R.F. induction furnace for silica-fibre drawing

An r.f. induction furnace is described to be used in a standard-type machine for drawing silica fibres for optical communication. The furnace consists of a small induction-heated graphite element which is fitted in a `concentrator¿ (stepdown transformer) placed directly in the tank coil of the r.f. generator, thus allowing one to maximise the matching efficiency between the generator and the heating element. The small dimensions of the graphite element make the furnace quickly responsive to input-power variations, so that it can be brought to a maximum temperature of 2180 K in 10 s. An argon atmosphere and an additional argon laminar flow are provided to avoid fibre contamination by the sublimated graphite, as well as to preserve the graphite susceptor. Successful tests of furnace operation have been carried out.