Abstract:
A roll formed sheet metal grid tee, having a multilayer web, is rigidified by a series of longitudinally spaced tabs lanced through the web. The tabs are cut with a dovetail shape and are foreshortened relative to the holes, made when they are formed, by bending them along a line parallel to a side of the tab that remains uncut. After being foreshortened, the tab is pressed back into its associated hole and tight locking interference is developed between the divergent dovetail sides of the tab and the hole. The tab is incompletely pushed back into the hole so that the layers of the tab are misaligned with corresponding respective layers of the web to assure that the tabs prevent relative shear-like movement and/or spreading of the web layers.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     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.  
       PRIOR ART  
       [0002]     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.  
       SUMMARY OF THE INVENTION  
       [0003]     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.  
         [0004]     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. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIG. 1  is a fragmentary perspective view of a grid tee embodying the invention;  
         [0006]      FIG. 2  is an enlarged fragmentary view of an area of the web of the tee of  FIG. 1  after being lanced;  
         [0007]      FIG. 3  is a cross-sectional view of grid tee lanced tabs in an intermediate formed condition taken in the staggered plane  3 - 3  in  FIG. 2 ;  
         [0008]      FIG. 4  is a cross-sectional view of other grid tee lanced tabs in an intermediate formed condition taken in the staggered plane  4 - 4  as indicated in  FIG. 2 ;  
         [0009]      FIG. 5  is a somewhat schematic enlarged view of one of the lanced tabs of  FIG. 2 ;  
         [0010]      FIGS. 6 and 7  are views similar to  FIGS. 3 and 4 , respectively, illustrating the lanced tabs in their final configuration pressed back towards the plane of the web;  
         [0011]      FIG. 8  is a fragmentary perspective view of a second embodiment of a grid tee embodying the invention; and  
         [0012]      FIG. 9  is a fragmentary cross-sectional view of a lanced tab area of the tee taken in the plane  9 - 9  indicated in  FIG. 8 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     Referring now to the drawings, and in particular to  FIG. 1 , there is shown a form of a grid runner  10  in the general shape of an inverted tee. The grid runner or tee  10  includes a lower horizontal flange  11  and a vertical web  12 . The body of the tee is preferably formed as a single strip of mild steel sheet roll formed into the illustrated profile. The sheet stock is folded on itself at each lateral side or section  13  of the flange  11  so that these flange sections are double layers. Similarly, the web  12  is a structure of double layers  16 ,  17  apart from where its upper region includes a third layer  18 . These three layers  16 - 18  exist between an upper edge  19  of one of the two main layers  16  and a downwardly facing edge  21  of the third or minor layer  18 . The third layer  18  is an integral extension of one of the double or main layers  17  and is folded downwardly over the upper edge  19  of the other major layer  16 . As seen in  FIG. 1 , for example, the layers  17 ,  18  sandwich and laterally trap the other layer  16 . The web  12  includes a reinforcing bulb  22  formed of opposed integral ribs rolled in the respective layers  16 ,  17 .  
         [0014]     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  FIG. 2 ) are displaced into the space below the plane of the drawing and the other pair of lances (at the right in  FIG. 2 ) are disposed into the space above the plane of the drawing. Each lance or tab  27  of a pair is oriented 180°, in a vertical sense, from the other tab.  
         [0015]     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 .  
         [0016]     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 .  
         [0017]      FIG. 5  is a diagrammatic illustration of this foreshortening effect where the cut edge or side  32  is displaced vertically from its corresponding edge  34  on the body of the web  12 . The theoretical area  36  lying between the obtuse tab edges  28  and corresponding web hole edges  37  is a measure of the tight interference that can be obtained with the disclosed technique of forming the tab  27  to foreshorten it.  
         [0018]     The second operation on the lances or tabs  27  involves pressing them back from the condition illustrated in  FIGS. 3 and 4  towards the plane of the web  12 . The tabs  27  can be returned through a distance of about 75 to 80% of the distance they are originally displaced from the plane of the web. Preferably, the tabs  27  are bent back so that as depicted in  FIGS. 6 and 7 , the tab layers are misaligned relative to the layers of the web. In particular, the tabs  27  are pushed back so that the middle layer of a tab straddles the middle layer  16  and one of the outer layers  17  or  18  of the web  12 . With reference to  FIG. 6 , in the lanced region the upper part of outer layer  18  and the lower part of outer layer  17  cannot move longitudinally relative to the middle layer  16  because they are trapped by the inner layer of the tabs  27 . With reference to  FIG. 7 , in the lanced region, the lower part of the outer layer  18  and the upper part of the outer layer  17  cannot move longitudinally because they are trapped by the inner layer of the tab  27 . The central layer of each tab  27  is reinforced and stabilized by the other two layers helping it to resist lateral deflection out of its final formed position straddling one or the other outer layers  17  or  18  of the web  12  at the opening formed by the respective tab.  
         [0019]     The section views of  FIGS. 3, 4  and  6 ,  7  are taken in vertical planes for clarity. It will be understood that the above discussion of the offset and straddling by the middle tab layer of the middle web layer  16  and one or the other outer web layers  17  or  18  is applicable at the interface between the tab edges or sides  28  and the edges of the opening corresponding to these tab edges.  
         [0020]     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 .  
         [0021]     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.  
         [0022]      FIG. 8  illustrates another embodiment of the invention applied to a grid runner or tee  41 . The grid runner  41 , in a generally conventional manner, includes a main body  42  and a cap strip  43 . The main body  42  is roll formed from a single sheet metal strip and includes a hollow bulb  44 , a double wall or layer web  46  and single layer flange portions  47 . The flange portions  47  are covered with the cap strip  43  which is folded over the outer edges of the flange portions  47  by a rolling process. The double layer web  46  is provided with lanced tabs  48  configured and grouped as described above in reference to the grid runner  10 . The tabs  48  differ from the tabs  27  in that they comprise only two layers of sheet metal as shown in  FIG. 9  but retain the dovetail profile so as to include an edge on each of its opposite sides at obtuse angles to the attached side.  FIG. 9  illustrates cross-sections of two typical lanced tabs  48 . As seen there, the tabs  48 , after being formed, are pushed back towards the plane of the web  46  so that one layer of each of the tabs is mechanically locked in a position where it straddles the two layers of the web. The lanced tabs  48  are preferably located near the flange portions  47  so that they are as far as practical, spaced from a neutral torsional axis to obtain greater effectiveness in resisting twisting about the longitudinal axis of the tee. Besides serving to torsionally stiffen a grid tee, the tabs can be useful in preventing the web layers from spreading apart which function can be especially important in certain special grid tee configurations such as disclosed in U.S. Pat. No. 4,535,580, for example. It will be understood that the tabs can be formed in a stamping press when other stamping operations are being performed on the grid tee.  
         [0023]     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.