HK1018965B - Turbine seal - Google Patents

Description

Turbine seal

Technical Field

The present invention relates to sealing of air flow between a stationary and a rotating member of a mechanical device, such as a turbine.

Background

A turbine is a known device which is characterised by a rotatable member which is rotated by a force. The force is typically generated by the flow of a high pressure gas, such as steam, over a series of blades connected to the rotating member. The efficiency of a turbine is determined by its ability to maintain rotation using as much of the force as possible. The sealing device prevents steam from escaping from the working space of the turbine and air from leaking into the working space of the turbine, thereby maintaining the efficiency of the turbine.

Various sealing devices used on turbomachines are known, such as gland seals, shaft seals, labyrinth seals, steam seals, diaphragm packings and pressurized packings. FIG. 1 illustrates a cross-sectional view of a typical vapor seal. In the figure, a plurality of sealing strips 4 extend towards a rotor 2. The sealing strip 4 preferably has a triangular edge. Distance C for clearance between seal strip 4 and rotor 2_SAnd (4) showing. These sealing strips 4 are supported by a ring 6. The ring 6 is mounted on a fixed part 8 of the turbine. A spring 10 presses the ring 6 inwards towards the rotor 2 and allows the radially expanded ring to move away from the rotor. Such seals are provided, for example, next to an opening in the turbine housing through which the rotor protrudes. In operation, these seals serve to trap most of the gas so that it cannot escape through the space between the rotor of the turbine and the stationary part surrounding the rotor.

In some applications, it is common to use several rings 6, each supporting several sealing strips 4. Fig. 2 is a cross-sectional view of a stationary part 8 of a turbine, on which rings 6 are mounted, each ring supporting a number of sealing strips 4.

FIG. 3 is a partial perspective view of a segment of a seal surrounding a rotor of a turbine. The seal includes a packing head 26 which is operatively mounted on a stationary member of the turbine to surround a portion of a rotating member of the turbine. Several ring segments 28 are fitted in the pockets 29 of the packing head. Each ring segment 28 supports a number of sealing strip segments 30. The segment seal is sealingly engageable with another segment to surround and seal a rotatable member of a turbine.

Figure 4 shows several ring segments 28 that may be used in the packing head shown in figure 3. Each ring segment supports several sealing strip segments 30. The sealing strip sections have an inner diameter R_SEAL. The inner diameter is selected to correspond to a portion of a rotating member of the turbine,so that the desired clearance is created when the ring segments seal with the rotor.

Figure 5 shows a seal for a rotatable member 2 having alternating high and low portions 12, 14 on its surface. The sealing strip 4 is chosen such that its inner diameter R_SEALSo that a gap C is maintained between the sealing strips 4 and the corresponding portion of the rotor 2 at the tip of each sealing strip 4_S。

US-A-4,979,755 describes A labyrinth seal having A flow barrier wall that reduces circumferential flow around the turbine rotor.

The effectiveness of the gland seal is greatly dependent on maintaining as little clearance as possible between the sealing strip and the rotating member. The contact between the sealing strip and the rotating member wears the sealing strip, so that the clearance increases and the sealing performance decreases. Contact is most likely to be caused by transient conditions in which the relative position of the rotating member and the seal deviates from the normal position. Transient conditions often occur when the turbine is turned on, off, unloaded or over-rated. Transient conditions can cause the rotating member to rub against the seal, wear the seal strip, and leave debris on the surface of the rotating member. It is therefore desirable to prevent the rotating member from coming into contact with the sealing strip.

Useful background information may also be found in Sanders' operating maintenance personnel turbine gas path engineering, 1988 edition; the content of which is included as reference material in the present specification.

Summary of the invention

A first aspect of the invention is to prevent contact between the sealing strips and a rotating member with which they form a seal, by means of a friction strip which engages with a sealing strip. The rubbing strip comprises a strip of material coaxial with the sealing strip of the gland seal, and the clearance between the rubbing strip and the rotating member is less than the minimum clearance of the sealing strip engaged therewith. In this structure, when the relative position of the rotor and the seal deviates from the normal position, the rubbing strip first comes into contact with the rotor. The material and cross-sectional shape of the rub strip may be selected according to the desired wear characteristics. The rubbing strip can be integrated with the sealing ring or can be inserted into a matching slot device on the sealing ring.

Another aspect of the invention is a packing head for a turbine, which incorporates a rub strip as described above. The rub strip is located on a seal ring supported by the stuffing head. The rubbing strip may be integral with a sealing ring or may be inserted into a slot in the sealing ring. The material and cross-sectional shape of the rub strip may be selected according to the desired wear characteristics.

Another aspect of the invention is directed to a ring segment for a seal. The ring segment includes one or more sealing strip segments and one or more friction strip segments. A plurality of such ring segments may be used to form a sealing ring. The friction bar segment is selected such that the inner diameter of the friction bar segment is less than the minimum clearance between the associated seal bar segment and the rotor.

Another aspect of the invention is a friction bar segment particularly adapted for use in a ring segment of a gland seal. The friction bar segment is selected to be: the clearance between the sealing strip and the corresponding part of a rotating piece is smaller than the minimum clearance between the sealing strip section matched with the sealing strip section and the rotating piece.

Another aspect of the invention is a method of using a turbine seal comprising a plurality of seal strip segments. A desired radial clearance between the seal bar segments and a rotor of the turbine is determined. A seal strip segment of the seal is then removed and replaced with a rub strip segment. The inner diameter of the friction bar segment may be such that the clearance between the friction bar segment and the rotor is less than the required radial clearance of the seal bar segments.

Other aspects of the invention are detailed below.

Brief description of the drawings

The present invention is best understood from the following detailed description and the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a prior art gland seal surrounding a rotating member.

FIG. 2 is a cross-sectional view of a prior art gland seal including a plurality of sealing rings.

Figure 3 shows a portion of a prior art packing head in which several sealing rings are installed.

Fig. 4 shows a prior art packing ring segment.

FIG. 5 is a cross-sectional view of a prior art gland seal surrounding a rotating member.

Fig. 6 shows a rub strip and a seal strip of the present invention.

FIG. 7 is a cross-sectional view of a vapor seal around a rotating member including the rub strip of the present invention.

FIG. 8 is a cross-sectional view of a vapor seal of the present invention including a rub strip in the "high" position.

FIG. 9 is a cross-sectional view of a vapor seal of the present invention including a rub strip in a "low" position.

FIG. 10 illustrates a ring segment of the present invention including a sealing strip segment and a friction strip segment.

FIG. 11 shows a friction bar segment of the present invention.

Best mode for carrying out the invention

Fig. 6 is a cross-sectional view of a rub strip 16 in use with a seal strip 4 in accordance with the present invention. The rubbing strip 16 is disposed beside a sealing strip 4. The friction strip 16 and the sealing strip 4 are supported by a ring 6 surrounding a rotatable member 2. The sealing strip 4 is held in place by a fillet 5, while the friction strip is preferably held in place by a base 20 inserted in a matching notch 21 of the ring 6. The clearance between the sealing strip and the rotating part is C_SThe clearance between the rubbing strip and the rotating member is C_R，C_SGreater than C_R. As can be seen from this figure, when the rotor 2 is out of its normal position relative to the rub strip 16 and the seal strip 4, the rotor contacts the rub strip 16, thereby lifting the ring 6 off the rotor rather than contacting the seal strip 4. The clearance between the rubbing strip and the rotating member is preferably as large as possibleCan be small but ultimately depends on design data. A gap of 0.0513-0.0641mm (0.0020-0.0025 inches) provides satisfactory performance. However, as will be appreciated by those skilled in the art, the gap between the rub strip and the rotor preferably does not result in constant contact.

The rub strip 16 of fig. 6 and other figures comprises a strip of rectangular cross-section and a base 20 of rectangular cross-section, both of which form a T-shaped cross-section that is inserted into a matching notch 21. Such a rub strip can be easily inserted into a ring 6, and then the ends of the ring are slightly deformed to hold the rub strip in place. The rubbing strip is preferably sized to form a gap C_AAnd C_XTo facilitate insertion and extraction of the rub strip. Although this cross-sectional shape is preferred for strength and ease of insertion and extraction, other shapes may be used and, in addition, the rub strip may be formed integrally with the ring 6.

The choice of material for the rub strip may be determined by the particular requirements of the application. It is generally preferred to select a wear resistant material that will not damage the rotating member when contacted. The coefficient of friction of such materials is generally less than that of steel. Examples of such materials are carbon and chromium steels.

Fig. 7 is a cross-sectional view of a first embodiment of the gland seal of the present invention. A ring 6 mounted on a stuffing head 8 supports a plurality of sealing strips 4. The ring 6 surrounds a rotor 2 such as a rotor. Preferably, the ring 6 has a rubbing strip 16 on each side. A spring 10 presses the ring 6 towards the rotor 2. Clearance C between friction bar 16 and rotor 2_RLess than the clearance C between the sealing strip and the rotor_S. As can be seen from this figure, when the rotor 2 is out of its normal position relative to the rub strip 16 and the seal strip 4, the rotor contacts the rub strip 16, thereby lifting the ring 6 off the rotor rather than contacting the seal strip 4. One of ordinary skill in the art will recognize that different numbers of rub strips may be used in a loop; if a single friction strip is used, the strip is preferably centered in the spring.

Fig. 8 is a cross-sectional view of another embodiment of the vapor seal of the present invention. A ring 6 mounted on a stuffing head 8 supports a plurality of sealing strips 4. The ring 6 surrounding a rotor or the likeHaving one or more high portions 12 and one or more low portions 14. Some of the sealing strips 4 correspond to the high part of the rotor and others of the sealing strips 4 correspond to the low part of the rotor. Two friction bars 16 are arranged on either side of the ring 6 in positions corresponding to the high portions 12 of the rotor 2. A spring 10 presses the ring 6 towards the rotor 2. Clearance C between friction bar 16 and rotor 2_RLess than the clearance C between the sealing strip and the rotor_S. As can be seen from this figure, when the rotor 2 is out of its normal position relative to the rub strip 16 and the seal strip 4, the rotor contacts the rub strip 16, thereby lifting the ring 6 off the rotor rather than contacting the seal strip 4. Fig. 9 shows another embodiment in which the friction bars 16 correspond to the lower part of the rotor 2. It will be appreciated by those skilled in the art that the present invention can be used with any type of rotating member, provided that a rub strip is used with an appropriate clearance to the rotating member.

It will be apparent to those skilled in the art from the foregoing embodiments that the illustrated ring 6 may be formed from the ring segments 28 shown in FIG. 4. Fig. 10 shows a ring segment 28 comprising a base 29 supporting a number of sealing strip segments 30 and two friction strip segments 32. The inner diameter R of the friction bar segments 32 and the seal bar segments 30_RUBAnd R_SEALA desired gap is formed with a corresponding portion of a rotating member (not shown). The inner diameter of the rub strip segment 32 is selected to form a gap that is less than the minimum gap of the seal strip segment 30. The ring segment 28 may include a spring (not shown) that biases the ring segment radially inward when mounted to a stationary member of a turbine. The friction bar section may be integral with the ring section or may be supported in a slot into which the bottom of the friction bar section is inserted.

It will be apparent to those skilled in the art that the ring segments 28, sealing strips 30 and rubbing strips 32 of fig. 10 can also be used with other types of rotating components, such as the steam seals shown in fig. 8 and 9. The radius of the rotor at the location corresponding to a friction or sealing strip section is then determined and the inner diameter is selected according to the invention so that the appropriate gap between the respective friction and sealing strip sections is formed.

FIG. 11 shows a friction bar segment 32 that may be used in the ring segment of FIG. 10 havingA slot into which the rub strip segment 32 is inserted. The rub strip segment 32 includes a strip 18 and a base 20. The strip 18 has an inner diameter R_RUBThe inner diameter is selected to correspond to a portion of the rotating member to form the desired clearance.

Although the invention has been described with reference to specific embodiments, it will be apparent to those skilled in the art that various modifications and alternatives can be made to the embodiments within the scope of the invention as defined in the claims.

Claims (34)

1. A seal for use between an outer stationary member and an inner rotating member of a turbomachine, comprising:

a ring arrangement (6) supportable by said outer stationary member (8) of said turbine for encircling said inner rotating member (2) of said turbine,

-at least one annular sealing strip (4) supported by said ring means (6) and extending from said ring means (6) towards an outer surface of said rotary member (2), characterized in that:

an annular rubbing strip (16) supported by said ring means (6) and extending from said ring means (6) towards said outer surface of said rotor (2),

a clearance C between the rubbing strip (16) and the outer surface of the rotating member (2)_RIs smaller than the minimum clearance C between the at least one sealing strip (4) and the outer surface of the rotating element (2)_S。

2. A seal as claimed in claim 1, wherein said sealing strip (4) and said rubbing strip (16) extend radially inwardly from said ring means (6) towards said outer surface of said rotary member (2).

3. The seal according to claim 1, characterized in that said ring means (6) is formed by a plurality of ring segments (28), each of said ring segments (28) supporting at least one sealing strip segment (30) comprising a segment of said at least one sealing strip (4) and a friction strip segment (32) comprising a segment of said friction strip (16).

4. A seal as claimed in claim 1, characterised in that said rubbing strip (16) is made of a material having a lower coefficient of friction than steel.

5. The seal of claim 4 wherein said material is carbon.

6. A seal as claimed in claim 4, wherein said material is chrome steel.

7. A seal as claimed in claim 1, characterised in that the cross-section of the rubbing strip (16) is rectangular.

8. A seal as claimed in claim 1, further comprising a spring means (10) for biasing said ring means (6) towards said rotary member (2), wherein said friction strip (16) is located centrally of said spring means (10).

9. A seal according to claim 2, wherein said at least one sealing strip (4) comprises a plurality of sealing strips extending radially inwardly towards said outer surface, and wherein a radial clearance C is provided between said rubbing strip (16) and said outer surface_RLess than the minimum radial clearance C between the sealing strips (4) and the outer surface_S。

10. A seal as claimed in claim 1, characterised by comprising two rubbing strips (16) spaced on either side of said ring means (6).

11. The seal of claim 10, wherein said at least one sealing strip (4) comprises a plurality of sealing strips extending radially inwardly toward said outer surface; a radial clearance C between the two friction strips (16) and the outer surface_RLess than the minimum radial clearance C between the sealing strips (4) and the outer surface_S。

12. A seal according to claim 1, wherein said rubbing strip (16) is axially spaced from each of said at least one sealing strip (4).

13. A shaft end packing for forming a seal around a rotor (2) of a turbine, comprising:

a stuffing head arrangement (26) surrounding the rotor (2), comprising slot means for insertion of one or more ring segments (28), and

a plurality of ring segments (28) mounted on said packing head means (26),

each of said ring segments (28) comprising:

at least one sealing strip segment (30) extending radially inwardly toward an outer surface of said rotor (2), characterized by:

a friction bar segment (32) extending radially inward toward the outer surface of the rotor (2),

between the friction bar segment (32) and the outer surfaceRadial clearance C of_RLess than a minimum radial clearance C between the at least one sealing strip segment and the outer surface_S。

14. The packing of claim 13, wherein each ring segment (28) further comprises spring means (10) biasing said ring segment (28) radially inwardly.

15. The packing of claim 13, wherein said friction bar segments (32) are formed of a material having a coefficient of friction less than that of steel.

16. The filler material of claim 15 wherein said material is carbon.

17. The filler material of claim 15 wherein said material is chromium steel.

18. The packing of claim 13, wherein said rub strip segment (32) includes a base (20) and a strip (18), said strip (18) being rectangular in cross-section.

19. The packing according to claim 14, wherein said ring segment (28) comprises a friction strip segment (32) centrally located in said spring means (10).

20. The packing of claim 19 wherein said ring segment (28) includes a plurality of sealing bar segments (30) extending radially inwardly toward said outer surface; a radial clearance C between the friction bar segment (32) and the outer surface_RLess than a minimum radial clearance C between the plurality of seal bar segments (30) and the outer surface_S。

21. The packing of claim 13 wherein said ring segment (28) includes two friction bar segments (32) spaced on opposite sides of said ring segment (28).

22. The packing of claim 21 wherein said ring segment (28) includes a plurality of sealing bar segments (30) extending radially inwardly toward said outer surface; a radial clearance C between the friction bar segment (32) and the outer surface_RLess than a minimum radial clearance C between the plurality of seal bar segments (30) and the outer surface_S。

23. The packing of claim 13, wherein said friction bar segment (32) is axially spaced from each of said at least one seal bar segments (30).

24. A ring segment (28) for a shaft end packing which forms a seal around a rotor (2) of a turbine, said rotor (2) having an outer surface, said packing ring segment (28) comprising:

a bottom part (29),

n sealing strip segments (30), said sealing strip segments (30) extending with said bottom (29) and radially inwardly from said bottom (29), each sealing strip segment (30) having an inner diameter R_NsealEach sealing strip segment (30) corresponding to one of N portions of the rotor (2), each of said portions of the rotor (2) having an outer diameter R_NrotorThe method is characterized in that:

a rub strip segment (32) extending with said base (29) and radially inward from said base (29), said rub strip segment having an inner diameter R_RUBThe outer diameters of the friction strip section (32) and the rotating piece are R_ROTORA part of (a) corresponds to (b),

the radial clearance between the inner surface of the friction bar segment (32) and the outer surface of the corresponding portion of the rotor (2) is less than the minimum radial clearance between the inner surfaces of the N sealing bar segments and the outer surface of the rotor (2).

25. The ring segment (28) of claim 24 further comprising biasing means (10) mounted to said ring segment (28).

26. The ring segment (28) of claim 24 wherein said friction bar segment (32) is formed of a material having a coefficient of friction less than steel.

27. The ring segment (28) of claim 26 wherein said material is carbon.

28. The ring segment (28) of claim 26 wherein said material is chrome steel.

29. The ring segment (28) of claim 24 wherein said friction bar segment (32) comprises a base (20) and a bar (18), said bar (18) being rectangular in cross-section.

30. The ring segment (28) of claim 25, wherein said ring segment (28) includes a friction strip segment (32) centrally located in said biasing means (10).

31. The ring segment (28) of claim 24 wherein said ring segment (28) comprises M friction bar segments (32), each of said friction bar segments (32) being attached to said base (29)

Extend together and radially inwardly from said bottom (29), each of said M rub strip segments (32) having an inner diameter R_MrubEach of said friction bar segments (32) corresponding to one of M portions of said rotor (2), each of said M portions of said rotor (2) having an outer diameter R_Mrotor-a radial clearance between the inner surface of each of said M rubbing strip segments and the outer surface of the corresponding portion of the rotor (2) is smaller than the minimum radial clearance between the inner surfaces of said N sealing strip segments (30) and the outer surface of the rotor (2).

32. The ring segment (28) of claim 24 wherein said rub strip segment (32) is axially separated from each of said N seal strip segments (30).

33. A method of using a seal for a turbomachine, the seal comprising a plurality of seal bar segments (30), each seal bar segment (30) having an inner diameter defining a radial gap with respect to a rotor (2) of the turbomachine, the method comprising:

(a) determining a minimum radial clearance C between the sealed sealing strip section (30) and the outer surface of the rotor (2)_S；

(b) Removing a sealing strip section (30) of the seal; and

(c) replacing the sealing strip section (30) with a friction strip section (32), the friction strip section (32) having an inner diameter such that a radial clearance C between the friction strip section and the rotor (2) is provided_RLess than the minimum radial clearance C determined in step (a)_S。

34. The method of claim 33, wherein said rub strip segment (32) comprises an arcuate member including a root (20) and a strip (18) integral with said root (20), said rub strip segment (32) having a T-shaped cross-section; step (c) of the method includes securing the root portion (20) of the rub strip segment (32) to the seal.