Duct connecting system having integral transverse flanges

A sheet metal duct having an integral transverse flange for connecting ends of sheet metal duct sections, the flange comprising:

• a section consisting of an integral part of a duct wall,
• a first upturned portion extending perpendicularly outwardly from said duct wall,
• a second portion bent rearwardly from the outer edge of said upturned portion into a position opposite an end of the duct wall,
• a third return portion turned away from said duct wall and rounded back toward said upturned portion from the outer edge of said second portion;
• and
• a fourth L-shaped portion extending from the outer edge of said return portion, said L-shaped portion having a first arm arranged adjacent to and in close relation with said rearwardly bent portion and a second arm arranged adjacent to and in close relation with said upturned portion, said second arm having a length substantially less than said upturned portion.

A sheet metal duct having an integral transverse flange for connecting ends of sheet metal duct sections, the flange comprising:

• a section consisting of an integral part of a duct wall, a first upturned portion extending perpendicularly outwardly from said duct wall,
• a second portion bent rearwardly from the outer edge of said upturned portion into a position opposite an end of the duct wall,
• a third return portion turned toward said duct wall and rounded back toward said upturned portion from the outer edge of said second portion;
• and
• a fourth L-shaped portion extending from the outer edge of said return portion, said L-shaped portion having a first arm arranged adjacent to and in close relation with said rearwardly bent portion and a second arm arranged adjacent to and in close relation with said upturned portion, said second arm having a length substantially less than said upturned portion.