Metallic evacuated double-walled vessel and production method therefor

Abstract: A method for making a metallic evacuated double-walled vessel consisting of metallic inner (31) and outer vessels (34) with an evacuated thermal insulating layer being formed by the space (35) between the inner vessel and the outer vessel. In the present invention, a prior-to-sealing double-walled vessel is formed by forming a concavity (43) in one of either the inner vessel and the outer vessel, and punching in the concavity an evacuation hole (44) through which to carry out vacuum evacuation. A solid sealing hot charge (42) is then disposed prior to vacuum heating at a position directly above the evacuation hole of the prior-to-sealing double-walled vessel with an interval of space being maintained between the sealing hot charge and the evacuation hole. The prior-to-sealing double-walled vessel is then placed inside a vacuum heating furnace, and vacuum evacuation of the cavity between the inner vessel and the outer vessel is carried out via the evacuation hole. The sealing hot charge (42) is heated and melts, causing it to drop down onto the evacuation hole (44) and the vicinity thereabout, filling the evacuation hole. The sealing hot charge then cools and hardens, vacuum sealing the vessel.

Description: The present invention relates to a metallic double-walled vessel such as a portable thermos, pot, jar or the like. As a method for producing a metallic evacuated double-walled vessel, there are available such conventional methods as, for example, a method wherein the evacuation of the space between an inner and an outer vessel is carried out by means of a chip tube attached to the outer vessel, and the chip tube is then pressure welded and sealed (Japanese Patent Application, laid open number Sho 59-37914, Japanese Patent Application laid open number Sho 59-103633); a method wherein an evacuation opening is provided to the outer vessel, a brazing metal material is piled around the periphery of the evacuation hole, a sealing member is placed on top of this with an interval of space being maintained between the sealing member and the evacuation hole, heat evacuation is carried out in a vacuum heating furnace, after which, the temperature is raised to the melting temperature of the brazing metal material, the sealing member is brazed, and the vessel is thus vacuum sealed (Japanese Patent Application laid open number Sho 58-192516); and a method wherein a small hole or cut-out is punched in the outer vessel, a brazing metal material is disposed in the vicinity thereof, heat evacuation in a vacuum heating furnace is then performed, the temperature is raised to the melting temperature of the brazing metal material causing the it to melt and flow into the small hole or cut-out, thus vacuum sealing the vessel (Japanese Patent Application Hei 1-106925 (U.S. Patent No. 5,153,977), Utility Model Application Hei 1-106837 or European application 0,497,064). In the above described method using a chip tube, because the chip tube projects out from the bottom of the outer vessel, it is necessary to attach a bottom cover in order to protect the chip tube. Accordingly, this is problematic because the height of the produced article becomes higher by the length of this protecting cover. Moreover, in the case of large capacity production, because it is necessary to seal and cut the chip tube for each article produced, operations become complicated. Moreover, as it is essential that the process for this sealing technique be highly accurate, great skill is required in the operation. Additionally, the seal is occasionally insufficient, giving rise to the problem that the degree of vacuum deteriorates and the thermal insulating ability is lost over time. Further, in a sealing method using a chip tube, in the case where evacuating the space between the inner and outer vessels, when stimulating the desorption of gas absorbed by the metallic surface by heating the entire vessel, the outer surface of the vessel is exposed to the atmosphere, and a reaction occurs with the oxygen in the atmosphere causing violent oxidation. Because the esthetic appearance and anti-corrosive character of the oxidized surface are impaired, it is necessary to provide a process step to eject such sub-standard articles. Accordingly, costs are increased. On the other hand, in a sealing method using brazing material, in order to achieve good wettability of the sealant with respect to the material of the outer vessel, it is necessary to remove any superficial oxidants in the material of the evacuation opening periphery. As a method therefor, there is available a method wherein heating is carried out at a temperature of 950° C or above and at a pressure of 1x10 -3 torr or less on stainless steel, which is preferably used in, for example, metallic isotherm bottles. In this case, a special vacuum heating furnace of the type which can be used at high temperatures of 950° C and above is necessary. Accordingly, this too is problematic because equipment costs become very expensive. Figure 7 is provided in order to explain an example of the production method of a conventional metallic evacuated double-walled vessel. This method corresponds to an embodiment of US-A-5,153,977 and appears to be the closest to the invention. This figure shows the state of a metallic evacuated double-walled vessel prior to vacuum sealing. This prior to vacuum sealing vessel consists of an inner casing 1 which is cylindrical in shape and has a bottom, and an outer casing 4 which consists of a cylindrical outer casing body portion 2 and an outer casing bottom portion 3. The mouth portion of outer casing body portion 2 is air tightly joined to the mouth portion of inner casing 1. At the same time, outer casing bottom portion 3 is air tightly joined to the opening at one end of the vessel which is opposite the mouth portion of the outer casing body portion 2. Further, in the approximate center of the outer casing bottom portion 3, a concavity 6 which is indented inward toward inner casing 1 is formed. In the approximate center portion of this concavity 6, a small hole 7 (evacuation hole) or slit for evacuation is formed passing through a cavity 5 between the inner casing 1 and the outer casing 4. In order to produce a metallic evacuated double-walled vessel by vacuum sealing this prior-to-sealing vessel, the vessel is inverted with the mouth portion of the prior-to-sealing vessel directed downward, a sealing hot charge 8, such as metallic brazing material, in a paste form is disposed in concavity 6, and the prior-to-sealing vessel is placed in a vacuum heating furnace. Melting and heating of the sealing hot charge 8 is carried out as the inside of the vacuum heating furnace is evacuate to a fixed degree of vacuum. The melted sealing hot charge 8 flows from the periphery therearound into the evacuation hole 7, plugging evacuation hole 7. Following this, sealing hot charge 8 is cooled and hardens, vacuum sealing evacuation hole 7. In this manner, a metallic evacuated double-walled vessel having an evacuated thermal insulating layer between the inner casing 1 and the outer casing 4 is produced. BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a front cross sectional view of a double-walled vessel prior to sealing, showing a first embodiment of the present invention. Figure 2 is a view of the bottom surface of the same prior-to-sealing vessel. Figure 3 is an enlarged cross sectional view of an essential composent of the evacuated double-walled vessel obtained by carrying out vacuum sealing to the same double-walled vessel. Figure 4 is a front cross sectional view of a double-walled vessel prior to sealing, showing a second embodiment of the present invention. Figure 5 is a bottom view showing an enlargement of an essential component of the same double-walled vessel. Figure 6 is a front cross sectional view of the double-walled vessel prior to sealing showing a third embodiment of the present invention. Figure 7 is a front cross sectional view of a prior-to-sealing vessel which is provided to explain the conventional art related to the present invention. Summary of the present invention The present invention is a production method for a metallic evacuated double-walled vessel according to claims 1-4 and a double-walled vessel according to claim 5. The essential characteristic thereof consists in the use in the method, or the presence on the vessel, of a sealing material consisting of a low temperature melting glass, the softening temperature of which is from 200°C to 600°C, in the vicinity of an evacuation opening leading to an evacuated volume between the walls of the vessel. Because the evacuation hole punched in one of either of the inner vessel or the outer vessel of the metallic double-walled vessel is sealed using a sealing material which consists of low temperature melting glass which softens at a temperature of from 200°C to 600°C, it is possible to reduce the temperature for vacuum sealing as compared to the conventional brazing method. For this reason, the temperatures used in the vacuum heating furnace can be lowered, equipment costs are reduced, and the production costs for the article are lowered. The low temperature melting glass used in the present invention is advantageous in that, even if oxidants are present on the surface of the metallic double-walled vessel, wettability is not impaired, making it possible to carry out a preferable sealing. Accordingly, it is also possible to omit the process of removing oxidants are removed by heating the surface of the metallic double-walled vessel to a high temperature. Production costs for the evacuated double-walled vessel are thereby further reduced. Further, when compared to the convention method using a chip tube, it is possible to produce a more compact article as there is no remnant of the chip tube to protrude out. Moreover, with regard to the sealing process, because the treatment in the vacuum heating furnace may be carried out with stability for a large number of articles simultaneously without the introduction of human labor, large capacity production is easily achieved and it is possible to reduce production costs. Moreover, with regard to the process of vacuum evacuation of the space between the inner and outer vessels, because the entire vessel is heated under a vacuum, there is no notable oxidation of the outer surface of the vessel, thus a final removal step may be omitted. Costs can therefore be reduced. Further, all vacuum evacuation and sealing operations can be carried out at a comparatively low temperatures in the range of from 200°C to 600°C, and the hardness of metallic material such as stainless steel or the like which constructs the vessel can be increased by low temperature annealing. As a result, using a metallic material having a high degree of hardness, the vessel can be made thinner, and the overall weight of the evacuated double-walled vessel can be reduced. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT INVENTION Embodiment 1 Figures 1 through 3 are provided to explain a first embodiment of the production method for a metallic evacuated double-walled vessel according to the present invention. The metallic evacuated double-walled vessel produced here is a portable isotherm bottle which consists of a stainless steel inner vessel 31 and a stainless steel outer vessel 34 which are joined together, with a cavity 35 between the inner vessel 31 and the outer vessel 34 forming an evacuated thermal insulating layer. In outer vessel 34, outer vessel bottom member 33 is joined air tightly to the bottom end of approximately cylindrical outer vessel body 32. Concavity 40 which is indented to form a semispherical shape is formed to the approximate center portion of outer vessel bottom member 33. A small evacuation hole 41 is punched in the center of concavity 40. The mouth diameter of evacuation hole 41 is preferably 0.1 to 2.0 mm. In order to produce this isotherm bottle, inner vessel 31 and outer vessel body 32 are air tightly joined at the mouth portions thereof, while at the same time, outer vessel bottom member 33 is air tightly joined to outer vessel body 32, forming prior-to-sealing double-walled vessel A (hereinafter, referred to as double-walled vessel). Next, as is shown in Figures 2 and 3, the mouth portion of double-walled vessel A is directed downward, and a rod shaped sealing material 42 is attached inside concavity 40 of outer vessel bottom member 33 with a interval of space maintained between sealing material 42 and evacuation hole 41. A low temperature melting glass, the softening point of which is from 200°C to 600°C is used in sealing material 42. Solder glass derived from B 2 O 3 -PbO, B 2 O 3 -ZnO, PbO-B 2 O 3 -ZnO-SiO 2 , PbO-B 2 O 3 -Al 2 O 3 -SiO 2 , PbO-B 2 O 3 -SiO 2 , or PbO-B 2 O 3 -BaO-SiO 2 may be used as the low temperature melting glass. In particular, a material having a coefficient of thermal expansion similar to that of stainless steel which is the material of the double-walled vessel is preferable. To attach rod shaped sealing material 42 in concavity 40, sealing material 42 may be simply pushed into concavity 40. However, in order to prevent positional displacement of sealing material 42, it is also possible to coat an adhesive agent to both ends of sealing material 42 and thereby fix it firmly inside concavity 40. Moreover, the shape of sealing material 42 is not limited to a rod shape, but may also be a solid shape. Next, double-walled vessel A, to which sealing material 42 is attached, is transferred to and disposed within a vacuum heating furnace in an inverted position. Vacuum heating is carried out by vacuum evacuating the inside of the furnace while heating is performed. The temperature for the vacuum heating is set so as to be within the range of 200°C to 600°C and such that sealing material 42 does not soften. The gas in the cavity between inner vessel 31 and outer vessel 34 is expelled through evacuation hole 41. After evacuating to a pressure of 1 x 10 -2 torr or less, the temperature inside the furnace is raised to a temperature which is in the range from 200°C to 600°C and which is a temperature above the softening point of sealing material 42. Sealing material 42 is softened and drops down under its own weight onto evacuation hole 41 and the vicinity thereabout, sealing evacuation hole 41. Following this vacuum sealing, the vessel is removed from the furnace. As a result, as shown in Figure 3, evacuation hole 41 is sealed with sealing material 42 which consists of low temperature melting glass, thus obtaining a stainless steel isotherm bottle (metallic evacuated double-walled vessel) having an evacuated thermal insulating layer 36 between inner vessel 31 and outer vessel 34. Via this vacuum sealing process, the double-walled vessel is heated at a temperature in the range of 200°C to 600°C, and the hardness of the stainless steel, which is the material of the double-walled vessel, is increased by low temperature annealing. Accordingly, the thickness of the stainless steel necessary to obtain the required shock and impact resistance is reduced. Thus, the vessel can be made thinner. In the production method according to the present embodiment, by sealing the evacuation hole of the metallic double-walled vessel by using a sealing material consisting of a low temperature melting glass which has a softening temperature in the range of 200° to 600°C, it is possible to reduce the temperature of vacuum sealing as compared to the convention brazing method. For this reason, the temperature utilized within the vacuum heating furnace can be lowered, equipment costs are reduced, and the production costs for the article can be lowered. This low temperature melting glass is advantageous in that wettability is not impaired even if oxidants are present on the surface of the double-walled vessel, making it possible to carry out a preferable sealing. Accordingly, it is possible to omit the process for removing oxidants by heating to a high temperature the surface of the double-walled vessel. Thus, the production costs for an evacuated double-walled vessel can be reduced. Further, when compared to the convention method using a chip tube, it is possible to produce a more compact product as there is no remnant of the chip tube to protrude out. Moreover, with regard to the sealing process, because treatment in the vacuum heating furnace may be carried out with stability for a large number of articles simultaneously without the introduction of human labor, large capacity production is easily achieved and it is possible to reduce production costs. Moreover, with regard to the process of vacuum evacuation of the space between the inner and outer vessels, because the entire vessel is heated under a vacuum, there is no notable oxidation of the outer surface of the vessel, therefore, a final removal process can be omitted. Thus, costs can be reduced. Further, all vacuum evacuation and sealing operations can be carried out at comparatively low temperatures in the range of from 200°C to 600°C, and the hardness of the metallic material such as stainless steel or the like which composes the vessel can be increased by low temperature annealing. As a result, using a metallic material having a high degree of hardness, the vessel can be made thinner, and the overall weight of the evacuated double-walled vessel can be reduced. Embodiment 2 Figures 4 and 5 are provided to explain a second embodiment of the production method for a metallic evacuated double-walled vessel according to the present invention. The double-walled vessel B shown in these figures is equipped with almost entirely the same structural elements as those shown in Figures 1 and 2. Structural elements shown in Figures 4 and 5 which are identical to those in Figures 1 and 2 have been labeled with the same symbols. In the double-walled vessel B shown in Figures 4 and 5, a long groove 43 is formed in the center portion of the bottom surface side of outer vessel bottom member 33, and a slit-shaped long hole 44 (evacuation hole) is formed in the bottom of long groove 43. As is shown in Figure 5, a rod shaped sealing material 42 consisting of low temperature melting glass and having a length which is shorter than the length of the slit shaped long hole 44 is disposed inside long groove 43 of the double-walled vessel B. Following this, as in the previous example, double-walled vessel B is placed inside a vacuum heating furnace, and vacuum heating is carried out while heating to a temperature which is within the range of 200°C to 600°C and is below the temperature at which sealing material 42 softens. After evacuating to a pressure of 1 x 10 -2 torr or less, the temperature inside the furnace is raised to a temperature which is in the range of from 200°C to 600°C and which is a temperature above the softening point of sealing material 42. Sealing material 42 is softened and flows onto slit shaped long hole 44, sealing it, and a stainless steel isotherm bottle (evacuated double-walled vessel) is thereby obtained. Embodiment 3 Figures 6 is provided to explain a third embodiment of the production method for a metallic evacuated double-walled vessel according to the present invention. The double-walled vessel C shown in these figures is equipped with almost entirely the same structural elements as those shown in Figures 1 and 2. Structural elements shown in Figure 6 which are identical to those in Figures 1 and 2 have been labeled with the same symbols. In the double-walled vessel C shown in Figure 6, a pocket shaped concavity 40 is provided to the shoulder portion of the outer vessel body 32, and a small evacuation hole 41 is formed inside concavity 40. To seal this double-walled vessel C, the opening of double-walled vessel C is directed upward, and a rod shaped sealing material 42 consisting of low temperature melting glass and is attached inside concavity 40. Double-walled vessel C is then placed inside a vacuum heating furnace, and, as in the previous example, vacuum heating is carried out while heating to a temperature which is within the range of 200°C to 600°C and is below the temperature at which sealing material 42 softens. After evacuating to a pressure of 1 x 10 -2 torr or less, the temperature inside the furnace is raised to a temperature which is in the range of from 200°C to 600°C and which is above the softening point of sealing material 42. Sealing material 42 is softened and drops down under its own weight directly onto evacuation hole 41 and the vicinity therearound, sealing evacuation hole 41. After vacuum sealing, the vessel is removed from the furnace, and a stainless steel isotherm bottle (evacuated double-walled vessel) is thereby obtained. Moreover, because vacuum sealing is carried out by allowing the melted sealing hot charge to drop directly down into the evacuation hole, such sealing defects as insufficient plugging of the evacuation hole by the sealing hot charge due to the surface tension forces of the sealing hot charge are eliminated, and the quantity of sealing hot charge required may be reduced, thus permitting a reduction in production costs.

Claims: A method for making a metallic evacuated double-walled vessel wherein said vessel (A, B, C) consists of metallic inner (31) and outer (34) vessels and the space between said inner vessel and said outer vessel forms an evacuated thermal insulating layer, the method comprising the steps of : (a) forming a double-walled vessel by joining together said inner vessel (31) and said outer vessel (34), one of either said inner vessel and said outer vessel having an evacuation hole (41, 44) ; (b) disposing a sealing material (42) to the vicinity of said evacuation hole ; (c) placing said double-walled vessel inside a vacuum heating furnace, and vacuum evacuating the cavity between said inner vessel and said outer vessel at a temperature lower than the softening temperature of said sealing material ; (d) heating said double-walled vessel to a temperature above the softening temperature of said sealing material, causing said sealing material to melt and flow into said evacuation hole, to seal said evacuation hole ; characterised in that said sealing material consists of a low temperature melting glass having a softening temperature in the range of 200°C to 600°C. A method for making a metallic evacuated double-walled vessel according to claim 1, wherein a concavity (40) and the evacuation hole (41) are formed in the bottom portion (33) of said outer vessel (34) of said double-walled vessel (1), characterised in that said sealing material (42) is disposed within said concavity at a position so as to be directly above said evacuation hole when said double-walled vessel is inverted with an interval of spacing being maintained between said sealing material and said evacuation hole, said double-walled vessel is inverted so that the mouth portion thereof is directed downward and is placed in a vacuum heating furnace, and vacuum evacuation and vacuum sealing are carried out. A method for making a metallic evacuated double-walled vessel according to claim 1, wherein a long groove (43) is formed in the bottom portion (32) of said outer vessel (B) of said double-walled vessel and a slit shaped long hole (44) is formed in the bottom of said long groove, said double-walled vessel is inverted so that the mouth portion thereof is directed downward, said sealing material (42) is rodshaped inserted inside said long groove, said double-walled vessel is placed inverted inside a vacuum heating furnace, and vacuum evacuation and vacuum heating are carried out. A method for making a metallic evacuated double-walled vessel according to claim 1, characterized in that a concavity and an evacuation hole are formed in the shoulder portion of said outer vessel (34) of said double-walled vessel (C), the sealing material (42) is disposed within said concavity (40) at a position so as to be directly above said evacuation hole (41) with an interval of spacing being maintained between said and said evacuation hole, said double-walled sealing material and said evacuation hole, said double-walled vessel is placed upright so that the mouth portion thereof is directed upward in a vacuum furnace, and vacuum evacuation and vacuum sealing are carried out. A metallic evacuated double-walled vessel (A, B, C), said vessel consisting of metallic inner and outer vessels and the space between said inner vessel and said outer vessel forming an evacuated thermal insulating layer, wherein an evacuation hole formed in one either of said inner vessel and said outer vessel is vacuum sealed with a sealing material, characterised in that said sealing material consists of a low temparature melting glass which softens at a temperature of from 200°C to 600°C.

Inventors: ISHII HIROSHI, ITOH SEIICHI, OCHIAI TOSHIMITSU, OTSUKA EIJI, SATOMI YASUHIKO, YAMAKI JUN, ISHII, HIROSHI, ITOH, SEIICHI, OCHIAI, TOSHIMITSU, OTSUKA, EIJI, SATOMI, YASUHIKO, YAMAKI, JUN
Applicants: NIPPON OXYGEN CO LTD, NIPPON SANSO CORPORATION
Application year: 1993
Main classification: A47J41
IPC codes: B23K1, F17C3