GB761475A - Improvements in or relating to the manufacture of helically corrugated metal tubing - Google Patents

Abstract

761,475. Making corrugated tubes. K. A. C., Ltd. March 23, 1955 [May 17, 1954], No. 14424/54. Classes 83 (2) and 83 (4). A method of producing helically-corrugated metal tubing comprises engaging the coils of a helical spring with one annular surface of the tube wall, applying fluid pressure to the other annular surface of the tube wall until the yield point of the metal is reached, and then applying endwise pressure to said tubing and spring so as progressively to reduce the length of the tubing as the wall thereof is forced between the coils of said spring and to simultaneously reduce the pitch of the spring. A thin seamless metal tube 1 is mounted within a cylindrical casing 2. One end of the casing is closed by a cap 3 and the other end carries a conical flange 7 providing a housing for a sealing ring 8 retained in position by a collar 9 secured to the flange by a clamping ring 11. The collar carries an extension 12 the inner surface being of conical form for receiving the conical portion of a plug 14 which clamps the end of the tube against the collar extension. A split-collar 18 surrounds the tube and abuts against the collar 9. A brass helical spring 19 having a cross-section as shown in Fig. 4 is a close fit within the casing 2 and around the tube. The other end of the tube is closed by a piston 20 carrying a conical plug 23 coacting with a retaining ring 24 which screws into the piston. In operation, fluid pressure is supplied to the interior of the tube through a bore 15 in the plug 14 until the tube wall expands outwardly as shown in Fig. 2. Simultaneously, fluid pressure is supplied to piston 20 to counterbalance the pressure on the plug 23. Thereafter the pressure in the chamber 21 is gradually increased to cause the piston to move and collapse the tubing and decrease the pitch of the spring until the sides 29 of the rectangular portion of the spring abut (Fig. 3). The ends of the collars 18, 18<SP>1</SP> adjacent the spring 19 are provided with grooves 30 (Fig. 2), which taper off the corrugations in the tubing. The corrugated tube is removed from the casing by releasing the clamping ring 11 and withdrawing the tube and spring assembly from the casing. Whereafter the plug 14 and piston 20 are removed and the spring screwed off the tubing. To facilitate removal of the spring the outer surface of the tube may be waxed before corrugating. Multi-start corrugations may be formed on the tube by utilizing, e.g. three springs 19, 19<SP>1</SP>, 19<SP>11</SP>, equally spaced around the tube (Fig. 6). The pitch of the spring may vary along its length so that the depthof the convolutions of the corrugated tube will also vary. The difference between the width of the projection 25 and the rectangular portion 29 of the spring cross-section (Fig. 4), may be reduced so that the side walls of the corrugations abut to provide a helical fin on the tube. Specification 732,442, [Group XXV], is referred to.