US2767603A - Semiautomatic screw-down control for rolling mills - Google Patents

Description

s. H. RENDEL Y sEMIAUToMAgIc SCREW-Down CONTROL' Fbi: ROLLING MILLS ocjf. 23, 1956 2 sheetslvsheet 2 Filed Aug: 6, 1952:-

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2,767,603 SEMIAUIOMATIC SCREW-DOWN CQNTRQL E93;

George H. Rendel, Pittsburgh, hPa., assignor ,to United vv,States Stool.r Corporation, a corporation of- Nevv Jersey @pasatiempos s 1,952, senta .Noalla@ 11 Claims. (Cl. Vitl-556) Loto moolhiolr, nearer its trailing ond thanelsovvhere, So Hnos by aS.- muoh as 8 to 10 poroout.. Tfheserheavy ends, known as. mill run-downs, are tapered and normaillvY .begin to appear aPproXimalolv lQQ to 200` loer fjromthe trailing endpof each strip.

The main factors whichcause mill run-downs, are believed t` o be' loss of tensionin the stripras' its trailing end leaves each roll stand and ther lower temperature onthe strip hear its trailing end. It is`recogniz d that substan- .tial savings would be realized byfeliminating `or minimizing` mill. run-downs.

"'Anobject. of 'the present invention is to provide an improved means. and method for reducinghot mill rundowns `by automatically turning down theslrevlvs ona roll-"stand as the trailing end'of 'a' strip approaches "the stand and thereby compensating for the factorsv which Qa'use rundowns; I i "A`fur`the'r object is to provide a semiautomatic control for screw `down nmotors, which control automatically 0pve'rates rst to turn d'own the' screws'as the trailing endyof approaches a roll stand and `slibSequently,to reset-thescqr'evvs afterthe trailingend exits from this stand.

` Further objects/,are to provide lsuch-.a'control whichfhas irlaes lomaloallv Provolioe its ialorforavvifhi'oor- ,mlopi loo' of the .Sorow-oowo motors ,and vvhellorztiooallv Y havo a variable temperature compensating l. oeoomplshos .those and other` obiootsof-lllo ,iovo ntion, I have Provided improved ,detalls of str. oturo,

eared form of-wmchris shQwn' in no @con ons drawigsin which: Figaro lisa Sohonoatlo Sido velevational View of .aooxios ofrolltStads ofy a hot Strip mill to whiohtho .Control of flolf osolioinvoaloo ,iS lapplied; Ijiglurezy is .al wiring diagram `ovfrtheyclontrol;` and Eigubre is a wiringdiagrmof a modilication.

W .on tho ooolrolpof ,lhopr'osonl invention isfapplietlffo rollI stands other than'lthenfirst of a series,fva `on' ven'ent referencevpointffrorl ,Which to operateth'e contr'olnls ljie exit ofnthe'trailing'end 'of each strip from a preceding stand. The control operates electrically, and I'hav'e illustrated a circuit which is set up by the entry ofeach strip tothe roll stand two ahead of stand thus controlled and which is actuated by the exit of the strip from'this same standi However, it isapparent that equivalent 'results'can be obtained with other means preceding the controlled stand-for registering the passing-of the trail- ,Patented Gets los ooo of .oooh Strip, for example a allolooloolrlo ,coll oir-,a mechanically yactuated switch located' a proper ay'stipljerlg foiled.

Eigure l s'howsschematically three hnishinghst/andsll), 12 and 13 of ah'otQstrip mill. Each stand includes'worlc rolls 'Hand screws 1st-er regulating the separation bef Y A l l the `first stand 4l0 is 'the reference'stan'df'and the control isv applied to the A Stallo 134. auf il is apparent that Similafloonlrolo' oo' eioalodlo as many. other v`Stands oIS dosirosl.

wooo flios rolls? la Elsloo The martyrs are energized frorrrD, C.1,1in e3s{i S 'p P passesthrough the roll standsfrorn. left thev circuit oordanoe. with, tho Present lnvonliolay to ,theldrive rnotor 1160i; .the referencefrollstand 1,0cong lns a` load rolay- W. When motori-6 idly drives the rolls, 1`4rofpstand Mbit d rayvs cornpara tivelyYsmallI curr rent. lWhen a Astrip P actually is between thesey'rolls, the strip. resistsA theirl rotation; vconseqllellllly:- they IILOIr drawsamuch-larger current' to, drivefthem; TheV relay yis adjustedto piclcup (i. e. tobezactuated) whenrthe motor. draws, .thelargercurrentand itogdrop' out (\i. e. t'osbe deactuated) when the motor draws onlytheismalleridling current. Relay W has a set of'normally. opencontatifs W1,'(i. e. make-,andobreakmeans), and as hereinafter explained, operates the semiautomatic con-trolon'st'an'dl'lI Th'escrewdown motors'll'A of the controlled rollstand 13 can'be operated to raise or lower the kscrevvslS by the usual master controller, not shown, andare-:thus operated 'to move saidscrews to their initialY setting. 'ti

accordancewith thepresent invention, the circuitfto these motors includes additional normally open contacts Di Whichwhen closed' complete a circuit 'for operating the m'otors'to move the' screws down, and. addit'ionali'nrl mally opencontacts U1, which whenv closed c'or'ripleteia circuit for operating the motors to'`move"fthe"sere `A `up". These contacts' are inmdown aiidm'up relaysi'b Whe control circuit,- hereinafter described. `A magnetic-iclutfch 20 has its Vdrive element oo nnected'to one` of lthelsicrews 15 of 'the rollstan'd 13'and its driven element connected to-acam 21 of a"gage-lirriity switchy 2 2 in the-se control. As hereinafterexplained, n *Y is4 'engagedwhenlthe s,reu/downirioto'rs are' e; rgihzed'via the 'contacts'DYror Uivo'f the semiautomati'contro ,r otherwise is disengaged so that normal oneratiqmomqtors '17 `b`y their masterlkcontroller doesnotgil'llrfere with ooortioo offy fl'o '.Somlaotomatio oootolaodvoo al' 'Flavio 2,. shows 'details of oprolforrod cirooitffof. o @lill ythe Serniautornaticcontrol. VThe drive ,motor-of? e con` olled rollstand y13 Ais .indicatiedat 21.3 andA load relayV lthereof at X. Thisload relayl likewisehasv af set of normally open contacts X1 (i. er make-,andybreak means); The controlA circuit isl energized? from A. lines .24;varrd 2,5 and includes, downiand ,upfrelayslD and; Ur which contain the aforementioned; contacts. D1 'anrillrln` The control circuitincludeslsix;additionalre lays Y, Z, A, B, C, and S, a time delay :relayTDfaigage limitfsw'itch 22v already referred to, electronic vacuum tubes-26. and 27, potentiometers 28 and"29,fand astep down transformer 30. Relay Y has,` one set'ofnornially open contacts Y1 and one setyofnormally closedcoiitactstYr.V Relay Z has two sets. of. normally'opencontacts Z1 and Zz. Relay A has three sets of normally open contacts A1, A2, and Aa. Relay B has six sets of nor mally open` contacts B1, Bs,k B3, B4, B5 and Bs. Relay C has two sets of normally open contacts C1 and C3 and one setof normally closed contacts C2. Relay S has one set of normally open contacts S1. Time delay relay TD has one set of normally closed contacts TD1. Gage lirnitswitch 22 has one set of normally closed contacts 22a and one set of normally open contacts 22b.

` A pair of conductors 31 and 32 are connected to lines 24 and 25 respectively. Conductor 32 contains a manual on-off"` switch 33 for the semiautomatic control. Conductor 31 contains a set of normally closed contacts 34, which lare in the master controller for the screw-down motors 17." Whenever the operator uses the master controller to run the screw-down motors in either direction, contacts 34 open and thusautomatically cut out the semiautomatic control. The coil of relay Y and the normally open contacts W1 of the load relay W of the reference roll stand are connected in series across condu-ctors 31 and 3'2. Likewise the coil of relay Z and the normally open contacts X1 of the load relay Xof the controlled roll stand 13 are connected in series across these same conductors. When the leading end of a strip P enters the reference stand 10 and relay'W picks up, relay Y also picks up.` When the leading end of this strip enters the controlled stand 13 and relay X picks up, relay Z alsofpicks up.` It follows that relays Y and Z also drop t out when `the trailing end of the strip exits from the respective stands.

A `conductor 35, which contains the normally open contacts Y1, connects one end of the coil of relay A with conductor 31. A conductor 36,` which contains the normally open contacts S1 andthe normally closed contacts TD1; connects the other end of this coil with conductor 32. Thus when relay Y picks up and its contacts Y1 close, they condition a current path through the coil of relay A from line 24 via conductors 31 and 3S, the relay coil, and conductors 36 and 32 to line 25. A conductor 37, which contains the normally open contacts Z1, connects one end of the coil of relay S with conductor 31.

The other end of this coil is connected to conductor 32.`

Thus when relay Z 4picks up and its contacts Z1 close, relay `Salso picks up. lClosing of contacts S1 completes the previously conditioned current path through the coil of relay `A, and this relay also picks up and closes its contacts A1, A2 and Aa. Closing of contacts A1 seals in relay A around contacts Y1, since contacts A1 are situated in a branch conductor 31a which is connected between . conductors 31 and 35 and shunts contacts Y1. Closing of contacts A3 seals in relay S around contacts Z1, since contacts As are situated in a second branch conductor `31b which is connected between conductors 31a and.37 and shunts contacts Z1.

A conductor` 38, which contains the normally open contacts A2, connects conductor 32 with one end of the coil of` relay B. A conductor 39, which contains the normally closedcontacts Y2, connects the other end of this coil with conductor 31. Closing of contacts A2 conditions` a current path through this coil from Iline 24, via conductors 31 and 39, the coil, and conductors 38 and 32` to line 25. At the stagewhere the strip is passing through lboth roll stands 10 and 13, relay Y is energized and itsnormally closed contacts Y2 are open, preventing 1 completion of this current path. summarizing, as long `as the strip P continues to pass throughboth roll stands 10 and 13,1relays W, X, Y, Z, A and S all are energized, relays A and S being sealed in; relay B is conditioned, butinot `yet energized; relays C, D, and U` and time delay -relay TD have not yet acted.`

Whenthe trailing end of the strip P exits from roll stand 10 and relays W and Y drop out, contacts Y2 close and lcomplete the previously conditioned current path through the coil of relay B, which thereupon picks up, and its `normally open contacts B1 to Bs all close. Closing of contacts B1 seals in relay B laround contacts Y2, since contacts B1 are situated in a branch conductor 31e which =is connected between conductors 31 and 39 and shunts contacts Y2. A conductor 40, which contains the normally open contacts Z2 and B2, connects one end of the coil of relay C with conductor 31. A conductor 41, which contains the normally closed contacts 22a of the gage limit switch 22, connects the other end of this coil with conductor 32. Therefore closing of contacts B2 energizes relay C, its effect being later described. A con ductor 42, which contains the normally open contacts B3 connects conductor 31 with one `end of the timing element of the time delay relay TD. The other end of this element is connected to conductor 32. Therefore closing of contacts B3 completes the circuit to the time delay relay which thereupon commences timing, its effect also being later described. The driving element of the magnet-ic clutch 20 is electrically connected to a current source 43, for simplicity illustrated as a battery, via conductors 44 and 45 which contain the normally open contacts B4 and B5. Therefore closing these contacts engages the magnetic clutch and mechanically connects both the cam 21 and the slider of the potentiometer 28 1 with one of the screws 1'5 of the roll stand 13.

The normally open contacts B6 are situated in conf ductor 32, which is connected to one end of the coilsof both the down and up relays D and U for the screw-down motors 17 of the roll stand 13. The other ends of the coils of relays D and U are connected to'I the plates of tubes 26 and 27 respectively. The primary' winding of transformer 30 `is connected to lines 24 and 25; the secondary Winding of this transformer energizes the filaments of both tubes via a pair of conductors 46 and.47. The cathodes of both tubes are connected to conductor 31 via conductort47, and a conductor 48 which is connected 'between conductor 47 and the branch conductor 31a. Thus closing of contacts Bs conditions a current path through the coils of both the down and up relays. For the down relay this current path is -from line 24, `via conductors 31, 31a, 48 and 47, tube 26, the -relay coil, and conductor 32 to line 25. For the up relay the current path is similar except that it is via tube 27. It is seen that with the current paths thus set up, it is only necessary for one of the tubes 26 or 27 to become conductive for the relay D or U to pick up, close its contacts, and energize the screw-down motors 17.

For controlling the charge` on and 27, the circuit includes a Wheatstone bridge 50 which contains the aforementioned potentiometers 28 and` 29 and is energized by a current source 51, for simplicity shown .as a battery. The slider of potentiometer 29 is adjustable manually beforehand to determine the distance the turn down screws are lowered by the semiautomatic control. The slider of potentiometer 28 is mechanically -connected to the driven element of the mag netic clutch 20 as already mentioned. The left ends of the resistors of both potentiometers are connected to the positive battery terminal, with a variable resistor R1 being interposed between potentiometer 28 and the battery. The right ends of the resistors of both potentiometers are connected to the negative battery terminals. A conductor 52 is connected between the slider of potentiometer 28 and one contact each of the normally open set C1, and the normally closed set C2. The other Contact of set C1 is connected to the slider of potentiometer 29 via a conductor 53,1While the other contact o'f set C2 is connected to the negative battery terminal via a conductor 54. Conductor 52 contains two resistances Rz Vand R3.

The grids of tubes 26 and 27 are connected to conductor 52 via resistances R4 and R5 respectively. In the t starting position shown in Figure 2, which is before relay C picks up, no current ilows through conductor 52, 54 since both ends are at the same negative potentiaL The grids 0f both tubes have a negative charge so that neither the grids of tubes 26` .i-tsnow .closed contacts C3.

tribe.. eenduefins.- s.,.elreay expelled, relayl C Pieke 11' when een! ,etea dese., wherjlutlllfit's. .imallyferil cts. .Cr and. Cfeleee and flsjnrmall'y eleeefd. e611- te'et ,C2 uien-v Cleeine ef in the relay stone-bridge, s'ince-.thefreis a di paniedby yclosingv of contacts'Ciunbalances,the Wheatsliderovf potentiometer 28. contact itsv resistor. Current now. flowsl from4 potentiometer. 29. through'conductor- 53, ,contactsv ,C1 and. conductorSZ-tolpotentiometer 28. The effectifs tohapply ajpo'sitive chargetothe grid ofy tube 26. -Resistancuesv Re and Rapreven't'applic'ation of a similar ehajrgerb the grid ,Qf tube 27. l

' 'Ifube 256. .becomesc0nducting,

contacts .the resistor thereot the and, .the current path previously.conditioned. by. the ,closingnA ofn contacts. B3 vnow is completed. The ,down Dlrisv'energiz'ed and its .contacts D; close, completing currentfpath to. the yscrew.-dovvn motorsl to lowerfthe screws .llS of the controlled.grollfstand 13@ Rotation, of thescrews 'rotates the cam the magnetic clutch beingengaged. WVCam 2n-1. operiates the gage limit switch, 22 andlopens 'its normally closed contacts 22a andV closes-its normally open contacts 22h. Opening of contacts helene-immediate effect, since. relay C is sealed in around-"them via Contacts 22h are situated .int a brarleh eenduefer 3.6.1.1r Whieh iS eeltleeted between eendueters $2 and 345i and. ehumeeentaete-TDL After eer-tee@ 212.1? eleee, the time delay-relay ED vtimes auf land its contacts TD1 open, but relay-A remains-*energized via contacts-22h Rotation .of the screws also moves the sliderl of potentiometer 28l to the leftacross-the resistor thereof- -Utimetely it reeehes a peint where its potential is the same as that of the slider of potentiometer whereupon the -Wheatstone bridgeasainis inbelanee and current ceases to owthrough conductor 52, The

ceases- .to conduct current. .The down relay D drops. Out andl the screw-down motors 1:7 stop. -It isy seen that the .grid y.of -.tube Y256y loses its posit-ive charge and the tube .distance whicht'nescrews .have been loweredbefore they stopis vdetermined byfthe position of adjustment of pOen- .tiometer 29, since .this adiustment determines the point at which the .bridge vcomes into. balance..

:The screws lSzof the controlled stand 13, remainthus lowered until the .trailing end. ofthe strip exits fromthis .stand and. relays X` and Z drop out. Contacts Zaopen as -.the latter relay drops out and. breaks .the current path to the coil of relay C, which also drops out. Theynormally. closed ycontacts. C2 .again .close` andV the normally .open .contacts C1 againy open. This action. agairnunvvbalances the -Wheatstone bridge Si?, with'the slider of the potentiometer 28 now beingmorepositive vthan the conductor' 54. -Current now flows from potentiometer 28 through conductor 52, 54 in the opposite direction `f-rorn itsl previous ilow.` The grid of tube 27 attains a Apositive charge and thetube becomes conducting. The 'previously conditioned current path through the coil of `relay--U--has remained conditioned since relay B still is energized. When tube -27 becomes conducting, this current Vpath is completed and relay U isA energizedVwherekupon its contacts Ur close and complete the current path tofrnotors 17 for raising the screws. Resistances Re and Yiria 'prevent applicationof a similar positive chargefto the grid'oftubef Rotation of the screws againrotates cam v21 and the slider of' potentiometer 28, sinceV the magnetic clutch 2t) remains'engaged, but rotates in the opposite direction frombefloref The potentiometer slider again reaches its foi-ig'inalV .position at which the Wheatstone -bridge is in balance and current flow ceases in conductor 52. .The

positive charge is removed from the `grid of tube 27,

.contacts 22b deenergizes relay la, whereupon its yThedistance which the screws are Ijo'were'd is u' ldown lin `this' manner increases the pressure of the.`

whereupon this tubeA ceasesA toconduct current and re= :lay-'Udrops out.` i' The screw-'down'r'notors17'thsstp with the screws back at "their"originalsetting.l Aft-57th; same 'time cam 21 operates' gagef limit switch `22 returns ncontacts 22a'y to their normal' closedposition4 and :contacts 'tootheir normal Aopen position. lClosing'of contacts ,22a conditions the current path to rela' 'a thaty later'it can pickup for thenext 'strip4 Op contactsl A1, z and Agcpen.v Qpening' ofj c ctsa'deenergizes relay B, while opening offcohtacts A3 "de giges relay ,S. Opening of Icontacts Bswwhenrelayf dropsA out deenergi'zes'the time delay relay: TD, andopenine-[Qi eenfeefe Brand B5 deeneaees the manetieleluteh 20.' Thus the semiautomatic controlis fullyreset.

From the foregoing description it is .spleenfthat Vthe Serew-down meters 17 Q11 the.eentr011ed"rellsfa @f1.3 automatically are operated to turn down the sere s I1x5 as the trailing end of each strip approach i by .thefposition of adjustment ofthe Slider .of 't tentiorneter 29, but once the adjustmentis ma tliis distance is `the .same lfor all strips. Turning the news on theftrailing end portion of thestrip. P and thus tends to reduethis portionto the. same thicknesses the remainder ,et the` Strip.-

Figure 3 shows a modification. in the Wheats'tone to regulate automatically the-distance which screws are turned down in accordance with Variationslinth'e temperature ofthe strip.

It is, desirable that the vcooler the strip the farther the screws are turned down.

in Figure 3 two additional potentiometers 575- and .A516 are Connected vin Series between the POSitl/e terminal# battery 51 and the resistor of the potentiometer 2:8.. The potentiometer 55 has a slider 57 mechanically connected tof'a pyrometer indicator, not shown', but which vis nresponsive tothe strip temperature. The pyrorneter moves the slider in a direction to short out more andmore of the resistor of the potentiometer the` vhotter the. strip. rIhe pyro'meter automatically disconnects itself from. the slider on attaining the. maximum temperature `of the strip. The potentiometer 56 is manually operated and regulates the degree of compensation' fontmperatu're. The less of the resistor that is shunted. out` in. potentiometer 56, the more the temperature compensation. It is seenthat the greater the resistance between the positive battery terminal and the vpotentiometer '28; the farther the slider of this potentiometer must travel to balance the bridge. Consequently the colder the' strip, the greater the distance whi'ch the' screws are' turned dpwnl An example using hypothetical values may be helpfulrin understanding the temperature compensationfeaturel Assume thevoltage across the battery 51 `is 10Q volts and the voltage drop across the potentiometers Y28, 55' and 56 is respectively 50 volts,2 5 volts 'and 25 volts. "If thelfstrip being rolled is to have the maximum of compensation for temperature, the slider ofthe potentiometerf56'i's ad justed sothat the potential from the slider is 50 volts positive when referred yto the negative battery terminal; that is none of the resistor ofthis potentiometer isshunt'ed out. To balance theVl/heatstonebridge,l the screw-down motors must lower the screws until tlieslrider'of potentionmeter 2,3 is at this same voltage. If the l'strip is so cold that the slider 57 of potentiometer" 55 does not move to short o ut any of the resistor of this potentiometer, the voltage drop across potentiometer 23 remains 50 Volts;the vscrewsarclowered by'an 'arrfont equal to the full travel of the slider of' potentiometer 2 8. Full travel on this potentiometermay bel equivalent'l to 0.100 inch vertical travel of the screwsjtherefore when the strip is cold, the controls lower.the.screws0..l00.inch and later return to their starting` position.

It the strip, is hot enough tomove. the slider 5]- etv potentiometer 55 far enough `to short out allof the resistor, the voltage drop across the potentiometer becomes zero. Now the voltage drops across potentiometers 28 and 56 are .662/3 and 33% volts respectively. The screws are lowered until the slider of potentiometer 28 reaches a position that is 50 volts positive. This position balances the bridge at a point where the slider is at 75 percent of full` travel, which corresponds with 0.075 inch vertical travel of the screwsp If the strip being rolled is to have the minimum of compensation for temperature, the slider of potentiometer 56 is moved manually to shunt out all the resistance thereof. Now there is a voltage drop of 66% volts acros potentiometer 28 and 331/3 volts across potentiometer 55. For the` same setting on potentiometer 29 of 50 volts from `its sliderto the negativeibattery terminal, when a cold .strip isirolled, the screw/down motors would lower the screws an ,amount equivalent to 75 percent of4 full travel of the slider of potentiometer 28 to balance the bridge. When the strip is hot enough to move the slider 57 of potentiometer 55` the full distance to shunt out all of its resistance, there would be 100 volts drop across poitentiometer 28 and the slider of potentiometer 28 would move only have its full travel to balance the bridge.

This example shows how the control can be regulated from `maximum to minimum temperature compensation by adjusting the slider of potentiometer 56.` The total amount which the screws are lowered can be regulated by adjusting the slider of potentiometer 29. Preferably both potentiometers 56 and 29 are located where they are convenient to the mill operator.

' While two embodiments of my invention have been shown and described, it will be apparent that other adaptations and modifications may be made without departing from the scope ofthe following claims.

I claim:

l. In a hot strip rolling mill which includes a plurality of roll stands, each of which has. a pair of work rolls, a drive motorfor said rolls, screws for regulating the separation between said rolls, and screw-down motors for turning said screws up and down, one of said stands being a reference stand anda succeeding stand beinga controlled stand, the combination with said controlled stand of a semiautomatic control comprising load relays in the circuits of the drive motors of said reference and said controlled stands, each of said relays being adapted to pick up when a strip is between the rolls of its stand and otherwise to drop out, a control circuit connecting the load relay of said reference stand and the screw-down motor of said controlled stand for turning down the screws of the latter stand whenthe load relay of the former stand drops out as the trailing end of a strip exits therefrom, and means in said control circuit connected t0 the `load relay of said controlled stand for resetting the screws thereof when this relay drops out as the trailing end of the strip exits from said controlled stand.

2. A combination as` defined in claim l in which said control circuit includes a normally balanced Wheatstone i bridge, connections between said bridge and the screwdown motor of said controlled stand for operating this motor when said bridge becomes unbalanced, connections between said bridge and the load relay of said reference stand for unbalancing said bridge when this relay drops out as the trailing end of a strip exits from this stand and thereby operating the screw-down motor of said controlled stand for turning down the screws thereof, and means for restoring the bridge to balance after the screws are turned down a predetermined distance.

3.` A combination as defined in claim 2 in which the re setting means includes connections between said bridge and the load relay of said controlled stand for unbalancing said bridge when this relay drops out and means for restoring the bridge to balance when the screws return to their original setting.

4. In a rolling mill for lengths of hot strip having leading and trailing ends, which will include a series of tit) roll stands each having a pair of work rolls, a drive motor for said rolls, screws for regulating the roll separation, and power means for turning said screws up and down, said roll stands being adapted to roll a strip under tension and thus tending to leave a tapered thicker portion in the strip near its trailing end, the remainder of the strip being of substantially uniform thickness, at least one of said stands being a controlled stand, the combination with said controlled stand of a control for the power means for its screws effective to turn them down as the portion of a strip near the trailing end is between the rolls of this stand and up after the trailing end exits therefrom, but allowing the screws of the controlled stand to remain at settings attained independently of the control when the rest of the strip is between the rolls thereof, said control comprising a circuit connected with the power means for the screws of said controlled stand, a first make-and-break means in said circuit, means for actuating said first make-and-break means when the leading end of a strip passes a point lo cated a predetermined distance ahead of said controlled stand and for deactuating said first make-and-break means when the trailing end passes said point, a second makeand-break means in said circuit, means for actuating said second make-and-break means when the leading end passes said controlled stand and for deactuating said second make-and-break means when the trailing end passes said controlled stand, means in said circuit conditioning a current path to the power means for the screws of said controlled stand when both said make-and-break means are actuated, means in said circuit completing this current path to operate said last mentioned power means to turn the screws down a predetermined distance when said first make-and-break means is deactuated, means for deenergizing said last mentioned power means after the screws are turned down said last mentioned predetermined distance, and means in said circuit completing a current path to operate said last mentioned power means to reset the screws when said second make-and-break means is deactuated.

5. A combination as defined in claim 4 in which said first make-and-break means and the actuating and deactuating means therefor include a load relay in the circuit to the drive motor of a roll stand preceding said controlled stand, and said second make-and-break means and the actuating and deactuating means therefor include a load relay in the circuit to the drive motor of said controlled stand, said relays picking up when a strip is between the rolls of the respective stands, but otherwise dropping out.

6. A comibnation as defined in claim 4 in which said circuit includes means for adjusting the predetermined distance by which the screws of said controlled stand are turned down on completion of the current path to the power means therefor.

7. A combination as defined in claim 4 in which said circuit contains a bridge across which the power means for the screws of said controlled stand is connected, said bridge remaining in balance when the circuit is conditioned, and means for unbalancing said bridge when said rst makeand-break means is deactuated to turn the screws down and again when said second make-and-break means is de actuated to turn the screws up.

8. A combination as defined in claim 4 in which said circuit includes means responsive to strip temperature for automatically varying the predetermined distance by which the screws of said controlled stand are turned down in accordance with strip temperature.

9. In a rolling mill for lengths of hot strip having leading and trailing ends, which mill includes a series of roll stands each having a pair of work rolls, a drive motor for said rolls, screws for regulating the rolls separation and power means for turning said screws up and down, said roll stands being adapted to roll a strip under tension and thus tending to leave a tapered thicker portion in the strip near its trailing end, the remainder of the strip being of substantially uniform thickness, at least one of said stands being a controlled stand, the combination with said con- 9 trolled stand of a control for the power means for its screws effective to turn them down as the portion of a strip near the trailing end is betwf,` :n the rolls of this stand and up after the trailing end exits therefrom, but allowing the screws of the controlled stand to remain at settings attained independently of the control when the rest of the strip is between the rolls thereof, said control comprising a bridge circuit having arms which contain normally balanced adjustable resistances, electrical connections to the power means for the screws of said controlled stand connected across said bridge circuit and thus normally keeping this power means deenergized, a first make-and-break means connected to said bridge circuit, means for actuating said first make-and-break means when the leading end of a strip passes a point located a predetermined distance ahead of said controlled stand and for deactuating said first make-and-break means when the trailing end passes said point, a second make-and-break means connected to said bridge circuit, means for actuating said second makeand-break means when the leading end passes said controlled stand and for deactuating said second make-andbreak means when the trailing end passes said controlled stand, successive actuation of both said make-and-break means conditioning said circuit and deactuation of said rst make-and-break means unbalancing said circuit to energize the power means for the screws of said'controlled stand to turn them down a predetermined distance, and a mechanical connection between one of the last mentioned screws and one of said adjustable resistances to restore said bridge circuit to balance and thus ydeenergize the power means when the screws are turned down said last mentioned predetermined distance, deactuation of said second make-and-break means unbalancing said bridge circuit in the opposite direction to energize the power means for the screws of controlled stand to reset these screws.

10. A combination as defined in claim 9 in which said mechanical connection includes a magnetic clutch normally disengaged to allow Operation of the power means for the screws of said controlled stand independently of said control, and said control comprises a circuit for engaging said clutch when the power means is operated by imbalance of said bridge circuit.

11. A combination as dened in claim 9 in which said first make-and-break means and the actuating and deactuating means therefor include a load relay in the circuit to the drive motor of a roll stand preceding said controlled stand and said second make-and-break means and the actuating and deactuating means therefor include a load relay in the circuit to the drive motor of said controlled stand, said relays picking up when a strip is between the rolls of the respective stands but otherwise dropping out.

References Cited in the le of this patent UNITED STATES PATENTS 1,814,354 Webster et al. July 14, 1930 1,969,536 Winne Aug. 7, 1934 2,003,160 Townsend May 28, 1935 2,275,509 Dahlstrom Mar. 10, 1942 2,300,990 Stoltz Nov. 3, 1942 2,339,359 Shayne Jan. 18, 1944 2,343,392 Whitten Mar. 7, 1944

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