US3422652A - Method and machine for changing the curvature of elongated workpieces - Google Patents

Description

Jan. 21, 1969 Filed July 21. 1966 H. LORENZ METHOD AND MACHINE FOR CHANGING THE CURVATURE OF ELONGATED WORKPIECES Sheet of 6 D m a MIME/V701? Jan. 21, 1969 H. LORENZ 3,422,552

METHOD AND MACHINE FOR CHANGING THE. CURVATURE OF ELONGATED WORKPIECES Filed .July 21, 1966 Sheet N OI INVENTOP Hdkfil' ween z Jan. 21, 1969 H. LORENZ I METHOD AND MACHINE FOR CHANGING THE CURVATURE OF ELONGATED WORKPIECES Filed July 21, 1966 7 Sheet 3 INVENTOR H0257 Law-W2 Jan. 21, 1969 'H. LORENZ 3,422,652

METHOD AND MA NE FOR CHANG THE CURVATURE OF ONGATED WORK CES Filed July 21, 1966 Sheet 5 of 6 W 15 /r/ \1 k j/A A J m \d I- 7W K it A J 1m JNVEIVTOR H0165; tail-NZ Jan. 21, 1969 H. LORENZ 3,422,552

1 METHOD AND M INE FOR CHANG THE CURVATURE ATED CES 0 LONG WORK Filed July 21, 1966 Sheet 6 of 6 L) Q k I g ID 0 @IO D A I l LT"? Q D Mlrewrok ar zaeavz M424 a [JI f/hlm, A4? 4770!?5) United States Patent 3,422,652 METHOD AND MACHINE FOR CHANGING THE CURVATURE 0F ELONGATED WORKPIECES Horst Lorenz, Solingen, Germany, assignor to Th. Kieserling & Albrecht, Solingeu, Germany Filed .luly 21, 1966, Ser. No. 567,010 Claims priority, appliclzitiog Germany, Sept. 17, 1965,

1.7.5. or. 72164 24 Claims 1m. c1. BZld 1/02; B2111 13/08; B21d 21/00 ABSTRACT OF THE DISCLOSURE The present invention relates to a method and machine for changing the curvature of elongated workpieces. More particularly, the invention relates to a method and machine for straightening or bending of elongated metallic workpieces having a rectangular, square or other noncircular cross-sectional outline. Still more particularly, the invention relates to a method and machine which may be applied to change the curvature of solid or tubular metallic workpieces, especially of heavy-duty tubular workpieces having cross-sectional dimensions, for example, in excess of two inches.

In accordance with presently known straightening methods, an elongated metallic workpiece is treated while advancing along a path defined by several sets of driven guide rolls. The application of straightening forces takes place in accordance with the so-called triangle principle which means that two longitudinally spaced portions of a workpiece are kept in abutment with rigid supports and an intermediate portion of the workpiece is subjected to stresses exceeding the elastic limit of treated material so that the workpiece cannot recoil because its material undergoes permanent deformation. It was found that such conventional methods are satisfactory only when the workpieces are not too heavy, i.e., if their cross-sectional area does not exceed a certain maximum value. Also, the wall thickness of tubular workpieces plays an important role in a bending or straightening operation because a thin-walled workpiece is very likely to develop dents, depressions and similar undesirable flaws which appear at the point or points where the bending forces are applied thereagainst. Therefore, heavy-duty tubular workpieces of other than circular outline are presently straightened by hand whereby the distance between such longitudinally spaced portions which are held against flexing while an intermediate portion undergoes deformation must be very large so that the machines used for carrying out such conventional methods occupy too much room, especially in view of the fact that their output is extremely low.

Accordingly, it is an important object of the present invention to provide a novel and improved method of changing the curvature of elongated metallic workpieces,

Patented Jan. 21, 1969 especially of tubular workpieces of rectangular or square cross-sectional outline, according to which such workpieces may be deformed to a desired extent, in a very simple and time saving manner, and without any danger of denting or other undesirable deformation of their walls or surfaces.

Another object of the invention is to provide a method of the just outlined characteristics according to which the extent to which the workpieces are being deformed (for example, straightened) may be determined and altered in the course of the actual bending or straightening operation.

A further object of the invention is to provide a method of changing the curvature of tubular metallic workpieces according to which the bending or straightening operation can be carried out in a small area, by resorting to a very compact and relatively simple machine, and in such a way that a series of workpieces may be treated in rapid succession and in a fully automatic way.

A concomitant object of the invention is to provide a machine which may be utilized for carrying out the above outlined method and to construct and assemble the machine in such a way that its dimensions need not exceed the dimensions of conventional machines despite the fact that the improved machine may be used for changing the curvature of exceptionally long, heavy and thick-walled solid or tubular workpieces.

Still another object of the instant invention is to provide the improved machine with novel means for regulating the extent of deformation in the course of the actual bending or straightening operation.

A further object of my invention is to provide a machine of the above outlined characteristics which can be readily and rapidly converted for bending or straightening of different types of workpieces.

Briefly stated, one feature of my present invention resides in the provision of a method of changing the curvature of elongated workpieces, particularly to a method of straightening tubular workpieces having a rectangular, square or other non-circular cross-sectional outline. Basically, the improved method comprises the steps of advancing the workpieces seriatim and lengthwise along a predetermined path in which the workpieces are guided and moved by sets of cooperating advancing and withdrawing rolls, subjecting successive portions of advancing workpieces first to the action of initial bending forces to stress such portions to slightly below the elastic limit of their material, and thereupon subjecting the initially stressed portions of successive workpieces to the action of additional or final bending forces to stress such portions beyond the elastic limit of their material and to thus effect permanent deformation of the respective workpieces. It was found that such stepwise application of bending forces prevents denting of tubular workpieces at the points where the initial and/or additional bending forces are applied thereto. The aforementioned sets of rolls also serve to hold the workpieces against turning during travel along the predetermined path. The magnitude of additional or final bending forces may be a small fraction of the magnitude of initial bending forces and such initial bending forces may be applied in a plurality of stages so that each successive portion of a workpiece advancing along the aforementioned path is subjected to stresses generated by more than two different bending forces. The initial and additional bending forces may be applied to successive portions of advancing workpieces in several directions so that the workpieces may be deformed in a plurality of planes whereby the deformation in one plane may but need not be the same as in the other plane or planes. For example, the bending forces may be applied in a horizontal and in a vertical plane, i.e., in two planes which make right angles with each other.

As a rule, the application of additional bending forces will take place upon a portion of a traveling workpiece which is disposed between two portions subjected to the action of initial bending forces. The magnitude of initial and/or additional or final bending forces may be varied while the workpieces travel along the aforementioned path.

The improved method is especially suited for bending or straightening of non-circular tubular workpieces; however, such method is equally useful in connection with treatment of solid non-circular workpieces as well as in connection with the treatment of solid and/or tubular workpieces of circular cross-sectional outline.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved bending or straightening machine itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic side elevational view of a straightening machine which embodies one form of my invention;

FIG. 2 is a top plan view of the straightening machine;

FIG. 3 is an end elevational view as seen from the left-hand side of FIG. 1 or 2;

FIG. 4 is a transverse vertical section as seen in the direction of arrows from the line AB of FIG. 1;

FIG. 5 is a transverse vertical section as seen in the direction of arrows from the line C-D of FIG. 1;

FIG. 6 is an enlarged fragmentary section as seen in the direction of arrows from the line E-F of FIG. 4;

FIG. 7 is a section as seen in the direction of arrows from the line G-H of FIG. 6;

FIG. 8 is a fragmentary section as seen in the direction of arrows from the line I] of FIG. 6;

FIG. 9 is a diagram showing the mode of operation of the straightening machine which is illustrated in FIGS. 1 to 8; and

FIG. 10 is a similar diagram but showing the operation of a slightly modified machine wherein the initial bending forces are applied in a plurality of stages.

Referring first to FIGS. 1 to 3, there is shown a straightening machine which comprises a base or bed In provided with two spaced supports or blocks 1 and 2. The block 1 supports three sets of driven feed rolls 3a, 3b, 3c and the block 2 supports three sets of withdrawing rolls 3d, 32, 3 These rolls together define an elongated horizontal path for workpieces 37 (see FIG. 9) of rectangular or square cross-sectional outline. The rolls 3a-3f also serve as a means for advancing successive workpieces along the horizontal path.

The drive for the rolls 3a-3f comprises an electric motor 4 and an infinitely variable-speed transmission 5 whose output shaft drives one pulley of a belt transmission 5a. A clutch 4a is interposed between the motor 4 and the input shaft of the transmission 5. The drive further comprises a gear box 7 which accommodates intermeshing gears (not shown) serving to drive three pairs of cardanic shafts 6 for the rolls 3a, 3b, 3c. A motion transmitting spindle 10 connects the gear box 7 with a second gear box 9 whose gears drive cardanic shafts 8 for the rolls 30., 3e, 3 All of the rolls 3a-3f are adjustable in directions toward and away from each other so that the machine may treat workpieces of different rosssectional dimensions. The means for adjusting the rolls 3a-3f with reference to the supports 1 and 2 is not shown in the drawings. For example, all the upper rolls 3a-3c and 3d-3f can be moved simultaneously nearer to or further away from the corresponding lower rolls, or vice versa.

The machine further comprises a group of centrally located straightening or bending rolls which form part of two stressing means for the workpieces 37 and two groups of holding rolls 12. The group of rolls 12a is disposed between the two groups of rolls 12 and its purpose is to subject the workpieces to the action of initial and additional or final bending forces in a manner to be described in connection with FIG. 9.

As best shown in FIGS. 2 and 4, the group of rolls 12a comprises three sets of four rolls each and each such set of four rolls is mounted in a carrier 11a which is secured to a two-armed lever 13 by bolts 11a or analogous removable fasteners. This enables the persons in charge to rapidly convert the machine for treatment of different types of workpieces. The machine is furnished with several sets of carriers 11a each provided with differently positioned and/ or dimensioned rolls 12a.

The arm 13a of each lever 13 has an opening (see FIGS. 6 and 7) which accommodates an annular adjusting member 14 surrounding a portion of a splined drive shaft 15. The adjusting member 14- accommodates a sleeve 15a which is internally splined to rotate with the drive shaft 15, see particularly FIG. 7. The sleeve 15a has a slotted flange 15b, best shown in FIG. 8, which is rotatable in an antifriction bearing 15c provided in a hearing block 15d. The end portions of the drive shaft 15 are mounted in fixed bearing blocks 15a, 15] shown in FIG. 2. This shaft 15 is driven by an electric motor 18 through an infinitely variable-speed transmission 17 and a cardanic shaft 16 shown in the upper right-hand portion of FIG. 2.

Each adjusting member 14 is shiftable in the axial direction of the drive shaft 15 and is formed with two parallel external faces 14a, 1411 Which are inclined with reference to the axis of the drive shaft and abut against two similarly inclined complementary internal faces of the respective eccentric ring 19. As shown in FIG. 6, each adjusting member 14 is surrounded by one such eccentric ring 19 which is received in an antifriction hearing 20 fitted into the opening of the respective arm 13a.

A round portion of each adjusting member 14 is received in antifriction bearings 21 (see FIG. 6) for a rack 22 which meshes with a gear 24 rotatable in a fixed 'frame 23 for the drive shaft 15. The gears 24 are rotatable by 'cardanic shafts 24a (see FIG. 2) Which receive motion from reversible electric motors 24b. Rotation of gears 24 results in movement of respective adjusting members 14- in the axial direction of the drive shaft 15 with resultant change in the throw of the associated eccentric rings 19.

Each lever 13 is fulcrumed on a pivot 25 (see FIG. 4) which is mounted in a slide 26. The slides 26 are reciprocable in horizontal slots 27 provided in the respective levers 13. Each pivot is further mounted in a forked bracket 2511 which is reciproca'ble in a dovetailed groove machined into ways 28 provided on the base 1a. Each such bracket 25a is formed with a spindle nut 25b which meshes with a horizontal spindle 29 rotatably mounted in the respective ways 28. The effective length of each arm of each lever 13 may be changed by rotating the associated spindle 29 to thereby move the respective pivot 25 nearer to or further away from the drive shaft 15. Depending on the direction in which a spindle 29 is rotated, the operator can change the path of movement of rolls 12a during a revolution of the drive shaft 15. Such adjustment can be carried out while the machine is in actual use.

Each group of holding rolls 12 also comprises two sets of four rolls each and each such set is mounted in a carrier 11 in a manner best shown in FIG 5. The carriers 11 are detachably secured to two-armed levers 30 by means bolts 11. The levers 30 are fulcumed on horizontal pivots 31 which are parallel to the pivots 25 and are mounted in brackets 32 provided with spindle nuts 32a. The lower portion of each bracket 32 is slidable in a dovetailed groove provided in ways 33 carried by the base 1a, and each of these ways 33 is provided with a horizontal spindle 34 which meshes with the respective spindle nut 32a so that it can shift the associated bracket 32 toward and away from the spindle 10. The longer arms 30a of the levers 30 are formed with vertical bores for elongated adjusting bolts 35 which are turnable on pins 36 carried by the base 1a and are provided with lock nuts 35a, 35b to hold the levers 30 in selected positions of inclination. In this way, the operator can select the exact level of the carriers 11, i.e., the distance between the respective set of holding rolls 12 and the ground.

The operation of the machine shown in FIGS. 1 to 8 is as follows:

Prior to introducing the first workpiece 37 between the pairs of feed rolls 3a, 3b, 3c, the operators select the exact position of the holding rolls 12 by manipulating the bolts 35 and nuts 35a, 35b (see FIG. 5) in order to move the corresponding carriers 11 to a desired level above the floor. As shown in FIG. 9, the holding rolls b (corresponding to the rolls 12 of FIGS. 1, 2 and 5) may be located at the same level. The operators then adjust the position of the brackets 25a and 32 by manipulating the corresponding spindles 29, 34 to thus select the exact position of axes for the levers 13' and 30. The levers 13 will be rocked in response to rotation of the drive shaft 15. If necessary, the operators also adjust the position of the adjusting members 14 by starting the corresponding motors 24b. Once the levers 13 and 30 are properly adjusted, the first workpiece 37 is introduced between the feed rolls a of FIG. 9 (corresponding to the feed rolls 3a, 3b, 3c of FIGS. 1 to 3) so that the leading end of the workpiece is advanced between the two left-hand sets of holding rolls b and enters the space between the lefthand rolls c (corresponding to the leftmost set of rolls 12a shown in FIG. 1). These rolls 0 are rocked by the drive shaft so that they move out of registry with the holding rolls b and subject successive portions of the workpiece 37 to the action of a bending force which is relatively strong but too weak to deform the material of the workpiece beyond the elastic limit. This initial force is indicated in FIG. 9 by the reference character P1. The thus initially stressed portion of the workpiece 37 then enters the space between the rolls d which correspond to the set of median rolls 12a in FIG. 1 and which subject the workpiece to the action of a relatively weak additional or final bending force P2 which is strong enough to deform the material of the workpiece beyond the elastic limit so that the deformation of the workpiece is permanent. The second set of rolls 0 shown in FIG. 9 corresponds to the rightmost set of rolls 12a shown in FIG. 1, and these rolls (2 again subject the workpiece 37 to the action of bending forces P1, i.e., the application of the final or additional bending force P2 takes place upon a portion of the workpiece located between two spaced portions which are subjected to the action of initial bending forces -P1. The rolls a, b, c, d of FIG. 9 also hold the workpiece 37 against rotation and, since the rolls b, c and d are disposed in sets of four each so that each side of a rectangular workpiece is engaged by one such roll, the workpiece may be simultaneously deformed in two directions, namely, in a horizontal and in a vertical plane.

The just described method of straightening or deforming the workpieces 37 insures that the bending or straightening operation cannot result in denting or other damage to the walls of a tubular workpiece. It was found that such denting normally takes place if an advancing workpiece is immediately subjected to the action of bending forces which are strong enough to plasticize the material, i.e., to stress the material beyond the elastic limit. However, and due to the fact that the improved machine generates bending or deforming stresses in a plurality of stages, the walls of relatively thin-walled tubular Workpieces will not buckle and will not develop dents or similar depressions.

It was also found that the force P2 may be relatively small, at least when compared with the forces P1. For example, and if a workpiece 37 having a given profile and a given wall thickness can be deformed close to the elastic limit of its material by the application of initial forces in the range of 5,000 mp., the additional force P2 need not exceed 1,500 mp., i.e., it can be a small fraction of the initial force.

The optimum distance e between the rolls b, c, d can be readily determined by simple experimentation. Such distance e will depend on the wall thickness of workpieces 37, on the width and height of the workpieces, and on the nature of the material of the workpieces. The same holds true for the magnitude of forces P1 and P2. The rolls b which correspond to the rolls 12 of FIG. I serve to hold in the predetermined path such portions of the workpiece 3-7 which have advanced beyond the feed rolls a (corresponding to rolls 3a-3c) and which are about to enter the gaps between the withdrawing rolls a (corresponding to the rolls 3d-3e of FIG. 1).

The various adjusting units of the machine shown in FIGS. 1 to 8 enable the operators to select the magnitude of bending forces P1 and P2 in a very simple and timesaving manner as well as with a requisite degree of accuracy, not only when the machine is idle but also in actual use. The latter feature is of particular advantage because the operators can visually observe or measure the deformation of workpieces and thereupon adjust the apparatus if the actual deformation exceeds or is less than an optimum deformation of the stock. Furthermore, the feature that the machine is adjustable in actual use saves much time when the workpieces 37 are treated one after the other in rapid sequence because the operation need not be interrupted at all but can proceed at full speed during adjustment of one or more carriers 11 and/ or 11a. Also, such construction enables my machine to process large numbers of workpieces without necessitating the provision of intermediate magazines which constitute essential components of many presently known straightening machines. Such magazines are normally provided upstream of the feed rolls, such as the rolls 3a-3c of my machine, to accommodate stock delivered by a continuously operating supply conveyor when a conventional straightening machine is brought to a standstill because its straightening rolls require adjustment.

The extent of movement of stressing means including the straightening or bending rolls 12a and their carriers 11a is controlled by eccentric rings 19 which are rotated by the drive shaft 15 and whose throw can be selected by the adjusting members 14. In heretofore known machines, the throw of such eccentrics can be adjusted only when the machine is idle. In my machine, the operators can select the throw of rings 19 by the simple expedient of starting the respective motors 24b and by thus changing the position of corresponding adjusting members 14 in the axial direction of the drive shaft 15. By rotating the worms 24, the motors 24b can alter the throw of eccentric rings 19 in an exceptionally simple and time-saving manner without interfering with the travel of workpieces 37 along the path defined by the rolls 312-31". The eccentricity of rings 19 determines the strokes of the carriers 11a and the magnitude of forces P1 and P2.

If the cross-sectional area of a workpiece 137 is very large, one can resort to a method which will now be described with reference to FIG. 10. This method is carried out by resorting to an apparatus which can apply to successive portions of workpieces 137 initial forces P1, P3 in two successive stages whereby the first application of the forces P3 precedes the application of the additional or final force P2. The force P3 is just strong enough to effect deformation of the material beyond the elastic limit whereas the forces P1, P2 together bring about a deformation close to the elastic limit. Of course, the teaching of FIG. can be carried still further by subjecting each successive portion of the workpiece 137 (or of a still heavier workpiece) to the action of three or more different initial forces and of thereupon subjecting the thus prestressed portions to the action of the final force P2 to bring about permanent deformation of the material.

The preceding description speaks of bending or straightening rolls, of a bending or straightening machine and of bending or straightening forces because the method and machine of my invention may be utilized to straighten a bent workpiece, to bend a straight workpiece, or to change the curvature of a bent workpiece. Therefore, the appended claims refer to a method or machine for changing the curvature of elongated workpieces whereby the original curvature may be zero or the curvature of the properly treated workpiece may be zero.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of my contribution to the art and, therefore such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is:

1. A method of changing the curvature of elongated workpieces particularly tubular workpieces of other than circular cross-sectional outline comprising the steps of advancing the workpieces lengthwise along a predetermined path, subjecting successive portions of advancing workpieces first to the action of initial bending forces to stress such portions to slightly below the elastic limit of their material; and thereupon subjecting the initially stressed portions to the action of additional bending forces to stress such portions beyond the elastic limit of their material and to thus effect permanent deformation of the respective workpieces.

2. A method as set forth in claim 1 further comprising the step of holding the workpieces against turning during travel along said predetermined path.

3. A method as set forth in claim 2 wherein the magnitude of said additional bending forces is a fraction of the magnitude of said initial bending forces.

4. A method as set forth in claim 2, wherein said initial bending forces are applied in a plurality of successive stages so that each successive portion of a workpiece advancing along said path is subjected to stresses generated by more than two different bending forces.

5. A method as set forth in claim 2, wherein each successive portion of a workpiece advancing along said path is subjected to the action of initial and additional bending forces acting upon the workpiece in a plurality of directions substantially transversely of the workpiece.

6. A method as set forth in claim 1, wherein said workpieces are metallic tubes of rectangular cross-sectional outline.

7. A method as set forth in claim 1, wherein said advancing step comprises guiding the workpieces between sets of cooperating rolls defining said predetermined path and wherein the application of said initial and additional bending forces is carried out by changing the position of selected sets of such rolls.

8. A method as set forth in claim 1, wherein the application of said additional bending forces takes place upon a portion of a workpiece disposed between two portions which are subjected to the action of said initial bending forces.

9. A method as set forth in claim 8, further comprising the step of changing the magnitude of said initial bending forces while the workpieces advance along said path.

10. A method as set forth in claim 8, further comprising the step of changing the magnitude of said additional bending forces while the workpieces advance along said path.

11. A machine for changing the curvature of elongated workpieces, particularly for straightening of elongated tubular workpieces of other than circular cross-sectional outline, comprising advancing means for moving the workpieces lengthwise along a predetermined path; first stressing means for subjecting successive portions of moving workpieces to the action of initial bending forces to stress such portions to slightly below the elastic limit of their material; and second stressing means for subjecting the initially stressed portions of moving workpiece to the action of additional bending fonces to stress such portions beyond the elastic limit of their material and to thus effect permanent deformation of the workpieces.

12. A machine as set forth in claim 11, wherein each of said stressing means comprises at least one set of work-engaging rolls, carrier means for such set of rolls, and drive means for moving said carrier means through distances of predetermined length substantially transversely of said path whereby the rolls apply bending forces to the workpieces in said path.

13. A machine as set forth in claim 12, wherein said drive means is arranged to move the rolls which respectively apply to moving workpieces initial and additional bending forces through different distances.

14. A machine as set forth in claim 13, wherein said sets of rolls form two spaced groups of rolls which apply initial bending forces and a further group of rolls which apply said additional bending forces, said further group of rolls being disposed between said spaced groups.

15. A machine as set forth in claim 12, further comprising adjusting means for regulating said distances while the workpieces are advanced along said path so that the magnitude of said initial and additional bending forces can be altered when the machine is in actual use.

16. A machine as set forth in claim 15, wherein said adjusting means comprises a two-armed lever for each of said carrier means, each of said levers being rockable about an axis which is substantially parallel with said path and each having a first arm connected with the respective carrier means and a second arm, an eccentric received in said second arm, an adjusting member rotatably received in and arranged to change the throw of said eccentric in response to axial movement with reference to the eccentric, and means for axially moving said adjusting member.

17. A machine as set forth in claim 16, wherein each of said adjusting members comprises a pair of parallel inclined external faces abutting against similarly inclined internal faces of the respective eccentric and the means for axially moving said adjusting members comprises a gear for each of said adjusting members, prime movers for rotating said gears in either one of two opposite directions, and racks provided on said adjusting members and meshing with the respective gears.

18. A machine as set forth in claim 17, further comprising antifriction bearing means interposed between each of said adjusting members and the respective rack.

19. A machine as set forth in claim 16, further comprising a common rotary drive shaft for said adjusting members and means securing said adjusting members for axial movement with reference to and for angular movement with said drive shaft.

20. A machine as set forth in claim 16, further comprising means for adjusting the position of pivot axes for said levers.

21. A machine as set forth in claim 16, further comprising holding rolls adjacent to said path upstream of said initial force applying rolls, carrier means for said holding rolls, and means for adjusting the position of said last named carrier means transversely of said path.

22. A machine as set forth in claim 11, wherein said advancing and said stressing means comprise rolls arranged to hold the workpieces against rotation during travel along said path.

23. A machine as set forth in claim 22, wherein said first stressing means comprises means for applying said initial bending forces in a plurality of stages.

24. A machine as set forth in claim 22, wherein said first stressing means comprises two spaced portions and said second stressing means is disposed between such portions of said first stressing mean.

10 MILTON S.

References Cited UNITED STATES PATENTS Davis 72-160 Haskin 72-164 Abramson 72-164 Smith 72-168 Mason 72-164 X Siegerist 72-164 X MEHR, Primary Examiner.

US. Cl. X.R.

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