JP2005003056A - Expanded graphite ring gland packing and seal mechanism for steam valve - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an expanded graphite ring gland packing having good sealing performance in a high temperature region with low fastening force while securing its soundness and long life, and to provide a seal mechanism for a steam valve. <P>SOLUTION: A packing body 5 is formed in a ring shape with knitting yarns 4 braided by stainless fine wires 3 for covering the outer periphery of an expanded graphite tape 2 and further braided in plural number. The packing body 5 has a square radial cross section and a pair of acute angle portions 6a, 6b at diagonal positions on the cross section. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ring-shaped gland packing made of expanded graphite and applied to a steam seal of a steam valve of a steam plant, for example, a main steam stop valve disposed in a steam turbine system of a nuclear power plant or a steam control valve. The present invention relates to a seal mechanism using a packing.
[0002]
[Prior art]
For example, in a nuclear power plant, periodic inspection of a nuclear reactor is carried out almost every year. At that time, a main steam stop valve disposed in a steam turbine system or a valve device in a steam valve such as a steam control valve. The overhaul inspection of the is also carried out at the same time.
[0003]
When disassembling and inspecting the valve device, the gland packing constituting the seal mechanism of the steam valve is replaced. In general, the basic operation cycle is to continue the operation of the plant without stopping during the period until the next periodic inspection after the periodic inspection. Therefore, if the plant is operating smoothly, it will be continuously operated for 13 to 14 months, and therefore it is indispensable to ensure soundness and extend the life of the sealing performance of the valve equipment.
[0004]
By the way, as for the gland packing that constitutes the seal mechanism of the steam valve such as the main steam stop valve or the steam control valve in a nuclear power plant, conventionally, the core is mainly composed of asbestos and mainly oil and graphite. A gland packing that can be used as a single unit is often used, which is formed by knitting the outer periphery of the bag with asbestos yarn containing metal wire and subjecting it to a lubrication treatment with a liquid lubricant and fine graphite.
[0005]
A gland packing using such an asbestos thread containing a metal wire is generally formed into a ring shape having a substantially square radial cross section, and is strong and non-fluid in material, that is, has a small deformation amount. . Therefore, each corner of the gland packing having a quadrangular cross section is rounded during molding, and conversely, the gland packing 1a cannot be completely molded into a quadrangle, for example, as shown in the cross-sectional shape of FIG. Sometimes, the gap b remains in the corner portion a in the seal box, and the constituent material of the gland packing 19 moves to the residual space b due to the influence of the valve shaft operation, and thereby the distortion rate and density of the gland packing 19 However, the seal performance may become unstable due to fluctuations depending on the location.
[0006]
As for the gland packing applied in other fields, a gland packing made of expanded graphite is known in which a tape-shaped material such as expanded graphite tape is wound in a spiral shape and die-molded into a ring shape ( Patent Document 1).
[0007]
However, in the case of an expanded graphite gland packing constructed by winding such a tape-shaped material in a spiral shape, it is inevitable that a minute gap is generally formed in the rolled portion of the tape-shaped material, There is a problem that the pressurized fluid permeates into the minute gap and the leakage of the pressurized fluid is likely to occur.
[0008]
In order to overcome this problem, in recent years, a structure in which a gland packing obtained by braiding a knitting yarn obtained by braiding the outer periphery of a tape-like expanded graphite with a fine stainless steel wire is die-molded into a ring shape has been proposed. (See Patent Documents 2 to 5).
[0009]
Further, as a shape of the gland packing, for example, a shape having a trapezoidal radial cross section is applied, and a plurality of gland packings having such a shape are stacked in a state where the trapezoidal sloping surface is in contact with each other, so A technique has also been proposed in which the mobility along the line is increased to improve the sealing performance (see Patent Document 6).
[0010]
However, even in the gland packing having such a configuration, the auxiliary material is hardened and deteriorated in an atmosphere where a high compressive force acts and is directly subjected to a load of a high-temperature fluid, and further cut in the case of asbestos fiber. Stress reduction occurred due to the decrease in the volume of the gland packing due to, and frequent tightening work was sometimes required.
[0011]
[Patent Document 1]
JP-A-7-301338
[Patent Document 2]
Japanese Patent Laid-Open No. 9-280379 [0013]
[Patent Document 3]
JP 2001-132848 A
[Patent Document 4]
Japanese Patent Laid-Open No. 2001-182841
[Patent Document 5]
Japanese Patent Laid-Open No. 2002-22023
[Patent Document 6]
Japanese Utility Model Publication No. 2-84062
[Problems to be solved by the invention]
As described above, in the prior art, in the case of packing using metal wire asbestos yarn, the structure is strong and the material does not have fluidity, that is, the amount of deformation is small. A gap remains in the seal box when the gland packing is installed, the gland packing moves to the residual space due to the effect of the valve shaft operation, and the distortion and density of the gland packing varies depending on the location, resulting in poor sealing performance. There was a problem to become stable.
[0018]
Also, in an atmosphere where high pressure is applied and directly subjected to a high-temperature fluid load, the auxiliary material may be hardened and deteriorated, and stress relaxation may occur due to volume reduction of the gland packing due to cutting of asbestos fibers. There was a problem to do.
[0019]
In addition, since a general gland packing has a square cross section, the stress conversion ratio is small when the clamping force is low, that is, the clamping force is not sufficiently transmitted to the packing and the sealing performance becomes unstable. There was a problem.
[0020]
On the other hand, with the conventional expanded graphite die-molded gland packing, it is inevitable that a minute gap is formed in the rolled portion of the tape-shaped material, and pressurized fluid penetrates into this minute gap and pressurizes. There was a problem that fluid leakage was likely to occur.
[0021]
Therefore, the sealing mechanism of a valve device applied to a steam plant or the like that has been exposed to high-temperature steam for a long period of time in the past, and the gland packing applied to it are satisfactory even under a low tightening force. The problems are that the sealing performance can be maintained, the soundness can be secured, the life can be extended, and the like.
[0022]
The present invention has been made in view of such circumstances, and in the case of a high temperature region and a low tightening force, while being able to exhibit good sealing performance, it is possible to ensure soundness and prolong life, etc. An object is to provide a ring-shaped gland packing and a seal mechanism for a steam valve.
[0023]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the invention according to claim 1 comprises a packing body in which a plurality of braided yarns whose outer periphery of an expanded graphite tape is braided and coated with a fine stainless steel wire are further braided and formed into a ring shape, An expanded graphite ring-shaped gland packing characterized in that a radial cross section of the packing body is a quadrangle and a pair of corners at diagonal positions of the cross section are acute angles.
[0024]
In the invention which concerns on Claim 2, the inner peripheral surface and outer peripheral surface of the said packing body are the cylindrical surfaces arrange | positioned on the ring line in parallel and concentric circles, and in the ring shape of the said packing body 2. The expanded graphite ring-shaped gland packing according to claim 1, wherein the radial cross section is a parallelogram.
[0025]
In the invention which concerns on Claim 3, the volume ratio which the said stainless steel fine wire occupies with respect to the said packing body is 2-6%, The expanded graphite ring-shaped gland packing of Claim 1 is provided.
[0026]
In the invention according to claim 4, the packing body is made of expanded graphite according to claim 1, wherein the packing body is impregnated with one or more lubricants selected from a tetrafluoroethylene polymer resin, a solid lubricant, and a liquid lubricant. Provide ring-shaped gland packing.
[0027]
The invention according to claim 5 provides the ring-shaped gland packing made of expanded graphite according to claim 1, wherein the packing body can be opened and closed through a cut surface formed at one place in the circumferential direction in the ring shape. .
[0028]
In the invention which concerns on Claim 6, the said packing body is set as the structure which superposed | polymerized in the said axial direction the some division body divided | segmented along the axial direction of the said ring shape, The inner peripheral surface in each said division body The overall length along the axial direction of the inner peripheral surface and the outer peripheral surface of the packing body at the time of polymerization is substantially the same while the length along the axial direction between the outer peripheral surface and the outer peripheral surface is different. An expanded graphite ring-shaped gland packing is provided.
[0029]
In the invention according to claim 7, a plurality of the expanded graphite ring-shaped gland packings according to any one of claims 1 to 6, and the tapered surfaces formed on the inner peripheral surface and the outer peripheral surface thereof are in contact with each other. The steam valve seal is characterized in that it is stacked along the axial direction and accommodated in a packing case formed around the drive shaft of the steam valve to seal the outer peripheral surface of the drive shaft. Provide mechanism.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of an expanded graphite ring-shaped gland packing and a seal mechanism according to the present invention will be specifically described below with reference to the drawings. First, an embodiment will be described with reference to FIGS.
[0031]
FIG. 1 is an enlarged perspective view showing a configuration of a ring-shaped gland packing made of expanded graphite according to an embodiment of the present invention as a partial cross section. As shown in FIG. 1, in the expanded graphite ring-shaped gland packing 1 of the present embodiment, for example, the outer periphery of a plurality of expanded graphite tapes 2 aligned in parallel is braided and covered with a thin stainless steel wire 3. One knitting yarn 4 is formed as a basic component. Expanded graphite is a material having a dense structure and excellent moldability and shape retention, and has a structure in which strength enhancement treatment is applied as a so-called knit knitting reinforcement by knitting coating of the fine stainless steel wire 3.
[0032]
A plurality of the knitting yarns 4 that are the basic constituent elements are further braided to form a thick string-like body. The desirable number of knitting yarns 4 for braiding the string-like body is four or more, and is nine in the illustrated example. In this way, by forming a string-like body with four or more knitting yarns 4, a three-dimensional configuration can be obtained. In the example of FIG. 1, a string-like body having a sufficient thickness in the vertical and horizontal directions is obtained by adopting a three-dimensional configuration in which three knitting yarns 4 are knitted in the vertical and horizontal directions.
[0033]
A ring-shaped packing body 5 is configured by loading such a string-like body into a mold (not shown) and die-molding it. As shown in FIG. 1, the packing body 5 has a ring-shaped radial cross section that is a quadrangle, and a pair of corner portions 6 a and 6 b that are diagonally positioned on the cross section has an acute angle. The angles of the pair of corners 6a and 6b that are acute angles are both 45 °, for example. Another pair of corner portions 7a and 7b at the diagonal positions different from the above in the packing body 5 are both obtuse angles of 135 °. However, these angles are not limited to the above example, and can be variously changed according to dimensions, tightening force, ambient temperature, and the like.
[0034]
The inner peripheral surface 5a and the outer peripheral surface 5b of the packing body 5 having such a ring shape are cylindrical surfaces arranged concentrically and parallel to each other with respect to the center line O in the ring shape. Moreover, the radial cross section in the ring shape of the packing body 5 is a parallelogram (for example, rhombus). Based on these components, the surfaces in the axis crossing direction (the upper surface 5c and the lower surface 5d in FIG. 1) in contact with the ring-shaped inner and outer peripheral surfaces are respectively tapered surfaces (umbrella shapes).
[0035]
In addition, the volume ratio which the stainless fine wire occupies with respect to the whole packing body 5 shall be 2-6%. This is because when the volume ratio occupied by the stainless steel thin wire 3 is less than 2%, the shape retention force decreases, and when it exceeds 6%, the flexibility decreases and the flexibility and lubricity also decrease.
[0036]
Further, the surface and the inside of the packing body 5 are impregnated with a solid lubricant 8 such as tetrafluoroethylene polymer resin (PTFE) or fine powder graphite and a liquid lubricant 9. A lubrication treatment is performed by impregnation of a tetrafluoroethylene polymer resin and fine powder graphite, and an impervious treatment of vapor, liquid, etc. is performed by impregnation of a liquid lubricant, and thereby a valve that is a target of a seal mechanism described later. Lubrication is promoted and fluid is prevented from entering the sliding contact surface with the drive shaft (valve rod) and the like.
[0037]
Note that the types of the lubricants 8 and 9 are merely examples, and other solid lubricants and the like can be applied. In other words, any structure that is impregnated with at least one lubricant selected from various solid lubricants 8 and liquid lubricants 9 may be used.
[0038]
FIG. 2 is a system configuration diagram showing a steam turbine plant including a steam valve to which the above-described gland packing 1 is applied. As shown in FIG. 2, the gland packing 1 of the present embodiment is applied to a steam valve provided in a main steam pipe in a nuclear power plant, for example. This plant includes a main steam pipe 11 that supplies steam from a reactor (not shown) to the steam turbine 10, and the main steam pipe 11 is provided with a main steam stop valve 12 and a steam control valve 13. The grant packing 1 is applied as the seal mechanisms 14 and 15 such as the main steam stop valve 12 and the steam control valve 13.
[0039]
A plurality of seal mechanisms 14, 15 are provided in seal boxes 20, 21 arranged on the outer peripheral surfaces of drive shafts (valve rods) 18, 19 of cylinder mechanisms 16, 17 that drive the main steam stop valve 12 and the steam control valve 13. For example, three (3) gland packings 1 are stacked and filled, and function as high-temperature steam leakage from the outer peripheral surfaces of the drive shafts (valve rods) 18 and 19.
[0040]
FIG. 3 is a cross-sectional view showing a state where the gland packing is attached to the steam valve or the like. In the example of FIG. 3, seal boxes 20 and 21 are formed around drive shafts (valve rods) 18 and 19 in a steam valve or the like, and three gland packings 1 are connected to the drive shafts (valve rods) 18 and 19. It is arrange | positioned around the circumference | surroundings, it is laminated | stacked in the superposition | polymerization state along the axial direction, and the state which has received the compressive force F by the packing presser 22 from the axial direction is shown. In the gland packing 1 of the present embodiment, the ring shape has an inner peripheral surface and an outer peripheral surface parallel to the central axis O, and the cross section is a parallelogram, so that the tightening force F along the axial direction is a radius. It is converted into a force f (seal pressure) in the direction, and the leakage of steam is prevented by this seal pressure.
[0041]
FIG. 4 is a plan view of the gland packing 1 in the present embodiment, and FIG. 5 is a side view of FIG. As shown in these drawings, the packing body 5 can be opened and closed through a cut surface 23 formed at one place in the circumferential direction in the ring shape. This cut surface is formed as a slope. And by giving the external force which goes to the direction which expands the packing body 5 from the cut surface 23, while being able to open the packing body 5, it can be closed by the external force of the opposite direction, and also to an axial direction The cut surface 23 as an inclined surface can be closed in a superposed state by the compressive force along.
[0042]
With such a configuration, when the gland packing 1 is attached to or removed from the drive shafts (valve rods) 18 and 19 such as steam valves, it can be attached from the direction perpendicular to the axis, and attachment / detachment work is facilitated. It can be carried out. However, this configuration exemplifies a desirable configuration that can be easily attached and detached. In the present invention, such a cut ring configuration is not necessarily required. For example, a closed ring configuration may be used.
[0043]
Next, functions based on the above configuration will be described.
[0044]
FIG. 6 is a characteristic diagram showing the relationship between the tightening pressure (vertical axis) and the distortion rate (horizontal axis) for the gland packing 1 of the present embodiment in comparison with the conventional asbestos gland packing.
[0045]
Regarding the gland packing 1 of the present embodiment, as shown by the characteristic line A (solid line) in FIG. 6, the change in the distortion rate with respect to the clamping pressure is small, whereas in the case of the conventional asbestos gland packing, As indicated by the characteristic line B (broken line) in FIG. 6, the change in strain rate with respect to the clamping pressure is large. This means that in the gland packing 1 of the present embodiment, the tightening pressure surely acts as the seal pressure on the seal portion, which indicates that the stress conversion ratio is large.
[0046]
As shown in FIG. 3, in this embodiment, the cross-sectional shape of the gland packing 1 is a parallelogram, and the pair of corners 6a and 6b facing each other in the radial cross section of the gland packing 1 are acute angles. This is because the side pressure transmission characteristic for converting the above-described tightening force F into the radial force f is improved, and the sealing performance can be stabilized.
[0047]
On the other hand, in the conventional general asbestos gland packing, since the radial cross section is formed in a substantially square shape, the stress conversion ratio is small at the time of low tightening force. It can be seen from the characteristics of FIG. 6 that the sealing performance may become unstable in the conventional configuration.
[0048]
FIG. 7 is a characteristic diagram showing the stress relaxation characteristics, and contrasts the change in the remaining time (vertical axis) of the clamping pressure with respect to the gland packing 1 of this embodiment over time (horizontal axis) with the conventional asbestos gland packing. As shown.
[0049]
As for the gland packing of this embodiment, as shown by the characteristic line C in FIG. 7, a high clamping pressure residual ratio persists for a long time, and the asbestos gland packing shown as the characteristic line D in FIG. In comparison, the stress relaxation rate is low.
[0050]
This is based on the fact that the gland packing of the present embodiment is made of expanded graphite and has a dense structure, and the amount of the fine stainless steel wire occupying the volume of the whole gland packing is 2 to 6 vol%.
[0051]
By having such stress relaxation characteristics, in the case of the present embodiment, it is possible to mold with a sharp corner structure while maintaining the strength of the corners 7a to 7d of the gland packing 1. In addition, there is no residual space (b in FIG. 9) between the seal boxes 20 and 21 and the packing retainer 22 when the gland packing is attached. Thereby, it is possible to prevent the movement of the residual space b due to the influence of the valve stem operation, and it is possible to avoid a decrease in tightening pressure due to a change in packing density.
[0052]
For this reason, as shown in FIG. 7, the sealing performance can be stabilized. And since the fall of clamping pressure can be avoided, a valve control function can also be stabilized.
[0053]
As a result, according to the present embodiment, when applied as a seal mechanism to a steam valve or the like, the stress relaxation characteristics of the gland packing 1 can be reduced. Therefore, unlike the conventional asbestos gland packing 1a, the gland packing 1a is frequently used. There is no need for additional tightening work, and the service life can be extended.
[0054]
Therefore, according to the present embodiment, good sealing performance can be exhibited even in a high temperature region and a low tightening force, and soundness can be ensured and the life can be extended.
[0055]
FIG. 8 is a sectional view showing another embodiment of the gland packing according to the present invention.
[0056]
In the embodiment shown in FIG. 8, the packing body 5 has a configuration in which a plurality of divided bodies 23 and 24 divided along the axial direction of the ring shape are overlapped in the axial direction. And while the length along the axial direction of the inner peripheral surface and outer peripheral surface in each division body 23 and 24 is different, the whole length along the axial direction of the inner peripheral surface and outer peripheral surface of the packing body 5 at the time of superposition | polymerization Are substantially the same.
[0057]
That is, the sectional shape of each of the divided bodies 23 and 24 is tapered from the inner diameter side to the outer diameter side, and one of the divided bodies (upper part in FIG. 8) 23 is the axial length (L1) of the inner peripheral surface. Is large, and the axial length (L2) of the outer peripheral surface is small. Conversely, the other divided body (lower part in FIG. 8) 24 has a small axial length (L2) of the inner peripheral surface and a large axial length (L1) of the outer peripheral surface. And when the divided bodies are superposed through the tapered surface, the overall length along the axial direction of the inner peripheral surface and the outer peripheral surface of the packing body 5 is the same (L1 + L2).
[0058]
In addition, since it is substantially the same as that of FIG. 1 about the component of each division body, the same code | symbol as FIG. 1 is attached | subjected to FIG. 6, and description is abbreviate | omitted.
[0059]
According to the configuration of the gland packing 1 in such another embodiment, by combining the inner and outer diameter lengths L1 and L2 as different from each other, the tightening force is applied to the tapered surface E, and the seal pressure is further improved. be able to.
[0060]
【The invention's effect】
As described above, according to the present invention, an expanded graphite ring-shaped gland packing capable of exhibiting good sealing performance even in a high temperature region and a low tightening force, and ensuring soundness and prolonging the life, and the like. A seal mechanism for a steam valve can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a gland packing according to the present invention.
FIG. 2 is a system diagram showing an application example of gland packing to a plant according to an embodiment of the present invention.
FIG. 3 is a cross-sectional view showing a sealing mechanism using a gland packing according to an embodiment of the present invention.
FIG. 4 is a plan view of an embodiment of a gland packing according to the present invention.
FIG. 5 is a side view of FIG. 4;
FIG. 6 is a characteristic diagram showing the relationship between the tightening pressure and strain rate of the gland packing in one embodiment of the present invention.
FIG. 7 is a characteristic diagram showing the stress relaxation rate of the gland packing in one embodiment of the present invention.
FIG. 8 is a cross-sectional view showing another embodiment of the present invention.
FIG. 9 is an explanatory view showing an example of a conventional asbestos gland packing.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Gland packing 2 Expanded graphite tape 3 Stainless steel wire 4 Knitting yarn 5 Packing body 6a, 6b Corner | angular part 7a, 7b Corner | angular part 5a Inner peripheral surface 5b Outer peripheral surface 5c Upper surface 5d Lower surface 8 Solid lubricant 9 Liquid lubricant 10 Steam turbine 11 Main steam pipe 12 Main steam stop valve 13 Steam control valve 14, 15 Seal mechanism 16, 17 Cylinder mechanism 18, 19 Drive shaft (valve rod)
20, 21 Seal box 22 Packing retainer 23, 24 Divided body E Taper surface F Compressive force f Radial force O Center line in ring shape

Claims (7)

A packing body in which a plurality of braided yarns whose outer periphery of expanded graphite tape is braided and coated with stainless steel wires is further braided and formed into a ring shape is provided, and the radial cross section of the packing body is square, and diagonal positions of the cross section A ring-shaped gland packing made of expanded graphite, characterized in that the pair of corners in FIG. The inner peripheral surface and the outer peripheral surface of the packing body are cylindrical surfaces arranged in parallel and concentric with the center line in the ring shape, and the radial cross section in the ring shape of the packing body is a parallelogram. The ring-shaped gland packing made of expanded graphite according to claim 1. 2. The expanded graphite ring-shaped gland packing according to claim 1, wherein a volume ratio of the stainless fine wire to the packing body is 2 to 6%. The expanded graphite ring-shaped gland packing according to claim 1, wherein the packing body is impregnated with one or more lubricants selected from a tetrafluoroethylene polymer resin, a solid lubricant, and a liquid lubricant. 2. The expanded graphite ring-shaped gland packing according to claim 1, wherein the packing body can be opened and closed through a cut surface formed at one place in a circumferential direction in a ring shape. The packing body has a structure in which a plurality of divided bodies divided along the axial direction of the ring shape are superposed in the axial direction, and in the axial direction between the inner peripheral surface and the outer peripheral surface of each divided body. 2. The expanded graphite ring-shaped gland packing according to claim 1, wherein the lengths along the axial direction of the inner circumferential surface and the outer circumferential surface of the packing body at the time of polymerization are substantially the same while the lengths are different. A plurality of expanded graphite ring-shaped gland packings according to any one of claims 1 to 6, wherein the taper surfaces formed on the inner peripheral surface and the outer peripheral surface thereof are brought into contact with each other and laminated along the axial direction. A steam valve sealing mechanism characterized in that the steam valve is housed in a packing case formed around the drive shaft of the steam valve to perform steam sealing of the outer peripheral surface of the drive shaft.

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