A joint assembly for connecting at their ends a pair of ducts each consisting of side walls formed of sheet material and having a generally quadrilateral cross sectional configuration is provided by a plurality of joint sections each including a pair of perpendicularly extending flanges formed with double walls. The joint sections are mounted on the ends of each of the ducts with a duct wall extending into engagement between the double walls of one of the flanges of a joint section. Angle plates including a pair of arms and a corner region are engaged with the arms thereof extending into engagement between the double walls of the other of said flanges and by thus mounting a plurality of joint sections and angle plates at the end of each of said ducts, the ducts may be joined together by fastening means which extend through the corner regions of the angle plates. The corner regions and the arms of each of the angle plates are brought into facing relationship along lateral surfaces thereof when the ducts are joined together and the angle plates are configured with a curved configuration along such lateral surfaces so that the ends of the arms produce a pincer effect tending to enhance the tightness of the joint assembly.

A gas duct is provided with a flange joint formed of a plurality of sheet-metal profiles each fitted over a respective duct side edge and of a plurality of corner pieces each joining together the two ends of two respective profiles. Each of these corner pieces is made of sheet metal and has a pair of legs formed with reinforcing corrugations. The legs fit into the ends of the profiles at the corners of the ducts. At the corner between the legs of each such corner piece is a hole surrounded by an annular corrugation that ensures proper spacing between two such corner pieces in a bolted-together joint assembly.

A duct jointing system is provided which includes a plurality of elongate frame members, each being a single piece of sheet metal folded to define a particular section. The section includes an open channel to receive an edge portion of the sheet metal duct, the channel having a base, a first web extending generally perpendicularly to said channel from a location adjacent the base, an outer portion at the end of the first web remote from the channel, the outer portion extending in the same general direction as the channel, and a second web extending obliquely toward the channel from a location adjacent the remote end of the first web. The single piece of sheet metal has an expanded portion constituting substantially the whole of the second web. A plurality of corner pieces are provided, each having two ends angled to each other, each end being insertable endwise into one end of one of the elongate frame members, and means are provided for securing together adjacent frame members on opposing duct ends.

A means for connecting together sheet metal ducts, e.g. forced air heating ducts, in end-to-end relationship, comprises hollow, roll formed flange members which extend along the edges of adjacent duct ends, and L-shaped corner pieces the limbs of which can be inserted into the ends of the flange members to complete the joint at the corners. A sealing agent or gasket is located between sets of flange members and corner pieces. The flange members have planar side end surfaces for sealing reception of the gasket, and lower protuberances, into which the ends of the metal ducts fit, the protuberances being arranged to bite into the gasket to improve the seal. The corner pieces have laterally offset portions, allowing the raw edge of the duct, at the corners, to project forwardly of the side surface of the corner piece, and hence to bite into the gasket at the corners to improve the seal. Channel shaped cleats are provided to assist in the attachment of pairs of profiles on adjacent end arranged ducts. Bolt holes are provided through the corner pieces for the primary attachment means.

A joint assembly for connecting the ends of a pair of generally rectangular sheet metal duct sections includes a pair of frame members secured to each other and connected to the respective duct end sections. The frame members each include four flange portions. Each flange portion has an upstanding channel shaped leg portion and an angularly extending duct receiving leg portion. A corner piece connects adjacent flange portions and extends into the channel portions of the upstanding leg portions to form the generally rectangular frame. The end portions of the ducts are inserted into longitudinal openings of the duct receiving leg portions. A flowing type gasket material is positioned in a longitudinal pocket of each flange. The end of each duct wall partially displaces the gasket material so that the gasket material extrudes outwardly around the duct wall and between the ends of the flange portion and the corner piece. The surface of the corner piece flange portion is displaced from the front vertical wall of the upstanding channel shaped leg portion so that the edge of the duct extends beyond the flange portion and penetrates an outside gasket member positioned on the upstanding channel shaped leg portion and the corner piece. This provides an effective seal to prevent air within the duct from flowing around the end of the duct and between the outer surface of the duct and the surface of the flange portion of the corner piece.