Patent Publication Number: US-6701686-B1

Title: Ceiling grid with seal

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a suspended grid ceiling, and particularly to such ceilings used in clean rooms and other closed environments. 
     2. The Prior Art 
     Suspended ceilings used extensively in building construction have a grid of intersecting beams suspended by wires from a structural ceiling. The grid supports panels laid in the grid openings. 
     The beams are generally formed of a web of flat steel roll formed into an inverted T. The panels are supported on the flanges of the T, with the hanging wires anchored above in the structural ceiling, and connected below to holes in the web of the beam. 
     The panels, and the upper side of the flanges of the beams, on which the panels rest, have relatively smooth surfaces so that they form a seal tight enough for virtually all ceiling installations. 
     However, the seal between the beam and the panel must be very tight in clean rooms such as operating rooms, and rooms for sensitive manufacturing operations, as well as rooms where the atmosphere is desirably contained, such as indoor swimming areas. 
     Various ways to form such very tight seals have been tried. One way was to adhesively apply foam strips to the upper sides of the flanges in the field. This is labor intensive, as each beam must be manually handled to apply the strip. Hold down clips compress the panel on the foam strips. 
     In another way, flexible tape has been used along the edges of the lower surface of the ceiling panels. This too is labor intensive as the edge of each ceiling panel must be taped manually prior to installation. 
     In still another way, an aluminum extruded inverted T-beam is used, that has a flat foam gasket applied at the factory. Such beam requires the beam to be specially extruded of aluminum, sometimes with a channel in the flange for the foam gasket, rather than being roll formed of relatively inexpensive steel by continuously passing a flat web of steel through successive rolls. In packing such beams having foam gaskets applied at the factory, the beams are laid in contact with with one another, side-to-side, in a packed container, such as a long cardboard box. The foam on a flange in such packed containers becomes compressed by the adjacent beam, and achieves a permanent set which then creates air leaks when the ceiling is constructed. Such a permanent set also occurs in other ways in beams that use foam gasketing material to seal. For instance, in a magnetic imaging room where heavy panels are inserted, the foam gaskets, with time, become set in a compressed state, and lose resiliency to compensate for any possible movement of the panels. 
     Other ways to create a seal between a panel and the supporting structure without foam gaskets have been attempted. One way has been to create a U-shaped edge cap around the panels with soft plastic fins extending downward, as in U.S. Pat. Nos. 4,967,530 and 5,033,247. Such an arrangement is labor intensive, since the edge cap must be applied to each panel individually. 
     In another way, channels in the horizontal flanges are filled with a jelly material. An L-shaped flange on the edge of the panel sinks into the jelly. 
     SUMMARY OF THE PRESENT INVENTION 
     The grid beam of the present invention, for a suspended ceiling, has a flexible flap of soft PVC plastic integrally extruded with a hard PVC plastic coating on a rolled steel inverted T-beam. The flexible flap of soft PVC forms a seal with a panel that is supported by the beam. The coating and flap, dually extruded, are continuously formed on the beam at a dual durometer coextrusion station, as the beam emerges from the roll forming operation. As well-known in dual extrusion, the soft PVC that forms the flexible flap is applied to the hard PVC coating while both are in the liquid state, so that the hard and soft PVC are integrally joined. 
     The dual extrusion compositions and methods used in the present invention are well-known in the prior art. Such methods and compositions are set forth, for instance, in the U.S. Patents cited below and incorporated herewith by reference. 
     When installed in the ceiling, the grid beam of the invention, before the panel is laid on the flange of the beam, has a resilient flap that extends, and is biased, upward and outward from the upper surface on the flange of the beam at each side of the web. The flap is in effect hinged to the hard plastic coating on the flange, and is integrally connected thereto. 
     When the panel is laid on a flange the flap yields but continues to be biased upwardly against the panel. Such upward bias of the relatively soft flap against the lower surface of the panel forms a tight seal with the panel, providing, in effect, a relatively airtight closure suitable for a ceiling requiring such tight seals. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view, taken from below, of a segment of a suspended ceiling, with the cross beams not shown. 
     FIG. 2 is a perspective view of a prior art grid beam having a foam gasket adhesively applied to the flanges. 
     FIG. 3 is a perspective view of a segment of a beam of the invention. 
     FIG. 4 is a cross-sectional view of the beam of the invention taken along the line  4 — 4  of FIG.  3 . 
     FIG. 5 is a cross-sectional view showing panels in a ceiling supported on a beam of the invention. 
     FIG. 6 is an enlarged view of the segment shown in FIG. 5 with a phantom view added of the flap on the beam in an extended position. 
     FIG. 7 is a view similar to FIG. 4 of an alternative embodiment of the invention in which soft flaps extend downwardly from the web of the beam. 
     FIG. 8 is a view similar to FIG. 5 showing soft flaps extending from the web, bent, in contact with the ceiling panels. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The suspended ceiling using the present invention is of the well-known type having a grid formed of intersecting main beams and cross beams. Such a ceiling and grid are shown, for instance, in FIG. 1 of U.S. Pat. No. 4,827,681, incorporated herein by reference. The inverted prior art T-beams primarily used in such grid are roll formed in the usual prior art way. A strip of flat sheet steel is fed through a series of roll forming stations to create the beam. 
     In grids for prior art clean room, there has also been used, as seen in FIG. 2, a prior art beam  10  of extruded aluminum  11 , having foam strips  12  adhered to the upper surface of the flanges. Such strip  12  was generally applied at the factory, after the beam  10  was extruded. A similar foam strip was also applied in the field, to grid beams formed of rolled flat steel. Whether the beam was extruded of aluminum, or roll formed from steel, the application of the foam strip was labor intensive, and, particularly when factory applied, created problems in storing and shipping the finished beam to avoid a set to the foam from a compressed state, as explained in the prior art section above. 
     In FIG. 1, there is shown a segment of a suspended ceiling  20  using the grid  21  of the invention having grid beams  22  and panels  23  supported on the beams  22 . In a ceiling installation, the beams  22  are supported by wires embedded in a structural ceiling at their upper end, and passed through holes in the webs of the beams at their lower end. The beams  22  form a grid  21  with rectangular openings of, for instance, 2′×2′, or 2′×4′, and a panel  23  is inserted in an opening and supported on all sides by the flanges of the grid beams  22 . In FIG. 1, the cross beams that would support the panels  23  at their sides have been omitted to more clearly show the invention. 
     A core  26  in beam  22  of the invention is roll formed in the prior art manner by passing a strip of steel through roll forming stations, which continuously shape the steel strip into a T cross section having a web  27  and flanges  28 , 29  of a double thickness of the strip. A typical strip would be 0.022 inches thick, and would be of hot dipped galvanized steel produced by rolling. 
     The beam core  26  has a typical web  27  and flange  28 , 29  thickness of 0.045 inches. The flanges  27 , 28  have a combined width of 1.480 inches, across the flanges, and the web has a height of 1.960 inches. 
     To this beam core  26  of the beam, there is applied, as the core emerges from its final roll forming station and passes through a plastic extruding station, a coating  30  of a rigid plastic PVC material. The hard rigid coating  30 , while soft when applied at a hot temperature to the metal flange, cools to a hard rigid state. 
     The hard rigid plastic coating  30  continuously applied to the flanges of the beam at the extruding station has a typical thickness of about 0.010 inches and is applied to the bottom surface of the flanges, around the edge of the flanges, and inward on each flange about 0.38 inches. 
     The extruded hard rigid PVC  30  is applied in a liquid state in a common prior art manner, for instance as disclosed in the patents cited below. 
     The construction of beam  22  of the invention utilizes techniques and compositions used, for instance, in the automotive industry to produce metal embedded extrusions, including trim sealing strips for automobile doors, windows, and luggage compartments. See U.S. Pat. Nos. 4,232,081; 4,339,860; 4,355,448; and 4,432,166; all of which are incorporated herewith by reference. Such strips include a metal embedded extrusion having a covering over a metal core, which in some instances is in the form of a binder coating, and sealing portions. The &#39;166 patent discloses a dual extrusion process so as to have any desired different hardnesses between the covering portion and the sealing portion. 
     At the extruding station, while applying the hard rigid coating  30  to the flange, there is also applied a hard stiffener  31  of hard rigid plastic, of an inverted U-shape in cross section, to the top of the web  27 . 
     Such stiffener  31  adds to the strength of the beam, and is a substitute for the prior art roll formed bulb. 
     The inverted U-shaped stiffener  31  is affixed to the top of the web  27  by side extrusions  32  that adhere to the top of the web  27 , and are integral with the stiffener  31 . 
     At the extruding station, with the coating  30  still hot and viscous, and before the coating  30  has cooled and the coating becomes hard and rigid, the beam  22  also has applied to it flaps  33  of a soft plastic PVC material extruded onto the flange coating  30  at the top of each flange ( 28 , 29 ). The soft PVC flaps  33  integrally bond with the hot viscous coating  30 . 
     The flaps  33  are formed as shown in the drawings with an upwardly-inclined flat portion  34  joined to the flange coating  30  at  35  and then extending upward and outward at an incline. The flaps  33  have at their outer end a downwardly extending continuous bead  36 . 
     When both the flange coating  30  and flap  33  have cooled and solidified after exiting the extrusion station, the continuous beam  22  is cut into suitable lengths, by, for instance, flying shears, and the necessary end connectors are applied, all in the well-known prior art manner. 
     In the field, the grid beams  22  of the invention are installed into a grid  21  for a suspended ceiling  20  in the conventional prior art manner, as shown, for instance, in the &#39;681 patent referred to above. 
     After the grid  21  is in place, panels  23  are laid into the grid openings. 
     As seen in FIGS. 5 and 6, a panel  23  laid on top of the flange  28  causes flap  33  to yield to a sealing position  37 . In such sealing position  37 , the lower surface of the panel  23  rests on the top surface of the flap  33 , causing the flap  33  to rotate to position  37  where bead  36  contacts the upper surface of flange  28 . In this position, the flap  33  seeks to return to its unloaded position  38 , pressing upward against the lower surface of panel  23 . This creates seal  40  between the flap  33  and the lower surface of the panel  23 , along the entire length of the beam  22 , and entirely around the perimeter of the panel  23 . 
     If the panel  23  is temporarily removed, as often occurs, to gain access to the space above the suspended ceiling  20 , and then replaced, the flap  33  returns to its unloaded, upward position  38 , until the panel  23  is replaced, after which the flap  33  will again acquire its sealing position  37 . 
     In an alternative embodiment of the invention, beam  41 , as seen in FIGS. 7 and 8, has flaps  43  of soft PVC that extend outwardly and downwardly from a coating of hard plastic or binder  45 , applied to the web  27 . 
     As with flaps  33  and coating  30 , soft PVC for the flaps  43  is extruded onto hard PVC, or an equivalent binder, to form the coating  45 , while the coating  45  is still hot and viscous, at the extruding station. The flaps are of a sufficient length and thickness to be biased outwardly, in a bent posture, as shown in FIG. 8, when panels  23  are seated on flanges  28 , 29 . Such flaps  43 , as seen in FIG. 8, provide an additional seal  47  between the grid beam  21  and ceiling tile  23  to that formed by flaps  33 .