Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16J—PISTONS; CYLINDERS; SEALINGS
  • F16J15/00—Sealings
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16J—PISTONS; CYLINDERS; SEALINGS
  • F16J15/00—Sealings
  • F16J15/44—Free-space packings
  • F16J15/441—Free-space packings with floating ring
  • F16J15/442—Free-space packings with floating ring segmented

Definitions

• the present invention relates to seals between rotating and stationary components of a machine, for example, a steam turbine, and particularly relates to combined labyrinth/ brush seal packing ring segments positively biased for movement between large seal clearance start-up and small seal clearance steady-state operating positions about a rotary component.
• the seal faces carry a radially directed array of axially spaced teeth and which teeth are radially spaced from an array of axially spaced annular grooves forming the sealing surface of the rotating component.
• the rotating component may have a smooth surface in radial opposition to the array of teeth on the seal faces.
• the sealing function is achieved by creating turbulent flow of a working media, for example, steam, as it passes through the relatively tight clearances within the labyrinth defined by the seal face teeth and the opposing surface of the rotating component.
• a combined labyrinth/ brush seal configuration may be used as part of the sealing faces of the segments. The primary seal is therefore accomplished by the brush seal, with the labyrinth teeth serving as back-up seals in the event of a failure of the brush seal.
• the annular groove of the stationary component is dovetail-shaped, having locating flanges directed axially toward one another and defining a slot therebetween.
• the stationary component is split lengthwise such that the semi-annular dovetail grooves may receive generally correspondingly shaped arcuate seal ring segments.
• the arcuate segments are similarly dovetail-shaped, having a pair of flanges directed axially away from one another for disposition within the dovetail groove and a neck joining the seal face and the flanges of the segment and passing through the slot defined by the locating flanges of the groove.
• the neck carries the arcuate seal face radially inwardly of the groove when installed.
• variable clearance packing ring seal between stationary and rotating components which uses thermal expansion characteristics of the various elements to enable a large seal clearance between the packing ring segment sealing face and the rotating component at start-up, while ensuring a small clearance and minimal inter-segment leakage therebetween at steady-state operation.
• the packing ring segment is supported by the centering rings and each segment is biased radially inwardly by springs acting between the segments and the stationary component.
• the packing ring segments engage contact surfaces on the opposite ends of the centering rings to maintain a large clearance position at start-up between the seal faces of the segments and the rotary component. In that position, the segment ends are closed.
• the centering rings have a greater coefficient of thermal expansion than the seal holder, rotor and packing ring segments. After start-up and as the temperature rises, the centering rings thermally expand in a circumferential direction to a greater extent than the packing ring segment.
• the contact surfaces, forming the support points for the packing ring segment on the centering rings, are therefore shifted CircumferentiaUy to enable the packing ring segment to be displaced radially inwardly.
• the packing ring segments engage the outer surface of uniform diameter of the centering rings, thus assuring concentricity of the packing ring segment sealing surfaces relative to the rotary component, enabling a small uniform clearance between the sealing faces of the segments and the rotary component and opening end gaps between the seal segments.
• the result is a uniform clearance seal that retains its labyrinth tooth geometry during start-up and a steady-state operation and has minimal bias leakage.
• labyrinth/ brush seal packing ring segments which are positively biased for movement between large seal clearance start-up and small seal clearance steady-state operating positions about a rotary component.
• Any form of bias may be applied to the packing ring segments of the present invention to move the packing ring segments between the large clearance start-up position and the small clearance operating position such as, for example, the specifically described positive pressure packing ring segments and thermally activated packing ring segments herein.
• W en employing brush seals in combination with the labyrinth seals in the positively biased packing ring segments hereof the advantages of providing a large clearance seal at start-up to avoid rubs and vibration problems at start-up, as well as to provide cooling flow along the seal, are combined with the advantages of a brush seal as the primary seal in the packing ring segments.
• the brush seal at start-up is spaced from the rotor and, hence, does not contribute to rotor vibrations due to contact and generation of heat by such contact.
• the brush seal may be spaced slightly from the rotor or lie in contact with the rotor to afford a primary effective seal between the stationary and rotary components.
• a movable packing ring assembly comprising a plurality of packing ring segments about the axis, the segments having arcuate seal surfaces in opposition to the rotatable component and carrying a brush seal having tips thereof radially inwardly of the surface, each segment having at least a first arcuate flange extending in an axial direction, a spring between the locating hook and the flange for biasing each segment for movement in a radial outward direction locating the brush seal tips in first positions spaced from the rotary component and a chamber between the stationary component and the segment for displacing the segment radially inwardly against the bias of the springs to locate the bristle tips radially inwardly of the first positions thereof.
• a variable clearance packing ring comprising a packing ring segment about the axis, the segment having an arcuate seal face in opposition to the rotatable component, at least a first arcuate flange extending in an axial direction and a brush seal extending from the arcuate seal surface toward the rotatable component and having a plate on at least one side thereof, an element engageable by one of the supports and engaging the first flange at a first location therealong for maintaining the segment seal face and brush seal in a first clearance position relative to the rotating component, the element having a coefficient of thermal expansion greater than a coefficient of thermal expansion of the segment, the element engaging the first flange at a second location therealong in response to relative thermal expansion of the segment and the element, enabling the segment for displacement radially inward
• a variable clearance packing ring comprising a packing ring segment about the axis, the segment having an arcuate seal face in opposition to the rotatable component and a brush seal extending from the arcuate seal face toward the rotatable component, an element engageable by the support and engaging the segment at a first location therealong for mamtaining the segment seal face and the brush seal in a first clearance position relative to the rotating component, the element having a coefficient of thermal expansion greater than a coefficient of thermal expansion of the segment, the element engaging the segment at a second location therealong in response to relative thermal expansion of the segment and the element, enabling the segment for displacement radially inwardly relative to the element to locate the seal face in a second clearance position relative to the rotating component and radially inwardly of
• FIGURE 1 is a fragmentary cross-sectional view illustrating a plurality of packing ring seal segments between a stationary and rotary component according to the prior art
• FIGURES 3 and 3A are fragmentary axial cross-sectional views thereof, respectively, in the large and small clearance positions;
• FIGURE 4A is a fragmentary axial cross-sectional view illustrating a further embodiment of a combined labyrinth/ brush seal packing ring segment according to the present invention in a large clearance position;
• FIGURE 4B is a view similar to Figure 4A illustrating the combined labyrinth/ brush seal packing ring seal segment in a small clearance position;
• FIGURES 5A and 5B are enlarged fragmentary cross-sectional views illustrating the ends of the packing ring segments and supports therefor of Figures 4A and 4B in the large and small clearance positions, respectively;
• a multi-stage labyrinth seal 16 includes a plurality of seal rings 18, 20 and 22 disposed about turbine shaft 12, the seal rings separating high and low pressure regions 28 and 30, respectively.
• Each seal ring is formed of an annular array of a plurality of arcuate seal segments 32.
• this conventional labyrinth seal 16 functions by placing a relatively large number of partial barriers to the flow of steam from the high pressure region 28 to the low pressure region 30.
• Each barrier forces steam attempting to flow parallel to the axis of turbine shaft 12 to follow a tortuous path whereby a pressure drop is created.
• the sum of all the pressure drops in the labyrinth seal 16 is, by definition, the pressure difference between the high and low pressure regions 28 and 30.
• each packing ring segment of Figures 2 and 3 includes a sealing face 34, radially projecting tapered labyrinth teeth 36 spaced axially from one another, a pair of flanges 38 extending axially in opposite directions, arcuate locating flanges or hooks 40 which extend in axially opposite directions away from one another and a neck 45 between the locating flanges 40 and seal flanges 38.
• the chamber 33 defined by the annular groove 42 and the radially outermost surface of the segment 32 may receive high pressure fluid, for example, via a passage 35 in the stationary component.
• the high pressure fluid may be supplied to the chamber in a number of different ways including by forming grooves along the upstream or high pressure side of the seal segment itself, communicating the high pressure fluid on the upstream side to the chamber 33.
• the sealing segment has a brush seal, generally designated 37.
• Brush seal 37 includes a plurality of metal bristles 53 disposed between a pair of plates 41 and 43.
• the brush seal 37 is disposed in a groove 47 disposed in the sealing face 34 of the sealing segment.
• One of the plates 43 has a hook 49 received in a complementary recess 51 of the segment for retaining the brush seal in the segment.
• the bristles 53 at their radially outermost ends may be welded to one another and to the plates.
• the bristles 53 have tips 39 which project beyond the radially innermost edges of the plates 41 and 43 to establish with the labyrinth teeth 36 a combined labyrinth/ brush seal sealing segment.
• the sealing segments are disposed in a large clearance, radially outward position under the bias of the leaf springs 31, spacing the labyrinth teeth and the tips 39 of the brush seal from the rotor 16. Consequently, at start-up, there is no rubbing contact whatsoever between the seal and the rotor which facilitates the elimination of vibration, as well as heat build-up in the seal.
• the fluid pressure provided chamber 33 via conduit 35 overcomes the bias of the springs 31 and displaces the sealing segments radially inwardly into a small clearance position. In that position, the brush seal forms the primary seal with the rotor.
• the segment includes, similarly as in the previous embodiment, a brush seal 37 having bristles 53 extending at a cant angle between plates 41 and 43, the brush seal 37 being retained in a groove in the brush seal segment by the lateral projection 49 in complementary recess 51.
• the seal segment is maintained in a large clearance position by temperature-responsive centering rings 50 biased to a small clearance position by springs 55.
• a plurality of packing ring segment supports 48 are disposed in the cavity 42 between the locating flanges 38 and 44 of the segments 32 and housing 14, respectively.
• the supports may comprise dowels 48 at CircumferentiaUy spaced positions along the cavity 42.
• a centering ring or element 50 is provided in the cavity 42 between the dowels of the seal holder and the locating flange 38 on each axial side of the neck.
• the centering rings 50 have a circumferential extent comparable to the circumferential extent of the packing ring segments and a uniform diameter radially outer surface 52. It will be appreciated that the undersides 57 of the locating flanges or hooks 40 also have a uniform diameter radially inner surface for mating with the surface 52.
• each centering ring 50 has radial outward projections 54 with a canted contact surface 56.
• the canted contact surface 56 may be linear, convexly arcuate or may comprise a contact area or point.
• Each of the opposing end surfaces of each locating flange 38 has a contact surface 58 engaging the contact surface 56 in the large clearance position of the seal segment relative to the rotor.
• the radially innermost surface of the centering ring 50 at its opposite ends is inset or recessed such that the centering ring 50 rests on dowels 48 along recessed surfaces 62.
• the centering ring 50 also has canted surfaces 64 for engaging the dowels to prevent the centering ring from displacement in a circumferential direction relative to the segment.
• the centering rings 50 are formed of material having a coefficient of thermal expansion greater than the coefficient of thermal expansion of the sealing ring segments, the seal holder, i.e., the housing 14, and the rotor 12. Thus, any material which has a higher coefficient than the coefficient of the adjoining elements may be used as the material for the centering ring consistent with the expansion required for operation and at the temperatures of the machine.
• the packing ring segment may be formed of 409 Stainless Steel or Invar (nickel iron alloy) while the centering rings may be formed of 304 Stainless Steel. Also, as illustrated in Figure 3A, the packing ring segments at their adjoining ends in the large clearance positions thereof provide a substantial gap therebetween.
• the various elements react dimensionally differently relative to one another and enable the packing ring segments to be displaced from the large clearance to the small clearance positions, increasing slightly the gap between adjacent ends of the packing seal ring segments.
• the centering rings 50 will expand in a circumferential direction, i.e., grow thermally in the circumferential direction to a greater extent than the circumferential growth of the packing ring segment.

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

Applications Claiming Priority (1)

Publications (1)

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Family Applications (1)

Country Status (4)

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• 2000
  • 2000-02-01 KR KR1020017007011A patent/KR20010112226A/ko not_active Application Discontinuation
  • 2000-02-01 JP JP2001556031A patent/JP2003521657A/ja not_active Withdrawn
  • 2000-02-01 EP EP00913310A patent/EP1169587A1/de not_active Withdrawn
  • 2000-02-01 WO PCT/US2000/002479 patent/WO2001057420A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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