STRAIGHTENING MACHINES AND METHODS

Abstract: A cross-roll straightener adapted to straighten round metal stock, wire, rods, bars and tubes by rotatingly advancing the stock through a central curved pass such that it is flexed beyond the yield point in a substantially uniform and gradual manner. A three pair roll (68, 70, 72, 74, 76, 78) arrangement provides uniform guidance and flexure while avoiding marking or collapsing of the stock.

Description: STRAIGHTENING MACHINES AMD METHODS BACKGROUND OF THE INVENTION Field of Invention The present invention is an improved cross-roll ~ straightener that straightens round metal stock, wire, rods, bars, and tubes, by rotatingly advancing the stock through a curved pass such that it is flexed beyond the yield Boint in a substantially uniform manner. Description of the Prior Art ~ - ~ Metal stock, such as wire, rods, bars and tubes, is formed by rolling, drawing and otherwise shaping the metal both while it is at elevated temperature and after it has cooled. The metal stock cools and cures in a heterogeneous manner such that a degree of warpage and curvature typically develops in the 15 stock. In the prior art, the stock has been straightened in machines known as cross-roll straighteners. Typically, such machines include one or more pairs of rolls that are disposed in skewed relation and spaced apart from each other. The space 20 between the member rolls of each pair is called a "pass''. Where more than one roll pair is used the roll pairs are adjacently arranged such that the "passes" of the roll pairs collectively define a "pass line" along which the stock travels through the cross-roll straightener. At least one of the rolls of each pair 25 are rotatingly driven such that the stock is rotatingly advanced therebetween along the pass line. In order to straighten the stock, conventional cross- roll straighteners generally apply a concentrated central load between supports to stress the stock beyond its yield point. Such 30 concentrated central loads produce a peak bending moment that is applied in the shape of a helix on the surface of the stock as it rotatingly advances through the machine. Unfortunately, such a peak bending moment nonuniformly flexes the stock such that it is not evenly straightened. Cross-roll straighteners of the prior art have many work roll arrangements that include various numbers of work rolls. For example, 2-roll straighteners of the prior art generally form a curved pass between a straight or convex roll and a roll having a concave contour. The straight or convex roll deforms the stock against the concave roll. However, such 2-roll straighteners require complex guides to maintain the stock in the roll pass, and have a limited capacity in straightening various sizes and materials. An improvement in 2-roll straighteners is described in U.S. Patent 3,047,046 in which a concave male roll is located on the convex side of the curved pass and is smaller in diameter than the ' female roll. Both rolls are contoured so that the stock is wedged between the rolls at the ends of the pass and thereby maintained in the curved pass without guides. The central portion of the curved pass in the straighteners of U.S. Patent 3,047,046 has a substantially parabolic curvature such that the bending moment on the stock is substantially that of a uniformly loaded beam. However, because both rolls were concave and were contoured to contact the stock throughout the curved pass, a relatively large roll angle change for the female roll was required whenever a different diameter stock was straightened. Specifically the roll angle adjustment for the female roll is much greater than the corresponding adjustment for the male roll. Consequently, excessive slippage between the two rolls and the stock occurred for certain stock sizes and materials where the opposed roll had substantially different contact angles with the stock. In cross roll straighteners having more than two work rolls, the rolls are generally arranged in a plurality of cross-roll pairs, each forming a straight pass. The cross-roll pairs are arranged in laterally offset fashion so as to flex the stock as it advances along the pass line. Such arrangements have generally been found to be faster and more efficient than 2-ro l straighteners. Typical examples are 5-roll and 6-roll straighteners. Conventional 5-roll straighteners have two pairs of cross-rolls and an intermediate single bending roll. Such 5-roll straighteners generally provide greater leverage for bending the stock than a single curved pass 2-roll straightener. However, 5-roll straighteners also require additional guides to maintain the stock in proper position as it passes through the machine. Conventional 6-ro l straighteners have three pairs of cross-rolls of equal diameter that form straight passes. The pass line is defined by a central pass that is laterally offset from the line between the end passes. As the stock moves along the pass, it is flexed between the central roll oair and κ_.ennr-)--»d by the two end roll pairs in a manner similar to a simple beam having a single load between two supports. 6-roll straighteners can generally be operated at higher speeds and without guides. 6-roll straighteners have generally been used for straightening tubular stock of small diameter and medium to low strength material. However, these straighteners have required a longer bending span than 5-roll straighteners and, therefore, cannot uniformly flex all stock sizes to a minimum ' radius of curvature as required to flex most of each section to or beyond the yield point of the material. Some restraining action on the stock occurs in the end- roll passes, as evidenced by the ■mailer slope of stock deflection at the ends of such straighteners. However, this restraining action i* insufficient to provide effective reverse bends for all portions of the stock, or to eliminate problems with the tables, particularly the outlet end table. Such moderate restraining action on the stock, OMPI VΛPO ,Λ. " together with the lack of guidance in the roll pairs, does not produce sufficient uniform flexure for good straightening and also limits the stock capacity of the machine and the throughput speed of the stock. Another problem has been that the passes in 5 conventional 6-roll straighteners do not provide positive guidance for the stock. Because of the longer bending span, non-uniform flexure, and poor guidance of the stock, prior multiple pair cross-roll straighteners were much less effective in straightening the stock 10 than 2-roll straighteners. In particular, the female roll of the central roll pair had a symmetrical roll contour that does not con¬ form to the surface of flexed stock. The'concentrated bending loads also resulted in concentrated roll pressure on tubular stock that is sufficient to oval thin wall tubular sections. 5 Prior attempts have been made to achieve more uniform distribution of the straightening loads in cross-roll straighten¬ ers, particularly for applications involving larger diameter tubing having a relatively thin wall. However, examples of such prior art as shown in U.S. Patents 2,376,401; 2,757,707; and * ~ ~ 3,008,510 have a straight central roll pass that interferes with the curved, flexed stock. In the prior art, rolls having various multi-sectional con¬ tours have been developed to improve the flexure of the stock and the machine capacity for straightening various stock sizes and materials. 25 For example, U.S. Patent 4,056,958 includes a roll having a two-section curvature defined by hyperboloids. However, since the contour is not symmetrical, these rolls cannot be used to flex and straighten a large variety of stock sizes and materials. U.S. Patent 2,655,194 describes a roll having a contour with five sections wherein the outer sections are used for straight passes of the stock, the central section is defined by a 30 cylinder of smaller diameter than the outer sections, and the intermediate sections are portions of circular cones. The central section is used to _ OMPI__ form a curved pass for straightening smaller stock sizes. The interme¬ diate sections are selected so that the roll can be manufactured in a single set up with a specially contoured grinding wheel. The problem with such multi-sectional contoured female rolls has been that they do not pro- vide a curved pass for a broad range of stock sizes and, particularly, for larger stock sizes. Furthermore, they generally do not provide a curved pass for smaller stock of high strength material. In the prior art, straightening stock in a curved pass has required different roll angle settings for the female roll and the male roll. The large difference in roll angle settings required to straighten small diameter or high strength stock as well as larger stock sizes in the same pair of rolls has greatly limited the capacity of conventional curved pass straighteners. Other difficulties also existed with the prior art cross-roll straighteners. For example, in roll angling mechanisms such as shown in U.S. Patent 3,604,236, the yoke tended to slip during the straightening operation so that the roll support would move axially after the angling screws were tightened. Other mechanisms tended to vary due to play in the adjustment screw threads or gears. In conventional 6-roll straighteners, angling of the rolls was somewhat cumbersome in that it required adjust¬ ment of twelve handwheels to angle and lock the rolls in position. As another example, the roll brackets were expensive and difficult to maintain. In removing the rolls, bearing caps had to be removed and retainer screws loosened, thus exposing the bearings. n order to obtain accurate axial roll adjustment, bearing retainers had to be loosened and shims added or removed. As still another example, the main frames of conventional straighteners such as shown in U.S. Patents 3,540,251 and 3,604,236 absorb moments from lateral forces at the top or bottom of loosely fitted tie rods that are deflected by lateral forces and vibrations. The tie rods are weakest where the moment is greatest and the restraining moments in the upper plate and the base are excessive due to the short distance of restraint. Accordingly, to provide higher operating speeds and improved straightening through uniform flexure, there was a need in the prior art for a straightener having the advantages of a curved pass 2-roll straightener but with greater straightening leverage, such as found in 5 and 6-roll straighteners, and better guidance. In addition, there was a need for a female roll suitable for use in a curved pass, but having a concave contour that would avoid excessive slippage between the rolls and stock for a broad range of stock sizes and materials. SUMMARY OF THE INVENTION In accordance with the present invention, stock is lexed in a curved pass to a minimum radius of curvature at which the stock is stressed beyond the yield point while the straightening loads are distributed more uniformly throughout the length of the curved pass. As the stock advances in rotary motion, it is posi¬ tively guided in the curved pass and flexed to a minimum radius of * curvature for at least one pitch of its surface, helical motion such that the stock is stressed in a substantially uniform manner. Preferably, the female roll forming one side of the curved pass includes a central portion having an abrupt concave curvature and end portions that have a less abrupt curvature. The end por¬ tions of the roll are for straightening larger sizes of stock, and the central portion for straightening, by more abrupt flexure, smaller stock sizes or stronger materials. Thus considerably less variation is required in the female roll angles. Preferably, the straightener includes three sets of cross-rolls with the central set laterally offset with respect to the other sets to increase or decrease the flexure of the stock as required while it is advanced in rotary motion by said rolls. Preferably, the rolls of the central roll pair are of unequal roll diameters to provide positive guidance of the stock. The rolls maintain the stock in the curved pass during the straightening operation and provide better guidance for both the leading and trailing ends of the stock as it enters and leaves the central pass. The central roll pair forms a curved pass that guides and complements the stock's flexure rather than merely applying a central load as in the prior art. Preferably, the flexure of the stock can be further improved by providing reverse flexures of the stock outside the curved pass as, for example, by outward adjustment or offset of the smaller, lower outer work rolls. Preferably, straight pass cradle rolls are provided at each end of the cross-roll straightener to continuously bend the stock in reverse flexures during its forward, rotary motion, thus providing greater leverage for straightening a larger range of stock sizes and materials. The inlet and outlet cradle rollers also position the stock in the pass line and substantially reduce whipping of stock that is crooked or has end hooks, thereby per¬ mitting substantially higher operating speeds. At the outlet end, the leading end of the stock is deflected in a generally horizontal direction, to protect the trough and rolls of the outlet table. The curved pass cradle roller assembly is comprised of generally inversely symmetrical twin rolls that provide a bending yoke between 3-roll clusters or between two cross-roll passes. When used as a bending yoke, the cradle rolls have an unsymmetrial contour and are arranged in reverse symmetry about their common central axis such that only half of each roll contour contacts the stock under flexure. In another application, the twin-roll bending yoke can be combined with an opposed female roll to act Λ» a single bending cluster. In this embodi¬ ment, the bending yoke is adjusted with respect to the female roll for stock size and flexure. In an alternative embodiment, the 3-roll cluster is used as a bending cluster in combination with two adja¬ cent 3-roll clusters. The 3-roll bending cluster is adjusted OMPI X-ϊy. ~ WIPO ~ Λ>J vertically in relation to the adjacent 3-roll clusters to augment the flexure obtained by the central bending rolls toward the bottom rolls of the adjacent 3-roll clusters. The twin-roll bending yoke comprised of rolls modified according to the subject invention can replace the single conventional bending roll of a conventional 5-roll straightener to great advantage, providing better guidance and better control of the stock's flexure while maintaining its smaller bending span and shorter roll center distances. The preferred roll brackets allow for angular adjust- roents of adjacent rolls spaced at relatively small center-distances by arranging supports for the rolls in reverse symmetry about each roll's axis in such a way that stronger sections of each bracket will absorb torque produced by its roll. Therefore, increased bearing capacity is provided for rolls spaced at given center-distance by providing more space for the bearings on near sides of adjacent bracket ends, than provided in prior roll brackets. The roll bracket construction also admits to rapid axial adjustment of the rolls by accessable adiustinα screws to correct for inaccurate bracket machining and to compensate for rolls that are machined or worn off center. Also, preferably, the upper roll adjusting screws are compactly preloaded in their respective screw box by adjustment of a spring loaded screw. Thus, the roll support will not move after the angling screws are tightened and will not sag when the angling mechanism is released or operated. The lower, central adjusting screw and the lower end rolls and their yokes are provided with hydraulically supported seats. Especially preferably on large machines, the roll angling mechanisms used for angling and locking the rolls include hydraulic cylinders and a single handwheel nut which limits the angular movement in only one direction. Preferably, the drive includes a gear box for one or more roll spindles in response to a variable speed motor. Also preferably, the drive mechanism includes a single variable speed motor for each drive, the motor being mounted on the same side of the gear box as the universal joint spindles. Alternatively, two variable speed motors can be provided for each gear box, one driving the central roll and the other driving the end rolls. Also preferably, the drive for the larger diameter roll in 2-roll straighteners includes a freewheeling clutch such that, after the stock has entered the pass, the surface speed of the larger roll will be substantially equal to the higher surface speed of the smaller roll. Other details, objects and advantages of the invention will become apparent as the following description of certain presently preferred embodiments and certain presently preferred methods of practicing the same proceeds. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings show certain presently preferred embodiments of the subject invention and illustrate presently preferred methods of practicing the same in which: Figure 1 is a plan view of a presently preferred embodi¬ ment of the subject invention in partial section, showing some of the bottom work rolls with their respective drive and showing, in phantom, some of the top work rolls and their drive. Figure 2 is an elevational view of the apparatus of Figure 1, portions of which have been Removed.to better disclose the details of the invention. Figures 3 and 4 show the bottom roll drive in Figure 1 with the drive spindles removed in Figure 3 and shown in phantom in Figure 4. Figures 5 and 6 show the roll angling mechanisms and support for the lower end rolls. In addition, Figure 6 shows an end view of the main frame. Figure 7 is a sectional view taken along line 7-7 of Figure 1 showing an adjustment mechanism for moving the roll bracket and roll axially. Figure 8 is a schematic of the roll arrangement of the subject invention wherein a pair of guide rolls at the entry end guide and support the stock into the first pass of the main working rolls, and a single guide roll and horizontal guide support the stock at the outlet end. Figure 9 illustrates how the stock if flexed in Figure 8. Figure 10 is a moment diagram for the stock of Figures 8 and 9. Figure 11 illustrates the wedge angles at the entry and exit ends of the central roll pair, where the female roll is of generally smaller diameter than the opposed, male roll. Figures 12 and 13 show an alternative embodiment of the roll arrangement of the subject invention wherein the bottom end rolls are of generally smaller diameter than the opposed top end rolls and are offset outwardly with respect thereto. Figure 14 is a moment diagram of the stock as flexed in Figure 12 beyond the yield point of the material to a constant radius of curvature over distance "x". Figure 15 is an illustration showing how the roll wedge- angles adjacent the central and end roll passes guide the stock during its forward travel in rotary motion. Figures 16 and 17 show an alternative guide and guide roll for use at the outlet or inlet end of the main working rolls. Figures 18 and 19 show the guide roll pair of Figure 8 supporting one stock size. Figures 20 and 21 are sectional views showing the guide rolls of Figure 1. Figure 22 shows a female roll, used in a curved pass for flexing and straightening round stock. Figures 23 and 24 show a pair of working rolls of a 2-roll straightener in which the male roll is of generally smaller diameter than the opposed female roll, with inlet and outlet guide rolls of the present invention. Figures 25 and 26 show a roll that is supported against deflection by adjustable back-up rolls. Figures 27, 28 and 29 show a 3-roll cluster curved pass that includes one female roll and two opposed male rolls. Figure 30 shows an alternative female roll having five sections. PREFERRED EMBODIMENT OF THE INVENTION A preferred embodiment of the subject invention is shown in Figures 1-7. The cross-roll straightener therein disclosed has a main frame including a main base 50 with integral extensions 52, 54 and 56 that are machined at the top. The main frame also includes main top plate 58 with integral extensions 60, 62 and 64, that are machined at the bottom to match main base extensions 52, 54 and 56. Extensions 52, 54 and 56 are fastened to extensions _OMPI 60, 62 and 64. Preferably, one or more bolts are provided for fastening each extension 52-60, 54-62, and 56-64 with at least one bolt in two of said extensions being body bound in order to accurately position the top plate on the main base and absorb the lateral forces or shear between the top plate and the main base. Alternatively, dowels or tongue and groove members may be used in place of body bound bolts and the joints can also be hinged. The largest moments due to lateral forces and vibrations in the main frame occur at the solid connections of extensions 52-56 and 60-64 to the main base 50 and top plate 58 while the moment at the midpoint connections 52-60, 54-62 and 56-64 is substantially zero. Thus the moments produced by shear forces are absorbed by the solid and integrally connected extensions at their strongest section. The - bolts securing the upper and lower extensions are relatively short and comprised of high strength material. The short length of the bolts helps reduce the elongation caused by the separating forces of the roll loads during the straightening operation. The body bound bolts withstand the shear forces transferred from the main top plate to the main base without slippage. Preferably, the bolts are preloaded. As shown in hidden lines in Figures 2 and 5, a central removable tie rod 66, can also be included to reduce deflection in the main frame where especially severe separating forces and vibrations are anticipated, such as when straightening bars and heavy wall tubing of high strength materials. The presently dis- closed main frame is more economical to assemble, and more precise and substantially stronger than conventional straightener frames, yet it facilitates rapid roll changes. The cross-roll straightener of the preferred embodiment further includes upper work rolls 68, 70 and 72 and lower work rolls 74, 76 and 78 which are arranged in pairs 68-74, 70-76, and 72-78. The opposed rolls of each roll pair are skewed or oppositely inclined with respect to the pass line. The angular inclination of the axes of rolls 68 and 74 are the same as rolls 72 and 78 respectively. During the straightening operation, roll pairs 68-74, 70-76 and 72-78 are separated by a distance equivalent to the diameter of the stock or slightly less, and have angular con¬ tact with opposite sides of the stock so as to advance it in rotary motion while flexing it in a curved roll-pass formed by the offset central roll pair 70-76. Work rolls 68-78 are mounted in brackets 80, which are fastened to plates 82 by bolts 84. Plates 82 are integrally connected to yokes 86, 136, or 146. Brackets 80 are constructed so as to support the roll neck bearinos in inverse βvtrtmβtrv about each roll's longitudinal axis. The straightening loads have a tendency to turn each bracket 80 in an anti-clockwise direction about its respective centerline 88. Therefore, roll bracket 80 supports the roll neck bearings laterally at portion 90 as well as vertically in the area where the main straightening load is transferred to plate 82 of yoke 86. The supporting portion 90 of bracket 80 is thus arranged to allow room for larger bearings and roll necks at adjacent ends 92 of the roll brackets as compared to conventional roll brackets on equivalent centers. As more specifically shown in Figure 7, a mechanism is also provided for axially adjusting the roll to compensate for uneven roll wear or inaccurate machining. Through this mechanism, the roll is adjusted to the center line of its support as well as the center line of its opposed roll and the pass line. A key 94 guides bracket 80 such that the roll moves along its axis when adjusted. The rolls are adjusted by loosening screw 96 and turning hollow screw 98, until the proper longitudinal position of bracket 80 has been reached, after which screw 96 is again tightened. In addition, screw 98 which is threaded in the lug of bracket 80, can be extended to provide room for a locknut (not shown) . In addition to the angular adjustment of the rolls and their brackets, the upper rolls 68, 70 and 72 and their brackets 80 are vertically adjustable to accomodate stock of various diameters. Furthermore, the central roll pair 70-76 is vertically adjustable to deflect the stock to stress the outer portions of the stock leyond the yield point of the material over a distance equiva¬ lent to one pitch of the stock's surface motion as hereinafter further explained and illustrated in Figures 8-10. Specifically, handwheel 100 operates through a worm and gear reducer 102 to control adjusting screw 104. Adjusting screw 104 engages screw box 106 which is secured to stem 108, thereby moving yoke 86 with its attached plate 82 and roll bracket 80 and roll 68 up or down, as desired. Adjusting screw 104 is clamped to main top plate 58 at shoulder 110 but is free to turn. Play between threads of screw 104 in screw box 106 is pre- vented by smaller diameter screw such as ball screw 112 which is threaded in a small diameter screw box 114 that is fixed in screw 104 and has the same thread pitch. Nut 120 is locked onto the smaller threaded portion at the end of screw 112 which is prevented from turning with respect to retainer 118. Ball screw 112 is preloaded by spring washers 116 of sufficient strength to urge retainer 118, yoke 86 and screw box 106 toward the lower side of the threads in screw 104. This arrangement prevents roll 68 from sagging when unloaded. Lower rolls 74, 76 and 78 are provided with hydraulic over-. load devices to prevent damage to the rolls, bearings, or other parts by yielding when the applied load exceeds an adjustable maximum limit such as caused by out-of-round or oversize stock. The overload devices are hydraulically interconnected and provided with a master control valve for fast simultaneous release of all the lower rolls. The lower adjusting screw 122 for the bending roll 76 and its bracket 80 are supported by a hollow piston 124 that is maintained in normal position by fixed retainer 126 under hydraulic pressure at cavity 12S. Hollow piston 124 and an extension or hollow rod are sealed at seals 130 and 132. Hollow piston 124 supports adjusting screw 122 at surface 134 which will yield together with piston 124 when applied roll pressure at roll 76 ex¬ ceeds a predetermined maximum limit. An adjustable pressure regulator and gage (not shown) are set to establish a maximum pressure limit at cavity 128 to enable the operator to control the load at which the respec¬ tive roll yields. Other details of the lower, central screwdown are similar to those for the upper screwdown previously described. The roll yokes for the lower end rolls 74 and 78 are sup- ported by relatively simple, inexpensive hydraulic cylinders. As shown in Figures 2, 5 and 6, rolls 74 and 78 and their roll brackets 80 and yokes 136 are supported by rods 138 of cylinder 140 mounted on main base 50. The rod ends are threaded in holders 142 that are provided with thrust bearings 144 on which yokes 136 are free to turn.* In Figure 6 the rods 138 are shown at the upper ends of their stroke in cylinder 140, from which they will yield when the roll loads on rolls 74 or 78 exceed the pressure for which the cylinders 140 have been set. The lower end-roll yokes may be set to yield at less load than the central bending roll, since they yield only when oversize stock is fed into the straightener and receive much less load from the straightening operation. Alternatively, a separate automatically controlled, rapid hy¬ draulic release of the roll pressure similar to that described for the central roll 76 can also be used for the upper roll 68 or lower roll 74 of the entering roll pair 68-74. This will allow the stock to be entered sideways between the rolls of roll pair 68-74 when the upper roll is retracted, thus facilitating quick startup of the straightening operation. In such a case the extensions 52 and 60 must be relocated. If an upper roll screwdown is furnished with the rapid release mechanism described for the central, lower adjusting screw, the screw preload mechanism, including screw 112, can be maintained. The mechanisms for angling the yokes that support the end rolls and the middle rolls are substantially similar. Central yoke 146 shown in"Figures 2 and 5 has two keyways 148 and 150 with which rounded key portions of spindles 152 and 154 slidingly engage. To decrease the roll angle of roll 76, cylinder 156 is activated to turn yoke 146 in a clockwise direction. When roll 76 is in the selected angular position, cylinder 156 is stopped and the piston is locked by tightening nut and handwheel 158 and pressure in cylinder 156 is reversed. To turn adjust¬ ing screw 122, pressure in cylinder 156 is temporarily released. In smaller machines, cylinder 156 can be substituted by another nut and handwheel similar to 158. Similarly, the end roll yokes 136 each have two keyways with which rounded key portions 160 and 162 of spindles 164 and 166 slidingly engage, cylinders 168 are activated to turn yokes 136 in the direction desired. When rolls 74 and 78 are in the selected an- gular position, cylinder 168 is stopped and the piston is locked by tightening nut and handwheels 170 and 172 and the pressure in cylinder 168 is opened to the piston side. Spindles such as 152, 154, 164 and 166 are prevented from turning by keys and keyways (not shown) . The threaded portions of the spindles having threaded handwheels, such as 158, 170 and 172, may be extended through the handwheels and provided with loeknuts, beyond the handwheels (not shown) in order to secure their adjusted posi¬ tions when the pressure in angling cylinders 156 and 168 is temporarily released for screwdown adjustments, for overload yield of the lower rolls, or for rapid release of the lower rolls. In such cases the relief of the pressure in the angling cylinders 156 and 168 should be automatic. For example, it could be activated by the movement of a lower roll and its support, as well as other methods and sensing devices known in the art. The angling mechanisms for the upper roll supports are similar to those shown for the lower roll supports. The previously described preloading mechanism for the upper screwdowns advantageously prevents sag in the roll supports during the angling adjustment as well as when the screwdowns are operated. The central adjusting screw 122 and the angular adjustment of the central lower roll 76 is operable regardless of the hydraulic pressure under supporting piston 124. The angular adjustment of the lower end-rolls 74 and 78 and their yokes 136 is only slightly affected by the weight on their supporting cylinder rods 138 and the friction in the thrust bearing 144 supporting the roll yokes 136 on the rod ends. In the preferred embodiment, the 6-roll straightener of the in¬ vention has two central rolls of generally unequal diameter while the end roll pairs have substantially the same diameters. Female roll 70 of the central roll pair is of generally smaller diameter than bending roll 76. Concave rolls 68 and 72 are on the same side of the stock as female roll 70, but of generally larger diameter than female roll 70. Rolls 68 and 72 are opposed by concave rolls 74 and 78 that are generally the same size and shape as rolls 68 and 72. Guide rolls 206-208 and 210 produce reverse flexures in the stock so that, considering the flexed portion _ι of the stock by itself, the major reacting shear forces Q occur outside of the central curved pass and act at the points of eontraflexure "P.C.", in the sense and direction shown dotted in Figure 9. Roll pairs 70-76, 68-74 and 72-78 are driven by drive units 174 and 176 that are connected to spindles 178 that drive rolls 74, 76 and 78 and spindles 180 that drive rolls 68, 70 and 72. Spindles 178 and 180 are of uneven lengths. Spindles 180 and drive 176 are connected to upper rolls 68, 70 and 72 through universal joints 184 and spindles 178 and drive 174 are connected to lower rolls 74, 76 and 78 through universal joints 182. vhd drive unit further includes a first common gearbox for spindles 178 and a second common gearbox for spindles 180. Preferably, each drive fur¬ ther includes three motors for individually driving spindles 178 and 180 with two of the motors located above the spindles and one below. Preferably foot mounted motors are used with two motors mounted to upper plate 186 (shown in phantom) and the lower mounted to lower plate 188, the motor shafts are connected to the pinion shafts by means of fle¬ xible couplings (not shown) . The motors are all shown flange mounted in Figure 4. In high speed applications, it may also be preferable that the ipindlββ are of equivalent lengths between the respective universal joints 182 and 184. In such cases, the splined shafts that rest in the hollow splined output shafts of the drive can be extended and mounted in a floating bearing mounted on plate 186 for support. Drive 174 is shown more particularly in Figures 3 and 4 wherein two upper motors 190 and 192 and one lower motor 194 drive pinions 196 and intermediate gears 198. Gears 198 in turn drive the output gears 200 mounted on hollow splined shafts, which drive spindles 178 by means of universal joints 182. Preferably gears 196, 198 and 200 are all straight spur or helical gears mounted on parallel shafts, to provide an efficient and economical arrangement. According to the disclosed arrangement, the distances BB-BB in Figure 3 can be increased in order to accommodate lar¬ ger frame motors without increasing the distance between spindles 178. Mounting motors 190, 192 and 194 on the same side as the drive spindles advantageously provide a more compact arrangement. Preferably motors 190, 192 and 194 are mounted on drive 174 or its bracket extension 186 or 188 and then, in field assembly, the drive with its motors ia mounted on bed plate 202 and main base 50. Top roll, drive 176 is substantially the same as bottom roll drive 174 except that the gear reduction for driving the smaller top roll 70 is lower in order to develop substantially the same circumferential speed for roll 70 as for the other working rolls. The operation of the present invention is generally illustrated in Figures 8, 9 and 10. As shown in Figure 8, roll pairs 70-76, 68-74 and 72-78 are inclined with respect to a longitudinal axis by roll angles A, B and C. The stock S is shown as moving in the direction of arrow 204 as it is rotated such that any point on the surface of stock S will move in the pattern of a lef hand helix. Roll pairs 68-74 and 72-78 have straight pass contours while roll pair 70-76 forms a curved pass for the stock. Roll 76 is the bending roll and is located on the convex side of the central curved pass. Roll 70 forms the concave side of the central curved pass. Roll angles A and B of the central rolls 70 and 76 are adjusted for flexure and site and roll angle C of the end rolls 68, 72, 74 and 78 are varied or adjusted to suit the various sizes of stock. The end roll pairs 68-74 -20- Fierore 11 further shows how the flexure of the stock S forces it into the angles W 2 and at both ends of the central curved pass. Figure 11 is taken along line 11-11 at the entry end of the central roll pair, but would be the same if taken in the opposite direction at the outlet end of the central roll pair. This is completely contrary to the roll diameter proportions as known in the prior art where the bending roll is smaller than the female roll and where the main bending forces are contained within the curved pass. An alternative embodiment of the cross-roll straightener of the subject invention is illustrated in Figures 12-15 wherein stock "S" is shown in exaggerated flexure. The embodiment illustrated in Figure 12 has a central curved pass that is formed by the male bending roll 76 and female roll 70 of generally smaller diameter opposed thereto. For the alternative roll arrangement of Figures 12-15, rolls 74 and 78 are of generally smaller diameter than rolls 68 and 72 and are offset from rolls 68 and 72 by an adjustable distance e along the longitudinal axis of the machine and outwardly from the center thereof. This adjustment is not required for the embodiment of Figures 1-8. As shown in Figure 15, the adjustable offset "e" of rolls 74 and 78 restrains the stock in the end passes by forming wedge angles ~~ and 4 adjacent the inside ends of roll pairs 68-74 and 72-78. Wedge angles W, and complement the wedge angles W 2 and W 3 adjacent to the ends of the central pass. The magnitude of offset "e" is thus selected to substantially reduce lateral movement of the stock adjacent the inside ends of roll pairs 68-74 and 72-78; to improve reverse flexure of the stock; and the entry and delivery of the stock. In some cases, particularly where the female roll is small in diameter with respect to the male roll, the diameter of the female roll at the contour end can be very large in propor¬ tion to the diameter of the female roll at the transverse axis. OMPI -19- and 72-78 and central roll 70 are adjusted to lower roll-angles B and C for smaller sizes of stock S. Because roll 76 is on the convex side of the curved pass, generally smaller changes in roll angle A are required to accommodate variations in stock sizes than are required for roll 70. In order to maintain a substantially * constant speed ratio between rolls 70 and 76 for the outside and inside curvatures of the stock as it moves forward in rotary motion, it is important that variations in the roll angle B of roll 70 to accommodate changes in stock sizes be small in relation to roll angle A. Roll angle B is thereby kept substantially equal to roll angles A and C for the full range of sizes and materials for which the straightener is intended to be used. As illustrated in Figures 8, 9, 10 and 11, the central roll .pair 70-76 of the present invention is designed to flex the stock to a desired minimum radius_of curvature over a distance x equivalent to at least one pitch of the helical travel of the stock surface. The central roll pair thereby flexes all portions of the stock to a substantially uniform radius of curvature in all directions for improved straightening by flexure. This flexure results in approximate loads B, A, C and D as illustrated in Figure 9. In addition, as illustrated in Figure 10, substantially constant moment MY is provided over distance x. Since the average diameter of roll 70 is smaller than the average diameter of roll 76, particularly the diameters at the roll ends the preferred embodiment provides substantial support in the wedge angles as well as elose guidance of the stock. As shown in Figure 11, an appropriate ratio between the opposed rolls 70 and 76 is selected with respect to the stock's flexure to form stock contact angles W 2 ana W, at the respective ends of the central pass. The rolls thus support the stock within angles 2 and W 3 at the ends of the intermediate roll pair to provide support throughout the curved pass. As illustrated by Shear Q, -22- Preferably, the guide rolls are provided with flexible, shock absorbing supports that absorb the impact of the whipping action of the stock as it is rotatingly advanced through the straightener. If the guide rolls 206-208 and 210 are not touching the stock, the latter will assume a single flexure between roll pairs 68-74 and 72-78, similar to a simple beam on two supports A-A. See Figures 8 and 9. Such a single flexure and moment diagram will produce the relatively smallest straightening loads A-A and C-C caused by the approximate roll loads D-D, and is sufficient to straighten the larger stock sizes. For smaller stock sizes, how¬ ever, more abrupt flexures are required and by adjusting the out¬ board guide rolls 206-208 and 210, vertically, so as to produce sufficient forces B that will subject the stock to reverse flexures; the single flexure will be reduced in length from the distance between the roll pairs 66-74 and 72-78 to the distance L, between the points of contraflexure P.C. as shown i*h Figures 9 and 10. In the latter case the straightening loads will be relatively larger, but for the small stock sizes the loads can still be held lower than those required to straighten the largest stock size in a single lexure. The curved pass of the central roll pair 70-76, together with the reverse flexures of the disclosed straightener provide improved means to straighten various stock sizes and materials over conventional multi-roll straighteners. ' For high speed, precision straightening, twin guide rolls 206 and 208 are preferably used both at the inlet and outlet ends of the straightener, as shown in Figures 1 and 2. The horizontal angling and vertical adjustment of the twin rolls is similar to that previously described for the lower, central adjusting screw as shown in Figures 2 and 5. As further shown in Figures 19 and 20, the angle ε determines the direction of the pass line of the twin rolls, while angles and γ., determine the stock diameter. -21- In such cases, it may be preferable when straightening large size stock that the stock does not touch the central portion of the contour of female roll 70 to avoid excessive "slippage" between the stock and the female roll through the central contour. Thus, the compound contour of the female roll will allow for a gap "t" as shown in Figure 12 to be main¬ tained between the stock and the female roll 70. On the other hand, by increasing all roll angles slightly and applying roll pressure on the stock at the transverse axis of the central roll pair, the female roll ends will not touch the stock, while the central "cold work" will augment the flex- ural stresses for more efficient straightening, particularly when the stock is tubing. Twin Guide Rolls In addition to the work roll pairs 70-76, 68-74 and 72-78, the subject invention can further include guide rolls at the inlet and outlet ends of the straightener. Figures 1 and 2 show a preferred embodiment - having twin guide rolls 206 and 208 at the entering and exit ends of the 6-roll straightener. Figure 8 illustrates the use of twin guide rolls 206 and 208 at the entering end in combination with a single guide roll 210 with a guide 212 at the exit end of the straightener. Single guide roll 210 and guide 212 are shown in detail in Figures 16 and 17. Twin guide rolls 206 and 208 and guide roll 210 in combination with guide 212 form straight passes. Guide rolls 206 and 208 are further provided with a vertical adjustment similar to that of roll 76 as may single guide roll 210. Used in combination with two horizontal guides 212 and 214, single guide roll 210 can be substituted for guide rolls 206 and 208 at the en¬ tering end of the 6-roll straightener. Such a combination is less expen¬ sive than twin guide rolls 206 and 208. As shown in Figures 1, 2 and 8, guide rolls 206, 208 and 210 are not driven but act as cradles to position the stock at the entering and exit ends of the straightener and to maintain the ends of the stock in the pass line. These guide rolls provide supports that flex the stock into reverse flexures, to better straighten reverse bends and end hooks in the stock. The guide rolls also reduce whipping of the stock caused by the crookedness thereof to allow higher operating speeds for the straightener. Twin rolls 206-208 of Figure 8 position and guide the stock by contacting the average stock size of diameter d on the lower side of the stock at the same angle C Q as the straight pass roll-angle C. As shown in Figures 20 and 21, rolls 206-208 are located side by side, but oppositely tilted by equal angles γl and γ2 with respect to a horizontal plane through a common roll transverse axis 216 parallel to the stock axis. Rollers 206 and 208 are positioned on the common trans¬ verse axis with a constant distance 22 between their longitudinal axes and at a variable angle ε to the stock axis. The relative angular loca¬ tion of rollers 206 and 208 varies for various stock sizes d. For example, angle ε must be increased and angles γl and γ2 decreased for full contact with larger stock sizes. Thus the angles γl and γ2 are aαjusted according to the stock size and ε is then adjusted according to the direction of the stock axis until it coincides with the axis of the straight roll passes between roll pairs 68-74 and 72-78. Both of these conditions are met by the adjustment mechanism shown in Figures 20 and 21. As shown in Figures 20 and 21, twin guide rolls 206 and 208 are mounted in tiltable roller brackets 220 and 222 in one stem and support 224, which is adjustable in a vertical direction and can be turned about its vertical axis for different stock sizes. Stem and support 224 has cylindrical segments 226 and 228, in which roller brackets 220 and 222 are supported. Angles γl and γ2 are the angles of the roller's longitudinal axes with respect to a plane 234 through centerline 216. Angular cross sections of segments 236 and 238 have gear teeth 240 and 242 that are separately engaged by pinions 244 and 246. Similar size pinions 248 and 250 engage each other at the front, as shown. By turning square 252, pinions 248 and 250 will turn in opposite directions as will pinions 244 and 246 and angle segments 236 and 238. Segments 236 and 238 are fastened to brackets 220 and 222 which carry rolls 206 and 208. Vertical angles γl and γ2 decrease or increase depending on whether square 252 is turned clockwise or counterclockwise. Centerline 216 is in a plane 234 that is parallel to the stock axis and is normally horizontal, except when the support for the stock is to be tilted. hen angles γl and γ2 are to remain constant but plane 234 is to be horizontally tilted, a dowel key is inserted at keyway 254 and pinion 250 is removed after removing retaining ring 256. Cap screws 258 must be loosened before square 252 is turned and, after adjustments have been completed, again tightened against the flat segment washer 260. Cap screws 258, in each segment move in the respective slots 262 and 264 in brackets 220 and 222. Brackets 220 and 222 are then fastened and locked in the respective segments 226 and 228 of stem and support 224. In an alternative embodiment. Figures 23 and 24 illustrate how twin guide rolls 206 and 208 and guide roll 210 can be used to position the stock at the ends of the curved pass of a single cro.s- roll pair 266-268. The stock is wedged by the straightening loads into angles W Q formed at the entering and exit ends of roll pair 266-268 to maintain it in the curved pass. Guide rolls 206, 208 and 210 tend to force the stock into the wedge angle K Q at both the inlet and outlet ends. In accordance with the present invention, the cross-roll pair 266-268 of Figures 23 and 24 is preferably combined with inlet and outlet supporting guide rolls. Since the larger diameter roll 268 is the female roll and the smaller diameter roll 266 is the male roll, the stock will be wedged into angles at the ends of the rolls and thus maintained in the curved pass, provided the stock is engaged throughout the pass. Therefore, as the stock enters the pass but before it becomes fully engaged, the rotational speed of the smaller roll 266 is made such that its peripheral speed is slightly higher than that of the larger roll 268. Since the smaller diameter male roll has a higher peripheral speed than the larger diameter female roll, the stock tends to be forced into the wedge angle and is thereby maintained in the curved pass at the entry end. Conversely, the peripheral speed of the smaller roll is made slightly lower than the peripheral speed of the larger roll as the trailing end of the stock leaves the outlet end of the curved pass so that the stock is forced into the wedge angle at the outlet end. Figures 23 and 24 illustrate how the differential peripheral speed dV forces the stock into a wedge angle at the entry end of the roll pair. A full length guide 269 laterally supporting the stock as indicated by "G" will thus maintain the stock in the pass, particularly when the trailing end of the stock has passed the central portion of the curved roll pass. Speed control is provided such that the appropriate speed differential is maintained, but that will permit the rolls to turn at an equal peripheral speed when both rolls engage the stock. There are several alternatives for accomplishing this variation in the relative speed of rolls 266 and 268. Xn a first alternative, the drives of rolls 266 and 268 are respectively provided with integral freewheeling clutches. Roll 268 i* driven at a peripheral speed that is slightly lower than that of roll 266. Upon engagement with the stock, roll 268 OMFI will then accelerate as the stock rotatingly advances through the curved pass. The straightener is further provided with a trip switch such as a limit switch or electric eye that senses the leading end of the stock es it leaves the curved pass so as to steadily increase the drive motor speed for roll 268 until the freewheeling clutch in the drive for roll 268 engages. Roll 268 is thereafter driven at a slightly higher peripheral speed than roll 266, thus tending to force the stock into the wedge angle M Q . The drive of roll 266 is also provided with a freewheeling clutch such that when roll 268 is driven at the slightly higher speed roll 266 is driven through engagement with the stock. The trailing end of the stock is sensed by the trip switch. The drive motor of roll 268 is then decelerated until roll 268 returns to its initial speed. The acceleration and deceleration of roll 268 can be accomplished mechanically such as by driving both rolls with one motor connected through a dif erential, or electrically by driving both rolls with separate motors having suitable speed control. In a second alternative for accomplishing the variation in speed of rolls 266 and 268, a freewheeling clutch is provided only in the drive of roll ' 268 and a guide 269 is provided that supports the-stock as indicated by G in Figure 24. As in the first alternative, as the stock enters the curved pass it engages the smaller roll 266. The smaller roll 266 has a higher peripheral speed than roll 268 such that, as illustrated in Figure 24, the speed differential dV, forces the stock into the wedge angle W at the entering end (not shown), until the stock engages both rolls 266 and 268. The freewheeling clutch then allows the larger roll to rotate faster in accordance with the peripheral speed of the smaller roll. As the trailing end of the stock leaves the curved pass it is held in the curved pass by guide 269. This alternative has the additional advantage that, if the stock is not maintained in the wedge angle because, for example, the stock is too small for the angle contact, guide 269 will still retain the stock. ' This alternative is equally applicable to cross- roll straighteners where the opposed rolls are of substantially the same diameter, although different roll sixes are preferred in order to reduce guide wear. Advantageously, in accordance with this alternative embodiment, only one guide is needed. Because of the difference in shape and size of the central rolls 70-76 of the 6-roll straightener arrangements of Figure 8 and 12, it is difficult to establish their ideal speed relationship. However, by providing a variable speed motor driving a differential with two output shafts, one for each of the rolls 70-76, the speed of the two mentioned output shafts, when geared in proportion to the roll diameters, will assume their ideal relative speed relationship as soon as the stock is entered in the pass between the central rolls. The variable speed motor can then be adjusted to equalize the speeds of the central roll pair in relation to the end roll pairs. To provide such e differential to equalize the relative speeds of two opposed rolls is not new in the art. However, it is new to use one variable speed motor to equalize the speed of one roll pair in relation to other roll pairs. Curved Pass Female Roll Contour Preferably, the central roll pair 70-76 forming a curved pass includes a female roll 70 having a three-section contour that includes an abruptly curved central section that tangents two outer sections. The outer sections are portions of a contour having a less abrupt curvature and a larger throat diameter than the central section. In contrast to the multi-sectional contoured rolls of the prior art, the central rolls of the subject invention provide a curved pass for large stock sizes as well as small stock sizes. λ female roll having a three-section contour in accordance with the subject invention is shown more specifically in Figure 22. Contours from points 270 to points 272 extend a length Z, along the axis and are defined by revolving a cylinder around the longitudinal axis of the roll, where the cylinder is spaced a predetermined distance and at a predetermined angle with respect to the longitu¬ dinal axis. The surface of the roll's central section 270-0-270 extends a. ength Z 0 but has a sharper curvature. The minimum or "throat" diameter "TD" of the central section is smaller than the minimum diameter defined by estrapolating the curves defining the end contours, between points 270 and 272 to the transverse axis of the roll. The end sections and the central section have the same tangents at points 270. Mien straightening high strength stock, the central curved pass of the subject invention reduces dependence on small roll center-distance in a multi-roll straightener. The outer contour of roll 70, from points 270 to points 272 forms a concave side of the curved pass for larger sizes of stock and materials of lower strength. The central portion of the roll 70, from point 0 to points 270, forms the concave side of the pass for smaller sizes of high strength stock which require more abrupt flexure to stress most of the section to or beyond the yield point of the material. When the roll angle is set for the larger stock sizes and lower strength materials, a small gap of clearance over the central portion of roll 70 is left. The difference 2dy between the throat diameters of outer contours 270-272 and the central contour 270-0-270 of roll 70 shown in Figure 22 is relatively small. Where roll 70 is intended to straighten, size and reduce a narrow range of stock sizes at only relatively small changes in roll angles A and B, it may be preferable to omit the central contour 270-0-270. ∑n this case the diameter of roll 70 can be made even smaller. However, where this is done, back-up rolls 274 and 276 as shown in Figures 25 and 26 may be required to provide the forces necessary to flex and size the stock. Such back-up rolls may also be required for male roll 266 of Figures 23 and 24. The three section contour of female roll 70 in the curved pass of the subject invention can be used in a 2-rol curved pass straightener, a 3-roll cluster curved pass straightener or as the female roll in a central roll pair of a curved pass multi-roll straightener. The outer sections of the three section contour serve as supports for flexing stock of larger diameters, while the central section provides for more abrupt flexure of smaller diameter stock and higher strength materials. The three-sectional contour for the female, roll is advantageous in that the variations required in the roll angles of the opposed working rolls for various stock sizes and materials are substantially lower than in the prior art. Thus, the range of bar and tube sizes and materials that the cross-roll straightener can accomόdate is significantly increased. Figures 27, 28 and 29 show three-section female roll 267, of a contour similar to roll 70, but of relatively larger diameter described herein as used in combination with a twin roll bending yoke 278 and 280 to form a curved pass three-roll cluster. The three- section contour of female roll 267 substantially increases the flexure capacity of the 3-roll pass comprised of rolls 267, 278 and 280. As shown in Figure 29, the twin male rolls 278 and 280 each have a male contour half 282 and 284 and a straight, cylindrical half 283 and 285. Twin rolls 278 and 280 are not symmetrical about their transverse axes 286; but are inversely symmetrical in relation to each other and to the stock pass. The stock is flexed into wedge angles W_ and W u by the sale rolls. Alternatively, the cylinder portions 283 and 285 -may have a concave contour, less abrupt than bending portions 282 and 284. The male contour portions 282 and 284 of the bending rolls produce a resultant load P that produces reactions V„ and H., at the near end of the curved pass and V_ and H_ at the opposite end of the curved pass. The bending load forces the stock "S" into wedge angles N and F at opposite ends of the curved pass between the ends of the female roll 267 and the male contour end of each male roll 278 and 280 as shown in Figures 27-29. Rolls 278 and 280 can be mounted in tiltable brackets similar to that for guide rolls 206 and 208 as shown in Figures 20 and 21 having a common support. Rolls 278 and 280 can thereby be vertically adjusted with respect to the stock and are angularly adjustable about a cαnmon support centerline. In addition, the vertical angle of rolls 278 and 280 with respect to a horizontal plane can also be adjusted to produce appropriate contact with the „ stock as it is flexed in the curved pass. As well as forming the bending yoke in a single 3-roll curved pass duster, a bending yoke comprised of rolls 278 and 280 can also be used between inlet and outlet cross-roll pairs or between conventional three-roll clusters. Figure 30 shows a ending roll having an even broader operating range than the 3-section working roll of Figure 22. The bending roll of Figure 30 has a 5-section roll contour especially suited for straightening a large variety of stock sizes and materials. The contour of the female roll shown in Figure 30 includes a concave central section 288 that is symmetrical about the roll centerline and the transverse axis and that has a throat diameter TO,. The roll contour further includes a first pair of symmetrically arranged conical frustrums 290 and 292 that tangent the central section at their small ends. The conical frustrums support smaller diameter stock and stock of high material strength as it is flexed into the central section by the male roll. Conical frustrums 290 and 292 make it possible to flex and straighten relatively much smaller stock OMPI IPO sizes than with conventional female rolls by substantially increasing the capacity of the female roll to support smaller, more abruptly flexed stock sizes. The roll contour further includes a second pair of symmetrical sections 294 and 296 that tangent the conical frustrums 290 and 292 at their large ends. Symmetrical sections 294 and 296 are portions of a concave contour defined by a cylinder disposed at a distance of 1/2 TO + δ from the center axis and inclined at a selected angle with respect to the roll axis. Outer sections 294 and 296 have a less abrupt contour than central section 288 to support and straighten larger stock sizes in a curved pass. The throat diameter of the concave roll contour is larger than that of the central section by 2 δ. The contour of the disclosed female roll is such that excessive slippage between the rolls and the stock is avoided over a broad range of stock sizes and material strengths. Specifically, the roll angle adjustment of the female roll is substantially the same as the roll angle adjustment for the male roll for different stock sizes and material strengths such that the contact angles of the opposed rolls with the stock is substantially the same. Also advantageously, the central section of the female roll can be used to round up and size the stock when used in combination with a male roll of suitable contour for compressing the stock. The preferred length at which the stock is compressed is a length that covers the entire surface of the stock as it is rotatingly advanced through the machine. Where sizing and rounding of the stock is not required, the length of central section 288 can be made substantially smaller such that high strength stock of extremely small diameter can be flexed and straightened. The female roll contours shown in Figures 22 and 30 are further preferable for 3-roll single clusters, such as shown in Figure 27, and especially for the basically 2-roll straightener of the curved pass Figure 23, where the female roll is of generally larger diameter than the opposed male rolls or roll, respectively; inasmuch as for such opposed rolls it is simpler to calculate the 5 approximate optimum proportion of the larger end diameter to the throat diameter of the opposed female and male rolls. Such propor¬ tions should be near the same, where the opposed rolls contact the stock. Similar to the 3-section female roll of Figure 22, the ° 5-section roll of Figure 30 can be used as the female roll in any curved pass cross-roll straightener including 2-rol straighteners having a concave female roll opposed by a concave, straight cylindrical, modified cylindrical, or convex roll or with a bending yoke of an opposed pair of asymmetrically mounted male rolls. 5 In an alternative application for flexing stock, separate controls may be provided for the individual operation of the double acting cylinder 128, Figure 2. The hollow piston 124 supports the lower adjusting screw 122 and may be used to flex the stock by hydraulic pressure, where operating the screw handwheel and drive cannot produce the force required. Thus, if in setting up the machine, a straight piece of round stock of a certain diameter con¬ tacts all rolls 68 to 78, inclusive, and a tube of the same diameter is inserted into the machine in order to straighten same, it must be flexed over roll 76 and contact roll 70. Roll 70 is, therefore, first backed off from the tube a desired amount for flexing the stock. Screw 122 is unscrewed by the same amount in screwbox and yoke 146 while low hydraulic pressure is entered on the upper side of hollow piston 124, thereby keeping roll 76 in the original position. The pressure is now reversed in the hydraulic cylinder forcing the hollow piston, its adjusting screw and attached roll 76, to flex the stock against roll 70. If the amount of flexure is sufficient to stress the stock material slightly beyond its yield point, in the outer fibres of the stock, the rolls may be -rotated to feed the stock through the machine thereby straightening the same, and other lengths of stock may be entered into the machine, to be continually flexed and straightened. It should be noted that roll 70 may be backed off simul¬ taneously with the mentioned hydraulic cylinder moving the hollow piston, its adjusting screw and the attached roll 76, at a slightly higher nominal speed than roll 70; thereby flexing the stock against roll 70 at a speed controlled by the speed of the latter. The advantage of such a procedure is that the stock will be held between rolls 70 and 76 while it is being flexed. Similarly, in any type of rolling mill apparatus where elongated stock is fed and/or reduced under pressure between rotating rolls, one roll may be automatically retracted to by-pass an obstruction, such as an upset end, a spliced or welded joint of continuously processed stock, and then automatically be brought to bear on the stock at the same pressure and the same adjusted pass opening as previously, by means of sensing devices that control the double acting cylinder backing the adjusting screw, its yoke and roll. Another alternative embodiment of the invention is an improvement on the conventional 7-roll straightener having two 3-roll end clusters and an intermediate single bending roll, which flexes the stock against a driven, bottom roll in each cluster. The straight pass twin guide rolls may be adjustably arranged opposite the single bending roll to guide the flexed stock under the bending roll into the leaving end pass. Such a pair of adjustable, straight pass, twin rolls provide necessary guidance particularly for smaller stock sizes and upset end tubing. Such O PI s W1PO ,Aι twin rolls could also be backed by a double stroke cylinder, similar to the central, lower adjusting screw of Figure 2. If so, the central cluster could normally contact the main diameter of the tubing and automatically be opened, by retracting the twin guide rolls, for the upset end of the tube to pass, and then automatically close down to normal pass opening, by having sensing devices acti¬ vating the twin roll backed double acting cylinder. Still another use of the twin guide rolls would be entering and leaving tables for cross-roll straighteners, piercing mills, reelers, sizing mills and the like. While certain presently preferred embodiments of the invention have been shown and described and presently preferred methods of practicing the invention have been illustrated, the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims. CiϊFI ^YATloΦ'

Claims: X Claim: 1. A cross-roll straightener that advances stock in rotary motion along a curved pass line, said straightener comprising: a central pair of rolls forming a curved pass, said rolls oppositely skewed with respect to the pass line of said cross-roll straightener, the rolls of said central roll pair being of generally unequal diameter; and two end pairs of rolls, arranged adjacent opposite ends of said central pair, the rolls of said end pairs being oppositely skewed with respect to the pass line of said cross-roll straightener and having substantially the same diameters. 2. The cross-roll straightener of Claim 1 wherein the female roll of said central roll pair ia smaller than the male roll of said central roll pair. 3. The cross-roll straightener of Claim 1 wherein said end pairs of rolls form straight end passes. 4. The cross-roll straightener of Claims 1, 2 or 3 wherein the and rolls are of generally larger diameter than the female roll of said central roll pair. 5. A cross-roll straightener that advances stock in rotary sβtion along a curved pass line, said straightener comprising: a central pair of rolls that are oppositely skewed with respect to the pass line for the stock, the female roll of said central roll pair being smaller than the male roll of said central roll pair; and two end pairs of rolls arranged adjacent opposite ends of said central pair, the rolls of each of said end pairs being oppositely O PI _ , βkewed with respect to the pass line for the stock and having substantially different diameters, one roll of each end roll pair being of set from the other roll of said end roll pair along the longitudinal axis of the straightener outwardly from the center of the straightener such that the stock is maintained between the central and two end roll pairs at the adjacent ends of said roll pairs. 6. The cross-roll straightener of Claim S wherein the roll of each of said end roll pairs that is offset is the smaller roll. 7. The cross-roll straightener of Claims 5 or 6 wherein said straightener provides reverse flexure in the stock. 8. A machine frame comprising: a top frame having downwardly extending arms that are integrally connected thereto; a main base having upwardly extending arms that are integrally connected thereto, the upwardly extending arms of said main base opposing the downwardly extending ends of said top frame such that a junction is formed between the ends of the main base arms and respective ends of the top frame arms approximately midway between said sain base and said top frame; and means for connecting the opposing ends of the main base arms and the top frame arms at the junction thereof. 9. The frame of claim 8 wherein said connecting means includes at least one positioning member in at least two of said arms. 10. A cross-roll straightener wherein stock is advanced in rotary motion along a pass line between opposed rolls that are arranged in skewed relation with respect to the pass line, said straightener comprising: roll neck bearings for rotatingly maintaining the neck portions of said rolls; and a bracket for supporting said roll neck bearings in inverse symmetry about the longitudinal axis of the roll such that said bearings are substantially supported both laterally and vertically in response to the straightening loads applied to the roll. 11. A cross-roll straightener wherein each roll can be axially adjusted with respect to the center line of its support said straightener comprising: a plate support; a roll bracket for maintaining one of the rolls, said bracket being keyed to the plate support; a hollow screw that is threadingly engaged in a hole in said roll bracket, the end of said screw abutting the plate support such that the longitudinal position of the roll bracket along the keyway is set by turning said hollow screw; and a fastening screw extending freely through the central bore of said hollow screw and in threaded engagement with the plate support such that said plate is secured egainst the end of such hollow screw by tightening said fastening screw. 12. A preloaded mechanism for adjusting a machine roll, tool, or the like with respect to a machine frame, said mechanism comprising: an adjusting screw having one end clamped to the machine frame but rotatable therein, and having an opposite end that is exteriorly threaded and has an interiorly threaded hole; a yoke that carries the machine roll, tool or the like, said yoke having one end threadingly connected to said adjusting screw such that said yoke is adjusted with respect to the frame by rotation of the adjusting screw; a retainer that is fastened to the end of said yoke opposite from said one end; a small diameter screw that is fixed with respect to said retainer, said small diameter screw having one end threaded in the interiorly threaded hole of said adjusting screw, the opposite end of said small diameter screw resiliently but non- rotatingly held in said retainer; and means for tensioning said small diameter screw with respect to said retainer such that one side of the threads of said one end of the yoke are maintained against the adjacent side of the external threads of the adjusting screw. 13. The preloaded mechanism of Claim 12 wherein said retainer is secured to a shoulder portion of said yoke and said small diameter screw extends through said retainer. 14. The preloaded mechanism of Claims 12 or 13 wherein the small diameter screw has threads of substantially the same hand and pitch as the external threads of said adjusting screw. 15. The preloaded mechanism of Claim 13 wherein said tensioning means comprises: a nut fastened to said small diameter screw; and at least one spring that surrounds the small diameter screw and is located between said nut and said retainer such that when said nut is tightened against said spring, the spring urges said retainer and yoke away from said nut. ^VATlC 16. A preloaded mechanism for adjusting a machine roll, tool or the like with respect to a machine frame, said mechanism comprising: an adjusting screw having one end clamped to the machine frame but rotatable therein with the opposite end of said adjusting screw being exteriorly threaded and having an interiorly threaded hole; • first screw box that threadingly engages the external threads of said adjusting screw; a yoke having a plate portion at one end and having a stem portion at the opposite end, said stem portion secured to said first screw box such that the first screw box and yoke are adjusted with respect to the frame by rotation of said adjusting screw; a small diameter screw box that is secured to the hollow end of said adjusting screw; a retainer that is secured to a shoulder portion of said yoke; a small diameter screw that is threaded in the small diameter screw box, said small diameter screw extending through said retainer; a nut fastened to the end of said small diameter screw that is opposite said threaded end; and at least one spring washer surrounding said small diameter screw and located between said nut and said retainer such that when said nut is tightened against said spring washer, the spring washer urges the retainer, yoke and first screw box away from said nut such that one side of the threads of said first screw box are held against the adjacent side of the external threads of said adjusting screw. 17. The mechanism of Claim 16 wherein the threads of said small diameter screw are of the same hand and pitch as the external threads of said adjusting screw, said mechanism further comprising: means for securing said nut such that it is non-rotatable with respect to said retainer. 18. Apparatus for supporting a machine roll assembly with respect to a machine frame, said apparatus comprising: a roll support for said roll assembly; a hydraulic piston head maintained within a bore in said frame, one end of said bore having a seat that limits the travel of said piston head in one direction, said piston having a first bore and a second bore that is of smaller diameter than the first bore, said first and second bores being arranged to form a seat therebetween. an adjusting screw having one end that threadingly engages said roll support and an opposite end that is rotatably clamped in the second bore of said piston head, said adjusting screw being rotatably supported by the seat between said first and second bores; a retainer fastened at the other end of said frame bore to limit the travel of said piston head in the opposite direction; and hydraulic means for maintaining said piston head against said retainer under an established pressure such that the position of the roll with respect to the frame is controlled by rotation of said adjusting screw, said hydraulic means yielding at pressures above said established pressure such that said piston moves toward the seat in said bore. 19. The apparatus of Claim 18 wherein said hydraulic means selectively applies controlled pressure to either side of the hydraulic piston head such that the position of the roll with respect to the frame is controlled by selectively controlling the hydraulic flow and pressure. 20. A method for controlling the position of a machine assembly with respect to a machine frame wherein the machine assembly is connected to an adjusting screw that is rotatingly clamped to a hydraulic piston that is slidingly supported in the frame, said method comprising: locating the machine assembly among discrete positions with respect to the machine frame by controlling the hydraulic flow and pressure on said piston; and rotating the adjusting screw for continuous adjustment of the machine assembly with respect to said hydraulic piston at discrete locations in said frame. 21. The method of Claim 20 further comprising: adjusting a stop mechanism to limit the movement of said piston. 22. A cross-roll straightener wherein stock is stressed by rolls that are mounted in a frame, said rolls being skewed with respect to the pass-line for the stock, the means for supporting at least one of said rolls from the frame comprising: a hydraulic cylinder mounted to the frame; a piston seated within said cylinder, said piston yielding above a predetermined pressure; a piston rod having one end connected to said piston; a holder that is threadingly attached to the distal end of the piston rod; a thrust bearing mounted on said holder; a yoke connected to said thrust bearing such that said yoke is rotatable with respect to said holder and piston rod; and a roll bracket for rotatingly maintaining said roll, said roll bracket connected to said yoke. 23. A drive unit for a cross-roll straightener, said drive unit comprising: at least one motor; a gearbox having a pinion sha t connected to the sha t of said motor; and a plurality of drive spindles that are connected to respective work rolls of the cross-roll straightener, said drive spindles being connected to said gearbox on the same side as the shaft of said motor. 24. The drive unit of Claim 23 including at least two motors with one of said motors being connected to the gearbox above the drive spindles and the other of said motors being connected to. the gearbox below the drive spindles. 25. The drive unit of Claim 23 wherein said gearbox includes: a pinion gear that is connected to the motor shaft; an output gear mounted on an output shaft; and ' *- ■ -— * • -. (/ * * ' , — C -- ; * _ * > i ' Q _ - at least one intermediate gear that is in interlocking engagement with βeid pinion gear and said output gear and that rotates said output gear in response to the rotation of said pinion gear. 26. Machine apparatus comprising: a pair of rolls for supporting round stock generally inversely arranged about a common transverse axis with respect to each other, removed from a stock pass line, each of said rolls having substantially the same concave contour; and means for mounting said rolls such that the intersection of the transverse and longitudinal axes of each roll is substan¬ tially the same distance from a plane through said pass line and orthogonal to said common transverse axis. 27. The apparatus of Claim 26 wherein the respective longitudinal axes of said rolls are contained in substantially parallel planes and wherein the rolls are tiltable about their transverse axis in opposite directions to adjust the rolls with respect to stock diameter. 28. The apparatus of claim 27 wherein the rolls are oppositely tiltable by substantially equal angles, said mounting means comprising: a support; roller brackets connected to said support rotatingly maintaining said rolls; cylindrical segments that are connected to said roller brackets, said cylindrical segments, having gear teeth on the arcuate side thereof; pinions that engage the gear teeth of said cylindrical segments; and •hafts that are interlocked to turn in opposite directions, said shafts being keyed to said pinions such that when said shafts are rotated, said pinions engage the gear teeth of said cylindrical segments and rotate said cylindrical segments and tilt said roller brackets and rolls in opposite directions at substantially equal angles with respect to said support. 29. The apparatus of Claim 28 wherein said roller brackets are further provided with a dowel keyway and slots, said mounting means further comprising: fasteners fixed to said support extending through the slots of said roller brackets and a dowel key that is insertable in the keyway of said roller brackets such that, with said interlocking shafts disconnected, said fasteners in a loosened position, and said dowel key inserted in the keyway, when one of said shafts is rotated, the respective pinion keyed to said shaft engages the gear teeth of a respective one of the cylindrical segments, to tilt both of said roller brackets •nd rolls in the same direction and in fixed relationship with respect to each other. 30. The apparatus of Claims 26, 27, 28 or 29 wherein the diameter of each roll in said pair of rolls is smaller at one end than at the opposite end. 31. A method for maintaining stock in the pass-line of a cross-roll straightener having a female roll of larger diameter than the male roll, said method comprising: rotating the smaller male roll at a higher peripheral velocity than the female roll such that the surface speed of the male roll is greater than the surface speed of the female roll and the female roll is driven by engagement with the stock as it enters the roll pass; increasing the angular velocity of the female roll when the stock is engaged with the male and female rolls throughout the roll pass until the surface speeds of the male and female rolls are substantially the same and the male roll is driven by engagement with the stock; and decreasing the angular velocity of the female foil after the stock has left the roll pass such that the surface speed of the female roll is less than the surface speed of the male roll. 32. A cross-roll straightener comprising: a cross-roll pair having a female roll and a male roll; an adjustable speed drive for rotating said rolls at controlled angular velocity; and a freewheeling clutch connected to the female roll such that said female roll rotates at least at the angular velocity of said drive and is free to rotate at higher angular velocities. 33. The cross-roll straightener of Claim 32 further comprising: a second freewheeling clutch connected to the male roll such that said male roll rotates at least at an angular velocity established by said drive and is free to rotate at higher angular velocities. 34. The cross-roll straightener of Claim 32 further comprising: a guide laterally disposed from and substantially parallel to the pass line of the male and female rolls such that the guide maintains the stock in the roll pass as it passes between the male and female rolls. 35. A pair of rolls for use in a cross-roll straightener, said rolls comprising: a male bending roll having a suitable contour for flexing stock into; a female roll having a concave contour, said female roll being of greater diameter than the bending roll, and cooperating with said bending roll to form a curved pass wherein the stock is maintained and supported between the ends of the roll pair, and wherein the average male roll angle is greater than the average roll angle of the female roll with respect to the curved pass. 36. A pair of rolls for use in a cross-roll straightener, said rolls comprising: a male bending roll having a concave contour; and a female roll having a concave contour, said female roll being of greater diameter than the bending roll, and cooperating with said bending roll to form a curved pass wherein the stock is maintained and supported between the ends of the roll pair, and wherein the roll angle of the male roll with respect to the curved pass is at least as great as the roll angle of the female roll with respect to the curved pass. 37. A cross-roll straightener that advances stock in rotary motion along a curved pass line, said straightener comprising: a first pair of rolls, of which the male roll is of larger diameter than the female roll, oppositely skewed with respect to the pass line of said cross-roll straightener and forming a curved pass therebetween; and second and third pairs of rolls arranged adjacent opposite ends of said first roll pair and forming straight passes therebetween, the rolls of said second and third roll pairs being oppositely skewed with respect to the pass line of said cross-roll straightener and arranged in parallel planes with respect to each other, the rolls of each of said second and third roll pairs being skewed at substantially the same average angle as the male roll of said first roll pair, and the female roll of said first roll pair being skewed at an angle that is at least as great as that of the male roll of ssid first roll pair. 38. A concave bending roll for use in a cross-roll straightener, said bending roll comprising: two end sections with a surface having a curvature defined by rotating said roll with respect to a cylinder at a predetermined distance and a selected angle with respect to the longitudinal axis of said bending roll; and a central section having end portions that abut the inner ends of said end sections and having a surface that is tangent to the surface of said end sections, the surface of said central section also having a sharper curvature than said end sections such that the minimum diameter of said central section is less than the minimum diameter of the surface defined by the cylinder that defines the curvature of said end sections. 39. The bending roll of Claim 31 wherein said bending roll lexes the stock to a minimum radius of curvature over a length of at.*least one pitch of the helical motion of the stock surface. 40. A female bending roll for straightening a large variety of stock sizes in curved passes, said bending roll comprising: a central section having a concave surface that is substantially symmetrical about the transverse axis of the roll; two intermediate sections having end portions that abut opposite ends of said central section, said intermediate sections each having a surface contour that is tangent to the surface contour of ■aid central section at the ends of said central section and in the shape of a conical frustrum that tangents the central section at the snail ends thereof; and two end sections that abut the outer ends of said inter¬ mediate sections, said end sections having a surface contour that is tangent to the surface contour of said intermediate sections at the outer ends of said intermediate sections and that is defined by rotation of said roll with respect to a cylinder located at a predetermined distance and a selected angle with respect to the longitudinal axis of said bending roll such that the curvature of the surface of said end sections are more gradual than the curvature of the surface of said central section. 41. A female bending roll for straightening a large variety of stock sizes in curved passes by varying the angle between the roll's axis and the centerline of the pass, comprising: a central section having a concave surface that is substantially symmetrical about the transverse axis of the roll; two intermediate sections that abut and tangent opposite ends of said central section, said intermediate sections each having a surface contour that is in the shape of a conical frustrum that tangents the central section at the small end thereof; and two end sections that abut and tangent the outer ends of said intermediate sections each defined by rotating a rod in a circle vertically to the roll's axis at its minimum diameter, said rod being of predetermined diameter flexed to a variable radius of curvature in a plane that intersects the roll's axis at a predeter- mined angle, said flexure being of preselected curvature symmetrical about a line through the rolls transverse axis such that the surfaces of said end sections are more gradual than the surface curvature of said central section. 42. A bending yoke comprising: a pair of bending rolls that are inversely arranged with respect to each other about a common transverse axis, a portion of the surface contour of each of said bending rolls being substantially concave and a portion of the surface contour of each of said bending rolls being substantially less concave, both of said contours having the same minimum diameter where they tangent parallel to the roll's axis. 43. The female bending roll of Claim 41 wherein the minimum diameter of said central section is less than the minimum diameter of a surface defined by the flexed rod that defines the surfaces of said end sections. 44. A cross-roll straightener that advances stock in rotary motion along a curved pass line, said straightener comprising: at least one pair of cross-rolls for advancing and flexing the stock and at least one outboard roll and a guide, substantially tangent to the roll at the pass line, for supporting said stock at the end of said cross-roll pair. 45. A cross-roll straightener that advances and flexes stock in rotary motion along a curved pass line, said straightener comprising: at least one pair of cross-rolls for advancing and lexing the stock and at least one pair of outboard twin guide rolls for supporting said stock at the end of said cross-roll pair. 46. A cross-roll straightener that advances and flexes stock in rotary motion along a curved pass line, said .straightener comprising: . one female roll and a pair of bending rolls, mounted in reverse symmetry opposing said female roll for forming a curved pass therebetween. 47. A cross-roll straightener that advances and flexes stock in rotary motion along a curved pass line said straightener comprising: two clusters of three cross-rolls each forming straight passes therebetween and an intermediate bending yoke, consisting of a pair of cross-rolls mounted in reverse symmetry, each having portions of a suitable contour for flexing the stock. 48. A cross-roll straightener that advances and flexes stock in rotary motion along a curved pass line, said straightener comprising: two 3-roll clusters forming straight passes and an intermediate 3-roll cluster having a pair of rolls mounted in reverse symmetry and an opposed concave roll. 49. A cross-roll straightener that advances stock in rotary motion along a curved pass line, said straightener comprising: two 3-roll clusters forming straight passes and an intermediate bending roll opposed by a pair of straight pass, twin guide rolls; thereby forming an intermediate 3-roll cluster for flexing and guiding the stock, between the mentioned straight end-pass clusters. 50. A cross-roll straightener according to claim 48 where said intermediate cluster comprises an adjustable ' female concave roll and an opposed pair of asymmetrical twin bending rolls, said intermediate cluster forming a curved pass for the stock to augment the flexure of the stock between the mentioned straight end-pass clusters. 51. The method of producing reverse flexures of stock in a cross-roll straightener by providing outboard concave rolls and guiding means adjacent to the entering and leaving ends of said cross-roll straightener to flex eaid stock in the opposite directions. 52. The method of varying the reverse flexure in stock, processed in a cross-roll straightener,by providing an adjustable concave roll and guiding means adjacent the end of a pair of working rolls in said straightener for deflecting the stock laterally to its assumed pass-line in said working rolls. 53. The method of varying reverse flexure in stock processed in a cross-roll straightener by providing adjustable, positively guiding concave roll assemblies edjaeent both ends of said straightener for deflecting the path of the stock laterally to its path at the ends of said straightener. 54. The method of providing additional guidance in a 5 straightener having a pair of different diameter cross-rolls comprising outboard roll supports that force the stock into roll wedge-angles at each end of said cross-rolls. 55. A method for flexing stock in a cross-roll straightener comprising: 0 three pairs of cross-rolls for feeding round stock in rotary motion, the central pair of which is laterally adjustable in relation to the other roll pairs for flexing the stock in one direction; two outboard adjustable roll supports, for flexing the 5 stock in the same direction as the central roll pair, particularly for smaller stock sizes and stronger materials, so as to enable the apparatus to flex stock in a substantially single flexure or in reverse flexures depending on the adjustment of said outboard supports; thereby to increase the capacity of the apparatus to straighten o a larger variety of stock sizes and materials. 56. A cross-roll mounted in e first yoke supported by at least one pair of back-up rolls mounted in a second yoke, said back-up rolls being adjustable toward said cross-roll by adjustable means for clamping opposed wedges against a double wedge supported by said first yoke, the double wedge and the opposed wedges all being partly cylindrical resting in partly cylindrical bores in said first and second yokes respectively, the eenterlines of said partly cylindrical wedges and bores all being parallel to the axes of said cross-roll and back-up rolls. 57. Drive for an intermediate roll pair in a multi- roll straightener, having other rolls driven by other means comprising: a variable speed motor for driving a differential having two output shafts; one for each roll in said roll pair, thereby substantially equalizing the peripheral speeds of the rolls when stock i* entered in the pass between tham, and means for varying the speed of said motor and roll pair in relation to other rolls, driven by other means, in aaid multi-roll straightener.

Inventors: NILSSON EINAR W, NILSSON, EINAR, W.
Applicants: NILSSON EINAR W, NILSSON, EINAR, W.
Application year: 1984
Main classification: B21D3
IPC codes: B21D3