Abstract:
A grid runner and method of its manufacture that saves material content with use of a serpentine sheet metal web configured to be essentially scrapless and that results in a parallel chord truss-like construction with open spaces between an upper reinforcing bulb and a lower flange.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to suspended ceiling grid construction. 
     PRIOR ART 
     Suspended ceilings typically include a rectangular metal grid on which are supported ceiling tiles or drywall panels. The commercial construction industry is highly competitive and, accordingly, the cost of building materials in this sector is important. Raw material consumption, particularly material without a large recycled content, is likewise a concern for preservation of the environment. Accordingly, there is a need for suspended grid products that consume less material and can be economically produced. 
     SUMMARY OF THE INVENTION 
     The invention is embodied in a suspended ceiling grid runner having a material saving open web construction. The inventive grid runner is an elongated assembly of main parts comprising a lower face flange, an upper reinforcing bulb and an open web extending vertically between the flange and bulb. The web has a novel serpentine configuration extending alternately from the flange to the bulb and from the bulb to the flange. The web is fixed to the flange and bulb at each juncture. By virtue of its serpentine configuration, the web is characterized by open spaces along the length of the runner that represent significant material savings. In the preferred runner construction, the flange and bulb are roll formed sheet metal strips while the web is a flat, stamped strip. These components are assembled together in a press that clinches the parts together at locally overlapping points. 
     The web strip is sheared from sheet stock, preferably supplied from a coil. The shear has specially shaped cutting edges corresponding to the serpentine form of the web. By way of example and not limitation, the web sheet stock is fed to a shear in ¾ in. increments while producing a web 1⅜ in. high without scrap. The inventive runner is advantageously assembled in a press operation that also performs the traditional cross tee slot and hanger hole punching. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a fragmentary side elevational view of a grid runner constructed in accordance with the invention; 
         FIG. 2  is an end view of the grid runner of  FIG. 1 ; 
         FIG. 3  is a cross sectional view of the grid runner taken in the plane  3 - 3  indicated in  FIG. 1 ; 
         FIG. 4  is a diagrammatic representation of a shearing process used to make a serpentine web of the inventive grid runner; 
         FIG. 5  is a diagrammatic representation of the assembly of three web inserts used in the construction of the main runner embodying the invention; and 
         FIG. 6  is a cross sectional view of a typical clinch joint between the web and the bulb or the flange of the grid runner. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A grid runner  10 , illustrated in  FIGS. 1-3 , is used in a conventional manner to construct a rectangular grid for a suspended ceiling. The illustrated grid runner  10  has the shape of an inverted tee in the orientation it is used. The grid runner  10 , which typically can have a height in the order of 1 9/16 in. can be provided as a main runner and have a nominal length of 12 ft. The runner  10  is an assembly of three main elongated parts comprising an upper hollow reinforcing bulb  11 , a lower face flange  12 , and a vertical web  13  extending between the bulb  11  and flange  12 . Identical end connectors  14  are provided on each end of the runner  10  (only one end is shown in  FIG. 1 ). The connectors  14  may, for example, be of the type illustrated in U.S. Pat. No. 6,729,100. 
     Preferably, the bulb  11  and flange  12  are each made by roll forming a single sheet metal strip, usually steel, with conventional techniques well known in the industry. The flange  12  can be pre-painted prior to roll forming on a side visible when installed. The bulb is hollow with a circular cross section. The bulb  11  can be formed with various other cross sectional shapes such as an oval, rectangle, triangle or other polygon. The bulb  11  is preferably formed with the hollow space essentially closed. The bulb  11  includes a depending rib  16  that lies in a vertical plane bisecting the hollow part, the latter comprising the bulb proper. 
     The illustrated flange  12  has the shape of an inverted short tee. In use, the flange commonly becomes the visible face of the grid runner  10  where the grid runner is used with ceiling tiles. A horizontal part  18  of the flange  12  extends widthwise, i.e. transversely to the longitudinal direction of the runner and symmetrically about a vertical upstanding stem or rib  19 . One side  21  of the horizontal flange part  18  is a double wall or two ply construction while an opposite side  22  is a single wall with a folded back hem  23  at an edge distal from the rib  19 . In ordinary use of the runner  10  in a suspended ceiling, edges of rectangular ceiling panels or tiles rest on upper surfaces of the flange horizontal part  18 . 
     The web  13  is a flat sheet metal stamping that serves to hold the bulb  11  and flange  12  in spaced relation in the manner of a parallel chord truss. Referring to  FIG. 4 , the web  13  is formed by shearing a strip from a sheet of steel or other metal  25 , typically from coil stock. The web strip is sheared along a serpentine line symmetrical with a line that is perpendicular to the feed direction of the sheet stock indicated by the arrows  26  from the supply coil. Alternatively, the serpentine strip or web can be sheared from a flat non-coiled sheet stock although this will involve greater scrap due to cuts at the end of the sheet stock. The serpentine cut profile of the web  13  is cut such that its top and bottom edges have the same geometry. This results from the sheared edge remaining on the stock supply becoming one of the edges of the next sheared web piece. 
     In profile, the web  13  can be described as having crests  31  and valleys  32  that, in the illustrated case, are flat at their respective top and bottom edges. The serpentine pattern of the web  13  allows the web to span, from the outside edges of the valleys  32  to the outside edges of the crests  31  a distance of 1⅜ in., for example, while the stock need only be fed ¾ in., for example, to produce this span. When assembled, the web crest flats and valley flats can abut the bottom of the bulb  11  and top of the single ply flange side  22 , respectively. 
     The grid runner  10  is assembled in a press of a length adequate to span the length of the grid runner. The disclosed grid runner construction is ideally suited for main runners which are nominally 12 ft. long or industry metric equivalent. When the runner  10  is this long, it is practical to use 2 or 3 web sections  33  arranged end to end. Making the full length web  13  from the sub-parts or sections  33  enables the use of light gauge coil stock of a conventional width. Preferably, the web sections  33  are slightly overlapped at their adjacent ends when assembled into a grid runner  10 .  FIG. 5  illustrates three web sections  33  with their adjacent ends aligned to be overlapped and joined in a single main runner  10 . 
     With reference to  FIG. 1 , the web  13  is fixed to the bulb  11  and flange  12  in a press. The web crests  31  are fixed to the bulb rib  16  and the valleys  32  are fixed to the flange rib  19 .  FIG. 6  illustrates a typical permanent clinch joint  30  made by a known technique such as that marketed under the trademark TOX® (a registered trademark of Pressotechnik GmbH &amp; Co. KG). The technique involves lapping these members and driving a part of the web into respective parts of the bulb and flange ribs  16 ,  19 . The same clinch location can be used to join the overlapped ends of the web sections  33  to a bulb rib or a flange rib. Cross tee slots  34  are preferably punched from the side of the runners from which the web  13  is assembled to simplify this punching operation. Hanger holes, not shown, can be punched in the bulb rib  16  and any overlying portion of the web  13  during the press operation. The end connectors  14  are metal plates assembled on the ends of the bulb  11  and flange  12 , preferably with the clinch shown in  FIG. 6 . The end connectors  14  can be of the general type shown, for example, in U.S. Pat. No. 6,729,100. 
     It is envisioned that a material savings up to about 30% can be obtained with the serpentine web  13  as compared to constructions having a conventional web with no large open areas. While the foregoing disclosure involves a main runner or main tee, the serpentine open web construction can be used to construct cross runners. The flange can have different cross sectional configurations other than the illustrated simple tee. Such configurations can include a downwardly open channel, sometimes referred to as a screw slot runner. 
     It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.