Abstract:
A suspended ceiling system comprising grid runners and downwardly accessible generally planar tiles mounted on the grid runners, peripheral tile edges having portions extending horizontally underneath an adjacent grid runner, opposed tile edges having a downwardly facing support surface, said opposed edges having a generally vertical abutment surface above its support surface and resting on an adjacent horizontal flange portion of a grid runner, the runners having locating surfaces of limited height above said flange portions and engageable with the abutment surfaces, the runners and tiles being arranged to permit one of the opposed tile edges to be lifted so that its abutment surface can be raised and thereafter be shifted towards the runner adjacent the lifted edge a distance sufficient to allow the opposite edge to drop below the flange portion of its associated runner.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to suspended ceiling grid tee and tile structure of a type, useful in applications where overhead clearance is limited, that can be removed downwardly. 
     PRIOR ART 
     Suspended ceilings typically comprise a metal grid of intersecting runners, usually in the form of inverted tees, and rectangular tiles supported on the grid runners or tees. 
     Downwardly accessible lift-and-shift tiles have been developed. Examples of such prior art are shown in U.S. Pat. Nos. 6,108,994 and 6,389,771, for example. Downward accessibility offers the recognized benefits of a suspended ceiling with removable and/or replaceable tiles and, additionally, the ability to be used where overhead clearance is limited. Among other benefits, this low clearance feature can be used in the original design of a building to save height at each floor level. In a high rise building, this height reduction can amount to a considerable savings of material and, therefore, overall construction costs even when only a few inches per floor level are involved. Additionally, by their nature, downwardly accessible tiles can be made to conceal parts of the faces of the grid tees to thereby obtain a different and, often, a richer or more refined appearance. 
     Prior art downwardly accessible ceilings have relied on tiles with multi-stepped kerfs or rabbeted edges to achieve their requisite functionality of being both self-centering and slightly liftable for shifting to provide access. These stepped edges can be difficult to manufacture with the required dimensional tolerances and can be susceptible to damage during shipment, handling, and installation. Accordingly, there remains a need for a downwardly accessible ceiling system that can be manufactured more easily and is more robust when being transported or otherwise handled. 
     SUMMARY OF THE INVENTION 
     The invention provides a downwardly accessible lift-and-shift suspended ceiling system that simplifies tile construction and thereby reduces manufacturing costs and difficulties as well as potential damage from mishandling. The invention achieves these benefits by assigning part of the tile centering function, in a unique manner, to specialized centering elements on the grid tees. 
     More specifically, in accordance with the invention, the grid tees are provided with locating surfaces on the top or backside of their flanges spaced laterally a predetermined distance from the plane of a central web and a predetermined distance from the distal edge of their respective flange portions. The locating surfaces are positioned in relation to the upper edge surfaces of the tiles associated with the kerfs or grooves to properly center a tile in the grid space. 
     The locating surfaces can be formed integrally with the grid tees or can be provided on separately formed bracket or clip attached to the tees when the grid tees are manufactured or in the field when the grid is originally installed or as a retrofit to an existing grid installation. 
     With the locating surfaces serving to horizontally position the tiles in the grid, the rabbets need less complexity in their shapes and are, therefore, easier to cut and involve less dimensional control. Besides being less susceptible to damage when being handled, ceiling tiles constructed in accordance with the invention with a proper kerf or edge design that do sustain physical damage that might detract from their ability to be properly centered when installed on a grid are readily seen and, therefore, can be corrected, or can be rejected by the installer before being installed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a fragmentary edge view of a pair of ceiling tiles and a grid tee constructed in accordance with the invention; 
         FIG. 2  is a view similar to  FIG. 1  showing an intermediate step of mounting or demounting a tile; 
         FIG. 3  is a view similar to  FIGS. 1 and 2  showing the opposite end of the tile shown in  FIG. 2 , in the intermediate step; 
         FIG. 4  is an end view of an alternative embodiment of a grid tee in accordance with the invention; 
         FIG. 5  is a perspective view of a first form of a clip usable with a conventional grid tee to practice the invention; 
         FIG. 6  is a perspective view of a second form of a clip usable on a standard grid tee to practice the invention; 
         FIG. 7  is a fragmentary edge view of a pair of tiles and the clip of  FIG. 6  installed on a conventional grid tee, and 
         FIG. 8  is a perspective view of an example of a ceiling tile for use in practicing the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the figures, a suspended ceiling system  10  comprises ceiling tiles  11  carried on grid tees  12 . A pair of ceiling tiles  11 , partially shown in  FIGS. 1-3 , and fully in  FIG. 8 , are mounted on grid tees, one of which is shown in  FIGS. 1-3 . The tiles  11  are of any rigid relatively low density composition, known in the art, and typically have acoustic and fire-resistant properties. The tiles  11 , as shown in  FIG. 8 , are generally planar and rectangular in plan view, being typically nominally 2 foot by 2 foot (or metric equivalent) square or rectangular with 2 foot by 4 foot (or metric equivalent) nominal dimensions. The tiles  11  have edge details that are the same at opposite parallel edges but, with respect to a specific edge, is different at adjacent perpendicular edges. Tile edges TE 1  correspond to rabbeted grooved edges shown in  FIGS. 1-3 , and tile edges TE 2  are simply rabbeted, preferably with a square cut, and can be devoid of any groove or undercut. Vertical edge surfaces  16  on the non-grooved edges TE 2  are arranged to center the respective tile  11  between grid tees  12  that are adjacent to them when installed on a grid by contacting the edges of the flanges of these tees. 
     The grid tee  12  of  FIGS. 1-3 , which can be a main tee and/or a cross tee is preferably roll-formed of sheet metal strips. The tee  12  has a main body  17  and a cap  18 . The strip of the main body  17  is fashioned to include a horizontal lower flange  19 , a vertical web  21  and an upper hollow reinforcing bulb  22 . The cap or strip  18  covers the lower side of the main body flange  19  and wraps over marginal edge portions of the upper side of the flange. Marginal edge areas of the cap or strip  18  are turned up to form a short vertical flange  23 , at each side of the tee  12 , running continuously along the length of the tee and spaced a predetermined distance laterally in from the distal edge of the flange  19  and outwardly from the web  21 . The height of the vertical flange  23 , measured from a lower visible face  24  of the cap  18  is less than the width, measured vertically, of a groove  26  in each of the grooved, rabbeted tile edges TE 1 . 
     The tile  11  illustrated in  FIGS. 1-3  and  8  has its lower vertical edge surface  28  laterally outward of an upper vertical edge surface  29 . The depth of the groove  26 , measured horizontally from the upper edge surface  29 , is preferably at least as large as the distance from a distal edge  31  of the capped flange  19  to an adjacent face of the web  21 . 
     As shown in  FIG. 1 , the vertical position or elevation of the tile  11  in the grid is established by a downwardly facing side  32  of the groove  26  resting on an upwardly facing side of a return or hem area  33  of the cap  18 . When the tile  11  is installed, the upper vertical surfaces  29  of the tile edges TE 1  abut or are spaced a small predetermined dimensional tolerance from an outer locating surface  34  of the cap vertical flange  23  thereby causing the tile to be centered in the respective grid space in the respective horizontal direction between the opposed grooved edges TE 1 . 
     The tilted tile  11  depicted at the left in  FIG. 3  can be understood to be the same tile as the tilted tile on the right in  FIG. 2 . Thus, the grid tee  12  shown in  FIG. 3  is parallel to the tee  12  in  FIG. 2  and is spaced therefrom by the selected grid module, typically  2  foot or metric equivalent.  FIGS. 2 and 3  show an instantaneous intermediate position or step in the mounting or dismounting of a tile  11  on the grid tees  12 . By lifting the edge TE 1  of the tile  11 , as shown in  FIG. 3 , the tile can be shifted horizontally until the upper vertical edge face  29  abuts the adjacent tee web  21 . This horizontal shifting permits the left edge TE 1  of the tile  11 , as shown in  FIG. 2 , to be lowered off of the flange  19 , including the cap  18 , of its respective tee  11 . Once the left edge TE 1  of the tile  11  is further lowered somewhat from that shown in  FIG. 2 , it can be shifted horizontally to the left until the right side is clear of the respective flange  19  and cap  18 . Then, the whole tile  11  can be completely removed. The steps for installation of a tile  11  are reversed from that discussed immediately above. It will be appreciated that when the tile  11  is lowered or raised in a tilting motion or in translation, the panel edges TE 2  are unhindered in vertical movement by their adjacent grid tees. 
       FIG. 4  depicts grid tees  36  with a modified form of cap  37  from that shown in  FIGS. 1-3 . The same numerals are used to designate the same or like parts of the tees  36 . The cap  37  has horizontal flanges  38  extending from upper edges of vertical webs  39  and running continuously along the length of the tee  36 . The grid tee  36  can be used with the tile  11  in essentially the same way as that described in connection with  FIGS. 1 and 3 . 
     More specifically, the tile  11  is centered with the grid tee  36  by restraint, within appropriate dimensional tolerances, between the upper vertical edge surface  29  and outwardly facing locating surfaces  40  of the vertical cap webs  39 . 
       FIG. 5  shows a separate clip  41  that can be installed on a conventional grid tee  45 , i.e. a tee without the vertical cap flanges  23  ( FIGS. 1-3 ) or vertical webs  39  ( FIG. 4 ). The clip  41 , which can be stamped out of sheet metal or can be molded of a suitable rigid plastic, includes a generally planar rectangular main body  42  and a set of oppositely facing, diagonally disposed upstanding U-shaped grips  43  and oppositely facing diagonally disposed vertical stops  44 . The clip or bracket  41  is installed on a grid tee  45 , typically of a standard cross-sectional profile, by pressing a top surface of the body  42  towards the lower face of the tee flange while its longitudinal axis is at an angle to the longitudinal direction of the tee. The clip  41  is then rotated so that the upper parts of the U-shaped grips  43  slide over the tops of the tee flange and then the short legs or stops  44  snap up and against the adjacent edges of the flange to thereby fasten the clip to the tee. A plurality of clips  41  are positioned at regularly spaced locations along a grid tee  45  so that preferably at least two clips are situated to be engaged by one edge TE 1  of a tile  11  to locate the tile properly. The U-shaped grips  43 , spaced inwardly from their outward extremities represented by generally vertical bights  46 , have generally upright legs  47  that provide vertical tile locating surfaces  48 . These uprights or legs  47  have their locating surfaces  48  in positions like the vertical locating surfaces  34  and  40  of the tees  12  and  36 , respectively, so that they perform the same tile locating functions as these latter surfaces. 
       FIG. 6  illustrates another version of a clip  51  that can be used with a grid tee  45  of a standard conventional inverted tee configuration. Overall, the clip  51  has an inverted U-shape when viewed on edge as in  FIG. 7  where the clip is shown installed on a grid tee  45  of conventional geometry. The clip or bracket  51  can be stamped out of steel sheet or can be molded of a suitable rigid plastic. At an upper end, the clip  51  has a bight or bridge section  53  proportioned to fit over the reinforcing bulb  54  of the tee  45 . Depending legs  56  extending from the bight  53  converge towards an imaginary central plane of the clip  51 . Lanced out of or projecting from the mid-section of the legs  56  are tabs  57  bent inwardly towards the imaginary mid-plane of the clip  51 . Free ends of the tabs  57  are spaced sufficiently below the upper bight  53  so that they can snap under the reinforcing bulb  54  and thereby retain the clip  51  in position on the tee  45 . 
     At their lower ends, the opposed legs  56  each include a generally horizontal foot  58  and at the distal end of each foot is a depending generally vertical flange  59 . The depending flange  59  provides a generally vertical locating surface  61  analogous to the surfaces  34 ,  40 , and  48  of the earlier described arrangements and, as indicated in  FIG. 7 , provide the same tile locating or centering function as these previously disclosed surfaces. 
       FIG. 7  illustrates a variation of the construction of a ceiling tile  66 . In this construction, the tile  66  is asymmetric when viewed from a vantage point corresponding to  FIGS. 1-3 . In  FIG. 7 , a panel  66  on the right side of the tee  45  has a grooved rabbeted edge corresponding to the edges of the tile  11  in  FIGS. 1-3 . By contrast, an opposite edge of the tile  66 , shown at the left side of the tee  45  in  FIG. 7 , has a rabbeted grooved edge wherein the groove is relatively narrow in a vertical direction with only adequate clearance to allow the tile  66  to be tilted when the opposite side is lifted and shifted as in  FIG. 3 . 
     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.