Fire damper frames

Claim 1

In a folded, one piece fire damper frame having a centrally open transverse cross section formed from a longitudinally extending unitary sheet metal blank, the combination of A. a longitudinally extending, planar, central web portion, 1. said web portion being of single blank thickness; B. a pair of transversely spaced, longitudinally extending, peripheraL mounting regions, 1. said blank being longitudinally bent to define the mounting regions, 2. said mounting regions being of double blank thickness to provide increased peripheral strength for fire damper mounting purposes; C. a pair of transversely spaced, longitudinally extending, parallel flanges disposed inwardly of the side peripheral mounting regions, 1. a plane through said flanges extending at right angles to a plane drawn through the web portion, 2. said flanges being formed of single blank thickness; D. a plurality of longitudinally spaced relief regions formed in each flange, 1. each relief region in one flange being in transverse alignment with a relief region in the other flange, 2. each relief region comprising a slit extending the entire height of the flange to define adjacent right and left flange sections, 3. at least one of the right and left flange sections adjacent each slit being curved out of the general plane drawn through the flange to form right or left curved regions, 4. each right curved region curving in a first direction from the plane through the flange and each left curved region curving in second direction from the said plane, said second direction being opposite the first direction, 5. the said frame being folded through the relief regions transversely to the length of the blank to form frame corners.