Abstract: Apparatus for use when machining or applying a textured finish to a surface of a workpiece comprises a receptacle for containing dielectric fluid which is closed on all sides excepting that side which, in use of the apparatus, engages the adjoining surface of the workpiece. The open side of the receptacle carries a flexible structure which can be moved towards and away from the workpiece surface between a first position in which the open side of the receptacle is spaced from the workpiece and a second position in which the workpiece surface closes off the open side of the receptacle. The flexible structure carries at its edge surface a resilient member whose contour can be varied to match the contour of the workpiece. In a preferred embodiment the flexible structure comprises a bellows-like structure.

Abstract: Electrical discharge apparatus for producing on the surface of an electrically conductive workpiece a textured or matt finish comprises a plurality of electrodes each connectable to an electrical power source and each carried by a head which in use of the apparatus can be moved linearly of the workpiece with the electrodes each spaced at a predetermined distance from the workpiece surface. A characteristics of the voltage conditions present within the gap existing between the electrodes and the workpiece surface is monitored and, the head is moved towards and away from the workpiece surface to maintain the monitored characteristic within predetermined limits. Dielectric fluid is retained within the gap existing between the electrodes and the workpiece surface, and a series of discrete electrical discharges is promoted between each electrode and the adjacent workpiece surface to cause particles to be removed from the workpiece surface and produce a textured or matt finish thereto.

Abstract: An electrical discharge apparatus comprises a plurality of electrodes mounted on an electrode carrier and spaced from a workpiece surface to define a gap across which a train of electrical pulses are transmitted. Dielectric fluid is present within the gap and controlled additions of solid particles are made to the dielectric fluid, with the particles being of a material of different electrical conductivity and/or permittivity to that or those of the dielectric fluid. The concentration by volume of the particles within the dielectric fluid lies within the range 0.05% to 7.0% and the size of the majority of the added particles is in excess of 7 microns. The particles are of a material having a relatively high electrical conductivity, e.g., graphite or metallic particles. Alternatively, the particles are formed from a material having good electrical insulating properties, e.g., glass, ceramic or certain metallic oxides.