JP5062911B2 - Expanded graphite sheet gasket - Google Patents

Description

  The present invention relates to an expanded graphite sheet gasket suitable as a gasket between pipes for transferring a cryogenic fluid.

  Natural gas and LP gas, etc., have a considerably large volume at normal temperature and normal pressure, which causes problems in transportation and storage. Therefore, natural gas and LP gas are liquefied and reduced in volume (liquefied gas ) Is generally performed. For example, if natural gas is cooled and liquefied at a low temperature of −162 ° C., the volume can be reduced to about 1/600 at room temperature. In order to transport such liquefied gas from the tanker to the equipment on the ground, a loading arm arranged on the ground (in the port) is used. As for the loading arm, the one disclosed in Patent Document 1 is known.

  As disclosed in Patent Document 2, the expanded graphite sheet gasket has excellent compatibility with the mating seal surface and excellent heat resistance, and is also used in a pipe connection portion between the loading arm and the tanker side. Yes. When loading and unloading the liquefied gas from the tanker, first, the tanker piping and the loading arm tip piping are fastened in a sealed state via an expanded graphite sheet gasket, and then delivery of the liquefied gas into the piping begins. Is done. When the transportation of the liquefied gas is completed, the loading arm tip pipe and the tanker side pipe are detached and the gasket is removed, but there is a fact that the replacement work of the gasket has become a bottleneck.

  That is, as described above, a cryogenic fluid such as liquefied gas flows in the pipe, so that the air around the loading arm is cooled and a large amount of dew condensation occurs in the pipe. Therefore, when the gasket is replaced, it is difficult to completely remove the water, although the water is sufficiently wiped off. Therefore, the gasket is often incorporated in a state with a slight amount of moisture, and moisture is solidified at the time of subsequent decomposition, and sticking occurs between the flange surface of the pipe and the gasket surface. Since the gasket made of expanded graphite sheet is formed in a layered form and is brittle and easily peeled off, forcibly removing the gasket fixed to the flange surface causes interface peeling and breaks.

  The peeled gasket cannot be used at first, so it must be replaced with a new one, but it cannot be sealed on the flange face with the gasket residue. Accordingly, it is necessary to peel off the fixed gasket and return the flange surface to the original clean surface, but the cleaning operation is cumbersome and cumbersome, and the work efficiency has been reduced. Therefore, an attempt was made to use a gasket whose strength was increased by using a reinforcing agent so as not to cause interface peeling. However, it turns out that the binder (rubber etc.) for mix | blending a reinforcing agent hardens | cures with a cryogenic fluid, lose | disappears a softness | flexibility, and becomes a very brittle thing, and it is still difficult to use as a gasket.

  As described above, the above-mentioned problem (inconvenience of fixing to the flange surface) when using an expanded graphite sheet gasket having excellent sealing properties in a cryogenic environment is still unresolved, and there is room for further improvement. Met.

JP 2003-32100 A JP-A-6-101863

  The purpose of the present invention is to prevent or suppress the phenomenon of sticking to the pipe flange surface even if moisture condensed by the cryogenic fluid remains and is assembled by adding further ideas to the components and configuration, etc. An object of the present invention is to provide an expanded graphite sheet gasket that can be easily and easily peeled off from the flange surface to improve working efficiency.

  The invention according to claim 1 is characterized in that, in the expanded graphite sheet gasket, a PP resin layer 2 is formed on the surface 1a of the expanded graphite sheet 1 by applying a PP resin.

  The invention according to claim 2 is the expanded graphite sheet gasket according to claim 1, wherein the thickness of the PP resin layer 2 is set to 20 to 40 μm.

  The invention according to claim 3 is the expanded graphite sheet gasket according to claim 1 or 2, wherein the value of the contact angle θ of the surface 2a of the PP resin layer 2 with respect to the water W is set to 72 degrees or more. It is a feature.

  The invention according to claim 4 is the expanded graphite sheet gasket according to any one of claims 1 to 3, wherein the PP resin layer 2 is subjected to a predetermined heat treatment after the PP resin is applied. It is characterized by this.

  The invention according to claim 5 is the expanded graphite sheet gasket according to claim 4, wherein the heat treatment is performed by heating to 150 to 160 ° C. and maintaining the state for 10 minutes or more. is there.

  According to the invention of claim 1, the PP resin layer formed on the surface of the expanded graphite sheet greatly improves the water repellency of the gasket surface, and even in an environment where the object to be sealed is a cryogenic fluid and freezes, It is possible to avoid sticking to the flange surface while maintaining good sealing performance. As a result, even if moisture condensed by the cryogenic fluid remains and is assembled, the sticking phenomenon to the pipe flange surface can be avoided or suppressed, and the work efficiency can be easily and easily peeled off from the flange surface during pipe separation. An expanded graphite sheet gasket can be provided.

  According to the invention of claim 2, by setting the thickness of the PP resin layer formed on the surface of the expanded graphite sheet in the range of 20 to 40 μm, the thickness of the PP resin layer is increased, and the original expanded graphite sheet is formed. The range in which the contact angle of water is not reduced due to the thin film thickness without interfering with flexibility, that is, a good sealing property and a good water repellency can be obtained. An expanded graphite sheet gasket capable of enhancing the effect can be provided. In this case, if the value of the contact angle with respect to water is 72 degrees or more as in the third aspect, a remarkable sticking prevention effect due to good water repellency can be obtained.

  According to the invention of claim 4, smoothness of the surface of the PP resin can be further increased by a predetermined heat treatment performed after the application of the PP resin. If the heat treatment is maintained for 10 minutes or longer, an expanded graphite sheet gasket having a very smooth surface state and capable of further strengthening the effects according to the inventions of claims 1 to 4 can be provided.

Cross section of expanded graphite sheet gasket Overall perspective view of expanded graphite sheet gasket Definition diagram showing contact angle with water Chart showing characteristics of each example and each comparative example Side view of the main part showing the state before fastening in the gasket usage example Side view of the main part showing the state after fastening in the gasket use example

  Embodiments of an expanded graphite sheet gasket according to the present invention will be described below with reference to the drawings. In FIGS. 1 and 2, etc., the dimensional ratio of each part is shown as deformed (transformed) for easy explanation and understanding.

  In order to improve the releasability so that an expanded graphite sheet gasket (hereinafter simply referred to as “gasket”) can be easily peeled off from the pipe flange surface, it is necessary to significantly reduce the affinity, that is, to impart water repellency. It is valid. By providing good water repellency, the gasket surface and ice can be easily peeled off in order to prevent the gasket and the pipe flange surface from sticking to each other.

  The gasket G according to the present invention has been conceived based on such an idea. As shown in FIGS. 1 and 2, by applying PP (polypropylene) resin to the front and back surfaces 1a of the expanded graphite sheet 1, as shown in FIGS. The gasket G is formed with the PP resin layer 2 and has an annular shape. The idea is to apply a polyolefin resin to the expanded graphite sheet and heat-treat, and PP resin is selected as a representative of the polyolefin resin.

  As an example of the heat treatment, heating is performed after the PP resin is applied to the front and back surfaces of the gasket, and the temperature is raised to 150 ° C. to 160 ° C., preferably, the PP resin is melted (melting of the PP resin is visually confirmed), And the means of maintaining the temperature for 10 minutes or more is mentioned. By doing so, as shown in FIG. 3, it was confirmed that the value of the contact angle θ with respect to the water droplet (water) W on the surface of the gasket G, that is, the surface 2 a of the PP resin layer 2 was 72 degrees or more. . In other words, it has succeeded in obtaining excellent water repellency.

  If the PP resin layer is thin, the water repellency will not be sufficient, and if the PP resin layer is thick, the flexibility of the expanded graphite will be limited, leading to a decrease in sealing performance. Therefore, the thickness of the PP resin layer is set to 20 to 40 μm as a range in which sufficient water repellency and sufficient sealability can be achieved. When the film thickness exceeds 40 μm, the leakage amount is 10 cc / min or more, which is NG in terms of sealing performance. Moreover, when the film thickness is less than 20 μm, it becomes difficult to set the contact angle to water to 72 degrees or more (see the characteristic table of FIG. 4).

  Next, various gaskets G, that is, the gaskets of Examples 1 to 3 and the gaskets of Comparative Examples 1 to 3 were prepared, and the characteristic table of FIG. 4 showing various characteristic data was obtained. In FIG. 4, the contact angle (θ) and the film thickness (μm) are the data of various gaskets, and it can be said that the sealing properties and the effect of preventing the flange surface from sticking are the performances of the various gaskets.

[Example 1]
In the gasket G according to Example 1, a PP resin layer 2, 2 having a thickness t of 20 to 40 μm (20 μm ≦ t ≦ 40 μm) is applied on the surface of the expanded graphite sheet 1 with PP resin, specifically PP dispersion. Is provided. A dispersion is a dispersion in which constituent solutes and solvents are uniformly dispersed. Then, the expanded graphite sheet with the PP resin layer formed thereon is heated to 150 ° C. and heated for 10 minutes (an example of a predetermined heat treatment) by a heating means such as being placed in a high temperature chamber. The PP resin layer 2 has a thickness t = 20 μm and a water droplet contact angle θ = 72 degrees (resin melting: yes).

[Example 2]
In the gasket G according to Example 2, the PP resin layer 2 has a thickness t = 30 μm and a contact angle θ = 77 degrees (resin melting: yes). The method for making the gasket G is the same as that in the first embodiment.

Example 3
In the gasket G according to Example 3, the PP resin layer 2 has a thickness t = 40 μm and a contact angle θ = 90 degrees (resin melting: yes). The method for making the gasket G is the same as that in the first embodiment.

[Comparative Example 1]
The basic method of making the gasket G according to Comparative Example 1 is the same as that of Example 1, except that the thickness t of the PP resin layer 2 is 10 μm. The contact angle θ = 65 degrees, which deviates from the condition of “72 degrees or more”.

[Comparative Example 2]
The gasket G according to Comparative Example 2 is manufactured in the same manner as in Example 1, except that the PP resin layer 2 has a thickness t = 50 μm. The contact angle θ = 96 degrees, which satisfies the condition of “72 degrees or more”.

[Comparative Example 3]
The gasket G according to Comparative Example 3 is the same as Example 1 except that the expanded graphite sheet on which the PP resin layer is formed is heated to 140 ° C., except that the PP resin layer 2 is not melted. . The contact angle θ = 38 degrees, which deviates from the condition of “72 degrees or more”.

  As can be seen from the characteristic table shown in FIG. 4, the gaskets G of Examples 1 to 3 in which the thickness t of the PP tree layer 2 is in the range of 20 to 40 μm and the contact angle θ is 72 degrees or more are sealed. Both the property and the effect of preventing the flange surface from sticking were good. However, in the gaskets G of Comparative Examples 1 to 3 in which at least one of the thickness t or the contact angle θ of the PP resin layer 2 is outside the conforming condition, at least one of the sealing performance and the sticking prevention effect is x (NG). Yes. Here, the criterion for determining the sealing property is “X” when the leakage amount is more than 10 cc / min, and “OK” when it is less than that. The effect of preventing the flange surface from sticking was judged by visual inspection in a state where the flange surface was actually disassembled after use.

  5 and 6 show a fixed test product as a reference. A test joint having a structure in which a gasket G is interposed between a pipe flange 3 having a pipe 3H and a simple flange 4 having no pipe. Five examples are shown. FIG. 5 shows a state before fastening of the test joint 5 with moisture, that is, before screwing with the bolt and nut 6, and FIG. 6 shows a state after fastening, that is, after the bolt and nut 6 are tightened. Yes. A hatched portion (hatched portion) in FIG. 5 indicates moisture (water) 7. In FIG. 5, the moisture 7 in the pipe 3H reaches the flange surfaces 3a and 4a. As shown in FIG. 6, the gasket G is interposed in the moisture atmosphere by tightening the bolts and nuts 6. And tightened.

  Regarding the adhesion mechanism of the expanded graphite sheet gasket at low temperature and the effect of the PP resin dispersion (polyolefin dispersion), the following 1. ~ 4. It seems like. 1. As shown in FIG. 5, when the flanges 3 and 4 are fastened with the gasket G sandwiched between the flanges 3 and 4 in a state where there is moisture 7 in the pipe or the like, the gasket G and the flange surfaces 3 a and 4 a In between, an ice layer (portion 8 shown in FIG. 6) is formed. 2. When the joint portion 5 is disassembled, the ice layer 8 between the gasket G and the flange surfaces 3a and 4a serves as an adhesive, and the gasket G and the flange surfaces 3a and 4a are fixed.

  3. When the gasket G is peeled off from the flange surfaces 3a and 4a in this state, the interface of the expanded graphite sheet 1 having the weakest strength in the gasket G is peeled off (the expanded graphite sheet has a structure in which the expanded graphite layers overlap each other). And the interface strength is weak). 4). However, when dense non-adhesive surfaces (PP resin layers) 2 and 2 are formed on the surface of the expanded graphite sheet 1 by applying and firing a polyolefin dispersion such as PP dispersion (PP resin), the gasket G and ice Since peeling occurs at the interface with the layer 8, the above-described sticking does not occur (the present invention). That is, 1. ~ 3. Represents the mechanism of fixation; Represents the effect of the present invention.

DESCRIPTION OF SYMBOLS 1 Expanded graphite sheet 1a Surface of expanded graphite sheet 2 PP resin layer 2a Surface of PP resin layer W Water θ Contact angle

Claims (5)

  An expanded graphite sheet gasket in which a PP resin layer is formed by applying a PP resin on the surface of an expanded graphite sheet.   The expanded graphite sheet gasket according to claim 1, wherein the PP resin layer has a thickness of 20 to 40 μm.   The expanded graphite sheet gasket according to claim 1 or 2, wherein a value of a contact angle with respect to water on the surface of the PP resin layer is set to 72 degrees or more.   The expanded graphite sheet gasket according to any one of claims 1 to 3, wherein the PP resin layer is formed by performing a predetermined heat treatment after application of the PP resin.   The expanded graphite sheet gasket according to claim 4, wherein the heat treatment is performed by heating to 150 to 160 ° C. and maintaining the state for 10 minutes or more.

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