JP2024070762A - Manufacturing method of vacuum sealing structure - Google Patents

Abstract

To provide a brazed type vacuum sealing structure which enables easy manufacturing and eliminates a need for maintenance.SOLUTION: A vacuum sealing structure for keeping an interior of a jacket 13 of a workpiece in a vacuum state includes: an exhaust socket 20 having an exhaust hole 18 allowing communication between the interior of the jacket 13 and the outside; and a sphere 30 housed in the exhaust hole 18. An inner wall surface 22 of the exhaust hole 18 has a conical surface portion 22a whose diameter is reduced toward the jacket 13. The conical surface portion 22a and the sphere 30 are placed in close contact to be brazed to each other in an airtight manner. A manufacturing method of the vacuum sealing structure includes: a preparation step in which the workpiece in which a first ring 26, the sphere 30, and a second ring 24 made of a brazed material are sequentially disposed in the exhaust hole 18 is set in a vacuum heat treatment furnace; an exhaust step in which air is exhausted from the vacuum heat treatment furnace until its vacuum reaches a target vacuum; and a heating step in which the interior of the vacuum heat treatment furnace is heated until the temperature reaches a target temperature.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for manufacturing a vacuum sealed structure, a vacuum sealed structure manufactured by the manufacturing method, and a vacuum insulated double pipe equipped with the vacuum sealed structure.

Generally, a vacuum insulated double pipe consists of an inner pipe that is in contact with the process liquid, and an outer pipe that is located on the outer periphery of the inner pipe and forms a gap (jacket) between the two to form a vacuum layer, and the jacket is evacuated to form a vacuum layer. Due to the presence of the vacuum layer with low thermal conductivity, the entire inner pipe is thermally insulated from the outside world, and the fluid flowing inside the inner pipe is not affected by the outside temperature.

For example, in food manufacturing plants, vacuum insulated double-walled pipes are used in piping systems for transporting fluids such as food ingredients. In the food industry, liquids to be produced are transported between facilities through piping in a heated or cooled state. In order to minimize the heat dissipation from the piping that occurs during this process (energy saving) and to keep the transported material at a constant temperature, vacuum insulated double-walled pipes are used.
In addition, in the food industry, equipment piping is often disassembled and cleaned on a daily basis to maintain hygiene, and a structure in which insulation material is wrapped around the outside of the piping is therefore inappropriate.

A method for manufacturing a vacuum insulated double-walled pipe by vacuum brazing in a vacuum heating furnace is known (Patent Document 1).

A known vacuum sealing structure is one in which an exhaust port is provided in an outer tube and sealed with silver solder or a nickel-based or glass-based solder material (Patent Document 2). For example, when silver solder is used, a sealing cylinder made of a conductive metal and having an exhaust port is attached to the outer tube, and a valve body is brazed to the exhaust port with silver solder.

The valve body is attached to the tip of the threaded rod. The valve body has a flange, and the front end side of the flange has a diameter that can enter the exhaust port, and the rear end side has a screw hole that receives the threaded part of the threaded rod. The flange of the valve body is the part that carries the silver solder.

The screw rod can be rotated and moved forward and backward by an external drive mechanism. By moving the screw rod forward, the flange of the valve body can be pressed against the shoulder of the exhaust port to close the exhaust port, and conversely, by moving the screw rod backward while rotating it, the screw rod can be separated from the valve body.

In manufacturing a vacuum insulated double pipe, first, the valve body is retracted to a position where it does not completely block the exhaust port, and a vacuum exhaust pump connected to the sealing cylinder via an exhaust pipe is operated to evacuate the inside of the outer pipe through the exhaust port.

When the target degree of vacuum is reached inside the outer tube, the screw rod is advanced to move the valve body for closing the exhaust port to a position where it closes the exhaust port.

Next, the sealing cylinder is heated by a high-frequency generator arranged around the sealing cylinder to melt the silver solder, and the molten silver solder fills the gap between the valve body and the sealing cylinder. When the heating is stopped and the cylinder is allowed to cool, the molten silver solder solidifies, completing the vacuum seal for the exhaust port.

Thereafter, the threaded rod is rotated and retreated to separate it from the valve body, the vacuum exhaust device including the exhaust pipe and the high-frequency heater are separated from the vacuum insulated double pipe, and the finished vacuum insulated double pipe is removed.

Japanese Patent Application Laid-Open No. 62-40968 JP 2005-337386 A

According to the above-mentioned conventional technology, the valve body carrying the brazing material must be held in a position in the vacuum heating furnace that does not completely block the exhaust port during the evacuation process and that closes the exhaust port during the heating process. Therefore, a device is essential for holding and moving the valve body carrying the brazing material at a predetermined position according to each process.

The object of the present invention is to eliminate such problems. That is, the present invention aims to provide a vacuum sealing structure and a manufacturing method thereof that do not require a device for holding and moving the valve body during the manufacturing process. Another object of the present invention is to provide a vacuum insulated double pipe equipped with such a vacuum sealing structure.

In order to solve the above problems, the present invention provides a vacuum sealing structure for sealing a jacket that is to become a vacuum layer, in which an exhaust socket with an exhaust hole that connects the inside of the jacket with the outside is provided in the jacket, and a sphere is vacuum brazed in a state where the sphere is in contact with the conical inner wall surface of the exhaust hole. This vacuum sealing structure can be applied to vacuum insulated double pipes as well as any type of vacuum container equipped with a vacuum layer.
Such a vacuum sealed structure can be obtained by interposing a first ring between the conical inner wall surface and a sphere, placing a second ring on top of the sphere, and undergoing an evacuation process and a heating process in a vacuum heat treatment furnace.

The first ring has a notch or a dent that can form an air passage between the sphere and the inner wall surface of the exhaust hole. In addition to providing a notch at one place on the circumference of the ring to make it a C-shaped ring, two or more dents distributed in the circumferential direction can also be used as long as the same ventilation effect is obtained. The material of the first ring has a lower melting point than the materials of the sphere and the socket, and does not necessarily have to be a brazing material.

The second ring is made of brazing material, which melts and penetrates between the sphere and the inner wall of the exhaust hole, brazing the sphere to the exhaust socket. Brazing is done by using a brazing material with a lower melting point than the base material, and melting the brazing material to join them. Therefore, when simply talking about brazing material, it goes without saying that a brazing material with a lower melting point than the exhaust socket and the sphere is selected.

During the exhaust process, exhaust is performed without any hindrance through the ventilation passage formed by the notches and dents in the first ring. During the heating process, the first ring that supported the sphere melts and the sphere falls under its own weight and fits snugly against the inner wall of the exhaust hole. In this way, the ventilation passage is automatically formed and closed without the need for an external device. During the heating process, the second ring melts while the sphere is in close contact with the inner wall of the exhaust hole, and penetrates between the sphere and the inner wall of the exhaust hole along the outer surface of the sphere, forming an annular molten pool around the entire circumference of the sphere, with the bottom being the contact point between the sphere and the inner wall of the exhaust hole.

More specifically, the vacuum sealing structure for sealing the jacket 13 to be the vacuum layer comprises an exhaust socket 20 provided in the jacket 13 with an exhaust hole 18 that connects the inside of the jacket 13 with the outside, and an inner wall surface 22 of the exhaust hole 18, at least in a partial area in the axial direction of the exhaust hole 18, having a conical surface-shaped portion 22a that narrows in diameter toward the jacket 13, a sphere 30 being accommodated in the exhaust hole 18 and brought into contact with the conical surface-shaped portion 22a around the entire circumference of the sphere 30, and the exhaust socket 20 and the sphere 30 being hermetically brazed along the contact portion to maintain a vacuum inside the jacket 13.

The brazing is performed by placing the first ring 26 having the notch 28 or dent, the sphere 30, and the second ring 24 made of brazing material in the exhaust hole 18 in this order, setting them in a vacuum heat treatment furnace, and going through an exhaust process and a heating process in the vacuum heat treatment furnace.

In the evacuation process, the jacket 13 is evacuated to a vacuum through an air passage formed between the first ring 26 and the sphere 30 and/or between the first ring 26 and the inner wall surface 22 of the evacuation hole 18 .

In the heating step, the first ring 26 and the second ring 24 are melted. The first ring 26 melts and flows down, causing the sphere 30 to fall until it contacts the conical surface portion 22a, and at the same time, the air passage disappears. The second ring 24 also melts, and the molten metal of the brazing material from the second ring 24 permeates from the contact portion between the sphere 30 and the conical surface portion 22a to the large diameter side of the conical surface portion 22a, and then solidifies.

The vacuum insulated double pipe 10 has an inner pipe 12 and an outer pipe 14 with a jacket 13 closed at the ends formed between them, an exhaust socket 20 is provided on the outer pipe 14, the exhaust socket 20 has an exhaust hole 18 extending radially from the outer pipe 14 to connect the jacket 13 to the outside, and an inner wall surface 22 of the exhaust hole 18 has a conical surface portion 22a that narrows in diameter toward the jacket 13 in at least a partial axial region of the exhaust hole 18, a sphere 30 is accommodated in the exhaust hole 18, the sphere 30 and the conical surface portion 22a are in contact around the entire circumference of the sphere 30, and the exhaust socket 20 and the sphere 30 are hermetically brazed along the contact portion, thereby maintaining a vacuum inside the jacket 13.

According to the present invention, since the vacuum sealing structure is a structure in which a sphere is brazed to the exhaust hole of the exhaust socket, a vacuum insulated double pipe that is maintenance-free for a long period of time can be provided. In particular, since the structure is such that the sphere is received by the conical inner wall surface of the exhaust hole, if the sphere and the first and second rings are first set in the exhaust hole, each step during the subsequent exhaust process and heating process can be performed without requiring any external device. Therefore, the vacuum sealing structure of the present invention and the vacuum insulated double pipe of the present invention equipped with such a vacuum sealing structure can be easily manufactured without requiring special equipment or devices for holding the workpiece or moving it between processes.

For example, in food processing facilities, there are lines where pipes are disassembled and washed by hand, or lines where they are circulated and cleaned using CIP (without disassembly and in place), and even for lines that undergo CIP cleaning, it is possible to provide maintenance-free vacuum insulated double pipes that can maintain their insulation properties for long periods of time.

FIG. 2 is a cross-sectional view of the vicinity of an exhaust socket of a vacuum insulated double pipe according to an embodiment of the present invention. 1A is an enlarged cross-sectional view of the exhaust socket portion, in which (A) shows the state in which the first ring, the sphere, and the second ring are set, (B) shows the initial stage of the heating process, (C) shows the final stage of the heating process, and (D) is a plan view of the first ring.

Hereinafter, an embodiment will be described with reference to the drawings.

An example of a finished vacuum insulated double pipe is shown in Fig. 1. This figure is a cross-sectional view of one end of the vacuum insulated double pipe.

As shown in the figure, the vacuum insulated double pipe 10 is composed of an inner pipe 12 and an outer pipe 14, with a vacuum layer (jacket) 13 formed between them. The inner pipe 12 is used for transporting fluid, and its inner surface is in contact with the transported object. The outer pipe 14 forms the jacket 13 on the outer periphery of the inner pipe 12. Due to the presence of the vacuum layer with low thermal conductivity, the entire inner pipe 12 is thermally insulated from the outside world, and the fluid flowing inside the inner pipe 12 is not affected by the outside air temperature.

In the finished product, the vacuum insulated double pipe 10, the jacket 13 is kept airtight. The illustrated embodiment is a case where a ferrule joint is used, and a ferrule 16 is formed at the end of the vacuum insulated double pipe 10. A ferrule joint is a joint in which ferrules are butted together with a ferrule gasket sandwiched between them and then fastened with a clamp, and can be connected and separated more quickly and easily than a flange joint that is fastened with bolts and nuts.

An exhaust socket 20 is attached to the outer pipe 14. In the illustrated example, the exhaust socket 20 is fixed to the outer pipe 14 by welding. The exhaust socket 20 is hollow and tubular, with an exhaust hole 18 penetrating through it. Therefore, in the uncompleted state (see FIGS. 2(A) and (B)), the exhaust hole 18 connects the jacket 13 to the outside of the outer pipe 14.

The inner wall surface 22 of the exhaust hole 18 has a conical surface shape whose diameter gradually decreases from the outside of the outer tube 14 toward the inside of the jacket 13. The conical surface portion 22a may extend over the entire length of the inner wall surface 22 when viewed in the axial direction of the exhaust hole 18, or may be present along part of the axial direction of the exhaust hole 18. The drawing shows an example of the latter, in which the conical surface portion 22a is located on the outside and the cylindrical portion 22b is located on the inside.

A sphere 30 is placed inside the exhaust hole 18 and brazed.
If the exhaust hole 18 is small, it takes a long time to exhaust, and if it is large, the brazing material will not be able to completely block the exhaust hole 18 when it melts and will flow down, so an effective inner diameter is set from this perspective, and the sphere 30 is made slightly larger in diameter than the exhaust hole 18. The maximum inner diameter of the exhaust hole 18 is larger than the outer diameter of the sphere 30, and the minimum inner diameter is smaller than the outer diameter of the sphere 30. Therefore, when the sphere 30 is placed in the exhaust hole 18 facing upward, the sphere 30 comes into contact with the conical surface portion 22a of the inner wall surface 22 of the exhaust hole 18 due to its own weight and stops at that position. As long as the exhaust hole 18 is not tilted excessively, the sphere 30 will not fall from the exhaust hole 18. The position of the sphere 30 at this time, that is, the stopping position of the sphere 30 in the axial direction of the exhaust hole 18 is determined by the outer diameter of the sphere 30, the inner diameter of the inner wall surface 22 of the exhaust hole 18, and the taper angle.

As a specific example of the material, the outer tube 14 and the socket 20 are generally made of stainless steel, and it is preferable to use stainless steel for the sphere 30 as well. In that case, copper brazing material can be used as the brazing material, and silver brazing material and nickel brazing material can also be used.

The brazing material used is in the shape of a ring. The inner diameter of the ring is set to be smaller than the outer diameter of the sphere 30, and the outer diameter of the ring is set to be larger than the inner diameter of the cylindrical portion 22b of the exhaust hole 18. If the cylindrical portion 22b is not provided, the outer diameter of the ring is set to be larger than the minimum diameter of the conical surface portion 22a.
Ring-shaped brazing material is disposed above and below the sphere 30 when viewed in the axial direction of the upward-facing exhaust hole 18, i.e., on both sides of the contact portion between the sphere 30 and the conical surface-shaped portion 22a of the inner wall surface 22. For ease of explanation, the lower one will be called the first ring 26 and the upper one the second ring 24.

Here, the ring shape may be a perfect circle or an incomplete circle with a part of the circumference cut out, i.e., a C-shape. An example of the cutout 28 is shown in FIG. 2(D). Furthermore, although not shown, a perfect circle ring with a partial dent may be used. In the case of the first ring 26, the dent on the outer periphery forms a gap between the inner wall surface 22 of the exhaust hole 18, and the dent on the inner periphery forms a gap between the sphere 30. In this way, the cutout or dent on the first ring 26 forms a gap between the inner wall surface 22 of the exhaust hole 18 and the sphere 30, and functions as an air passage during the evacuation process. Therefore, as long as an air passage with a cross-sectional area required for the evacuation process can be secured as a whole, the dent may be a single dent or two or more dents distributed in the circumferential direction.

Since the second ring 24 is intended to provide the amount of brazing filler required for brazing, the ring diameter and/or wire diameter are set from that viewpoint. From the same viewpoint, it is also possible to use two or more second rings 24 stacked together. In that case, the ring diameters and wire diameters of the multiple second rings 24 may be the same or different. Figure 2 (A) shows an example in which two second rings 24 with different ring diameters are used.

The second ring 24 may have the same shape as the first ring 26. The second ring 24 melts in the heating process simply by being placed on the sphere 30, so there is no problem even if it has a notch or dent. In fact, when the same ring is used as both the second ring 24 and the first ring 26, there is no need to distinguish between them, which is convenient for workability and storage.

The first ring 26 melts during the heating process and flows down the inner wall surface 22 of the exhaust hole 18. In other words, the first ring 26 is interposed between the sphere 30 and the inner wall surface 22 of the exhaust hole 18, and the notch or dent plays a role of securing an air passage during the exhaust process, and is not involved in the brazing itself. In that sense, the first ring 26 does not necessarily have to be made of the same material as the second ring 24. For example, by using a material for the first ring 26 that has a lower melting point than the second ring 24, it is possible to adjust the timing so that the second ring 24 begins to melt after the first ring 26 melts and flows down and the sphere 30 comes into contact with the inner wall surface 22 of the exhaust hole 18. Furthermore, it is also possible to use a material that is not generally used as a brazing material for the first ring 26.

When the first ring 26 melts and flows down from the exhaust hole 18, a portion for receiving and collecting it, such as an annular groove, may be provided at the lower end of the exhaust hole 18 or the lower end surface of the exhaust socket 20.

Next, a method for manufacturing a vacuum insulated double-walled pipe having the above-mentioned vacuum sealing structure will be described with reference to Fig. 2. A vacuum heat treatment furnace capable of performing heat treatment under vacuum evacuation and high vacuum is used, but since the configuration of the furnace is known, detailed description thereof will be omitted.

(1) Preparation Step In the preparation step, a vacuum insulated double pipe is prepared as a workpiece by stacking the second ring 26, the sphere 30, and the first ring 24 in this order inside the exhaust hole 18 of the exhaust socket 20. Then, this workpiece is carried into a vacuum heat treatment furnace and set in a predetermined position with the exhaust hole 18 facing upward.

In the evacuation process, ^the inside of the vacuum heat treatment furnace is evacuated to ^a predetermined vacuum level.
During the exhaust process, the first ring 26 forms a gap between the sphere 30 and the inner wall surface 22 of the exhaust hole 18, ensuring an air passage, so that the inside and outside of the jacket 13, i.e., the furnace atmosphere, are in communication, and exhaust is carried out without any hindrance.

(3) Heating Step When the inside of the vacuum heat treatment furnace reaches the target vacuum level, heating is started while maintaining the vacuum level. A specific example of the target heating temperature is 1000 to 1100°C.

During the heating process, the first ring 26 melts and flows down, and as a result, the sphere 30 that had been supported by the first ring 26 falls under its own weight and comes into contact with the inner wall surface 22 of the exhaust hole 18, specifically the conical portion 22a.

On the other hand, the second ring 24 melts and becomes fluid molten metal, which flows down along the surface of the sphere 30 and penetrates into the gap between the inner wall surface 22 of the exhaust hole 18 and the sphere 30. At this time, since the sphere 30 is in contact with the inner wall surface 22 of the exhaust hole 18, the lower limit of the downward movement of the molten metal is the contact point between the inner wall surface 22 of the exhaust hole 18 and the sphere 30. As a result, the molten metal from the second ring 24 flows in the circumferential direction of the sphere 30 and spreads all around, forming an annular molten pool.

(4) Cooling process After a predetermined time has elapsed since the target heating temperature was reached, heating is stopped and the inside of the vacuum heat treatment furnace is gradually cooled. The molten pool from the second ring 24 is cooled and solidified. This completes the brazing and vacuum sealing at the same time.

(5) Removal Step The workpiece is removed from the vacuum heat treatment furnace, and the finished vacuum thermal insulation double pipe 10 is obtained, in which the jacket 13 is completely sealed, i.e., equipped with a vacuum sealed structure.

Although the embodiment of the present invention has been described above based on the examples illustrated in the attached drawings, it goes without saying that the present invention is not limited to the embodiment described and illustrated herein, and various modifications can be made without departing from the scope of the claims. In particular, the vacuum sealing structure is not limited to double pipes such as vacuum insulated double pipes, but can be applied to all types of vacuum containers equipped with a vacuum layer.

Reference Signs List 10 Vacuum insulated double pipe 12 Inner pipe 13 Jacket 14 Outer pipe 16 Ferrule 18 Exhaust hole 20 Exhaust socket 22 Inner wall surface 22a Conical surface portion 22b Cylindrical portion 24 Second ring 26 First ring 28 Notch 30 Sphere

The present invention relates to a method for manufacturing a vacuum sealing structure.

The object of the present invention is to eliminate such problems, that is, to provide a manufacturing method for a vacuum sealing structure that does not require a device for holding and moving the valve body during the manufacturing process .

According to the present invention, a vacuum sealing structure that is maintenance-free for a long period of time can be provided, in which a sphere is brazed to the exhaust hole of an exhaust socket. In particular, since the vacuum sealing structure is a structure in which the sphere is received by the conical inner wall surface of the exhaust hole, if the sphere and the first and second rings are first set in the exhaust hole, each step during the subsequent exhaust step and heating step can be performed without requiring any external device. Therefore, such a vacuum sealing structure and a vacuum insulated double pipe equipped with it can be easily manufactured without requiring special equipment or devices for holding the workpiece or moving it between steps.

Claims (10)

A vacuum sealing structure for maintaining a vacuum inside a jacket of a workpiece, comprising: an exhaust socket having an exhaust hole that connects the inside of the jacket with the outside; and a sphere accommodated in the exhaust hole, the inner wall surface of the exhaust hole includes a conical surface portion that narrows toward the inside of the jacket, and the exhaust socket and the sphere are hermetically brazed together by tightly contacting the conical surface portion and the sphere;
a step of placing a first ring having a notch and/or a dent on its inner and/or outer circumferential surface, the sphere, and a second ring made of brazing material in the exhaust hole in this order in a vacuum heat treatment furnace;
an evacuation step of evacuating the inside of the vacuum heat treatment furnace until a predetermined degree of vacuum is reached;
A method for manufacturing a vacuum sealed structure, comprising a heating step of heating the inside of a vacuum heat treatment furnace until a predetermined temperature is reached. 2. The method for manufacturing a vacuum sealed structure according to claim 1, wherein the first ring is interposed between the sphere and the inner wall surface, and the notch and/or the dent forms a gap between the first ring and the sphere and/or the inner wall surface to allow ventilation during the exhaust process. 3. The method for manufacturing a vacuum sealing structure according to claim 2, wherein in the heating step, the first ring melts down, causing the sphere to drop and come into close contact with the inner wall surface of the exhaust hole, thereby blocking the ventilation. 2. The method for manufacturing a vacuum sealing structure according to claim 1, wherein in the heating step, the second ring melts and penetrates between the sphere and the inner wall surface of the exhaust hole, hermetically joining the sphere and the exhaust socket. A vacuum sealed structure in which a jacket to be used as a vacuum chamber is provided with an exhaust socket having an exhaust hole that connects the inside of the jacket with the outside, and the inner wall surface of the exhaust hole has a conical portion with a diameter that narrows toward the jacket, at least in a portion of the axial direction of the exhaust hole, a sphere is accommodated in the exhaust hole, and the conical portion and the sphere are brought into contact over the entire circumference of the sphere, and the exhaust socket and the sphere are airtightly brazed along the contact portion, thereby maintaining a vacuum inside the jacket. 6. The vacuum sealing structure according to claim 5, wherein the brazing step includes setting a first ring having a notch or dent in the exhaust hole to form a gap between the conical surface portion or the sphere, the sphere, and a second ring made of brazing material in this order at a predetermined position in a vacuum heat treatment furnace, evacuating the vacuum heat treatment furnace to a predetermined vacuum level, and heating the vacuum heat treatment furnace to a predetermined temperature. 6. The vacuum sealing structure according to claim 5, wherein molten metal of the brazing material originating from the second ring permeates and solidifies from the contact portion between the sphere and the conical surface portion to the large diameter side of the conical surface portion. A vacuum insulated double pipe having an inner pipe and an outer pipe forming a jacket between them that is closed at one end, an exhaust socket is provided on the outer pipe, the exhaust socket has an exhaust hole extending radially from the outer pipe to connect the inside of the jacket to the outside, the inner wall surface of the exhaust hole has a conical portion that narrows in diameter toward the jacket, at least in a partial axial region of the exhaust hole, a sphere is accommodated in the exhaust hole and the sphere and the conical portion are in contact around the entire circumference of the sphere, and the exhaust socket and the sphere are hermetically brazed along the contact portion to maintain a vacuum inside the jacket. The vacuum insulated double pipe described in claim 8, wherein the brazing includes setting a first ring having a notch or dent in the exhaust hole that forms a gap between the conical surface portion or the sphere, the sphere, and a second ring made of brazing material in this order at a predetermined position in a vacuum heat treatment furnace, evacuating the vacuum heat treatment furnace to a predetermined vacuum level, and heating the vacuum heat treatment furnace to a predetermined temperature. 9. The vacuum insulated double pipe according to claim 8, wherein molten metal of the brazing material derived from the second ring penetrates and solidifies from the contact portion between the sphere and the conical surface portion to the large diameter side of the conical surface portion.

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