Abstract: A method of manufacturing cooled aerofoil blades in which blade parts are bonded together to provide complete blades. The blade parts are provided with mating surfaces which are simultaneously spark erosion machined to match the same prior to the blade parts being brazed together. Spark erosion machining is performed by maintaining the mating surfaces to be matched at a constant distance apart from each other and translating a tensioned wire electrode along a path passing mid-way between the mating surfaces.

Abstract: A closed container has openings at an input end for drawing air into the container and openings at the output end for passing air out of the container. An ozone generator is disposed inside the container adjacent the input end and a corona generator is disposed in the container adjacent the output end. The corona generator includes a dielectric made of a material having a dielectric constant of 1000 or greater. Impure air which is drawn in at the input end passes over the ozone generator whereby the ozone reacts with the impurities of the impure air to provide purified air. The purified air with remaining ozone is passed over the corona generator means to destroy the remaining ozone.