METHOD OF COLD FORMING TUBULAR MEMBERS WITH AXIAL PASSAGES OR CHANNELS

1,274,194. Making heat exchangers; extruding; forging. GKN FLOFORM Ltd. 20 May, 1969 [21 May, 1968], No. 24123/68. Headings B3A, B3H and B3P. A tubular metal blank is deformed by extrusion over a grooved mandrel 27 through a die 30 to produce channels 11 on the inside wall of the blank and then by pressing in a ring die 62 with a punch 67 to wholly or partially close the channels. The extrusion press comprises a base 20, upper crosshead 26 on which the mandrel is mounted and a plate 25 guided on pins 22 and having a stripper sleeve 29. The upper crosshead 26 is acted upon by an hydraulic ram. The die 30 may be grooved to form external ribs 17 or the extrusion may be done in two-stages, firstly to form the channels and then the ribs. In operation a pair of blanks are placed one above the other in a guide block 34 and the crosshead lowered to force the lower blank through the die 30. After the extrusion of the lower blank the crosshead is raised and the blanks stripped from the mandrel by the sleeve 29 since the plate 25 is prevented from rising by toggles 36. The extruded blank falls through the hole 21 in the base 20 and the other blank is positioned in the guide block 34. The extruded blank is then placed in the ring die 62 and pressed by the punch 67 which is of larger diameter than the inside diameter of the blank. The punch deforms the walls of the channels 11 to wholly or partially close them. If the channels are closed the inside wall of the blank is brazed to seal the channels and form a heatexchanger tube.