US3357587A

US3357587A - Thermal insulation suitable for vacuum bottles and the like

Info

Publication number: US3357587A
Application number: US530739A
Authority: US
Inventors: Weishaupt Josef
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 1962-01-04
Filing date: 1965-11-12
Publication date: 1967-12-12
Anticipated expiration: 1984-12-12
Also published as: DE1218331B; GB979951A

Description

Dec. 12,1967, J. WE|SHAUPT 3,357,587,

THERMAL INSULATION SUITABLE FOR VACUUM BOTTLES AND THE LIKE Filed Nov. 12., 1965 5 Shets-Shee 1 7m Q v O I O O O 15: 15b A A Fig.2

lnvenfor 0 0551 WE/SHAUPT Dec. 12,1967 J, WEISHAUPT 3,357,587

THERIIIAL INSULATION SUITABLE FOR VACUUM BOTTLES AND THE LIKE Filed Nov. 127} 1965 s Sheets-Sheet 2 7/ 7/ I I j/ "'4 'llnmetalhzed- O. Layer w:

4 Metallized 0'1 1/ Layer Q llnmetallize'd layer Metallized layer 7 /N VENTOR,

JO SEF WEISHAUPT I ATTORNEYS Dec. 12, 1967 J. WEISHAUPT THERMAL INSULATION SUITABLE FOR VACUUM BOTTLES AND THE LIKE Filed Nov. 1965 3 Sheets-Sheet 5 Fig. 3a

Layer INVENTOQ a055 .WE/5HA UPT A T QNEVS United States Patent 34 Claims. 61420-4 This is a continuation-in-part application of application Ser. No. 247,393,filed Dec. 26, 1962, claiming priority of German application G 33,943 VIb/ 80b, filed Jan. 4, 1962.

This invention relates to insulation, particularly thermal insulation, and even more particularly to insulation which is highly useful in the manufacture of vacuum bottles and the like.

In the manfacture of liquefied gases such as hydrogen and helium, it is conventional to utilize storage containers which are essentially vacuum bottles, that is, there is an outer jacket afiixed to these containers, and a vacuum is maintained therein. The vacuum functions to eliminate the transfer of heat by convection, and to a large extent by conduction; however, it is necessary to provide additional insulation for the prevention of heat transfer by radiation. It is thus well known that for small glass containers, a silver mirror is conventionally employed, but for larger metallic containers, it is necessary to employ special insulation inside the evacuated jacket.

One type of insulation for this purpose consists of a mixture of powdered metal and non-metallic insulating material. This type of insulation, however, is disadvantageous because it is difiicult to evacuate, is likely to stratify, and is difiicult to repair. To overcome some of these disadvantages, it would be possible to fabricate the insulation from alternate metallic and non-metallic materials, but even so, the final product would nevertheless be difiicult to evacuate, and additionally, would not exhibit maximum thermal insulation because between the metallic reflective layers, there would exist the poorly reflective non-metallic foil.

The object of this invention, therefore, is to provide an improved thermal insulation which is particularly suitable for the manufacture of vacuum bottles and the like, and which, to a large degree, avoids the disadvantages of the prior art materials.

Another object of this invention is to provide a process for the fabrication of the novel insulating material of the present invention.

Upon further study of the specification and appended claims, other objects and advantages of this invention will become apparent.

Briefly, the improvement provided by the present invention entails the deposition of a metallic coating on a non-metallic, preferably air-permeable, film, as will be seen from the accompanying drawings, wherein:

FIGURE 1 is a cross-sectional view of a vacuum bottle containing the insulation of the present invention;

FIGURE 2 is a schematic diagram of a process for th fabrication of the insulation of the present invention; and

FIGURE 3 is a magnified drawing of the insulation, FIGURE 3a being a magnified portion thereof, showing the interrelationship of the radiation reflecting surfaces.

The non-metallic base is any conventional thermal insulating material which can be fabricated in the form of a film having a thickness of about 0.005 to 2.0 mm., preferably about 0.3 mm. suitable examples of satisfactory materials include mica, plastic films (e.g., polyadipamide of hexamethylene diamine, other polyamides, polyterephthalates, and polyacrylonitrile), cellulose derivatives, such as cellulose triacetate, and conventional paper.

"ice

It is preferred, moreover, to employ air-permeable films so that they can be evacuated without much difiiculty. Non-woven materials made by the conventional papermaking process are particularly suitable, for example, fiberglass paper, and papers made of polyacrylonitrile, polyterephthalate, or polyamide fibers.

In addition to non-Woven fabrics or papers, it is also possible to employ woven materials made of fibers of polyamide, polyterephthalate, and polyacrylonitrile. Among the woven materials, woven fiberglass is especially suitable for insulating purposes.

These air-permeable base films in contrast to homogeneous films of plastics or rubbers, exhibit high porosities. For example, the porosity, i.e., the proportion of the total volume of the films occupied by pores, is about 88- 98%, preferably 94%. The average pore diameter in a layer consising of two fiber layers is about 0001-001 mm., preferably about 0.004 mm. These two fiber layers are to be considered as a film consisting of fiberglass paper having a thickness of about twice the diameter of a single fiber. It is thus estimated that the number of holes per mm. is on the order of about 1.5.10 The average pore diameters may, of course,.vary according to the thickness of the films. Consequently they may, therefore, lie also beyond the given ranges.

The most preferred base material is fiberglass paper having a thickness of about 0.0052 mm., preferably 0.1 to 2 mm., most preferably about 0.3 mm., wherein the individual fibers of the paper have a diameter in the range of 0.3-1040- mm., preferably about 0.6- 10- mm. This fiberglass paper is also advantageous because it is noncombustible and exhibits high mechanical strength.

The non-metallic base is coated with a metallic layer on one or both sides. It is desirable to employ coatings of metals having a low emission (less than about 5%), but a high reflection (not less than about 95%), such as gold, silver, copper, or aluminum, and alloys thereof which yield the desired properties, the preferred metals being aluminum and silver. The metallic layer should be of sufficient thickness so that it will effectively stop even infrared rays, this thickness being about 0.01-O.2'10 mm., preferably about 0.025-10- mm., or on the order of about 10* mm. Of course, heavier layers of the metallic coating can be applied, but this would be undesirable from the economic standpoint; and if too thick a layer Were applied to porous materials, then of course there would be the danger of making the final product nonporous.

One preferred embodiment of this invention is a multiple layer construction wherein a plurality of metallized films are superimposed over each other, it being particularly desirable to employ at least films. Another preferred embodiment is a sandwich-type insulation wherein one or several (preferably about 50) metallized films and one or several non-metallized films are superimposed alternately, one over the other. The function of the nonmetallized base in the sandwich construction is to provide an additional barrier against heat transfer by conduction.

The metallic coating can be deposited by any of several methods. One such method is to deposit the metallic layer by immersing the non-metallic base in a solution of a salt of a metal, or by spraying it with such a solution. The coated base is then passed into a reducing solution in order to precipitate the metal in situ on the base. Another possibility is to deposit the metal from a suspension thereof in a solvent, for example, a colloidal suspension. The solvent is then evaporated to dryness. Still another method involves vapor deposition of the metal.

If the base material is fabricated from fibers, either woven or non-woven, it is also possible to coat the individual fibers with metal before the film is formed,

The final insulation of this invention has important advantages. The highly subdivided reflecting surfaces with point-like contacts between particles result in low thermal conductivity. Since the spacing between metallized fibers is much smaller than the usual spacing of films of known heat insulating materials, the temperature difference between adjacent reflecting surfaces and hence also the heat transmission will be appreciably smaller.

These insulating materials can also be fitted more readily to curved surfaces; thus, there is assured a more uniform insulation over large surfaces. Additionally, the manufacture and use thereof are generally simplified.

For attaching the insulation to the inner wall of the vacuum jacket, it is possible .to use such expedients as wire bands, or nets of wire or plastic or textile fibers, the latter being preferred because of their low thermal conductivity. For maintaining or improving the vacuum inside such a filled insulation, it is preferred to incorporate an adsorbent in or under the insulation, examples of adsorbents being silica gel, active charcoal, and molecular sieves.

The insulating material of this invention is useful not only for the insulation of containers, but also as generaluse thermal insulation, particularly for low temperature equipment, e.g., for the insulation of low temperature components of hydrogen and helium liquefying apparatus, and for the insulation of measuring means. Thus, it is obvious that it is useful for any apparatus provided with a vacuum insulating space.

Referring now to the drawings, FIGURE 1 shows a thermally insulated container for liquid hydrogen or helium which has been insulated with the material of this invention. The primary container 1 is preferably made of copper, or aluminum, or tombac (copper-base zinc alloy), or V2A (austenitic steel containing 18% Cr and 8% Ni). Tube 2 is used for filling and emptying the container. Reference numeral 3 is the vacuum jacket, 4 is a tube for evacuating, and 5 is a partial and highly magnified representation of the insulation of this invention.

Elements

3 and 1 thus represent spaced-apart wall means defining a confined insulating space.

FIGURE 2 shows an apparatus that is suitable for producing the heat insulating material of this invention. At 6 is shown a supply roll of fiberglass paper. This paper is led across the driven and guide rollers 7 while being passed through a first spraying chamber 8 in which both sides of it are sprayed by nozzles 9 with an ammoniacal solution of silver nitrate, and then through a second spraying chamber 10 in which both sides of it are sprayed by nozzles 11 with a reducing solution of 'Seignettes salt. The paper is then passed through a drying chamber 12 in which it is dried by a current of warm air 13. The finished insulating material is then wound upon the roll 14, which may be given the same shape as that of the container to which the insulation is to be applied. Numerals 15a and 15b are drainpipes for removing excess liquids from the spraying chambers.

FIGURE 3 shows a magnified portion (about 12.5X) of the surface insulation made by applying a metal coating onto fiberglass paper. As can be seen, there are several superimposed layers of fiberglass paper alternatingly metallized and non-metallized.

FIGURE 3a shows a magnified portion (about 100x of natural size) of FIGURE 3. The reflecting surfaces consist of a multitude of metallized fibers with only a spotlike interfiber contact. This very fine division of the reflecting surfaces results in an extremely low heat conduction. Since the distances between the metallized fibers are much smaller than those between the foils of known insulating materials, the difference in temperature and therewith the heat exchange between adjacent radiationrefiecting layers is smaller, too.

These air permeable metal coated fiberglass layers, in contrast to metallized foils of a homogeneous material, exhibit nearly as high porosities as the aforementioned unmetallized fiberglass layers, for the thickness of the metal coating amounts to approximately one tenth of the thickness of the fiber.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.

Consequently, such changes and modifications are properly, equitably, and intended to be, within the full range of equivalence of the following claims.

What is claimed is:

1. Thermal insulation body suitable for low temperature use, comprising a plurality of films superimposed over one another, each of said films consisting essentially of a non-metallic thermal insulating fibrous material, which fibrous .material is permeable to air and which has a porosity of 88-98%, individual fibers located on at least one of the surfaces of at least one of said films being coated directly on their outward sides with a thin layer of a metal of low emissivity and high reflectivity, said layer having a thickness of 0.01-0.2-10- mm., with the provision that not all of the fibers of said thermal insulation body are completely coated with said thin layer of metal.

2. Thermal insulation as defined by claim 1 wherein the average pore diameter in a layer having a thickness of about twice the diameter of a single of said fibers amounts to about 0.001-O;0l mm.

3. Thermal insulation as defined by claim 1 wherein said fibrous material is predominantly fiberglass-paper having fiber diameters of 0.3-10- 10* mm., and wherein said metal is selected from the group consisting of gold, silver, copper, and aluminum.

4. A thermal insulation body as defined by claim 1 wherein said individual fibers are coated substantially only on their outward sides.

5. A thermal insulation body as defined by claim 1 wherein said thin layer of metal comprises subdivided reflecting surfaces with point-like contacts between particles, whereby said thin layer exhibits a low thermal conductivity as compared to a homogeneous layer of metal.

6. A thermal insulation body as defined by claim 1 wherein said body is non-combustible.

7. A thermal insulation body as defined by claim 1, comprising at least metallized films.

8. A thermal insulation body as defined by claim 1, comprising a sandwich-type construction of alternating metallized and non-metallized films, said metallized films being metallized 'on both sides.

9. In an apparatus having spaced-apart wall means defining a confined insulating space, said space being at least partially filled with thermal insulation at below atmospheric pressure, the improvement which comprises the employment of a thermal insulation body as defined by claim 1 in said confined insulating space.

10. In an apparatus having spaced-apart wall means defining a confined insulating space, said space being at least partially filled with thermal insulation at below atmospheric pressure, the improvement which comprises the employment of a thermal insulation body as defined 'by claim 2 in said confined insulating space.

11. Thermal insulation as defined by claim 3 wherein all said films are coated directly on at least one surface with said metal of low emissivity and high reflectivity.

12. A thermal insulation body as defined by claim 3 wherein said individual fibers are coated substantially only on their outward sides.

13. A thermal insulation body as defined by claim3 whereing said thin layer 'of metal comprises subdivided reflecting surfaces with point-like contacts between particles, whereby said thin layer exhibits a low thermal conductivity as compared to a homogeneous layer of metal.

14. A thermal insulation body as defined by claim 3, comprising at least 100 metallized films.

'15. A thermal insulation body as defined by claim 3,

comprising a sandwich-type construction of alternating metallized and non-metallized films, said metallized films being metallized on both sides.

16. In an apparatus having spaced-apart wall means defining a confined insulating space, said space being at least partially filled with thermal insulation at below atmospheric pressure, the improvement which comprises the employment of a thermal insulation body as defined by claim 3 in said confined insulating space.

17. In an apparatus having spaced-apart wall means defining a confined insulating space, said space being at least partially filled with thermal insulation at below atmospheric pressure, the improvementwhich comprises the employment of a thermal insulation body as defined by claim 11 in said confined insulating space.

18. In an apparatus having spaced-apart wall means defining a confined insulating space, said space being at least partially filled with thermal insulation at below atmospheric pressure, the improvement which comprises the employment of a thermal insulation body as defined by claim 4 in said confined insulating space.

19. In an apparatus having spaced-apart wall means defining a confined insulating space, said space being at least partially filled with thermal insulation at below atmospheric pressure, the improvement which comprises the employment of a thermal insulation body as defined by claim 5 in said confined insulating space.

20. In an apparatus having spaced-apart wall means defining a confined insulating space, said space being at least partially filled with thermal insulation at below atmospheric pressure, the improvement which comprises the employment of a thermal insulation body as defined by claim 6 in said confined insulating space.

21. A thermal insulation body as defined by claim 12 wherein said thin layer of metal comprises subdivided refleeting surfaces with point-like contacts between particles, whereby said thin layer exhibits a low thermal conductivity as compared to a homogeneous layer of metal.

22. In an apparatus having spaced-apart wall means defining a confined insulating space, said space being at least partially filled with thermal insulation at below atmospheric pressure, the improvement which comprises the employment of a thermal insulation body as defined by claim 12 in said confined insulating space.

23. In an apparatus having spaced-apart wall means defining a confined insulating space, said space being at least partially filled with thermal insulation at below atmospheric pressure, the improvement which comprises the employment of a thermal insulation body as defined by claim 13 in said confined insulating space.

24. In an apparatus having spaced-apart wall means defining a confined insulating space, said space being at least partially filled with thermal insulation at below atmospheric pressure, the improvement which comprises the employment of a thermal insulation body as defined by claim 21 in said confined insulating space.

25. In an apparatus having spaced-apart wall means defining a confined insulating space, said space being at least partially filled with thermal insulation at below atmospheric pressure, the improvement which comprises the employment of a thermal insulation body as defined by claim 7 in said confined insulating space.

26. In an apparatus having spaced-apart wall means defining a confined insulating space, said space being at least partially filled with thermal insulation at below atmospheric pressure, the improvement which comprises the employment of a thermal insulation body as defined by claim 14 in said confined insulating space.

27. In an apparatus having spaced-apart wall means defining a confined insulating space, said space being at least partially filled with thermal insulation at below atmospheric pressure, the improvement which comprises the employment of a thermal insulation body as defined by claim 8 in said confined insulating space.

28. In an apparatus having spaced-apart wall means defining a confined insulating space, said space being at least partially filled with thermal insulation at below at-.

mospheric pressure, the improvement which comprises the employment of a thermal insulation body as defined by claim 15 in said confined insulating space.

29. A film consisting essentially of a non-metallic thermal-insulating fibrous material, which fibrous material is permeable to air and which has a porosity of 88-98%, individual fibers located on at least one of the surfaces of said film being coated directly on their outward sides with a thin layer of a metal of low emissivity and high reflectivity, said layer having a thickness of 0.010.2 10 mm., with the provision that not all of the fibers of said film are completely coated with said thin layer of metal.

30. A film as defined by claim 29 wherein said fibrous material is predominantly fiberglass-paper having fiber diameters of 0.310 10* mm., and wherein said metal is selected from the group consisting of gold, silver, copper, and aluminum.

31. A film as defined by claim 29 wherein said thin layer of metal comprises subdivided reflecting surfaces with point-like contacts between particles, whereby said thin layer exhibits a low thermal conductivity as compared to a homogeneous layer of metal.

32. In an apparatus having spaced-apart wall means defining a confined insulating space, said space being at least partially filled with thermal insulation at below atmospheric pressure, the improvement which comprises employing as said thermal insulation, a film as defined by claim 29.

33. In an apparatus having spaced-apart wall means defining a confined insulating space, said space being at least partially filled with thermal insulation at below atmospheric pressure, the improvement which comprises employing as said thermal insulation, a film as defined by claim 30.

34. In an apparatus having spaced-apart wall means defining a confined insulating space, said space being at least partially filled with thermal insulation at below atmospheric pressure, the improvement which comprising employing as said thermal insulation, a film as defined by claim 31.

References Cited UNITED STATES PATENTS 2,357,851 9/1944 Scheyer 117-160 2,616,165 11/1952 Brennan 117-107 2,630,620 3/1953 Rand 117-160 2,731,046 1/1956 Bachner 161-216 2,814,162 11/1957 Toulmin 117-126 2,822,509 2/1958 Harvey 117-160 2,919,970 1/1960 Russell 117-126 2,921,864 1/1960 Heberlein et al 117-107 2,951,771 9/1960 Butler 117-126 3,009,601 11/1961 Matsch 220-9 3,241,702 3/1966 Navikas 220-9 THERON E. CONDON, Primary Examiner.

JAMES R. GARRETT, Examiner.

Claims

1. THERMAL INSULATION BODY SUITABLE FOR LOW TEMPERATURE USE, COMPRISING A PLURALITY OF FILMS SUPERIMPOSED OVER ONE ANOTHER, EACH OF SAID FILMS CONSISTING ESSENTIALLY OF A NON-METALLIC THERMAL INSULATING FIBROUS MATERIAL, WHICH FIBROUS MATERIAL IS PERMEABLE TO AIR AND WHICH HAS A POROSITY OF 88-98%, INDIVIDUAL FIBERS LOCATED ON AT LEAST ONE OF THE SURFACES OF AT LEAST ONE OF SAID FILMS BEING COATED DIRECTLY ON THEIR OUTWARD SIDES WITH A THIN LAYER OF A METAL OF LOW EMISSIVITY AND HIGH REFLECTIVITY, SAID LAYER HAVING A THICKNESS OF 0.01-0.2$10**-3 MM., WITH THE PROVISION THAT NOT ALL OF THE FIBERS OF SAID THERMAL INSULATION BODY ARE COMPLETELY COATED WITH SAID THIN LAYER OF METAL.