JP5012768B2 - Manufacturing method of fusible stopper - Google Patents

Description

  The present invention relates to a method for producing a soluble stopper used as a safety device for a high-pressure container such as a refrigeration apparatus.

  The fusible stopper is a screw-like member provided on a side wall or a liquid reservoir of a high-pressure container such as a refrigeration apparatus. This screw-like member is provided with a relief hole (through hole) that conducts the inside and outside of the high-pressure vessel, and this through-hole has a low melting point that is lower than the critical temperature of the refrigerant or the like stored inside the high-pressure vessel. Filled with melting point metal. Utilizing the property that the temperature of the refrigerant rises when the refrigerant stored inside the high-pressure vessel is abnormally pressurized for some reason, the low melting point metal filled in the through hole of the fusible cap softens and dissolves, causing high pressure By releasing the refrigerant in the container to the outside air, it is possible to prevent the pressure container from rupturing.

  As a low melting point metal used for the fusible stopper, there is an alloy made of tin (Sn), bismuth (Bi) and indium (In) (for example, see Patent Document 1). This alloy can be melted and filled into the through holes to produce a fusible plug. In addition, in order to improve the wettability between the screw-shaped member (blank material) having a through-hole serving as the main body of the fusible plug and the low-melting-point metal, a flux is applied to the inner wall of the through-hole, and then the low-melting-point metal is applied. A method of filling through holes is disclosed (for example, see Patent Document 2).

  As a characteristic required for the fusible stopper, as described above, when the internal pressure of the high-pressure vessel is abnormally increased, the low melting point metal is surely softened and melted and the refrigerant in the high-pressure vessel can be released into the outside air. At the same time as the characteristics, reliability (referred to as creep resistance) that does not cause a malfunction such as a minute leak is required even when a low-melting-point metal is installed for many years under a normal use environment of a soluble stopper at 60 ° C. and 4 MPa. As a means of improving the creep resistance, a metal layer mainly composed of nickel (Ni) is formed on the inner wall of the through hole, and a low melting point metal mainly composed of molten tin (Sn) is formed in the through hole. There is disclosed a fusible plug in which a low melting point metal in the escape hole is fixed by pouring and cooling (see, for example, Patent Document 3).

WO 2006/057029 (page 4, FIG. 1) JP 2003-130240 A (page 5, FIG. 1) Japanese Patent Laying-Open No. 2001-201218 (page 3, FIG. 1)

In recent years, the internal pressure of high-pressure vessels tends to increase due to the application of natural refrigerants such as HFC refrigerant and CO ₂ and NH ₄ that can further save energy instead of downsizing refrigeration equipment and conventional fluorine-based refrigerants. . Therefore, higher creep resistance has been demanded for the fusible stopper. In the conventional method of applying a flux or a metal layer to the inner wall of the through hole in order to improve the wettability between the through hole of the fusible plug and the low melting point metal, the main body of the fusible plug and the low melting point metal Although the creep resistance is improved by improving the bonding strength, there is a limit to the creep resistance. In particular, when a low melting point metal containing antimony is used, there has been a problem that even if a metal layer mainly composed of Ni is formed on the inner wall of the through-hole, the improvement in creep resistance cannot be obtained remarkably.

  The inventor investigated the cause of the creep resistance when using a low melting point metal containing antimony, that is, the cause of microleakage under normal operating conditions of 60 ° C. and 4 MPa. It was found that voids (bubbles) present in the low melting point metal filled in the metal became a deformation starting point of the alloy with respect to pressure in a long-time environment of about 60 ° C. and 4 MPa, causing microleakage.

  An object of the present invention is to obtain a method for producing a fusible plug capable of reducing the voids present inside the low melting point metal and further improving the creep resistance when a low melting point metal containing antimony is used. To do.

  The manufacturing method of the fusible plug according to the present invention includes a step of coating a low melting point metal containing antimony on an inner wall of a through hole of a blank material having a through hole, and a molten state in a through hole in which the inner wall is coated with a low melting point metal. The method includes a step of filling a low melting point metal and a step of cooling and solidifying the low melting point metal filled in the through hole.

  In the method for producing a fusible plug according to the present invention, when a low melting point metal containing antimony is used, the through hole is filled with the low melting point metal containing antimony after the inner wall of the through hole is coated with the low melting point metal. Therefore, voids existing inside the low melting point metal can be reduced and the creep resistance can be further improved.

Embodiment 1 FIG.
FIG. 1 is a schematic view of a fusible plug according to Embodiment 1 for carrying out the present invention. The blank material 2 which becomes the main body of the fusible plug 1 has a screw-like shape and has a through hole 3 at the center. The through hole 3 is filled with a low melting point metal 4.

  The manufacturing method of the soluble stopper in this Embodiment is demonstrated. As the blank material 2, a brass member having a through hole 3 with a hole diameter of 6 mm, an outer diameter of a screw part of 11 mm, and a length of 21 mm was prepared. A brass lid was placed at the tip of the threaded portion, and this lid was placed on a hot plate heated to 350 ° C. with the lid down. The molten low melting point metal 20Sn-35In-40Bi-5Sb (wt%) is poured from the upper opening through hole, and the molten low melting point metal is discharged by lifting only the blank material to the outside of the through hole. The blank was cooled by air cooling. Finally, the blank was ultrasonically cleaned in acetone for about 5 minutes. In this way, a low melting point metal film having a thickness of about 100 μm was formed on the inner wall of the through hole. Next, a brass lid was placed at the tip of the threaded portion of the blank with the low melting point metal coated on the inner wall of the through hole, and this lid was placed on the hot plate with the lid down. 20Sn-35In-40Bi-5Sb (wt%), which is a low melting point metal processed into a small piece of φ2mm x 1mm from the upper open through hole, is packed and heated to a hot plate temperature of about 350 ° C. The low melting point metal inserted in is melted. At this time, small pieces of low melting point metal were appropriately added so that the through holes were completely filled with the low melting point metal, and the mixture was stirred with a stainless steel stirring rod. Finally, the heating of the hot plate was finished, the lid was removed after the low melting point metal solidified by air cooling, and the fusible plug of this embodiment was produced. In this way, five soluble stoppers of the present embodiment were prepared (Examples 1 to 5).

Next, for comparison, a comparative example was prepared in which the inner wall of the through hole was not covered with a low melting point metal. Using the same blank as in the above example, a brass lid was placed at the tip of the threaded portion, heated for about 10 minutes in a thermostatic bath maintained at 350 ° C., and then placed on the gypsum board with the lid down. 20Sn-35In-40Bi-5Sb (wt%), which is a rod-like low melting point metal of φ2 mm × 300 mm coated with a rosin flux (for example, Deltalux 523H manufactured by Senju Metal Industry Co., Ltd.) at the tip, It was filled while melting by bringing it into contact with the inner wall. Finally, after the low-melting point metal was solidified by air cooling, the lid was removed to prepare five soluble stoppers as comparative examples (Comparative Examples 1 to 5). In order to remove bubbles, when the low melting point metal was filled while being melted in the through-hole, the low melting point metal was appropriately stirred up and down with a stainless steel stirring rod, and then produced in the present embodiment. In the fusible stoppers of Examples 1 to 5 and Comparative Examples 1 to 5, the void ratio, operability, and creep resistance were evaluated. These evaluation methods will be described.

  The void ratio is obtained by acquiring a transmission image of a fusible plug from all directions using a three-dimensional transmission X-ray device, then binarizing the transmission image with an image processing device and integrating the area of the white portion estimated as a void. Then, the ratio of the void integrated area to the total area of the low melting point metal was calculated, and the average value obtained from the images in four directions of this ratio was defined as the void ratio (%).

  A fusible stopper was attached to the pressure vessel to evaluate operability and creep resistance. A nitrogen cylinder equipped with a pressure gauge and a pressure reducing valve is connected to this pressure container via a pipe equipped with a sealing valve, and the sealing valve is opened and nitrogen gas is sealed from the nitrogen cylinder into the pressure container. When the pressure gauge indicated 4.5 MPa, the sealing valve was closed. This pressure vessel was submerged in a water tank whose water temperature could be adjusted by a temperature control device.

  The operability means that the fusible stopper leaks reliably at at least 75 ° C. or lower in order to reduce the internal pressure when the refrigerant or the like inside the high pressure vessel is abnormally pressurized and the temperature of the refrigerant rises. . When bubbles are generated from a soluble stopper at 75 ° C or lower when the water temperature is kept at a constant temperature from 60 ° C to 80 ° C for 1 minute and then raised by 1 ° C for a submerged pressure vessel. Judged that the fusible stopper worked, and if no bubbles were generated even at 75 ° C., it was judged that it did not work.

  Creep resistance means that no leakage or the like occurs when the high-pressure vessel is held for a long time in a normal state of 60 ° C. or lower. A pressure vessel similar to the pressure vessel used for the above-described operability evaluation is used. In the operability evaluation, the internal pressure of the pressure vessel when closing the sealing valve was set to 4.5 MPa. At the time of evaluation, the internal pressure of the pressure vessel was 9 MPa. The pressure vessel thus submerged by setting the internal pressure is maintained for 100 hours with the water temperature kept constant at 60 ° C., and bubbles are generated from the fusible stopper and the low melting point metal is removed every 2 hours. Observed popping out. If no bubble generation and low-melting point metal jump are observed until 100 hours have elapsed, the creep resistance is acceptable, and either bubble generation or low-melting point metal jumping is observed before 100 hours have elapsed. The creep resistance was rejected.

  Table 1 shows the void ratio, operability, and creep resistance of the soluble plugs of Examples 1 to 5 and Comparative Examples 1 to 5 in the present embodiment. Regarding the operability, “◯” indicates that it has operated, and “X” indicates that it has not operated. Regarding creep resistance, “◯” indicates a case of passing, and “X” indicates a case of failure.

  From Table 1, as in Examples 1 to 5 in the present embodiment, the low melting point metal that is the same as the low melting point metal that fills the through hole is coated on the inner wall of the through hole in advance, and then the low melting point metal is filled. It can be seen that the generation of voids can be suppressed and the creep resistance is also improved.

  The reason why the creep resistance is improved by previously coating the inner wall of the through hole with the low melting point metal containing antimony and then filling the same kind of low melting point metal is expected as follows. Since the low melting point metal containing antimony reduces the wettability of the low melting point metal, when the inner wall of the through hole is not covered as in Comparative Examples 1 to 5, it directly contacts the inner wall of the through hole. Since the low melting point metal needs to be in a molten state for a long time, an oxide is easily generated. As a result, the generation of voids is considered to increase. On the other hand, when the inner wall of the through hole is previously coated as in the embodiment, since the coating has a thin film thickness of about 100 μm, it can immediately melt and diffuse to ensure wetting (cooling and solidification). . As a result, it is considered that an oxide is hardly generated and generation of voids can be suppressed.

  In this embodiment, 20Sn-35In-40Bi-5Sb (wt%) is used as the low melting point metal, but other SnInBiSb alloys such as 17Sn-35In-41Bi-7Sb (wt%) are used. Even if it is used, the same effect can be obtained.

  In the present embodiment, the thickness of the coating on the inner wall of the through hole is about 100 μm, but the thickness of this coating may be in the range of 10 to 100 μm. If it is this range, since there exists an effect | action which suppresses the production | generation of an oxide before a film is cooled and solidified, generation | occurrence | production of a void can be suppressed and creep resistance can also be improved.

  Furthermore, in the present embodiment, the low melting point metal that covers the inner wall of the through hole and the low melting point metal that fills the inside of the through hole have the same composition, but they do not necessarily have the same composition. Any SnInBiSb alloy containing 3 to 10 wt% of antimony may be used.

  In this embodiment, the low melting point metal is melted at 350 ° C., but it is desirable that the melting temperature is higher. The higher the melting temperature is, the faster the low melting point metal melts and the time until all the low melting point metals become a liquid phase is shortened, and the viscosity decreases in a short time, so that the generation of voids can be further suppressed. In particular, this effect becomes more remarkable when the melting temperature is 400 ° C. or higher.

Embodiment 2. FIG.
In the first embodiment, a comparative example in which a coating is not formed on the inner wall of the through hole is shown. In the second embodiment, a comparative example in which a coating containing Ni as a main component is formed. In the present embodiment, Examples 1 to 5 of the fusible plug are the same as those of the first embodiment. The manufacturing method of the soluble stopper used as the comparative examples 6-10 is demonstrated.

  A blank material similar to that of the first embodiment was prepared, and a Ni film was formed on the inner wall of the through hole using plating. The thickness of this Ni coating is about 10 μm. A blank material in which a Ni coating is formed on the inner wall of the through-hole is made of 20Sn-35In-40Bi-5Sb (wt%), which is a low melting point metal, using a hot plate or the like, as in Examples 1 to 5 of the first embodiment. ) Was filled in the through holes. Thus, the five comparative examples in this Embodiment were prepared (comparative examples 6-10). Furthermore, the void ratio, operability, and creep resistance were evaluated as in the first embodiment.

  Table 2 shows the void ratio, operability, and creep resistance of the soluble plugs of Comparative Examples 6 to 10 in the present embodiment. For comparison, Examples 1 to 5 shown in the first embodiment are also shown.

  From Table 2, even if the inner wall of the through-hole is previously coated with a low-melting point metal different from the low-melting point metal filling the through-hole as in Comparative Examples 6 to 10 in the present embodiment, the generation of voids can be suppressed to some extent. However, it can be seen that the improvement in creep resistance is insufficient. On the other hand, as in Examples 1 to 5, voids are generated by filling the inner wall of the through-hole with the same low-melting-point metal as the low-melting-point metal that fills the through-hole in advance and then filling the low-melting-point metal. As well as creep resistance can be improved.

Embodiment 3 FIG.
In the first embodiment, when filling the through-hole with the low melting point metal, the solid piece was inserted and then heated to 350 ° C. above the melting point of the low melting point metal, but in the second embodiment, An example in which a through-hole is filled with a low-melting-point metal in a molten state is shown.

  As in the first embodiment, a film of 20Sn-35In-40Bi-5Sb (wt%), which is a low melting point metal having a thickness of about 100 μm, is formed on the inner wall of the through hole of the blank material. Next, a brass lid is placed at the tip of the threaded portion, heated for about 10 minutes in a thermostatic bath maintained at 350 ° C., placed on a gypsum board with the lid down, and a rosin-based flux ( For example, 20 Sn-35In-40Bi-5Sb (wt%), which is a rod-like low melting point metal of φ2 mm × 300 mm coated with Deltalux 523H manufactured by Senju Metal Industry Co., Ltd., is melted by contacting the inner wall of the through hole. While filling. Finally, after the low-melting point metal was solidified by air cooling, the lid was removed to prepare five soluble stoppers as comparative examples (Examples 6 to 10).

  Table 3 shows the void ratio, operability, and creep resistance of the fusible plugs of Examples 6 to 10 in the present embodiment.

  From Table 3, as in Examples 6 to 10 in the present embodiment, the low melting point metal that is the same as the low melting point metal that fills the through hole is previously coated on the inner wall of the through hole, and then the low melting point metal is filled while melting Even in this case, as in Examples 1 to 5 of the embodiment in which the low melting point metal is inserted in a solid state, it is understood that generation of voids can be suppressed and creep resistance is also improved.

  In this embodiment, the low melting point metal is melted at 350 ° C., but it is desirable that the melting temperature be higher. The higher the melting temperature is, the faster the low melting point metal melts and the time until all the low melting point metals become a liquid phase is shortened, and the viscosity decreases in a short time, so that the generation of voids can be further suppressed. In particular, this effect becomes more remarkable when the melting temperature is 400 ° C. or higher. When the melting temperature of the low melting point metal is set to 400 ° C. or higher, it is preferable to use an inorganic flux containing phosphoric acid, chlorine or zinc, which has higher heat resistance than the rosin flux.

Embodiment 4 FIG.
In Embodiment 4, when filling a through-hole with a low melting-point metal in Embodiment 1, when inserting a small piece of a solid state, the example which dripped a flux simultaneously is shown.

  First, a flux (for example, Deltalux 523H manufactured by Senju Metal Industry Co., Ltd.) was filled in a syringe. In the same manner as in the first embodiment, a low melting point metal film having a thickness of about 100 μm was formed on the inner wall of the through hole. Next, a brass lid was placed at the tip of the threaded portion of the blank with the low melting point metal coated on the inner wall of the through hole, and this lid was placed on the hot plate with the lid down. When packing 20Sn-35In-40Bi-5Sb (wt%), which is a low melting point metal processed into a small piece of φ2 mm × 1 mm from the upper open through hole, a predetermined amount of flux is simultaneously injected into the through hole from the syringe. It was dripped in. Thereafter, the temperature of the hot plate was heated to about 350 ° C. to melt the low melting point metal inserted into the through hole. In this embodiment, the amount of flux dropped varies from 0.0 (no flux), 0.1, 0.3, 0.5, 0.7, 1.0, 1.5, and 2.0 cc. A soluble stopper was prepared. Furthermore, the void ratio was measured in the same manner as in the first embodiment with respect to the soluble stopper in which the dropping amount of these fluxes was changed.

  FIG. 2 is a characteristic diagram showing the relationship between the flux dripping amount and the void ratio in the present embodiment. From FIG. 2, it can be seen that the void ratio is lower than that in the case where the flux is not dropped in the range where the flux is dropped from 0.1 to 0.5 cc. Further, from the correlation between the void ratio and the creep resistance of Examples 1 to 10 in Embodiment 1 and Embodiment 3, if the void ratio is 8% or less, improvement in creep characteristics is seen, so that the flux dripping By setting the amount to 0.1 cc or more and 1.0 cc or less, creep resistance is improved and a highly reliable soluble stopper can be produced.

  The amount of the flux dropped as described above varies depending on the size of the fusible plug, the filling density of the low melting point metal, the heating temperature, the type and concentration of the flux, but there is no problem in the range of the amount dropped as described above. I think that the.

It is a schematic diagram of the soluble stopper in Embodiment 1 of this invention. It is a characteristic view of the fusible plug in Embodiment 4 of this invention.

Explanation of symbols

1 Fusible stopper 2 Blank material 3 Through hole 4 Low melting point metal

Claims (3)

Coating the low melting point metal containing antimony on the inner wall of the through hole of the blank material having the through hole;
Filling the through hole whose inner wall is coated with the low melting point metal with the low melting point metal in a molten state;
And a step of cooling and solidifying the low melting point metal filled in the through hole. Coating the low melting point metal containing antimony on the inner wall of the through hole of the blank material having the through hole;
Inserting the low melting point metal in a solid state into the through hole whose inner wall is coated with the low melting point metal;
Heating the low melting point metal to a temperature equal to or higher than the melting point to melt the low melting point metal;
And a step of cooling and solidifying the low melting point metal filled in the through hole. The method for producing a fusible plug according to claim 2, wherein in the step of inserting a low melting point metal into the through hole, a flux is injected into the through hole.

Images