Sealing device for high-rotating-speed large-shaft-diameter expansion machine

Abstract

The sealing device comprises a shaft sleeve, a sealing seat, a main static ring seat and an auxiliary static ring seat, one end of the shaft sleeve is close to the main static ring seat, the other end of the shaft sleeve extends to an inner cavity of the sealing seat, and a transmission key is arranged between the inner wall of one end of the shaft sleeve and a rotating shaft. The other end of the shaft sleeve is connected with the rotating shaft through a plurality of fastening screws; a mounting boss is arranged on the outer side of the end, located in the inner cavity of the sealing seat, of the shaft sleeve. A main seal and an auxiliary seal are assembled between the two axial ends of the mounting boss and the main static ring seat and between the two axial ends of the mounting boss and the auxiliary static ring seat respectively. The side wall of the sealing seat is provided with a liquid inlet channel and a liquid outlet channel which are used for allowing flushing liquid to enter and exit, the inner wall of the sealing seat is provided with two flushing rings, and the two flushing rings are each provided with a plurality of flushing holes which are distributed in the circumferential direction and communicate with the liquid inlet channel. The utility model provides a sealing device for a high-rotating-speed large-shaft-diameter expansion machine, which can adapt to large-torque starting force, and is good in sealing performance, good in sealing surface cooling effect and long in service life.

Description

Technical Field

[0001] The utility model relates to the technical field of mechanical seals, in particular to a sealing device for a high-speed and large-diameter expander. Background Art

[0002] A turbo expander is a mechanical device driven by gas dynamic expansion. Its working principle is similar to that of a turbine. It is usually used to convert the kinetic energy of high-temperature and high-pressure gas into mechanical energy. Therefore, it is widely used in the energy field, especially in power plants, chemical processes, refrigeration and air conditioning, etc., to provide power, energy recovery and compressed air systems. Turbine expanders have the advantages of compact structure, simple manufacturing process, low price, few wearing parts, long operation cycle, small maintenance workload and high efficiency, so the application of turbo expanders is becoming more and more extensive.

[0003] The general operating conditions of traditional expanders are below 3600 rpm and the shaft diameter is within 200mm; there is another type of expander with a speed of 5000 or even 10000 rpm, but the shaft diameter is usually less than 100mm. Therefore, the mainstream mechanical seals on the market are designed for these two working conditions and can generally meet the requirements.

[0004] With the continuous expansion of the application scope of turbo expanders, the main shaft speed of a few operating conditions has reached 5000-10000 rpm, and the shaft diameter has expanded to more than 100mm. For this type of working condition, no mechanical seal in the existing technology can be well applied because of the large shaft diameter and very high linear speed. Traditional mechanical seals have the following defects: the drive structure of the sleeve and the rotating shaft cannot adapt well to the start-up of large shaft diameter and large torque; the PV value exceeds the standard due to the limitation of the sealing surface material; the friction heat cooling effect of the sealing surface is poor. The above shortcomings lead to the existing sealing structure having problems such as short life and unstable drive when used in the above special working conditions.

[0005] Therefore, it is necessary to develop a sealing device specifically for the above-mentioned special working conditions to ensure stable density performance and long service life. Utility Model Content

[0006] The problem solved by the utility model is to provide a sealing device for a high-speed large-diameter expander in order to overcome the defects in the prior art, which can adapt to large torque starting force, has stable sealing performance, good sealing surface cooling effect, and long sealing ring service life.

[0007] In order to solve the above problems, the utility model provides a sealing device for a high-speed large-diameter expander, comprising a sleeve sleeved on the outside of a rotating shaft, a cylindrical sealing seat sleeved on the outside of the sleeve, and two ends of the sealing seat are respectively connected to a main static ring seat and a secondary static ring seat, one end of the sleeve is close to the main static ring seat, and the other end extends to the inner cavity of the sealing seat, a transmission key is arranged between the inner wall of one end of the sleeve located in the inner cavity of the sealing seat and the rotating shaft, and a plurality of set screws distributed along the circumference of the sleeve are pierced on the side wall of the other end of the sleeve; an annular mounting boss is arranged on the outer side of one end of the sleeve located in the inner cavity of the sealing seat, a main seal is arranged between one axial end of the mounting boss and the main static ring seat, and a secondary seal is arranged between the other axial end of the mounting boss and the secondary static ring seat;

[0008] The side wall of the sealing seat is provided with an inlet channel and an outlet channel for the flushing liquid to enter and exit. The inner wall of the sealing seat is equipped with two flushing rings corresponding to the main seal and the auxiliary seal respectively. The radial outer walls of the two flushing rings are both concavely provided with a transition groove connected to the liquid inlet channel. The radial inner walls of the two flushing rings are both provided with a plurality of flushing holes distributed along the circumferential direction and connected to the transition grooves.

[0009] Compared with the prior art, the sealing device of the utility model has the following advantages:

[0010] 1. The transmission connection between the integral mechanical seal and the rotating shaft adopts dual drive of set screws and key connection structure, which has strong stability, especially in the field of large shaft diameter and large torque, and the key transmission is more stable and reliable.

[0011] 2. The double-end mechanical seal is adopted. The two sealing surfaces make the sealing performance higher. In the case of leakage in the first main seal, the second auxiliary seal can continue to play a sealing role, thereby ensuring the stability of the seal.

[0012] 3. In the new double-end face seal structure, the two sealing parts share a mounting boss structure during installation, which effectively shortens the axial dimension of the entire sealing structure, thereby saving the axial installation space of the seal and improving product competitiveness.

[0013] 4. Two independent flushing rings and circumferentially distributed flushing hole structures ensure the effective flushing efficiency of the sealing surface to the maximum extent, take away the heat of the sealing surface in time, avoid thermal deformation of the sealing surface at ultra-high speed, ensure sealing performance, and increase the service life of the sealing ring.

[0014] Furthermore, an annular positioning block is provided on the inner wall of the sealing seat, and the main static ring and the auxiliary static ring seat are provided with positioning bosses matched with the two ends of the inner cavity of the sealing seat at one end near the sealing seat, and one end of the two flushing rings is respectively against the two ends of the positioning block, and the other ends of the two flushing rings are respectively against the end faces of the two positioning bosses. In the above structure, the two flushing rings are axially clamped and limited between the corresponding side of the positioning block and the main static ring or the auxiliary static ring seat, without the need for other fasteners, with a simple structure and convenient disassembly and assembly.

[0015] As an improvement, both ends of the positioning block are provided with positioning pins, and one end of the two flushing rings is provided with positioning pin grooves that cooperate with the corresponding positioning pins. In the above improved structure, the flushing ring is limited by the positioning pins to avoid circumferential rotation under the force of the flushing liquid and produce abnormal noise.

[0016] Furthermore, a throttling groove is provided on the inner wall of the auxiliary static ring seat away from the sealing seat, a liquid collecting groove is provided on the inner wall of the other end of the auxiliary static ring seat, and a leakage collection channel connected to the liquid collecting groove is provided on the sealing seat. In the above improved structure, the throttling groove is designed so that the medium will not leak to the atmosphere immediately after the auxiliary seal leaks, avoiding splashing of the leaked medium, causing environmental pollution and personal injury; in addition, the medium blocked by the throttling groove can be collected through the collection channel.

[0017] In a further improvement, a purge channel connected to the inner wall of the throttle ring is further provided on the side wall of the sealing seat. In the above improved structure, the purge channel is a spare channel, that is, when the seal leaks, by blowing air into the purge channel, the leaking medium on the rotating shaft can be urged to enter the liquid collecting tank along the axial direction or directly overflow from the atmospheric end, thereby preventing the leaked liquid from accumulating on the rotating shaft.

[0018] Furthermore, the main seal includes an active ring and a main static ring, one end of the active ring is fitted to one end of the mounting boss, one end of the main static ring is fitted to one end of the main static ring seat, the other end of the main static ring is rotatably abutted against the other end of the active ring along the circumferential direction, and a first elastic compensation piece is arranged between one end of the main static ring away from the active ring and the main static ring seat.

[0019] Furthermore, the secondary seal includes a secondary dynamic ring and a secondary static ring, one end of the secondary dynamic ring is fitted to the other end of the mounting boss, one end of the secondary static ring is fitted to one end of the secondary static ring seat, the other end of the secondary static ring is rotatably abutted against the other end of the secondary dynamic ring along the circumferential direction, and a second elastic compensation piece is arranged between one end of the secondary static ring away from the secondary dynamic ring and the secondary static ring seat.

[0020] Preferably, the active ring, main static ring, auxiliary dynamic ring and auxiliary static ring are all made of silicon carbide composite materials containing free graphite. The dynamic and static ring materials use silicon carbide as the matrix and add graphite elements, which greatly improves the PV value of the material, reduces the thermal deformation of the sealing surface and the deformation under pressure, and can be applied to 10,000 rpm or even higher working conditions.

[0021] Other improved features and advantages of the utility model will be described in the subsequent specific embodiments, and partly become apparent from the description, or understood by implementing the utility model. The purpose and other advantages of the utility model can be achieved and obtained through the structures specifically pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a front view of the sealing device for a high-speed and large-diameter expander of the utility model;

[0023] Figure 2 for Figure 1 Middle AA section view;

[0024] Figure 3 for Figure 1 Middle BB section view;

[0025] Figure 4 for Figure 3 The structure diagram is enlarged at the X in the middle;

[0026] Figure 5 It is a stereoscopic diagram of the sealing device for a high-speed and large-diameter expander of the utility model.

[0027] Description of reference numerals:

[0028] 1. Bushing; 2. Sealing seat; 3. Main static ring seat; 4. Auxiliary static ring seat; 5. Transmission key; 6. Set screw; 7. Mounting boss; 8. Liquid inlet channel; 9. Liquid outlet channel; 10. Sealing chamber; 11. Flushing ring; 12. Transition groove; 13. Flushing hole; 14. Positioning block; 15. Positioning boss; 16. Positioning pin; 17. Positioning pin groove; 18. Throttle groove; 19. Liquid collecting groove; 20. Leakage collecting channel; 21. Purge channel; 22. Active ring; 23. Main static ring; 24. First elastic compensating member; 25. Auxiliary active ring; 26. Auxiliary static ring; 27. Second elastic compensating member; 28. First connecting bolt; 29. ​​Second connecting bolt. DETAILED DESCRIPTION

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0030] In the description of the present invention, it should be noted that the terms "outer wall", "inner wall", "bottom" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as a limitation on the present invention. In addition, in the description of the present invention, the terms "first" and "second" are only for the convenience of description and distinction, and have no specific meaning.

[0031] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connection" and "assembly" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0032] See attached Figures 1 to 5 The utility model provides a sealing device for a high-speed large-diameter expander, comprising a sleeve 1 sleeved on the outside of a rotating shaft, the sleeve 1 being transmission-connected to the rotating shaft, that is, the sleeve 1 rotates synchronously with the shaft during the rotation of the rotating shaft; a cylindrical sealing seat 2 is sleeved on the outside of the sleeve 1, and the two ends of the sealing seat 2 are respectively connected to a main stationary ring seat 3 and a secondary stationary ring seat 4. Specifically, as Figure 2 As shown, the main stationary ring seat 3 is provided with a plurality of first connecting bolts extending axially and distributed circumferentially, each of which is connected to one end of the sealing seat 2; similarly, as Figure 5 As shown, a plurality of second connecting bolts extending axially and distributed circumferentially are provided on the secondary static ring 26, each second connecting bolt is connected to the other end of the sealing seat 2, and the main static ring seat 3, the sealing seat 2 and the secondary static ring seat 4 are axially detachably connected by the first connecting bolts and the second connecting bolts.

[0033] In addition, one end of the sleeve 1 is close to the main stationary ring seat 3, and the other end extends to the inner cavity of the sealing seat 2. A keyway is provided on the inner wall of one end of the sleeve 1 located in the inner cavity of the sealing seat 2, and a transmission key 5 matching the keyway is connected to the outer wall of the rotating shaft to realize the transmission connection between the sleeve 1 and the rotating shaft. Figure 2 , 5 shown.

[0034] The side wall at the other end of the sleeve 1 is pierced with a plurality of set screws 6 distributed along its circumference. When the sleeve 1 is installed on the rotating shaft, in addition to the transmission key 5 for transmission cooperation, the transmission connection can also be performed through a plurality of set screws 6. In this structure, the set screws 6 and the transmission key 5 are used for double transmission connection, and the transmission structure is more stable. It can not only adapt to the starting of large shaft diameter and large torque, but also save the axial space of the sealing design.

[0035] In this embodiment, an annular mounting boss 7 is provided on the outer side of one end of the shaft sleeve 1 located in the inner cavity of the sealing seat 2, a main seal is arranged between one axial end of the mounting boss and the main static ring seat 3, a secondary seal is arranged between the other axial end of the mounting boss 7 and the secondary static ring seat 4, and a sealing cavity 10 is formed between the main seal, the secondary seal, the sealing seat 2, the main static ring seat 3 and the secondary static ring seat 4; a liquid inlet channel 8 and a liquid outlet channel 9 connected to the sealing cavity are provided on the side wall of the sealing seat 2, two flushing rings 11 corresponding to the main seal and the secondary seal are provided on the inner wall of the sealing seat 2, and a plurality of flushing holes 13 distributed along the circumference thereof and connected to the liquid inlet channel 8 are provided on the two flushing rings 11, as shown in FIG. Figure 4 shown.

[0036] In the above structure, a concave transition groove 12 is provided in the middle of the radial outer wall of the two flushing rings 11, and each flushing hole 13 is opened on the radial inner wall of the flushing ring 11 and communicated with the transition groove 12; and the transition grooves 12 of the two flushing rings 11 are both communicated with the liquid inlet channel 8; that is, after the external flushing liquid enters from the liquid inlet channel 8, it is divided into two paths and flows to the transition grooves 12 of the two flushing rings 11 respectively, and then flushes the sealing surfaces of the main seal and the secondary seal through the circumferentially distributed flushing holes 13 on the two flushing rings 11. The distributed flushing structure setting maximizes the effective flushing efficiency of the sealing surface, takes away the heat of the sealing surface, and avoids thermal deformation of the sealing surface at ultra-high speed.

[0037] On the other hand, the sealing device in this embodiment is a containerized structure, that is, before being installed on the rotating shaft of the expander, the various components of the entire sealing device are pre-assembled into an integrated structure. When installed with the expander, it is only necessary to put the sleeve 1 of the sealing device on the rotating shaft, cooperate with the rotation through the transmission key 5, and use the set screw 6 on the sleeve 1 to achieve the rotation connection with the rotating shaft; and the sealing seat 2 is connected and fixed to the installation cavity of the expander. The containerized sealing device is simple to install and operate, and has very low requirements for installation technology, which improves the work efficiency of workers in assembling machine seals; at the same time, it avoids seal damage or failure caused by installation problems to the greatest extent; from another perspective, it also reduces the seal maintenance cost and saves maintenance time.

[0038] On the other hand, in this embodiment, a double-end mechanical seal is used, that is, it includes two sealing surfaces, the main seal and the auxiliary seal, so that the sealing performance is higher. In the case of leakage in the first main seal, the second auxiliary seal can continue to play a sealing role, thereby ensuring the stability of the seal. In addition, in the sealing structure of this embodiment, the two sealing parts share a mounting boss 7 structure when installed, which effectively shortens the axial dimension of the entire sealing structure, thereby saving the axial installation space of the seal and improving the competitiveness of the product.

[0039] In this embodiment, an annular positioning block 14 is protruding outwardly on the inner wall of the sealing seat 2, and the main static ring 23 and the auxiliary static ring seat 4 are respectively provided with positioning bosses 15 matched with the two ends of the inner cavity of the sealing seat 2 at one end, and one end of the two flushing rings 11 is respectively abutted against the two ends of the positioning block 14, and the other ends of the two flushing rings 11 are respectively abutted against the end faces of the two positioning bosses 15, and the two flushing rings 11 are connected and fixed by radial clamping.

[0040] More specifically, in the above structure, positioning pins 16 are provided at both ends of the positioning block 14, and one end of the two flushing rings 11 is provided with a positioning pin groove 17 that cooperates with the corresponding positioning pin 16. The positioning pin 16 is provided to achieve a circumferential anti-rotation effect of the two flushing rings 11, thereby ensuring the stability of the two flushing rings 11 during use.

[0041] A throttling groove 18 is provided on the inner wall of one end of the auxiliary static ring seat 4 away from the sealing seat 2, a liquid collecting groove 19 is provided on the inner wall of the other end of the auxiliary static ring seat 4, and a leakage collection channel 20 connected to the liquid collecting groove 19 is provided on the sealing seat 2.

[0042] On the other hand, in the above structure, a purge channel 21 connected to the inner wall of the throttle ring is further provided on the side wall of the sealing seat 2. Gas is introduced through the purge channel 21, and the leaked medium quickly enters the liquid collecting tank 19 or directly flows out from the atmosphere side under the action of the purge gas, thereby preventing the leaked medium from accumulating on the rotating shaft.

[0043] In this embodiment, Figure 2As shown, the main seal includes an active ring 22 and a main static ring 23. One end of the active ring 22 is fitted into the first dynamic ring groove at one end of the mounting boss 7, and sealing rings are arranged between the active ring 22 and the bottom and side walls of the first dynamic ring groove; one end of the main static ring 23 is axially slidably and sealingly fitted into the first static ring groove at one end of the main static ring seat 3, and the other end of the main static ring 23 and the other end of the active ring 22 are circumferentially rotatable relative to each other to form a first friction pair; in addition, a first elastic compensation piece 24 is arranged between the end of the main static ring 23 away from the active ring 22 and the main static ring seat 3, that is, between the main static ring 23 and the first static ring groove. Specifically, the first elastic compensation member 24 includes a plurality of cylindrical first springs, and the bottom of the first static ring groove is provided with a plurality of first spring holes distributed along the circumferential direction. One end of each first spring is installed and limited in the first spring hole, and the other end abuts against the end of the main static ring 23 away from the active ring 22, which is used to compensate for the wear of the first friction pair and ensure that the sealing surfaces of the active ring 22 and the main static ring 23 are always tightly fitted. Under high speed and large shaft diameter conditions, the anti-vibration ability, sealing stability and reliability of the static ring compensation type seal are more reliable than the dynamic ring compensation type seal.

[0044] Similarly, the secondary seal includes a secondary dynamic ring 25 and a secondary static ring 26. One end of the secondary dynamic ring 25 is fitted into the second dynamic ring groove at the other end of the mounting boss 7. Similarly, a sealing ring is arranged between the secondary dynamic ring 25 and the bottom and side wall of the second dynamic ring groove. One end of the secondary static ring 26 is axially slidably and sealingly fitted into the second static ring groove at one end of the secondary static ring seat 4. The other end of the secondary static ring 26 and the other end of the secondary dynamic ring 25 are circumferentially rotatable relative to each other to form a second friction pair. A second elastic compensating member is arranged between the end of the secondary static ring 26 away from the secondary dynamic ring 25 and the secondary static ring seat 4, that is, between the secondary static ring 26 and the bottom of the second static ring groove. 27 The structure and installation method of the second elastic compensating member here are similar to those of the first elastic compensating member 24 at the position of the main static ring 23, and will not be elaborated here.

[0045] In addition, the materials of the active ring 22, the main static ring 23, the auxiliary dynamic ring 25 and the auxiliary static ring 26 involved in this embodiment are all silicon carbide composite materials containing free graphite. While greatly improving the PV value of the dynamic and static ring materials, it also enhances the self-lubricating performance of the sealing surface and prolongs the service life of the mechanical seal.

[0046] Although the disclosure is disclosed as above, the protection scope of the disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the disclosure, and these changes and modifications will fall within the protection scope of the utility model.

Claims

1. A sealing device for a high-speed and large-diameter expander, characterized in that: The invention comprises a shaft sleeve (1) sleeved on the outside of a rotating shaft, a cylindrical sealing seat (2) sleeved on the outside of the shaft sleeve (1), and two ends of the sealing seat (2) are respectively connected to a main static ring seat (3) and a secondary static ring seat (4), one end of the shaft sleeve (1) is close to the main static ring seat (3), and the other end extends to the inner cavity of the sealing seat (2), a transmission key (5) is arranged between the inner wall of one end of the shaft sleeve (1) located in the inner cavity of the sealing seat (2) and the rotating shaft, and a plurality of set screws (6) distributed along the circumference of the shaft sleeve (1) are pierced on the side wall of the other end of the shaft sleeve (1); an annular mounting boss (7) is arranged on the outer side of one end of the shaft sleeve (1) located in the inner cavity of the sealing seat (2), a main seal is arranged between one axial end of the mounting boss (7) and the main static ring seat (3), and a secondary seal is arranged between the other axial end of the mounting boss (7) and the secondary static ring seat (4); The side wall of the sealing seat (2) is provided with a liquid inlet channel (8) and a liquid outlet channel (9) for the inlet and outlet of flushing liquid. The inner wall of the sealing seat (2) is provided with two flushing rings (11) corresponding to the main seal and the auxiliary seal, respectively. The radial outer walls of the two flushing rings (11) are both provided with a transition groove (12) connected to the liquid inlet channel (8). The radial inner walls of the two flushing rings (11) are both provided with a plurality of flushing holes (13) distributed in the circumferential direction and connected to the transition groove (12).

2. The sealing device for a high-speed large-diameter expander according to claim 1, characterized in that: An annular positioning block (14) is protruding outwardly from the inner wall of the sealing seat (2); one end of the main static ring (23) and the auxiliary static ring seat (4) close to the sealing seat (2) are respectively provided with positioning bosses (15) matched with the two ends of the inner cavity of the sealing seat (2); one end of the two flushing rings (11) respectively abuts against the two ends of the positioning block (14), and the other ends of the two flushing rings (11) respectively abut against the end faces of the two positioning bosses (15).

3. The sealing device for a high-speed large-diameter expander according to claim 2, characterized in that: Both ends of the positioning block (14) are provided with positioning pins (16), and one end of the two flushing rings (11) is provided with a positioning pin groove (17) that matches the corresponding positioning pin (16).

4. The sealing device for a high-speed and large-diameter expander according to claim 1, characterized in that: A throttling groove (18) is provided on the inner wall of one end of the auxiliary stationary ring seat (4) away from the sealing seat (2), a liquid collecting groove (19) is provided on the inner wall of the other end of the auxiliary stationary ring seat (4), and a leakage liquid collection channel (20) connected to the liquid collecting groove (19) is provided on the sealing seat (2).

5. The sealing device for a high-speed and large-diameter expander according to claim 4, characterized in that: A purge channel (21) connected to the inner wall of the throttling groove (18) is also provided on the side wall of the sealing seat (2).

6. The sealing device for a high-speed and large-diameter expander according to any one of claims 1 to 4, characterized in that: The main seal comprises an active ring (22) and a main static ring (23), one end of the active ring (22) is fitted to one end of the mounting boss (7), one end of the main static ring (23) is fitted to one end of the main static ring seat (3), the other end of the main static ring (23) is rotatably abutted against the other end of the active ring (22) along the circumferential direction, and a first elastic compensation piece (24) is provided between one end of the main static ring (23) away from the active ring (22) and the main static ring seat (3).

7. The sealing device for a high-speed and large-diameter expander according to claim 6, characterized in that: The secondary seal comprises a secondary dynamic ring (25) and a secondary static ring (26), one end of the secondary dynamic ring (25) is fitted to the other end of the mounting boss (7), one end of the secondary static ring (26) is fitted to one end of the secondary static ring seat (4), the other end of the secondary static ring (26) is rotatably abutted against the other end of the secondary dynamic ring (25) in the circumferential direction, and a second elastic compensation piece (27) is provided between one end of the secondary static ring (26) away from the secondary dynamic ring (25) and the secondary static ring seat (4).

8. The sealing device for a high-speed and large-diameter expander according to claim 7, characterized in that: The active ring (22), the main static ring (23), the auxiliary active ring (25) and the auxiliary static ring (26) are all made of a silicon carbide composite material containing free graphite.

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