US Duct provides duct with flanges (angle rings) in black iron, galvanized or SS and with or without holes. The duct to which these flanges are attached it available in sizes 3″ and up, and also in black iron, galvanized or SS. Construction methods range from lock seamed pipe and mechanically lock elbows in lighter gauges to full welded product in heavy gauge (even up to 1/4″)- all depending upon the application.
The following are some facts about the options with regard to how the flanges can be utilized.
Vanstone – This term refers to a technique where by a flange is used to mate 90deg lips turned onto the pipe or duct component. In this method the flange is placed onto the pipe, the lip turned back and the flange left loose. Typically the lip is 1/2″ tall (or wide depending on your perspective) When the flanges are pulled together, the VanStoned lips of the pieces that are being connected, are pressed together to make a secure metal to metal connection. Because the flanges are loose on all pieces, alignment of the centerline of the components is easily accomplished.
– This refers to the fact that the flanges are welded to the duct and the faces of the flanges are the mating surface as opposed to the Vanstone where the duct lips are mating. The flanges can be FULL WELDED meaning that there is a continuous weld or INTERMITTENTLY WELDED meaning that there is a weld an intervals around the duct.
Aligning Components with Welded Flange
– Because the flanges are welded to the duct and cannot be ‘rolled' it is important that the flanges be aligned to the center line of the fittings and will therefore all line up. There are two options for this alignment. Centerline to the centerline of the holes (align to one hole) or centerline to the center point between the holes. Either is acceptable and is a matter of choice (OR MORE IMPORTANTLY) to the existing duct where present.
Field fitting Flanged Duct
– In the case of Vanstone flanges where the flange is left loose, the pipe is typically cut 1/2″ long and then a lip is hammered back at 90 degrees to the pipe by using the flange as an anvil. This is best accomplished by using deep throat vice-grips to hold the flange squarely on the pipe and far enough back to create the desired lip. In the case of Welded flanges- the pipe is cut to length and then the flange welded in place. (Remember to line up the flange with the centerline.)