US3707252A

US3707252A - Automatic tensioning device for multiple line strip

Info

Publication number: US3707252A
Application number: US179401A
Authority: US
Inventors: Joseph J Kasecky; Charles W Thompson
Original assignee: Allegheny Ludlum Industries Inc
Current assignee: Allegheny Ludlum Corp
Priority date: 1971-09-10
Filing date: 1971-09-10
Publication date: 1972-12-26
Anticipated expiration: 1989-12-26

Abstract

An automatic tensioning device for separate strips in a multiple strand process line for preventing sagging of lines of strip and thereby guiding the strip in separate paths of travel and preventing their drifting into each other and characterized by separate sets of strip-engaging rolls which are responsive to strip sagging. Each set of rolls has one roll which drops by gravity in response to reduction in strip tension, thereby maintaining the tension necessary for guiding the individual strip in its designated line of travel. The apparatus includes a position-control servomechanism responsive to the position of the one roll and directed to strip drive rolls for increase of the strip speed and returning said one roll to its home position.

Description

United States Patent Kasecky et al.

[ AUTOMATIC TENSIONING DEVICE FOR MULTIPLE LINE STRIP FOREIGN PATENTS OR APPLICATIONS "779,112 7/1957 GreatBritain ..226/1l3 [72] Inventors: Joseph J. Kasecky, New Kensington;

Ch l w, Th Bl hi11 Primary Examiner-Allen N. Knowles b th f P Attorney-Vincent G. Giola et al.

[73] Assignee: Allegheny Ludlum Industries, Inc., [57] ABSTRACT Pittsburgh, Pa. D An automatic ten'sioning device for separatestrips in a [22] Flled: P 1971 multiple strand process line for preventing sagging of lines of strip and thereby guiding the strip in separate [21] Appl NO" 179,401 paths of travel and preventing their drifting into each other and characterized byseparate sets of strip-en- [52] US. Cl ..226/25, 226/113 gaging rolls which are responsive to strip sagging. [51] Int. Cl. ..B65h 25/04 Each set of rolls'has one roll which drops by gravity in [58 Field of Search ..226/1l3, 118, 119, 195, 25, sp to reduction in strip i thereby i taining the tension necessary for guiding the individual strip in its designated line of travel. The apparatus in- [56] References Cited cludes a position-control servornechanism responsive to the position of the one roll and directed to strip UNITED STATES PATENTS drive rolls for increase of the strip speed and returning said one roll to its home position. 2,277,658 3/1942 Anderson ..226/ll9 5 3,502,535 3/1970 Bongers et al. ..226/l19 X 14 Claims, 4 Drawing Figures l 1 J 4 L f? o o /2,/4,/6,32 48 0 0 ::28v .0 34 a0 82 I4 /4 49 82 F ,6 7e /4 /2,/6 i 96 54 46 f 78 64 60 q 0 4 /s 66 24 20 /2,/4,/a /0 l2 o o 9 22 PATENTED DEC 2 6 1972 SHEET 2 OF 3 PATENTED DEC 26 1912 SHEET 3 BF 3 AUTOMATIC TENSIONING DEVICE FOR MULTIPLE LINE STRIP BACKGROUND OF THE INVENTION strip out of its prescribed line of travel due to slack in the strip.

2. Description of the Prior Art The production of elongated strips of material, such as steel, usually occurs in a processing line involving one or more work stations and it is necessary to maintain continuous operation to derive uniform treatment throughout the length of the material. For example, some types of steel strip are passed through a heat treating furnace at a uniform rate. It is conventional to use horizontal looper cars for accumulating processed strip during the time intervals required to remove the coils of finished strip to maintain tension in the strip and to prevent it from moving aimlessly. Removalof the coils involves a sequence of operations including a number of exit end stops and starts including cutting the strip at the end of the coil to be removed, advancing the strip for two or three feet and then stopping again to cut a test piece such as for magnetic properties, and

then advancing the strip to insert its end portion into the clamp of the coiler for winding another coil of strip. Where the line is a multiple strip line, all of the lines are stopped even though the coil of one line is being removed. As a result, the line from which the coil is removed often sags and shifts in an unguided manner into paths of travel of adjacent strips, causing strip damage and considerable down-time of the line.

Associated with the foregoing is a problem involving bridles, or sets of drive rolls, for maintaining tension between the looper car and the recoilers. Separate bridles are provided for each line of strip. To maintain substantially equal tension between the recoiler and the looper each bridle is provided with a motor and brakes. Although the motors and brakes for the bridles may be adjusted for simultaneous. operation to maintain substantially equal tension in the adjacent strip lines, it has been found that maintaining the adjustments for continuous synchronized operation of the rolls has been practically impossible. In other words, each motor and brake has individual mechanical and electrical characteristics which prevent continual simultaneous stopping and starting. For example, the difference of only six inches in strip travel due to a delayed or slow action of one motor or brake in stopping a strip roll will cause a significant sag in the strip between the guide rolls and the loop car. As a result, a desired no slack condition in the looper car is actually unattainable, and a sagging strip moves laterally and into contact with an adjacent strip or an auxiliary guide member causing damage to the strip edges.

Other prior art means included speed adjusters for each motor in a bridle but such adjusters were unsatisfactory because they required constant adjustment due to variations in the strip shape, such as one edge of the strip being longer than the other edge.

2 SUMMARY or THE INVENTION In accordance with this invention it has been found that the foregoing problems may be overcome by providing additional strip tensioning means between the loop car and the tension bridle which means respond to any slack in a strip and thereby maintain guiding of the strip from the loop car to the coiler. The means includes a a strip-guide roll that is essentially free to float on a strip and follow any variation in strip tension or position. Thus, tension is maintained in the strip when the coiler is stopped under any conditions. During normal operation of the line, however, the control of slack is also unpredictable due to such factors as variations in strip thickness and acceleration in a motor due to a desired line speed change. Each strip-guide roll takes up the slack in the strip and has a positioncontrol 'servomechanism for signaling the particular bridle motor involved to accelerate in order 'to take up slack incurred and thereby return the tension roll to its home position. v

The advantage of the device of this invention is the provision of tension responsive means-for preventing .the occurrence of slack in a strip line which causes the strip to wander out of its designated path of travel and result in strip buckling and torn edges as the strip contacts fixed mechanical guides or adjacent lines of strip. The device is completely independent of the cause of the sagging condition in the strip but is effective in correcting the sag and returning the line to a normal operating condition. Accordingly, a multiple strip line having individual tensioning means for each line is provided.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of the exit end of a multiple strip line showing the path of travel of a plurality of strips of steel as they pass from a heat treatment furnace to separate recoilers;

FIG. 2 is an enlarged end view of the multiple strip tensioning rolls of this invention;

FIG. 3 is a plan view of the multiple strip tensioning rolls as taken on the linIII-III of FIG. 2; and

FIG. 4 is a schematic view showing means for varying the speed of the bridle drive motor in response to the roll position.

DESCRIPTION OF THE PREFERRED EMBODIMENT Although the device of this invention is shown in conjunction with a heat treating furnace such as a normalizing furnace for strip steel, the device may be used in conjunction with any other steel strip-treating operation, whether heat treating or otherwise, as well as for other types of strip material including non-ferrous metals and non-metals such as paper and plastic.

In FIG. 1 a strip line 8 of steel, such as silicon steel strip having a thickness of about 0.0l l to 0.032 inch issues from the exit end of a conventional normalizing furnace 10 where it is heated to a temperature to about l800 F. The strip line 8 shown in the drawings is actually a multi-strip line composed of three separate strips about 30-40 inches wide and disposed in substantially the same plane as they issue from the furnace 10. However, it is understood that for the purpose of this invention a single strip may be processed and the various devices involved will function in substantially the same way as for two or more strips. I

' After leaving the furnace at a speed of about 300 feet per minute the three

strips

12, 14 and 16 with a strip 14 being intermediate, pass through a tension device or first bridle 18 including three

successive rolls

20, 22 and 24 from where they rise to guide

rolls

26 and 28 on a platform 30 from which rolls the

strips

12, 14 and 16 pass through-an automatic tensioning device generally indicated at 32 which is the device of this invention and which will be described more fullyhereinbelow. Y i

.The bridle 18 is a single motor bridle in which the drive motor operates the roll 22 and provides separations in the tension zone; that is, a lower tension tureas-compared to higher tensions permissible in the strip after it passes the bridle 18.

From the device 32" the

several strips

12, 14 and 16 move through and around a. strip loop car 34 from where they passover guide rolls36 and 38 and then downwardly to a tension device or second bridle 40 from where the

adjacent strips

12, 14 and" 16 .pass through

separate recoilers

42, 44 and 46, respectively.

In prior practice, the strands of

strip

12, 14 and 16 have moved from the

guide rolls

26 and 28 to the loop car 34 without passing through the automatic tensioning device 32. in a conventional manner when the

recoilers

42, 44 and 46 are stopped to remove coils of processed strip from one recoiler, the loop car 34 having wheels 48 and guide rolls S0 and 52 travels to the right (as viewed in FIG. 1) on tracks 54 in response to a pulling force applied by a cable 56. Thus, strips are accumulated by the loop car 34 without stopping the continuous passage of the

strips

12, 14 and 16 through the furnace 10. When the recoilers42, 44 and 46 resume ceiling of the strip, the loop car 34 pays off the strips 12, 14- and 16 at a faster rate, such as about 600 feet per minute, as the car moves to the left to its home position (as shown in FIG. 1).

When the

recoilers

42, 44 and 46 are stopped for any purpose including the removal of a full coil of strip or an emergency, the second bridle 40 stops movement of the

several strips

12, 14 and 16 and the loop car 34 immediately begins to accumulate the strips. The bridle 40 includes a plurality of

rolls

58, 60, 62, 64 and 66 of which the

rolls

60 and 66 carry the center strip 14 and the

rolls

62 and 64 carry the near and far

strips

12 and 16. The roll 58 is common to all

strips

12, 14 and 16. The

rolls

60 and 66 have separate drive motor and brake means 68 and 70, respectively. The

rolls

62 and 64 are radially split into half portions on the same axis (not shown in the drawings) for handling the near and far

strips

12 and 16 and each half portion of each roll is provided with separate drive motor and brake means 72 and 74 as shown for the nearer halves of the

rolls

62 and 64, respectively. Accordingly, the nearer strip 12 being wrapped around the nearer half portions of the rolls 62 and 64 (As viewed in FIG. 1) is moved and stopped by the drive and brake means 72 and 74, while the far strip 16 is handled by the far half portions of the

rolls

62 and 64 havingseparate drive motor and brake means.

During the operation of the mill without inclusion of the automatic tension device 32, it was found that simultaneous stopping of all the rolls in a synchronized manner continually was practically impossible. Frequent attempts to adjust the brakes to maintain them in the necessary mechanical and electrical condition to insure simultaneous stopping on a continuing basis was a constant maintenance problem. For example, if one strip stopped momentarily sooner than the other two strips so as to provide for, say 6 inches in strip travel, a significant sag or slack in that strip occurred between the

guiderolls

36, 38 and the loop car 34. Guiding of the strip between the loop car and the rolls 36 and 38' is dependentupon all of the strips being in a substantially equaltension condition to maintain the strips in adjacent paths of travel and space from each other. Thus, where there is a loss of tension in a strip due to slack, it travels through and away from the loop car in an uncontrolled guided condition towards the

rolls

36 and 38 as the mill resumes operation so that a slack strip wanders out of its designated path of travel and into contact with an adjacent strip or a fixed mechanical guide means. i H Moreover, the problem was aggravated by the fact thateach time the strip is stopped by the bridle 40, the strip is held fixed by pinch rolls 76 as the strip is cut by shears 78. Thereafter, the strip 12 is advanced for a distance of two or three feet and stopped again in order to cut a section of strip for magnetic test purposes. Similar pinch rolls 80 and shears 82 are provided for the recoilers 44 and 46. As a result, the additional stopping and starting often results in a cumulative effect on the slack in the strip involved, therebyaggravating the problem of guiding the strip as it passes between the bridles l8 and 40 leading to and from the loop car The automatic tensioning device 32 (F 108. 2 and 3) alleviates the problem of maintaining tension in one or more of the

strips

12, 14 and 16 when slack occurs for any reason including those mentionedabove with regard to operation of the bridle 40. The device 32 includes a plurality and preferably three

idler rolls

84, 86 and 88 which'are mounted on similar shafts 90, the opposite ends of which are journally mounted in similar pillow blocks 92 and 94 on opposite sides of the plat form 30. The portion of the platform above which the

rolls

84, 86 and 88 are mounted has an opening 96 in which a plurality, such as three, tension rolls 98, and 102 (R6. 3) are mounted, the number of tension rolls corresponding to the number of strips being processed. The near and far strips 12 and 16 (FIG. 3) extend over the idler rolls 84 and 86 and wrap under and around the tension rolls 100 and 102, respectively, and then over the idler roll 88. The center strip 14 extends over the idler roll 84, under and around the ten sion roll 98, and then horizontally across the idler rolls 86 and 88 to the loop car 34 with the near and far strips 12 and 16.

During normal operation, the tension rolls 98, 100 and 102 are held in their uppermost positions (H6. 2) by the corresponding strips 14, 12 and 16. When slack develops in one of the strips the corresponding

roll

98, 100 or 102 drops by gravity to a lower position, such as a lowermost position as shown in broken-line positions for the

rolls

98 and 100 in FIG. 2. The

rolls

98, 100 and 102 are similarly mounted. For-example, the roll 98 on a shaft 104 is mounted in a yoke having opposite shaftsupporting

arms

106 and 108 extending from a transverse yoke member 110 which by connecting links 112 is secured to a shaft 114 in journals 116 on the frame of the platform 30. I

As shown in FIG. 2, fluid-cushioning means for counter-balancing the weight of the roll 98 and the yoke are provided such as a pneumatic cylinder 118. The upper .end of the shaft of the cylinder 118 is pivotally mounted at 120 to the underside of the yoke. The lower end of the cylinder 118 is pivotally mounted at 122 to a support member-124 below the platform '30. Inoperation, whenslack develops in one of the strips such as the strip 14, the roll 98 drops in response tothe reduced tensionin the strip until the slack is taken up. In some cases the roll 98 may drop to the lowermost (broken-line) position 98a of the roll. The roll 98 would drop to the lowermost position only under extreme irregularities in the operation of the drive motor and brakes for the several rolls in the bridle 40. In a similar manner, the tension rolls 100 and 102 drop in response to any slack in the near and far strips 12 and 16, respectively, with similar cylinders serving as counterbalance means for lifting the weight of the roll and the yoke so that the roll is essentially free to float and follow variations in the strip tension or position.

Upon resumption of operation of the line the slack in one or more of the

strips

12, 14 and 16 is taken up and the affected tension rolls 98, 100 or 102 normally return to their uppermost (home) positions. During a 1 coil removal cycle the cylinders 118 retract as the strip loses tension and holds tension for approximately six feet of slack; that is, the axis for shaft 104 of the tension rolls may drop about three feet. This provides the necessary tension for tracking and guiding and thereby preventing edge damage and downtime due to torn strip. Accordingly, when the loop car 34 operates in response to stopping of the bridle 40, the tension device 32 cooperates to maintain all of the strip in substantially equal tension and thereby maintains a controlled guidance of the strip to and away from the loop car.

During normal operation of the line when the rolls of the bridle are rotating slack may also develop in one or more of the

strips

12, 14, 16 due to other causes such as irregularities in the gauge of the strip causing it to stretch as it is pulled through the furnace 10, or slight increases or decreases in the speed of the drive motors operating the rolls in the bridle 40. Whatever the cause, slack often develops in the moving strip during normal operation when the loop car 34 is in the home position as shown in FIG. 1. In response to such slack the corresponding

roll

98, 100 or 102 responds in the manner set forth above and thereby maintains substantially equal tension so that controlled guiding of the strip is maintained at all times.

However, when such slack develops, it is necessary to eliminate the slack and restore the guide r'olls 98, 100 or 102 to home positions as soon as possible, thereby alleviating the possibility that the tension roll involved may have dropped to its lowermost position without completely'alleviating the slack conditibn. For that reason, means are provided in conjunction with the yoke of each

tension roll

98, 100 and 102 and the drive motor of the

corresponding bridle roll

66, 62 or 64, respectively, for accelerating the motor to take up the undesirable slack.

To coordinate the speed of the drive motors to the position of the corresponding guide rolls 98, and 102, means are provided that are responsive to the position of the rolls for varying the speed of the motors. Such means may. include, for example, the system shown in FIG. 4 wherein a selsyn transmitter 126 having an input shaft 128 is attached to the end of the shaft 114. As the roll 98 drops, a signal is transmitted to a selsyn receiver 130 that is operatively connected to a movable tap 182 of a potentiometer 134. The tap 132 is connected to a motor control which, in turn, is connected to the drive motor 70 for the roll 66, whereby the speed of the roll is proportional to the position of the guide roll 98; i.e., the roll 66 turns faster as the roll 98 drops. The resulting speed of the strip 14 removes the slack therein and raises the tension roll 98, ultimately to the home position. Thus, the selsyn is used to electricallyindicate the position of the drive roll and so long as the roll is below the home position a signal in volts is fed tothe appropriate bridle motor. When the tension roll 98 is in the home position, no signal in volts is generated. The distance of deviation signal which is proportional to the distance of deviation of the tension roll from its home position is preferably used to operate the appropriate drive motor in the bridle 40 at a speed proportional to the distance of deviation.

Accordingly, the device of the present invention provides slack takeup means in a strip mill in conjunction with a loop car type of operation which means it is responsive solely to the tension in the line of strip involved. The device is useful under static operations, where the end portion of the strip is stopped for removing finished strip from a recoiler, as well as under dynamic or normal operations where the strip is moving and slack develops due to irregularities in mechanical or electrical characteristics of the mill or in the strip per se.

The above-described device operates more efficiently in a multi-strip line but it may be used in a single line such as where there is an accumulator, cutting and coil replacement.

Although the invention has been shown in connection with certain specific embodiments, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

We claim as our invention:

1. In a line for processing at least one strip that moves continuously in a path of travel at a presettable speed through a work station in the line in which there are a strip recoiler at the end of the line, a horizontalcar looper between the work station and the recoiler, a drive bridle between the work station and the looper, and a tension bridle between the looper and the recoiler comprising a set of strip-tensioning rolls for the strip, the improvement wherein there are tensionresponsive means between the drive bridle and the tension bridle for preventing slack in the strip due to changes in tension of the strip.

2. The apparatus of claim 1 wherein the tensionresponsive means are disposed between the drive bridle and the looper.

3. The apparatus of claim 1 wherein there are a plurality of strips moving Continuously in parallel paths of travel at equal speeds and the tension bridle includes a separate set of strip-tensioning rolls with drive motors for each strip. a

4. The apparatus of claim 2 wherein the tensionresponsive means includes a'pair of spaced rolls for guiding engagement on one side of the strip and'in cludes a third roll for guiding engagement on the other side of the strip and being located with respect to the path of strip travel between the pair of spaced rolls, and the third roll being movable against the strip in response to a reduction of tension below a prescribed tension in the strip.

5. The apparatus of claim 4 wherein the third roll is movable vertically against the strip.

6. The apparatus of claim "2 wherein the tensionresponsive means include a pair of spaced horizontal rolls for guiding engagement on the undersurface f the strip, a third horizontal roll for guiding engagement on the top surface of the strip and being located at its strip engagement location between the strip engagement locations of the pair of spaced rolls, and the third roll being movable vertically against the strip'for maintaining a prescribed tension in the strip.

7. The apparatus of claim 3 wherein the tensionresponsive means include a pair of spaced rolls for guiding engagement on one side of the strips and includes a third roll for each strip and for guiding engagement on the other side of each strip and being located between the spaced rolls with respect to the paths of travel of the strips.

8. The apparatus of claim 7 wherein the third roll for each strip is movable vertically against the strip.

9. The apparatus of claim 8 wherein yoke means in cluding a pivot shaft are provided for guidingly mounting, each third roll for movement between upper and lower positions, each third roll being retained in the upper position and adjacent to the pair of rolls in response to a prescribed tension in the corresponding strip, and each third roll being gravitationally movable to a lower position in response to a proportionally lesser strip tension than the prescribed tension.

10. The apparatus of claim 9 wherein weight counterbalancing means are attached to the yoke means.

11. The apparatus of claim 10 wherein means responsive to the position of the thirdroll for varying the speed of the bridle drive motor are disposed between the third roll and the drive motor.

12. The apparatus of claim 10 wherein one end of the means responsiveto the position of the third roll is rotatably responsive to the yoke means for sensing the position of the third roll, and, the other end of said means is attached to the drive motor of the correspond- .ing strip-tensioning roll in the tension bridle for increasing the speed of the strip-tensioning roll, whereby tension in the strip is increased to cause the third roll to be raised to the upper position.

13. The apparatus of claim 11 wherein the means responsive to the roll position is a selsyn transmitter attached to the pivot shaft of the yoke means for transmitting a signal to a selsyn receiver attached to the drive motor. i

14. In a line for processing a plurality of strips moving continuously in parallel paths of travel at a constant speed through a work station in a line in which there are a recoiler at the end of. the line, a horizontal-car looper between the work station and the recoiler, a drive bridle between the work station and the looper, a tension bridle between the looper and the recoiler, the improvement in which the tension bridle includes a separate set of strip-tensioning rolls for each strip path of travel, and means between the looper and the drive bridle for preventing slack in any of the strips due to changes in operational speed of one set of strip-tension rolls, whereby the strips in adjacent paths are maintained in individual tension between the looper and the v tension bridle.

Claims

1. In a line for processing at least one strip that moves continuously in a path of travel at a presettable speed through a work station in the line in which there are a strip recoiler at the end of the line, a horizontal-car looper between the work station and the recoiler, a drive bridle between the work station and the looper, and a tension bridle between the looper and the recoiler comprising a set of strip-tensioning rolls for the strip, the improvement wherein there are tension-responsive means between the drive bridle and the tension bridle for preventing slack in the strip due to changes in tension of the strip.

2. The apparatus of claim 1 wherein the tension-responsive means are disposed between the drive bridle and the looper.

3. The apparatus of claim 1 wherein there are a plurality of strips moving continuously in parallel paths of travel at equal speeds and the tension bridle includes a separate set of strip-tensioning rolls with drive motors for each strip.

4. The apparatus of claim 2 wherein the tension-responsive means includes a pair of spaced rolls for guiding engagement on one side of the strip and includes a third roll for guiding engagement on the other side of the strip and being located with respect to the path of strip travel between the pair of spaced rolls, and the third roll being movable against the strip in response to a reduction of tension below a prescribed tension in the strip.

6. The apparatus of claim 2 wherein the tension-responsive means include a pair of spaced horizontal rolls for guiding engagement on the undersurface of the strip, a third horizontal roll for guiding engagement on the top surface of the strip and being located at its strip engagement location between the strip engagement locations of the pair of spaced rolls, and the third roll being movable vertically against the strip for maintaining a prescribed tension in the strip.

7. The apparatus of claim 3 wherein the tension-responsive means include a pair of spaced rolls for guiding engagement on one side of the strips and includes a third roll for each strip and for guiding engagement on the other side of each strip and being located between the spaced rolls with respect to the paths of travel of the strips.

9. The apparatus of claim 8 wherein yoke means including a pivot shaft are provided for guidingly mounting each third roll for movement between upper and lower positions, each third roll being retained in the upper position and adjacent to the pair of rolls in response to a prescribed tension in the corresponding strip, and each third roll being gravitationally movable to a lower position in response to a proportionally lesser strip tension than the prescribed tension.

11. The apparatus of claim 10 wherein means responsive to the position of the third roll for varying the speed of the bridle drive motor are disposed between the third roll and the drive motor.

12. The apparatus of claim 10 wherein one end of the means responsive to the position of the third roll is rotatably responsive to the yoke means for sensing the position of the third roll, and the other end of said means is attached to the drive motor of the correspoNding strip-tensioning roll in the tension bridle for increasing the speed of the strip-tensioning roll, whereby tension in the strip is increased to cause the third roll to be raised to the upper position.

13. The apparatus of claim 11 wherein the means responsive to the roll position is a selsyn transmitter attached to the pivot shaft of the yoke means for transmitting a signal to a selsyn receiver attached to the drive motor.

14. In a line for processing a plurality of strips moving continuously in parallel paths of travel at a constant speed through a work station in a line in which there are a recoiler at the end of the line, a horizontal-car looper between the work station and the recoiler, a drive bridle between the work station and the looper, a tension bridle between the looper and the recoiler, the improvement in which the tension bridle includes a separate set of strip-tensioning rolls for each strip path of travel, and means between the looper and the drive bridle for preventing slack in any of the strips due to changes in operational speed of one set of strip-tension rolls, whereby the strips in adjacent paths are maintained in individual tension between the looper and the tension bridle.