GB641659A - Methods of and machines for forming hollow metal articles - Google Patents

Abstract

641,659. Making superheater return bends. TUBE TURNS, Inc. July 11, 1947, No. 18556. Convention date, Aug. 17, 1946. [Classes 83 (ii) and 83 (iv)] [Also in Group XI] Curving; mandrels.- In making curved tubes, e.g. superheater bends, straight tubular blanks are pushed in succession over a curved mandrel for expanding and bending the blank while simultaneously inducing a circumferential heating current in the blank over a short axial length, to heat the blank at a high rate to a temperature within the plastic temperature range, the speed of movement of the blank limiting its further temperature rise after passing the metal shaping region of the mandrel. The leading end of the tube 14a is preheated by one coil 57 and further heated by a main coil 51 shaped to provide a particular heat distribution. The mandrel 12 has a waist 12a to form a heat insulating air layer 58, and is mounted on a rod 14. The coils 51, 57 are adjustably mounted on a frame 40 having rollers 46 supporting the blanks 14a and the rod 14, and a cross-head 23 slotted to receive the rod 14 and engage the tubes 14a for pushing them over the mandrel 12 is carried by a moving cylinder 26 supported by rolls 37 and cooperating with a fixed, fluid-pressure piston. The rod 14 is detachably coupled to a tie-bar 17 and is raised into alignment with a tube trough 42 for reloading. The mandrel 12 is austenitic steel and local heating is restricted by the skin effect of using high intensity, low-frequency magnetizing current with a high reversal rate. In operation the initial heating of the mandrel is accelerated by feeding a blank slowly over it, or by leaving the heated last blank of the previous operation in place. The blanks 14a for use as return bends are curved through slightly more than 180 degrees to allow for springing contraction on cooling. Any tendency for the tubes to twist may be overcome by applying cold air jets. For blanks greater than 2¢ inch diameter 60 cycle supply is used, and for smaller blanks 360 to 10,000 cycles. Specification 517,040 and U.S.A. Specification 1,648,161 are referred to.