GB697614A - A process for the production of machine parts from ceramic semi-conductive materials by electric heating - Google Patents

Abstract

697,614. Heating ceramics by etectricity. MASCHINENFABRIK AUGSBURGNURNBURG AKT.-GES. June 29, 1950 [Oct. 11, 1949], No. 16279/50. Drawings to Specification, Class 39 (iii)] In the production of machine parts from semi-conductive ceramic material, e.g. gas turbine blades, the sintering temperature is produced in the ceramic by supplying electrical energy directly thereto at least during the final phase of the heating either by passage of current therethrough or by dielectric heating, the energy supply circuit having means for observing a change in an electrical characteristic of the ceramic part, the current being cut off when the means indicate a predetermined value. When current is passed through the part, the circuit includes an ammeter and voltmeter, and current is cut off when the resistance of the .part reaches a predetermined value corresponding to the required mechanical and thermal properties of the part, e.g. when its conductivity is at a maximum or before its conductivity decreases. When dielectric heating is used, a tuning indicator in the circuit shows a change of conductivity of the part, the electrodes being arranged to create a uniform temperature therein. When the ceramic part includes silicon carbide, fine crystals thereof are formed at the sintering temperature and the conductivity then increases.