Metal deforming – By use of 'flying tool' engaging moving work – Included in plural deforming stations or passes
Reexamination Certificate
1999-11-30
2001-07-24
Larson, Lowell A. (Department: 3725)
Metal deforming
By use of 'flying tool' engaging moving work
Included in plural deforming stations or passes
Reexamination Certificate
active
06263715
ABSTRACT:
The present invention relates to continuous cold-forming of strip material and particularly but not exclusively to sheet metal strip to produce building elements having transverse ribs extending across at least part of the element.
In a continuous cold-forming line for forming such elements a strip is generally passed to a rib-forming stand where the strip is passed through the nip of a pair of cylindrical rolls having respectively a plurality of mating projections and recesses, elongated axially of the rolls and spaced apart on their circumference. Generally the rolls are geared to each other to maintain mating projections and recesses in register with each other thereby portions of the strip material are pushed into the recesses to permanently deform the strip to form the ribs.
However it has been found that continuous cold-forming of transverse ribs in strip by such means generally produces undue residual stresses in the strip, which can cause twisting, buckling and other warping of the formed strip.
A number of prior art proposals have been put forward to continuously cold-form transverse ribs in strip. For example;
U.S. Pat. No. 3,673,838 describes a cold-forming line for continuously forming transverse stiffening ribs on metal strip, the line having a set of transverse rib forming rolls intermediate a back tension roll and a forward tension roll, wherein the strip passing through the nip of the rib-forming rolls is held in tension by the forward and back tension rolls. The forward tension roll and the die roll (one of the rib-forming rolls) form a nip through which the ribbed strip is passed. The forward tension roll engages the back face of the strip devoid of projecting ribs while the ribs remain in recesses in the die roll.
U.S. Pat. No. 3,394,573 describes apparatus for continuously cold-forming transverse corrugations on metal strips, the apparatus having a set of corrugating rolls intermediate a back tension roller set and a forward tension roller set. The formed strip has a web provided with transverse corrugations and cold-formed side flanges. The back tension roller set cold-forms the flanges and tightly holds the strip in the nip between the rollers. The forward rollers conform to the form of the strip passing through the rotating die rolls. That is to say that they are provided with respective mating projections and recesses corresponding to those of the die rolls.
U.S. Pat. No. 4,027,517 also describes cold-forming apparatus for providing strip with transverse corrugations between profiled longitudinal flanges. The apparatus comprises continuous corrugating embossing means and means to hold the strip under tension as it passes through the embossing means. In one of the embodiments described a roll is provided downstream of a downstream tensioning roll to apply “flattening pressure on the sheet metal”. The flattening roll engages only those portions of the sheet that have not been induced into die recesses and portions of the sheet metal between transverse indentations.
U.S. Pat. No. 4,059,000 also describes apparatus for continuously cold-forming transverse corrugations on metal strips, the apparatus including means to maintain the strip in tension as it passes through embossing rolls and straightening/flattening means.
In all the above proposals the strip passing through the nip of the rib-forming rolls is held in tension, and in many, the line is further provided with downstream straightening means.
U.S. Pat. No. 3,137,922 proposes a somewhat different approach in that it proposes a cold-forming/working line for continuously forming metal roof panels having centrally disposed transverse stiffening ribs from metal strip in which the line includes a plurality of flange forming stations, a combined cold-reducing and embossing stand and straightening roll stands. The combined cold-reducing embossing stand is provided with cold-reduction/drawing means to variably elongate the central portion of the strip prior to the strip being passed through the nip of a pair of embossing rolls which provide transverse ribs in said central portion of the strip. The embossing rolls are geared to each other to maintain mating projections and recesses in register with each other. The straightening stand comprises a downstream roll stand having a number of sets of upper and lower rolls engaging only the flanges of the strip to straighten any irregularities in the flanges resulting from the cold working and embossing operations and for drawing the strip through the apparatus. Intermediate the downstream roll stand and the embossing rolls the strip is passed beneath a manually operated downwardly-moveable wooden shoe for engaging the upper surface of the embossed sheet, said upper surface being devoid of transverse ribs, “to relieve rolling stresses resulting from the embossing operation and thus preventing later distortion and twisting of the panel”. Intermediate the flange-engaging portions of the upper and lower rolls in the downstream roll stand there is further provided a manually operable upwardly-acting pad underlying the strip for engagement therewith to assist in the further relief of embossing stresses. Thus when flanges of the strip are gripped by the upper and lower rolls, a lever is manually operated so that the central portion of the strip is engaged by the pad. This proposal addresses the problem of providing transverse ribs by (1) providing upstream pre-conditioning or pre-elongating means for the central portion of the strip prior to that portion entering the rib-forming nip, (2) providing downstream flange gripping straightening means to straighten irregularities and to draw the strip from the rib-forming rolls, thereby tensioning the strip as it passes through the nip of the embossing rolls.
Other problems associated with prior art proposals include the complexity and cost of the cold-forming line and in the latter proposal the need to manually control some of the operations.
The present invention is particularly but not exclusively directed to a method and apparatus for continuously cold-forming strip to produce building elements having a generally channel shaped cross-section comprising a web and side walls in which the web is provided with longitudinally extending strengthening ribs and the side walls are provided with transverse ribs or corrugations extending across at least part of each side wall, of the kind described in Australian patent application number AU 48883/90. In this document each free edge margin of each side wall is flanged by downstream rolls engaging only the edge margins of the strip. It has been found that formed strip issuing from apparatus of this kind is also prone to twisting, buckling and other warping.
An object of the present invention is to addresses one or more of the problems of the prior art.
The present invention provides a cold-forming line for continuously forming metal building elements having transverse ribs extending across at least part of the element from strip, comprising means for forming transverse ribs in the strip and stress relief means for applying compression load to the transverse ribs wherein said stress relief means comprises a first roller means and a second roller means forming a nip for receiving ribbed strip, wherein each roller means is adapted to engage an outer crest portion of each rib projecting towards it.
It is preferred that the second roller means comprises a pair of substantially parallel coextensive spaced apart second rollers.
Preferably the first roller means comprises a first roller, said first roller being substantially parallel to, coextensive with and equi-spaced from each of said second rollers.
It is preferred that each roller applies a compression load to its respective ribs to at least partially relieve stresses in the strip produced by the rib forming means and more preferably the rollers engage only the outer crest portions of the respective ribs.
It is preferred that the second rollers lie in a common plane substantially parallel to the plane of the strip and are spaced apart so that
Larson Lowell A.
Larson & Taylor PLC
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