Spiral wound gasket and fabrication method thereof

Abstract: A spiral wound gasket is formed by winding combinedly and spirally a metal strip (5) having at least one bending cross section in the cross direction and a belt-shaped filler in such a way that the metal strip and the filler are piled up in the longitudinal direction and the filler protrudes from the both edges of the metal strip (5) in the cross direction. The spiral wound gasket employes, as the filler, a flexible tape (1) of carbon/carbon composites having a structure in which a carbon fiber (2) in a bundle or string is contained in the thickness direction of an expanded graphite tape (1a) and the carbon fiber (2) is caused to locate in the bending section of the flexible tape (1) formed when the flexible tape (1) and the metal strip (5) in a pile are wound. The spiral wound gasket is used as a pipe fitting etc. for use under high temeprature and pressure conditions.

Description: (a) Field of the Invention: The present invention relates to a spiral wound gasket employing carbon/carbon composites of the soft type, which is used as a pipe fitting etc. for use under high temperature and pressure conditions, and a fabrication method thereof. (b) Description of the Prior Art: Spirally wound gaskets known in the art generally consist of alternate layers of a thin gauge metal strip, such as stainless steel, and a thin strip of a soft, non-metallic filler material which together were wound in a spiral metallic filler material which together are wound in a spiral to form an annular ring, as is a roll of adhesive tape. The layered edges of the strips form the sealing surfaces. Suitable filler materials include various fluorocarbon polymers, asbestos, Grafoil R and ceramic. Spiral wound gaskets of this sort, as disclosed in Japanese Utility Model Laid-Open No. 101253/1981 (Applicant: Japan Pillar Industries Co.) by way of example, employ a tape made of asbestos or expanded graphite as a filler and have a structure of a metal strip having a V-shaped cross section, made of aluminum or copper, and said tape are laminated together in the longitudinal direction and wound spirally. (FIGS. 3 and 4) Another example of a prior art wound gasket and a method for fabrication thereof may be seen from U.S. Pat. No. 4,673,187 which forms the bess for the preambles of independent claims 1 and 3, in which a temperature sensitive spiral wound gasket comprised of alternate windings of a bimetallic strip and a soft, non-metallic filler is disclosed. The U.S. Pat. has a structure similar to that of a gasket as illustrated in FIGS. 3 and 4 and briefly stated, the invention is a temperature-sensitive spiral wound gasket comprised of alternate winding of a bimetallic strip and a soft non-metallic filler. A preformed generally V-shaped fold or indentation in the bimetallic strip runs along the strip, preferably on its central axis and for its entire length. Extending from either side of the V-shaped fold are substantially flat portions, each terminating at the side edges of the strip. The V-shape enables the resident or elastic deformation of the bimetallic strip when its edges are compressed between the surrounding surfaces to be sealed. The filler material assumes the V-shape of the bimetallic strip when wound. The present invention relates to: a spiral wound gasket formed by winding combinedly and spirally, a metal strip having at lest one bend in the lateral direction and a belt-shaped filler in such a way that said metal strip and said filler are laminated together in the longitudinal direction and said filler protrudes from both edges in the lateral direction of said metal strip, characterized in that said filler is a flexible tape of carbon/carbon composites having a structure in which a carbon fiber, in a bundle or a sting, is contained in the interior in the thickness direction of an expanded graphite tape and said carbon fiber is located at the bend of said flexible tape formed when the laminate of said flexible tape and said metal strip are wound; and a method for fabricating a spiral wound gasket of said structure, which comprises laminating together, in the longitudinal direction, a metal strip having at least one bend in the lateral direction and a filler made of a flexible tape of carbon/carbon composites, in which a bundle- or string-shaped carbon fiber is contained in the interior in the thickness direction of an expanded graphite tape, in such a way that said carbon fiber is located at the bend of said flexible tape formed when the laminate of said flexible tape and said metal strip in a pile are wound, and the width of the tape is larger than that of said metal strip, winding spirally the resulting laminate, and fixing both longitudinal ends of said metal strip at the start and end of the winding. According to the present invention, it is possible to obtain a spiral wound gasket having excellent sealing performance by the use of a flexible tape employing soft-type carbon/carbon composites comprising a carbon fiber and an expanded graphite as a filler. Further, the aforesaid flexible tape employed in said spiral wound gasket has an increased strength so that it improves the efficiency of the winding operation of said metal strip laminate with said flexible tape. 4. Brief Description of the Drawings : Fig. 1 is a cross section illustrating the structure of a composite tape for use in the fabrication of a spiral wound gasket according to the present invention. Fig. 2 is a cross section of a spiral wound gasket obtained in an example of the present invention. 5. Detailed Description of the Preferred Embodiments : In the present invention, the expanded graphite tape is prepared by applying pressure, for example, by subjecting expanded graphite particles to rolling or compression molding by a conventional procedure. The carbon fiber is a bundle or string of a plural number of filaments, which is well-known in the art and may preferably have a high strength. The number of filaments in the carbon fiber may properly be chosen according to the size of a desired spiral wound gasket. However, commercially available carbon fibers having 1,000 - 3,000 filaments may commonly be used satisfactorily. The flexible tape made of carbon/carbon composites of the soft type (hereinafter referred to as "composite tape") according to the present invention is prepared by sticking two expanded graphite tapes 1a and 1b together, between which a carbon fiber 2 in a bundle or string is held, as shown in Fig. 1. The position of the carbon fiber 2 is, for example, the center in the cross direction of the expanded graphite tapes 1a and 1b, when the bending section of a metal strip having a V-shaped in cross section is located at the center in the cross direction of said metal strip. As seen in Fig. 2, this is because the carbon fiber 2 is caused to locate in the bending section of the composite tape 1 when the metal strip 5 having a V-shaped in cross section and the composite tape 1 are piled up and wound. For a larger spiral wound gasket, it is recommended that the cross section of the metal strip is made W-shaped or the like so that the metal strip may have a plurality of bending sections. In this case, the composite tape may be prepared similarly in such a way that a bundle- or string-shaped carbon fiber is caused to locate in each of a plurality of the bending sections of said composite tape formed when the metal strip and the tape are piled up and wound. No particular restrictions are imposed on the width of the composite tape, which is selected in accodance with the size of a desired spiral wound gasket. It is however necessary for the composite tape to have such a width that its both edges in the cross direction protrude from the edges of the metal strip when the metal strip and the tape are piled up and wound. The thickness of the composite tape may suitably be chosen depending on the use purpose of a desired spiral wound gasket. Further, as seen in Fig. 1, the position of the carbon fiber 2 in the thickness direction of the composite tape 1 is determined by the selection of the thickness of the expanded graphite tapes 1a and 1b. Here, it is desirable to place the carbon fiber 2 in a position between one-thirds and two-thirds of the thickness of the composite tape 1. In Fig. 1, the composite tape 1 is obtained by sticking the expanded graphite tapes 1a and 1b together in such a way that the carbon fiber 2 is held in between. The sticking is carried out by applying a vanish made of a thermosetting resin such as phenol resin and furan resin on either one or both of the surfaces of the expanded graphite tapes 1a and 1b to stick the two surfaces together, the surfaces holding or being in contact with the carbon fiber 2, and then causing the vanish to cure with heat. If necessary, the resin is carbonized by treating the combined tapes at a higher temperature (e.g. 1,000°C). Thermoplastic resins may also be used as the adhesive resin depending on purposes. Further, the composite tape 1 may also be prepared not by way of the sticking but by incorporating a carbon fiber into an expanded graphite tape while the tape is being molded. Preferred metal strips will have high strengths and superb weldabilities. Hoop materials made of stainless steel are generally used. The metal strip is smaller in width than the expanded graphite tapes 1a and 1b and has, for example, a V- or W-shaped in cross section. The spiral wound gasket is fabricated by winding circularly and spirally the metal strip with the composite tape piled up and fixing both longitudinal ends of the metal strip by spot welding or the like. Here, it is preferable to wind only the metal strip 1 - 6 times at each of the start and end of the winding so that the inner and outer parts of the spiral wound gasket are composed only of the metal strip. Further, the composite tape and the metal strip are so wound that the tape protrudes from the edges of the metal strip on the both sides in the cross direction of the spiral wound gasket. Embodiments of the spiral wound gasket and the fabrication method thereof according to the present invention will further be illustrated specifically by reference to the drawings hereunder. Example 1: On an expanded graphite tape (HGP-207, made by Hitachi Chemical Co., Ltd.: 200 g/m² in weight per unit area, 0.2 mm in thickness, and 6.2 mm in width) 1b was applied a phenolic resin vanish (VP11N, made by Hitachi Chemical Co., Ltd.) as a binder and a carbon fiber (HTA-7, a PAN type fiber made by Toho Rayon Co., Ltd.; 1,000 filaments) 2 in a bundle was placed on the center of the tape. Then, an expanded graphite tape 1a, similar to the expanded graphite tape 1b, was pressed down thereon, and the resulting combined tapes were heated at 160°C to cure the aforesaid resin and thereby to bind the two expanded graphite tapes 1a and 1b together. Thus, a composite tape 1 with a thickness of 0.4 mm and a width of 6.2 mm was prepared, as seen in Fig. 1. Then, as shown in Fig. 2, a metal strip (0.2 mm in thickness and 5.8 mm in width when extended) 5, which is a stainless steel hoop material molded in a V-shape in advance, and the foregoing composite tape 1 were wound circularly and spirally while being piled up in such a way that the V-sahped bending section of the metal strip 5 was coincident in position with the carbon fiber 2 in the composite tape 1. Thus, a spiral wound gasket with an inner diameter of 90 mm, an outer diameter of 110 mm and a height of 4.5 mm was obtained. Here, the composite tape 1, i.e. the filler, was allowed to protrude by about 0.2 mm from the both edges in the cross direction of the metal strip 5. The metal strip 5 was wound solely 6 times at each of the start and end of the winding, and the both ends in the longitudinal direction of the metal strip 5 were fixed respectively by spot welding. Comparative Example 1: A spiral wound gasket was obtained in the same manner as in Example 1, except for the use of an asbestos tape (0.4 mm in thickness and 6.2 mm in width) in place of the composite tape 1 described in Example 1 as the filler. Comparative Example 2: A spiral wound gasket with the same shape and size as that obtained in Comparative Example 1 was fabricated in the same manner as in Comparative Example 1, except for the use of an expanded graphite tape (HGP-207, manufactured by Hitachi Chemical Co., Ltd.; 400 g/m² in weight per unit area, 0.4 mm in thickness and 6.2 mm in width) in place of the asbestos tape described in Comparative Example 1 as the filler. Example 2: A spiral wound gasket was obtained in the same manner as in Example 1, except for the alteration of the number of filaments in the carbon fiber to 3,000. Example 3: On an expanded graphite tape (HGP-207, made by Hitachi Chemical Co., Ltd.; 200 g/m² in weight per unit area, 0.26 mm in thickness and 6.2 mm in width) was applied a phenolic resin vanish (VP11N made by Hitachi Chemical Co., Ltd.), and a carbon fiber (HTA-7, a PAN type fiber made by Toho Rayon Co., Ltd.; 1,000 filaments) was placed on the center of the expanded graphite tape. Then, an expanded graphite tape (HGP-207, made by Hitachi Chemical co., Ltd.; 200 g/m² in weight per unit area, 0.14 mm in thickness and 6.2 mm in width) was pressed down thereon. The two expanded graphite tapes sticked together in the same manner as in Example 1 to obtain a composite tape having the same size as that used in Example 1. A spiral wound gasket was then prepared in the same manner as in Example 1 by using the composite tape and the same metal strip as employed in Example 1. Example 4: A spiral wound gasket was fabricated in the same manner as in Example 1 except that the front (top) and the back (bottom) of the composite tape given in Example 3 were reversed (turned upside down). Example 5: The composite tape given in Example 1 was burned at a temperature of 800°C in an atmosphere of nitrogen to carbonize the phenolic resin used as the binder. Using the resulting composite tape, a spiral wound gasket was prepared in the same manner as in Example 1. The tensile strength of the asbestos tape in Comparative Example 1, the expanded graphite tape in Comparative Example 2 and the compsoite tape in each Example as well as the sealing performance of the spiral wound gasket obtained in each of the Examples and Comparative Examples are shown in Table 1. Tensile strength of tape (kg/cm²) Sealing performance of gasket (He permeability: cm2/sec) Comp.Ex. 1 80 5.2 x 10⁻⁴ Comp.Ex. 2 50 5.7 x 10⁻⁷ Example 1 2,000 2.9 x 10⁻⁸ Example 2 2,500 7.7 x 10⁻⁸ Example 3 2,000 5.0 x 10⁻⁹ Example 4 2,000 1.3 x 10⁻⁷ Example 5 2,000 2.2 x 10⁻⁷ In this Table, the sealing performance was determined as He permeability k(cm²/sec) in accordance with the following equation using the data obtained by placing a jig sealed hermetically with a spiral wound gasket in a vacuum apparatus to evacuate the outer periphery of the spiral wound gasket, sealing helium (He) gas in the jig at 1 atmosphere and measuring the volume of the helium gas permeating from the inner periphery to the outer periphery of the spiral wound gasket. K= ℓn r o /r i 2π x FRT LP r o : outer diameter of spiral wound gasket (cm) r i : inner diameter of spiral wound gasket (cm) F : flow rate of helium (mole/sec) R : gas constant (cm³·atm/K·mole) T : absolute temperature (K) L : height of spiral wound gasket (cm) P : gas pressure difference between inner and outer peripheries (atm) As is obvious from Table 1, the tensile strength of the composite tapes in Examples 1 through 5 is far higher than that of the abestos tape in Comparative Example 1 or that of the expanded graphite tape in Comparative Example 2, and the spiral wound gaskets in Examples 1 through 5 have lower He permeabilities K than those in Comparative Example 1 and Comparative Example 2 and hence are superior in sealing performance.

Claims: A spiral wound gasket formed by winding combinedly and spirally a metal strip (5) having at least one bend in its lateral direction and a belt-shaped filler (1) made of a flexible tape in such a way that said metal strip (5) and said filler (1) are laminated together along their longitudinal direction and said filler protrudes from both lateral edges of said metal strip, said gasket being characterized in that said filler (1) is a flexible tape of carbon/carbon composites having a structure in which a carbon fiber (2) in the form of a bundle or a string is contained in the interior of an expanded graphite tape (la, 1b) and said carbon fiber (2) is located at and extends longitudinally along the bend in said flexible tape (1) formed when the laminate of said flexible tape (1a, 1b) and said metal strip (5) are wound. A spiral wound gasket according to claim 1 wherein said carbon fiber (2) contained in the interior of said flexible tape (1) of carbon/carbon composites is located at a position between one-thirds and two-thirds of the thickness of flexible tape (1). A method of fabricating a spiral wound gasket formed by winding combinedly and spirally a metal strip (5) having at least one bend in its lateral direction and a belt-shaped filler (1) made of a flexible tape in such a way that said metal strip (5) and said filler (1) are laminated together along their longitudinal direction and said filler protrudes from both lateral edges of said metal strip, characterized in that said method comprising laminating, along its longitudinal direction, a metal strip (5) having at least one bend in its lateral direction together with a filler (1) made of a flexible tape of carbon/carbon composites, in which a carbon fiber (2) in the form of a bundle or string is contained in the interior of an expanded graphite tape (1a, 1b) in such a way that said carbon fiber (2) is located at and extends longitudinally along the bend in said flexible tape formed when the laminate of the flexible tape (1a, 1b) and said metal strip (5) are wound, the width of said filler (1) being larger than that of said metal strip (5); winding spirally the resulting laminate; and attaching both longitudinal ends of said metal strip (5) at the start and end of the winding. A method of fabricating a spiral wound gasket according to claim 3, characterized in that at a position between one-third and two-thirds in the interior of an expanded graphite tape (1a, 1b), said carbon fiber (2) is located in such a way that it extends along the bend in said flexible tape (1a, 1b) formed when the laminate of the flexible tape and said metal strip (5) is wound, the width of said filler (1) being larger than that of said metal strip (5), winding spirally the resulting laminate; and attaching both longitudinal ends of said metal strip (5) at the start and end of the winding.

Inventors: AIZAWA JUNICHI, KODAMA KAKUICHI, OMATA YASUSHI, SHIMOYAMA TATSUO, AIZAWA, JUNICHI, KODAMA, KAKUICHI, OMATA, YASUSHI, SHIMOYAMA, TATSUO
Applicants: AGENCY IND SCIENCE TECHN, AGENCY OF INDUSTRIAL SCIENCE AND TECHNOLOGY OF MINISTRY OF INTERNATIONAL TRADE AND INDUSTRY
Application year: 1990
Main classification: F16J15
IPC codes: F16J15