GB811921A - Improvements relating to manufacture of blading for axial-flow fluid machines - Google Patents

Abstract

811,921. Making turbine and compressor blades. ROLLS-ROYCE Ltd. March 9, 1956 [March 10, 1955], No. 7127/55. Class 83 (2). A method of making a turbine or compressor blade comprises drilling axially-extending passages 11 adjacent the peripheral surface of a slug 10, hot working the slug by extrusion, rolling or forging to elongate the drillings and reduce their cross-sectional area, drilling or machining a central hollow formation 12, Fig. 4, in the hot worked blank leaving material between the drillings and the hollow 12, and pressing the blade portion of the blank to the required aerodynamic shape, Fig. 3 (not shown). The blank is preferably of " Nimonic " (Registered Trade Mark) and has ridges 10a, 10b formed before or during the hot-working operation and corresponding to the leading and trailing edges of the blade. Drill holes 11a, 11b are formed adjacent the ridges. The billet is then preferably hot extruded using glass as a lubricant, an enlarged root portion 15 remaining on the blank. The hollow 12 is then machined in the blank, leaving a blind end 12a, said hollow being tapered so that the cross-sectional area of the remaining blade material decreases from the root end towards the tip. Alternatively the reduction in area may be obtained by hot swaging after forming a central bore of uniform diameter. Material 13, 14 at the ends of the blank is then removed by machining whereby the passages 11<SP>1</SP> emerge laterally of the blank at its root end and axially at its tip end. A slot 12c is then cut near the blind end 12a and the blank is pressed or forged at elevated temperature or low temperature to aerodynamic profile. A filling medium, such as low-melting point metal, may be used during the pressing. The root end 15 is subsequently broached to fir-tree root form 16, Fig. 5a; other forms of root such as bulb root may alternatively be used. The tip end of the blade is then slit and the two tongues 19 thereby formed are folded over and flattened and a reinforcing plate 20 is welded thereto. A drilling 12d is provided for the escape of coolant when the blade is in use. Alternatively, the tongues may be initially folded over to close the ends of the holes 11<SP>1</SP> and subsequently further holes may be drilled through the shroud to connect with the holes 11<SP>1</SP> whereby the cooling gas exhausts above the shroud. Alternatively a separate shroud may be welded to the tip and drillings are then made to enable the cooling gas to exhaust above or below the shroud. The blades may be assembled in a stator or in a turbine rotor disc provided with passages for the supply of cooling air as described in Specification 811,922, [Group XXVI].