Profiled metal panels or sheets are commonly used in the construction industry for roofing or wall panels or the like. They comprise a sheet of metal formed to have longitudinal corrugations or castellations in the form of a series of alternating elongate troughs and ridges. Typically such troughs and ridges are trapezoidal in transverse cross section.

Problems have in the past been encountered where trying to produce a smooth curved bend transverse to the longitudinal direction of the panel or sheet since during bending the panels tend to "kink" or buckle at the edges of the trapezoidal troughs and ridges.

Various attempts have been made to overcome these difficulties, and, for example, U.K. patent specification 2153721 discloses apparatus for bending profiled sheet metal. Such apparatus is relatively complex in terms of construction and operation.

We have now devised an improved method and apparatus for bending profiled metal sheet which offers advantages over prior art proposals in terms of efficiency and reliability of operation, and simplicity of apparatus.

According to a first aspect of the invention, there is provided apparatus for bending profiled sheet metal transversely to the longitudinal direction of the troughs and ridges in the profiled sheet, which apparatus comprises: a) first clamping means arranged to clamp said metal sheet at a first longitudinal location thereof, said first clamping means being provided with a die element having a curved surface, and being pivotable about a first pivot axis transverse to said longitudinal direction such that the curved surface of said curved die element is caused to engage and cause deformation of said metal sheet; b) second clamping means arranged to clamp said metal sheet at a second location longitudinally spaced from said first location, said second clamping means being pivotable about a second axis substantially parallel to said first axis, said second clamping means and said second axis being longitudinally movable relative to said first clamping means and said first axis; and c) tensioning means for imparting a tensile load to said sheet in said longitudinal direction whilst said sheet is clamped between said first and second clamping means.

It is preferred that both the first and second clamping means comprise pairs of respective upper and lower clamping members having clamping surfaces complementarily shaped to engage and receive the longitudinal troughs and ridges of the profiled sheet.

In one embodiment, the tensile load may be imparted in said sheet by the inertia of the second clamping means as the first clamping means pivots about the first pivot axis causing the second clamping means to move in the longitudinal direction.

_A dvantageously the die element is in the form of an extended portion of one of the pair of clamping members comprising the first clamping means, which portion extends from the first clamping means towards the second clamping means, with the curved surface curving away from the general plane of the metal sheet.

Preferably the first pivot axis is arranged to lie on the general plane of the metal sheet, with, advantageously the second pivot axis also being arranged to lie on the general plane of the metal sheet.

It is preferred that the second clamping means is pivotally mounted on a carrier structure which carrier structure is movable along elongate guide members relative to the first clamping means.

Advantageously, the tensioning means is in the form of one or more hydraulically actuable cylinder and ram arrangements arranged to impart a force acting on the second clamping means or carrier structure.

Preferably, the tensioning means is operable such that as the second clamping means moves towards the first clamping means, the tension in the metal sheet remains substantially constant.

It is preferred that torque means is provided for selectively applying a turning moment to the first clamping means such that it pivots about the first pivot axis. Advantageously such a

turning moment may be applied hydraulically by means of a cylinder ram and torque arm arrangement.

According to a second aspect of the invention, there is provided a method of bending profiled sheet metal transversely to the longitudinal direction of troughs and ridges in the profiled sheet, which method comprises: a) clamping said metal sheet at two longitudinally spaced portions thereof, b) imparting a tensile load in the longitudinal direction in said sheet, and c) bending said sheet about a pivoting curved surfaced die, such that a plastically deformed longitudinal profile is imparted to said sheet, whilst maintaining said tensile load in said sheet at a substantially constant value.

The invention will now be further described in a specific embodiment, by way of example only, with reference to the accompanying drawings, in which,

Figure 1 is an elevation of a first end of apparatus according to the invention;

Figure 2 is an elevation of a second end of the apparatus of

Figure 1;

Figure 3 is a side view of the apparatus of Figures 1 and 2; and

Figures 4a and 4b, are schematic representati is of apparatus and method according to the invention.

Referring to the drawings, the apparatus generally designated 1, has a mounting frame 2 upon which is mounted a forward clamping die structure 3 and rearward clamping die structure 4. The forward clamping die structure comprises a housing 5 for a fixed lower steel clamp 6 and an upper steel clamp 7. The lower clamp 6 is provided with longitudinal ridges and troughs on its upper surface 8 profiled to receive and locate the longitudinally extending ridges and troughs of the metal sheet to be bent. The surface 8 is also profiled in the longitudinal direction of the ridges 9 having a flat portion 10 and a curved die portion 11. The upper clamp 7 is movable in the housing 5 under the influence of hydraulically activated rams 29, along guide posts 14 into clamping engagement with the profiled surface of the lower clamp 6, the lower surface 12 of the upper clamp 7 being profiled complementaril to the surface 8 of the lower clamp 6 such that the profiled sheet to be bent can be clamped therebetween. The surface 12 is generally flat in the direction of the longitudinal ridges 9 and the zone of clamping engagement is confined to the region adjacent the surface 12 of the upper clamp and the flat portion 10 of the lower clamp.

The housing 5 is pivotally mounted on the frame 2 on projecting shafts 13 which are rotatable bushed pivot structures 14. the outermost ends of the shafts 13 are fixed to, and will rotate as one, with, first ends of respective downwardly extending torque arms 15, the other ends of the arms 15 being pivotally connected to the rams 16 of respective hydraulically activated cylinders 17.

The cylinders 17 are themselves pivotally mounted on the frame 2 at their lowermost ends in bushed pivot structures 18. The rearward clamping structure 4 comprises a housing 19 pivotally mounted in bushed pivot structures 20, to a carriage structure 26 on laterally projecting shafts 21. The housing 19 supports a fixed lower steel clamp 22 havng surface profile ridges 23 identical to those on the forward clamping die structure 3. An upper steel clamp 24 is movable, under the influence of the rams 25a and hydraulically actuated cylinders 25b, into clamping engagement with the lower clamp 22, such that a generally planar sheet of profiled metal may be clamped therebetween. In order to facilitate this, the upper clamp 24 has a surface profiled for complementary engagement with the profiled surface 23 of the lower clamp 22.

The carriage structure 26, and therefore also the housing 19, is slidably movable relative to the frame 2 along peripheral longitudinally extending support and guide rails 27.

Peripheral hydraulic cylinders 28 are pivotally connected at one of their respective ends to the forward clamping die structures 3 with the distal ends of their longitudinall extending rams 28a being pivotally connected to respective sides of the carriage structure 26.

In operation (and as shown schematically in Figures 4a and 4b) a preformed generally planar profiled metal sheet 31 having longitudinally extending grooves and ridges of trapezoidal cross-

section is slid into position from the rear of the press through the open rearward clamping structure 4. When.in position, the grooves and ridges of the sheet will be supported on the complementary groove and ridge formations on the surface 23 of the rearward clamping structure 4, and on the ridge and groove formations 9 on the flat portion 10 of the forward clamping die structure 3.

The hydraulic cylinders 25 in the rearward clamping structure 4 are first actuated to bring the upper die 24 into engagement with the profiled metal sheet such that the sheet is firmly clamped and held between the upper and lower clamps 24 and 22. Next the hydraulic rams 29 are actuated to bring the upper clamp of the forward clamping die structure 3 into engagement with the profiled metal sheet such that the sheet 31 is firmly clamped between the upper clamp 7 and flat portion of the lower clamp 6.

The peripheral cylinders 28 are then actuated such that their rams 28a will extend slightly, forcing the carriage 26 to move along guide rails 27 slightly away from the forward die structure 3. In so doing the metal sheet extending between and clamped by the clamping structures 3 and 4 is put under tensile loading (as illustraded in Figure 4a). At this stage, hydraulic cylinders 17 are activated such that their rams 16 extend upwardly having a line of action through the pivotal connection between the rams 16 and the torque arms 15, causing the torque arms 15 and shafts 13 to rotate as one in the pivot structures 14; the housing 5 is

-8- therefore also caused to rotate forward on its mounting shafts 13. As the housing 5 rotates forward, the metal sheet (in tension) is pulled forward, with the ridges and troughs 9 of the curved portion 11 of the lower clamp 6 (which rotates forward with the housing 5 in the direction of arrow A, Fig 4b) being caused to enter into and locate the complementary shaped ridges and troughs on the underside of the metal sheet. In this way the metal sheet is wrapped and plastically deformed around the curved portion 11 of the lower die 6 to produce the required curved longitudinal profile.

As the housing 5 (and therefore clamps 6 and 7) is rotated progressively further forward, the curvature of the surface of the die portion 11, and the location of the pivot axis will cause the vertical height of the sheet in the region of the housing 5 to increase relative to the vertical position of the rearward clamped dies 22 and 24. To allow for this, the housing 19 is able to pivot under the tension in the direction of arrow B in the clamped metal sheet on the projecting shafts 21 in the bushed pivot structures provided on the carriage structure 26.

It is important to note that as the housing is rotated progressively further forward, the carriage structure 26 supporting the rearward clamping structure 4 is pulled (in the direction of arrow C) along the guide rails 27 under the tension in the metal sheet, towards the forward ends of the press. As the carriage structure 26 moves forward the rams 28a of the

peripheral hydraulic cylinders 28 will retract in unison therewith. The cylinders 28 allow the hydraulic fluid to bleed therefrom such that a "back pressure" exists resisting the retraction of the rams. This back pressure is maintained at a constant level such that the tension in the "unbent" metal sheet is kept substantially constant throughout the bending operation.

Once the metal sheet has been bent to the required degree of longitudinal curvature, the hydraulically operated clamps 6,7,22 and 24 are separated and the now longitudinally curved profiled metal sheet removed from the forward end of the press. The press is than returned to its initial state, in readiness for receiving the next profiled sheet to be bent, by reverse actuation of the various hydraulic cylinders.