US3268985A

US3268985A - Method and apparatus for bending structural members

Info

Publication number: US3268985A
Application number: US284404A
Authority: US
Inventors: Ralph G Smith
Original assignee: Individual
Current assignee: Individual
Priority date: 1963-05-31
Filing date: 1963-05-31
Publication date: 1966-08-30
Anticipated expiration: 1983-08-30

Description

R. (5. SMITH Aug. 30, 1966 METHOD AND APPARATUS FOR BENDING STRUCTURAL MEMBERS Filed May 31, 1963 6 Sheets-Sheet 1 INVENTOR. RALPH Q, SMITH ATTORNEYS R. G. SMITH Aug. 30, 1966 METHOD AND APPARATUS FOR BENDING STRUCTURAL MEMBERS 6 Sheets-Sheet 2 Filed May 31, 1963 INVENTOR RALPH 6, SMITH ATTORNEYS R. G. SMITH Aug. 30, 1966 METHOD AND APPARATUS FOR BENDING STRUCTURAL MEMBERS Fil ed May 31, 1963 6 Sheets-Sheet 3 I ENTOR. RALPH Q; M1TH fimd $16M? 4%: ATTORNEYS JZM R. G. SMITH Aug. 30, 1966 METHOD AND APPARATUS FOR BENDING STRUCTURAL MEMBERS Filed May 31 1963 6 Sheets-Sheet 4 1 ENTORL RALPH g MlTH BY ATTORNEYS Aug. 30, 1966 R. 6. SMITH 3,268,985

METHOD'AND APPARATUS FOR BENDING STRUCTURAL MEMBERS Filed May 31, 1963 6 Sheets-Sheet 5 5 INVENTOR;

RALPH 6; SMITH 25 6m 16d r/M ATTORNEYS Aug. 30, 1966 R. G. SMITH 3,263,935

METHOD AND APPARATUS FOR BENDING STRUCTURAL MEMBERS Filed May 31, 1963 6 Sheets-Sheet 6 FIG. I!

INVENTOR. Rm. PH gSMrrH BY 25 wrfm ATTORNEYS 3,268,985 METHUD AND APPARATUS FOR BENDING STRUCTURAL MEMBERS Ralph G. dmith, 5000 dtecker, Whitmore Lake, Mich. Filed May 31, 1963,8121. No. 284,404 16 Claims. (Cl. 29-155) This invention relates to bending and particularly to the bending of structural members such as I-beams, channels and the like to predetermined curvature.

It has been heretofore customary in order to bend structural members such as heavy channels or beams to utilize an apparatus which comprises basically three rolls. The third roll is adapted to be moved generally radially toward the other two rolls which are driven. As the structural member is moved between the rolls, the third roll cooperates with the other two rolls to deform the structural members. In such a method of bending, the structural member is progressively passed between the rolls with the third roll being moved in increments between each pass toward the other two rolls to progressively increase the curvature until the structural member has been bent to the desired shape. Such a method of bending is not only slow but also depends upon the operators skill in progressively moving the rolls together during successive passes. Accordingly, the method is not adaptable to high production.

It is an object of this invention to provide a method and apparatus for bending a structural member to a desired curvature without the use of heat and in a single pass.

It is a further object of the invention to provide such a method and apparatus wherein the bending can be accomplished quickly, accurately and economically.

It is a further object of the invention to provide a method and apparatus for bending structural members wherein a continuous length of structural member can be successively bent and cut off into predetermined shorter lengths.

In the drawings:

FIG. 1 is a plan view of an apparatus embodying the invention.

FIG. 2 is a plan view showing the apparatus adjusted for bending a structural member of a different curvature.

FIG. 3 is a fragmentary perspective view of various structural members that can be bent in accordance withthe invention.

FIG. 4 is a bottom plan view on a reduced scale showing the drive mechanism.

FIG. 5 is a part sectional elevation of a drive roll assembly utilized in the apparatus.

FIG. 6 is a part sectional elevational view of an idler roll assembly utilized in the apparatus.

FIG. 7 is a plan view of the drive roll assembly shown in FIG. 5.

FIG. 8 is a fragmentary sectional view taken along the line 8-8 in FIG. 7.

FIG. 9 is a plan view of the idler roll assembly shown in FIG. 6.

FIG. 10 is a fragmentary sectional view on an enlarged scale taken along the line 1010 in FIG. 2.

FIG. 11 is an end view of a structural member showing how it is cut to facilitate bending.

FIG. 12 is a view of the member shown in FIG. 11 in its final shape for initiating bending.

FIG. 13 is a partly diagrammatic plan view of an apparatus for bending a continuous length of structural member.

Referring to FIGS. 1 and 2, the apparatus embodying the invention comprises a base or table 10 on which a pair of drive roll assemblies 11, 12 and a plurality of idler roll assemblies 13 are positioned. The leading end of a struco 4 3,268,885 O Patented August 30, 1966 tural member which is to be bent is delivered between the rolls of the drive roll assembly 12 and then fed progressively by the drive rolls 12 between sucessive pairs of idler rolls 13 and then between the drive rolls of the drive roll assembly 11.

The planes containing the axes of the pairs of rolls in the drive and idler roll assemblies are angularly related to one another in such a manner that the first pair of drive rolls and the first pair of idler rolls tend to bend the structural member to a parabolic curvature and the last pair of idler rolls and the second pair of drive rolls finally bend the structural member to the desired curvaturc.

As shown in FIG. 3, the apparatus is intended for bending structural members of heavy cross section such as the H section, I section or channel section.

Each of the pairs of driven and idler rolls are so mounted that the axes of the rolls are in fixed unyielding relation when the apparatus is being operated. The drive rolls are driven in synchronism at substantially the same peripheral speed.

DRIVE ROLL ASSEMBLY Each of the drive roll assemblies 11, 12 is of substantially the same design and for purposes of clarity only one of the drive roll assemblies will be described.

Referring to FIGS. 5, 7 and 8, drive roll assembly 12 comprises a rectangular frame including a bottom plate 14, top plate 15 and

end plates

16, 17. A drive shaft 18 is journalled between the top and

bottom plates

15, 14 and also in the table 10 so that the frame can be swung about the axis of the shaft 18 as presently described.

A serrated drive roll 19 is fixed on the shaft 18. The top and

bottom plates

15, 14 are provided with

longitudinal slots

28, 21 in which the

legs

22, 23 of a slide 24 extend. The slide is intended to be moved longitudinally of the frame and held in fixed position therein by a screw 25 threaded into the end plate 16 and journalled in the cross member of the slide 24 by a journal connection 26. A lock ring 27 locks the slide in adjusted position. A second serrated drive roll 28 is keyed to a shaft 29 which is journalled between the

legs

22, 23 of the slide 24. The slide is maintained in assembled relation to the frame by a plate 30 fixed to the top leg 22 (FIG. 7). By this arrangement, the drive roll 28 can be moved toward and away from the drive roll 19 to adjust the space between them and accommodate structural. members of different sizes.

Gears

31, 32 are keyed to

shafts

18, 29, respectively, so that the

rolls

19, 28 are driven in synchronism when shaft 18 is rotated as presently described.

Referring to FIG. 4, which is a bottom plan view of the table 10, the shafts 18 of the two drive roll assemblies project downwardly to the underside of the table 10 and sprockets 35 are keyed to the shafts 18. A chain 36 is trained over the sprockets 35. Chain 36 is also trained over a drive sprocket 37 on a gear reduction mechanism 38 driven by chain 39 and a sprocket on a motor 41 The tension on the chain 36 can be adjusted by a mechanism 41 which holds the sprocket 37 in position and can be loosened to permit the sprocket 37 to be moved toward and away from the chain 36.

As shown in FIG. 5, the serrated rolls can be made of a multiplicity of sections and spacers 42 can be used in association therewith so that the rolls can be readily changed to accommodate structural members of different widths.

In addition, grooves 45 can be provided in the serrated rolls to accommodate the flanges of the structural members where the member is being bent in a curvature at right angle to the web. 7

The angle which the plane containing the axes of each pair of drive rolls 19, 28 makes with the table can be IDLER ROLL ASSEMBLY Referring to FIGS. 6, 9 and 10, each of the idler roll assemblies 13 is substantially identical and for purposes of clarity only one will be described.

As shown in FIGS. 6 and 9, each idler roll assembly 13 comprises a slide 50 which is adapted to be moved radially between slide guides 51 fastened to the table by bolts 52. After being adjusted to the desired position, the slide is locked in position by lock plates 53 and bolts 54 on each end of slide 50. An angularly adjustable frame 55 is provided on the slide 50 and comprises a bottom plate 56, top plate 57 and end members 58, 59. A first shaft 60 is journalled between the top and

bottom members

57, 56 and extends and is journalled also in the slide 50. By this arrangement, the frame 55 can be swung relative to the slide about the axis of the shaft 60.

A serrated idler roll 61 is rotatably mounted on the shaft 60. A second shaft 62 is journalled between

slides

63, 64 extending in slots 65, 66 in the top and

bottom members

57, 56, respectively. A second idler roll 67 is rotatably mounted on the shaft 62. Each of the

slides

63, 64 is adapted to be adjusted toward and away from the roll 61 by an arrangement which includes screws 68 threaded into the end member 58 and operating in an opening in the

slides

63, 64. Looking nuts 69 and collars 70 are provided to lock the screws 68 in adjusted position.

As in the case of the drive rolls, the idler rolls can be made of various sections to accommodate structural members of different widths and may be provided with grooves 75 (FIG. 6) to accommodate the flanges of an H member when it is bent in a direction wherein the plane of curvature is at a right angle to the web.

In order to lock the frame 55 in angularly adjusted relation to the slide 50, the end of the base or bottom member 56 is curved as at 75 with a radius of curvature having as its center the axis of the shaft 60 and a locking plate 76 having a comparable curved portion 77 is provided and engages a shoulder 78 to clamp the bottom member 56 in position. Plate 76 is locked in position by bolts 79 extending through plate 76 and threaded into table 10. When it is desired to adjust the frame 55 angularly relative to the slide 50, the bolts 79 are loosened and the frame is swung to the desired position after which the bolts 79 are tightened clamping the member 76 against the shoulder 78 and maintaining the surface 79 in contact with the surface 75 so that the frame is positively locked in angularly adjusted relation.

In the bending of certain sections such as an H section shown in dotted lines in FIG. 6, the use of guide rolls 80 rotatably mounted on brackets 81 fixed to the top and

bottom walls

57, 56 is advisable to maintain the web of the section in a plane at a right angle to the axes of the rolls 61, 67. The guide rolls 80 are mounted with their axes at right angles to and intersecting the axes of the rolls 61, 67.

Referring to FIG. 1, in operation, a length of structural member is fed between the drive rolls of the drive roll assembly 12 in the direction of the arrow. The drive rolls, in turn, feed the length successively through the pairs of idler rolls of the idler roll assemblies 13 and then to the drive rolls of the drive roll assembly 11. Since the rolls of the drive and idler roll assemblies have their axes fixed and unyielding, the structural member is bent progressively to the desired shape in a single pass. The first set of drive rolls and idler rolls, being positioned to bend the length of structural member in a parabolic curve, begin the bending and the remaining two pairs of idler roll assemblies increase the bending action until the final bending is achieved to the desired curvature by the final pair of idler rolls in combination with the final pair of drive rolls, the final pair of idler rolls and the final pair of drive rolls being positioned so that the planes containing the rolls intersect at the center of curvature of the curve desired for the final curvature of the structural member.

It has been found that by utilizing the apparatus heretofore shown and described, it is possible to bend structural members, that is, members which are adapted to take heavy loads and have substantial sections in a single pass. For example, structural members having a channel cross section, American Standard 8 x 2% have been bent to a radius of two feet.

As a further example, a WP shape, 4 x 13, has been bent with the web thereof extending radially to a radius of as small as two feet.

In order to adjust the apparatus to bend the structural member to a different radius of curvature, each of the idler and drive roll assemblies is adjustable as heretofore described. Thus, the assemblies can be adjusted as shown in FIG. 2 to obtain a greater radius of curvature. This greater radius of curvature is superimposed in a broken line in FIG. 1.

Referring to FIG. 2, the drive roll assemblies 11 and 12 have been swung outwardly relative to the table 10 about axes of the shafts 18 so that the angle between the planes containing the axes of the drive rolls is larger than the angle in FIG. 1. Similarly, the central idler roll assembly has been moved radially outwardly and the outer idler roll assemblies move radially outwardly and also swing outwardly about the axes of the shaft 60 so that the curvature provided to the structural member has a smaller radius.

In order to adjust the apparatus to cross sections of different sizes, the various drive and idler rolls are made of sections which can be changed in thickness and combined with spacers of different thickness to accommodate the various dimensions of flanges or webs of the sections such as shown in FIG. 3. In order to facilitate the insertion of an end of an H section (FIG. 3), a triangular piece is cut out of the web as shown at in FIG. 11, and the flange 91 is bent against the free edge of the web (FIG. 12) to provide a tapered end to the structural member. The structural member is then fed to the bending apparatus with the bent flange 91 radially outwardly from the center of bending. This prevents any tendency for the end of the flange 91 to cut into the bending rolls.

In the form of apparatus shown in FIG. 13, a continuous length of structural member L is initially fed by hand or otherwise to the apparatus, after which the operation of the apparatus is completely automatic. As shown, the bent end B comes into the vicinity of a light beam from a light source 93. When the passage of the beam from light source 93 to photo cell 94 is interrupted, the drive to the motor M of the bending apparatus is also interrupted and a saw 94 is energized to cut off a predetermined length. After the length is cut oil, the reestablishment of the passage of the beam of light to the photo cell 94 stops the operation of the saw 94' and energizes the motor M to continue the bending of the length L. In practice, successive lengths on the order of 60 to 65 feet are welded to one another so that the bending continues without interruption and without need for feeding separate lengths to the bending apparatus.

It can thus be seen that there has been provided a method and apparatus for bending structural members without the use of heat and in a single pass to a predetermined accurate curvature economically and quickly. The bending is achieved without spring back so that the structural member is to the desired curvature immediately upon leaving the bending apparatus.

What is claimed is:

1. The method of bending a structural member to a predetermined curvature without the application of heat and in a single pass which comprises the steps of directing the leading end of said length of structural member between a pair of continuously driven rolls, rotating said rolls to cause said leading end to be pulled through said rolls, thereafter directing the leading end of said length between at least three pair of spaced idler rolls,

positioning said first pair of idler rolls adjacent said first pair of drive rolls with the axes of said rolls lying in a plane such that the length of the structural member between the first pair of drive rolls and the first pair of idler rolls tends to assume a parabolic curvature,

directing the leading end of said length after passage through said pairs of idler rolls between a second pair of driven rolls,

rotating said second pair of driven rolls at substantially the same peripheral speed as said first pair of driven rolls,

and positioning said second pair of driven rolls with relation to said last pair of idler rolls such that the length of structural member assumes the desired configuration between said second pair of driven rolls and said last pair of idler rolls.

2. The method of bending a structural member to a predetermined curvature of constant radius without the application of heat and in a single pass which comprises the steps of directing the leading end of said length of structural member between a pair of continuously driven rolls, rotating said rolls to cause said leading end to be pulled through said rolls, thereafter directing the leading end of said length between at least three pair of spaced idler rolls,

directing the leading end of said length after passage through said pair of idler rolls between a second pair of driven rolls,

rotating said second pair of driven rolls at susbtantially the same peripheral speed as said first pair of driven rolls,

and positioning said second pair of driven rolls with relation to said last pair of idler rolls such that the plane containing the axes of each pair of rolls intersect at a center of curvature corresponding to the desired curved configuration of said structural memher.

3. The method of bending a structural member to a predetermined curvature without the application of heat and in a single pass which comprises the steps of directing the leading end of said length of structural member between a pair of continuously driven rolls mounted with their axes fixed against lateral movement,

rotating said rolls to cause said leading end to be pulled through said rolls, thereafter directing the leading end of said length between at least three pair of spaced idler rolls mounted with their axes fixed against lateral movement,

directing the leading end of said length after passage predetermined curvature of constant radius without the application of heat and in a single pass which comprises the steps of directing the leading end of said length of structural member between a pair of continuously driven rolls mounted with their axes fixed against lateral movement,

rotating said rolls to cause said leading ends to be pulled through said rolls,

thereafter directing the leading end of said length between at least three pair of spaced idler rolls mounted with their axes fixed against lateral movement,

directing the leading end of said length after passage through said pair of idler rolls between a second pair of driven rolls mounted with their axes fixed against lateral movement,

and positioning said second pair of driven rolls with relation to said last pair of idler rolls such that the plane containing the axes of each pair of rolls intersect at a center of curvature corresponding to the desired curved configuration.

5. An apparatus for bending a length of structural member to a desired configuration without heating and in a single pass which comprises a base,

a pair of drive roll assemblies in spaced relation on said base,

at least three pair of idler roll assemblies positioned in spaced relation to one another between said drive roll assemblies,

each said drive roll assembly comprising a frame,

a first shaft journalled in said frame and extending through an opening in said base,

a first serrated drive roll mounted on said first shaft,

a second shaft,

means for adjustably and fixedly mounting said second shaft on said frame with its axis parallel to the axis of said first drive shaft,

a second serrated drive roll on said second shaft,

means for driving said second drive roll in synchronism with said first drive roll,

each said idler assembly comprising a frame,

a first idler roll journalled in said frame,

a second idler roll,

means for adjustably and fixedly journalling said second idler roll in said frame toward and away from said first idler roll,

means for mounting the frame of each said drive roll assembly for swinging movement on said base,

means for mounting the frame of each said idler roll assembly for sliding movement and radial movement relative to said base.

6. An apparatus for bending a length of structural member to a desired configuration without heating and in a single pass which comprises a base,

a pair of drive roll assemblies in spaced relation on said base,

at least three pairs of idler roll assemblies positioned in spaced relation to one another between said drive roll assemblies,

each said drive roll assembly comprising a substantially rectangular frame including a bottom plate, a top plate and end plate,

a first shaft journalled in said top and bottom plates and extending through an opening in said base,

a first serrated drive roll mounted on said first shaft,

a slide provided in said frame,

means for adjusting the position of said slide within said frame toward and away from said first shaft,

a second shaft journalled in said slide with its axis parallel to the axis of said first shaft,

a second serrated drive roll on said second shaft,

each said idler roll assembly comprising a rectangular frame including a bottom plate, a top plate and end plates,

a first idler r-oll journalled between said top and bottom plates,

a slide in said idler frame,

means for adjusting said slide toward and away from said first idler roll,

a second idler roll journalled in said slide, means for mounting the frame of each said drive roll assembly for swinging movement relative to said base,

means for mounting the frame of each said idler roll assembly for arcuatemovement and radial movement reltaive to said base.

7. An apparatus for bending a length of structural member to a desired configuraton without heating and in a single pass which comprises a base,

a pair of drive roll assemblies in spaced relation on said base,

at least three pair of idler roll assemblies positioned in spaced relation to one another between said drive roll assemblies,,

a shaft journalled in said top and bottom plates and extending through an opening in said base,

a first serrated drive roll mounted on said shaft,

a drive chain extending between the shafts of said drive roll assemblies,

a slide provided in said frame,

means for fixedly adjusting the position of said slide within said frame toward and away from said first drive roll,

a second drive roll journalled in said slide with its axis parallel to the axis of said first drive roll,

means for driving said second drive roll in synchronism with said first drive roll comprising meshed gears on said drive shafts,

a first idler roll journalled between said top and bottom plate,

a slide in said frame,

means for fixedly adjusting said slide toward and away from said first idler roll,

a second idler roll journalled in said slide,

means for mounting the frame of each said drive roll assembly for swinging movement on said base about the axis of said first drive shaft,

means for mounting the frame of-each'said idler roll assembly for sliding movement and swinging movement relative to said base about the axis of said first idler roll.

8. An apparatus for bending a length of structural member to a desired configuration without heating and in a single pass which comprises a base,

a pair of drive roll assemblies in spaced relation on said base,

each said drive roll assembly comprising a frame,

a first serrated drive roll mounted on said first shaft,

a second shaft,

21 second serrated drive roll on said second shaft,

each said idler assembly comprising'a frame,

a first idler roll journalled in said frame,

a second idler roll,

means for adjustably and fixedly journalling said second idler roll in said frame toward and away from said first idler roll, means for mounting the frame of each said drive roll assembly for swinging movement on said base,

means for mounting the frame of each said i-dler roll assembly for sliding movement and radial movement relative to said base,

said last-mentioned means comprising an intermediate support mounted for sliding movement beneath each idler roll assembly,

the path of sliding movement of each said intermediate support being angularly related to the adjacent intermediate Support,

the shaft of the first idler roll of each said idler roll assembly extending downwardly and being journalled in said respective support,

and a guiding and locking member engaging the end of said frame for locking said frame to said respective support.

9. An apparatus for bending a length of structural member to a desired configuration without heating and in a single pass which comprises a base,

a pair of drive roll assemblies in spaced relation on said base,

a first serrated drive roll mounted on said shaft,

a drive chain extending between the shafts of said drive roll assemblies,

a slide provided in said frame,

each Said idler assembly comprising a rectangular frame including a bottom plate, a top plate and end plates,

a first idler roll journalled between said top and bottom plate,

a slide in said frame,

a second idler roll journalled in said slide,

means for mounting the frame of each said drive roll assembly for swinging movement on said base about the axis of said drive shaft,

and means for mounting the frame of each said idler roll assembly for sliding movement and radial movement relative to said base about the axis of said first drive roll,

10. The method of bending a structural member to a predetermined curvature without the application of heat and in a single pass which comprises the steps of directing the leading end of said length of structural member between a pair of continuously driven rolls, rotating said rolls to cause said leading end to be pulled through said rolls, thereafter directing the leading end of said length between at least three pair of spaced idler rolls,

and positioning said second pair of driven rolls with relation to said last pair of idler rolls such that the length of structural member assumes the desired configuration between said second pair of driven rolls and said last pair of idler rolls,

causing the bent end of said length of structural member to move past a sensing device,

creating a signal in response to said bend and past said sensing device,

interrupting the drive to said rolls in response to said signal,

and cutting off said bent portion of said structural member after the drive is interrupted.

11, The method set forth in claim including the step of welding successive lengths of structural member to said first length of structural member whereby bending and cutting off of successive lengths is achieved substantially continuously.

12. The method of bending a structural member having an H cross section to a predetermined curvature without the application of heat and in a single pass which comprises the steps of directing the leading end of said length of structural member between a pair of continuously driven rolls with the web of the structural member extending radially of the rolls,

rotating asid rolls to cause said leading end to be pulled through said rolls, thereafter directing the leading end of said length between at least three pair of spaced idler rolls,

and laterally stabilizing the webs of said structural member during its passage through at least some of said rolls.

13. The method set forth in claim 12 including the step of removing a portion of the web of the leading end of the structural member prior to insertion between the rolls and bending one flange against the web to provide a narrow leading end.

14. An apparatus for bending a length of structural member to a desired configuration without heating and in a single pass which comprises a base,

a pair of drive roll assemblies in spaced relation on said base,

each said drive roll assembly comprising a frame,

a pair of drive rolls mounted on said frame,

means for driving said drive rolls in synchronism,

each said idler assembly comprising a frame,

a pair of idler rolls journalled on said frame,

and means for mounting the frame of each said idler roll assembly for sliding movement and radial movement relative to said base.

15. The combination set forth in claim 14 including means for laterally stabilizing said structural member during its passage through at least some of said rollsv 16. The combination set forth in claim 1.4 wherein said one pair of drive rolls and the adjacent idler rolls are positioned such that the structural member passing therebetween assumes a parabolic configuration,

the other pair of driven rolls and the adjacent pair of idler rolls being positioned such that the structural member assumes a curvature corresponding to the desired curvature of the structural member.

References Cited by the Examiner UNITED STATES PATENTS 972,928 10/ 1910 Schneider 29-480 1,043,832 11/1912 Herr 72-471 2,937,821 5/ 1960 OBrien 72-171 2,959,849 11/1960 Rubin 29-417 2,978,805 4/ 1961 Greenberger 29-430 JOHN F. CAMPBELL, Primary Examiner.

THOMAS H. EAGER, Examiner.

Claims

1. THE METHOD OF BENDING A STRUCTURAL MEMBER TO A PREDETERMINED CURVATURE WITHOUT THE APPLICATION OF HEAT AND IN A SINGLE PASS WHICH COMPRISES THE STEPS OF DIRECTING THE LEADING END OF SAID LENGTH OF STRUCTURAL MEMBER BETWEEN A PAIR OF CONTINUOUSLY DRIVEN ROLLS, ROTATING SAID ROLLS TO CAUSE SAID LEADING END TO BE PULLED THROUGH SAID ROLLS, THEREAFTER DIRECTING THE LEADING END OF SAID LENGTH BETWEEN AT LEAST THREE PAIR OF SPACED IDLER ROLLS, POSITIONING SAID FIRST PAIR OF IDLER ROLLS ADJACENT SAID FIRST PAIR OF DRIVE ROLLS WITH THE AXES OF SAID ROLLS LYING IN A PLANE SUCH THAT THE LENGTH OF THE STRUCTURAL MEMBER BETWEEN THE FIRST PAIR OF DRIVE ROLLS AND THE FIRST PAIR OF IDLER ROLLS TENDS TO ASSUME A PARABOLIC CURVATURE, DIRECTING THE LEADING END OF SAID LENGTH AFTER PASSAGE THROUGH SAID PAIRS OF IDLER ROLLS BETWEEN A SECOND PAIR OF DRIVEN ROLLS, ROTATING SAID SECOND PAIR OF DRIVEN ROLLS AT SUBSTANTIALLY THE SAME PERIPHERAL SPEED AS SAID FIRST PAIR OF DRIVEN ROLLS, AND POSITIONING SAID SECOND PAIR OF DRIVEN ROLLS WITH RELATION TO SAID LAST PAIR OF IDLER ROLLS SUCH THAT THE LENGTH OF STRUCTURAL MEMBER ASSUMES THE DESIRED CONFIGURATION BETWEEN SAID SECOND PAIR OF DRIVEN ROLLS AND SAID LAST PAIR OF IDLER ROLLS.