GB1177257A - Method and Apparatus for Heat Treating Metals - Google Patents

Abstract

1,177,257. Electrostatic annealing and hardening. C.A. BAUMGARTNER. Sept.12, 1967, No.41666/67. Heading C7N. [Also in Division H5] A metal part, e.g. of Cr, Nb, Ta, Mo, W, Ti, Be or alloy thereof, is treated by heating it to a selected elevated temperature, then cooling it e.g. to room temperature while impressing on the part an electrostatic charge of sealed magnitude and polarity, to alter selected physical properties of the part. When the metal is negatively charged during cooling, its ductility and malleability are improved; when positively charged, these properties are reduced. The part 38 may be disposed on one of two spaced electrodes 17, 18 disposed in a vacuum chamber 11 as shown. During cooling, there is applied between the other consumable electrode 18, e.g. of graphite or Cu, and the part which is earthed, a D. C . potential of predetermined polarity, e.g. using polarity reversing switches 29, and of selected value, e.g. using potential selecting switch 28 and adjustable transformer 21, insufficient to create an arc between the part and other electrode. Heating may be effected by applying between the electrodes a D.C. potential sufficient in magnitude to produce an arc manifested by a corona discharge enveloping the part. Alternatively the part may be heated by gas jets 46 or an electric induction heater (not shown). Heating and/or cooling may be carried out under sub-atmospheric pressure. For treating a Ti part engaged in a support 37, the chamber atmosphere preferably contains acetylene, e.g. introduced from source 53, during cooling to enhance its machinability; an oxygenrich atmosphere, e.g. introduced from source 50, produces an opposite effect. The consumable electrode 18 may be continuously advanced to maintain a constant air gap G; the air gap may be varied by moving the electrode axially through gears 34, 35, as shown.