Abstract: The apparatus forms fiberboard hollow ducts from fiberboard and comprises means for collapsing or partially collapsing the fiberboard into a flat collapsed fiberboard or partially collapsed fiberboard for advancing the collapsed or partially collapsed fiberboard through a preheating and heating stage while heat sensitive tape is applied to the linear seam of the advancing fiberboard. After tape is applied, means for applying pressure and cooling operate to permanently set the tape.

Abstract: The apparatus forms fiberboard hollow ducts from fiberboard and comprises means for collapsing the fiberboard into a flat collapsed fiberboard means for advancing the collapsed fiberboard through a preheating and heating stage while heat sensitive tape is applied to the linear seam of the collapsed fiberboard. After tape is applied, means for applying pressure and cooling operate to permanently set the tape.

Abstract: Fibrous board transition parts are produced on the job site from standard lengths of preformed fiberboard duct units. Transition parts are interposed between linear runs of duct pieced together to change direction of the duct work. The transition parts, sometimes referred to as elbows or bends, can be easily fabricated on the job site by modifying standard lengths of preformed linear duct by cutting and removing pie-shaped sections from the duct. The modified duct can be bent inwardly to form a one-piece arcuate transition part wherein the outer wall section remains intact and provides structural strength to the transition part. The seams are secured with structural adhesive tape wrapped around the transition part.