EASY CUT SUSPENSION GRID

BACKGROUND OF THE INVENTION

The invention pertains to suspended ceiling grid and, in particular, to a grid runner construction that eases the task of its installation.

PRIOR ART

Suspended ceiling grid typically is in the form of metal runners having an inverted tee cross-section. Ceiling grid is erected on site, there ordinarily being no practical or cost-effective way to prefabricate an installation or even a part of an installation. Moreover, it is obvious that the installation work cannot be done on the actual floor surface or by an installer standing directly on the floor. Rather, a technician or installer works off a rolling scaffold or other elevating appliance. In this situation, there is typically no convenient workbench or like table to support the grid elements while length measurements are being made and transferred to a grid tee and while a grid tee is actually being cut to the proper length. It is axiomatic that time is money and the quicker and easier a piece of grid tee can be grasped, marked for cutting, cut and installed, the more profitable a job can be. Currently, despite the proliferation of power tools, including portable power tools, the industry largely relies on manual cutting devices in the form of snips, sometimes referred to as aviation snips. Repetitive manual cutting of tees in the customary manner can lead to fatigue in the installer's hand and a consequent loss of productivity. The foregoing illustrates that a grid tee that does not sacrifice performance but is easier to manually cut than that presently available, would be an advance in the art.

SUMMARY OF THE INVENTION

The invention provides a grid tee that can be manually cut with reduced effort and thereby makes its installation easier, resulting in the technician or installer experiencing less fatigue and, potentially, greater productivity. More specifically, the invention brings the insight that a major source of resistance of a grid tee to being cut is the compressive strength of the typical hollow

reinforcing bulb formed at the upper part of the tee. With still greater insight, the invention recognizes that the gripping force required of a technician using the usual pair of snips is related to the compression strength of the bulb structure, as distinguished from the compressive strength of the bulb material per se, at the point furthest from the pin joint of the pair of pivoted blades in the snips. The base area of the bulb is the part of the tee encountered by the blades that is furthest from the pivot pin of the hand snips when the initial effort is made to cut the top of the tee. This area, therefore, has a relatively large lever arm of resistance measured from the pivot point of the snips and thus can create a high resistance to the closing snip's blades and prevent the metal stock of the tee to be sheared easily.

The invention reduces the problem of high forces that are otherwise ordinarily necessary to manually cut a tee. This is accomplished according to the invention by incorporating certain structure/geometry in the base of the bulb, the location of the tee structure that is the greatest distance from the pivot pin of the snips when the bulb is being cut. These structures are used to more readily initiate buckling or crushing of the bulb base area when it is subjected to the lateral compressive forces being applied by the snip blades. Once the bulb has been crushed and flattened by the blades, the blades can shear the bulb stock more readily, especially if the snips are urged forwardly into the actual cutting zone, thereby keeping the leverage of the handles high.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an end view of a conventional style grid tee; FIG. 2 is an end view of a first embodiment of a grid tee according to the invention; FIG. 3 is an end view of a second embodiment of a grid tee according to the invention; and

FIG. 4 is an end view of a third embodiment of a grid tee according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a traditional prior art grid tee or runner 10 in profile or cross- section. This prior art style grid tee 10 and the grid tees described hereinbelow incorporating the present invention are elongated shafts assembled into a rectangular gridwork typically suspended from overhead or superstructure and on which tiles are mounted to construct a suspended ceiling. The gridwork, typically, comprises main tees and intersecting cross tees; grid modules are typically 2 foot by 2 foot or 2 foot by 4 foot or metric equivalent. The main tees are provided with regularly spaced slots in their midsection or web that accept connectors provided on the ends of cross tees as is customary in the industry. Main tees are connected end-to-end with suitable end connectors, known in the art, to span the ceiling area. The main and cross tees can have the same cross section or profile or the cross tees can have a lighter duty section such as having a reduced height.

The grid tee 10 of FIG. 1 and the others disclosed hereinafter are formed of sheet metal, usually steel, by known roll forming processes. The grid tee or runner 10 has a lower horizontal flange 11, a vertical web 12, and a hollow reinforcing bulb 13 formed of one metal strip. The tee 10 includes a sheet metal cap strip 14 that forms a lower normally visible face 16. The cap strip 14 is captured on the flange 11 by marginal hems 17 folded over the backside of the flange. Commonly, acoustic, fire-resistant tile is laid between the tees forming the suspended grid to rest on the flanges 11 , thereby making up a ceiling.

Referring now to FIG. 2, there is shown a grid tee 21 embodying one form of the present invention. For the sake of simplicity, parts of the tee 21 of FIG. 2, as well as those to be described in connection with FIGS. 3 and 4, having the same construction and/or function as the corresponding parts of the tee 10 of FIG. 1, are designated with the same numerals.

The grid tee 21 includes an upper hollow reinforcing bulb 22. The bulb has an upper generally horizontal wall 23 joined at each of its edges by folded corners to respective generally vertical flat sidewalls 24, 25. The sidewalls 24, 25 extend to folded corners where they are joined to generally horizontal walls 26, 27. In turn, the horizontal walls 26, 27 extend to corner folds where they are joined to respective layers of a vertical

web 12. The vertical bulb wall 24, shown on the left in FIG. 2, is somewhat shorter than the right vertical bulb wall 25 and the horizontal bulb walls 26, 27 lie on different horizontal planes. Specifically, the left-hand generally horizontal bulb wall 26 is at an elevation above that of the right-hand generally horizontal bulb wall 27. In the installation of a ceiling grid, standard lengths of grid tees are joined together. Usually, some of the tees have to be cut to fit a grid to the boundaries of a ceiling area and around structures or accessories that penetrate the plane of the ceiling. Commonly, grid tees are cut to length in the field, based on actual field measurements. This practice typically involves the use of so-called "aviation snips" or tin snips that are hand-held and hand-powered. Presumably, this is the tool of choice of installers because it is lightweight, durable, and enables the installer to use it for "fancy" cuts at special or odd junctures such as involving angles other than a perpendicular cut and for similar duty. A difficulty lies in cutting a conventional prior art tee 10 in the area of the bulb 13. Several factors contribute to the difficulty. It is to be realized that the snips cut by shearing action between its opposed blades. However, before effective shearing action by and at the blades can occur, the grid tee bulb 13 must first be crushed to bring the walls of the bulb on opposite sides of the central imaginary plane of the web together.

Unlike the hollow reinforcing bulb 13 of the prior art grid tee 10 which is symmetrical about a central imaginary vertical plane bisecting the double layer web 12, the tee 21 shown in FIG. 2 has an upper hollow reinforcing bulb 22 that is asymmetrical about the imaginary vertical plane bisecting its double layer web 12.

To embrace the width of a hollow bulb requires that the blades and, therefore, the handles of a snips be considerably open thereby making it difficult to get a good, strong finger grip on the handles. The lower part or bottom part of the bulb, that is the wide bulb part furthest from the top of the bulb, can ordinarily present the greatest difficulty by resisting crushing forces, because it has the greatest leverage, measured by its distance from the pivot of the blades, as compared to other parts of the bulb.

The invention comprehends the provision of a deliberate eccentricity of the structure at the base of the bulb that promotes or encourages buckling in this area when a lateral compressive force is applied to the sides of the bulb by the blades of a snips. This eccentricity is accomplished in the embodiment of FIG. 2 by creating the structure at the

base of the bulb 22 represented by the horizontal walls 26, 27 where these walls cannot strongly support one another when they are subjected to lateral compressive forces. The walls 26, 27 are unable to laterally support one another because they are misaligned so as to deliberately be situated in different planes, the plane of the wall on the left being higher than the plane of the wall on the right. This difference in height or degree of eccentricity is preferably greater than the thickness of the walls 26, 27. By way of contrast, inspection of FIG. 1 reveals that the lower wall portions of the reinforcing bulb 13 of the conventional prior art grid tee are in alignment. That is, these lower walls of the prior art tee bulb 13 converge at the web 12 at the same vertical location and, further, lie in a common imaginary horizontal plane.

FIG. 3 illustrates a grid tee 31 made according to a second embodiment of the invention, where again, a lower part of a reinforcing bulb 32 is deliberately made incapable of strongly resisting lateral compressive loads imposed by the blades of a snips. In this embodiment, the lower part of the bulb 32 is represented by left and right lower or base walls 33, 34, each converging with a respective layer of a web 12 at different elevations and with vertical bulb sidewalls 38, 39 at similarly different locations. FIG. 3 reveals that the walls 33, 34 cannot support one another against a lateral compressive load since they are misaligned where they intersect with the web 12. Moreover, the walls 33, 34 do not lie in horizontal planes which would otherwise present them in a more or less stable condition to resist lateral forces. The inclination of these walls 33, 34 from a horizontal plane encourages them to fold upwardly and thereby collapse when subjected to lateral compressive forces. Additionally, the bulb 32 has an inclined or slanted top wall 36 which can be more prone than a horizontal wall to collapse by folding inwardly at an acute corner 37 when squeezed between the blades of a snips. FIG. 4 illustrates a grid tee 41 of still another embodiment of the invention. In this embodiment, both lower wall portions 42 and 43, and upper wall 44 of a hollow reinforcing bulb 45 are constructed to more easily buckle under the lateral compressive forces developed by the blades of a snips being used to cut the tee as compared to generally flat horizontal walls. The lower wall portions 42, 43 of the bulb are arranged with two features that can be operative to produce a structure prone to collapse or buckle under lateral applied forces. The lower wall portions 42, 43 are oriented, in an overall

sense, at an inclined angle of, for example, about 45 degrees. Still further, the walls 42, 43 are creased or folded inwardly or concavely at their mid-points 46 making them weak against lateral forces and any force along an imaginary plane between their points of convergence with a bulb sidewall 47 and a vertical web 12. It will be seen that the crease 46 in these lower wall portions 42, 43 is at a depth, i.e. the wall portion deviates from a flat plane, that is preferably greater than the gauge thickness of the sheet material from which the tee 41 is made. The upper wall 44 of the tee bulb 45 is also arranged to collapse under lateral loading when compressed by a snips. In this arrangement on each side of an imaginary mid-plane vertically through the web 12 the upper wall 44 is formed with a crease 48 that is concave with reference to the bulb exterior. Like the crease 46 in the lower walls 42, 43, this formation promotes buckling action in the upper bulb wall 44.

A grid runner for a suspended ceiling having a lower flange extending generally horizontally, a web extending upwardly from the flange, and walls forming a hollow reinforcing bulb at the upper end of the web, the web lying generally in an imaginary vertical plane, a portion of the walls forming the bulb being disposed on and laterally spaced from the imaginary vertical plane, a wall area of the bulb on an upper side of the bulb bridging the space between the bulb walls on opposite sides of the imaginary plane, the bulb having lower wall portions forming its base and configured such that the bulb will readily collapse at the base when a lateral shear force is applied to the bulb walls by a hand-operated snips whereby the force to manually field cut the tee is reduced.

The vertical flat sides of the reinforcing bulbs 22, 32, and 45, are preferably relatively long in vertical extent, being at least as long as the respective bulb is wide, to impart to the respective tee a high vertical beam strength and high resistance to lateral bending. While the illustrated tees are shown as roll-formed sheet metal products, it is contemplated that the invention can be utilized in extruded tees and the tees can be made of aluminum or suitable rigid plastic.

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.