Patent GB-1203232-A (GB)
Title: Electrodes for the electrochemical production of multi-stage turbine rotors
IPC: B23H9/10
Filed: 1967-10-04
Abstract: 1,203,232. Electrolytic machining. SIEMENS A. G. Oct. 4, 1967 [Sept. 2, 1967], No. 45331/67. Heading C7B. A hollow electrode, suitable for the electrochemical machining of a turbine rotor, comprises a metallic electrode stem 35 having an inner surface contour defining the cross-section of a rotor blade and an outer surface contour, both of which are electrically insulated when the electrode is in use; and a metallic electrode base 34, whose working surface is cylindrically concave and is in electrical contact with the electrode stem, and which has an inner edge contour 26 registering with the inner surface contour of the electrode stem and has an outer edge contour 25 which extends beyond the outer surface contour of the electrode stem and which is defined by (a) first and second portions I, II which each extend between a pair of imaginary points on first lines parallel to imaginary tangents which themselves are parallel and are taken at points of substantially maximum separation of the inner edge contour 26, said first lines being outside the space enclosed by the inner edge contour, and the distances along said lines between said imaginary points both being greater than the longest line which could be drawn within said inner edge contour parallel to said imaginary tangents, and each pair of said imaginary points having one point on either side of the normal from said points of substantially maximum separation of the inner edge contour to said first lines, and by (b) third and fourth portions III, IV which join said first and second portions and whose shape is such that, if the distances along said first lines between said imaginary points were gradually and simultaneously reduced in length by equal increments until the closer pair of said imaginary points coincide (or both pairs coincide if the distances along said first lines between said imaginary points are equal) and said first and second portions are ignored, the resulting figure contains no real points of intersection. The portions III, IV may be straight lines but as shown are curved and preferably the inner edge of the working surface of the electrode is bevelled at 36. For electro-machining a ring of turbine blades on a rotor shaft, a block of metal is mounted for rotation about an operative axis passing through the block and is held stationary as anode which the electrode as cathode is gradually moved radially inwards at a feedrate equal to the rate of metal removal from the block until the electrode base is in a position whereat the centre of curvature of its cylindrical face coincides with the axis of rotation of the block, and after the production of one blade 22 and before production of the next 23, the block of metal is rotated through 360/n  where n is the number of blades to be formed in the ring, the third and fourth portions, III, IV of the outer edge of the electrode base being shaped so that in the two successive positions 210, 211 of the base the edge portions overlap so that unwanted metal between the blades is removed. If more than one blade ring is to be formed on the same rotor shaft, after formation of one blade ring the block of metal is moved along the operative axis and a second ring formed in the same way as the first.