US2544467A - Tension control system - Google Patents

Description

March 6, 1951 M. MICHEL TENSION CONTROL SYSTEM Original Filed Feb. 11, 1944 IN VENTOR Hafiz/as Mic/rel BY ham/6.7 M

ATTORN EY in ii II II Patented Mar. 6, 1951 UNITED STATES PATENT OFFICE TENSION CONTROL SYSTEM Continuation of application Serial No. 521,947. February 11, 1944. This application January 31, 1947, Serial No. 725,709

Claims. (Cl. 80-351 This invention relates to tension control systems, more particularly to control systems having a tensioning element operating on a strip of material undergoing working under tension in rolling mill apparatus having tandemly arranged roll stands.

Rolling of strip metal under tension is presentLv recognized as being highly desirable, and in my copending application Serial No. 438,686, filed April 13, 1942, now Patent No. 2,345,765, issued April 4, 1944, I have disclosed a control system in which tension is provided by means of a pressure roller bearing against the strip as it passes between adjacent roll stands. The tension value is maintained substantially constant by motor speed control throughresulator operation in response to positional changes of the roller from a given strip tensioning position, an electric operating connection being provided between the regulator mechanism and the tensioning roller in the form of an electrical torque or motion transmitting and receiving system. Automatic regulation or control of tension at a given value is thereby provided.

Sometimes, however, it is necessary to change the tension value during the rolling operation in order to impose a different than normal tension on some portions of the strip. For example, if a portion of the strip has cracked edges and it is subjected to normal tension, breakage of the strip is liable to, and frequently does, occur, and for this condition it is desirable to reduce the tension until the defective portion has passed the tensioning zone. An increased tension is desired to maintain a longitudinally cambered or bowed piece of material centered in the mill. In case the strip is passed through a multiplicity of tensioning bones, such as occurs in the operation of a continuous mill, the tension in each zone should be reduced whenever necessary so as not to lose" the strip by breakage. Moreover, an increase in tension is desirable to prevent oil-gauge rolling of the trailing portion of the strip which occurs when the end of the strip leaves the respective stands of the mill. At present, in this latter situation, a considerable scrap loss is occasioned by the oil-gauge condition of a considerable length of the trailing portion of the strip, but it has been found that this loss may be re duced to a minimum by subjecting the length of strip extending between the pair of roll stands immediately following the roll stand from which the tail end of the strip emerges, in succession, tov increased tension.

In any of these cases, it is necessary that the 2 change in tension be eil'ected quickly and accurately to the desired extent, and continued regulation of the tension at the selected value is, of course. important. Attempts to obtain these results by changing the thrust or pressure of the strip tensioning roller against the strip have not proven satisfactory because of sluggishness in the pressure system (particularly where a fluid pressure system is used to actuate the tensioning roll- .er) due to inability to change from one operating pressure to another and then, as needed, return to the same first operating pressure accurately and quickly.

A particular object of the invention, therefore, is to'provide control means for subjecting strip metal during rolling operation to selected tensions other than the predetermined normal tension.

Another object of the invention is to provide control means for effecting an immediate change in tension to a difierent than normal tension value for as long a period as required, in a control system of the type referred to, without dispensing with automatic tension regulation at the new tension value.

A further object is to provide a tension control system for strip rolling apparatus wherein motor speed control means responsive to positional changes of a strip deflecting roller is provided to maintain tension uniformity together with means acting on the control means to initiate a temporary new value of tension by motor speed change and to maintain such new value at the original motor speed.

A still further object is to provide control means for a continuous mill which shall be responsive to emergence of the tail end of the strip from successive roll stands to produce increased tension in the strip in the tension zone immediately following each of said roll stands.

In accomplishing these and other objects of the invention, which will become apparent, I provide selectively operable means for establishing through motor speed control either a normal or temporary tension in the strip of desired values. In particular, the invention contemplates the provision of an adjusting or biasing means to cause actuation of a speed controlling regulator mechanism in such a manner that the speed of the regulated motor will be manipulated to cause a strip tensioning roller to assume temporarily a different regulating position, in which new 'position the roller will perform through its opfor speed. In brief, then, as will be more fully described hereinafter, the adjusting or biasing means is rendered operative to effect recalibration of the regulator'so that it functions to give automatic regulation with the pressure roller in a new position.

A fuller understanding of the nature and advantages of the invention in the tension rolling of strip metal will be apparent from the following detailed description taken in conjunction with the accompanying drawing, wherein Fig. 1 shows diagrammatically a system embodying the invention;

Fig. 2 is a detail view of a modification for the regulator shown in Fig. 1; and

Fig. 3 is a simple schematic illustration of a modification of the system of Fig. 1.

Referring to Fig. 1 of the drawing, a strip of metal l travels in the direction of the arrow, through pairs of reducing rolls i I and i2, respectively, of adjacent roll stands which, for example, may constitute a two-stand tandem cold mill or may represent several of the stands of a continuous mill, such as is illustrated schematically in Fig. 3. The rolls 1 i and i2 are driven by suitable driving means illustrated as direct current electric motors l3 and il, respectively, the armatures of which are supplied with power from a suitable source shown as power lines It, suitable starting devices It and I1, conventionally illustrated, being included in the respective armature circuits. The motors are provided with shunt field windings I8 and i9, respectively, and power for exciting them may be drawn from a suitable source of excitation, here illustrated as supply lines 20. In series with the field windings It and is are adjustable resistances 2i and 22, respectively, whereby the speed of each motor may be initially adjusted to any desired rolling schedule.

A strip tensioning device 23 is utilized, and although it may take various forms, it is here shown as comprising an upwardly movable roller 24 carried by arms 25 of hell crank levers that are secured to a shaft 26 journalled in bearings 21, and power cylinders 28 whose pistons 29 are connected to arms 20 of the bell cranks. Fluid under substantially constant pressure is admitted to the cylinders 28 to cause the roller 24 to bear against the strip in and lift or deflect it to a given height above the normal straight pass line between the two stands, thereby tensioning the strip. The roller is disposed to engage the strip at a point substantially midway between the two roll stands, and in its normal tensioning position the strip is deflected about 2 or 3 inches above the pass line. As will be appreciated, the strip tension will remain substantially constant so long as the strip is maintained in this deflected position under a constant force, but upon increue or decrease in the length of strip between the two roll stands, the deflecting force applied by the roller changes and consequently the tension value will change. Tension variations, of course, are reflected in changes in position .of the tensioning roller 24.

In order to maintain strip tension substantially constant, suitable regulator mechanism, indicated generally by the numeral II, is provided to control the speed of at least one of the driving motors with respect to its initially adjusted rolling speed so as to increase or decrease the length of strip between the adjacent roll stands responsively to displacement or positional changes of the roller 24. As here shown, the motor It is selected for automatic speed control and its speed may be controlled by suitably varying the excitation current in the field winding ll. Desirably, this may be accomplished by selective operation of field resistance control means, preferably comprising a pair of shunting relays 22 and 83 having operating coils connected to fixed contacts I and 35, respectively, of the regulator 2|. Relay 22 controls a circuit including adjustable resistor 30 for increasing motor speed through reduction in field strength, while relay 2! controls a circuit including resistors 22 and 21 for decreasing motor speed through increase in acid strength. Instead of using direct field control as shown, the controlled motor may be excited from a pilot exciter and the field of the pilot exciter may be controlled to bring about changes in the motor speed. Also, use of a controlled booster generator for controlling the motor speed is contemplated and may be employed if desired.

The regulator II is provided with a control or contact member 28 loosely mounted on a shaft 8|, and it carries contact points It for cooperating with the contacts 34 and 25, whereby the relays 32 and 22 may be selectively operated. An operating member ll is fixed to the shaft 2! and has a yieldable operating connection with the member 38 which may suitably be a tension spring 42, so that angular displacement between the two members may occur after motion of the member 20 is arrested through engagement of its contact ll with either of the fixed contacts "-48. Also, interconnecting the two members is a variable tie device comprising an air dash pct 42 connected to one of the members and having a piston l4 therein connected to the other member, adjustable air valve 46 serving to control flow of air into and out of the dash pot. This variable tie device, as fully explained in the application above referred to, functions under rapid movement of the operating member ll toward normal position to force the contact member It out of circuit closing position, but under relatively slow movement of the operating member does not actuate the control member. Counterweights ll may be used to balance the member 28 so that it will not move until compelled to do so by the operating member.

Each of the relays 22-43 is provided with contacts 41 connected in parallel to control the circuit of an electromagnetic device is having a plunger 49 connected to the operating member H. In the neutral position of the member I I, the plunger is in a centered position. Responsive to operation of either of the relays 22-", this electromagnetic device will be operative to impose a counteracting force on the member ll in opposition to the primary operating force or torque applied thereto.

Through the medium of an elastic Operating connection between the shaft 29 of the regulator 1i and the shaft 28 of the tensioning device 23, a primary operating force varying in intensity in conformity with the extent of displacement of the tensioning roller 24 from its normal position is applied to the shaft 89 to actuate the member ll. Preferably the operating connection comprises an electrical tie or motion transmitting and receiving system having a transmitter unit II and a-receiver unit 52. The rotor of transmitter Ii is mechanically connected through gear elements 53 to the shaft 26 of the tensioning device 22, while the rotor of receiver 52 is directly coupled to shaft 22 of the regulator. Each of the units "-52 may be energized from suitable power conductors 54, and the transmitter II is electrically connected by conductors ll to the receiver 32 to actuate the latter in a well known manner. With "roller 24in its normal position, the transmitter and the receiver will be prise an eye or bifurcation in the end of the arm through which a rod 3i secured to the plunger 30 extends and a disc 82 carried by the rod below the arm 51. A bracket 33'may be provided to support the plunger by seating of the disc thereon. The" coil 59 is adapted to be energized from the power conductors 23 by closure of a push button 54. By reason of the lost motion connection, the regulator is enabled to operate freely in a normal fashion when the device 53 is deenergized. When'the device 53 is actuated, it modifies'the operation of the regulator so as to establish a temporary new operating position for the roller 24 and a new tension value in the strip, as hereinafter more fully described.

In operation, andwith the device 53 out of service, in case thelength'of strip passing between adjacent roll stands increases, the tension decreases androller 24 moves upwardly. Responsively thereto, transmitter is operated to actuate the receiver 52, and the operating member 4| through spring 42 pulls contact member 38 into contact with ilxed contact 34, whereupon relay 32 is operated to cause the motor to accelerate. Thereby slack in the strip is taken up to restore normal tension and to return the roller 24 to normal position, excessive speed correction and travel of the roller past normal position being prevented by operation of electromagnet 48 in the manner fully described'in the application referred to hereinabove. Likewise, in case strip tension increases, the roller 24 moves down and the same regulator action occurs except that this time the motordeceleration circuits become effective through operation of relay 33. Stating the operation in other words, so long as roller 24 remains in approximately its normal position with normal tension in the strip, the regulator 3| will remain in its neutral position and the motor l4 will run at its initially adjusted or normal rolling speed. Upon the occurrence of change in strip length between the roll stands, the roller 24' moves from its normal position and through the electrical devices 5] and 52 causes actuatio'nof regulator 3| Inturn, the regulator. depending on the] direction offroller movement, renders either the motor acceleration 'or its deceleration circuit eiiective thereby. changing the ileldcurrent of'nibtor l4 with respect to its preset normal speed field strength" andvthe motor speeds' up .or slows downlas'the case maybe to efiect,'r'eturn ofthe1 roller to normal position and strip tension to normal value. Responsively thereto, theregulator isbroughtback toits neutral position or-s,tate. of control, thereby wiping out the change'in field strength so thta the ,motor i4 again operatesv at substantially it s normal rolling speed. "@The normal automatic operation of the system occurs wlienever corrective adjustment of'motor speediis' r ee d'ed, to accommodate forfluctuations or variations in tension so as to maintain tension substantially constant at a given value.

The mill operator; of course, will be on the lookout for the appearance of deiectivestrip portions such as would be liable to rupture it subjected to normal tension. Each'of such portions desirably will be rolled underreduced tension, and immediately after it has passed the tension zone between adjacent roll stands, tensionwill be returned to normal value. -When a defective portion of the strip is observed, before it enters the tensioning zone, the' operator depresses push button 84 and holds it depressedfor as long a period as is required to let the defective strip pass through the tensioning zone. Assuming that the roller is in normal position, the transmitter Ii and the receiver 52 will be in phase and the regulator contacts will be open. Thus, as'a result of depressing the push button, the electromagnet 33 is energized to pull up its plunger. In so doing, disc 62 engages arm 51 and rotates shaft 39 sufilciently in a clockwise direction to cause the operating member 4|, through spring 42, to close regulator contacts 3540, and to effect phase or angular displacement between the transmitter BI and the receiver 52. whereupon the speed reducing circuit for motor i4 is rendered operative by actuation'of relay 33 to decrease the speed of motor [4. The decrease in motor speed causes the length of the strip extending between the adjacent roll stands to increase so that the tensioning roller 24 consequently moves upwardly relative to its normal position and the deflection angle changes, as does the value of tension; In response to'operation of relay 33, the electromagnet 43 is energized and, at this time, due to the upward movement of the roller, the electrical tie units and the electromagnet 48 function conjointly to effect opening of the regulatorcontacts so that relay 33 de-energizes and renders the speed reducing circuit and the efectromagnet 43 inactive, so that motor speed returns to original speed and the operating force of electromagnet 43 is removed.

In this open contact position of the regulator,

the plunger of the electromagnet 58 continues to impose a biasing force on the regulator so long as the push button 64 is held closed, the intensity of this force being regulatable by adjustable resistor 65. Hence, if the regulator contacts are to remain open, the torqueoi' receiver 52 and the biasing force of electromagnet 53 will have to substant ally balance each other. As is well known, phase or angular displacement between the receiver and transmitter elements is necessaryin order for the receiver to develop torque, so that to establish the balance between receiver torque and the biasing force, the transmitter 3| must be'angularly displaced relative to the receiver'by an amount'proportional to the biasing force." Accordingly, roller 24 will have to be moved up to sucha'new operating positionrelative to its normal position as topmduce the required' displacement between the receiver and transmitter. However, roller 24" maynot have completed -its 'movement to the new operating position at the time the relay 33' has been de 'energizeda Then the continued existence of the has: ing force imposed by electromagnet 53 without a balancing torque in the receiveryfl will; cause repetition of the energizing and de-energizing of relay 33 with consequent motor changes until the roller 24 has completed its movement to the new operating position. Once the two opactuated to effect corrective speed adjustments in the same way as before described. except that the roller will be returned to its new position and tension regulated for the new value. Thus, there is no sacrifice of automatic control protection. After the defective portion has passed through the tensioning zone, the push button is released, whereby the biasing force is removed from the regulator, and it operates in normal fashion to bring the strip back to normal roller back to normal position.

In some cases, such, for example, a when a cambered or bowed piece of worlr or strip is passing through the mill. it is desired to subject it to greater tension in order to prevent the work piece from running into the mill housings and roll necks. To accomplish this, the regulator will be provided with a biasing element, in duplication of the element ll, arranged at the opposite side tension and the of shaft II in order to pull the contact member as into engagement with the fixed contact 3| and a push button control circuit, similar to the circuit controlled by push button 84, whereby the duplicate element may be operated. Otherwise, the operation of the regulator will be exactly the same as heretofore described except that the speed of motor I will be momentarily increased to shorten the length of strip in the tension zone and thereby establish a predetermined greater tension in the material than under normal conditions. I

In the modification shown in Fig. 2, shaft. 39 of the regulator is provided with a double arm extension 01 having lost motion operating connection at its left-hand end with an element I that corresponds to the element BI, and at its right-hand end has similar connection with a second element or electromagnet I. A push button control circuit (not shown), corresponding to the circuit controlled by push button M, is pro- .vided for each of the elements It and II whereby they may be selectively actuated. By selective operation of the biasing elements GI and II, the regulator will be biased in one direction or the other in the manner heretofore described whereby either increased tension or decreased tension with respect to normal tension is established as desired to suit operating conditions.

In the continuous mill layout illustrated in 11s., a multiplicity of roll stands is shown 8 through which the strip is direction of the arrow. the by the reference numerals source indicated by plus and minus signs. Regulator RI may be arranged to control either the motor Ml or the motor M2 responsivcly to movements of the tension device Ti of the first tension zone and also responsively to selective operation of the push button control circuits associated therewith. The regulators for the other tensioning zones may likewise 'be arranged to control the speed of certain of the motors driving the mills defining the tension zones. In a particular installation, regulator RI is arranged to control motor Ml to control tension in the first zone, R2 is connected to control motor M2 to control tension in the second zone, and regulator R3 is arranged to control motor M4 to regulate tension in the third zone. Hen it is to be noted that the tension control for motor M4 is identical to, and has the same electrical connections as. that described in detail for controlling the motor ll of Fig. 1. At the first and second zones, the regulation is the same in substance, but since the motor of the leading roll stand is being controlled instead of the motor of the following roll stand relative to the direction of strip travel, the control is such that motor speed is increased to reduce tension and it is decreased to increase tension. This is effected merely by reversing the connections at the fixed contacts "-38 of the regulator for the control relays 32 and It.

The foregoing system, in addition to affording automatic tension egulation for each of the tension zones through which the strip passes and imposition of selected tensions at will by operation of the control push buttons selectively to prevent strip rupture or to prevent sidewise movement of the strip, is further operative to subject the trailing end of the strip to increased tension to reduce oil-gauge rolling thereof to a minimum. This operation may be accomplished by manual control of the respective regulators to increase the tension in the tensioning zones. in succession, before the tail end of the strip reaches each of them. Preferably automatic means is provided to increase the tension in each zone, in succession, in to movement of the end of the strip past predetermined points. As herein shown, this means comprises load relays HI and Ii having normally closed contacts I! and II. one less load relay being provided than there are tension son The operating coil of load relay II is connected across a shunt It in the armature circuit of motor ill of the first roll stand, and the operating coil of the load relay II is connected across a shunt II in the armature circuit of motor are responsive to load on the and II, respectively. the load relays as the strip is passing M2 so that they motors Mi beingenergiaedsolons through the roll stands} with which the relays I I anociated. thereby holding the contacts thereof inopenposition.

As the tail end of the strip emerges from No. 1 roll stand, the load relay II, responsive to drop in load, de-energiaes and its contacts 12 close to complete a circuit for the biasing coil or element I of the regulator R2 associated with the second tension none. As a resultvof its operation, speed of motor M2 is reduced to increase the tension on the strip extending between roll stands I and I. The tension in the first zone obviously is dissipated whenthe end of the strip leaves the first roll stand. Heretofore the loss of tension in the flrst tension none is reflected by a reduction'in tension in succeeding zones and loss of tension at the entry side of the No. 2 stand, and this is repeated at the succeeding roll stands. Then, as the trailing end of the strip pro through the mi l, it is not reduced in gauge to the same extent as is eflected in preceding portions of the strip, and this considerable length of oil-gauge end portion needs to be sheared of! and scrapped. However. it has been found that the increase in tension in the second zone following loss of tension in the first zone is effective to cause the strip in the second or No. 2 stand to be reduced more nearly to the gauge for which the mill is set. Likewise. upon emergence of the strip from No. 2 mill stand. its associated load relay de-energizes and completes a circuit to energize the biasing coil is of regulator R1, th reby causing tension in the strip between roll stands 3 and l to increase with the res ts above stated. The total results of subjecting the length of strip extending between the pair oi. roll stands immediately following the roll stand from which the end of the strip emerges is that a greater length of the trailing end portion of each strip rolled is effectively elongated and reduced to within allowable gauge tolerances and consequently scrap loss is reduced to a minimum. Moreover, the regulators operate 1 to prevent breakage of the strip by controlling tension at the increased value.

While a concrete embodiment of the invention is herein illustrated and described in connection with tandem strip rolling. it will be apparent to persons skilled in this art that the invention is susceptible oi other uses, and that various modiflcations and changes in the various component parts of the system and in the construction and operation thereof will be readily suggested from the disclosed embodiment and may be made without departing from the spirit of the invention or the scope of the appended claims.

This application is a continuation of my copending application, Serial No. 521,947, tiled February 11. 1944. and now abandoned.

What is claimed is:

1. In a tension control system for tandemly arranged strip operating devices, in combination, a driving motor for at least one of said devices, speed controlling means for said motor, a strip deflecting element having a normal operating position and a temporary operating position for subjecting the length of strip extending between said devices to a normal tension and to a temporary tension, respectively, means for imposing substantially constant operating pressure on said deflecting element in 'both operating positions thereof, said deflecting element being movable from one to the other of said operating positions responsively to a momentary motor speed change, regulator means for controlling the operation of said speed controlling means responsively to fluci0 tuations in said normalstrip tension and in said temporary strip tension to maintain the respective values of said tensionssubstantially uniform, electromagnetic means 'operatively associated with said regulator means for actuatingthe same to effect said momentary change in motor speed, whereby said deflecting element is moved "from one of said operating positions to the other, means for selectively renderingsaid electromagnetic means operative and inoperative, and means providing a lost motion operating connection between said electromagnetic means and said regulator means, whereby regulatory operation of the latter is. normally unaffected by said electromagnetic means in its inoperative condition.

2. In a strip tension control system for tandem rolling mills and the like, the combination of a deflecting element for tensioning the strip, electrical means for changing thespeed of at least one mill motor, control means responsive to positional changes of said deflecting element from a normal position for initiating operation of said electrical means, means controlled by operation of said electrical means for rendering said control means inoperative prior to full return of said deflecting element to said normal position and being effective to render said control means inoperative only when said deflecting element reaches a given pointin its return to said normal position, biasing means for rendering said control means operative to actuate said electrical means at will whereby through change in motor speed strip tension is changed to a temporary new value dependent upon the intensity of the force applied to said control means by said biasing means, said control means being operable when biased to effect corrective adjustment of motor speed responsively to variations in strip tension at said new value.

8. In a tension control system for tandemly arranged strip working devices, in combination. driving motors for said devices, speed controlling means for one of said motors including a pair of control relays, regulator means having contact elements and a contact member cooperating therewith for selectively actuating said relays, an operating member yieldingly connected to said contact member to actuate the same, a deflecting element having a normal operating position for placing the length of strip extending between said working devices under a normal tension, means comprising motion transmitting and receiving elements for actuating said operating member directionally and with a variable operating force in accordance with the direction and extent of displacement of said deflecting element from its normal position thereby to move said contact member and effect actuation of one of said control relays to bring about corrective changes in motor speed sufllciently to return strip tension to said normal value, electromagnetic means rendered operative by actuation of either of said relays for applying a counteracting force to said operating member to prevent overchange in motor speed by eflecting movement of said contact member to a neutral position during return of said deflecting element to said normal position,

a second electromagnetic means for imposing a biasing force on said operating member, whereby said deflecting element is moved from said normal position to a new operating position and strip tension is changed to a new value dependent upon the intensity of said biasing force, and control means for controlling the operation of said second electromagnetic means.

4. In a strip tension control "system, a plurality of devices arranged in tandem for operating on strip material, a driving motor !or each of said devices, a strip engaging roller movable from a normal operating position in response to variations in strip tension, regulating means including a movable operating element for adjusting the speed oi one of said motors to maintain tension in said strip substantially constant at a selected value for normal operating conditions, means comprising motion transmitting and receiving elements ior directionally moving said operating element in conformity with movements of said roller from its normal position, whereby the speed adjusting means is rendered operative to eflect corrective adjustments of motor speed, an electromagnet having a plunger, means providing a lost-motion operating connection between said plunger and said operating element to bias said element for movement in one direction, and manually operable means to control energization of said electromagnet, said regulating means being operable when said electromagnet is energized to establish a reduced strip tension and to aflord regulation at said reduced tension, and said electromagnet being actuated prior to and during passage of selected portions of the strip from the first to the second of said devices.

5. In a tension control system for tandemly arranged strip operating devices, in combination, a driving motor for at least one of said devices, a deflecting element for tensioning the strip extending between said devices, means for actuating said element at one operating pressure while deflecting the strip, automatic control means for regulating the speed or said motor responsive]; to positional changes of said deflecting element from a normal position, to maintain strip tension substantially constant, said control means includin a regulator provided with a control member movable directionally from a neutral control position and electrical motion transmitter and receiver devices operatively connected respectively to said deflecting element and to said control member for efl'ecting actuation of said control member from its neutral position in a direction conformable with that of said deflecting element from its normal position, normally de-energised electrical means associated with said receiver device for eflecting and maintaining phase displacement oi' said receiver relative to said transmitter in a selected direction when energized. whereby strip tension is changed to and is automatically controlled at a new value determined by the extent or said phase displacement. and means for energizing said electrical means whenever a selected portion of the strip is to be subiected to said new tension value.

MATHIAS MICHEL.

REFERENCES CITED The following references are of record in the flle of this patent:

UNITED STATES PATENTS Number Name I Date 2,223,718 Cook Dec. 3, 1940 2,273,714 Lessmann Feb. 17, 1942 as 2,345,765 Michel Apr. 4, i944 Certificate of Correction Patent No. 2,544,467 March 6, 1951 MATHIAS MICHEL It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 1, line 18, for the Word electric read eZastic; line 38, for bones read zones;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 24th day of April, A. D. 1951.

THOMAS F. MURPHY,

Assistant Oomm'issz'oner of Patents.

Certificate of Correction Patent No. 2,544,467 March 6, 1951 MATHIAS MICHEL It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 1, line 18, for the Word electric read elastic; line 38, for bones read zones;

and that the said Letters Patent should be read as corrected above, so that the same mayeonform to the record of the case in the Patent Oflice.

Signed and sealed this 24th day of April, A. D. 1951.

THOMAS F. MURPHY,

Assistant Oommz'ssz'oner of Patents.

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