Method of high vacuum insulation and a vacuum heat insulator used therein

Abstract: The invention is composed of the following (a) and (b). (a) Non-aluminium metallic foil (4) with a ceramic particle dotted layer (5a) formed on one side thereof is used and the non-aluminium metallic foil is wound on the peripheral surface of an inner shell (2) of a duplex shell body in a state that the ceramic particle dotted layer is faced inwardly. (b) The circumference of the multi-layeredly wound layer is covered with an outer shell (3) of the duplex shell body, and a space between the inner shell and the outer shell is sealed and evacuated. The invention performs following effects (I) and (II) because of the above-mentioned compositions (a) and (b). (I) As a vacuum heat insulator, non-aluminium metallic foil with a ceramic particle dotted layer formed on one side of thereof is used, so that it does not take so long time in evacuating even if the metallic foil is applied in a high moisture atmosphere, and the evacuation can be conducted at high temperature to be able to realize to shorten exhaust time of occluded gas in composing material of the duplex body shell. (II) In the ceramic particle dotted layer, clearance is produced between each particle. Therefore, when the vacuum heat insulator is wound in multi-layeredly and evacuation is conducted, the clearance becomes a passage of air to be able to evacuate the space between the outer shell and the inner shell efficiently.

Description: This invention relates to a method of high vacuum heat insulation wherein a space between an inner shell and an outer shell of a vacuum heat insulation duplex shell body such as a vacuum heat insulation duplex pipe and a vacuum heat insulation duplex vessel is heat insulated by evacuating, and to a high vacuum heat insulator used therein. Conventionally a vacuum insulation duplex tube is used for a liquid pipeline to transfer fluid with ultra low temperature such as liquid nitrogen from a view of heat insulation property. In general, a multi-layer vacuum heat insulation method (so called superinsulation) is employed as a method of vacuum heat-insulation of a vacant space between an inner pipe and an outer pipe of the vacuum heat insulation duplex tube. In this multi-layer vacuum thermal insulation method, aluminium foil 13 and asbestos paper, so-called Dexter paper 14, which are vacuum insulators, are wound alternately in multi-layer (about 25 to 50 layers) on a peripheral surface of the inner pipe 11 of the vacuum insulation duplex pipeline and then the most outer layer of the lapped body is covered by the outer tube 12 having an interval. In this state a space between the outer pipe 12 and the inner pipe 11 is evacuated to high vacuum (to less than 10 -4 Torr). Fig. 5 shows an enlarged view of thus obtained space between the inner pipe 11 and the outer pipe 12 of the vacuum insulation duplex pipeline. In the figure, the space between the inner pipe 11 and the outer pipe 12 is in a vacuum state and in the space the lapped body in which the aluminium foil 13 and the Dexter paper are wound alternately in a multi-layered state is formed. However, in the above-mentioned method, aluminum foil 13 and the Dexter paper 14 are used as a vacuum heat insulator and the heat insulator is wound multi-layeredly. In this case, the Dexter paper 14 becomes moisture rich because of high water absorption property of the Dexter paper itself. That is, when the Dexter paper 14 is used in an atmosphere containing high moisture, the Dexter paper 14 absorbs water content in the air since it is exposed to a high moisture atmosphere. Accordingly, even if the space is evacuated in such a high moisture absorbed state, it takes long time (for example, more than 480 hours) to evacuate because of the high moisture content being a resistance of evacuation. In order to exclude this disadvantage, whole of the duplex tube is heated to evaporate the moisture absorbed in the Dexter paper 14 prior to said evacuation. It allows to save time a little in evacuating. However, raising temperature is limited to 170 °C to 180 °C since fusion temperature of aluminum is low. So that it takes a long time to exhaust H 2 , O 2 , N 2 , water content and the like adsorbed and occluded in the inner tube and outer tube of duplex stainless or the like. The temperatures can not also vaporize the absorbed water in the Dexter paper swiftly. Therefore, the time is, in fact, not shortened enough even by the above-mentioned heating. FR2378576 shows a thermally insulating element formed by stacking sheets of metal on which are deposited grains of thermally insulating material. The powder deposit is produced by cold projection onto the substrate of a mixture comprising a diluent, the powder in suspension and a binder. Accordingly, it has been desired to provide a method of high vacuum heat insulation and a vacuum heat insulator used therein which can shorten evacuating time and maintain the insulation property for a long time. This invention provides a method of high vacuum heat insulation comprising winding non-aluminum metallic foil having a ceramic particle layer on one side on the outer peripheral surface of an inner member such that the ceramic particle layer faces toward the inner member. The foil is wound in more than one layer and provides a fluid passage between adjacent layers of the foil and between the foil and the inner member. An outer member is placed around the foil wrapped inner member, spaced from the wound foil layers, and the space between the outer member and inner member is sealed and evacuated. The ceramic particle layer is formed by flame-spraying ceramic particles onto the foil at predetermined intervals from each other. In a second aspect, the present invention provides a thermal insulator comprising an inner member and an outer member around and spaced from the inner member. The thermal insulator is characterized in that it further comprises non-aluminum metallic foil wound around the outer peripheral surface of the inner member in a plurality of layers, the outer member being spaced from the wound foil layers. The foil has a layer of ceramic particles on one face formed by flame-spraying ceramic particles onto the foil at predetermined intervals from each other. The ceramic particle layer faces towards the inner member and provides a fluid passage between adjacent layers of the foil and between the foil and the inner member. The space between the inner and outer members is evacuated. The inner and outer members are preferably pipes. The ceramic particle dotted layer used herein refers to a layer in which ceramic particles are fixed tightly on one side of metallic foil at predetermined intervals. Each particle is fixed with a predetermined interval from adjacent ceramic particles. That is, in the method according to the present invention, after non-aluminum metallic foil with a ceramic particle dotted layer formed on one side thereof is used as an insulator, this layer is wound multi-layeredly on the peripheral surface of an inner shell of a high vacuum duplex tube in a state that the ceramic particle dotted layer faces inwardly, then the most outer layer of the lapped layers formed on the peripheral surface of the inner shell is covered with an outer shell of the duplex pipe having an interval, a space between the outer shell and the inner shell is sealed and in that state the space is evacuated. In this case, it does not take a long time to evacuate even if the above-mentioned metallic foil is applied under a high moisture atmosphere because the ceramic particle dotted layer has very little water absorption property compared with the Dexter paper. The ceramic particles are fixed in a scattered or dotted state, so that clearance between each particle performs as a passage of air to evacuate efficiently, when the non-aluminium metallic foil insulator is wound multi-layeredly and evacuation is conducted. Followings are detailed description of this invention. In this invention, non-aluminum metallic foil means various metallic foils except aluminum foil. If the non-aluminium foil is possible to be wound, thick one may be adopted, for example, of about 20 to 50 µm. In particular, a metallic foil which has high fusion temperature and has high radiation efficiency such as stainless steel foil and nickel foil is preferably used. The ceramic particle dotted layer formed on one side of the metallic foil is generally formed by moving strip metallic foil longitudinally and by flame-spraying ceramic particles on the moving strip metallic foil, wherein a flame-spraying nozzle is moved reciprocately in a orthogonal direction against the moving surface of the moving direction of the strip metallic foil. Diameter of thus dotted and fixed particle in the formed ceramic particle dotted layer is set about 5 to 50 µm. Therefore the thickness of the layer is almost the same as the diameter. An interval between each ceramic particle is set about 50 to 500 µm, preferably the diameter 10 to 30 µm and the interval 100 to 200 µm. High vacuum heat insulation using the heat insulator according to the invention is performed, for example, as follows. At first, non-aluminium metallic foil with a ceramic particle dotted layer formed on one side thereof is wound multi-layeredly on the peripheral surface of a inner shell of a vacuum heat insulation duplex shell body in a state that the dotted layer is faced inwardly, whereby the ceramic particle dotted layer and the metallic foil are lapped alternately and at the same time the presence of the dotted layer therebetween prevents contact of each metallic foil. Then the outer shell is covered around the most outer layer of the multi-layered body having an interval, the space between the inner and outer shell is sealed and evacuated to give a vacuum heat insulation duplex shell body. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows an explanatory view of a high vacuum heat insulation duplex tube using an example according to the invention, Fig. 2 shows a perspective view of non-aluminium metallic foil composing vacuum insulator of an example according to the invention, Fig. 3 shows a cross-sectional view of the vacuum heat insulator according to the invention, Fig. 4 shows a perspective view when the vacuum insulator shown in Fig. 3 is observed from a ceramic particle dotted layer side, and Fig. 5 shows an enlarged view of a space between an inner tube and an outer tube in a conventional example. This invention is further described in detail based on an example. EXAMPLE 1 Fig. 1 shows an example of the vacuum insulation duplex pipe according to the invention. A heat vacuum insulator 6 is wound multi-layeredly between an inner pipe 2 and outer pipe 3. The vacuum insulator 6 comprises of non-aluminium metallic foil 4 shown in Fig. 2 and a ceramic particle dotted layer which is fixed on one side of the non-aluminium metallic foil 4. As the non-aluminum metallic foil 4, stainless steel foil is used in this example. The stainless steel foil 4 has higher fusion temperature than the aluminium metallic foil, so the stainless steel foil 4 can tolerate heating with high temperature such as 350°C to 400 °C . To this stainless steel foil 4 a dotted layer 5 (interval between each particle: 100 ± 10 µm) comprising ceramic particles 5a having diameter of 50± 5 µm is formed by flame-spraying on one side (back side) as shown in Figs. 3 and 4. Particles of forsterite (2MgO · SiO 2 ), magnesia(MgO), Alumina(Al 2 O 3 ) and the like are used as materials to compose the ceramic particle dotted layer 5. Vacuum insulation between the inner tube 2 and the outer tube 3 of the vacuum heat insulation duplex tube 1 using such an insulator 6 is conducted as follows. The vacuum insulator 6 is wound multi-layeredly on peripheral surface 2a of the inner tube 2 for flowing ultra low temperature fluid such as liquid nitrogen. In this case, the ceramic particle dotted layer 5 is faced inwardly. Then, the most outer layer of the insulator lapped layer body is covered by the outer tube 3 having an interval and the space between the inner tube and the outer tube is sealed. The space between the inner tube 2 and the outer tube 3 is evacuated (24 to 50 hours) to high vacuum (to less than 10 -4 Torr) through an exhaust pipe 7. The reference numeral 8 refers to a filter disposed at the exhaust pipe 7. EFFECTS OF THE INVENTION As mentioned above, in the method of high vacuum heat insulation according to the invention, as a vacuum heat insulator, non-aluminium metallic foil with a ceramic particle dotted layer formed on one side thereof is used. The ceramic particle dotted layer has little water absorption property, so that it does not take so long time even if the metallic foil is applied in a high moisture atmosphere. Since what the ceramic particles are fixed on the non-aluminium metallic foil is used as the vacuum heat insulator, fusion of the metallic foil is not caused even if the evacuation is conducted at high temperature. Therefore, it makes possible to exhaust of H 2 , O 2 , N 2 and the like occluded in the stainless steel inner and outer tubes composing the duplex shell body in short time. The ceramic particle dotted layer is formed by fixing ceramic particles not closely, but roughly so that some clearance or interval is formed. Therefore, when a space between the inner shell and the outer shell is provided with the vacuum heat insulator multi-layeredly and then evacuated, the clearance becomes a passage of air to be able to evacuate efficiently.

Claims: A method of high vacuum heat insulation comprising: winding non-aluminium metallic foil having a ceramic particle layer on one side, the ceramic particie layer having been formed by flame-spraying ceramic particles onto the foil at predetermined intervals from each other, on the outer peripheral surface of an inner member such that the ceramic particle layer faces toward the inner member, the foil being wound in more than one layer and providing a fluid passage between adjacent layers of the foil and between the foil and the inner member; placing an outer member around the foil wrapped inner member, the outer member being spaced from the wound foil layers; sealing the space between the outer member and the inner member; and evacuating the space. A thermal insulator (1) comprising: an inner member (2); an outer member (3) around and spaced from the inner member; characterised in that it further comprises non-aluminium metallic foil (4) wound around the outer peripheral surface of the inner member in a plurality of layers, the outer member being spaced from the wound foil layers, the foil having a layer (5) of ceramic particles (5a) on one face formed by flame-spraying ceramic particles onto the foil at predetermined intervals from each other, the ceramic particle layer facing towards the inner member and providing a fluid passage between adjacent layers of the foil and between the foil and the inner member and in that the space between the inner and outer members is evacuated. A thermal insulator according to claim 2 in which the inner (2) and outer (3) members are pipes.

Inventors: YOSHINO AKIRA, YOSHINO, AKIRA
Applicants: DAIDO HOXAN INC, DAIDO HOXAN INC.
Application year: 1991
Main classification: F16L59
IPC codes: F16L59