GB833485A - Extended surface tubes and the fabrication thereof - Google Patents

Abstract

833,485. Making heat-exchanger tubes; welding by pressure; coiling. ABBOTT, L. C. July 12, 1957 [April 12, 1956], No. 11205/56. Classes 83 (2) and 83 (4). [Also in Group XIII] An extended surface tube comprises a tube embraced by one or more fin members, each in the form of a channel, the flanges of which are interrupted along the length of the channel and the web of which is welded continuously or at intervals along the length of the channel so that the flanges form outwardly extending fins, the total area over which the web of the or each channel is welded to the surface of the tube being not less than the total cross-sectional area of the flanges taken on a surface parallel with the surface of the tube and passing through the junction of the flanges and web. The tube 1 is supported in bearing 12 mounted on wheeled trolleys 11 which are movable on a track formed by the upper surface of an I-beam 6 carried by supports 7. A wheeled drive device 13 on the track has a chuck 14 rotatable by a motor 15 clamped to one end of the tube and has a driven screw-threaded rod 16 engaged in a nut 17 fixed to the beam. The nut may be driven and the rod fixed. Centrally of the track is a spot-welder having an upper roller electrode 19, which may be driven, urged downwardly by a piston and cylinder device 24 and a lower electrode, having an upper concave surface to fit the tube, urged upwardly by a piston and cylinder device 25. A bearing 26 comprising three circumferentially-spaced rollers supports the tube on each side of the welder. The channel member is formed by bending a flat strip to square U-section and then slitting each flange at positions along its length, the member being wound on a drum. In operation the web of the end of the channel is initially held between the upper electrode and tube and then the rotation and axial movement of the tube by the device 13 is commenced simultaneously with passage of welding current so that the channel is welded in a helical path to the tube. The tube may be fluid cooled after welding and the lower electrode may be a wheel of larger diameter and tread than the upper wheel. The channel may be of truncated V-section and a plurality of helical or annular channel members may be welded to the tube. Where two channel members are welded simultaneously the welder may have two electrodes, one engaging the web of each member, current passing between the two electrodes through the tube. The slits in the opposite flanges may be in or out of line and the channel may be bent prior to welding.