A circular sheet metal duct having a sealant applied across the longitudinal seam. The sealant will improve the efficiency and will reduce or eliminate air leakage from the longitudinal seam. The sealant is applied during the manufacturing processes so that an installer does not have to seal the duct work. The method of manufacturing the sealant is provided.

This invention provides for a sealed drive slip that may be roll-formed from sheet metal. The sealed drive slip has a gasket on the flat portion of the sheet metal and prevents air leakage between the inside and outside of the air duct.

A method includes: bending a sheet about a mandrel such that the sheet is tubular, wherein the sheet includes a first longitudinal end portion and a second longitudinal end portion; engaging the first longitudinal end portion with the second longitudinal end portion; and passing the sheet between a first knurling wheel and a second knurling wheel such that the first knurling wheel applies a first knurling pattern to the sheet over the first longitudinal end portion and the second longitudinal end portion and the second knurling wheel applies a second knurling pattern to the sheet over the first longitudinal end portion and the second longitudinal end portion.

A method includes: bending a sheet about a mandrel such that the sheet is tubular, wherein the sheet includes a first longitudinal end portion and a second longitudinal end portion; engaging the first longitudinal end portion with the second longitudinal end portion; and passing the sheet between a first knurling wheel and a second knurling wheel such that the first knurling wheel applies a first knurling pattern to the sheet over the first longitudinal end portion and the second longitudinal end portion and the second knurling wheel applies a second knurling pattern to the sheet over the first longitudinal end portion and the second longitudinal end portion.

A method includes: bending a sheet about a mandrel such that the sheet is tubular, wherein the sheet includes a first longitudinal end portion and a second longitudinal end portion; engaging the first longitudinal end portion with the second longitudinal end portion; and passing the sheet between a first knurling wheel and a second knurling wheel such that the first knurling wheel applies a first knurling pattern to the sheet over the first longitudinal end portion and the second longitudinal end portion and the second knurling wheel applies a second knurling pattern to the sheet over the first longitudinal end portion and the second longitudinal end portion.

A device for forming seam of elbow duct is provided, and the device for forming seam of elbow duct that molds a lockseam by bending a flange of one pair of adjacent unit members, of a plurality of unit members constituting the elbow duct, including a base that supports a lower portion of the one pair of unit members; an elevating part that moves the base up and down; an angle adjustment part that adjusts a supporting angle of the base; a fixing chuck that supports an inner circumferential surface of a connecting portion of the one pair of unit members; a rotating part that rotates the fixing chuck; and a forming part that bends the flange of the one pair of unit members in a state where the flange is in contact to each other, to form the seam.