US2767604A - Apparatus for monitoring the operation of rolling mills - Google Patents

Description

Oct. 23, 1956 M. E. WHALEN, JR

APPARATUS FOR MONITORING THE OPERATION OF'ROLLING MILLS 3 Sheeis-Sheet l Filed Jan. 19, 1953 oh! 2 R mm E INVENTOR MARK E..WHA\.EN,JR.

BY M E 7 7 ATTORNEY 2,767,604 APPARATUS. Fok MONITORING. THE OPERATION OF ROLLING} MILLS Fileddaln. 19. 1953 -Oct. 23, 1956 M. E. WHALEN, JR

3' Sheets-Sheet 2 ZPO:

INVENTOR MARK E. WHALEN, \TR. BY M f ATTORNEY 2,767,604 APPARATUS "FOR MONISORING THE OPERATiON 0 RbLnING MILLS Oct. 23, 1956 M. E. WHALEN, JR

3 Sheets-Sheet 3 Fil'd'Jan. 19, 1953 IN VENTOR MARK E. WHALEN, U12.

BY W

ATTORNEY United States Patent APPARATUS FOR MONITORING THE OPERATION OF ROLLING MILLS Mark E. Whalen, In, Youngstown, Ohio Application January 19, 1953, Serial No. 331,931 Claims. (Cl. 805I6i) The present invention relates to the art of rolling metal strip and sheet, and more particularly to improvements in controls for metal rolling mills whereby the same may be continuously and automatically monitored for the purpose of assuring the production of sheet or strip of the required thickness or gauge.

The ultimate object of this invention is the provision of a practical control system for incorporation into a metal rolling mill which is operative to monitor the operation of the mill and to automatically effect adjustments therein, as necessary, in order that the product of the mill may be maintained uniformly at a predetermined thickness, or within commercial tolerance limits, insofar as is practical in the normal operation of the mill.

Another object of this invention is the provision of a control system for the above-mentioned purpose which is adapted to integrate a plurality of control stimuli and to therefrom determine an appropriate control adjustment based on the plurality of stimuli which may include, in addition to strip thickness, metal temperature and roll loading, for example. Thus, in some instances a first control stimulus may indicate that strip being rolled is not within prescribed tolerances and correction would be apparently desirable, while a second control stimulus may indicate that the mill is overloaded, for example, or that the strip is not of the desired temperature, and the second stimulus may override the first and prevent adjustment of the mill which maybe only apparently and not actually desirable.

Another object of the invention is the provision of a control system of the type mentioned above which is adapted for incorporation into a multi-stand rolling mill whereby when adjustment of the mill is desired, as indicated by the integrated result of a plurality of control stimuli, such adjustment may be effected in the correct proportion at a plurality of stands of the mill whereby each of such stands may be at all times burdened with a proportionate share of the overall load on the mill. In this respect it will be understood that in a multi-stand mill the increment of reduction of the strip is smaller at each succeeding stand since it becomes increasingly difiicult to further reduce the material as it becomes progressively thinner at each stand. Accordingly, when adjusting each stand it is desirable to adjust succeeding stands in proportionately different amounts but in proper relation to the overall adjustment required. And the apparatus of the present invention is intended to so function.

Another object of the present invention is the provision of a control system of the above described nature which is operative to effect corrections or adjustments in one 65 or more mill stands in such a manner that hunting or continual compensating adjustment caused by previous overadjustment, for example, is virtually eliminated. Thus, the invention seeks to provide a control system wherein mill adjustments may be effected in a step-by-step 70 manner, each step being of less magnitude than the prescribed tolerance range whereby no adjustment of the mill will cause strip thickness to be corrected from one side of the tolerance range to the other. Past attempts to automatically control mill adjustments of the type herein contemplated have almost universally met with failure due to the continual hunting of the adjusting mechanisms which necessarily operate at a substantial time lag with respect to the control stimuli therefor. For example, in prior control arrangements of which I am aware a suitable adjusting mechanism operated in response to a control signal indicating that the strip was not Within prescribed tolerance limits. However, unavoidable time lags in the system resulted in the adjusting mechanism functioning for a certain time after the proper adjustment had been accomplished and often a new adjustment became necessary immediately upon completion of a preceding adjustment. This type of operation resulted in considerable wear on the mill equipment, and in an imperfect product. Accordingly such prior control systems have not been accepted commercially.

Yet another object of the invention is the provision of a control system of the type and for the purpose described which may be readily incorporated into presently existing rolling mill installations utilizing a bulk of the control instrumentalities conventionally provided with such mill installations.

Other objects and advantages of the invention will become apparent upon full consideration of the following detailed specification and accompanying drawing wherein are illustrated certain preferred embodiments of my invention.

In the drawing:

Figure 1, shown on two sheets as Figure 1a and Figure 1b, is a simplified schematic diagram of the last or finishing stands of a multi-stand continuous hot strip rolling mill and of the control system of my invention as arranged for monitoring the operation of the mill; and

Figure 2 is a simplified schematic view of my control system as utilized for the purpose of monitoring the operation of a cold-reducing or so-called Steckel mill.

Referring initially to Figures la and 1b I have shown three reducing stands, numbered 10, 11 and 12, respectively, of a multi-stand rolling mill, which stands may constitute Nos. 8, 9 and 10 of a ten stand mill, for ex ample. In accordance with conventional mill construction each of the stands 10-12 comprises upper and lower large- diameter backing rolls 13 and 14, and upper and lower small- diameter work rolls 15 and 16 between which strip stock 17 passes in its traverse through the mill. Also conventionally, the stands 10-12 are provided with independently controllable drive motors 1840, respectively, and independently controllable screw-down adjusting mechanisms including electric motors 21-23 as shown.

In the usual rolling practice corrections are made in the mill settings whenever an operator notices that the strip 17 leaving the final stand 12 is not within the prescribed gauge limits. And generally such correction or adjustment is effected in the last stand 12 and, if possible, in the next preceding stand 11. Such adjustment is ordinarily accomplished by energizing screw-down adjustment 23, and, if two stands are to be adjusted, also screw-down adjustment 22. However, in most cases it is difiicult for an operator or operators to properly correlate the necessary adjustments into two stands, and accordingly, the entire correcting adjustment is made at the final stand 23, it being understood, of course, that such corrections are often of small magnitude. Every stand is nevertheless provided with an independently adjustable screw-down control for the purpose of initially setting the plurality of mill stands at their nominally correct settings.

To energize the various screw-down adjustments 21-23 adapted to selectively connect the respective adjustment mechanism with a source of direct-current energy whereby ,depending upon which one of a pair of relays is energized the related mechanism will effect an adjustment of the mill stand either in an upward or downward direction. In the present illustration adjustment of stand 12 is controlled by relays 12U and 12D. which are arranged respectively to efiect upward and downward adjustment at the stand 12. Similarly, relays 11U and 11D control stand 11 and relayslOU and D control stand 10. Under present practice these relays are energized at the discretion and judgment of the operator. However, the invention concerned herein teaches the automatic control of such relays utilizing as control stimuli factors upon which the judgment of an operator is presently based.

In order. to properly judge when mill stand corrections or adjustments are necessary and desirable an operator must correlate certain information regarding the performance of the mill and the condition of the strip, as for example, strip thickness, metal temperature and loading of the mill stands. Thus there is commonly provided a suitable thickness gauge 24 at the discharge, side of the last stand 12, a temperature indicating device 25 positioned adjacent the stand '12, and individual load indicators 26-28 for drive motors, 1820, respectively, which may be connected in series relation to the drive motors whereby to indicate if and when the work rolls 15 and 16 of each stand are being excessively loaded and in danger of breaking. Load indicating devices 2648 may be in the nature of suitably calibrated current responsive devices or ammeters. Thickness indicator 24 may be a conventional X-ray gauge. And temperature indicator 25 may comprise a suitable radiation pyrorneter, for example.

In the usual rolling practice an operator observes primarily the thickness indicator 24 in order to determine when the strip 17 is being produced off gauge. If, for example, indicator 24 shows the strip 1.7 to be toothick a suitable downward adjustment of the last stand 12 and next preceding stand 11 may be in order. However, before such action should be taken the operator should check the temperature gauge 25. He may, for example, find thatthe strip temperature is somewhat below the prescribed tolerance for proper rolling. And if such as the case a downward correction of one or more of the mill stands may be in fact undesirable even though the indicator 24 shows the strip 17 tobe off gauge. In this respectit will be understood that in hot strip rolling the original slabs of metal are preheated to a desired temperature and thereupon sentthrough the mill one at a time, the slabs being subjected to apredetermined reduct tion at each stand of the millwhereby upon the same having passed through the entire mill it is reduced to strip of the desired thickness. It may occur, however, that one or two of the slabs in a days production will be sent through the mill at, for example, lower than prescribed temperature in which case the strip as it passes through each successive stand will be reduced an amount somewhat less than that desired, finally emerging from the mill thicker than desired. In such a case it is not desirable to adjust the mill stands downwardly since by the time the adjustment is affected the off-temperature slab is usually through or substantially through the mill and the adjustment will affect only the next subsequent slab which in all probability is at the proper temperature and whichwill, if the. apparently proper correction is made for the off-temperature slab, emerge from the mill thinner than desired. Not only does this result in two off-gauge strip lengths, but requires two mutually correcting adjustments of the mill, all of which is undesirable and serves no useful purpose. A similar but reversed situation prevails when slabs are sent through the mill at higher than the prescribed temperature range.

Similarly, an operator should refer to the load meter for any stand before effecting. a downward adjustment of the same since if the stand is overloaded correction should be applied to another stand or not all, it being preferred that a strip length pass through off-gauge than to risk the breakage of the rolls and consequent shutdown of t the entire mill.

The apparatus of my present invention automatically takes the above factors into account before effecting any adjustment of the mill stands and thereby eliminates the possibility of an error in judgment of the operator and/or the possibilityof neglect by an operator to ob serve and consider any one of the above-mentioned factors.

Thus, to control the energization of relay 12D for downward adjustment of stand 12 I have provided a plurality of control relays 12DT, 12DTH, 12DHL, 12DNL and 12DTM (see Figure lb) each of which has contacts connected in series with the energizing coil of relay 12D through conductor 29. Relay 12DTH is the. primary controlling relay for relay 12D and is energized to close its normally open contacts in response to an indication on the thickness gauge 12 that the strip 17 is too thick. It will be observed that the gauge or indicator 24 is provided with electrical contacts. at each the upper and lower tolerance limits for strip thickness, which tolerance limits may be adjusted to suit existing requirements. Indicators of this type are comon commercial products.

At such time as the indicator needle of gauge 24 contacts the right-hand limit contact an electrical circuit is completed throughconductors 3t) and 31 and thereby through the energizing coil of a sensitive relay DTI-I, contacts of which are connected in series with the energizing coil of relay 12DTI-I through conductors 32 and 33.

The arrangement is such that relay 12DTH is energized indirect response to a gauge indication of excessive thickness of the strip, intermediate relay DTI-I serving in the capacity of an amplifier so that current flow through the contacts of gauge 24 may be maintained at an absolute minimum.

Relay 12DT is also provided with normally open contacts and hence must be energized to effect a downward adjustment of stand 12. The energizing circuit of the last-mentioned relay includes normally open contacts of an amplifying relay DT and conductors 34 and 35, the amplifying relay DT being energized by the temperature indicatingdevice 25 through conductors 36 and 37.

It will be understood that the temperature indicator 25 will register zero at all times when no strip is passing thereunder i. e. in the interval between the rolling of successive slabs of metal, and that upon the strip passing beneath the device 25, assuming the strip to be within the proper temperature range, the indicating pointer 33 will respond accordingly, moving past a minimum temperature contact member 39 whereby to effect an instantaneous closing of the energizing circuit for relay DT. In the illustrated embodiment of the invention relay DT is provided with a suitable ratcheting or latching device 40 whereby upon the relay being energized even instantaneously the same will be held in a closed position until a next subsequent instantaneous energization, whereupon the latch will be released to permit the relay to assume its normal open position. Relays so constructed are of course common commerical products.

Thus, it will be observed that as the pointer 38 of temperature indicator moved to the right past the contact 39 relays DT and 12DT will be energized until the pointer 38 again moves past the contact 39, as for example when a slab has been completely processed in the mill and strip is no longer passing under the temperature indicator 25.

Relay 12DHL is energized through conductors 41 and 42 and contacts of amplifying relay 12DHL' which is in turn energized through a circuit including conductors 43 and 44 and limit contacts at the load indicator 28. The arrangement is such that if at any time the drive motor 20 for stand 12 becomes loaded to a greater extent than is desirable the load indicator 28 causes energization of relays 12DHL and 12DHL'. Relay 12DHL is provided with normally closed contacts in the energizing circuit for relay 12D as will be apparent, and it thus becomes a condition precedent to the energization of relay 12D and consequent downward adjustment of stand 12 that such stand not be in a then overloaded condition. And it will be further observed that if, as a result of a partial downward adjusting movement of the stand 12 the same becomes overloaded relay 12DHL will immediately become energized to prevent further adjustment.

Relay 12DNL is energized through conductors 45 and 46 and contacts of amplifying relay 12DNL', the lastmentioned relay being energized through a circuit including conductors 47 and 43 and load indicator 28 whereby downward correction of the stand 12 is prevented at all times when the same is operating under no load conditions. This provision is desirable in instances where, for example, the trailing edge of a strip has just passed through the stand 12 leaving the same under no operating load, while at the same time the control stimulus from thickness indicator 24 may be signifying a need for downward adjustment of the stands, the strip at such time being out of the reducing stands, but not yet past the thickness indicator. Where such a condition exists it is undesirable to adjust the stand downwardly since the same may have been previously operating at maximum load and further downward adjustment would be likely to cause the stand to be overloaded at such time as the next subsequent strip length enters the stand.

Relay 12DTM is a timing relay the energizing circuit of which is connected in parallel with relay 12DTH whereby both relays are simultaneously energized in response to control stimuli from thickness gauge 24 indicating the need for downward adjustment. The relay 12DTM, in accordance with the principles of the invention is of a type which operates a predetermined adjustable time period subsequent to its energization, and is provided with normally closed contacts in the energizing circuit for relay 12D. The arrangement is such that downward adjustment of stand 12 will be terminated after a predetermined adjustment time. And it is in accordance with the teachings of the invention that such time period be of a sufficiently small duration that the magnitude of adjustment which may be effected in such period of less than the tolerance range set by the thickness indicating gauge 24. This arrangement prevents hunting of the adjusting apparatus due to overcorrection since it is not possible to execute a correcting adjustment which would alter the thickness of the strip 17 from one side to the other of the prescribed tolerance range.

A summary of the control of the downward adjustment of stand 12 is as follows: No downward correcting adjustment which may otherwise appear desirable may take place unless the strip is at least at a predetermined minimum temperature which may be regulated as desired by adjustment of contact member 39. Nor can any adjustment take place unless the mill is under operating load, but within a predetermined safe load range. Assuming that the temperature and loading are within proper limits, a signal from the thickness or deviation gauge 24 will cause downward or closing movement of the stand 12, such downward movement continuing only until timing relay IZDTM opens regardless of whether at the end of such time the thickness gauge signifies that the strip 17 is within the prescribed tolerance limits. If, however, at any time while the adjusting movement of the stand 12 is taking place load meter 28 indicates that the same has been loaded to maximum capacity further adjustment is prevented by opening of relay 12DHL, regardless of whether relay 12DTM has timed out or whether the strip 17 has been brought to the desired size.

Downward adjusting movement of stands 11 and 10 is controlled by relays 11D and 10D, respectively, which relays are in turn controlled in a manner similar to relay 12D as prescribed above. Thus, each of the relays 11D and 10D is provided with DT, DTH, DHL," DNL and DTM relays, as indicated in Figure 1b, which perform the same function as the corresponding relays described in relation to the control of stand 12.

In accordance with the teachings of the invention, when a roll adjustment is necessary it is desirable that the same be distributed over a number of stands, rather than merely the last, and that such adjustments be made in greater proportion on certain of the stands so that during any adjustment the plurality of stands affected will each sustain approximately equal increases or decreases in loading. In the illustrated control, therefore, wherein the last three stands of a multistand mill are provided with automatic adjusting control, I provide that stands 10, 11 and 12, in that order, have proportionately smaller adjusting movements, the sum total of all adjustments, however, comprising the desired alteration in strip thickness. Thus, it will be observed that the DT, DTH, and DTM relays for the stands 10, 11 and 12 are connected in parallel whereby, for example, when amplifying relay DT is energized relays 10DT, 11DT and 12DT are simultaneously energized and an adjusting correction will be simultaneously initiated at the three aforementioned mill stands, assuming of course that other factors are such that adjustment is desired. At a predetermined time later timing relay 12TM opens to stop further adjustment of stand 12, while adjustment of stands 11 and 10 is continued. A predetermined time subsequent to the opening of relay 12DTM, relay llDTM times out and opens stopping further adjustment of stand 11. And at a still later time relay 10DTM opens to complete the adjustment of stand 10. It is contemplated by this invention that relays 12DTM, 11DTM and 10DTM will be independently adjustable as to timing periods so that the proportion of adjustment to be applied to each stand may be regulated as may the total increment of adjustment which is applied to the strip 17.

It should be observed that the DHL and DNL relays for each stand are provided with independent amplifying relays, designated by prime reference, as for example 10DHL, and for each stand there is an independent load meter 26, 27 or 28 for controlling the last-mentioned amplifying relays. Thus, the plurality of automatically controlled stands 10, 11 and 12 are subject to independent load control, and while the three stands are simultaneously undergoing an adjusting movement, further adjustment of any one of the stands may be prevented upon the same becoming overloaded while the adjustment may be continued at the other stands which may not be so heavily loaded. Also, if the three stands are undergoing adjustment as the trailing end of a strip length passes through stand 10, for example, further adjustment of that stand will be prevented by energization of relays 10DNL and 10DNL', while the adjustment may continue at the other stands.

To make an upward adjusting correction in the mill stands I have provided in series with the thickness or deviation meter 24 an amplifying relay UTH which is arranged to be energized when theindicating needle of the meter 24 contacts the left-hand limit contact of the meter. Upon relay UTH closing energizing potential is applied to UTM and UTH relays for each stand (see Figure 1b) closing energizing circuits to relays 10U, 11U and 12U and ultimately effecting upward adjustment of the stands 10-12. In accordance with the teachings of the invention relays 12UTM, llUTM and 10UTM are timing relays which open in succession in the order named at predetermined times after energization in order to limit the adjustment of each of the stands 10-12 to a predetermined increment. It is contemplated ,by the invention that the timing periodsof .thelast-mentioned UTt 1 relays will :be individually adjustable so thattthe increment of adjustment of each=stand :may be ,varied to suit the requirements; of the operation. Usually it is desirable that the, timing periods of the UTM? relays .berthe same as those of the corresponding .DTM relays so that correction increments in either. direction will be substantially equal. 1

As noted before, it is not unusual inhot strip mill operation for occasional off-temperature slabs to be sent through the mill. Andwhere, for example, a slab is at a temperature above the desired rolling temperature range the material ,will be relatively soft'and will emerge from the mill somewhat ,undersizta-even though the mill stands are correctly adjusted. I have found that it is not desirable to adjust the standsupwardly in such instances, even though the deviation meter -24 may so indicate, and I naveaccordingly provided .UT relays in the energizing circuits of relays IOU, 11U :and 12U, which UT relays are energized upon contactof members 38.and 47 of temperature responsive device 25. An amplifying relay UT is of course provided and :this relay is energized directly by the temperature responsive, device 25 whenever the same indicates thestrip to be above a predetermined temperature range. It will be noted that the above-mew. tioned UT" relays are provided with normally closed contacts in the energizing circuits for relays U,11U. and 12U whereby these relays cannot be energized if the strip 17 is above the desired temperature rangeand accordingly no upward correcting adjustment can take place.

The control apparatus above described is intended primarily for use on hot strip millslwherein individual slabs of heated metal are sent through the mill one after another, each slab emergingin the form of an elongated strip as will be understood. -I have found that these slabs usually make a-complete traverse through the mill in such a short interval of. time. that not more than one correcting adjustment may take place during passage through the mill of a single 81215.1 vAnd accordingly, I havemadeno provision for making repeated correcting adjustments. Thus, it will be notedthat if *timing relays 10DTM, liDTM and 12DTM are energized by the deviation gauge 24 they1will remain-so energizeduntil indicator of the deviation gauge moves away from its right-hand limit contact, which, in some instances, it may not do after only a single correctingadjustment. However, since only one correction per slab is desired I utilize the short interval. of time between passage of successive slabs through the mill, to permittthe control relays to be reset for a subsequent adjustment. Thus, in the aforementioned time interval the gauge: 24 willindicate no thickness and will accordingly permit the various DTM relays to become deenergized and reset. Also, as the trailing end of a strip passes under the temperature gauge 25 the indicator 38 will fall to zero, contacting member 39 as it so falls, and thereby temporarily energizing the latching relay DT and permitting the same to assume its normal open position. t

Where, for example, ,a strip length passes out of the mill while the indicator of the deviationpr thickness gauge 24 is resting on the left-hand or minus contact relays lllUTM, llUTM and 12UTM are deenergized by opening of relay UNL which is energized in response to a no load indication on, meter 28 which monitors the loading of the last stand 12. Relay UNL is a time delay relay which when deenergized .upon the entry of a subsequent strip length between therolls of stand 12 will drop into a closed position onlyafter a predetermined time. This delay period should be sufiicient to permit the leading end of the strip. length to move from the stand .12 to a point adjacent the thickness gauge 25 so that the last-mentioned gauge will indicate truestrip thickness, and not merely the lack of any strip at all, at such time as the contacts of relay UNL close. It will be understood that otherwise an upward correcting adjustment would be called for by the gauge 24 each time the leading end of a strip length entered the stand 12 and applied a load there- Where it may be desired to modify the control of Figures la and lb so that several correcting adjustments may be made during the passage through the mill of a single length of strip, as in certain cold rolling practices, for example, it is merely necessary to incorporate a suitable interrupter in the conductor 30 leading to the indicating needle of thickness gauge 24. Such interrupter may comprise, for example, a conductor 50, rotating switching contacts 51 and a variable speed motor 52 for rotating the contacts 51. As will be understood,.the interrupter may be connected into the circuit of conductor 30 by removing a jumper conductor indicated at 30 and substituting therefor the circuitincluding conductor and contacts 51. With the modified arrangement the DTM" or UTM timing relays are deenergized and reset each time the contacts rotate to open the circuit through gauge 24. And it upon subsequent closing of this circuit further adjusting correction is required the same will be effected as will be readily apparent.

In Figure 2 I have illustrated my control as incorporated into rolling mill apparatus of the so-called Steckel type which is commonly utilized for the purpose of cold working and reducing steel strip. The mill apparatus may conventionally comprise a single rolling stand having a pair ofsmall diameter working rolls 53 and large diameter back-up rolls 54 and 55, and a suitable screwdown mechanism, as illustrated at 56, driven by an electric motor57. The conventional Steckel mill is provided with coiling and uncoiling stands 58 and 59, respectively. And in accordance with a common construction the coiling stand or reel 58 'is provided with a drive motor 60 with which strip 61 may be drawn through the rolls 53. Adjacent the coiling and uncoiling stands 58 and 59 are idling rolls 6?. and 63 about which the strip 61 is passed in the manner shown. Control relays U and D connect the screw-down drive motor 57 with a source of power 64 in one of two polarities whereby the motor 57 may be operated in forward or reverse directions to raise or lower the roll 54 as the situation may require. In the illustrated circuit it is contemplated that rclay U, when energized, will cause upward adjustment of roll 54 while relay D, when energized, will cause downward adjustment.

To energize relay U in response to a requirement for an upward adjustment of the roll 54 I have connected the energizing coil of the relay in series with a thickness indicating or deviation gauge 65 so that when the indicating needle of the gauge 65 rests in contact with an adjustable limit stop indicating that the strip 61 is not being sufliciently reduced in the mill.

The gauge 65 may be of a clitferential type which is provided with suitable drive means for registering the rotation of the idle rolls 62 and 63. Roll 62 will, of course, rotate faster than roll 63 by an amount directly related to the amount of reduction imparted to the strip 61 by the working rolls 53. Gauges of this type are conventionally utilized on mills of the type disclosed.

As will be observed, the energizing circuit for relay U included, in addition to the gauge 65, conductors 66, 67 and 68, the energizing coil of an adjustable timing relay TR, conductor 69, rotating current interrupter 70 and conductor 71. The arrangement is such that when the interrupter 70 is conditioned to provide a complete circuit, as shown, and the indicator of gauge 65 rests on the minus contact, relays U and TR will be simultaneously energized and an upward correcting adjustment of roll 54 will be initiated. After a predetermined time interval 1 relay TR opens to disconnect the motor 57 from its power source 64 to terminate the adjustment. In accordance with the teachings of the invention, the adjustment time afforded by timing relay TR is less than the time required for the motor 57 to effect an adjustment which will carry the indicator of gauge 65 from one limit contact to the other so that continuous hunting of the apparatus is avoided. I

It will be noted that if after timing out of relay TR to terminate an adjustment the gauge 65 continues to indicate a need for upward adjustment the same will take place upon subsequent interruption and reestablishment of the energizing circuit by the rotating contact 70. The frequency of circuit interruption may be regulated by motor 72 which may be of the variable speed type.

Control relay D is arranged to be energized in response to a requirement for a downward adjustment of roll 54 and is accordingly provided with an energizing circuit comprising the indicating needle and upper of plus limit contact of gauge 65. As will be observed, the energizing circuit for relay D also includes normally closed contacts of an overload relay OL as well as the energizing circuit of timing relay TR.

Relay OL is energized in direct response to energization of an amplifying relay OL' which is provided with an energizing circuit in series with an overload limit contact load gauge 73. And in accordance with usual practice the load gauge is connected in series, for example, with the main drive motor 60 whereby to indicate indirectly the loading applied to working rolls 53. Thus it will be observed that downward adjustment of the mill cannot take place if the same is already overloaded since relay OL, when energized, will prevent energization of control relay D. Also, the period of energization of relay D is at all times limited by the timing relay TR, which is in the energizing circuits for both control relays U and D so that timing periods are the same for both control relays.

Where a plurality of downward correcting adjustments are required to obtain strip of prescribed thickness, the same will be effected in a step-by-step manner by reason of the interrupter, as will be understood. And no adjustment will be of sufficient magnitude to carry the indicator of gauge 65 from one side to the other of the tolerance settings, all in accordance with the teachings of the invention.

Many modern Steckel mill installations are of the reversing type wherein drive means is provided for both stands 59 and 58 whereby the same may be alternately employed in a coiling and uncoiling capacity and a single coil may be subjected to a series of reductions upon successive reversals of the mill. For such installations my control may be readily adapted by merely providing duplicate controls where necessary. Many of the components could be commonly employed, however, as will be understood.

It should now be apparent that the objects initially set forth have been fully accomplished. My invention provides a control arrangement for hot or cold strip rolling mills which is operative to perform functions heretofore left to the judgment and discretion of the mill operators and accordingly heretofore subject to occasional erroneous judgment. My control operates to integrate the various factors or considerations which concern proper mill operation and upon which mill operators presently rely in order to determine when mill adjustments are desirable. In this regard it will be understood that mill adjustments are not necessarily in order or desirable upon the mere consideration that the strip produced in the mill is not within the prescribed tolerance range. Thus, if the mill is loaded to capacity no downward adjustment of the mill stands may be effected where my control is utilized regardless of the character of the strip produced. And this single feature alone represents a substantial improvement over existing control practices and arrangements since breakage of expensive mill rolls from overloading is thereby virtually precluded, while it is well known that such occurrences are not extraordinary under present mill practices.

My invention effectively overcomes objections heretofore advanced against automatic control of rolling mill equipment in that hunting or continual compensating adjustment of the mill apparatus is prevented. This is due in part to my novel integration of control considerations, and in part to my novel arrangement whereby adjustments are effected in a step-by-step manner, each step being of less magnitude than the tolerance range utilized.

An obvious advantage of the invention resides in the fact that my control may be readily applied to a number of roll stands of a multi-stand milll whereby adjustments may be effected at a number of stands, rather than at the last one or two only, and in the proper relative proportion. Thus, where my control is applied to the last three stands of the mill, as in the illustrated circuit, I may arrange the control so that the magnitude of adjustment be diminished from stand to stand so that the desired percentage reduction, for example, at each stand remains substantially the same.

It will be apparent, moreover, that my control may be readily integrated into existing mill systems utilizing in a large degree the control components conventionally provided for such mills.

It should be understood, however, that the embodiments of my invention herein illustrated and described in detail are intended to be representative only and reference should therefore be had to the appended claims in determining the true scope of the invention. For example, it will be readily recognized by one skilled in the art that the teachings of my invention may be advantageously applied to apparatus utilized for rolling materials other thanmetal. And it will be further apparent that many basic concepts of my invention reside in the method of control as distinguished from the various combinations of apparatus elements contemplated by the disclosure.

I claim:

1. In combination with a' rolling mill of the type having a plurality of roll stands, drive motors for each of said stands, and screw-down motors for each of said stands; means responsive to the thickness of strip at greater or less .thicknessthan predetermined maximum and minimum limits to energize said screw-down motors, and means responsive to the temperature of said strip to disconnect and maintain said screw-down motors in a de-energized condition when said strip is above or below a predetermined temperature range to prevent screw-down adjustment of said roll stands when said strip is at lower than predetermined minimum temperature or is at higher than predetermined maximum temperature.

2. In combination with a rolling mill of the type having a plurality of roll stands, drive motors for each of said stands, and screw-down motors for each of said stands; individual control relays for each of said screw-down motors for selectively energizing said screw-down motors to effect downward or upward adjustment of the mill stands, means to energize said control relays comprising a gauge device positioned adjacent one of said mill stands and adapted to measure the thickness of strip passing through the gauge device, said gauge having upper and lower limit contacts for completing electrical circuits upon said strip becoming either too thick or too thin, said control relays being energized in response to completing said electrical circuits, time delay means operative a predetermined time after energization of said control relays to de-energize the same, and means individually associated with said drive motors operative in response to the power input to any of said motors reaching a predetermined maximum load to disconnect and maintain the screwdown motor for the stand driven by such drive motor in a de-energized condition to prevent downward adjustment of such stand.

3. In combination with a rolling mill of the type having a plurality of roll stands, drive motors for each of said stands, and screw-down motors for each of said stands; individual control relays for each of said screw-down motors for selectively energizing said screw-down motors to effect downward or upward adjustment of the mill stands, means to energize said control relays comprising a gauge device positioned adjacent one of said mill stands and adapted to measurethe thickness of the strip passing therethrough, said gauge having upper and lower limit contacts for completing electrical circuits upon said strip becoming either too thick or too thin, said control relays being energized in response to completing said electrical circuits, time delay means operative a predetermined time after energization of said control relays to de-energize the same, and a temperature responsive device operative responsive to said strip being above or below a predetermined temperature range to disconnect and maintain said screw-down motors in a tie-energized condition to prevent adjustment of said stands.

4. In combination with a rolling mill having a roll stand and a screw-down motor for said stand; means responsive to the thickness of strip passing through said mill at greater or less than predetermined maximum and minimum limits to energize said screw-down motor, and means responsive to the temperature of said strip to disconnect and maintain said screw-down motor in a de-energized condition when said strip is above or below a predetermined temperature range to prevent screw-down adjustment of said roll stand when said strip is at lower than predetermined minimum temperature or is at higher than predetermined maximum temperature.

5. In combination a rolling mill comprising a plurality of roll stands, drive motors for each ofsaid stands, and

screw-down motors for each of said stands; control devices for each of saidscrew-down motors for selectively energizing the same to efiect downward or upward adjustment of the roll stands, guage means operatively connected with said mill and adapted in response to the passage past said guage means of strip which is above or below predetermined maximum and minimum thickness limits to activate said control devices for energizing said screw-down motors, thereby effecting a correcting adjustment of said roll stands, a preset maximum load limit means connected to each drive motor of each stand, means at each stand operatively connecting the maximum load limit means in the circuit of the screw-down motor of that stand, said load limit means being operative in response to a predetermined load of the drive motor of that stand for disconnecting the circuit of the screw-down motor of that stand during the existence of a load above said maximum.

6. Apparatus according to claim 5 further characterized by said load limit means comprising current responsive means, said current responsive means being operative in response to a predetermined maximum flow of electric current to its said drive motor.

7. In combination a rolling mill comprising strip reducing rolls, a drive motor and a screw-down motor; guage means operatively connected with said mill and adapted in response to the passage past said guage means of strip which is above or below predetermined maximum and minimum thickness limits to activate said screw-down motor for effecting a correcting adjustment of said strip reducing rolls, a preset maximum load limit means open atively connected to said drive motor, means operatively connecting the said load limit means in the circuit of said screw-down motor, said load limit means being operative in response to a predetermined load of the drive motor for disconnecting the circuit of the screw-down motor during the existence of a load above the preset limit.

8. Apparatus according to claim 7 further including time delay means in the circuit of said screw-down motor automatically operative a predetermined time after activation of said screw-down motor to disconnect and deactivate the same.

9. Apparatus according to claim 8 further including means operative periodically to reset said time delay means tothereby condition said circuit of the screw-down motor for further activation of said screw-down motor.

10. Apparatus according to claim'7, further including temperature responsive means connected in said screwdown motor circuit operative to disconnect said circuit and maintain said screw-down motor in a deactivated condition when said strip is above or below a predetermined temperature range to prevent adjustment of said mill when said strip is at lower than predetermined minimum tem perature or is at higher than predetermined maximum temperature.

References Cited in the file of this patent UNITED STATES PATENTS Whitten Oct. 24,

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