JPH07127791A - Vacuum insulation pipe and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a vacuum insulation pipe excellent in heat insulation characteristic simply and at a low cost by engaging an inner cylinder with an outer cylinder through a vacuum layer to form a double pipe, expanding the inner cylinder at designated spaces, and directly airtightly joining the inner cylinder to the outer cylinder by the expanded pipe parts to reduce the number of parts. CONSTITUTION:An inner cylinder 10 is fitted in the interior of an outer cylinder 20. The inner cylinder 10 is expanded at parts corresponding to both end parts of the outer cylinder 20. That is, expanded pipe parts 11 having an outside diameter larger than a value obtained by subtracting the wall thickness of the outer cylinder 20 from the inside diameter of the outer cylinder 20 are formed on both end parts of the inner cylinder 10 by a rubber bulging method or the like. After the inner cylinder 10 and the outer cylinder 20 are directly joined to each other and airtightly connected to each other by the expanded pipe parts, the space part 30 between the cylinders is evacuated to a designated degree of vacuum. Thus, the need of the conventional sealing cover or the like can be eliminated, and a welding part and welding manhour can be reduced. Accordingly, the cost of a vacuum insulation pipe and the frequency of occurrence of defect can be decreased, and a product excellent in quality stability can be manufactured at high yield rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vacuum heat insulation pipe used for transporting a high or low temperature fluid, such as a steam pipe for district heating and cooling, a pipe for hot water supply equipment, a pipe for transferring a low temperature fluid and the like, and its manufacture. Regarding the method.

[0002]

2. Description of the Related Art When a high or low temperature fluid is transported, a thermal gradient occurs between the fluid flowing inside the pipe and the ambient temperature. According to this thermal gradient, the heat of the high temperature fluid is dissipated from the pipe into the atmosphere, or the low temperature fluid absorbs the heat from the atmosphere and rises in temperature. As a result, the high temperature fluid or the low temperature fluid will deviate from the required temperature when it reaches the point of use.
In order to bring the high-temperature fluid or the low-temperature fluid sent to the place of use to a predetermined temperature, a method of heating the high-temperature fluid or cooling the low-temperature fluid to a temperature condition in consideration of heat loss during transportation is adopted. However, overheating or undercooling for compensating for unavoidable heat loss should be set as small as possible in terms of thermo-economics, and it is preferable to suppress heat loss during transportation as much as possible.

Heat loss is suppressed by using a heat insulating pipe having a double pipe structure in which a vacuum heat insulating layer is provided between an inner cylinder and an outer cylinder. The inner cylinder and the outer cylinder are fixed to each other by various methods. For example, JP-A-61-99795 and JP-A-3-20190 disclose that the end opening of the outer cylinder is hermetically sealed by welding or brazing using a metal sealing lid. ing. Further, in Japanese Patent Laid-Open No. 1-240619, the end portion of the inner cylinder is expanded into a trumpet shape by flare processing and is welded to the inner surface of the outer cylinder.

[0004]

When airtight sealing is performed using the sealing lid, the sealing lid is welded to the opening portions at both ends of the inner cylinder and the outer cylinder, that is, at a total of four places. Man-hours increase. Further, since complicated quality control is required for each member of the inner cylinder, the outer cylinder and the sealing lid, the heat insulating pipe obtained is inevitably high in cost, and the usage form is restricted in terms of cost. It The method of flaring the end portion of the inner cylinder into a trumpet shape also has a drawback that the structure of the heat insulating pipe tends to be complicated. Therefore, the manufacturing process requires a lot of man-hours, and the cost cannot be reduced yet. The present invention has been devised in order to solve such a problem, and by directly welding the inner cylinder to the outer cylinder via an expanded portion formed by bulging or the like, airtightness at heat shrinkage is maintained. It is an object of the present invention to provide a vacuum heat insulating tube in which an inner cylinder and an outer cylinder are airtightly connected to each other with a simple structure without decreasing the temperature.

[0005]

The vacuum heat insulating tube of the present invention comprises:
In order to achieve the object, it has a double pipe structure in which an inner cylinder and an outer cylinder are fitted with each other through a vacuum layer, and the inner cylinder is expanded by a pipe expanding portion formed by expanding the inner cylinder at predetermined intervals. It is characterized in that it is directly airtightly joined to the cylinder. The vacuum heat insulating pipe of the present invention expands the inner cylinder at a predetermined interval so that an expanded pipe portion having an outer diameter larger than a size obtained by subtracting the thickness of the outer cylinder from the outer cylinder inner diameter is formed, and the outer cylinder is expanded by the expanded pipe portion. It is manufactured by air-tightly fixing the inner cylinder to and vacuuming the space between the inner cylinder and the outer cylinder. That is, by partially expanding the inner cylinder to near the inner diameter of the outer cylinder and directly joining the outer cylinder to the outer expansion part, a space part that is maintained in a vacuum atmosphere without requiring parts such as a sealing lid. Is formed.

In the vacuum heat insulating tube according to the present invention, the inner cylinder 10 is fitted to the outer cylinder 20 as shown in FIG. 1, for example. The inner cylinder 10 is expanded at a portion corresponding to the end of the outer cylinder 20. In this portion, the pipe expanding portion 11 having an outer diameter d _out larger than a value D _in -T obtained by subtracting the outer cylinder wall thickness T from the outer cylinder inner diameter D _in.
Are formed by a rubber bulge method or the like. The outer cylinder 20 is preferably provided with a corrugated portion 21 that absorbs thermal expansion and contraction. After air-tightly connecting the inner cylinder 10 and the outer cylinder 20, the space 30 is evacuated to a predetermined degree of vacuum. Inner cylinder outer diameter d
_{When out} is maintained _in the relationship of d _out ≧ D _in −T, the inner cylinder 10 can be hermetically joined to the outer cylinder 20 by welding without causing defects in the joint. When the inner cylinder outer diameter d _out is smaller than the value D _in −T, welding becomes difficult and a good airtight connection cannot be obtained. However, since the inner cylinder 10 is inserted into the outer cylinder 20 and welded, the inner cylinder outer diameter d _out of the expanded portion is equal to the outer cylinder inner diameter D.
Required to be less than _in .

The expanded portion 11 is formed by, for example, the inner cylinder 1 in the next step.
Attached to 0. First, the steel pipe material 12 used as the inner cylinder 10 is set in the pipe expanding device 40 as shown in FIG. The portion of the steel pipe material 12 to be expanded is located in the molds 41, 42. A slide mandrel 43 driven by hydraulic pressure F is inserted into the steel pipe material 12, and a fixing nut 44 is fixed to the slide mandrel 43. Slide core metal 4
An annular elastic body 45 made of urethane rubber or the like is attached to 4. One side of the annular elastic body 45 faces the fixed nut 44 via the spacer 46, and the other side faces the stopper 47. When the slide core 43 is pulled in the direction of the arrow by the hydraulic pressure F, the fixed nut 44 integrated with the slide core 43 also moves in the same direction, and presses the annular elastic body 45 via the spacer 46. The annular elastic body 45 is compressed because the other side is regulated by the stopper 47. When the slide core 43 is further slid by the hydraulic pressure F, the annular elastic body 45 causes the steel pipe material 12 to move to the mold 41,
It deforms so as to be pressed against 42. As a result, the steel pipe material 12 is processed into a shape that follows the recessed shapes of the molds 41 and 42 as shown in FIG. 2B, and the expanded pipe portion 11 is formed.

The amount of deformation of the steel pipe material 12 depends on the slide core metal 4
3 is related to the hydraulic pressure F when sliding 3. Therefore, by adjusting the hydraulic pressure F, the pipe expanding portion 11 having a target pipe expanding diameter is formed. The inner cylinder 10 provided with the pipe expanding portion 11 is inserted into the outer cylinder 20 and then directly joined to the inner surface of the outer cylinder 20 at the outer peripheral surface of the pipe expanding portion 11 by laser welding or the like. After joining, a small hole is formed in a part of the outer cylinder 20, and the space portion 30 is evacuated to, for example, 10 ⁻³ Torr or less through the small hole. Then, the vacuum insulation tube is obtained by closing the small holes by laser welding or the like.

[0009]

[Example] The inner cylinder 10 has a wall thickness of 1.2 mm and an outer diameter of 34
A SUS304 stainless steel tube of mm and length of 3 m was used. The tube expanding device 40 shown in FIG. 2 was used to expand the tube at a slide pressure of 200 to 600 kgf / cm ² , and nine kinds of inner cylinders 10 were produced. The outer cylinder 20 has a wall thickness of 0.4
mm, outer diameter 44.8 mm, inner diameter 44.0 mm, and length 2.7 m of SUS304 stainless steel pipe, and outer diameter 62 mm and pitch 14 mm, four corrugated parts 21
Attached. The inner cylinder 10 was inserted into the outer cylinder 20, and the weldability by laser welding was investigated. As is clear from FIG. 3 showing the investigation result, the inner diameter D _in of the outer cylinder 20 and the outer diameter d of the expanded portion 11 are shown.
When the difference between the _out is smaller than the thickness 0.4mm of the outer cylinder 20, it was found that sufficient weld sealed by penetration of the outer tube 20 generated during the laser welding can be obtained. On the other hand, the outer cylinder 2
The difference between the inner diameter D _{in of} 0 and the outer diameter d _out of the expanded portion 11 is the outer cylinder 2
When the wall thickness of No. 0 was greater than 0.4 mm, a gap was formed between the inner cylinder 10 and the outer cylinder 20 during laser welding, and an airtight welded joint could not be obtained.

Durability of seven types of vacuum heat insulation tubes that could be welded and sealed was examined under the following conditions. Outer cylinder 20 and inner cylinder 1
The amount of expansion and contraction in the axial direction when the temperature difference from 0 is set to 80 ° C is set to 4 mm, which is larger than the expansion and contraction amount of 3.7 mm, and the thermal expansion and contraction is performed once a day and the service life of the vacuum insulation pipe is 30 years. Assuming that, expansion and contraction were repeated. As a result, all of the vacuum heat insulating tubes exhibited sufficient heat insulating properties and strength to withstand use even if the target expansion and contraction times exceeded 10,000 times. In addition, the space portion 30
However, no decrease in vacuum was observed.

[0011]

As described above, in the vacuum heat insulating tube of the present invention, the expanded tube portion is formed in a part of the inner tube, and the inner tube is directly joined to the outer tube on the outer peripheral surface of the expanded tube portion. . Therefore, compared to the method of using the sealing lid and the method of joining the flared tube-shaped expanded portion by flare processing to the outer cylinder, the welding points are reduced without the need for parts such as the sealing lid. The man-hour required for the welding process is reduced. As a result, not only the cost of the obtained vacuum heat insulating tube is reduced, but also the frequency of defects is reduced as the number of welding points is reduced, and the vacuum heat insulating tube having excellent quality stability is manufactured with a high yield.

[Brief description of drawings]

FIG. 1 Vacuum insulation tube according to the present invention

FIG. 2 is an inner cylinder (a) before expansion and an inner cylinder (b) after expansion.

FIG. 3 is a graph showing the influence of the outer diameter of the expanded portion on the weldability.

[Explanation of symbols]

10: inner cylinder 11: expanded part 20: outer cylinder 21:
Corrugated part 30: Space part maintained in vacuum atmosphere 40: Tube expanding device 41, 42: Mold 43: Slide core metal 44: Fixed nut 45: Annular elastic body 46: Spacer 47: Stopper F: Hydraulic pressure

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naofumi Nakamura 1 Tsurumachi, Amagasaki City, Hyogo Prefecture Nisshin Steel Co., Ltd.

Claims (2)

[Claims] 1. A double tube structure in which an inner cylinder and an outer cylinder are fitted together via a vacuum layer, and the inner cylinder is expanded to the outer cylinder by a pipe expanding portion formed by expanding the inner cylinder at predetermined intervals. A vacuum insulation tube that is directly joined in an airtight manner. 2. An inner cylinder is expanded at a predetermined interval so that an expanded tube portion having an outer diameter larger than a size obtained by subtracting the outer tube wall thickness from the outer tube inner diameter is formed, and the inner tube is expanded into the outer tube by the expanded tube portion. A method for manufacturing a vacuum heat insulating tube, comprising airtightly fixing a cylinder, and evacuating a space between the inner cylinder and the outer cylinder.