Abstract: Rectangular sheet metal duct sections with integral outwardly-and-rearwardly formed end flanges are conventionally made from coiled strip metal to lengths provided by the width of the coil stock, ordinarily slightly less than five feet. As is common practice, outward-and-reverse facing flanges are formed on both ends of each wall of the duct section. The spaces between the flange ends at the corners of the duct section are filled by heavier cornerpieces having arms projecting at right angles. Crimping the outstanding flanges over the corner arm portions completes a duct section. According to the present invention, a linear array of embossed surface portions is formed in the duct wall close to each outwardly projecting flange portion and beneath its reverse-facing portion.

Abstract: Modifying that type of integral flange outstanding from a sheet metal duct characterized by an outstanding first width of sheet metal and a second substantially equal width bent reversedly back to extend at 180.degree. from the first, in the present flange a sheet edge margin is bent reversedly back and inwardly between the second and first such widths. As compared to prior art flanges, this results in substantially lessened deflections under internal duct pressures without appreciable increase in sheet metal used. An added advantage is that the sheet metal edge is positioned so that it cannot endanger workmen's hands.

Abstract: A progressive rollformer machine is readily adjustable, without removal of rolls or use of spacers, to produce sheet metal workpiece margin flanges of variable depth. The machine includes a gear train housing having perpendicularly extending spindle shafts and idler gear shafts, and two forming roll housing sections, with their rolls mounted outboard. One of these, conventionally fixed relative to the gear train housing, provides one reference line of forming. The other forming roll housing section provides a second reference line of forming--it may be positioned at a variable distance from the gear train housing, at a spacing adjustable by a screw drive. Tracking throughout all roll stations is made possible by using the adjustable-position forming roll housing first in line of flow, with supplemental tracking rolls mounted onto the ends of the spindle shafts.