Patent GB-597165-A (GB)
Title: Improvements relating to the construction of stator elements of turbines, compressors or like machines
IPC: F01D25/24
Filed: 1945-01-23
Abstract: 597,165. Turbines; axial-flow compressors. POWER JETS (RESEARCH & DEVELOPMENT), Ltd., and McLEOD, R. C. Jan. 23, 1945, No. 1855. [Classes 110 (i) and 110 (iii)] In order to maintain the blade tip clearances during starting and changes of temperature, the rotor blade shrouding of a compressor or turbine is formed as an inner wall which has freedom for circumferent ial expansion located in a rigid outer casing so that it may expand without increasing its diameter. which is fixed by the outer casing. The rotor blade shrouding 27, Fig. 2 and 3, consists of a number of segments interconnected by strips 28 slidably located in slots in the segments. Clearance spaces 29 allow expansion in the peripheral direction. The segments are supported by steps 27a which engage the rear edges of inlet blade platforms 17 and flanges 32 provided with a lug which engage a peripheral groove in the outer casing 20. A cooling air space 30 is formed between the segments and the casing 20. Both the outer casing and the inner walls are built up of a number of rings. The first casing ring 13 forms the outer wall of the turbine nozzles and is slotted to receive ribs or keys 18 attached to the nozzle platforms 17. The ribs or keys 18 are provided, at their rear ends, with teeth 19 which are adapted to engage a recess formed in the rear edge of the ring 13. The blades are held in place by a second ring 20 which is bolted to the ring 13 and forms therewith a cooling chamber 23. The rotor shrouding segments are placed in position in the casing 20 and are retained by the roots 38 of a row of stator blades 39 which are clamped between the flange 26 of the casing ring 20 and the third casing ring 35. An axial rib on the flange 36 locates the roots 38 and forms with the edge of the ring 35 a cooling air passage 41. The roots 38 are recessed at 42 to form another cooling air passage. The second shrouding ring 45 is mounted in the casing ring 35 in a similar manner to that of the shrouding 27. The shrouding 45 is retained in place by the flanges of the exhaust duct 50 and associated shield 49. The cooling air for the stator assembly passes from the compressor or other source through an inlet 25 and cooling chamber 23 to spaces between the ribs 18 of the blades 16 and from there through ports 31 to the cooling chamber 30. After leaving the chamber 30, the cooling air passes through the passage 41, 42 in the blade roots 38 to the cooling chamber 46. The nozzles 16 are supported at their inner tips by a ring built up of two angle rings 51, 52 bolted to the wall 3 of the inner air casing. The flanges 53, 54 of the angle rings co-operate to form seats for spigots 55 attached to the blades. The angle rings and the blade platforms 56 define a chamber 57 for cooling air supplied through a passage 58 discharged through a passage 59. The gap between the rotor elements 60, 61 is supplied with cooling air from the hollow shaft 5 through the passage 64 which also supplies air to the rear face of the element 61. The rotor elements are reinforced by an annular disc 66 which engages at its inner edge ribs 68 and has at its outer edge an annular flange 71 having driving dogs engaging dogs on ribs 72 on the elements. Passages 69 and clearance between the dogs allows cooling air to be supplied to the chambers 73 and the blade roots. To avoid internal stressing of the disc 66 due to differences of temperature between the rim 70 and the hub of the disc, saw cuts are made in the rim. The edges of these saw cuts are burred over to close the slot prior to the final machining of the rim and the weak flanges so formed are crushed at the first expan-. sion of the rim so that the slots, although open when the disc is cold are closed at the working temperature. This arrangement prevents leakage of cooling air from the chambers 73 when the engine is running. To maintain a balanced flow past the blade roots of the rotor elements 60, 61, the chambers 73 are sealed from each other by means such as grub screws in the radial part of the slots and by plugging the drilled holes which normally form the radially inner ends of the slots. The forward face of the rotor 60 and the rear face of the rotor 61 are screened by air guides 74, 76. Cooling air is supplied to the guide 74 through the bearing 75 and chamber 79 from the pressurised chamber formed between the inner air casing 3 and the shaft 5.