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You are an expert at summarizing long articles. Proceed to summarize the following text: 
This application is a divisional of U.S. patent application Ser. No. 11/283,619, entitled “GRID TEE FOR SUSPENSION CEILING,” filed Nov. 21, 2005, hereby incorporated by reference. The invention relates to suspended ceiling systems and, in particular, to an improved grid tee. 
    
    
     BACKGROUND OF THE INVENTION 
     Prior Art 
     Suspended ceilings, extensively used in commercial buildings, typically employ a rectangular grid system that supports lay-in ceiling panels or tiles. The grid is made up of regularly spaced runners intersecting at right angles. The runners are ordinarily in the form of inverted tees. The tees are normally suspended by wires and the ceiling panels or tiles rest on the flanges of the tees. 
     The suspended ceiling products industry has refined the design and manufacture of grid tees to a high degree. The continuous efforts for improvement have contributed to the high acceptance of these ceiling systems in the construction industry. Challenges have remained in creating improvements in the performance and in reducing the cost of the grid systems. 
     SUMMARY OF THE INVENTION 
     The invention provides an improved grid tee for suspended ceilings that, compared to prior art constructions can facilitate installation of lay-in tiles, can be produced with less material cost and can obtain greater strength and rigidity. The invention, in one design, utilizes a single strip of sheet metal folded on itself in such a manner that the bending and torsional stiffness as well as suspension wire breakout can be increased even while metal content can be decreased. The folded cross-section of the single strip design advantageously employs the visible face of the tee as a primary structural element so that the face serves to increase rigidity. Employing the face material as a structural element is particularly advantageous because the face material is at a location where it can be of maximum benefit as it contributes to the polar moment of inertia. The longitudinal edges of the strip are folded into mutual contact and are locked together both laterally and longitudinally, thereby significantly increasing the torsional stiffness of the tee. 
     Multiple layers of sheet material at the top of the inverted tee section permit suspension wires to be threaded through this area without the risk of low breakout strength. The multiple layer top edge surmounts a laterally extending reinforcing bulb. This geometry avoids the necessity of wrapping the bulb itself with a loop of suspension wire. As a result, the suspension wire loop can be smaller than the width of the bulb. Consequently, the ceiling tiles can be easily and quickly installed or removed without damage or difficulty from interference with what otherwise would be an oversize wire loop of suspension wire. As disclosed, the inventive feature of a narrow top wire receiving stem portion can be applied to other tee constructions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a grid tee constructed in accordance with the invention; 
         FIG. 2  is a cross-sectional view of the grid tee on an enlarged scale; 
         FIG. 3  is an enlarged elevational view of a part of an upper portion of the grid tee; 
         FIG. 4  is a cross-sectional view of the upper portion of the grid tee taken on the plane  4 - 4  indicated in  FIG. 3  showing one manner of locking the grid tee layers together; 
         FIG. 5  is a view similar to  FIG. 4  with another example of a manner of locking the layers of the grid tee upper portion together; 
         FIG. 6  is a perspective view of a section of a grid tee in accordance with another embodiment of the invention; 
         FIG. 7  is a cross-sectional view of the grid tee taken in the plane  7 - 7  indicated in  FIG. 6 ; 
         FIG. 8  is a cross-sectional view of a modified grid tee; 
         FIG. 9  is a cross-sectional view of another modified grid tee; 
         FIG. 10  is a cross-sectional view of a further modified grid tee; and 
         FIG. 11  is a cross-sectional view of still another modified grid tee. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A grid tee  10  is preferably formed of a sheet metal strip which can be galvanized or otherwise treated to resist corrosion. The tee  10  is made, preferably by roll-forming techniques known to those skilled in the art, into the cross section illustrated, for example, in  FIG. 2 . A center section  12  of the strip  11  is preferably painted before the strip is formed into the tee cross-section. The painted center section  12  forms a visible face  13 . The sheet metal strip  11  is folded back on itself at opposed edges of the face  13  to form a double layer flange  14  extending laterally on opposite sides of a central web or stem  16 . Inner layers  17  of the flange  14  extend from the laterally outward extremities of the flange to a central imaginary plane  18  and preferably abut the outer layer or center section  12  substantially along their full widths. The inner layers  17  of the flange  14  intersect at the imaginary plane  18  where the sheet metal strip is bent at right angles to form the web  16  as double layers  19 ,  20 . At a distance above the flange  14 , preferably greater than about half the total height of the web  16 , the web layers  19 ,  20  are each formed with a channel  21  open on an inside face. The channels  21 , ideally, are mirror images of one another symmetrically disposed about the central imaginary plane  18  and cooperating to form a hollow reinforcing bulb  22 . The illustrated bulb  22  is generally circular in cross-section but can have other shapes such as rectangular. 
     At an upper portion  24  of the web  16  above the bulb  22 , the two web layers  19 ,  20  abut at or adjacent the imaginary central plane  18  for a vertical distance that, in the illustrated case, is the about the same as the vertical extent of the bulb  22 . The layer  20  of one side of the web  16  is somewhat wider than the other side enabling an excess width part  26  to be folded over the other layer  19 . As a result, the upper edge of the web  16  comprises three layers of sheet stock. The layers  19 ,  20  and  26  at this upper edge portion  24  of the web  16  are fixed relative to each other by lanced tabs  31  cut through the material of these layers with suitable punches. Each lanced tab  31  can be distorted to foreshorten it and then be set back partially into the plane of the web  16  but out of registration with its original layer so that it is locked against the edge of an adjacent layer thus locking such adjacent layers from moving in the longitudinal direction of the tee relative to each other as well as in any other direction relative to one another. In the illustrated example, the lanced tabs  31  are in groups of four, a pair on the right is displaced above the plane of the drawing of  FIG. 3  as shown in  FIG. 4 . The pair at the left are similarly spaced below the plane of the drawing. 
     The lower part of the web  16  is formed with longitudinally spaced slots  36  aligned through both layers  19 ,  20  for receiving end connectors of cross tees as is conventional. Holes or apertures  37  are punched or otherwise formed in the upper part  24  of the web  16  spaced along the length of the tee  10 . These holes  37  are provided for suspending the tee  10  and ultimately the ceiling tiles supported on the tees, with wires such as that shown in  FIG. 2 . The disclosed arrangement wherein the suspension wires  38  are assembled through flat, vertical abutting layers  19 ,  20 ,  26  of the web  16  above the reinforcing or stiffening bulb  22 , permits the profile or spread of a wire loop  39  around the upper web portion  24  to be relatively narrow and have less width in a plane transverse to the longitudinal direction of the tee than the width of the bulb  22 . This is a significant advantage when installing and removing ceiling tiles since interference between the wire loops  39  and tile is effectively eliminated and, the risk of damage to the tile is effectively avoided. This feature can reduce overall installation time and cost of a ceiling system. 
     Various methods, besides the lanced tabs  31 , can be used to lock the sheet metal layers  19 ,  20  and  26  at the upper region  24  of the web  16  together so that there is no longitudinal slippage of these layers relative to one another.  FIG. 5  illustrates one alternative for locking these layers  19 ,  20  and  26  together and is disclosed in greater detail in U.S. Pat. No. 6,041,564. A hole  40  is pierced through these layers  19 ,  20  and  26 , and the material of one layer  19  is formed into an integral rivet or eyelet  42 . The hole  40  can be used for suspending the grid tee by threading the suspension wire  38  through it. U.S. Pat. Nos. 5,979,055 and 6,047,511, for example, show other methods of locking the stem layers together with material integral with the stem. Alternatively, the layers  19 ,  20  and  26  of the upper region or portion  24  can be fixed against relative movement by other methods such as with separate fasteners, welding, and/or adhesives, for example. With the layers of the stem or web  16  fixed together, the torsional stiffness of the tee or grid member is increased from what would occur where the layers were free to slide relative to one another. 
       FIGS. 6 and 7  illustrate a second embodiment of a grid tee  50 , constructed in accordance with the invention. The tee is formed of a single metal strip  51  preferably with its center region painted on one side to finish a face  52  of an exposed layer  53 . The strip is ideally galvanized or otherwise finished prior to finish painting to avoid corrosion. The strip  51  is preferably shaped by roll-forming techniques, and is folded back on itself to form opposite sections  54  of a lower flange  56 . Inner flange layers  57  ideally abut the face layer  53  along substantially their full width, which is short of half the width of the face layer. At interior edges of the inner flange layers  57 , the tee sheet material is bent up vertically to form respective sides  58  of a hollow bulb  59  forming a lower section of a web or stem  61 . At the top of the bulb  59 , layers of the sheet or strip  51  are turned towards a central imaginary plane  62  and at the central plane are then folded or bent upwardly so that sections  63  of the metal strip  51  form an upper region  65  of the web  61 . The web upper region layers  63  are fixed together by integral rivets or grommets  60  each formed from the material of one layer  63  displaced through a hole in the other layer and then upset or clinched to form a flange  64  on the outer side of the other layer. The upper region  65  of the web  61  can be constructed like the analogous region  24  of the tee  10  shown in  FIG. 2 , if desired, thereby comprising three layers in this web region. A suspension wire  38  can be passed through a selected hole or aperture  66  of a rivet  60  and looped around a portion of the upper web section as shown in  FIGS. 6 and 7 . As with the grid tee  10 , the upper portion  65  of the web  61  can have its layers locked together with other alternative or supplemental techniques such as staking, use of separate fasteners, welding and/or adhesives, for example. Along the length of the tee  50  at regularly spaced centers, such as every six inches the sides  58  of the hollow bulb  59  are locally deformed with oval or oblong depressions  71  of sufficient depth to cause the sheet material of each of the sides  58  to abut. The depressions  71  are of sufficient height to allow a vertical slot  72  to be formed in each of the layers of the sides  58  for the reception of end connectors of cross tees. The height and width of the depressions  71  is sufficient to receive an end connector and allow it to pass through the respective slot  72 . Less than all of the holes formed in the upper region of the web can be clinched in the manner of a grommet. 
     The ends of the tees  10  and  50  can be provided with standard connectors; typically the ends of the tee  50  are flattened by pressing the walls or sides  58  together to accommodate a standard connector. 
       FIGS. 8-11  illustrate additional alternative embodiments of tee constructions. In  FIG. 8 , a sheet metal tee  75  formed in the manner described above has a flange  76  and a stem  77  including a hollow bulb portion  78  and an upper portion  79  formed of a single strip of metal stock. The strip is doubled on itself, as described above, in the flange and stem areas apart from the hollow bulb  78 . The upper stem area or portion  79  is sandwiched by a separately formed inverted U-shape metal channel  81 . The channel  81  can be roll formed from a sheet metal strip. The layers of the upper stem portion  79  and channel  81  are fixed together by any of the methods of the previously described tees. 
     A tee  85  depicted in  FIG. 9  is similar in construction to the tee  75  of  FIG. 8  and has certain parts designated with the same numerals. The upper stem portion  79  has its layers reinforced by an intermediate strip  86  preferably of a suitable metal such as steel. As before, the abutting layers of the upper portion of the stem  79  and strip  86  are locked together by one of the techniques described above. 
       FIG. 10  illustrates an extruded tee  90  having a flange  91  and stem  92 . The stem  91  includes a hollow bulb  93 . The tee  90  can be formed of aluminum or other suitable metal or plastic. 
       FIG. 11  illustrates still another tee  95  formed, like earlier described tees of strips of roll formed metal sheet stock. The tee  95  comprises a main body strip  96  and a cap strip  97 . The main body strip  96  forms an upper or inner layer of a flange  98  and a stem  99 . The cap strip  97  forms the cover or outer face layer of the flange  98  and includes opposed in-turned hems  101  that lock the cap strip  97  on the main strip  96  and the adjacent areas of the stem  99  together. The stem  99  includes a hollow bulb  102  and an upper portion  103 . 
     In each of the arrangements of  FIGS. 8-11 , holes  106  can be spaced along the length of the tee in the upper stem portion and any associated structure. Suspension wires  38  can be looped through such holes  106  in the upper portion of the tee stem or web above a hollow bulb. This feature, as in the arrangements of  FIGS. 1-7 , permits the wire loop  39  to be at least as small in width as the width of the respective bulb thereby avoiding interference with installation or removal of a ceiling tile. 
     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. For example, the upper edge region of the web can be formed with more than three layers of sheet metal by making additional folds. 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.

Summary:
In one embodiment, a roll-formed sheet metal tee for grid type suspended ceilings with the face of its flange integral with the stem and the layers of the stem fixed together for improved torsional strength. An upper region of the stem can have one or more of its layers folded to increase suspension wire breakout strength. A stiffening bulb is below suspension wire receiving holes so that a loop of the suspension wire through the tee has a narrow profile and thereby avoids interference with ceiling panels during their installation or removal. Other embodiments of a tee share the feature of a narrow, suspension wire receiving upper stem portion.