Abstract:
A support bar, and method of its manufacture, for suspending grid members of a suspended ceiling, the bar being formed of a length of a sheet metal strip, a lower portion of the bar having regularly spaced holes for receiving and supporting bulbs of grid runners, an upper portion of the bars having longitudinally extending formed ribs, the ribs extending laterally from both sides of a central plane in which the lower portion lies.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to suspended ceiling systems and, in particular, to improved support bars for carrying grid runners. 
     PRIOR ART 
     Support bars are known, for example, from U.S. Pat. Nos. 7,578,107 and 8,898,986. The products disclosed in these patents can be used to suspend main runners or tees so that suspension wires are reduced and the suspension grid is more uniformly positioned vertically and horizontally. 
     Typically, support bars are produced with regularly spaced formations that capture the reinforcing bulbs of a grid main runner. The support bars are joined at their ends to span distance greater than their individual lengths. There is a need to reduce the cost of manufacture of support bars, to increase their vertical and horizontal beam strength for a given weight, to reduce packaging volume, and improve handle-ability, and to facilitate their installation. 
     SUMMARY OF THE INVENTION 
     The invention provides an improved sheet metal support bar and a method of its manufacture. The inventive support bar includes novel longitudinally extending ribs at a region adjacent an upper edge. Besides a primary function of vertically and laterally stiffening the sheet metal support bar, the ribs serve to vertically index the end of a support bar being installed to the end of the last installed support bar. The support bars can be quickly and accurately indexed to one another by holding their ends lapped together and by sliding the support bar currently being installed until preformed screw holes in both support bars are at least partially aligned. A pointed screw driven through both holes assures accurate, full horizontal and vertical registration between the support bars previously installed and presently being installed. 
     The disclosed stiffening ribs, additionally, serve to guide a suspension wire into a preformed receiving hole so that precise alignment of the suspension wire with a suspension hole is unnecessary. 
     The suspension holes are advantageously located relative to a central plane of the support bar so that the support bar hangs vertically thereby making later assembly of a grid member more easily accomplished and with greater positional accuracy. A formation for receiving a grid member is preferably proportioned to develop a friction locking fit so that the risk of relative slipping between the support bar and grid runner is reduced. The disclosed rib configuration is compatible with existing clip hardware used, for example, to attach grid runners to wall mounted angles and channels. 
     The support bar is preferably made from coiled sheet metal stock by a rolling process to achieve a low manufacturing cost. The support bar has an asymmetric section with reference to a longitudinal axis in the plane of the sheet stock and centered between top and bottom edges of the support bar and has a slotted bottom edge. This asymmetry and slotted edge make roll forming problematic. The invention overcomes this circumstance by simultaneously roll forming a pair of support bars in a mirror image relation from a common sheet metal strip. Once the cross-sections are established, the strip or ribbon of stock material is split along its center to yield two support bars. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a fragmentary side view of a support bar embodying the invention, being foreshortened to obtain a sufficiently large scale; 
         FIG. 2  is a fragmentary side view of the support bar on an enlarged scale; 
         FIG. 3  is an end view of the support bar; 
         FIG. 4  is a plan view of a section of a punched sheet or ribbon of coil stock; 
         FIG. 5  is a plan view of the sheet metal ribbon after passing through a roll forming station and a cutoff station; 
         FIG. 6  is a cross-section of the strip of  FIG. 5 ; 
         FIGS. 7A and 7B  together show stamping, roll forming and cutoff machinery for producing the support bar of the invention; 
         FIG. 8  is a diagrammatic isometric view from above of a suspended ceiling employing the support bars of the invention; and 
         FIG. 9  is an enlarged fragmentary isometric view of an attachment clip and support bar assembly. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIGS. 1-3  illustrate details of a support bar of the invention used to suspend main grid runners for a suspended ceiling such as that depicted in  FIG. 8 , designated by the numeral  12 . The support bar is a sheet metal body, preferably roll formed, of, for example, 0.032/0.036 inches gauge, G40 hot dipped galvanized (HDG) stock. A convenient length of the support bar is 109½ inch, although other lengths may be produced as desired. The illustrated support bar has a nominal height of 2⅛ inches, although other heights can be provided. 
     A grid runner bulb engaging feature with the general shape of a rectangular hole  13  is repeated at regular intervals, for example, on an 8 inch spacing, at a lower edge  14  of the support bar. A slot  17  centered with the rectangular hole  13  is open from the hole to the edge  14 . Angled slots  18  leave hinge areas  19  to facilitate manual bending of a left or right tab  21  out of the plane of the support bar. Such displacement of a tab  21  permits a grid runner bulb  22  to be assembled with lateral movement into the area of the hole  13 . The bent tab  21  is thereafter bent back into the plane of the support bar to capture the grid runner bulb  22  in the hole  13 . The lower half of the hole  13  may be somewhat narrower to provide, for example, 0.005 inches of interference with the sidewalls of a bulb  22 . When captured by the restored tab  21 , the support bar suspends the grid runner  11  and, when the ceiling is completed, any associated underlying areas of the ceiling structure. 
     A set of four spaced holes  26 , two symmetrically disposed on each side of a vertical center line of a rectangular hole  13  ( FIG. 2 ) are punched or otherwise formed in the support bar  10  for optional use when the support bar is an additional support bar as explained below. Larger holes  27  are punched or otherwise formed on centers above the rectangular holes  13  and midway between adjacent rectangular holes. 
     A series of longitudinally extending stiffening ribs  30  are formed in the upper half of the support bar  10 . Preferably, the ribs  30  have V-shaped cross-sections with flat sides disposed at right angles relative to each other and at 45 degrees relative to the plane of a lower half  31  of the support bar. In the illustrated arrangement, the peaks of the ribs  30  on both sides of the support bar  10  have the same distance from the plane of the lower half  31  of the support bar. In the illustrated example, the peak-to-peak distance (from the left side to the right side of  FIG. 3 ) is nominally 0.29 inch. Upper ones of the small holes  26  and the larger holes  27  can be advantageously centered on a crease in the sheet metal at a peak of one of the ribs  30 . 
       FIGS. 7A and 7B  illustrate a roll forming process for producing the support bar  10 . A strip of sheet metal stock  36  is fed from a supply coil  37  by feed apparatus  38  having a pair of feed rollers  39 . The feed apparatus or station  38 , feeding the coil stock  37  intermittently, delivers sheet stock to a punch press  41  where holes  13 ,  26 ,  27 , and slots  17 ,  18  are progressively punched out of the sheet stock  36 . An accumulator or sag section  42  of sheet stock material is established between the punch press  41  and a roll set  43 . The length of the section  42  varies cyclically to account for the intermittent feed through the punch press  41  and a uniform line speed established through the roll set  43 . In the illustrated example, the profile of the support bar is formed in the first eight roll passes. 
     The support bar is inherently difficult to roll form because of the ribs  30  on one lateral side and the slots  17  at the other. This difficulty is overcome, in accordance with the invention, by forming two support bars simultaneously on a single strip or ribbon of stock  36 .  FIGS. 4-6  illustrate details of this process.  FIG. 4  shows the holes  13 ,  26  and  27  and slot  17 ,  18  as they are produced in the punch press  41 . These features are arranged as mirror images with one another such that they are symmetrical about a longitudinal center line of the sheet metal strip or ribbon  36 . 
     In the roll forming station  43 , opposite marginal areas of the strip are formed with the ribs  30 , again symmetrically disposed with respect to the longitudinal center line of the strip. The strip  36  is slit at the second last roll station and reformed at the last roll station. 
     A flying cutoff device  45 , with blades moving in unison with the line speed of the stock  36  in the roll forming station cuts the strip  36  to the length of the support bar. This involves cutting a slug of 2.5 inches from the strip which is divided between the trailing ends of two support bars and the leading ends of two successive support bars. This slug cutoff is depicted at the right of  FIG. 5 . The support bars can be stacked in a carton or otherwise readied for packaging after being cut to length at the cutoff station. For a given line speed, the disclosed apparatus and method has twice the production of equipment that would form a single support bar from a metal strip. 
       FIG. 8  illustrates an example of a suspended ceiling in which the support bar  10  is used. Typically, the support bars  10  are located on 4 foot centers and are suspended by wires  48  from overhead structures, as is customary. Inspection of  FIGS. 2 and 3  reveals that the top edge of the suspension wire hole  27  is preferably in, or at least immediately adjacent, the plane of the lower half of the support bar  10  so that the support bar hangs vertically, making measurements and other steps in the ceiling installation more convenient, accurate and faster. 
     At the perimeter of the ceiling  12 , the support bar can be anchored to a wall using conventional clips  49  ordinarily used to anchor grid runners. The width of the support bar measured between two opposed ribs  30  is sufficiently narrow to fit in the clip where ordinarily a reinforcing bulb of a grid runner would be received. Preformed holes  51  in the clip  49  for screws, ordinarily used to attach to a reinforcing bulb of a grid runner, can be used to anchor the clip to the support bar with self-drilling screws  52 . Grid runners  53  are assembled to the support bar by positioning their upper reinforcing bulbs  22  in a respective hole  13  when one of the tabs  21  is manually bent out of the plane of the support bar  10  using a pliers or other suitable tool. With a bulb  22  received in a hole  13  and properly located longitudinally, the associated tab  21  is manually bent back into its original plane. The hole  13 , as mentioned, is slightly smaller than the bulb  22  so that the grid runner  11  is frictionally locked in position. 
     As shown in  FIG. 8 , the ceiling  12  can include wall channels  56  for supporting ends of grid runners  11 . An upper flange  57  of a wall channel  56  can be locally cut on both sides of a support bar location for clearance with the end of the support bar. The severed part of the flange  57  can be bent upwardly to a vertical position. The clip  49  can be assembled behind the channel and fastened to a wall with a suitable screw. 
     The disclosed features of the support bar facilitate assembly of multiple support bars where the span of the ceiling area is greater than the length of a single support bar. Referring to  FIG. 5 , it will be understood, due to the slug cutoff discussed above, the end of a support bar will not interfere with the last hole  13  or a grid runner in such hole where the ends of two support bars are lapped and the center-to-center distance between hole  13  is maintained. 
     The ribs  30  make the lapped support bar ends self-centering in the vertical direction and guide the ends horizontally until a set of holes  26  are roughly aligned. A self-tapping screw driven in any pair of the roughly aligned holes will precisely register the support bars together with the desired center-to-center distances of the holes  13  of lap-jointed support bars  10 . 
     The geometry of the support bar lends itself to a compact stacking arrangement for packaging since the ribs  30  nest on one another and no lateral shifting of a stack is experienced. Moreover, the lateral stiffness of the support bar makes a package of multiple support bars more handleable than that of prior art products. 
     While the illustrated suspended ceiling is faced with drywall sheets attached to the lower faces of the grid runners  11 , it will be understood that the support bar is readily used with grid runners supporting acoustical tiles. 
     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.