Abstract:
The invention relates to an improved system for connecting the ends of sheet metal ducts wherein each duct end is provided with an integral frame. Corner connectors defining perpendicularly extending arms are associated with each frame, and bolts or other fasteners are utilized for connecting the connectors and integral frames. The sections include an upturned portion extending perpendicularly outwardly from the duct wall, a second portion bent rearwardly from the outer end of the first portion, a third portion extending from the outer end of the second portion and forming an L-shaped double wall portion. When the frame is formed in this fashion, it is adapted to receive the side edges of respected arms of corner connectors whereby the ducts may be efficiently assembled by locating corner connectors in place and thereafter applying the fasteners used for maintaining the assembly.

Description:
FIELD OF INVENTION 
     This invention relates to an improved system for connecting the ends of four sided rectangular sheet metal ducts wherein each duct end is provided with an integral transverse flange having a L-shaped double wall portion. The duct sections connected using the improved flange of the invention have increased strength over the prior art. 
     BACKGROUND OF THE INVENTION 
     This invention relates to an improved means for connecting the ends of a pair of sheet metal duct sessions. The invention particularly involves an assembly of the type including frame members defining integral transverse flanges located at a duct end with adjacent frame members joined to each other by angular corner connectors. 
     The prior art, particularly Heilman et al U.S. Pat. No. 4,466,641 and Fischer et al U.S. Pat. No. 4,579,375, the disclosures of which are incorporated herein by reference, disclose duct connecting systems using integral transverse flanges. These arrangements include a first portion extending perpendicularly outwardly from the duct wall and a second portion bent rearwardly from the outer end of the first portion thereby forming opposing channels. The side edges of an arm of a corner connector are adapted to be snapped and crimped into place in these channels for secure assembly. To hold the adjacent duct sections together, the adjacent sections are bolted to each other at their four corner connectors, thereby forming an assembled section of duct. 
     Apparatus to manufacture the Heilman et al. invention is manufactured and sold by The Lockformer Company of Lisle, Illinois and is referred to in the industry as the TDC (“Transverse Duct Connector”) system. Apparatus to manufacture the Fischer et al duct is manufactured and sold by Engel Industries, Inc. of St. Louis, Mo. and is referred to in the industry as the TDF (“Transverse Duct Flange”) system. While both systems have provided the industry with a useful duct system, primarily the TDC system, there remains a need in the industry for improvements to the systems as discussed herein. 
     FIG. 1 illustrates in cross section the roll-formed shape of the end  10  of one duct, and the roll-formed shape of the end  12  of an adjacent duct as disclosed in Heilman et al. The frame includes a first upturned portion  14  extending perpendicularly outwardly from the duct wall  16  and a second portion  18  bent rearwardly into position opposite an end portion of the duct wall. The width of an arm of a corner connector  20  substantially corresponds to the distance between the rearwardly bent portion  18  and the end portion of the duct wall. The side edges of each such arm of a corner connector  20  are adapted to engage the respective surfaces of the rearwardly bent second portion  18  and duct wall end portion whereby the corner connector  20  is held in position relative to the frame by a retainer means defined by the rearwardly bent second portion  18 . 
     The preferred embodiment of the Heilman et al invention includes a third outwardly facing return portion  22  at the outward edge of the rearwardly bent second portion  18  thereby forming a bead  24 . A first channel  26  is formed between the bead  24  and the outwardly extending upturned portion  14 , and a second channel  28  is formed in the duct wall opposite the first channel  26 . The side edges of an arm of a corner connector  20  are adapted to be snapped into place in these channels  26 ,  28  for secure assembly of the corner connectors relative to a frame. It has been found, however, that the corner connectors will b displaced during manufacture and transport of the duct. Therefore, the duct flanges must be crimped (not shown in FIG. 1) over the adjacent arms of a corner connector to secure the corner connector in place within a duct flange. 
     Pursuant to Heilman et al, when assembling one duct with another, the respective frames and associated corner connectors  20  are brought together, and bolt  30  or other suitable fastener is employed for achieving the desired connection. Prior to completion of this connection, a gasket  12  may be located between the respective frame portions for conventional purposes. 
     In order to strengthen the resultant duct joint formed by the Heilman et al invention, each of the arms of a corner connection  20  is provided with an offset ear which may be used for retaining a stiffener means, comprising a strip of spring steel or the like. Each stiffener means is held at its end beneath the offset ear and at its sides between channels  26  and  28 . Furthermore, a clip  34  may also be engaged around the adjacent frame portions to provide a smooth exposed joint and to strengthen the joint. 
     The Fischer et al duct flange, illustrated at FIG. 2, uses a modification of the Heilman et al invention and discloses a duct connecting system having an outstanding web portion  36  extending at 90 degrees from the duct wall  38 , with an outward-formed tracking ridge  40  spaced inwardly thereof and formed outwardly of the surface of the assembled duct wall  38 . At the outer extremity of the web  36  is an outer flange  42  having a turned-under rounded edge  44 , formed at an angle slightly in excess of 180 degrees and terminating in a spring margin  46  which extends back toward the web  36  and normally stands inwardly away from the outer flange  42 . “Button lock” lances are said to be provided through the rounded-back edge  44  projecting aft. The spacing between the web  36  and the tracking ridge  40 , which corresponds to the spacing from the web  36  of the somewhat bulbous rounded portion of the turned-under edge  44 , is fixed to accommodate the side edges of an arm of a corner connector. The depth between the spring margin  46  and the outer surface of the duct wall  38  between the ridge  40  and the web  36 , is such that the leg portions of a corner connector will snap into position and are said to be held by the spring margins  46  and the lanced projections, trapped by the tracking ridge  40 . However, it has also been found that corner connectors will fall out of the Fischer et al. duct flange without crimping. Accordingly, the duct flange of the Fischer et al. duct, in practice, is crimped to hold a corner connector in place. 
     As with the Heilman et al invention, the Fischer et al. duct can be readily joined with an adjacent duct end by means of bolts or fasteners. Furthermore, gasket material may also be located between adjacent frames without difficulty to decrease leakage. 
     In order to increase duct flange strength about the duct joint formed by the Fischer et al invention, optional reinforcing bars may be utilized between the arms of adjacent corner pieces. Each bar may be snapped in position behind the outwardly-formed ridge  40  and the rounded edge  44  of the outer flange  42 , and retained by the lanced projections. If desired, and elongated clip can also be positioned around the joint formed by adjacent duct flanges to support the middle portion of the integral flanges. Incorporation of the clip and reinforcing bar with adjacent duct flanges, helps to prevent bellowing and leakage caused by pressure exerted by materials flowing within the duct. 
     After issuance of the Heilman et al and Fischer et al patents, the corner connector was manually inserted into the duct flange and then manually crimped with a hammer or the like. This was, among other things, time consuming, hard on the worker and expensive to the sheet metal contractor. These problems were solved by the Cornermatic® machine sold by Iowa Precision Industries, Inc., Cedar Rapids, Iowa, and covered by U.S. Pat. Nos. 5,321,880 and 5,283,944 to Goodhue. These patents disclose an automated method and apparatus, respectively, for placement of corner connectors in transverse duct flanges. The Cornermatic® apparatus and method automatically insert a connector, such as described in Goodhue U.S. Pat. No. 5,342,100, in a duct flange and secure the connector within the flange by crimping the outer portion of the flange over the adjacent arms of the corner connector. The inventions of the Goodhue patents have been a commercial success in the industry. 
     BRIEF DESCRIPTION OF THE INVENTION 
     A primary object of the invention is to provide an integral transverse duct flange having an L-shaped double wall portion arranged adjacent to the flange and opposite a duct wall. 
     A further primary object of the invention is to provide a transverse duct flange which provides increased strength and rigidity across the joint created by adjacent integral transverse duct flanges. 
     A further primary object of the invention is to provide a transverse duct flange which will allow for the use of the thinner gauge sheet metal in the construction of duct while providing the strength of a conventional duct flange using heavier gauge sheet metal. 
     Another object of the invention is to provide a transverse duct flange having additional strength which will alleviate the problems of bulging and leakage at adjacent duct flange joints. 
     A further object of the invention is to provide a transverse duct flange having additional strength which will alleviate the need to insert stiffeners or reinforcing bars, in certain applications, into the duct flange in order to strengthen the duct flange as is currently implemented with the prior art flanges. 
     A further object of the invention is to decrease the number of clips that are engaged about the respective connected adjacent flange portions to prevent leakage. 
     A further object of the invention is to provide a more cost efficient means of manufacturing and connecting sheet metal duct than the prior art. 
     The purposes of this invention are accomplished by providing for frame members defining integral transverse flanges located at a duct end with adjacent frame members joined to each other by angular corner connectors. The integral flange comprises an upturned portion extending perpendicularly outwardly from the duct wall, and a second portion bent rearwardly. The end of the second rearwardly bent portion is turned away from the duct wall and rounded back toward the upturned portion and bent under the upturned portion, forming a third bent portion. This third bent portion provides an L-shaped double wall portion having one arm of the L arranged adjacent to the surface of the upturned portion. 
     In the alternative, the third bent portion may be turned toward the duct wall and rounded back toward the upturned portion and bent on top of the upturned portion, thereby forming a L-shaped double wall portion having one arm adjacent to the surface of the rearwardly bent portion and the other arm of the L arranged adjacent to the surface of the upturned portion. 
     The L-shaped double wall portions disclosed above may also include a bead formed therein similar to the bead disclosed in the Heilman et al patent, thereby providing for a first channel formed between the bead and the upturned portion. A second channel may be formed in the duct wall opposite the first channel as generally disclosed in Heilman t al. the channel can be formed by creating a depression in the outside of the duct wall, as disclosed in Heilman et al, or by forming an outwardly facing ridge along the surface of the duct wall, as disclosed in Fischer et al. The side edges of an arm of a corner connector are adapted to be positioned into place in these channels, and thereafter the duct flange is crimped over the corner connector to secure it in place. 
     Assembling section of sheet metal duct having an integral flange arrangement of the type described by the present invention results in a stronger transverse duct joint. The stronger duct joint allows a contractor to use lighter gauge sheet metal, and ultimately less metal, than he would use if a duct flange is implemented. Moreover, the increased transverse duct joint strength recognized when using the present invention potentially alleviates the need for employing stiffeners or reinforcing bars when assembling sections of duct. As a consequence of using lighter gauge sheet metal and removing the need for stiffeners or reinforcing bars, the present invention provides a more cost efficient means of connecting sheet metal duct than previously known. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a fragmentary, cross-sectional view of a duct joint representative of the duct connecting system disclosed by Heilman et al; 
     FIG. 2 is a sectional view of a duct wall and flange representative of the duct flange disclosed by Fischer et al; 
     FIG. 3 is a sectional view of an integral duct flange representative of a preferred embodiment of the present invention; 
     FIG. 4 is a perspective view of an integral duct flange representative of the preferred embodiment of the present invention; 
     FIG. 5 is a fragmentary, cross-sectional view of a duct joint representative of the preferred embodiment of the present invention; and 
     FIG. 6 is a sectional view of an integral duct flange representative of an alternative to the preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiment of the integral transverse duct flange is shown in FIGS. 3,  4  and  5  where like numerals illustrate like portions of the invention. An alternative embodiment of the invention, which does not share like numbering with FIGS.  3 , 4  and  5  is illustrated in FIG.  6 . 
     FIG. 3 illustrates a horizontal, sectional view of an integral transverse duct flange representative of the preferred embodiment of the present invention. FIG. 4 illustrates perspective view of a duct flange with an assembled corner connector as characterized by the features of this invention, and showing the duct flange crimped to hold the corner connector in place. FIG. 5 illustrates a fragmentary, cross-sectional view of a duct joint which includes integral transverse flanges characterized by the features of this invention (the crimping is not shown in this Figure). 
     The integral transverse duct flange generally comprises a duct having a duct wall  50  and a flange  52 . Duct wall  50  has an inside surface  54  and an outside surface  56 . The flange  52  has an inside surface that is continuous with inside of duct wall  50  and an outside surface that is continuous with the outside surface of duct wall  50 . The flange  52  includes an upturned portion  58  extending perpendicularly from the duct wall  50 . 
     More specifically, the flange  52  comprises the upturned portion  58  which extends perpendicularly from duct wall  50  and a second rearwardly bent portion  60  extending opposite a portion of duct wall  50 . The end of rearwardly bent portion  60  is turned away from duct wall  50  and rounded back toward the upturned portion  58 , forming a return portion  62 . Return portion  62  delineates inside surface  54  of flange  52  from outside surface  56  of flange  52 . Return portion  62  is extended to form a L-shaped double wall portion  64  having a first arm  66  arranged adjacent to and in close relation with the inside surface of rearwardly bent portion  60  and a second arm  68  arranged adjacent to and in close relation with the inside surface of upturned portion  58 . 
     Second arm  68  extends toward duct wall  50  a distance substantially less than the length of upturned portion  58 . As shown in FIG. 3, the second arm  68  of L-shaped portion  64  extends a distance less than half the length of upturned portion  58 . 
     Referring now to FIG. 4, there is shown a perspective view of a duct flange with an assembled corner connector  70  having substantially perpendicular arms  72 ,  74 , and a bolt hole  76 . The corner connector  70  is as disclosed in U.S. Pat. No. 5,342,100 to Goodhue, and is incorporated herein by reference. The corner connector  70  is preferable inserted into duct  50  by the Cornermatic® machine, although other means are also acceptable. Arms  72 ,  74  are adapted to engage the respective surfaces of rearwardly bent portion  60  and duct wall  50  whereby corner connector  70  is held in position relative to the flange  52  by a retainer means defined by rearwardly bent portion  60 . Corner connector  70  is positioned adjacent to and in close relation with the outside surface of upturned portion  58  and is secured within flange  52  by crimping rearwardly bent portion  60  and return portion  62  over arms  72 ,  74  or corner connector  70 . the placement of corner connector  70  into flange  52  and subsequent crimping to secure corner connector  70  within flange  52  can be accomplished manually, but it is preferred that these steps be performed by the Corner Cadet™ machines covered by these patents and U.S. Pat. No. 5,926,937. 
     Referring now to FIG. 5, the integral transverse flange of the invention of FIGS. 3 and 4 is shown connecting two adjacent sections of duct to provide a duct joint. When assembling adjacent duct sections, the respective flange portions and associated corner connectors are brought together, and a bolt  78  or other suitable fastener is employed for achieving the desired connection. Prior to completion of this connection, a gasket  80  may be located between the respective flange portions for conventional purposes. A clip  82  may also be positioned engaging the respective connected adjacent flange portions. Clip  82  serves to decrease leakage about the duct joint. The crimping of the duct flange to maintain the corner connection in place is not shown in FIG.  5 . 
     The above-described invention will be useful with 16 gauge to 26 gauge sheet metal duct. Generally, the L-shaped portion of the duct for 16 to 26 gauge sheet metal will be in the range of about 0.44 inches, and the second leg of the L being in the range of about 0.40 inches. It has been found that the L-shaped double wall portion defined in the present invention will provide additional strength to the resultant duct joints. By utilizing the invention and the automatic crimping mechanism of the Goodhue patents, U.S. Pat. Nos. 5,321,880 ; 5,283,944, and 5,926,937, it is not necessary to use the channel means of the Heilman et al and Fischer et al patents. Additionally, prior to Goodhue inventions, it is not believed that the manual crimping methods would have provided operable crimping to a double wall portion. 
     An example of the invention is provided based on 20 gauge sheet metal thickness of about 0.035 inches. In this preferred embodiment the upturned portion  58  has a length of about 1.210 inches, rearwardly bent portion  60  a length of about 0.370 inches, L-shaped portion  64  a total length of about 1.002 inches, the first arm  66  being 0.721 inches and the second arm  68  being about 0.281 inches. In this embodiment, it can be calculated that there will be additional strength to the duct joint on the order of about 20% over the conventional TDC based on moment of inertia calculations with a load being applied to the duct wall. 
     A modification of the embodiment of the invention not shown FIGS. 3,  4  and  5 , provides additionally for an inwardly-formed channel formed in duct wall  50  opposite of rearwardly bent portion  60  and L-shaped double wall portion  64 , similar to the channel disclosed in Heilman et al and incorporated herein by reference. The side edges of an of a corner connector  70  can be positioned against the channel and against rearwardly bent portion  66  for assembly of the corner connectors relative to a frame. Also, with additional reforming steps a second channel may be formed in the rearwardly bent portion  60  and L-shaped double wall portion  64  similar to that disclosed in Heilman et al, although such channel is not presently preferred due to the additional steps and costs in forming the flange. 
     A further modification of the embodiment of the invention not shown in FIGS. 3,  4  and  5 , provides additionally for an outwardly-formed tracking ridge, similar to the ridge discussed in Fischer et al and incorporated hereby by reference, formed outwardly from the duct wall  50  and parallel to upturned portion  58 . The tracking ridge protrudes outwardly from duct wall  50  a distance sufficient to form a channel between upturned portion  58  and the tracking ridge capable of accommodating the side edges of an arm of a corner connector  70 . 
     An alternative embodiment to the inventions disclosed in FIGS. 3,  4  and  5 , is shown in FIG.  6 . This embodiment provide for a duct wall  90  having a transverse duct flange  83  having an inside surface  84  and an outside surface  86 . The flange includes an upturned portion  88  which extends perpendicularly from the duct wall  90  and a second rearwardly bent portion  92  extending opposite a portion of duct wall  90 . The end of rearwardly bent portion  92  is turned over toward duct wall  90  and rounded back forming a return portion  94 . Return portion  94  delineates inside surface  84  of flange  83  from outside surface  86  of flange  83 . Return portion  94  is extended to form a L-shaped portion  96  having a first arm  98  arranged adjacent to and in close relation with the outside surface of rearwardly bent portion  92  and a second arm  100  arranged adjacent to and in close relation with the outside surface of upturned portion  88 . 
     Second arm  100  extends toward duct wall  90  a distance substantially less than the length of upturned portion  88 . As shown in FIG. 6, the second arm  100  of L-shaped portion  96  extends a distance less than half the length of upturned portion  88 ; and preferably about 0.40 inches depending on the gauge of the sheet metal. The preferred dimensions for the flange discussed for the embodiment shown in FIG. 3 are also applicable for this embodiment. 
     An example of this embodiment is provided based on a 20 gauge sheet metal having a thickness of 0.035 inches. The upturned portion  88  has a length of about 1.313 inches, rearwardly bent portion  92  a length of about 0.932 inches, wherein the first arm  98  is about 0.651 inches and the second arm  100  is about 0.281 inches. 
     Further modifications of the embodiment of the invention shown in FIG. 6 can be made bases on the disclosures in the Heilman et al and Fischer et al patents as discussed above for FIGS. 3,  4  and  5 . 
     It is understood that various changes and modifications may be made to the above described inventions without departing from the scope of the invention and as particularly as defined in the following claims: