Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
  • F01D5/00—Blades; Blade-carrying members; Heating, heat-insulating, cooling or antivibration means on the blades or the members
  • F01D5/12—Blades
  • F01D5/22—Blade-to-blade connections, e.g. for damping vibrations
  • F01D5/225—Blade-to-blade connections, e.g. for damping vibrations by shrouding
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
  • F01D9/00—Stators
  • F01D9/02—Nozzles; Nozzle boxes; Stator blades; Guide conduits, e.g. individual nozzles
  • F01D9/04—Nozzles; Nozzle boxes; Stator blades; Guide conduits, e.g. individual nozzles forming ring or sector
  • F01D9/042—Nozzles; Nozzle boxes; Stator blades; Guide conduits, e.g. individual nozzles forming ring or sector fixing blades to stators
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
  • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
  • F05D2260/00—Function
  • F05D2260/30—Retaining components in desired mutual position
  • F05D2260/37—Retaining components in desired mutual position by a press fit connection

Definitions

• the present invention relates to a novel construction for diaphragms of the type used in axial flow turbomachines. It is particularly, but not exclusively, relevant to steam turbine diaphragms.
• Figure 1 A is a perspective view of a static blade or vane
• Figure 1 B is a view on a radial section of a diaphragm during manufacture, including the static blade.
• the ends of the aerofoils 1 are integral with radially inner and outer
• platforms 2, 3, the aerofoils and platforms being machined from solid.
• Figure 1 A an adjacent blade shape is shown in dashed lines, a complete annulus of static blades being built up by assembling successive combined aerofoil/platform components 4 into an annular array between inner and outer diaphragm rings 5, 6 and welding the platforms to the diaphragm rings.
• the inner and outer diaphragm rings and platforms are further machined as appropriate to accommodate turbine sealing features and to fit adjacent turbine features. When the assembly is finished, the inner and outer platforms
• the current practice for HP and IP steam turbines employing platform construction is to build the blades onto the inner diaphragm ring and then to shrink the outer diaphragm ring on to the blades.
• the inner diaphragm ring is required to support the static blades and to give the diaphragm rigidity against forces that tend to distort it during assembly and operation of the turbine.
• a turbine diaphragm comprises: an annulus of static blades, each static blade comprising an inner platform, an aerofoil and an outer platform; and an outer diaphragm ring surrounding the annulus of static blades and welded to the outer platforms; wherein the inner platforms serve the function of an inner diaphragm ring, confronting edges of the inner platforms have an interference fit with each other and the aerofoils are in a state of torsional stress between the inner and outer platforms.
• the invention eliminates the prior art inner diaphragm ring and the welds that attach it to the blade inner platform, so reducing the material and manufacturing requirements for the diaphragm. Furthermore, elimination of the inner diaphragm ring, with accompanying increase in the radius of the turbine rotor against which the inner platforms must seal, reduces the total pressure load of the turbine working fluid on the diaphragm.
• Torsional stress in the aerofoils is achieved during assembly of the diaphragm by: initially assembling the annulus of blades so that selected confronting edge portions of neighbouring inner platforms are in contact with each other, while all confronting edge portions of neighbouring outer platforms have clearances between them; and radially compressing the annulus of blades with the outer diaphragm ring to a predetermined final diameter by forcible contact between an internal surface of the outer diaphragm ring and external surfaces of the outer platforms, so that clearances between selected confronting edge portions of the neighbouring outer platforms are closed up, the contact between the selected confronting edge portions of the neighbouring inner platforms becomes an interference fit, and an elastic torsional stress is built into the aerofoils.
• the selected confronting edge portions of neighbouring outer platforms comprise an edge portion that is axially aligned and an edge portion that is inclined with respect to the circumferential direction.
• Figures 1 A and 1 B illustrate the prior art "platform" type of turbine diaphragm construction, Figure 1 A being a perspective view of a static blade or vane, and Figure 1 B being a partial view on a radial section of a diaphragm during the manufacturing process;
• Figure 2 shows a partial radial sectional view of two moving turbine blade rows, and a fully assembled turbine diaphragm in accordance with the invention, located between the moving blade rows;
• Figures 3A and 3B are isometric perspective views of a single static blade from a diaphragm similar to that shown in Figure 2, Figure 3A being a view on the concave (pressure) side of the blade aerofoil and Figure 3B being a view on the convex (suction) side of the blade aerofoil;
• Figure 4 illustrates the process of cutting a number of half diaphragm rings out of a metal plate, in accordance with the invention
• Figure 5 illustrates the construction of a whole diaphragm ring from two half diaphragm rings;
• Figure 6 is a radial section through the radially outer part of a turbine diaphragm assembly according to the invention.
• FIGS. 7 A and 7B illustrate part of the process of assembling a turbine diaphragm according to the invention
• Figures 8A and 8B compare inter-platform clearances and contacts in a prior art platform type of turbine diaphragm construction with those in a construction in accordance with the present invention
• Figure 9 is a diagrammatic radial section through the outer part of a turbine diaphragm during a welding process according to the invention.
• Figure 10 is an isometric perspective view of the end of a half diaphragm after a machining process has been carried out on the welds of Figure 9 to split the welded diaphragm into two halves for further machining.
• FIG. 2 is partial radial sectional sketch of an embodiment of the invention, showing a fully assembled diaphragm 10 located between successive annular rows of moving blades 12, 13 in a steam turbine.
• the moving blades are each provided with radially inner "T-root" portions 14, 15 located in corresponding slots 16, 17 machined in the rim of a rotor drum 18.
• They are also provided with radially outer shrouds 19, 20 that seal against circumscribing segmented rings 21 , 22.
• sealing between the 19, 20 shrouds and the rings 21 , 22 is accomplished by fins 23, 24, which are caulked into grooves machined in the rings 21 , 22.
• Diaphragm 10 comprises an annular row of static blades, each having an aerofoil 30 whose radially inner and outer ends are integral with radially inner and outer platforms 31 , 32, respectively.
• Figures 3A and 3B are pictorial views of the opposite sides of a static blade before it is assembled into a diaphragm, showing the shapes of the inner and outer platforms 31 , 32.
• the radially outer surfaces of platforms 32 are welded onto the inner diameter of a massive outer diaphragm ring 33, which stiffens the diaphragm and controls its thermal expansion and contraction during operation of the turbine.
• the inner platforms 31 are made thick enough to house a floating labyrinth seal 31 A or the like, which seals between the diaphragm 10 and the rotor drum 18.
• Another feature of the present invention is that the shapes and relative dimensions of the inner and outer platforms 31 , 32, and the assembly process for the diaphragm 10, as described below, enable the aerofoils to be subjected to a degree of twist between their radially inner and outer ends; i.e., compared to their condition before assembly into the diaphragm, the assembly process rotates the inner platforms 31 slightly relative to the outer platforms 32 about an axis of twist running roughly radially through each blade. This pre-stresses the blades, which has a favourable effect on the dynamic behaviour of the blades under load.
• Figure 8A illustrates contacts and clearances between neighbouring platforms in a finished prior art construction
• Figure 8B illustrates contacts and clearances for a finished construction of the present invention.
• the approximate positions of the aerofoils 30 relative to the platforms 31 , 32 are shown in dashed lines.
• the inner platforms are narrower in the circumferential direction than the outer platforms.
• the inner and outer platforms in Figure 8A have the same axial width.
• the axial width of the outer platforms is shown as being greater than the axial width of the inner platforms, though they could also be of the same width.
• Neighbouring inner and outer platforms in both Figures 8A and 8B have an interlocking zigzag or cranked shape along their interfaces when seen in plan view.
• the inner platforms 31 have circumferentially extending leading and trailing edges L(i), T(i), relative to the steam flow through the turbine passages, whose direction is shown by the block arrows.
• the circumferentially extending leading and trailing edges of the outer platforms 32 are labelled L(o), T(o).
• the cranked shape of the interface between the inner platforms in Figure 8A is achieved in that the mutually confronting edges 80(i) of neighbouring platforms comprise first and second, respectively shorter and longer, axially aligned edge portions 81 (i) and 82(i) that are circumferentially offset from each other, so forming first and second axially extending arms of the crank shape.
• the first axially aligned edge portion 81 (i) is followed by an inclined edge portion 83(i) that forms the inclined arm of the crank shape and connects the first axially aligned edge portion 81 (i) to the second axially aligned edge portion 82(i).
• the edge portion 83(i) is inclined at an angle - ⁇ to the circumferential direction.
• ⁇ is about 25 degrees, but may be more or less than this at the discretion of the designer.
• the mutually confronting edges 80(o) of neighbouring outer platforms in Figure 8A have first and second, axially aligned, circumferentially offset edge portions 81 (o) and 82(o), respectively, connected by inclined edge portions 83(o).
• FIG 8B illustrate features in accordance with the invention
• Figures 3A and 3B are pictorial views of a blade incorporating the same features.
• the inner platforms 31 have the same basic shape as described above for Figure 8A, and the confronting edge portions that make up the cranked shape of the interface between their confronting platform edges are therefore similarly labelled.
• the outer platforms 32 are different, in that the interface between their confronting platform edges 80(o)1 forms a double cranked shape. This is achieved in that platform edges 80(o)1 each comprise first, second and third axially aligned edge portions 81 (o), 84(o) and 85(o), respectively.
• first, second and third axially extending arms of the crank shape are circumferentially offset from each other, so forming first, second and third axially extending arms of the crank shape.
• the first axially aligned edge portion 81 (o) is shorter than the second axially aligned edge portion 84(o) and the third axially aligned edge portion 85(o) is shorter than the first axially aligned edge portion 81 (o).
• the first axially aligned edge portion 81 (o) is followed by a first inclined edge portion 83(o) that forms a first inclined arm of the crank shape and connects the first axially aligned edge portion 81 (o) to the second axially aligned edge portion 84(o).
• Edge portion 84(o) is followed by a second inclined edge portion 86(o) that forms a second inclined arm of the crank shape and connects the second axially aligned edge portion 84(o) to the third axially aligned edge portion 85(o).
• the edge portion 83(o) is inclined at the angle - ⁇ to the circumferential direction.
• the edge portion 86(o) is inclined at a different angle + ⁇ to the circumferential direction.
• ⁇ is about 45 degrees, but may be more or less than this at the discretion of the designer.
• the outer platforms in Figure 8A have the same contact and clearance characteristics as the inner platforms, though clearances may differ in exact dimensional terms.
• Figure 8B shows that the inner platforms are dimensioned so that in the fully assembled state:
• the initial steps in manufacture of the diaphragm 10 are production of the diaphragm ring 33 and the static blades, the latter comprising aerofoils 30 formed integrally with inner and outer platforms 31 , 32.
• the diaphragm ring 33 In a known method of manufacturing the diaphragm ring 33, it is cut out of heavy gauge steel plate as a complete ring, machined to a desired sectional profile, and then cut along a diameter into two semi-circular pieces to enable assembly and disassembly of the blades within its inner diameter.
• the preferred method for the present invention is to start by making the diaphragm ring in two halves 33A, 33B, by cutting each half ring separately from the plate material. As shown in Figure 4, this allows more efficient use of the plate material, so reducing material costs, since the half-ring shapes 33A, 33B for cutting out from the plate 34 can be partially nested inside each other.
• the confronting ends 101 of the two half-rings 33A, 33B are drawn together into interfering contact with each other by inserting threaded studs 36A into the threaded holes 37, 38, putting spacers 36B and washers 36C over the ends of the studs 36A in the recesses 38A where the studs 36A project above the holes 38 in the half-ring 33A, and tightening clamping nuts 36D on the studs against the spacers 36B until a predetermined torque value is obtained.
• the solid lines show the outline of the outer platform 32 and the diaphragm ring 33 after initial machining and assembly into a diaphragm and before final machining.
• the chain-dashed lines show their outlines after final machining to shape as a complete diaphragm.
• their inner circumferences are machined to produce raised lands 39, which facilitate later welding of the assembled diaphragm ring 33 to the outer platforms 32.
• the inner surfaces of lands 39 on the half-rings and the outer surfaces 32A of outer platforms 32 have been machined so that the lands 39 have a taper angle, ⁇ .
• the taper angle ⁇ is about 5 Q relative to a plane P parallel to the axis of rotation of the turbine rotor.
• the angle ⁇ could be more or less than this, at the discretion of the designer, taking into account the diaphragm assembly technique to be adopted (see below), any axial taper of the outer platforms, and the fluid dynamic requirements of the turbine stage.
• the outer platforms' thickness may be tapered in either an upstream or downstream axial direction, so reducing or increasing the taper angle ⁇ required for the lands 39.
• the taper angle ⁇ depends on the flare angle of the outer wall of the turbine passage, this being the angle at which it converges towards, or diverges away from, the axis of rotation of the turbine rotor in the downstream direction. Note that in a steam turbine it is possible for high pressure (HP) turbine stages near the HP steam entry to exhibit negative flare, i.e., they may have a local angle of convergence. Hence, the taper angle ⁇ could also be negative for such a turbine stage.
• a ring of the static blades comprising aerofoils 30 and inner and outer platforms 31 , 32, are assembled on to a location plate 40 on a horizontal assembly table 41 , as shown in the sectional side view of Figure 7A.
• the blades are initially arranged so that the inclined edge portions 83(i) of neighbouring inner platforms 31 are in contact with each other, there being clearances between the other mutually confronting edge portions 81 (i) and 82(i).
• Figure 7A shows that there is a radial clearance of X between the circumference of the location plate 40 and a lip 32B that delimits a location step on the edges of the outer platforms 32. Accordingly, there are clearances between the confronting edges 80(o)1 of neighbouring outer platforms.
• the diaphragm ring 33 is held horizontally and concentrically with the ring of static blades, then lowered so that the inner surface of the welding land 39 slides evenly onto the outer surfaces 32A of the outer platforms 32.
• the diaphragm ring 33 is then forced further down onto the outer platforms 32, thereby bringing the second inclined, mutually confronting, edge portions 86(o), and the second axially extending, mutually confronting, edge portions 84(o) of neighbouring outer platforms into contact.
• small clearances are maintained between mutually confronting edge portions 81 (o) and 83(o).
• the final position of the diaphragm ring 33 is as shown in Figure 7B, in which its upper face is in-line (or very nearly so) with the leading edges L(o) of the outer platforms 32 and the clearance X has closed up to a small nominal value.
• the diaphragm ring 33 can be forced down to the position shown in Figure 7B by means of an array of clamps (not shown) that are equally spaced around the circumference of the diaphragm ring and act compressively between the table 41 and the diaphragm ring.
• the radial compression produces an interference fit between the initially contacting edge portions 83(i) on neighbouring inner platforms of the blades, thereby putting the required degree of twist into the aerofoils.
• This pre-stressing of the blades favourably influences their dynamic behaviour in the diaphragm.
• the interference fit between the edge portions 83(i) on the inner platforms produces a rigid band around the inner diameter of the completed diaphragm, thereby favourably influencing diaphragm dynamic behaviour.
• An alternative way of closing up clearances between confronting edge portions 84(o) and 86(o) of neighbouring outer platforms would be to heat the assembled diaphragm ring 33 (and optionally also cool the ring of blades), place the diaphragm ring over the ring of blades, and then shrink the diaphragm ring onto the outer platforms as the diaphragm ring cools down.
• a further alternative way of achieving the same end would be to position the half-rings 33A, 33B ( Figure 5), one on each side of the ring of blades, insert the bolts and spacers, etc., 36A - 36D, and gradually draw the half-rings together until their confronting end surfaces 101 meet, the appropriate interference between them being achieved by tightening the bolts to a predetermined value of torque.
• twisting of the aerofoils between the inner and outer platforms during assembly of the diaphragm 10 results in pre-stressing of the blades. This twisting is accomplished by:
• a second location plate 42 (see Figure 9) is placed over the leading edges of the blade platforms, the second location plate having a diameter sufficient to overlap the inner diameter of the leading edges L(o) of the outer platforms.
• the second location plate is then clamped to the first location plate 40 by means of a number of nut and bolt arrangements (not shown) that pass through both location plates at equi-angularly spaced locations within the inner diameter of the inner platforms. Smaller clamps attached to the second location plate 42 hold the diaphragm ring 33 in the correct position against the taper for further processing.
• both of the location plates 40, 42 are welded to the outer platforms of the blades, as shown in Figure 9 where triangular weld beads 90 are shown joining the location plates to the platform edges.
• This gives adequate support to the assembly during the main welding process in which, as shown in Figure 9, the diaphragm ring 33 is welded to the outer platforms 32 by filling in the annular spaces 91 between them with welds 92. Because the annular spaces 91 are axially deep, the welds 91 may be produced in two or more weld passes, the spaces 90 being partially filled during each weld pass.
• Figure 9 shows the situation after three out of four weld passes, two weld passes having been completed on the platform leading edge side of the assembly and one weld pass having been completed on the platform trailing edge side of the assembly.
• splitting of the welded diaphragm into two half-diaphragms can done by machining pockets 100 into the deep welds 92 previously produced between the diaphragm ring 33 and the outer platforms 32, so that over a short circumferentially extending length of the welds 92 on both sides of the diaphragm, the weld material is completely removed.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Turbine Rotor Nozzle Sealing (AREA)

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• 2007
  • 2007-01-12 GB GB0700633A patent/GB0700633D0/en not_active Ceased
• 2008
  • 2008-01-08 WO PCT/EP2008/050130 patent/WO2008084038A1/en active Application Filing
  • 2008-01-08 CN CN201510077475.5A patent/CN104763479B/zh not_active Expired - Fee Related
  • 2008-01-08 CN CN200880001871.8A patent/CN101578429B/zh not_active Expired - Fee Related

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