JP2004286220A - Gasket for sanitary piping and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To securely prevent penetration leakage which is a fatal material defect without eliminating characteristics and meanings produced by using porous polytetrafluoroethylene as a structural material in a gasket for sanitary piping of porous polytetrafluoroethylene. <P>SOLUTION: The surface layer of a gasket inner peripheral portion 1c in direct contact with fluid to be sealed is molten and solidified to form a non-porous molten and solidified layer 1'c. The molten and solidified layer 1'c is thick at the center portion thereof in the thickness direction of the gasket 1 and thin at both end portions thereof. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a gasket for sanitary piping made of porous polytetrafluoroethylene used for a joint portion of a sanitary piping in a production device for pharmaceuticals, foods, and the like, and a method of manufacturing the same.

  As the gasket for sanitary piping, there is generally a rubber annular gasket made of silicon rubber or the like or a polytetrafluoroethylene annular gasket. However, those made of rubber tend to elute the plasticizer during long-term use, and are difficult to apply to sanitary piping that requires a high degree of cleanliness. Further, in the sanitary piping, steam sterilization processing is frequently performed recently, but when such processing is performed, the gasket is used under high-temperature conditions, so that the gasket is easily deteriorated and has a problem in durability. In particular, when the cutting is performed with deterioration, leakage occurs, and the predetermined sealing function cannot be exhibited. On the other hand, those made of polytetrafluoroethylene do not have the above-mentioned problems due to the characteristics of polytetrafluoroethylene, but are inferior in flexibility, adaptability, restorability, etc. because they are hard. Therefore, in order to exert a predetermined sealing function, an extremely large tightening torque is required, frequent retightening work is required, and it is difficult to recover the sealing function by retightening.

  Therefore, recently, as a solution to the problem of such a gasket made of silicon rubber or a gasket made of polytetrafluoroethylene, a porous polytetrafluoroethylene, that is, a polytetrafluoroethylene made porous by stretching was used as a constituent material. An annular gasket for sanitary piping (hereinafter referred to as “conventional gasket”) has been proposed (for example, see Patent Document 1). Such a conventional gasket is made of porous polytetrafluoroethylene, which is a soft material, so that the inherent properties of polytetrafluoroethylene, such as excellent durability, cleanliness, and chemical resistance, are ensured. It has excellent flexibility, conformability, resilience, etc., which cannot be obtained with ordinary polytetrafluoroethylene gaskets, and can be suitably used even under severe sealing conditions in sanitary piping. .

However, in the conventional gasket, since the gasket is made of a porous material, the sealed fluid permeates from the inner peripheral portion of the gasket that directly contacts the sealed fluid, and thus there is a possibility that so-called leakage may occur. Such permeation leakage does not occur so much when the sealed fluid is a liquid, but is severe when used as a gas seal or as a vacuum holding seal. It is conceivable to increase the molding density of the gasket in order to prevent seepage leakage. However, there is a limit to increasing the molding density, and it is impossible to reliably prevent penetration leakage. Further, if the molding density is increased more than necessary, the original properties (flexibility etc.) of porous polytetrafluoroethylene will be impaired, and the significance of using porous polytetrafluoroethylene as a constituent material will be lost. Will be. As described above, in the case of the porous gasket made of porous polytetrafluoroethylene, permeation leakage is a fatal defect in terms of the material, and the actual use thereof is greatly restricted.
JP-A-5-99343

  The present invention has been made in view of the above point, and the penetration leakage, which is a fatal defect in the material of a porous polytetrafluoroethylene gasket, is characterized by using porous polytetrafluoroethylene as a constituent material. It is an object of the present invention to provide a gasket for sanitary piping that can be reliably prevented without losing its significance, and to provide a method for suitably manufacturing such a gasket for sanitary piping.

  The gasket for sanitary piping according to the present invention that solves this problem is an annular gasket made of porous polytetrafluoroethylene. In order to achieve the above object, particularly, the surface of the inner peripheral portion of the gasket that directly contacts the sealed fluid. The layer is a non-porous melt-solidified layer that is thicker at the center in the thickness direction of the gasket and thinner at both ends.

  In addition, the method of the present invention for manufacturing such a gasket for sanitary piping includes heating and melting a surface layer of a gasket inner peripheral portion of a porous polytetrafluoroethylene annular gasket that directly contacts a sealed fluid. By cooling and solidifying, a non-porous melt-solidified layer is formed. In this method, it is preferable that the solidification treatment of the surface layer is performed at 420 to 460 ° C. for 10 to 30 seconds. Further, it is preferable that the heat melting treatment of the surface layer is specifically performed by bringing a heated metal member into full contact with the surface layer.

  ADVANTAGE OF THE INVENTION According to the gasket for sanitary piping of this invention, the penetration leakage from the gasket inner peripheral part which is a fatal defect can be reliably prevented, without impairing the original characteristic of the porous polytetrafluoroethylene gasket. . Therefore, the sealing characteristics (gas sealing, airtightness, etc.) of the porous polytetrafluoroethylene gasket can be greatly improved as compared with the conventional gasket, and the use of the gasket can be greatly expanded. it can.

  Further, according to the method of the present invention, a gasket for sanitary piping having the above-described permeation leakage prevention structure can be suitably manufactured.

  Since a non-porous melt-solidified layer is formed on the inner peripheral portion of the gasket that directly contacts the sealed fluid, the leakage from this portion is ensured despite the fact that the gasket is made of a porous material. Is prevented. Moreover, since the melt-solidified layer is only the surface layer of the inner peripheral portion of the gasket, the original characteristics of porous polytetrafluoroethylene, such as flexibility and adaptability, are not impaired as a whole gasket. The significance of using does not disappear.

  Hereinafter, the configuration of the present invention will be specifically described based on the embodiment shown in FIGS.

As shown in FIG. 1, the gasket 1 for sanitary piping according to this embodiment is obtained by press-molding an annular material punched from a porous polytetrafluoroethylene sheet material using a metal mold. An annular plate shape is formed by projecting annular projections 1a and 1b. In addition, as a sheet material made of porous polytetrafluoroethylene, for example, a polytetrafluoroethylene material is subjected to crystal orientation treatment by a pressure roll, and then stretched at a temperature of less than 327 ° C. by a rubber-coated pinch roll. The one having a porosity of 40 to 86% stretched at 300% is used.

  As shown in FIGS. 2 and 3, the gasket 1 is inserted between ferrules 3a, 3b formed at the ends of the sanitary pipes 2a, 2b in a sandwiching state, thereby connecting the joints of the sanitary pipes 2a, 2b. It functions to seal. That is, the gasket 1 is positioned at a predetermined position between the ferrules 3a and 3b, that is, a position concentric with the pipes 2a and 2b. This positioning is performed by engaging the ridges 1a and 1b of the gasket 1 with the annular concave portions 4a and 4b formed on the opposing surfaces of the ferrules 3a and 3b. Then, the ferrules 3a and 3b are tightened by the clamp band 5 to press the gasket 1 between the ferrules 3a and 3b. The clamp band 5 generally has a two- or three-segment structure composed of two or three arc-shaped segments 5a... Connected in a ring shape, and the ring is tightened by connecting screws between the segments 5a. By reducing the diameter of the shape, the space between the ferrules 3a and 3b can be tightened.

  Therefore, by properly setting the tightening surface pressure of the gasket 1 by the ferrules 3a and 3b, that is, the tightening torque of the clamp band 5, the ferrules 3a and 3b are sealed by the gasket 1, but the ferrules 3a and 3b are sealed. As described above, the gasket 1 is made of porous polytetrafluoroethylene as a component from the inner peripheral portion 1c of the gasket which comes into direct contact with the sealed fluid in the pipes 2a and 2b without any restriction by the gasket. Because of this, there is a possibility that leakage of the seepage will occur. In this embodiment, the gasket inner peripheral portion 1c has the following permeation leakage prevention structure, thereby effectively preventing such permeation leakage.

  That is, as shown in FIGS. 1 to 3, the surface layer of the gasket inner peripheral portion 1c is a nonporous melt-solidified layer 1'c over the entire inner peripheral portion 1c.

  Manufacture of the gasket 1 for sanitary piping having such a permeation leakage prevention structure is performed by heating and melting the surface layer of the gasket inner peripheral portion 1c, and then cooling and solidifying the surface layer. Such heat treatment can be performed by various methods. In this embodiment, in consideration of the fact that the gasket 1 is annular, the molten and solidified layer 1 ′ is formed by using a cylindrical metal member having a heater mounted therein. c is formed. That is, the metal member is a cylindrical member whose outer diameter is approximately equal to the inner diameter of the gasket 1. The metal member is heated by a heater to an appropriate temperature equal to or higher than the melting point of the porous polytetrafluoroethylene, and then the gasket is heated. 1 is fitted to and held on the metal member, and the inner peripheral portion 1a of the gasket is uniformly contacted with the outer peripheral portion of the metal member over the entire circumference. Then, after the surface layer of the gasket inner peripheral portion 1c that is in contact with the outer peripheral portion of the metal member is simultaneously and uniformly melted over its entire circumference, the heating of the metal member by the heater is removed, and the molten portion is removed. Is cooled and solidified to form the surface layer of the gasket inner peripheral portion 1c as a non-porous melt-solidified layer 1'c. As shown in FIG. 3, the melt-solidified layer 1'c thus formed is thicker at the center in the thickness direction of the gasket 1 and thinner at both ends (hereinafter, such a layer cross-sectional shape is referred to as "middle-high shape"). . That is, as shown in FIG. 3, the ineffective molten and solidified layer 1'c has a shape protruding outward in the cross-sectional view of the gasket diameter, and its inner peripheral portion 1c has a cross-sectional view. Has a smooth surface that is linear. It is preferable to use a heater whose temperature can be controlled.

  If the surface layer of the gasket inner peripheral portion 1c is formed as the non-porous melt-solidified layer 1'c in this way, even if the gasket 1 is made of a porous material, the gasket inner peripheral portion 1c can be penetrated from the gasket inner peripheral portion 1c. Leakage is effectively prevented by the melt-solidified layer 1'c. The surface layer 1'c of the melt-solidified gasket inner peripheral portion 1c is hard, but the melt-solidified layer 1'c is extremely thin and is formed only in a portion directly contacted by the sealed fluid. However, the properties (such as flexibility, adaptability, and resilience) of the porous polytetrafluoroethylene as a whole are impaired by the presence of the melt-solidified layer 1'c. There is no. That is, it has the same function as the conventional gasket except that it can prevent seepage leakage. In particular, when the melt-solidified layer 1'c is formed in the above-mentioned middle and high-profile shape, when the gasket 1 is compressed in the thickness direction (pressed by the ferrules 2a and 2b), the thin portions at both ends of the melt-solidified layer 1'c are thick at the center. Since the gasket 1 is easily deformed as compared with the portion, the adverse effect of the presence of the melt-solidified layer 1'c on the elastic properties (flexibility, adaptability, etc.) of the gasket 1 can be sufficiently eliminated.

  As described above, the gasket 1 for sanitary piping in which the surface layer of the inner peripheral portion 1a of the gasket has become the molten and solidified layer 1'c can effectively prevent permeation leakage, and is excellent in gas sealability and airtightness. Is confirmed by the experiment described below.

  That is, in this experiment, first, a plurality of porous polytetrafluoroethylene gaskets I to VI were manufactured under the same conditions using a porous polytetrafluoroethylene sheet as a raw material. Each of the gaskets I to VI has the same shape, and is an annular plate having an inner diameter of 23.2 mm, an outer diameter of 50.5 mm, and a thickness of 2 mm, which has the shape of the gasket for sanitary piping shown in FIG.

  Further, for the gaskets I to V excluding the gasket VI, a molten solidified layer was formed on the inner peripheral portion of the gasket under the above-mentioned heat treatment conditions but under different heat treatment conditions. That is, the gasket I was set at 420 ° C. for 10 seconds, the gasket II was set at 440 ° C. for 10 seconds, the gasket III was set at 440 ° C. for 20 seconds, and the gasket IV was set at 440 ° C. for 30 seconds. In the gasket V under the conditions of 460 ° C. and 10 seconds, the inside of the gasket was obtained in the same manner as in the above embodiment (using a thin metal cylinder equipped with a temperature-adjustable heater inside). A middle-high-level melt-solidified layer was formed around the periphery. The gasket VI is a conventional gasket that does not perform any of the above heat treatments, that is, has no molten solidified layer.

  The following confirmation experiments were performed on the sealing properties of each of the gaskets I to VI. The experimental apparatus has the same structure as the sanitary pipe joint structure shown in FIG. 2 in which the pipes 2a and 2b are closed with blind plugs, and the closed space in which the closed pipes 2a and 2b are sealed by the gasket. Hereinafter, referred to as “inspection space”). Note that, for convenience of description, the reference numerals assigned to the corresponding members in the sanitary pipe joint structure shown in FIG.

That is, in the first experiment, each gasket I to VI was clamped and held between the ferrules 1a and 1b as in the sanitary pipe joint structure shown in FIG. Then, the pressure in the inspection space was set to 2.0 kgf / cm ^2, and the pressure in the inspection space after a certain period of time was measured. This experiment was performed when the tightening torque of the clamp band 5 was set to 25 Kgf · cm and 100 Kgf · cm. In the former case, the pressure after 1 hour was measured, and in the latter case, 1 hour passed. The pressure at the time and the pressure at the lapse of 18 hours were measured. The results were as shown in Table 1. In addition, about the conventional gasket VI, the pressure measurement after 18 hours could not be performed. This is because the pressure in the examination space completely disappeared before the elapse of 18 hours.

  From this experimental result, it was confirmed that the gaskets I to V on which the molten and solidified layers were formed had almost no drop in the pressure in the inspection space regardless of the tightening torque, and the leakage was effectively prevented. . On the other hand, it is understood that the pressure of the conventional gasket VI in which the melt-solidified layer is not formed is greatly reduced with the passage of time regardless of the tightening torque, and that the leakage is caused. Therefore, it is understood that the gas sealing characteristics of the porous polytetrafluoroethylene gasket can be significantly improved by forming the melt-solidified layer in the sealed fluid contact portion.

  In the second experiment, the inside of the inspection space of the experimental apparatus was evacuated to -700 mmHg by a vacuum pump, and 1 hour passed when the tightening torque of each gasket I to VI was 25 kgf · cm. When the pressure in the inspection space at the time was set, and when the tightening torque was 100 kgf · cm, the pressure in the inspection space after one hour and the pressure in the inspection space after two hours were measured, respectively. The results were as shown in Table 2. The measured value of the conventional gasket VI after 2 hours is not shown, but this is because the vacuum state was completely released before the lapse of 2 hours.

  From this experimental result, it can be seen that the gaskets I to V on which the melt-solidified layers are formed can exhibit a completely airtight function when the tightening torque is large (100 kgf · cm), and can surely prevent permeation leakage. confirmed. In addition, it is understood that even when the tightening torque is small (25 kgf · cm), penetration leakage is effectively prevented, and an excellent airtight maintenance function is exhibited. On the other hand, regarding the conventional gasket VI, it is understood that even if the tightening torque is increased, the function of maintaining the airtightness is not sufficiently exhibited, and the permeation leakage is extremely large. Therefore, it is understood that the hermeticity retention characteristics of the porous polytetrafluoroethylene gasket can be significantly improved by forming the melt-solidified layer in the sealed fluid contact portion.

  In the third experiment, the gaskets I to V were subjected to the same pressure measurement as in each of the above experiments after repeating the steam sterilization of the pipes 2a and 2b three times. The results are as shown in Table 3. Met.

As understood from the experimental results, the gaskets I to IV having the melt-solidified layer can exhibit excellent gas sealing properties and airtightness even under such severe conditions. Is understood. Therefore, by applying the permeation leakage prevention structure of the present invention, the porous polytetrafluoroethylene gasket can be suitably used even in a sanitary pipe which is legally required to perform steam sterilization. It is understood that it is possible.

Further, in the fourth experiment, the gaskets I to V were immersed in a water tank with the piping axis horizontal, and nitrogen gas was supplied into the inspection space. The amount of air bubbles, that is, the amount of nitrogen gas leaking from the gasket, was measured by constantly maintaining the pressure and collecting air bubbles floating on the water surface using a measuring cylinder. In this experiment, when the tightening torque was 25 Kgf · cm and 40 Kgf · cm, the amount of leakage when the pressure in the inspection space was maintained at ² Kgf / cm ² , the amount of leakage when the pressure in the inspection space was maintained at 3 Kgf / cm ² , and The leakage amount when the pressure in the inspection space was maintained at 4 kgf / cm ² was measured. For the gasket III, the leakage was also measured when the tightening torque was 100 kgf · cm and the pressure in the inspection space was kept at 4 kgf / cm ² . Further, among the gaskets III, those for which the above-described experiment was performed with a tightening torque of 25 kgf · cm were collected from the experimental device after the experiment, and the collected gasket (hereinafter, referred to as “gasket iii”) was again It was assembled in an experimental apparatus with a tightening torque of 100 kgf · cm, and the amount of leakage when the pressure in the inspection space was kept at 4 kgf / cm ² was measured in the same manner as described above. The results were as shown in Table 4.

  As understood from the experimental results, it was further confirmed that the gaskets I to V on which the molten and solidified layers were formed could reliably prevent the leakage of the gasket regardless of the tightening torque and the pressure of the sealed fluid. In addition, the reuse gasket iii was confirmed to have a sufficient sealing function, and depending on the formation of the melt-solidified layer, there was no improvement in the original properties, such as the resilience, of the porous polytetrafluoroethylene gasket. It is understood that no adverse effect is caused.

  Further, in order to examine the influence of the formation of the melt-solidified layer on the flexibility of the gasket, the gasket hardness of each of the gaskets I to VI was measured. The hardness was measured at three points on the radial line of the gasket using a durometer hardness meter (type C) manufactured by Asker. In other words, there are three locations: an inner peripheral end position where the melt-solidified layer is formed (position A shown in FIG. 1), a position near the ridge (position B) and an outer peripheral end position (position C). . At the time of hardness measurement, the ridges 1a and 1b of the gasket were cut in advance with a cutter knife.

  The results of the hardness measurement are as shown in Table 5, and it was confirmed that the hardness was substantially the same irrespective of whether or not the melt-solidified layer was formed. From this, it is understood that the formation of the melt-solidified layer does not impair the flexibility, which is the original characteristic of the porous polytetrafluoroethylene gasket.

  It should be noted that the present invention is not limited to the above-described embodiment, and can be appropriately changed and improved without departing from the basic principle of the present invention. For example, the gasket density can be appropriately set according to sealing conditions and the like within a range that does not lose the original characteristics of porous polytetrafluoroethylene. Further, a method of manufacturing the permeation leakage prevention structure, that is, a method of forming a melt-solidified layer is also optional. For example, the formation of the melt-solidified layer is performed at the same time as forming a gasket or forming a gasket material (sheet material or the like). It is also possible.

BRIEF DESCRIPTION OF THE DRAWINGS It is a half cut perspective view which shows one Example of the gasket for sanitary piping which concerns on this invention. It is a longitudinal side view which shows the sanitary piping joint structure equipped with the same gasket. FIG. 3 is an enlarged detail view showing a main part of FIG. 2.

Explanation of reference numerals

  Reference numeral 1 denotes a gasket for sanitary piping, 1c denotes an inner peripheral portion of the gasket, and 1'c denotes a melt-solidified layer.

Claims (5)

  An annular gasket made of porous polytetrafluoroethylene, wherein an inner peripheral portion of the gasket directly in contact with the sealed fluid has a non-porous melt-solidified layer that is thicker at the center in the thickness direction of the gasket and thinner at both ends. A gasket for sanitary piping characterized by the following.   In the annular gasket made of porous polytetrafluoroethylene, the surface layer of the inner peripheral portion of the gasket that directly contacts the sealed fluid is heated and melted, and then cooled and solidified to form a nonporous molten and solidified layer. A method of manufacturing a gasket for a sanitary pipe, characterized in that:   3. The method for manufacturing a gasket for a sanitary pipe according to claim 2, wherein the surface layer is melt-solidified at 420 to 460 [deg.] C. for 10 to 30 seconds.   4. The manufacturing of a gasket for a sanitary pipe according to claim 2, wherein the heat-melting treatment of the surface layer is performed by bringing a heated metal member into full contact with the surface layer. Method.   The heat-melting treatment of the surface layer is performed by externally holding an annular gasket on a heated cylindrical metal member and bringing an inner peripheral portion of the gasket into contact with an outer peripheral surface of the cylindrical metal body. A method for manufacturing a gasket for sanitary piping according to claim 3 or 4.

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