TECHNICAL FIELD

This invention relates to the cold roll-forming of sheet metal articles wherein discrete longitudinally extending bands or zones of the article are plastically strained by cold-working during the roll-forming operation. Typically, the cold-working may comprise knurling the bands or cold-reducing them.

BACKGROUND ART

Cold roll-forming sheet metal articles is a well known process. Briefly stated, a sheet metal workpiece is passed through a sequence of stands of forming rolls. Each stand produces some modification of the cross-sectional shape of the workpiece as received by the stand, and their combined effect is to bring the workpiece in a step-by-step manner into the shape of the required article. It is also known for at least one of the roll-forming stands to impress a surface pattern or otherwise cold work the workpiece in a manner not substantially modifying its cross-sectional shape. For example, one stand of rolls may knurl one or more bands of the workpiece. Indeed, the invention was developed with knurling in mind and is described primarily with reference to that mode of cold working hereinafter.

It will be appreciated, however, that the invention is applicable to other cold working processes wherein the working is restricted to such bands or zones. For example, the invention is applicable to the production of roll-formed sheet steel articles wherein narrow bands of

the article are cold-reduced in thickness, so as to work harden the bands and thereby stiffen the finished article.

The knurling process comprises pressing a tool against the metal surface to impress a pattern therein. A typical knurling pattern comprises two sets of closely spaced, parallel, thin, rectilinear grooves in the knurled surface, with the grooves of each set intersecting the grooves of the other. In effect, the pattern then becomes a regular grid of small, closely spaced mounds, each being a quadrilateral bounded by short lengths of groove. The grooves frequently cross each other obliquely, for example with an included angle of 60° between intersecting grooves, so that each quadrilateral is diamond shaped. Other fine grained, regular knurling patterns are known, and the present invention is not only not restricted to knurling as the mode of cold- working, but also is still less restricted to any particular knurling pattern. Furthermore it extends to other forms of uniform surface patterning, that may sometimes be more usually described as dimpling, perforating and the like, and the term "knurling" is intended to be construed widely as covering all such forms of impressed surface patterning.

Knurling may be applied to an article for various reasons, for example to increase the coefficient of friction so as to render an article less slippery, to provide a key for adhesive or the like, to camouflage surface defects, or simply for its ornamental effect.

DISCLOSURE OF INVENTION

In the manufacture of roll-formed, lengthy, sheet metal articles of the kind in question it is convenient, but not essential, to cold work bands of the flat strip of metal from which the article is roll-formed,

before it is so formed. This may be done conveniently by passing the strip between a pair of plain or patterned pressure rolls, which indeed may be the first met rolls of a multi-stand roll former.

If the cold working reduces the thickness of the band it will be apparent that the metal is caused to flow laterally. Furthermore, since a knurling pattern is simply pressed into the metal surface, that is to say it is not cut in and no metal is removed, the base metal is also caused to flow laterally. In the case of thin sheet metal, this flow or plastic deformation tends to enlarge the area of the or each worked on band.

Lateral extension of a band usually presents little trouble as the side edges of the workpiece may move apart by a small amount to accommodate it. However longitudinal extension of the worked band to accommodate the working is resisted by the adjacent unworked bands, and this leads to internal stresses in the workpiece that may cause buckling or other unwanted distortion in it and/or in the finished product.

One way of addressing the above identified problem in respect of knurling would be to knurl the whole of the surface of the workpiece, as shown for example in the specification of lapsed Australian patent application 295730 (The Flintkote Company). However this introduces difficulties in the subsequent roll-forming, in that the knurling grooves tend to open up if the knurling coincides with fold lines in the finished product, leading to cracking and, if the workpiece is painted or otherwise coated, coating failure at the folds. Furthermore, if the working comprises cold reduction it is difficult if not impossible, using conventional roll-forming machines, to generate the force required to cold reduce the whole of a broad workpiece.

Therefore an object of the present invention is to overcome the above mentioned problems by very simple means whilst retaining selectivity in respect of the worked areas.

According to the invention a sheet metal workpiece having a cold- worked band extending therealong, is stress relieved by superimposing a regular embossed pattern on said band, that is to say by pressing a substantially regular array of small portions of that band from the plane of the sheet. The number, size, shape and spacing of the embossments (the displaced portions) are largely matters of choice that may be determined, for the most part, by cosmetic considerations, provided that the embossments form a pattern that is uniform and of sufficiently small scale to ensure that the act of forming the embossed pattern as aforesaid would cause effectively uniform contraction in at least the longitudinal direction of the embossed band. In any particular instance the degree of that contraction may be set or adjusted by setting or adjusting the extent to which the embossments project from the plane of the sheet.

In practice, one or two trial runs may be made before commencing production, and the extent of the displacement of the embossments adjusted, so that the finished workpiece displays little or no distortion to the eye, after having been roll-formed to shape. In this event the expanding effect of the knurling or other cold working is substantially cancelled by the contracting effect of the embossing.

The effect of the embossed pattern is the same irrespective of whether the embossments project from the surface of the workpiece to which knurling is applied or from the opposite surface. In the latter instance the knurled side of the workpiece would display a pattern of

recesses or dimples, each corresponding to an embossment on the reverse side of the workpiece.

Thus, the invention consists in a method of making a cold roll- formed sheet metal article having at least one longitudinally extending cold worked zone characterised by the step of stress relieving said zone by impressing a regular embossed pattern thereon.

Ideally, if the band were free to extend, that is to say separated from the remainder of the workpiece, the longitudinal contraction resulting from the application of the embossed pattern would substantially equal the longitudinal extension resulting from the cold working.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example, an embodiment of the above described invention is described in more detail hereinafter with reference to the accompanying drawings.

Figure 1 is a perspective view of a portion of a sheet metal wall stud according to the invention.

Figure 2 is side elevation of a portion of the wall stud of figure 1

Figure 3 is a detail sectional view taken on line 3-3 of figure 1 drawn to a larger scale.

BEST MODE OF CARRYING OUT THE INVENTION

The illustrated wall stud may be roll-formed from sheet steel coated with zinc or an alloy of aluminium and zinc. It may be generally channel sectioned, and comprise two channel flanges 4, a web 5 interconnecting the flanges and inwardly directed lip flanges 6. In those particulars the stud may be completely conventional.

The outer surface of both flanges 4 has a band of knurling extending therealong. The knurling is intended to provide a key for an adhesive whereby a wall cladding panel may be secured to each of the flanges 4. In this instance, the band of knurling comprises four stripes 7 of a conventional diamond knurl pattern.

In accordance with the invention a plurality of embossments 8 overlie the knurling. Each embossment 8 is circular and presents a mound on the outer face of the flange and a corresponding depression in the inner surface thereof, that is to say each mound is hollow. Thus the central parts of each embossment 8 are displaced from the plane of the sheet metal flange.

The embossments 8 are arranged in four rows respectively coinciding with the knurling stripes 7. The embossments in neighbouring rows are staggered, so that all together they constitute a regular pattern of embossments evenly distributed over the band of knurling.

Both the knurling and the ^■ embossments may be formed by passing the sheet metal workpiece between appropriately shaped stands of pressure rolls. In the case of the embossing rolls, the roll forming the

concave surface of each embossment may be a metal roll with part- spherical mounds projecting from it. The roll contacting the convex side of each embossment may be a tough resilient roll, or a metal roll with shallow holes in register with those mounds.

In that event, the mounded roll may be screw adjustable in position to provide for adjustment of the extent to which the central parts of the embossments are displaced from the plane of the workpiece.

As indicated earlier, the forms of the embossments (and the embossment pattern) may be many and varied. Furthermore they be shaped such that their contracting effect on the workpiece in the longitudinal direction exceeds that in the transverse direction. For example, each embossment may be elongated in the transverse direction of the knurled band. In the ultimate, each may be an elongated hump extending from edge to edge of the knurling band (with a corresponding groove on the opposite side of the workpiece).

It will also be appreciated that the invention may be applied to sheet metal articles generally, and the illustrated wall stud is purely exemplary. For example, in respect of reduced stiffening zones it is particularly applicable to roof and wall cladding panels, roll-formed beams, architectral elements and sheet metal structural and frame members, whereas in respect of knurling or the like for enhancing the non-slip character of articles it is particularly applicable to metal planks, stair treads, walkway panels, metal floor tiles, ladder rungs and the surfacing members of all steel materials handling pallets.