We recently had quite a challenge from Metraflex regarding a transparent tight-radius 4” pipe 90° bend. They required a transparent 4” Sch 40 long-radius elbow to observe a metal fin in a fluid system. The pipe bend needed to maintain a tight tolerance for ovality as it was to contour to the 6” radius fin.
By definition, a long radius pipe elbow has a curvature 1.5 times the nominal pipe diameter. Long radius elbows, as well as short elbows, are normally cast and welded in steel and are injection molded in plastics. However, to our knowledge, no one has ever thermally bent them before and maintained a consistent ID.
Metraflex sent us a print of the needed bend, as well as a 3D printed model. The 3D printed bend served well as packing material for the fin but was not transparent as they had first hoped.
Although clear CAB injected molded pipe fittings were produced decades ago, they are not available now.
We deduced that we could make the bends in two ways: positive placement bending or a multi-sectioned mitered bend. We made both.
These bends were made out of Cellulose Acetate Butyrate (CAB) formula 570 UV Stabilized.