GB362539A - Improvements in and relating to the production of hollow metal bodies - Google Patents

Abstract

362,539. Making hollow bars. POLLAK, J. E., 20, Holborn, London. Sept. 15, 1930, No. 27553. [Class 83 (iv).] Cores.-In making hollow metal bars or pipes, such as borers, stay-bolts, hollow shafts, by forging or rolling a hollow blank on a metal core and then removing the core, a steel alloy core is used having no transition point or a transition point below that of the steel of the blank and the composite bar after reduction is cooled from a temperature above the transition point of the bar to a temperature below that point, but above the transition point of the core, if any, and the core is withdrawn when the temperature falls between these limits. The expansion of the bar during transformation from gamma to alpha steel separates the blank from the core which can thus be easily removed without applying tension. A suitable core is formed of a steel alloy containing nickel, chromium, manganese or silicon, or a combination thereof. The temperature required for finishing the rolling may be above the transformation point of the bar, or the composite blank may be subsequently heated to that temperature, preferably electrically. The cooling from this temperature may be effected in water, oil or air. Before the blank is heated for the reduction process, the ends of the core and blank may be partly or entirely connected by welding &c. so as to vary the supply of air in order to obtain a film of oxide between the surfaces during heating, to act as a lubricant and facilitate subsequent removal of the core. The parts for this purpose are previously cleaned by pickling.