Method of and apparatus for removing camber from strips

Abstract: The invention relates to a method of and apparatus for removing excess longitudinal camber from MULT (multiple) strips (14, 18) cut from a rolled thin gauge steel sheet (12). Each cambered MULT strip is passed through a rolling mill (30) having rolls (32, 34) with strip-contacting surfaces (35, 33) which are vertically adjustable. One roll (32) is inclined relative to the other roll (34) so as to reduce the thickness of the MULT strip (14) from its concave shorter edge (20) in reduced amounts thereacross to the opposite convex longer edge (22), so as to eliminate or reduce camber in the MULT strip prior to passing the strip through a roll-forming and punching line.

Description: This invention relates to roll-forming strips which have a substantial length, and in particular to eliminating the excessive lengthwise curvature or camber which occurs in strips. It has always been a goal in steel rolling mills to roll thin gauge sheets which have uniform thickness across the sheet; however, it has been very difficult to obtain. The rolling forces transmitted to the rolls due to the squeezing action on the sheet apply a substantial bending load and deflection across the width of the roll with its maximum point of deflection usually at the center of the roll. These roll-separating forces acting on the rolls can be substantial, and are affected by the hardness of the steel being rolled along with the reduction in thickness which the mill is rolling. Various techniques have been historically used to eliminate this roll deflection, such as large diameter back-up rolls and applying reverse bending forces in the neck areas of the rolls. While numerous attempts to achieve uniform thickness across the sheet have been attempted, most rolled thin sheets do not have uniform thickness thereacross, and are usually tapered from the outer edges inward, with the thickest area in the center. This non-uniform rolling creates compressive and tensile residual stress problems in the rolled sheet. When these stresses exceed certain limits, the sheet exhibits a phenomenon called "buckling" which is described in detail in US-A-4,033,165. Variations in the thickness distribution across the width of a rolled sheet are influenced, not just by deflection of the rolling mill rolls, but also other factors, such as thermal expansion of the mill rolls caused by the heat input from the sheet being rolled, wear of the mill rolls, and other factors. In the roll-forming technology, a master coil is typically cut into a plurality of strips, called MULTS, an acronym for multiple strips, by a slitter device generally typified in US-A-5,158,002. The MULT strips can vary in width up to 61cm (24 inches) or more, and can include 2 or more strips depending upon the width of the master coil and the width of the individual MULTS. Since the overall thickness across the sheet of the master coil varies, the MULT strips will also vary in thickness across their width. Typically the outer MULT strips will have excessive camber along their length, as seen in plan, which is unacceptable in certain applications. If the MULT strips are intended for roll-forming or press-braking into elongated sections, such as zee (Z-section) purlins, excessive camber creates problems. More than 1.27cm (1/2 inch) of camber in 6.1 m (20 feet) of length is unacceptable with some roll-formed sections, and in some applications even less than that is unacceptable. The prior art has attempted to solve this problem by pushing the edges of the sheet to eliminate camber. The prior art has also tried to reverse twist a formed purlin. Camber is also a problem in stamping, punching and bending by press brakes. JP-A- 63013616 discloses a method of and an apparatus for removing camber from and effectively straightening a strip of material as indicated in the pre-characterising portions of claims 1 and 3. From one aspect, the present invention provides a method of removing camber from. and effectively straightening a strip of material, as defined in claim 1. From another aspect, the invention provides an apparatus for removing camber from, and effectively straightening a strip of material, as defined in claim 3. Reference will now be made to the accompanying drawings, in which:- FIGURE 1 is a cross-sectional view across the width of a master coil slit into three MULT strips; FIGURE 2 is a plan view of the MULT strips of FIGURE 1 with portions removed and the camber in the strips exaggerated; FIGURE 3 is a transverse view, partly in section, of a rolling mill stand symbolically shown with the roll gap reduced along its left edge; FIGURE 4 is a schematic representation of a slitter and a recoiler of the MULT strips; and FIGURE 5 is a schematic representation of a typical roll-forming line for structural purlins embodying the present invention. Referring now to the drawings and more specifically to FIGURES 1 and 2, a coil of sheet steel as it comes from the mill can be rolled in various widths and gauges and is referred to as a master coil. A cross-section of the coil sheet 12 is illustrated in FIGURE 1 with exaggerated variations in thickness. As shown in FIGURE 4, the master coil 10 is unwound and the resultant sheet 12 is run through a slitter device 24, well known in the prior art, which slits the sheet 12 into a plurality of side-by-side longitudinal strips, generally referred to in the art as MULTS. In FIGURES 1 and 2, the coil sheet 12 is slit into three MULT strips 14, 16 and 18. The strips can vary in width from 5.1cm to 61cm (2 inches to 24 inches) and each strip can vary in thickness from one edge to the other up to 0.127mm (0.005 inches). The sheet material can vary in gauge from 7 to 16 and the master coil may have a width up to 183cm (72 inches). The thickness across the width of the sheet in the master coil will vary. However, typically the edges of the master sheet will be thinner than the center section, as shown on an exaggerated scale in FIGURE 1. While steel companies strive to roll a flat sheet, most of them produce a sheet similar to that shown in FIGURE 1. Typically, the outer MULTS 14 and 18, once they are severed from the master sheet 12, will take up a curved shape, as illustrated in FIGURE 2, with an amount of camber X, as shown in relation to MULT strip 18. Portions of the strip length are not shown, and the camber amount is exaggerated for purposes of illustration; however, the maximum acceptable amount of camber in a 6.1m (20-foot) strip could be 1.27cm (one-1/2 inch) in some applications, but in others it could be 0.16cm (1/16 inch). Quite often the MULT strips in the center of the master coil will not have excessive amounts of camber, as illustrated by center MULT strip 16. MULT strip 14 has a short concave edge 20 and a long convex edge 22. FIGURE 3 illustrates a basically conventional rolling mill 30 which includes a pair of pinch rollers 32 and 34, each having strip-contacting surfaces 33 and 35 which define the roll gap between the rolls. At least one of the pinch rolls, for example, the upper pinch roll 32, is adjustably positioned, for example vertically adjustable, by hydraulic cylinders 38 which urge roll bearings 36 against adjustable wedge members 38 and 40. The wedge members, in turn, are urged against bearings 37 which support lower pinch roll 34 against the frame member of the rolling mill. In this embodiment of the invention, the roll gap on each side of mill 30 is set so that the gap A on the left side will roll the short, left edge 20 sufficiently to increase the length of the short edge 20 to more closely correspond with the length of the long edge 22. The roll gap B on the right side of the mill 30 is set with a roll gap approximately the same as the thickness of the long, right edge 22. The amount of rolling achieved by the mill varies across the strip from a maximum at the left edge 20 to zero or a minimum at the right edge 22. This rolling across the full width of MULT strip 14 extends the- length of the strip on its left edge 20 so as to substantially remove the camber from the overall strip 14. The roll gap in rolling mill 30 can be adjusted to suit the particular MULT strip being rolled. For example, if the short side of the MULT strip is on the right, roll gap B will be adjusted so as to roll the short edge of the MULT strip sufficiently to elongate it and reduce or eliminate its camber. FIGURE 4 illustrates a master coil 10 feeding the un-slit sheet 12 to a slitter 24 which in turn feeds a series of MULT strips onto a recoiler 26. The MULT strips can either be recoiled, or they can be selectively passed directly into the processing line. FIGURE 5 illustrates a recoiled MULT strip 14 which feeds rolling mill 30, a straightening roll leveler line 42, a loop pit 44, a shear 46 and a roll-forming line 48 which produces the completely formed product, such as a zee (Z-section) purlin 50. Whether the MULT strips are recoiled and stored before use or left flat in the processing line is a matter of choice. It will be understood that the above-described embodiments of the invention are for the purpose of illustration only. The invention may be applied to strips cut from sheets rolled from metals other than steel, and from non-metallic sheets, or to other types of strips, the camber or equivalent of which is to be eliminated.

Claims: A method of removing camber from and effectively straightening a strip of material (14) having an initial amount of camber and forming a structural member (50) from the strip of material (14), the strip (14) having a relatively short concave edge (20) and a relatively long convex edge (22), with the use of a pair of rollers (32, 34) having a first roll gap (A) between them, the first roll gap (A) being located at a first end of each of the rollers (32, 34), and a second roll gap (B) between them the second roll gap (B) being located at a second end of each of the rollers (32,34), characterised in that each of the first and second roll gaps (A, B) are independently adjustable via a pair of adjustment mechanisms (38, 40), said method comprising the successive steps of: setting the first and second roll gaps (A, B) between the pair of rollers (32, 34) via the independently adjustable adjustment mechanisms (38, 40) to different widths so that when the strip (14) is passed between the rollers (32, 34), the relatively short concave edge (20) of the strip (14) is lengthened; passing the strip (14) between the rollers (32, 34) so that the relatively short concave edge (20) of the strip (14) is lengthened to reduce the initial amount of camber and effectively straighten the strip (14); and passing the strip (14) through a roll-forming line (48) to form a structural member (50) after the strip (14) is passed between the rollers (32, 34). A method as defined in claim 1, wherein a first (32) of said rollers (32, 34) has a longitudinal central axis associated with it and wherein a second (34) of said rollers (32, 34) has a longitudinal central axis associated with it, and wherein said roll gaps (A, B) are set so that said longitudinal central axis associated with said first roller (32) is not parallel to said longitudinal central axis associated with said second roller (34). An apparatus for removing camber from and effectively straightening a strip of material (14) having an initial amount of camber and forming a structural member (50) from the strip of material (14), the strip of material (14) having a relatively short concave edge (20) and a relatively long convex edge (22), said apparatus comprising: a first roller (32) having a first end and a second end; a second roller (34) having a first end and a second end; a first adjustment mechanism (38) associated with said first end of said first roller (32) and said first end of said second roller (34), said first adjustment mechanism (38) allowing a first roll gap (A) between said first end of said first roller (32) and said first end of said second roller (34) to be set to a first width; characterised in that said apparatus further comprises a second adjustment mechanism (40) associated with said second end of said first roller (32) and said second end of said second roller (34), said second adjustment mechanism (40) allowing a second roll gap (B) between said second end of said first roller (32) and said second end of said second roller (34) to be set to a second width, said second width being different than said first width so that when the strip (14) is passed between said rollers (32, 34), the relatively short concave edge (20) of the strip (14) is lengthened to reduce the initial amount of camber and effectively straighten the strip (14), said first and second adjustment mechanisms (38, 40) being independently adjustable; and a roll-forming line (48) coupled to receive the strip (14) after the strip (14) is passed between the rollers (32, 34), said roll-forming line (48) forming a structural member (50) from the strip (14). An apparatus as defined in claim 3, wherein said first roller (32) has a longitudinal central axis associated with it and wherein said second roller (34) has a longitudinal central axis associated with it, and wherein said roll gaps (A, B) are set so that said longitudinal central axis associated with said first roller (32) is not parallel to said longitudinal central axis associated with said second roller (34).

Inventors: VOTH KARL E, VOTH, KARL E.
Applicants: BRADBURY COMPANY INC, THE BRADBURY COMPANY, INC.
Application year: 1996
Main classification: B21D1
IPC codes: B21B15, B21D1, B21B37