PACKING MATERIAL AND PACKING MADE OF THE SAME

Abstract: This improved packing material is made of a flexible graphite sheet (of 1mm or less thickness) which is cut into a 5 mm or smaller width and surface covered with a fibre. The packing material is made of 1-10 flexible graphite sheets which are laminated and covered with fibres selected from among metal fibres such as stainless steel, inorganic fibres such as asbestos, ceramics, glass fibres and carbon fibres, and organic fibres suich such as cotton, rayons, phenols, PBI, PTFE, PPS etc. The covering fibres can be surface-treated with graphite powder, silicon oil, a rubber adhesive or PTFE The surface of the covering fibres can be treated with Zn or NaNO2 as an anticorrosive. The flexible graphite sheets can be laminated with reinforcing fibres or foil and then covered with fibres to form the packing materials. The reinforcing fibres are of the same type as the covering fibres. The foil is selected from among metal foils such as Zn, Cu, Al or nonmetal foils such as pulp sheet, PTFE sheet, PEI sheet etc. Rod-shaped packing materials can be obtained by mixing graphite particles with at least one material chosen from short fibres, rubber, resin, or lubricant and then covering with fibre.

Description: FIELD OF THE INVENTION This invention relates to packing material and packing preferably suitable to gland packing or the like for use in a shaft seal part of a hydraulic machine. PRIOR ART A variety of gland packings in which flexible graphite is used as a base material have been hitherto known for use in a shaft seal part or the like portion of a hydraulic machine, for example. Gland packings of this sort are manufactured by various techniques, such as laminating, die molding, chip molding, and ribbon packing. However, these techniques require that the graphite material must be previously molded into a ring shape conforming to the diametral size of a shaft with which suck packing is to be used; as such, the packing cannot be used with any shaft having a different diameter. Therefore, such packing lacks versatility in use. Another, difficulty with such packing is that since flexible graphite is of low tensile strength and brittle in itself, once the packing is mounted in position it is extremely difficult to remove same when replacement is required, which means less usability. An example for a sealing is disclosed in the US-A- 4 157 835. Concavo-convex portions are formed on the sealing surface, thus improving the resiliency so that the sealing performance with respect to a fastening force is advantageously improved. However, the packing material according to this reference is of a so-called ribbon-pack type and can therefore not overcome the problems above-mentioned. Further, afore said manufacturing techniques individually have drawbacks of their own. The laminating technique involves the problem of poor yield, which leads to higher cost. Where the die molding or chip molding technique is employed, dies or metal molds are required, which means higher cost, and the packing produced is less versatile. The ribbon packing technique provides no good workability. These difficulties may be overcome by forming the flexible graphite into a cord-like structure so that it may be used by being cut to a specified length conforming to the diameter of the shaft, as is the case with such other type of packing as fiber braided or knitted; but the trouble is that flexible graphite cannot be braided or knitted because, as pointed out above, it is in itself of low tensile strength and so brittle that its compressibility and allowable limit of twist are both extremely low. Therefore, it has hitherto been considered impossible to use such packing in such way as is usual with aforesaid fiber braided or knitted type of packing, that is, in such a way that the braided or knitted packing is cut to length according to the diametral size of the shaft with which it is to be used, the so cut packing being then wound about the outer periphery of the shaft. A possible solution of these problems is given in the EP-A-0 253 031 (publication date 20-01-1988). However, this reference discloses a basic invention which overcomes these basic problems rather than an optimized packing material. There is still a need for a better packing in view of contribution to industrial markets by application of a packing to higher technology. Most specifically it is desired to supply cheaper expanded graphite packing to industrial markets and to provide a packing which can be applied to changes in a variety to technical conditions. DISCLOSURE OF THE INVENTION In order to overcome aforesaid difficulties it is hence a primary object of this invention to present a packing material which can be either twisted or braided, and a twisted or braided cord-like packing by using the same packing material, by using a flexible graphite sheet cut to a width of less than 5 mm in order to advantageously utilize a characteristic feature of flexible graphite in sheet form in particular that if such sheet is cut to a width of less than 5 mm, both its compressibility and its allowable limit of twist are significantly increased as shown in Fig. 11, Fig. 12, and by covering the flexible graphite sheet with a fiber material order to attain the synergistic action of the fiber material and flexible graphite sheet. Coated fibres are impregnated with the corrosion preventive agent. This prevents a machine concerned from being corroded for a long period of time. This lengthens the maintenance period together with excellent wear resistance of expanded graphite. It is a second object of this invention to present a packing material which can be either twisted or braided and is small in elongation and high in strength, and a twisted or braided cord-like packing by using the same packing material, by using a flexible graphite sheet cut to a width of less than 5 mm, laminating this flexible graphite sheet with at least one of reinforcing fiber material or foil material, and covering this surface with the fiber material to attain the synergistic action of the fiber material and flexible graphite sheet, and the reinforcing fiber or foil material. It is a third object of this invention to present a packing material which can be either twisted or braided, and a twisted or braided cord-like packing by using the same packing material, by forming a bar mainly composed of flexible graphite sheet material having a width of less then 5 mm and containing at least one of short fiber, rubber, resin or lubricant, and covering this surface with fiber in order to attain the synergistic action of the fiber material and the bar. It is thus intended to improve the usability and versatility. In the packing material of this invention, since a flexible graphite sheet cut to a width of less than 5 mm is used, the compressibility and the allowable limit of twist are increased to make it possible to twist or braid, and moreover since the surface is covered with fibers, the toughness against bending and sliding may be also enhanced. Furthermore, when a flexible graphite sheet cut to a width of less than 5 mm is laminated with at least one of reinforcing fiber or foil material, the strength is further increased and the longation is decreased. By covering this surface with the fiber, moreover, the toughness against bending or sliding may be improved. Meanwhile, by forming a bar by using flexible graphite particles as the base material and containing at least one of short fiber, rubber, resin or lubricant, twisting or braiding is enabled, and by adding at least one of short fiber, rubber and resin to the base material mainly composed of flexible graphite particles, the strength is increased and the elongation is restricted. When the surface is further covered with fiber, the toughness against bending or sliding may be improved. Therefore, any of the these packing materials permits a cord-like structure to be cut to a specified length conforming to the shaft diameter, which was impossible until now, and to be used as a gland packing by bending this cut cord-like structure in a ring form, so that the usability and versatility may be greatly enhanced. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partially cutaway view in perspective showing a first embodiment of the packing material; Fig. 2 is a partially cutaway view in perspective showing a cord-like packing formed by square braiding eight knitting threads by using the packing material in Fig. 1; Fig. 3 is a partially cutaway view in perspective showing a twisted cord-like packing formed by bundling a plurality of the packing material in Fig. 1; Fig. 4 is a partially cutaway view in perspective showing a second embodiment of the packing material; Fig. 5 is a partially cutaway view in perspective showing a cord-like packing formed by square braiding eight knitting threads by using the packing material in Fig. 4; Fig. 6 is a partially cutaway view in perspective showing a twisted cord-like packing formed by bundling a plurality of the packing material in Fig. 4; Fig. 7 is a partially cutaway view in perspective showing a third embodiment of the packing material; Fig. 8 is a partially cutaway view in perspective showing a cord-like packing formed by square braiding eight knitting threads by using the packing material in Fig. 7; Fig. 9 is a partially cutaway view in perspective showing a twisted cord-like packing formed by bundling a plurality of the packing material in Fig. 7; Fig 10 is a partially cutaway view in perspective-showing a fourth embodiment of the packing material having a bar-shaped core material; Fig. 11 is a graph showing the relationship between flexible graphite sheet cut width and its compressibility; and Fig. 12 is a graph showing the relationship between flexible graphite sheet cut width and its allowable limit of twist. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, the present invention is described in details below. In Fig. 1, of the flexible graphite sheets less than 1 mm in thickness and less than 5 mm in width, six pieces of the most preferable flexible graphite sheet 1 measuring 0.38 mm in thickness and 3 mm in width are prepared, and the surface of these six flexible graphite sheets 1 .... is covered with knitted Aramid fiber or Inconel 600 fiber to form a knitting thread 4, and this knitting thread 4 is used as the packing material. Fig. 2 shows a cord-like packing, in which eight knitting threads 4 shown above are used, and are square braided to form a cord-like structure 5, and the surface of knitting threads 4, that is, the surface of the knitted covering fibers is impregnated with at least one of silicone oil, scale-form graphite and rubber-based adhesive [or PTFE (polytetrafluoroethylene) instead of rubber-based adhesive], or with preferably these three sealers 6 together with zinc or sodium nitrite as corrosion preventive. The packing in Fig. 3 is manufactured by bundling six knitting threads 4 and roll forming while twisting 20 turns/m to form a cord-like structure 5, and impregnating the surface of knitting threads 4, that is, the surface of knitted covering fibers with at least one of silicone oil, scale-form graphite and rubber-based adhesive (or PTFE instead of rubber-based adhesive), or preferably with these three sealers 6 together with zinc or sodium nitrite as corrosion preventive. Fig. 11 presents experimental results on the relationship between cut width and compresssibility with respect to a flexible graphite sheet having a thickness of 0.38 mm, and Fig. 12 presents experimental results on the relationship between cut width and allowable limit of twist with respect to a 1-meter long flexible graphite sheet having a thickness of 0.38 mm. It can be seen from these figures that the flexible graphite sheet has a characteristic feature that if its cut width is less than 5 mm, both its compressibility and its allowable limit of twist are remarkably increased. This fact assures easy and accurate formation of a packing in a cord-like structure 5 as shown in Fig. 2 and Fig. 3, from the packing material (knitting thread 4) having the surface of six flexible graphite sheets 1 cut to a width of less than 3 mm with knitted Aramid fibers or Inconel 600 fibers. In other words, eight-thread square braiding and also twisting can be satisfactorily carried out without breakage being caused to the flexible graphite sheet 1 or the core material, that is, to the knitting thread 4. Therefore, the cord-like structure 5 may be readily cut to a specified length conforming to the diameter of the shaft, for example, for use as gland packing. This means improved usability and versatility. In Fig. 4, of the flexible graphite sheets less than 1 mm in thickness and less than 5 mm in width, three pieces of the most preferable flexible graphite sheet 1 measuring 0.38 mm in thickness and 3 mm in width are prepared, and these three flexible graphite sheets 1 ... and four lead foils 7 of 0.1 mm in thickness and 3 mm in width are alternately laminated to form a core 3, and the surface of this core 3 is covered with knitted Inconel 600 fibers to form a knitting thread 4', which is used as the packing material. Fig. 5 shows a cord-like packing, in which eight knitting threads 4' shown above are used, and are square braided to form a cord-like structure 5', and the surface of knitting threads 4', that is, the surface of the knitted covering fibers is impregnated with at least one of silicone oil, scale-form graphite and rubber-based adhesive (or PTFE instead of rubber-based adhesive), or with preferably these three sealers 6 together with zinc or sodium nitrite as corrosion preventive. The packing in Fig. 6 is manufactured by bundling six knitting threads 4' and roll forming while twisting 20 turns/m to form a cord-like structure 5', and impregnating the surface of knitting threads 4', that is, the surface of knitted covering fibers with at least one of silicone oil, scale-form graphite and rubber-based adhesive (or PTFE instead of rubber-based adhesive), or preferably with these three sealers 6 together with zinc or sodium nitrite as corrosion preventive. Also from such packing material (knitting thread 4') manufactured by alternately laminating three flexible graphite sheets 1 cut to a width of 3 mm and four lead foils 7 to form a core 3, and covering the surface of this core 3 with knitted Inconel 600 fibers, a packing in cord-like structure 5' is obtained easily and securely as shown in Fig. 5 and Fig. 6. In other words, eight-thread square braiding and also twisting can be satisfactorily carried out without breakage being caused to the flexible graphite sheet 1 or the core material, that is, to the knitting thread 4'. What is more, this knitting thread 4' is remarkably increased in strength owing to the intervening existence of lamination of lead foil 7, and since the surface is covered with knitting of Inconel 600 fibers, the bending performance is improved. Accordingly, the cord-like structure 5' can be cut to a specified length conforming to, for example, the diameter of the shaft for use as gland packing, which means improved usability and versatility. Fig. 7 shows a modified example of the packing material in Fig. 4. Four flexible graphite sheets 1 of 0.38 mm in thickness are cut to a width of 3 mm, and a reinforcing fiber 2 made of 0.15 mm⊘ Inconel 600 is laminated between the two layers in the top and bottom to form a core 3, and the surface of this core 3 is covered with knitted 0.1 mm⊘ Inconel 600 fibers to form a knitting thread 4'', which is used as the packing material. Fig. 8 shows a cord-like packing, in which eight knitting threads 4'' shown above are square braided to form a cord-like structure 5'', and the surface of knitting threads 4'', that is, the surface of knitted covering fibers is impregnated with at least one of silicone oil, scale-form graphite and rubber-based adhesive (or PTFE instead of rubber-based adhesive), or preferably with these three sealers 6 together with zinc or sodium nitrite as corrosion preventive. Fig. 9 shows a cord-like packing, in which six knitting threads 4'' are bundled, and are roll formed while twisting 20 turns/m to form a cord-like structure 5'', and the surface of knitting threads 4'', that is, the surface of knitted covering fibers is impregnated with at least one of silicone oil, scale-form graphite and rubber-based adhesive (or PTFE instead of rubber-based adhesive), or preferably with these three sealers 6 together with zinc or sodium nitrite as corrosion preventive. In Fig. 8 and Fig. 9, too, the cord-like structure 5'' can be easily and securely formed by the knitting thread 4'', and eight-thread square braiding and twisting can be satisfactorily carried out without breakage being caused to the flexible graphite sheet 1 or the core material, that is, to the knitting thread 4''. Still more, the strength is remarkably increased by the reinforcing fiber 2 and knitted covering fiber (Inconel 600), and the bending performance is also improved. Therefore, the cord-like structure 5'' can be cut to a specified length conforming to the diameter of the shaft, for example, so as to be used as gland packing, which means the improved versatility and usability. Fig. 10 represents an example of preparation of packing material, in which 60% of flexible graphite particles, 25% of natural graphite as lubricant, 10% of rubber, and 5% of Aramid short fiber are kneaded, and a circular solid bar-like structure 8 of 3 mm⊘ is formed by an extrusion forming machine, and the surface of this bar-like structure 8 is covered with 0.1 mm⊘ Inconel 600 fiber by knitting to form knitting thread 4''', which is used as the packing material. From such packing material, that is, knitting thread 4''', a cord-like packing can be formed by square braiding eight knitting threads 4''' to form a cord-like structure same as in Fig. 5, and by impregnating the surface of knitting threads 4''' with at least one of silicone oil, scale-form graphite and rubber-based adhesive (or PTFE instead of rubber-based adhesive), or preferably with these three sealers 6 together with zinc or sodium nitrite as corrosion preventive. It is also possible to form a cord-like packing by bundling six knitting threads 4''', and roll forming while twisting by 20 turns/m to form a cord-like structure same as in Fig. 6, and by impregnating the surface of knitting threads 4''' with at least one of silicone oil, scale-form graphite and rubber-based adhesive (or PTFE instead of rubber-based adhesive), or preferably with these three sealers 6 together with zinc or sodium nitrite as corrosion preventive. In order words, even from the packing material (knitting thread 4''') as stated above, a cord-like packing can be formed easily and securely, and eight-thread square braiding or twisting of the knitting threads 4''' ... can be satisfactorily carried out without breakage being caused to the bar-like structure 8 mainly composed of flexible graphite particles or the core material, that is, to the knitting threads 4'''. Still more, since rubber and Aramid short fiber are kneaded, the strength is significantly increased, and the bending performance is improved, and this cord-like packing can be cut to a specified length conforming to the diameter of the shaft for use, for example, as a gland packing, which means the improved versatility and usability. As the reinforcing fiber 2 and covering fiber in the above embodiments, 0.1 mm⊘ Inconel 600 is used, but it is not limitative, but other materials may be used depending on the purpose of such, for example, metal fibers such as Monel and stainless steel, inorganic fibers such as asbestos, ceramic fiber, glass fiber and carbon fiber, and organic fibers such as cotton, rayon, phenol, Aramid, PBI (polybenzimidazole), PTFE (polytetrafluoroethylene), PEI (polyetherimide), PPS (polyphenylene sulfide), and PEEK (polyether etherketone). As the foil material, 0.1 mm thick lead foil is used in the example, but metal foils such as copper and aluminum, pulse sheet, Aramid sheet, PBI sheet, PTFE sheet, PEI sheet, PSS sheet, PEEK sheet and others may be used depending on the purpose of use. As the short fiber to be kneaded with flexible graphite particles, in the above embodiment, Aramid short fiber was used, but it is not limitative, and other materials may be used depending on the purpose of use, for example, metal short fibers such as Inconel, Monel and stainless steel, inorganic short fibers such as asbestos, ceramic fiber, glass and carbon, and organic short fibers such as cotton, rayon, phenol, Aramid, PBI, PTFE, PEI, PPS and PEEK. As the rubber, nitrile rubber, chloroprene rubber, fluororubber and others may be properly used selectively, and examples of resin may include, in particular, phenol resin and epoxy resin. As the lubricant, aside from the aforesaid natural graphite, expanded graphite, mica, petroleum wax and others may be used depending on the purpose of use. In the illustrated example, the solid bar-like structure 8 is formed by extruding a mixed material mainly composed of flexible graphite particles, but the bar-like structure 8 may be formed in a circular solid section by rounding a flexible graphite sheet of less than 5 mm in width, or a flexible graphite sheet cut in a rectangular form with width of less than 5 mm may be mixed together with at least one of short fiber, rubber and resin, and formed in a circular solid section. In the above embodiments, the knitting threads 4, 4', 4'', 4''', are preapred by bundling a plurality and twisting or braiding, but it is also possible to composed a gland packing by twisting a single knitting thread 4, 4', 4'' or 4''' so as to be suited to the dimensions or composition of the shaft seal part. Meanwhile, in the aforesaid embodiments, the knitting threads 4, 4', 4'', 4''' are square braided, but, of course, braiding by tubular plain stitch or lattice braiding may be used. As the covering fiber, aside from the knitting shown above, tubular plain stitch, conduit knitting or tubular weaving may be applied, too. The measured data of knitting threads are shown in Table 1. As clear from Table 1, the packing materials No. 1, No. 2, No. 3, No. 4 and No. 6 of this invention, are higher in strength and smaller in elongation as compared with the packing material No. 5, and it is also known that twisting and braiding can be carried out satisfactorily. In the above embodiments, it is explained that the knitting threads 4, 4', 4'', 4''' are braided to be used as gland packing, but not limited to such gland packing, by ribbon stitching or plain stitching of knitting threads 4, 4', 4'', 4''', it may be possibly applied as a sealing packing between static members, and in this case, too, the same action and effect as in fabrication of gland packing will be obtained. POSSIBILITY OF INDUSTRIAL UTILIZATION Thus, in the packing material and packing according to this invention, being composed of flexible graphite, it is not necessary to make as many packings as the number of different dimensions of shaft seal members, and bending and toughness are improved, and it may be preferably used as the gland packing or sealing material of static members.

Claims: A packing material for glands or similar elements, comprising flexible graphit sheet, wherein the flexible graphite sheet is either a single sheet or a laminated structure characterized in, that the graphite sheets have a width of less than 5 mm, that said graphite sheet or laminated structure is covered with a fiber to form a thread (4), several such threads (4) beeing formed into a cord like structure (5). that the covering fiber is impregnated with surface treatment material in particular graphite powder, silicone oil, rubber based adhesive or PTFE, and that the surface of covering fibers is impregnated with zinc or sodium nitrite for corrosion protection. A packing material according to claim 1, characterized in, that the covering fibers are knitted, tubular plain stitched, conduit knitted or tubular woven. A packing material according to claim 1 or 2, characterized in, that the thickness of the flexible graphite sheet is less than 1 mm. A packing material according to at least one of claims 1 to 3, characterized in, that the covering fibers consists of any material as selected from metal fibers such as Inconel, Monel and stainless steel, inorganic fibers such as asbestos, ceramics fibers, glass fiber and carbon fiber and organic fibers such as cotton, rayon, phenol, Aramid, PBI, PTFE, PEI, PPS and PEEK. A packing material according to at least one of claims 1 to 4 characterized in, that the cordlike structure (5) is formed by twisting either a single piece or a bundle of a plurality of pieces. A packing material according to at least one of claims 1 to 4 characterized in, that the cordlike structure (5) is formed by square braiding, tubular plain stitching, lattice knitting, ribbon weaving or plain stitching and braiding. A packing material for glands or similar elements comprising a plurality of flexible graphite sheets (1) laid in superposed relation to one another, characterized in, that the graphite sheets having a width of less than 5 mm are laminated with reinforcing fiber or foil material to form a laminated structure (3), said laminated structure being covered with a fiber material to form a thread (4), several such threads (4) beeing formed into a cord like structure (5). A packing material according to claim 7, characterized in, that the reinforcing fibers may be any material as selected from metal fibers such as Inconel, Monel and stainless steel, inorganic fibers such as asbestos, ceramics fibers, glass fiber and carbon fiber and organic fibers such as cotton, rayon, phenol, Aramid, PBI, PTFE,PEI, PPS and PEEK. A packing material according to claim 7, characterized in, that the foil material is a metallic foil consisting of lead, copper, aluminium, or a nonmetallic foil such as pulp sheet, Aramid sheet, PTFE sheet, PEI sheet, PPS sheet and PEEK sheet. A packing material according to at least one of claims 7 to 9, characterized in, that the covering fibers consist of any material as selected from metal fibers such as Inconel, Monel and stainless steel, inorganic fibers such as asbestos, ceramics fibers, glass fiber and carbon fiber and organic fibers such as cotton, rayon, phenol, Aramid, PBI, PTFE,PEI, PPS and PEEK. A packing material according to at least one of claims 7 to 10, characterised in, that the covering fibers are knitted, tubular plain stitched, conduit knitted or tubular woven. A packing material according to at least one of claims 7 to 11, characterised in, that the thickness of the flexible graphite sheet is less than 1 mm. A packing material according to at least one of claims 7 to 12, characterised in, that the number of graphite sheets is between 1 and 10. A packing material according to at least one of claims 7 to 13, characterised in, that flexible graphite sheets and fiber or foil material are alternately layered. A packing material according to at least one of claims 7 to 14, characterised in, that the cordlike sructure (5) is formed by twisting either a single piece or a bundle of a plurality of pieces. A packing material according to at least one of claims 7 to 14, characterised in, that the cordlike structure (5) is formed by square braiding, tubular plain stitching, lattice knitting, ribbon weaving or plain stitching and braiding. A packing material according to at least one of claims 7 to 16, characterized in, that a surface treatment agent is used, such as graphite powder, silicon oil, rubber based adhesive or PTFE. A packing material according to at least one of claims 7 to 17, characterized in, that either zinc or sodium nitrite is used for corrosion protection. A packing material for glands or similar elements comprising a flexible graphite sheet material, characterized in, that the graphite sheet material has a width of less than 5mm, and that the graphite material is mixed with short fiber, rubber or resin material and with lubricant material to form a bar- like structure (8), said bar-like structure (8) beeing covered with fiber material to form a thread (4') being formed into a cord like structure. A packing material according to claim 19, characterized in, that the short fibers comprise materials, selected from metal short fibers such as Inconel, Monel and stainless steel, inorganic short fibers such as asbestos, ceramics fiber, glass fiber and carbon fiber, or organic short fiber such as cotton, rayon, phenol, Aramid, PBI,PTFE, PEI, PPS and PEEK, that the rubber is selected from nitrile rubber, chloroprene rubber and fluor rubber, that the resin is selected from phenol resin and epoxy resin, and that the lubricant is selected from natural graphite, expanded graphite, mica and petroleum wax. A packing material according to claim 19 or 20, characterized in, that it comprises reinforcing fiber that consists of selected metal fibers such as Inconwel, Monel, and stainless steel, inorganic fibers such as asbestos, ceramics fiber, glass fiber, carbon fiber, and organic fibers such as cotton, rayon, phenol, Aramid, PBI,PTFE,PEI,PPS and PEEK A packing material according to at least one of claims 19 to 21, characterized in, that the covering fibers are knitted, tubular plain stitched, conduit knitted or tubular woven. A packing material according to at least one of claims 19 to 22, characterised in, that the cordlike structure (5) is formed by twisting either a single piece or a bundle of a plurality of pieces. A packing material according to at least one of claims 19 to 22, characterised in, that the cordlike structure (5) is formed by square braiding, tubular plain stitching, lattice knitting, ribbon weaving or plain stitching and braiding. A packing material according to at least one of claims 19 to 24, characterized in, that graphite powder, silicon oil, rubber based adhesive or PTFE is used as surface treatment agent. A packing material according to at least one of claims 19 to 25, characterized in, that either zinc or sodium nitrite is used for corrosive protection. A packing material according to at least one of claims 19 to 26, characterized in, that the bar-like structure is solid and circular in section.

Inventors: SHIOMI, TOMIKAZU, UEDA, TAKAHISA
Applicants: NIPPON PILLAR PACKING CO., LTD.
Application year: 1987
Main classification: F16J15
IPC codes: C09K3, F16J15