Patent GB-815236-A (GB)
Title: Hollow blades for turbines and the like
Inventor: DENNIS LEONARD JAMES
IPC: F01D5/18
Filed: 1956-03-14
Abstract: 815,236. Making turbine blades. NAPIER & SON Ltd., D. Feb. 28, 1957 [March 14, 1956], No. 7940/56. Class 83 (2). [Also in Group XXVI] A hollow blade for a turbine or compressor comprising an aerofoil portion, a root portion and a stem portion between the aerofoil and root portions is formed wholly or partly from a single piece of sheet metal. A blank 10 of sheet metal is shaped by means of a pressing operation to the form shown in Fig. 1 which provides a ridge 13 and a trough 14, a channel-section portion 16 and a flap portion 17 projecting from one edge of the channel portion. The pressing is then folded about the line 15 so that the trough 14 enters the concavity within the ridge 13 and the flap 17 closes the open side of the channel 16, the parts 13, 14 affording the convex and concave sides respectively of the blade aerofoil portion, and the parts 16, 17 affording a hollow box-like portion which is subsequently shaped to provide the blade root and stem portions. The edges of the flap 17 and channel 16 are joined by brazing or welding and the narrower sides of the box-like portion are then cut back so as to leave two projecting tongues 20, 21 as shown in Fig. 4, the two tongues being subsequently shortened and thickened and then grooved and bent inwardly so as to constitute a fir-tree root portion. A baffle 33 is inserted into the blade before the tongues 20, 21 are closed together, the baffle comprising two concave portions which have raised ribs along their lengths which engage the inner surfaces of the blade aerofoil portion. The baffle 33 at its lower end is of channel section, one or both sides 36 of the channel being welded to the inner surface of the sides of the stem portion 26; the flange of the channel is indicated at 37. The baffle 33 defines a passage for cooling fluid adjacent the leading edge of the blade. An insert 22 of triangular shape is disposed in the blade root portion, the sides of the triangle being shown at 23, 24. A projecting tab 31 of the insert 22 is bent down to close the end of the root portion adjacent the leading edge, while a tab 27 in the base of the insert is bent downwardly to provide an opening 28 through which cooling fluid admitted through the opening 32 into the root portion may flow into the cooling fluid passage within the blade. Another tab 30 on the insert 22 is bent so as to project beyond the fir-tree root portion thus affording a stop to limit movement of the blade root in its mounting slot in the rotor. A further tab 29 on the insert is bent up to engage the stem portion to provide a sealing member. The insert 22 is brazed or welded into position and finally a sealing projection 42 is welded on to the leading edge side of the stem portion. Openings 41 for the discharge of the cooling fluid are provided along the trailing edge of the blade aerofoil portion. Instead of a fir-tree type blade root, a bulb-type root may be provided by bending the ends of the tongues 20, 21 back upon themselves and then closing the remaining parts of the tongues together: alternatively, the ends of the tongues may be wrapped around an insert to form the bulb-type root. Specifications 729,665, [Group XXVI], and 796,296 are referred to.