US2651954A

US2651954A - Method of and means for rolling strip material

Info

Publication number: US2651954A
Application number: US118145A
Authority: US
Inventors: Frank P Dahlstrom
Original assignee: Individual
Current assignee: Individual
Priority date: 1949-09-27
Filing date: 1949-09-27
Publication date: 1953-09-15
Anticipated expiration: 1970-09-15

Description

p 1953 F. P. DAHLSTROM METHOD OF AND MEANS FOR ROLLING STRIP MATERIAL 6 Sheets-Sheet 1 Filed Sept. 2'7. 1949 ATTOR N EY$ Sept. 15, 1953 F. P. DAHLSTROM METHOD OF AND MEANS FOR ROLLING STRIP MATERIAL 6 Sheets-Sheet 2 Filed Sept. 27. 1949 ATTORNEY Sept. 15, 1953 F. P. DAHLSTROM METHOD OF AND MEANS FOR ROLLING STRIP MATERIAL Filed Sept. 27, 1949 6 Sheets-Sheet 3 ATTOR N EYS Sept. 15, 1953 F. P. DAHLSTROM METHOD OF AND MEANS FOR ROLLING STRIP MATERIAL 6 Sheets-Sheet 4 Filed Sept. 2'7. 1949 LW L 4. 4

ATTORN EYS Sept. 15, 1953 F. P. DAHLSTROM METHOD OF AND MEANS FOR ROLLING STRIP MATERIAL 6 Sheets-Sheet 6 Filed Sept. 27. 1949 Zhmentor (Ittornegs Patented Sept. 15, 195?:

UNITED STATES PATENT OFFICE METHOD OF AND MEANS FOR ROLLING STRIP MATERIAL 3 Claims.

This invention relates to a method of and apparatus for rolling strip material, and more particularly to a method and apparatus for the cold rolling of metal into thin strip or sheet form.

In cold rolling metal to form thin strips or sheets, it has generally been the practice to pass the material between two cooperating rolls, usually referred to as the work rolls. The material is delivered to the rolls from a pay-off reel and is wound'up about a take-up reel at the other side of the roll stand. Usually one passage through the work rolls is insufficient if a considerable reduction in the thickness of the work is to be made, and, in such cases, a plurality of passes are made to effect progressive reductions in the thickness of the strip or sheet.

In this operation, tension, which may be termed forward tension, is normally applied to the strip in a direction to draw it through the rolls, and in most instances a back tension is also applied to the strip in a direction to resist its passage through the rolls. This back tension is usually less than the forward tension, so that the net result or difference between the two is a pull upon the strip in a forward direction. The forward tension is usually effected by driving the take-up reel upon which the strip is wound. The back tension may be applied by means of a braking action upon the pay-off reel, this action being effected in any one of a plurality of ways. As the tension to which the strip is subjected has an important bearing upon the reduction in gauge accomplished through the work rolls, the reason for placing back tension on the strip will be readily apparent, and the back tension may be equal to the forward tension, in which case the strip-propelling force is furnished entirely by the work rolls.

Also, it is common practice to drive the work rolls either directly or indirectly, in addition to the force which may be applied to them by the net forward tension upon the strip. This drivmg force may be applied directly to the work rolls, but in the present embodiment of my in vention is preferably applied to so-called backup rolls placed above and below the work rolls to support the latter against deflection. Owing to the fact that the problem of rolling sheet materials to thin gauges can best be handled by work rolls of relatively small diameter, which are too weak to withstand the required rolling pressures, it has been common practice to employ such hack-up rolls to support the small work rolls.

In short, a common and widely used arrangement for rolling sheet material has been the socalled four-high mill in which each work roll is supported by a single back-up roll, the axes of the four rolls being disposed in parallel relation and in a vertical plane. Under some conditions it is advantageous and under other conditions necessary to offset the work rolls, as will be later explained. The back-up rolls are of considerably larger diameter than the work rolls, and are supported in large bearings which can withstand relatively great rolling pressures. Usually with such a construction the work rolls have been power driven, which requires the necks of the rolls to be sufiiciently large to transmit the required torque without breaking. Such an arrangement puts a limit on the smallness of the work rolls, and, for that reason, the present invention makes provision for applying the driving power to the back-up rolls and for driving the work rolls indirectly through friction from the back-up rolls. As will be apparent as the description proceeds, there is another distinct advantage obtained from applying the driving force to the back-up rolls.

It has been previously stated that in many instances there is a net forward tension applied to the strip so that the strip is pulled through the rolls at least partly by this forward tension, or by the excess of the power applied to the takeup reel over the braking power applied to the pay-off reel. It will be apparent, however, that the horizontal force exerted by the strip upon the work rolls in a forward direction tends to deflect them, particularly at their middle portions, as they are held against movement at their ends, the deflection taking place in a direction in which the strip moves, and this deflection may be of such an excessive amount as to interfere with the uniformity of the gauge of the material being used, and if the rolls are too small they might even break.

It will be apparent that if power is applied to the back-up rolls of a four-high mill and the work rolls are driven entirely through friction with the back-up rolls, the latter must be driven in a direction opposite to that of the work rolls, and the tangential force exerted on the latter by the back-up rolls would tend to move them latorally in a direction opposite that of the movement of the strip, while the net forward tension to which the strip is subjected by power applied to the take-up reel would tend to deflect the work rolls in the same direction as the movement of the strip, or in a direction counter to that resulting from the drive of said work rolls by the back-up rolls.

In the present invention, as in that of my copending application Serial No. 686,746, filed July 27, 1946, now Patent No. 2,601,792, gran d July 1, 1952, Apparatus for Rolling Strip Material, I take advantage of the above considerations and apply power to the work rolls, in part by means of power applied to the back-up rolls and in part by means of net forward tension applied to the strip. If these driving forces so applied to the work rolls are equal, then the tendency of these rolls to be moved or deflected will also be equal, but will be in opposite directions so that they will cancel out, and thus permit very small Work rolls to be employed.

In the present invention, as in that of my aforesaid copending application, I employ the movement or displacement of the work rolls horizontally to control the driving force applied to the work rolls by the back-up rolls with respect to the force applied to the work rolls by the net forward tension of the strip so as to keep these forces equal, and, therefore, correct such deflection before it reaches a point which would be sufficient to break the rolls. Small movements of the work rolls in a horizontal direction or in a direction parallel to the plane of the strip are permissible in rolling mill operations, and these small movements by the present invention are employed in a manner superior to that of my aforesaid copending application to increase or decrease the magnitude of one or both of these driving forces before the movement becomes excessive. For example, these slight movements of the woi'k rolls may be employed to increase or decrease, as may 'be required, the amount of power applied to the back-up rolls or to increase or decrease the amount of power applied to the winding or take-up reel, or, if desired, these slight movements may be employed to increase or decrease the back tension applied to the strip by resisting rotation of the pay-off or supply reel. If found desirable, any combination of these forces may be varied in order to maintain the proper tension upon the strip, and at the same time equalize the two deflecting forces applied to the work rolls so that there will be no tendency of these rolls to move laterally.

As illustrated in the accompanying drawings, I control the power applied to the back-up rolls by the movement of the work rolls, the latter being carried in cradles so that they are permitted a certain amount of lateral movement. Levers pivoted to the roll housing are actuated by the movements of the cradles, and these levers in turn actuate electric controls to increase or decrease the power applied to the back-up rolls.

One object of the present invention is to provide improvements, generally, in strip rolling apparatus of the type and mode of operation disclosed by my aforesaid copending application, and in particular to minimize and stabilize the work roll displacements.

Another'ob ject is to provide in such apparatire, for adjustably offsetting the work rolls, in relation to the back-up rolls, thereby to introducea factor which tends to counteract, in whole or in part, the rearward mill reaction of back-up roll drive, and so allows the forward and back tension on the strip to be substantially balanced.

To these and other ends the invention consists in the novel feature and combinations of parts to be hereinafter described and claimed.

'In the accompanying drawings:

Fig. 1 is a front elevational view of a rolling mill embodying my invention;

Fig. 2 is a sectional View online 2-2 of Fig. 1;

Fig. 3 is a horizontal sectional view on line 3--3 of Fig. 2;

Fig. 4 is a diagrammatic view of the driving and control arrangement of said mill and of the means for applying power to the pay-off and take-11p reels and to the back-up rolls;

Fig. 5 is a perspective View of the lower portion of the rolling mill, some parts being shown in section;

Fig. 5A is a View similar to Fig. 5 showing a modified form of my invention;

Figs. 6 and 6 are diagrammatic views showing existing rolling conditions in single and tandem mills, when the axes of the work rolls are in the plane of the axes of the back-up rolls;

Fig. 7 is a diagrammatic View illustrating conditions existing in a mill in which th work rolls may be offset with respect to the plane through the axes of the back-up rolls; and

Fig. 8 is a diagrammatic view of a modified form of the control means for offsetting the work rolls.

To illustrate a preferred embodiment of my invention, I have shown in the drawings a house ing It of more or less conventional form, having mounted therein a pair of work rolls II and a pair of back-up rolls l2, as is the usual arrangement in a four-high mill. The back-up rolls are supported in bearings or journals l3 and the upper journal is held down by means of the conventional adjusting screws I4, so that the amount of separation of the work rolls may be varied as desired.

As stated, the work rolls l l are mounted in cradles which are permitted a certain amount of lateral movement. These cradles, as shown more particularly in Figs. 2 and 5, are provided for each work roll by a pair of opposed L-shaped members l6, extending lengthwise of the roll;

and to which are secured plates l7, thus to form on opposite sides of each roll an inwardly opening channel or guideway 8-. The two L-shaped members iii of each cradle are connected to-. gether at their ends by yoke members I9 so as to provide a rigid cradle structure for each of; the work rolls. As will be apparent, these yokes I9 extend below the lower work roll and above the upper work roll, and the channels [8 of each cradle are substantially in the horizontal plane of the respective roll with which the cradle is associated.

It will be understood that one of these cradles is provided for each of the work rolls, and as they and the associated mechanism are alike, the description of the mechanism associated with one of the rolls will suffice for both.

Supported in each of the channels 18 are blocks 2i, here shown as three in number on each side of the work roll. Each block 2!: provides a pair of inwardly extending ears 2 2, serv-.. ing as journals for a bearing roller 23, these rollers being designed to contact the work rolls on each side and to occupy substantially the same plane as the associated work roll, as shown in Fig. 2. As will be apparent from Figs. 2 and 5, the ears 22 are cut away at their inner portion so that they do not engage the work roll, while they permit such engagement by the bearing rollers 23. In each ofthe channels i rearwardly of the blocks 2| are oppositely tapered

shims

24 and 25, whereby, when these shims are driven into the channels from either end, the blocks 2| will be forced outwardly or toward the work rolls so. as to set the bearing rollers up against the work rolls. The spacing of the bearing rollers 23 on one side of one of the work rolls with respect to those on the other side can thus be varied.

As shown in Figs. 2 and 5, the lower cradle is supported at one side upon upright posts 26, which extend upwardly from the lower journals E3, the cradle resting freely upon the tops of said posts so that it may shift or move with respect thereto. The same side of the upper cradle is also supported from the lower cradle upon posts 21, extending upwardly from said lower cradle, and the upper cradle may likewise move laterally, sliding upon the tops of the posts 21. At the other side of each cradle, angle irons 29 are secured to the members l6, and a pair of plates 39 extend horizontally forward from each of these angle irons.

The front faces of the housing sides, above and below the pass line, carry pairs of brackets 31, for the support of two transverse horizontal fulcrum shafts 32. On each shaft 32 is pivotally mounted a substantially vertical lever element, designated as a whole by the numeral 33; each lever element 33 provides short inner arms in the form of pairs of ears 34, that are pivotally connected by pins 35 to the ends of the associated plates 39. Each lever element has longer oppositely extending arms 31, near the ends of which are provided apertures for the loose passage therethrough of bolts 38, extending forwardly from cross members 39 that are attached to the front faces of the housing sides, above and below the pass line. Encircling each bolt 38, on opposite sides of the lever arm 31 through which it passes, are a plurality of compressible rubber disks 49, held against movement by a suitable retaining and adjusting nut 36. By thus substantially anchoring the outer ends of the lever elements 33, the desired stabilization of the cradles of each of the work rolls H, H is obtained, it being understood that said cradles can shift horizontally in either direction only to the slight extent permitted by the compressibility of the rubber disks or

washers

40, 40.

As shown in Fig. 5 of the drawings, three of the bearing rollers 23 are provided upon each side of each of the work rolls, one adjacent each end of the roll and one adjacent the central portion thereof. It will be understood, of course, that as many of the bearing rollers may be provided as desired. Only the outer of these rollers normally bear on the work roll. The middle roller is ground slightly smaller than the outer rollers, and acts only in an emergency, for example, when the range of the control means is momentarily exceeded during the starting of the mill. It will be understood that the outer bearing rollers 23 will be adjusted so that they bear upon the work rolls at all times, and that when either of the work rolls tends to move laterally in either direction, the corresponding cradle will also be urged in that direction. This causes the associated lever element 33 to swing on its fulcrum shaft 32, to the limited extent permitted by the compressibility of the rubber washers 49. As will be explained hereinafter, this limited movement of the free ends of the arms 31 is employed to control or vary the power applied to the back-up rolls, which power in turn drives the work rolls, and thus the balance of forces applied to the work rolls will be adjusted to restore the latter to their original positions.

The mill may be provided with a device to spread the work rolls when necessary, this device being shown more especially in Figs. 1' and 3. A yoke 42 may be secured at one side of the housing, the left, as shown in these figures, this yoke rotatably carrying the disk 43 having a beveled edge 44 which is disposed between the beveled ends of the work rolls ll. At the other side of the housing a yoke 45 is provided, this yoke being connected with the yoke 42 by means of tie rods 46. Secured to the yoke 45 is an hydraulic cylinder 41 containing a piston whose rod 49 is secured to a yoke 49 which rotatably carries a second disk 59 having a beveled edge 5| which enters between the beveled ends of the work rolls on that side of the housing.

It will be apparent that when hydraulic pressure is introduced into the cylinder 41 to drive the piston rod 49 to the left, as shown in Fig. l, the

disks

43 and 50 will be urged toward each other and will enter to a further extent between the beveled ends of the work rolls to spread the latter apart.

The means by which the application of power to the back-up rolls is varied, by and in accordance with the movement of the work rolls, is shown diagrammatically in Fig. 4. In this figure it is considered that the strip is moving toward the right, the pay-01f or supply reel being shown at 55, and the winding or take-up reel at 56. The reel may be driven through gearing designated generally at 51 from the shaft 58 of a motor 59, while the take-up reel is driven by gearing 60 from the shaft 6| of a motor 62.

Rotation is imparted to the back-up rolls by means of a motor 63, the shaft 64 of which drives gearing 65, which through the shaft 66 drives intermeshing gears 61 and 68, the latter gears being directly connected to the shafts of the back-up rolls [2.

It will be seen from Fig. 5 of the drawings that, adjacent the lower end of one of the lever arms 31 is a potentiometer 10, from which extends a pin or plunger H into engagement with the free end of the adjacent arm 31, so that this plunger will be moved by movement of the arm 31 in either direction. A similar potentiometer 19, as shown in Fig. 4, is provided for each lever arm 31 associated with the upper work roll.

The motor 59 of the supply reel receives current from the main generator 13 driven by the motor 14 which receives its power from any conventional source of supply. In the

supply lines

15 and 76 leading from the generator 13 to the motor 59 is a booster generator 11 driven by the motor 78. The current in the field '19 of the booster generator may be varied by a potentiometer 89 so as to increase or decrease the voltage supplied to the motor 59 and thereby vary the torque applied by this motor to the supply reel 55, thus varying the back tension upon the strip. The potentiometer 89 may be automatically controlled, if desired, but as illustrated is designed to be controlled by hand, and, as will be hereinafter explained, the torque applied to the backup rolls is automatically controlled relatively to that applied by the motor 59.

Likewise, the take-up reel motor 62 receives current from the generator 13, and the voltage delivered to the motor 62 may be varied by a booster generator 82 driven by a motor 83, and having its field 84 controlled by a potentiometer 85. Variation in the voltage of the current sup-.- plied to the motor 62 will vary the torque applied to the take-up reel 56 and, thereby, vary the front tension.

The mill motor 63 is also supplied with current from the generator 13, and in the line leading to the motor 63 is .a third generator B'l driven by the motor 88. The voltage applied to the field 89 of the generator 81 is automatically controlled through the potentiometers 10, as will now be explained, and, as illustrated, when the current passes through the field 89 in the direction of the arrow 98, or downwardly as shown in Fig. 4, the booster generator 81 will tend to weaken the current delivered to the motor 63 by the generator l3 and will effect the application of a lower torque to the back-up rolls by the motor 63. This will reduce the force tending to move the work rolls to the left, which means that they will move to the right. Also the winding reel motor must do a larger share of the work, which will still further tend to force the rolls to the right. On the other hand, when the current passes through the field winding 89 in the direction of the arrow 9|, or upwardly, as shown in Fig. 4, the voltage delivered to the mill motor 63 will be increased, and an increased torque will, therefore, be applied to the back-up rolls through the gearing 65.

One terminal of the field winding 89 is connected by the wire 94 to one of the levers 31 and the other terminal of this winding is connected to the other lever 31, the outer ends of these levers forming part of the potentiometers heretofore referred to, which potentiometer-s are connected by wires 96 .and 91 to the lead-in

current wires

98 and 99, these wires being connected to any suitablesource of direct current.

The potentiometers 10 are so arranged that, when the levers 31 are moved so as to move plungers II, the current may be made to flow in either direction through the field 89, or when the plungers are each in neutral positions there will be no current flow to the field 89 in either direction.

The position of the levers 31, as shown in Fig. 4, is that occupied when there is no deflection or displacement of the work rolls in either direction, and the levers 31, therefore, occupy a neutral position so that the levers 31 are at the same polarity, andno current will be delivered to the field 89.

It has already been stated that the torque applied to the back-up rolls l2 will tend to displace the work rolls toward the left, as shown in Fig. 4, or in a direction opposed to the direction of travel of the strip, while the'net forward tension on the strip (that is, the excess of tension applied by the take-up reel 55 over the back tension applied through the supply reel 55) will tend to cause displacement of the rolls in the same direction as that of the strip travel, or that in which the strip is moving. As there will always be net front tension applied to the strip to draw it through the rolls, it will be seen that, if the torque applied to the back-up rolls is varied so that it will be equal to that applied to the work rolls by the net front tension, there will be no tendency of the work rolls to be displaced in either direction.

In my co-pending application, Serial No. 686,746, filed July 2'7, 1946, now Patent No. 2,601,792, granted July 1, 1952 (of which this application is a continuation-in-part), an arrangement is disclosed which apportions the power so that the tangential deflecting forces produced on the work rolls by the back-up rolls will be sub- J stantially balanced by the deflecting forces produced on said work rolls by the strip tension exerted by the winding reel minus the back tension, if any, exerted by the delivery reel, it being assumed that the axes of the work rolls. and the back-up rolls are normally in the same plane or in substantially vertical alignment.

In such cases it was shown that there will be no force tending to deflect the work rolls When the required mill reaction equals the front pull minus the back pull. It is understood that mill reaction is the frictional force exerted between the back-up rolls and the work rolls which tends to rotate the latter. Forward pull is the force exerted by the winding .reel, and back pull is the force exerted by .the delivery or pay- .Off roll in a direction opposite to strip movement, or by any other device used in the art to exert such a force. As the mill reactionis always backward, it is seen that the backward reaction exerted by the mill and the pay-off reel must balance the forward pull exerted by the winding reel, or, to state the equation in a different form, forward pull must equal mill reaction plus back pull. The strip-propelling force, or force tending to draw the strip through the mill, will be equal to the mill reaction plus the difference between the forward and back pulls, and if the balance between the three forces is maintained as above described (that is, forward pull equals mill reaction plus back pull), the strip-propelling force, mathematically, will always be double the mill reaction.

This is shown by the following table:

force required to propel the strip will be 100 units, and, therefore, the mill reaction must always be '50 units. Also, it will be noted that the forward pull must increase with the back pull in order that the balance be maintained according to the above equation.

In usual rolling mill practice the back pull is readily adjusted by the operator, as is also the forward pull, and according to the present invention a typical operating condition is shown by case C above, where units of mill reaction and 50 units of back pull are balanced by units of forward pull. Such condition is shown, for example, in Fig. 6 for a single four-high mill, and it is seen that the amount of forward pull is double that of the back pull.

It will be apparent, however, that if we place another mill in tandem with the mill shown in Fig. 6 as illustrated, for example, by Fig. 6 the forward pull upon the strip passing through the work rolls in the latter figure can be no more than 50 units (the same as the back pull of mill A), which is /2 of-the forward pull of mill A. It will be evident, therefore, that in tandem installations, and there are such installations employing 2, 3, 4 or 5 roll stands, the arrangement described in my aforesaid copending application might not be practical, due to the fact that the forward pull must continually increase from the first to the last of the stands and the back pull likewise continually increase, thus resulting in excessive tension in the outgoing stands. It is necessary, therefore, for tandem installations, to provide means for obtaining substantially equal front, and back tensions.

The ideal situation in tandem rolling, therefore,

is to maintain front and back tensions substantially equal, and this may be done if the mill reaction is balanced by some other force in order to maintain the equation of forces so that there will be little or no tendency to displace or deflect the rolls in either direction. It is possible, as will now be shown, to balance the mill reaction by shifting the work rolls forward in the direction of strip movement, which will provide a new component in the direction of the forward pull supplied by the winding reel, this component tending to shift or deflect the work rolls in the direction of strip movement.

In normal cold rolling practice, the reducing force or total rolling pressure applied to the strip may be from to 30 times the tangential force at the surface of the work rolls. If, therefore, we assume a force of times, then the mill reaction will be balanced by providing a component tending to displace the work IOlls forwardly equal to of the reducing pressure. Therefore, a displacement of the work rolls of 4 of the sum of the radii of the work and back-up rolls will provide a horizontal component of ,4 of the reducing pressure on the top and bottom sides of the strip, or a total horizontal component of /2 of the reducing pressure to the strip. To illustrate this numerically, if a mill is provided with a 4" work roll and a 32 back roll, the displacement would be 2 plus 16 over 40, or of an inch in order substantially to balance the mill reaction. With such a displacement, these two forces would balance and thus allow the front and back pulls to be substantially equal, and there would be little tendency to deflect or displace the work rolls in either direction from their off-set position. This will permit successful tandem operation regardless of the number of individual stands.

In Fig. 7, I have shown diagrammatically a roll stand in which the work rolls are offset forwardly with respect to the back-up rolls by an amount just sufficient to provide a component substantially equal to the mill reaction so that the front and back pulls may be equal. These may be of any desired value to place the required tension upon the strip, and this is of extreme importance when rolling high silicon strip, which is quite brittle and also contains edge cracks, and, therefore, will not permit the use of high tension. High tensions, of course, may be employed if desired. In order to show the practical value as well as the possibilities in the use of offset rolls, the following table has been prepared:

In all cases, the net strip-propelling force required to roll is taken as 100 units, and there are five groups of computations, the back pull in each group being the same but varying from group to roup from 11 1 0 This is a practical mill condition where the back pull can be, and usually is, automatically maintained at any predetermined value as adjusted by the operator. He then adjusts the mill to make the required reduction and shifts the rolls horizontally to the necessary offset, and the mill will then operate with the backward and forward forces balancing according to the law-back pull plus mill-roll reaction equals offset component plus forward pull-under which condition there will be no tendency to displace or deflect the work rolls.

Referring to case A of the table, the back pull and, oifset component are both set at 0, and the mill-roll reaction is equal to the forward pull. In the next case, A the offset component is adjusted to 50, which would increase the tendency to displace the rolls in the direction of strip movement by this amount, and would overbalance the mill-roll reaction. This would tend to cause the rolls to be displaced still further to the right by an amount depending upon the resiliency of the control means, which would cause the mill motor to increase its share of the load and thereby reduce the load on the winding reel motor. Therefore, the mill-roll reaction would be increased and the forward pull would be decreased by the same amount which, as shown, would bring the mill-roll reaction to 75 and the forward pull to 25. The mill-roll reaction is now balanced by the sum of the offset component and the forward pull, which latter two forces are in a direction opposite to that of the mill-roll reaction. It is noted that the power available to roll in each case is units, which is the sum of the mill-roll reaction and the forward pull (the back pull being zero in this example). For the succeeding cases, where there is a back pull on the strip, the power available to roll will, of course, be the sum of the mill-roll reaction plus the forward pull minus the back pull.

In case A the mil1-roll reaction has been increased to 100 units, and therefore supplies the entire strip-propelling force. The offset component has likewise been increased to balance the mill-roll reaction, and hence the back pull is equal to the forward pull, which in this case is 0.

In the rest of the Table I-A similar computations are made for back pull values of 25, 50, '75 and 100 units, and in the last case in each group the back pull and forward pull are equal. Case E for example, represents extreme conditions of very high tension, such as is desirable for certainstainless steels which are ductile and can withstand such tensions. In every case, however, the front pull is equal to the back pull, which permits tandem operation. The net strip-propelling force (mill reaction plus front pull minus back pull) is 100 units, and the forces are so balanced that those tending to displace the work rolls rearwardly will be equal to those tending to displace the work rolls forwardly.

One means of obtaining this result is shown in Fig. 5 The construction of the mill shown in this figure is similar to that described in Figs. 1 to 5 of the drawings, except that means are provided for shifting the work rolls in either direction so that the axes may be offset from the vertical plane passing through the back-up rolls. To effect this result, each of the shafts 32 corresponding to the fulcrum shafts 32 of Figs. 1 to 5, is provided with eccentric portions I05 upon which the lever arms 3'! are pivoted, and the rods 32 are rotatably journaled in the bearing bracket 3 l Secured to one end of each of the rods 32* 11 is an arm Ifl6 having its free end bifurcated, as shown at I67, to embrace a block I88, the bifurcated ends of the arm I66 being provided with pins I09 rotatably mounted in the block I88 so that the arm I83 will be movable angularly with respect to the block.

The block I08 is loosely mounted on a shaft I Iii between two positioning collars III so that the block will move up and down with the shaft l 58.

The shaft I II] is rotatably mounted at its lower end in a stirrup H2 and held against longitudinal movement with respect to the stirrup by a collar H3. The stirrup H2 is provided at the upper end of a piston II4 mounted in an hydraulic cylinder II5 into which fluid pressure may be introduced through the pipes I I6 and I I? to move the piston in either direction. With this construction, it will be apparent that, when the shaft H is moved upwardly or downwardly by the piston H4, the arm I will be swung about the axis of the shaft 32 so that this shaft will be positively rotated, and, through the eccentric portions I85, will move the lever arms 37 outwardly 0r inwardly, thus moving the cradle structures previously described and shifting the work rolls in a forward or rear direction as required. Thereafter, the control mechanism described in connection with Figs. 1 to 5 will automatically maintain the balance of forces heretofore described, so that there will be no tendency for the rolls to be displaced from this position. It will be understood that the control mechanism shown in Fig. 5 is, of course, duplicated for the upper of the two work rolls.

The shaft I I8 passes loosely through a bracket I20 and is provided with rightand left-hand threads I2I and I22, respectively. Upon the threaded portions of the shaft are received nuts E23 and I24, these nuts being prevented from turning by engagement with the base of the bracket I 26. The shaft may be rotated by the hand wheel I25 in order to bring one or the other of the blocks I23 or I24 to a position to bear against the bracket I20 to limit longitudinal movement of the shaft II8 by the piston Il l, so as to determine the amount of offset of the rolls due to the position of the eccentrics I85. It will be obvious that if the mill is reversed (and it is common to operate such mills in either direction) the other of the two nuts will engage the bracket I28 so as to automatically limit the offset position of the work rolls by the eccentrics for a reverse operation.

With the arrangement shown in Fig. 5 it will be apparent that the offset adjustment of the rolls determined by the position of the eccentrics I05 through movement of the shaft I it! will effect an approximate balance of forces so that there will be little tendency to displace the work rolls. The final accurate balance of forces will be secured by the control mechanism shown in Fig. 4 through the variation in power applied to the driving motors, so that the balance of forces will always be correctly maintained to place the desired tension upon the strip, and at the same time maintain in balance the various forces tend-- ing to move or displace the work rolls in either direction.

In Fig. 8 of the drawings I have shown, in a diagrammatic form, a modified structure for adjusting the shaft 32 which carries the eccentrics I55. In this case the shaft 32 is adjusted electrically through a connection with the forward and reverse motors of the mill after the adjustment-limiting means have been set to the proper positions by the operator.

The shaft 32 and eccentric I05, shown in Fig. 8, correspond to the same elements shown in Fig. 5*. On the end of the shaft 32 is secured a worm wheel I30, which driven by a worm I3! mounted on a shaft I32, which latter shaft is driven through reduction gears I33 and I34 from the shaft I35 of a motor I36 having reversing fields I31 and I38.

The gear I38 is provided with a pin I3 adapted to engage the movable elements MI and I 5; of switches I43 and I44, threadedly mounted by rightand left-hand threads, respectively, I i-5 and I45, on an adjusting shaft I41, which may be rotated by the hand wheel I48 to effect relative approaching and separating movements of the switches I43 and I44. This adjusts the distance of the movable switch elements I4! and I42 from the pin I39 so as to adjust the amount of rotation of theg'ear I30, from a central or neutral position, required to engage the pin I39 with one of the members I4I or I42.

As shown, the field-I38 is energized by the conductor I58 which leads to the switch I44, and a conductor I5I leads from this switch to the reverse motor of the mill. Similarly, the field I 31 is energized by a conductor I52 leading to the switch I43, and a conductor I54 leads from this switch to the forward motor of the mill. A conductor I55 connects the other pole of the motor with a source of current. With this arrangement the operator may, by turning the hand wheel I 48, move the switches I43 and I44 to the'proper position, so that the shaft 32 will be permitted to rotate through the required angle in either direction to give the necessary adjustment to the eccentrics I to bring about the approximate offset position of the work rolls necessary to effect the balance of forces above described. After the switches Hi3 and I44 have been so adjusted, when the mill motor is set into operation in a forward direction, the line I54 will be energized, and if the switch I43 is closed (as it will be when the movable member -I-4I thereof is not engaged by the pin I39), the field I31 will be energized so to effect rotation of the motor I36 in the proper direction to effect movement of shaft 32 in the proper direction to offset the work rolls forwardly. When the mill is reversed and the reversing-motor is energized, current will be present in the line I5I, and, if the switch I4 is closed, the field I38 will be energized to operate the motor I36 in the reverse direction. So soon, however, as the pin I39 strikes either of the movable switch members I-4I or I42, current to the fields I31 or I38 will be out off and the rotation of motor I36 and gear I38 will immediately cease. Thus the eccentrics I85 will be moved to, and held in, the proper positions. The operator may, therefore, move the switches I43 and I44 to the proper positions, depending on the amount of offset desired, and this offset will then be automatically obtained when the mill motors are placed in operation.

In mill practice, the operator would set the back tension at the required amount, depending upon the type of material being rolled. For the more brittle steels, such as the high-silicon steels, this would be a relatively low tension, as represented, for example, in cases B B and B of Table I-A, and for the more ductile hightensile stainless steels, the back tension would be a greater amount, such, for example, as the units represented in the table in cases E E1 and-E He then adjusts the roll pressures in order to obtain the required reduction in the thickness of the strip. He then observes the front tension or forward pull by the reading of the current being used by the winding reel motor, and according to this reading he manually adjusts the position of the mill rolls in order to produce an offset component of the proper magnitude.

In the event that the back pull is 25 units and the amount of current being used by the winding reel would indicate that the forward pull is '75 units, the rolls would be manually ofiset in an amount to reduce this current reading to 25 units in order to bring about the conditions represented in case B of the table, where the forward pull is equal to the back pull, thereby not overstressing the more brittle high-silicon steels. Such material is highly strategic and is used in connection with radar and similar very high-frequency installations, and it is, therefore, necessary to be able to reduce it to extreme thinness without breakage.

In the event that the mill is working upon the more ductile materials, and where the back tension has been previously set at 100 units, as in case E the rolls would, if desired, be offset to obtain such an offset component as to bring the forward pull also to 100 units, the same as the back pull. It is understood that the above adjustments will probably be made when the mill is being operated at a very slow speed. Themill is now ready for operation at commercial speeds.

During all these described operations of the mill, including operations at commercial speeds, the forces as described above and as set forth in Table I-A are maintained in balance by the automatic control mechanism illustrated in Fig. 4 of the drawings.

While, as above described, the slight movements of the work rolls are employed to vary the application of power to the back-up rolls, and through them to the mill rolls, it will be obvious that the correction of forces can be effected by varying the power applied to the takeup reel, or to both the take-up reel and the back-up rolls simultaneously, as illustrated in my copending application heretofore referred to, and as shown by the dotted lines I60 and I6! in Fig. 4 of the drawings, which lead to the field 84 and the potentiometer 85. The same result may also be effected by varying the back tension applied to the pay-off reel, or by any combination of the power applied to the winding reel, mill motor, or pay-01f reel.

While I have shown and described some preferred embodiments of my invention, it will be understood that it is not to be limited to all of the details shown, but is capable of modification and variation within the spirit of the invention and within the scope of the claims.

What I claim is:

6 1. In apparatus for rolling strip material, a

four-high stand of rolls comprising a pair of small diameter laterally movable work rolls providing the reducing pass and a large diameter back-up roll for each work roll, driving means connected to the backup rolls for imparting frictionally through the latter the strip-propelling rotation of said work rolls, thereby normally creating a mill reaction tending to displace said work rolls in a direction opposite to the materials movement through said reducing pass, a supply reel and a take-up reel for the material undergoing reduction, driving means for each of said reels for respectively producing on said strip a back tension and a forward tension each of regulable amplitude, whereby to obtain, by preponderance of said forward tension a net forward tension tending normally to displace said work rolls in the same direction as said materials movement through said reducing pass, adjustable means for initially offsetting said work rolls, forwardly or rearwardly in relation to the plane containing the axes of the back-up rolls, thereby subjecting said work rolls to lateral forces in opposition selectively to those arising normally from said mill reaction or to those arising normally from said net forward tension, whichever is preponderant, means differentially actuated during the rolling operation by the two-directional lateral movements of said work rolls, and means connecting said last named means to each of said driving means, for decreasing the driving power of that driving means whose ascendant lateral forces have produced such displacement and for increasing the driving power of the other driving means, thereby to return said work rolls to their initially adjusted positions and to substantialiy balance the opposed lateral forces to which said work rolls are subjected.

2. Apparatus as claimed in claim 1, having as the differentially actuated means, a pair of levers, each connected to a work roll and moved thereby, and each lever having an eccentric mounting on an associated pivot shaft, whereby angular adjustment of said shafts obtains the offsetting of said work rolls from the plane containing the axes of the back-up rolls.

3. Apparatus as claimed in claim 2, wherein each levers movement is opposed, in both directions, by a stationary member of compressible material, thereby to stabilize and limit the lateral movements of said work rolls.

FRANK P. DAHLSTROM.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,466,459 Perry Aug. 28, 1923 1,953,165 George Apr. 3, 1934 1,964,504 Coryell June 26, 1934