Vanstone Flanges are a very practical and labor saving method for connecting Spiral duct and Fittings. Van Stone connections consist of a face flange, and a backing flange, with a slip fit over duct. The face flange is mechanically formed from the end of duct section by turning the edge of the duct and forming a “lip” with an outside diameter small enough to clear the connecting bolts, as shown on the illustration. Spiral Manufacturing Co., Inc. has a special design built machine to automatically square up and turn the face flange for a perfect factory installed Van Stone Flange (see video).
The complete joint consists of two matching sets of face and backing flanges. If the duct wall selection for an industrial duct application is based on an “un-stiffened” design, the backing flanges may remain unattached with respect to the duct wall (standard). If the design requires a stiffening contribution from the flanged joint, flanges must be stitch welded to the duct wall per your specifications to ensure a dependable load sharing mechanism between the duct wall and the joint.