finished thick-` ness of the strip and which have not been compensated forby the anticipating control mechanism. Another object is to provide an appara-` tus which will adjust y`a`vrolling mill to compensate for whatever .variations in thickness of flnishedstrip may occur even though the thick- The eld-:currentmay be supplied to the motor through' conductors 40 and 4I leading to the ness of the strip entering the mill remains con-.-

stant. It is another object to providel apparatus of simple and sturdy construction which can be constructed at relatively low cost and whichcan be readily adapted to existing mills. `lA further object is top'rovidean apparatus vwhich will automatically make a correct initial setting of the mill in accordance with the thickness of the fin-- ished strip and thereafter maintain the production of strip of correct thickness by means actuated in response to changes in thickness of the entering strip. Further objects and advantages of my invention will become apparent from the following description of a preferred form thereof, reference being made4 to the accompanying drawing which diagrammatically illustrates a preferred form of my control mechanism as applied to a rolling mill of conventional construction.

In the drawing, apparatus is shown as applied to an ordinary two-high mill indicated generally at III and having rolls II and I2 adapted to act upon the strip S which may be fed to the mill.

from a coil I3 and delivered to a coil III, although it vwill be obvious that the inventionmay be applied to mills of different types such as fourcuit from the negative side of the control circuit line' through conductor 33, contacts 3l and conductors 36 and 31 to energize solenoid 2II. Ener gization of solenoid I9 closes contacts 38 completing the circuit from the power supply lines to the armature of the motorI'L'throug'h the acfte` operate the motorjto raise the screw-downs.

settinglof the' mill rolls can be manually controlled in thev conventional manner. To provide power supplylines. y

By means ofthe. above described controls the automatic control of the sttingfof the mill rolls I preferably employ the instrumentalities/ about to be described all ofjwhich function in response .'to changes in the thickness o f the material being.

operated upon by ther'nillto control. the screwdownmotor through the reversing controller-I8 by energizing the solenoids I9 or 20 asthecase may-be' to lower4 or raise the screw-down mechanism. v

strip and includingfcontinuous gaging vdevice 45 which engages the strip immediately -afterit has passed through the mill rolls. -Preferably Vthe gage is of the type manufactured by the Pratt 8:

Whitney Company, of. Hartford, Connecticut-and marketed by. them4 under the name Electrof Limit continuous gage. Briefly, this type of gage comprises vrollers 48 and 41 engaging opposite sides of the strip,lvariations in distance between the rollers being reected by movement of the armature 48 Abetween the coils 49 and' 5I) which constitute part of an inductive bridge completedr by the coils 5I andA 52. The bridger is supplied with .alternating current through the conductors 53 and SII. Movementsof the a'rina-v ture 48 between the coils 49 and 5I) result in varihigh mills or tandem mills embodying a plurality of roll stands.

The rolling pressure exerted by the mill mayxv be controlled by a conventional screw-down mechv anism I5 operated through the gear train indicated generally at I6 by means .of a motor I'I. All of the parts described above are conventional and require no further description here.

Manual controla- To control the operation of the screw-down motor I1 I may employ a reversf ing controller I8 which controls the. current supplied to the armature of the motor I1. The controller includes solenoids I9 and 20 which may be energized through the common conductor 2l leading to the control voltage supply line L+.l

' When the master control switch 30 is swung to -its manual control position (to the/left inthe drawing) to close the contacts -3I operation of the `push button 25 will complete the circuit through the conductor 33, the contacts 3I, and conductors 24 and 23 to energize coil I9. Similarly the operation of the push button 35 will close the cirations in the impedance of these coils which willv be reflected by variations in the voltage delivered ammeter 58, the circuits ordinarily` being `arranged so that an increase in lthe spacing between the rolls results in ain increase in current flowing through the micro-ammeter.

The gage is constructed so that for any setting, the needle 59 of'the micro-ammeter re mains in the center when strip of the standard thickness for which the gage is set is passing between the rolls 46 and 41.. That is, the output voltage of the bridge circuit is constant and the instrument is calibrated so that the output of the gage maintains the needle in a central position so long asthe rolls are spaced aparta distance equal to the lstandard thickness for which the gage is setf Variations in strip thickness above and below standard result in increases and decreases in output of the gage,

which are indicated by movement of the micro-v a'mmeter needle to the rightl and left, respectively. Movement of the needle along the scale is substantially in proportion to variations in thickness, and the instrument is sensitive to eg described below.

u an inchl` 1Thistill-lenig gaging` apparatus is "ing -the Oscillating relay "Tlgto rotate shaft tion,` breaking the "Il andstopping the screw-downmotor.. i i .Similarly an increase in thickness of themafBy` this means the variationsfof less than one-ten thousandths of well `known 1in` the art` andwi1l not be de scribed l "further hereinas `the gage per se forms no n part of the presentl invention;

To `utilize the gage for controlling thel screw` downfmotor, I `connect; inparallel with the micro- `amrneten58 a contact-making `micro-ammeter n or relay lihgwhich is arranged to operate the u screw-down motor `to"redu`ce the ypressure on the millirolls upon decrease 1in thickness `of the Ystrippa`ssing between the rollers `of `the gage l 45 und` to increase the rolling pressure upon inmill when` no `substantial change` takes `place in of the factors listed above will result in a variacrease of thickness of the strip passing through the` gage `I5.` This operation `is 'carried out through the electrical circuits shown, wherein lthe frelay is supplied with a control current `through the conductoriGZ, movement of the con-` tactor; 63 of the relay to the left, for example,

into engagement with contact 6I in response to a reduction in the output lvoltage i of ther gage caused `by reduction in thicknessofthe material Abyan amount exceeding `the established `tolerances,` resulting in ,closing the circuit `between the .conductors 62 and 65, thereby energizing o field coil S6 of oscillating relayBl, which is connected to the other iside off the control circuit throughconductor E8. u t

Assuming that the armature 69 of thezoscillatn "relay 6I` isenergized` throughtconductors 'Ill and II and connections to `bedescribed in detail below then the energization of field coil iwill "cause theiarmature` Sito rotate (ina clock-` wisedirection` in the embodiment shownrv the shaft 'IZEto move the contactor 13 of therelay into engagement withicontactsul thus completing the circuit `through conductors 'I5 and I6 and `energizing the solenoid 2li of the reversing controller; Il and causing `the screw-down motor ,I1` tooperate inya` direction' to raise the `screwf-down and reduce the rolling pressure appliedto `thestrip until `the strip passing between the` rolls `ofthe gage `becomes of the standard `thickness for which thegage is set, atwhich u time the `contactar 63wi1l moveback to its centrai position `thus `de-energizingeld coils of` and i permitting i the spring 'I2 back` to its neutral posicircuit` between the contacts oscillatingrelay,`;` which is wound oppositely to coilzitand'ca in a" direction ing the armature 69 torotate to move the contactar I3-into engagement withcontactsl. closing the circuit between" conductors `I5 i and 3.; thus energizing solenoid I9 toyclose the contacts 3l and thereby operate ina direction to n pressure applied to the strip. o screw-downs may be auto `lnatically operated to insure production of` strip increase `the rolling passing through the gage strip of uniform thickness and uniform `physical characteristicsis fed to `a. mill 1having a given roll. setting and operating under uniform conditions, a definite and uniform percentagelof reduction of thickness in the strip will take place.` Thus thethickness of `therolled` product will be uniform. .'However; 'any `changes `in'any tion in the thickness of` the finished product unless the millis adjusted tov compensate for such variations. l It has been my observation that most of the variations in thickness of the finished product are caused by non-uniform thicknessof the enteringustrip.

will now vbe described.

Forconvenience inidescription it will be assumed thatthe master control 3U is swungto `the right to `closecontacts 80 to-set thef device for automatic operation, `that the circuits are completed through the lockoutrelays 9| and 92, the automatic control holding contacter 95,and that the finished strip l-isof substantially Standard thicknessso `that the oscillating relay 6I is in its neutral position thus completing the circuitbetweenicontacts 96. `The operation "of these `various instrumentalities willA be described below it being necessary that thercircuits be arranged as justpointed out in order for the anticipating control tobe placed in operation.

The anticipating control mechanism' comprises a continuous gagingdevice |00 which may be similaryin al1 `material respects to the gage `I5 heretofore described; `The passed through'a rectier llll, and thenceto supplying current tothe screw-down motor I`I `totausethe motor to of f the `thickness for which the` gage 45 isset. l

This `inodeiof operation,l however, `is preferably only employed in the initial operation oflu the mill when the strip -is firstfed therethrough or totake care ofl changes in thickness orrnished strip which `may occur due to changes inthe operatinguconditionsof theymill or changes; in

n established conductor 31 V an indicatingmicro-ammeter |32 `and a contact makingmcro-ammeter or relayY |03. `The gage i is set by the operator for `the average'standard thickness ofthe entering strip andso long as the strip entering the milldoes notvary from the standard `thickness by an amount exceeding the Itolerance, the contactor I" of the relay `Ill; will remain in the center and therewill be no change in the operationof the mill. However, should the strip thickness decrease by an amount `exceeding the tolerance then the coni tactor llwill swing to the left into engagement with contact I B5l thus completing the circuit from the control circuit supply .through conductors |06 and ID'L the relay 9|, and contacter 94 tothe which complet-es the circuit through coil 20 of reversing controller I 8 thus energizing the armature of `thescrew-doun motorII and causing themotor to operate in a direction jto raisethe screw-down to sure applied to the strip;` thus reducing the percentage of reduction taken bythe inill and compensating for thejreductionin thickness of the entering strip.

Similarly, anincrease in `the thickness of the entering strip exceeding the established tolerance will cause `the `contact IM to swingto the right engaging contact lill and completing the circuit through` conductors |05 and IIB, relay 19| and contactar 94 to conductor noid I! oflreversing. controllerfl and .closing contacts 38 to supply power to the motor II to the character of material passing through? the In order lto-Leliminate errorsl in finished strip thickness due to such non-uni- Y Vformity I preferablyemploy an anticipating control mechanism the principal elements of which Ycontactor` 94; and the i output of the vgagefis reduce the rollingpres- 23 thsenergizing sole-f i operate in the' opposite direction to increase the rolling pressure exertedy on the strip, thus in- ..1 `creasing the percentage `of reduction taken by the imilland compensating fori the increase in the thickness ofthe entering strip. Variable speed control f screwdoum.-Under ||5 in the; armature circuit of motor I1, an additional controlcircuit being employed to cut out the resistancey in the event of a relatively large y change inthe thickness ofthe material passing through thegage. v.This operation is eiected by relay |03.` which is provided with additional con- `tactfpoints IIS and "`||1; A wide swing of the` contactor |04fingeither direction will complete the circuit between the conductor |06 and conductor ||6 to which both contact points |I6 and ||1are connectedmcompletng this circuit results in the energization vof the magnetic switch I I9 which is connected to the control line through Y conductor |20, thereby placing the conductor 2| in parallel with the resistance ||5 and thus increasing the speed of `the motor I1 regardless of the vdirection of its; rotation. Y l

r Balancing circuit-,To prevent `hunting and to ,insure that the screw-down motor will operate yjust, suillciently tol correct the setting of the mill, I preferably employ a compensating or balancing i circuit :in conjunction with the relay |03'which` functions to maintain the contactor of the vrelay Vin its central or oi `position whenever the 'screwdownl has operated `just suiiiciently to compensate `forthefvariations in `thickness of the material entering the mill. This is accomplished by applying to the relay, |03 a balancing electro-motive force controlled in accordance ywith the`position of the screw-down `and in accordance with thev thickness of the material fdelivered by the mill. The `main balancing circuitA is connected in serieswith the relay by the conductors |25 and |26. The circuitincludes the compensating or balancingpotentiometer indicated generally at |21 andcomprising a suitable resistance |28y connected at its center to conductor I 26, and a sliding contactor I 29` which engages the resistance |28 and` makes contact through the slide` |30 with the conductor I 25. ,Y

The sliding contactor |29 maybemoved either to theV rightor to the'left ofits neutral position vby a'` worm I 35 driven bythe screw-downmotor v|1 through/magnetic clutch |36 and gears |31. Thus-whenever the clutch is engaged,. the position of `the contactor `|29 is controlled by and varies with the position of the screw-down mechianism, theA contactor remaining in neutral position so longy as the strip entering the mill is of standard thickness. As the ends of resistance |28'are connected to a `source vof electromotive force through conductors |38 and` |39 the polarity and` intensity of the balancing `voltage applied to relay |03` is'varied by movement offsliding contactor |29; vthe balancing voltage increasing as lthe contactorJ is moved from its neutral position and the` polarity being reversed as the contactor imov'es' from one Aside of the neutral position'to the other.

- enough from its lneutral position to closefthe l control circuits and the control mechanism will not operate; However,`` assuming for example that'the strip thickness becomes greater than standard by an amount exceeding the established tolerance, then the gage |00 will operateto increase the current flowing through the relay |03 causing the contactor to swingto the right and operating the reversing switch I0 to start `the screw-down motor in a direction" to increase the pressure applied to the strip. This operation of the screw-down motor also drivesthe worm |35 which controls the output of the compensating potentiometer |21, movingthe slidingrcontact |29 away from its central or neutral position in t a direction (to the left, in the apparatus shown) tending to apply a balancing or-compensating voltage Vto the relay |03 through the conductors |25 and |26 opposing the output voltage of the gage and thus tending to restore the contactor ofi'l the relay to its central or oif position. The restoring effect increases in proportion to the distance the contact |29 is moved from its central position, and thus the restoring eiect increases inV proportion to the movement of the screwdown. When the-screw-down has operated suiiciently to compensate for the increase in thickness in the strip, the balancing voltage will be suilicient to movethe contactor oflrelay |03to its central or oi position,'th`e `screw-down motor Iwill stop and will not operate again untilv a fur- Y ther change in conditionsoccurs.

. If a reduction in thickness of the strip passing i through the mill occurs, the operation of the gagel |00 will result` in a decrease in the current ilowing through' the relay |03 thus causingth'e contactorl to swing to the left and operating the reversing controller I8 to start the screw-down motor in a direction to-decrease the 'pressure applied to the strip. This operation will result in the movement of the contactor |29 of the balancing potentiometer towards the right, thus decreasing the opposing balancing voltage applied tothe relay |03, if the contactor. 16 was ina position to the left of center when the reduction in thickness occurred; or applying 'a balancing voltage of the same "polarity as the outputvoltage of the gage if the contactor moves to the'right f of the relay to its central or off position. As bei fore, the restoring eiiect increases in proportion to the distance the contactor |29 has been moved and because of this mode of operation all `tpossibility ofhunting is eliminated. 7

Calibrating control`.`-The balancing potentiometer can be arranged so" that `for a given `set Y of operating conditions andffor operations carasy longa'stne tflcknes,ofy the strip entering i the mill Aremains,within the predetermined limits, the contactor of relay |03 Vwill not swing far of operation of the screw-downs for a givenrvar iation in thickness can be readily adjusted'by` varying the voltage applied to the compensating potentiometerthrough' the conductors |39 and |39. Thus if` the screw-downs should be overcorrecting, then the electromotive force applied to the potentiometer should be increased so that asmaller movementl of the Ac'cr'itactc'ir |29 would result in a greater changein the balancing voltageA applied to `tl'i'e relay |03, andif the screw- `downs are under-correcting the appliedele'ctromotive force'should be-reduced. The voltage Supplied vto the compensating potentiometermfay be Calibrating control contactor |56.

der automatically to calibrate, the anticipating control mechanism to prevent error from occurring by reason of changes in the operating conditions of the mill or changes in the physical characteristics of the material being rolled, thereby insuring the production of nishedmaterial of substantially uniform thickness.

The control of the applied voltage is carried out by mechanism including gage 45, and the contact making micro-ammeter or relay 60 previously described in connection with the control of the screw-down in accordance with variations in thickness of the nishedistrip. Preferably the` circuits from `relay 60 are arranged so that whenever `the contactor or s lider |29 moves from neu- `tral` position by more th'an a predetermined amount, relay 60 operates to control the balancing voltage supplied tothe balancing potentiometer |21 by conductors |38 and |39 instead of i controlling the screw-down motor through oscillating relay 61. Thus so long as 'contacts |45 in conductor 10 are bridged by contactor |46 mounty ed on but insulated from sliding contactor |29, current can flow from the control voltage supply line through conductors |20 and |41, conductor 10 and relay 92 to energizethe armature 69 of oscillating relay 61. Whenever sliding contactor |29 is moved away from its central position, contactor |46 is disengaged from contacts |45 and thus armature 69 is de-energized and the oscillating relay 61 is rendered inoperative.

i The `output of the potentiometer |13 is connected to the ends of the resistance |28 of the balancing potentiometer |21 through the conductors |38 and |39. Thus the operationof the motor |10 and movement of the sliding contactor |12 along the resistance |14 and sliding contact varies the output of potentiometer |13 and the voltage applied to the balancing potentiometer, thereby changing the effect` ofthe balancing potentiometer and varying the balancing or restoring voltage appliedto th'e anticipating control relay |03. y

Assume, for example, that strip of greater instead the mill produces material which is` thicker than standard. Then the contactor 63 of the relay 60 will move to the right, energizing the magnetic switch |54 to close the circuit to age applied to the balancing potentiometer |21,

thereby reducing the balancing voltage applied to the relay |03 and causing the relay to close the Vcircuit through contact |04 until such time as the motor |1 operates the screw-down sufciently to insure the production of strip of proper gage, and rotates the Worm sufficiently to move the sliding contactor |29 away from its central position an additional amount sunicient to offset the decrease in the applied voltage, thus -again increasing the balancing voltagefand bringing the relay |03 back into balanceand to its 05" position. i

Similarly, if the entering strip is thicker than standard but the product is thinner than standard, then the relay 60 will actuate the the switch |55 to operate the motor |10'1n the opposite direction, moving the Contact |15 to increase the voltage applied to the compensating potentiometer, thus throwing the relay |03 out of balance again but in the opposite direction,

|1 raises the screw-downs from normal position and moves the contactor |29 to the right of its central position. Closing this circuit operates reversing switch |62 which reverses the connections between the relay and the magnetic switches |54 and |55. The control circuit for switch |62 is completed throughconductors |20 and 83.

Assuming that a lstrip of thickness less than t .normal is being fed to the mill, then the motor |1 will operate to raise the screw-downs, moving the contactor |29 tothe right. If the cornpensating potentiometer reaches a position where the relay |03 is balanced before the screw-down has operated suiciently to produce strip of proper thickness, so that the finished stripV is too thin, then the relay 60, through the reversing switch |62, will close` the magnetic switch |54 to operate the motor |10 to move the contactor |12 to decrease the voltage applied to the compensating potentiometer, thuscausing the motor |1 to further raise the screw-downs until `a balance is reached and material of the proper gage is being delivered.v `If the entering strip is too thin but the strip leaving the mill is too thick, the relay 60 will close the' circuit to the magnetic switch |55, thereby operating the motor |10 in the direction to increase the voltage applied tothe compensating potentiometer, causing the relay |03 to close the circuit through conductor |08 andoperating the motor |1 to lower thescrew-downsthereby moving the contact |29 :toward the center `of the compensating potentiometer which reduces its output, thus cancelling the effect-of the increased input voltage and thereby restoring the relay |03 to balance. n

Control of sequence of operations-As those skilled in the art will appreciate, it is desirable that the various controls heretofore described function at different times and under different conditions of the mill.- Thusgages 45l and |00 should both be ineffective to actuate the screwdowns when there is 'no material between the rollers of the. gages. During the `:initial operation of the mill, when a strip is rst introduced therein, it is desirable that the screw-downs be initially adjusted by operation of the gage 45.

Afteran initial settinghas been made it is preferable that the screw-downs be controlled by the anticipating `mechanism, in conjunction with gage |00. Under some circumstances variations in thickness of the nished product mayr occur ing control will be ineffective to properly correct the setting oi the-mill, for when thecontactor |29 of the balancing potentiometer |21 is at or near its neutral position, a change in the voltage applied to the balancing potentiometer will have `no appreciable effect on its output voltage.

Under such circumstances adjustment of the potentiometer |13 will be ineffective andvaccord ingly, under such circumstances it is preferable that the screw-down motor lbe controlled in response to variations in thickness of the rfinished strip.

The several relays and switches for changing the mode of operation of the apparatus in ac- .cordance with the various conditions Vnoted above are described in the following paragraphs.

Lockout relays-To` prevent operation of the control mechanism by either gage 45 or |00 when there is no material between fthe rolls of `the gages, I preferably employ lockout relays 9| and 92.. Lockout relay 9| is energized by the gage |00 through conductors |85 and |86 and vacuum tube relay |81. The output of the gage is reduced as the rolls approach each other and the circuits are arranged so that relay 9| will open the circuits including conductors |01 and |08 when the rolls of the gage are in engagement with each other. Thus unless strip is pass ing through the gage |00 the controls leading from the relay |03 will be interrupted and ineiiective to operate the screw-down motor.

' Anticipating control starting relay and autovnessand when the material entering the mill position` thus completing the circuit from the holding contactor 95` through conductors 20| and 202 to contacts 203 of the contactor 94 and also 'to the starting relay 93. The

coils

204 and 205 of the starting relay are connected to the control supply line through conductor 209 and are energized through conductors v|01 and 201 or "|08 and 208 whenever the contactor of the relay |03 is swung to either side of its central position into engagement with contact or contact ||0. Thus coils 204 and 205 of relay 93 are energized, opening-the circuit through the relay, whenever strip which is not of standard gage is passing through gage |00. The circuit through the relay, however, is closed whenever contactor |04 is inl its central position, and if this occurs at a time when oscillatingy relay 61 is in its neutral position thus closing contacts 96, then solenoid 2|0 of the automatic control contactor 94 will be energized, closing the circuits through contacts 203, 2| l, 2|2, 2|3 and 2|4. This action can take place only when the thickness of the strip entering the mili corresponds to the setting of gage I 00 and the thickness of the strip produced by the mill corresponds to the setting of gage 45.

Closing of contact 203 in contactor 94 completes a holding circuit through coil 2|0 so that after the contacthas once been made it will remain closed so long as contacts 96 are closed even though the circuit through relay 93 is open. Contacts 2|| and 2|2 close the circuits between conductors |01 and 31, and |08 and 23, respectively, leading to the screw-down motor reversing controller I8. Closing contact 2|3 completes the circuit through conductors 2I5 and |20 to energize magnetic clutch |36, thus coupling the screw |35 to the screw-down motor Il. Closing contacts 2|4 completes the circuit throug'hconductors |53, contact I|52 and contactor |5| to coils :g4 and |55 of the Calibrating control contactor 6. Anticipating'control cutout.-When the sliding contactor |29 of the balancing potentiometer is in its central position the contacts |5| and |52 are opened by Vcam |50,` and the contacts leading to the armature 69 of the oscillating reing `contacts 203, 2||, 2|2, 2|3 and 2|4. Preferv ably the contactor. 94 is provided with a time is of the thickness set on the gage |00. To complete the anticipating control circuit I preferably employ relay 93 and conta'ctor'94 in conjunction with contacts 96 which are closed lay 61 is closed. Thus the screw-down motor will be controlled by gage 45-through relay 64 andvoscillating relay 61 in response to variations in the thickness of the finished strip.

Movement of the armature of oscillating relay 61'in response to variations in thickness of the nished strip will break the circuit between contacts 96 thus de-energizing the holding coil 2|0 of the automatic 'control contactor 94 and opendelay device such as the dash-pot 220 so that the circuit will not be broken unless strip of incorrectthickness is being produced by the mill for an appreciable period of time, `for example l or 2 seconds. When contactor 94 opens the circuits therethrough the` anticipating control mechanism is rendered ineiTective by opening contacts 2|| and 2|2, the magnetic clutch |36 is cle-energized by opening contacts 2|3, while the opening of contacts 2|4 opens the circuit through conductors |53 to the coils |54 and |55 of the reversingcontactor |56. Under these circumstances the screw-down motor will be controlled solely by the thickness of the iinished strip and this mode of operation will continue thethickness of the entering strip simultaneously corresponds to the setting of gage |00, whereupon the anticipating control mechanism will be started again by the closing of contacts 96 and the de-energization of the automatic control starting relay 93, resulting in the closing of contactor 94,

4Summary of operation- The mill may be controlled manually in the usual manner by swinging the master `control switch 30 to the left to close contacts 3| whereupon the screw-down `the gage and the mill preferably being correlated with the speed of the strip and the speed of operation of the screw-down motor so that Y the` mill setting `will be substantially corrected motor can be controlled through push buttons.`

25 and 35 respectively to lower and raise the screw-downs, the push `buttons controlling the operation of the contactor I0.

To initiate automatic operation the operator sets the gage 45 for the thickness desiredyadjusts the gage |00 for the average thickness of theientering strip, and sets sliding contactor |29 of the balancing potentiometer to the central position. Also, the mill may be adjusted to approximately the correct setting by the push button control although this operation is not necessary as the automatic control will take care of setting the mill rolls.

The master controller is then set to the automatic position to close contacts 90 and the strip is fed through the mill. Passing the strip between rollers of the gage |00 energizes the lockout relay 9| and when the strip passes between the rollers of the gage 45 the lock-out relay 92 will be energized. Thus the yapparatus is set for automatic operation. Inasmuch as the slider |29 of the balancing potentiometer is in its central position thus cutting out the anticipating control, the screw-downs will be adjustedto produce strip of correct nished thickness by the gage `45 acting through the contact making microammeter B0 and the oscillating relay 61 to `control reversing controller I3, the circuit to the armature of the oscillating relay 61 being completed through contacts |92 of the lock-out relay 92 and the contacts |45 engaged by contact-or |46 on the slider |29. Under these conditions the automatic control contactor 94 is not energized and the anticipating control is ineffective until such time as the finished thickness of the strip corresponds to the setting of gage 45 so that the armature of the oscillating relay 61 is` in its neutral position thus closing contacts 96, and simultaneously the c ontac'tor |04 of the relay |03 is in its neutral position, indicating that strip of correct thickness is being fed to the mill, thus de-energizing the

coils

204 and 205 of the automaticl control starting'relay 93.

When these two conditions occur simultaneously the coil 2|0 of the contacter 94 is `energized thus closing contacts 203, 2| I, 2|2, 2|3 and 2|4 and permitting control of the screw-down motor by the anticipating gage |00 through relay |03 and the contactor |8. At the same time closing ofthe contact 2|3 energizes clutch |36 thus `coupling the screw |35 of the balancing povscrew-down motor through the by the time that portion of the strip of greater or lesser thickness reaches the mill. Balancing voltages are applied to restore relay |03 to its neutral position 'by the `balancing potentiometer |21, the magnitude of the balancing voltage applied for a given travel of the screw-down being determined by the setting of the potentiometer |13 which in turn is controlled automaticallyby gage 45 through relay 60, contactor |56, and motor |10 in response to variations in thickness of the finished strip.

When the trailing end of the strip passes through gage 00 lock-out relay 9| is de-energized thus opening the circuit from relay |03 to contactor I8 and preventing operation of the anticipating control. When the trailing end of the strip passes through gage 45 lock-out relay 92 is de-energized thus opening contacts |9|,

|92 and |93. Opening of contact |92 breaks the circuit leading to armature 69 of the oscillating relay 61 thereby preventing it from rotating so that the screw-down can not be operated by gage 45 after the strip has left the mill, and opening form of my invention it will be seen that I have provided a method and apparatus for controlling rolling mills which is` completely automatic in that the mill is adjusted automatically to pioduce strip of the correct gage. Under normal operating conditions, after the apparatus has adjusted itself to produce strip of the correct thickness, the mill will be controlled in response to variations in thickness of the entering strip. By the reason of the balancing potentiometer all possibility of hunting is eliminated and the mill setting will be adjusted only suiciently to pro-` duce a strip of correct thickness. The anticipating control mechanism is continuously calibrated by the action of the gage controlling the potentiometer |12 and is thus corrected to compensate for changes in the operating conditions of the mill or in the physical characteristics of the material being rolled. The mechanism is arranged automatically to compensate for errors in nished thickness which occur without any error in the thickness of the material entering the mill tentiometer to the screw-down motor and placing the `anticipating control mechanism in operation. The gage 45 and relay 60 will not operate the screw-down motor under these circumstances as the contacts 14 and 82.0f oscillating relay 61 are open.` The screw-down will be operated in response tovariations in thickness of the entering strip `by the gage |00 and relay |03 to correct the setting of the mill for any change in thickness of the strip, the distance between and, by reason of the lock-out relays, the control mechanism will not operate when there is no stripipassing through the gages. Thus` the mechanism is substantially fool-proof and will operate i to produce rolled material in which the thickness `is maintained much more accurately than has heretofore been possible.

The various gages, relays and contactors employed in my apparatus may be of standard construction and all of the instrumentalities are sturdy and will operate accurately over long periods of time. The mechanism can` be adapted readily to existing mills without any expensive changes in the mill set-up being required.

In the foregoing specification I have described 'a preferred embodiment of my invention as applied to an ordinary two-high mill adapted for the rolling of different materials all without departing from the spirit and scope of my invention. Therefore it is to be understood that my patent is not limited to the preferred form of my invention described herein or in any manner I claim:

1. 4In combination with a rolling mill, means positioned in advance of the mill for measuring the thickness of the material entering the mill, means controlled by said measuring means for adjusting the reduction effected by the mill in response to variations in thickness of material entering the mill, a second measuring means positioned beyond the mill for measuring the thickness of the material delivered by the mill and connections operable in the event that the adjustment effected by said iirst measuring means fails to adjust the mill to produce material of correct thickness whereby said second measuring means modifies the amount of adjustment effected by said rst measuring meansV mill, control means for said adjusting means actuated by said measuring means, a second measuring means positioned beyond `the mill ior measuring the thickness of the material delivered by the mill, and means controlled by said second measuring means for Calibrating said rst control 'meansto insure the production of nished material of the desired thickness.

3. In combination with a rolling mill, means positioned in advance of `the mill for measuring the thickness of the material entering the mill, means for adjusting the reduction effected by the mill controlled by said measuring means when the thickness of the entering y material varies from a predetermined standard, a second measuring means positioned beyond the mill for measuring the thickness of the material delivered by the mill, and connections whereby said second measuring means controls saidadjusting means in the event that variations in thickness of the material delivered by the mill occur in the absence ofv variations in the thickness of the material delivered to the mill.

4. Means for controlling a rolling mill having a power operatedscreW-down mechanism, comprising a gage adapted continuously to measure the thickness of the material entering the mill,

said gage producing a voltage which varies in accordance with variations in thickness of the material, a relay automatically operable in response to variations in said voltage for operating said screw-down mechanism to increase the rollmeans controlled by the movement of said screwdown mechanism for applying a balancing volt-` age to said relay tending to restore said relay to its neutral position and thereby to stop operation of said screw-down mechanism after said mechanism has operated sufiiciently to compensate for the variation in thickness of the material entering the mill.

5. Means for controlling a rolling mill having a power operated screw-down mechanism comprising a gage adapted continuously to measure the thickness of the material being rolled before other than by the scope of the appended claims. i

it enters lthe mill, said gage producing a voltage which varies in accordance'with variations in thickness of the material, a relay automatically operable in response to variations in said voltage for operating said screw-down mechanism to increase the rolling pressure applied by the mill.

in the event of an increase in thickness of the material entering the mill and 'to decrease the `rolling pressurei applied by the mill in the event ing the mill, means controlled by the movement of said screw-down mechanism for applying a` balancing voltage to said relay tending to bring said relay back to a neutral position thereby to ing pressure applied by the mill in the event of an increase in thickness of the material entering the mill and to decrease the rolling pressure applied by the mill in the event of a decrease in thickness of the material entering the mill, and

stop operation of said screw-down mechanism after said mechanism has moved sufficiently to compensate for the variation in thickness of the material entering the mill, and means controlled in response to variations in the thickness of the strip leaving the mill for varying the amount said balancing Voltage is changed in response to a given movement of the screw-down mechanism.

6. Means for controlling a rolling mill having a power operated screw-down mechanism, comprising a gage adapted continuously to measure the,thickness ofthe material being rolled before it enters the mill, said gage delivering an electric current which varies in accordance with variations in thickness of the material, a relay automatically operable in response to variations in said current for operating said screw-down mechanism to increase the rolling pressure applied by the ymill in the event of an increase in thickness of the material entering the mill and to decrease the rolling pressure applied by the mill in the event of a decrease in thickness of the material entering the mill, a -balancingpotentiometer controlled by the movement of said screw-down mechanism for applying a balancing voltage to said relay tending to bring said relay back to a neutral position and to stop operation of said screw-down mechanism, and means for controlling the input voltage supplied to said potentiometer, thereby to control the `amount of changevin the balancing voltage applied to 'said relay in response to a given movement of said screw-down mechanism.

.'7. Means for controlling a rolling mill having a power operated screw-down mechanism, comprising a gage adapted continuously to measure the thickness of the material being rolled before it enters the mill, said gage delivering an electric current which varies in accordance with variations in thickness of the material, a relay automatically operable in response to variations 'in said current for operating said screw-down mechanism to increase the rolling pressure ap plied by theA mill in the eventl of an increasein thickness of the material entering the mill and to decrease the rolling pressure applied by the mill in the event of a decrease in thickness of the material entering the mill, a balancing potentiometercontrolled by thejmovement of said screw-down mechanism for applying a balancing l themill for varying the input voltage supplied to said balancing Ypotentiometer thereby varying said current for operating said screw-down lmechanism `to increase the rolling pressure applied by the mill in the event of an increase in thickness of the material `entering the mill and to decrease the'rolling pressure applied by the mill in the event of a decrease in thickness of the material entering the mill, means controlled by the movement of said screw-down mechanism the amount said balancing voltage is changed in l response to a given movement of the screwdown mechanism; the connection being such that the balancing voltage restores the relay to neu- Y tral position, thereby-stopping operation of the screw-down mechanism, substantially as soon as said mechanism has operated sufficiently to compensate for a variation inthickness of `material entering the mill.

8; Means. for controlling a rolling mill having a power operated screw-down mechanism, comprising a gage adapted continuously to measure the thickness of the material being rolled before it enters the milLsaid gage delivering an electric current which varies in accordancewith variations in thickness of the material, a relay automatically operable in response to variations in Vfor applying a balancing voltage to said relay tending yto bring said relay back to a neutral position thereby to stop operation of said screwdown mechanism after said mechanism has Amoved suiciently to compensate for the variation in thickness of the material entering the mill, a second gage adapted to measure the thickness of the material after it leaves the mill,

means controlled by said second gage in response to variations in the thickness of the strip leaving the mill for varying the amount Vsaid balancing voltage is changed in response to a given movement of the screw-down mechanism, and lockout relays in conjunction with both said gages for preventing the respective control mechanism as sociated with said gages from operating when `there is no material passing through said gages;

FRANK P. DAHLSTROM.