JPH0465265B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a gland packing used in nuclear reactors and the like to seal valve stems of gate valves, etc., and a method for manufacturing the same. (Prior art) This type of conventional ground packing (hereinafter abbreviated as GP) is made by bag-weaving asbestos string with a mixture 2 of asbestos, graphite, etc. and oil and fat that provides sealing properties, as shown in Figure 5. One wrapped with a braided body 1, one formed by winding a tape-shaped expanded graphite sheet (expanded graphite tape) 3 shown in the cross-sectional view of FIG. 6, and one formed by stacking a plurality of annular expanded graphite sheets 3'. (Figure 7) is known. Figure 4 is a cross-sectional view showing how to use GP.
Insert GP10 from the top of 3 (6 pieces in the figure)
It is stored in a packing box 11. Next, hold the GP10 from above with the gland 12, and then tighten the screw 1.
6 to compress the GP 10 and prevent fluid such as water from leaking along the valve stem 13 from the lower gap 17. When the machine moves, the valve stem 13 moves up and down as shown by the arrow and slides on the inner peripheral surface of the GP 10. Usually, a combination of GP containing fibers such as asbestos and GP made of expanded graphite alone is used to maintain sealing properties. (Problem to be solved by the invention) However, GP containing oil has the disadvantage that the oil oozes out at high temperatures of 100°C or higher, reducing sealing performance.
GP) has excellent sealing properties at high temperatures, but
The winding type shown in FIG. 6 has a slightly large sliding resistance because graphite tends to adhere to the valve stem, etc., and the stacking type shown in FIG. 7 has the disadvantage of poor flexibility. GP is often used with a notch 6 as shown in Figure 2.
The left end 7 and right end 8 of the valve are spread vertically by hand and passed through a valve stem or the like. At this time, the notch 6
The vicinity of point 9 on the opposite side of 180 degrees acts as a fulcrum and is twisted, but if the flexibility is poor, delamination or breakage may occur. For this reason, the laminated type
The ring is divided into two parts and used in combination.
The workability of inserting and removing GP is poor. An object of the present invention is to solve the above-mentioned problems and provide graphite GP which has low sliding resistance and excellent flexibility, and a method for producing the same. (Means for Solving the Problems) As a result of intensive study from various angles by the present inventors,
If we use a GP made by laminating expanded graphite sheets formed into a corrugated shape instead of a GP made by laminating and molding flat expanded graphite sheets, the stress of deformation will be absorbed by the corrugated part, and the flexibility and sealing performance will be significantly improved. The present invention was completed based on the discovery that the present invention is possible. The present invention involves molding expanded graphite powder or a flat expanded graphite sheet punched into an annular shape to form an annular expanded graphite sheet having corrugations concentrically in the radial direction, and then filling the annular space of a mold with expanded graphite at the bottom. Powder or a molded product thereof is spread, a plurality of annular expanded graphite sheets having concentric corrugations are stacked on top of the powder, expanded graphite powder or a molded product thereof is placed on top of the annular expanded graphite sheet, and the expanded graphite powder or a molded product thereof is placed on top of the sheet and then pressed with an annular upper punch. The present invention relates to a method for manufacturing a gland packing that is molded and integrated, and a gland packing manufactured by the method. In the present invention, an annular expanded graphite sheet having concentric corrugations in the radial direction (hereinafter referred to as a corrugated ring) is used to form an annular shape of a mold consisting of, for example, a die, a core, and a lower punch having concentric corrugations on the upper surface. The space is filled with expanded graphite powder, and the expanded graphite powder is compressed by the lower punch and an annular upper punch whose lower surface has a concentric waveform consisting of valleys or peaks that match the waveform peaks or valleys of the lower punch. Obtained by molding. Instead of the expanded graphite powder, a flat expanded graphite sheet punched out into an annular shape and molded using the mold described above may be used. The lower punch and core described above may be integrated or used in combination. The number of peaks or valleys in the waveform ring may be one or more, and the pitch thereof is not particularly limited. The radius of curvature at the top of the valley is preferably 0.5 mm or more. If it is too small, it will be easy for the corrugated ring to become rough. In addition, expanded graphite powder is obtained by immersing graphite powder such as natural graphite, pyrolytic graphite, and Kitsushi graphite in a mixture of concentrated sulfuric acid and an oxidizing agent such as concentrated nitric acid, potassium chlorate, and potassium permanganate, and then washing it with water. It is made by rapidly heating to about 1000℃ to expand the interlayer graphite (in the C-axis direction), and this is formed into a sheet by rolling etc. to form a flat expanded graphite sheet. Both the powder and the sheet are known. use. The bulk density of the expanded graphite powder and the thickness of the expanded graphite sheet are not particularly limited, but the thickness of the sheet to obtain a corrugated ring is 0.1
~1.0 mm is preferred. Figure 3 shows an example of a wave ring,
a is a plan view, b is a cross-sectional front view taken along line A-A′ of a;
Two valleys 15 are arranged concentrically in the radial direction on both sides of one peak 14. GP usually consists of a die attached to a press, a core, and a lower punch with a flat top surface. In the annular space of the mold, expanded graphite powder is first stored at the bottom, and multiple corrugated rings are stacked on top of it. Expanded graphite powder is placed on top of it, and the above-mentioned article is pressure-molded and integrated with the upper punch and the lower punch, each of which has a flat lower surface. The upper and lower sides are sandwiched between expanded graphite molded bodies (one-sided corrugated ring) 5 each having a corrugated one side. In the above manufacturing method, instead of using expanded graphite powder, a one-sided corrugated ring in which expanded graphite powder has been formed into a corrugated shape on one side may be placed above and below the corrugated ring. If the corrugated rings are adhered to each other and/or the corrugated ring and the one-side corrugated ring using a flexible adhesive, it is more effective to prevent peeling. It is also possible to form a corrugated GP by laminating and molding only the corrugated ring. (Function) Even if GP is twisted when passing through a valve stem, etc., the stress of deformation is absorbed by the corrugated portion, preventing delamination and breakage. (Example) Next, an example of the present invention will be described. Example 1 An expanded graphite sheet (manufactured by Hitachi Chemical Co., Ltd., trade name: Carbofit) with a thickness of 0.38 mm was punched into an annular shape, and then a die with an inner diameter of 48 mm and a diameter of 32 mm was attached to a press.
It is stored in the annular space between the mm core and compression-molded with an annular upper punch and lower punch (the valleys of the upper punch and the peaks of the lower punch coincide) with concentric waveforms to a total thickness of 3 mm. , the third with an outer diameter of 48 mm and an inner diameter of 32 mm.
A wavy ring having peaks 14 and valleys 15 as shown in the figure was obtained.
Note that the top of the valley of the wavy ring was 1R. Next, replace the upper punch and lower punch with ones whose lower and upper surfaces are flat, and fill the annular space in the mold with a bulk density of 0.002g/
cm ³ expanded graphite powder (manufactured by Hitachi Chemical, HGP-7)
2g of the expanded graphite powder was added and molded lightly so that the volume was reduced to half, then 28 of the above corrugated rings were added, and on top of that, 2g of the expanded graphite powder was added and pressure molded under a total pressure of 3 tons to give a thickness of 8mm. got a GP. Comparative Example 1 The same expanded graphite sheet used in Example 1 was
33 pieces punched to 48mm and 32mm inner diameter are stacked together.
Pressure molding was performed using the press used for molding the GP in Example 1 to obtain a GP with a thickness of 8 mm and a cross section shown in FIG. 7. Comparative example 2 Carbofit tape with a thickness of 0.38 mm and a diameter of 32 mm.
This was wound around a core having an outer diameter of approximately 48 mm, and this was pressure molded using the press used for molding in Example 1 to obtain a GP having the same dimensions as in Example 1. The GP obtained in Example 1 and Comparative Examples 1 and 2 was cut using a diamond cutter as shown in Figure 2.
A 45 degree cut 6 was made and the following test was conducted. (1) Flexibility test A test was conducted on 8 GPs in which the left end 7 and right end 8 of the notch 6 in Figure 2 were manually expanded up and down to a valve stem diameter of 32 mm (the GP was twisted). The GPs of Example 1 and Comparative Example 2 had no abnormalities, but all of the GPs of Comparative Example 1 caused delamination. (2) Sliding test In Figure 4, 8 pieces of the same type of GP are assembled in a packing box, and the tightening pressure by the gland is
Table 1 shows the frictional resistance (sliding resistance) when the valve stem is moved up and down at 300Kg/cm ² and 400Kg/cm ² . Incidentally, there was almost no adhesion of graphite powder to the valve stem when the GPs of Example 1 and Comparative Example 1 were used, but adhesion was observed when the GP of Comparative Example 2 was used. (3) Compression Ratio In (2), the compression ratio when the GP was tightened to 400Kg/cm ² was also measured and is shown in Table 1. The compression ratio was calculated using the following formula from the values of the thickness T ₁ before compression and the thickness T ₂ after compression. Compression ratio (%) = T ₁ - T ₂ / T ₁ × 100 (4) Water leak test In Fig. 4, 8 GPs of the same type are used, the tightening pressure is 400 kg/cm ² , and the valve stem is stationary. Water pressure was applied from below, and the water pressure was measured when water began to leak from the gap between the valve stem and the valve stem. The test results are shown in Table 1.

[Table] As can be seen from Table 1, the resistance of the GP of Example 1 when moving the valve stem up and down is the same as that of the laminated flat plate of Comparative Example 1, and is superior to that of Comparative Example 2 of the wrapping method. The compressibility showed an appropriate value that was better than that of the comparative example, and unexpectedly good results were obtained in the water leakage test. This is thought to be because GP stretches well in the radial direction due to compression and has restoring force. Example 2 An adhesive (Design Bond, manufactured by Sumitomo 3M) was sprayed on both sides of the corrugated ring in Example 1, and a GP was obtained in the same manner as in Example 1. In a flexibility test, this GP did not cause delamination even when the cut ends were pushed apart to a distance of 40 mm. The sliding resistance, compressibility and water leakage pressure showed almost the same values as the GP of Example 1. (Effects of the Invention) According to the present invention, a GP with excellent flexibility, low resistance when the valve stem etc. slides, and unexpectedly good fluid sealing performance can be obtained, and a seal with low pressure can be obtained. For equipment, only the GP of the present invention can be used with asbestos fibers.
Can be used without combining with GP.

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway sectional view of the GP of the present invention, Fig. 2 is a partially cutaway sectional view of the GP of the present invention;
The figure is a perspective view of the GP with a notch, and Figure 3 is a corrugated ring used in an embodiment of the present invention, a is a plan view, and b
is a front view, FIG. 4 is a sectional view explaining how to use GP, FIG. 5 is a partially cutaway sectional view of a conventional GP, and FIG. 6 is a partially cutaway sectional view of a rolled expanded graphite tape. FIG. 7 is a partially cutaway sectional view of another conventional GP. Explanation of symbols 1...braided body, 2...mixture, 3...expanded graphite tape, 4...corrugated ring, 5...unilaterally corrugated ring, 6
...notch, 7...left end, 8...right end, 9...
Point, 10...GP, 11...Packing box, 1
2...Ground, 13...Valve stem, 14...Mountain, 15...
Valley, 16... screw, 17... gap.

Claims (1)

[Scope of Claims] 1. Expanded graphite powder or a flat expanded graphite sheet punched into an annular shape is molded into an annular expanded graphite sheet having concentric corrugations in the radial direction, and then the bottom part is placed in the annular space of the mold. Expanded graphite powder or a molded product thereof is spread on the surface, a plurality of annular expanded graphite sheets having concentric corrugations are stacked on top of the expanded graphite powder, and expanded graphite powder or a molded product thereof is placed on top of the annular expanded graphite sheet, and an annular upper punch is formed. A manufacturing method for gland packing characterized by pressure molding and integrating. 2. A ground packing manufactured by the method for producing a ground packing according to claim 1.