The invention relates to improvements in suspended ceiling grid members and, in particular, to features for improving the structural integrity and performance of such members.
Grid members for suspended ceilings are typically made from steel strip stock roll formed most commonly into a T-shape that, in use, is inverted. Roll formed sheet metal tees customarily have the vertical portion of their cross-sections made of multiple layers of sheet stock. It is known from U.S. Pat. Nos. 4,489,529, 5,979,055, 6,047,511, and 6,446,407, for example, to secure the double layers of a grid tee together by deforming spaced local areas of the web into stitches for holding the layers in abutting contact. The latter patents disclose the formation of stitches in a strip rolling process.
The invention involves the lancing of multiple layers of a web in a roll formed sheet metal grid runner to create formations that prevent relative movement between the layers and thereby improve the performance of the grid runner. The disclosed lanced formations can be effectively used to improve the torsional rigidity of a grid runner by locating the formations distal from a neutral torsional axis of the runner. Additionally, the lanced formations can serve to maintain the web layers in abutting contact and thereby ensure that the visual appearance of certain types of grid runners remain uniform.
In the disclosed embodiments, the lance is in the form of a tab with an angular profile having one side remaining attached to the main body area of the web and the other sides at least partially cut from the main body of the web and at obtuse angles relative to the attached side. The lanced tab is formed with a bend parallel to the attached side to foreshorten the tab relative to the plane of the web and the opening in the web from which it is cut. This foreshortening of the tab in combination with the obtuse angles of its sides assures that a tight fit between its edges and the edges of the hole is created. The tab is preferably bent so that the tab edge of one web layer abuts the hole edge of another web layer and thereby locks the layers together in particular against relative sliding movement between the layers. By resisting relative sliding motion between the layers, the lanced tabs, when properly located on the web, can give the grid tee relatively high torsional rigidity.
Referring now to the drawings, and in particular to
The web 12 is lanced above the bulb 22 at locations 26 spaced along the length of the runner 10. In the illustrated example, the lance 27 is arranged in groups of four at each location 26. The lances, designated 27, of a group are identical except for orientation; a pair of the lances 27 (at the left in
Each lance or tab 27 is partially cut through each of the layers 16-18. The tab 27 when viewed in a plane parallel to the web 12 preferably has a polygonal profile and at least one side 28 that lies at an obtuse angle with a side 29 that remains uncut. The illustrated tabs 27 are shaped like a dovetail having two opposed sides 28 that are cut at obtuse angles with respect to the uncut side 29. The tab 27 includes a fully cut side 32 extending between the obtuse sides 28 that, in the illustrated case, is parallel to the uncut side 29.
The tabs 27 are formed in two operations. In the first operation, the far edge or side 32 remote from the uncut side 29 and portions of the obtuse edges or sides 28 remote from the uncut side are sheared from the three web layers 16-18. At the same time, the tool shears the tab from the main areas of the web layers, it operates to form the tab material by bending it along a line 33 parallel to the sides 29, 32. The bend 33 requires the tab material on the side of the bend remote from the uncut side 29 to be drawn or to flow towards the bend. The tab 27 is thus foreshortened when viewed in a plane parallel to the plane of the web 12.
The second operation on the lances or tabs 27 involves pressing them back from the condition illustrated in
The section views of
It will be noted that a single one of the lances or tabs 27 is capable of locking the several layers together when formed according to the invention in the described manner. The disclosed arrangement of four tabs affords a high level of redundancy in gripping action to assure reliable interlocking of the layers 16-18.
When an elongated body made of folded or rolled sheet such as the grid runner 10 is subjected to torsion about its longitudinal axis, the layers of the body tend to shift longitudinally relative to one another. When the lances or tabs 27 are used to improve the torsional stiffness of a tee, it is desirable that the tab edges 28 are oriented at acute angles of between, for example, 0 and 45°, to a line perpendicular to the longitudinal direction of the grid runner. This orientation assures that the reaction forces between the tab and opening from which it is cut when a torque is applied to the grid runner work to resist relative longitudinal slippage between the layers. The position of the lanced tabs 27 near the upper extremity of the web 12 and therefore remote from a neutral torsional axis of the grid member enables the tabs 27 to more effectively resist twisting of the grid member.
While the invention has been shown and described with respect to particular embodiments thereof, this is for the purpose of illustration rather than limitation, and other variations and modifications of the specific embodiments herein shown and described will be apparent to those skilled in the art all within the intended spirit and scope of the invention. Accordingly, the patent is not to be limited in scope and effect to the specific embodiments herein shown and described nor in any other way that is inconsistent with the extent to which the progress in the art has been advanced by the invention.
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