US3532476A

US3532476A - Method of producing a metallic multilaminated tube

Info

Publication number: US3532476A
Application number: US862263A
Authority: US
Inventors: Martin Peehs; Heinz Schorner
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1968-10-01
Filing date: 1969-09-30
Publication date: 1970-10-06
Anticipated expiration: 1987-10-06
Also published as: FR2019593A6; GB1239005A; DE1800307B1

Description

Oct. 6, 1970 E s ETAL 3,532,476

METHOD OF PRODUCING A METALLIC MU'IILAMINATED TUBE Filed Sept. 30, 1969 United States Patent US. Cl. 2925.13 6 Claims ABSTRACT OF THE DISCLOSURE Method according to Pat. No. 3,461,523 includes applying both to the elongated metallic member, before spraying the latter with the layer of insulating material, and to the layer of insulating material thereafter, at least one layer, respectively, of metal having a lower melting point than that of the insulating layer and relatively good wetting characteristics with respect to the metal material in engagement therewith.

Our invention relates to method of producing a metallic multilaminated or compound tube and more particularly to a method according to our Pat. No. 3,461,523 issued Aug. 19, 1969.

In our just-mentioned patent, we disclose a method of producing a metallic multilaminated tube having at least one electrically insulating lamination wherein we spray a layer of insulating material on an elongated metallic member and move the insulation-coated metallic member and a hollow metallic tube, having an inner diameter greater than the outer diameter of the insulation-coated member, axially relative to one another so as to locate the metallic tube around the insulation-coated member. We then heat the metallic tube in zones progressively along the length thereof to a temperature at which the material of the tube is in plastic state and simultaneously apply tensile stress to the metallic tube in the longitudinal direction thereof so as to deform the plastic material in the heated zones whereby the metallic tube is shrink-fitted onto the insulation-coated metallic member. The insulating layer consists, for example, of A1 0 ZrO or BeO and is applied to the metallic member by a conventional plasma spraying technique. This method of our aforementioned patent is especially suited for producing anode tubes of cylindrical thermionic converters which are formed, for example, of a respective inner and outer niobium tube as well as of a layer of insulation, suitably ground or cut in accordance with its purpose, disposed between the two niobium tubes.

Such multilaminated or compound tubes must possess as high a thermal conductivity as possible in addition to having adequate insulating resistance and, as a further requirement, these characteristics should remain constant over very long periods of time i.e. even for years.

It is an object of our invention to improve the heat passage or conduction through such multilaminated or compound tubes.

With the foregoing and other objects in view, after further experimentation, we have succeeded in markedly improving the thermal conductivity of such tubes by providing a method according to our aforementioned patent including the additional steps of applying both to the elongated metallic member, before spraying the latter with the layer of insulating material, and to the layer of insulating material thereafter, at least one layer, respectively, of metal having a lower melting point than that ice of the insulating layer and relatively good wetting char acteristics with respect to the metal material in engagement therewith.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as method of producing a metallic multilaminated tube, it is nevertheless not intended to be limited to the details shown, since various modifications may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The invention, however, together with additional objects and advantages thereof will be best understood from the following description when read in connection with the accompanying drawing, in which:

FIG. 1 is a sectional view of a multilaminated tube produced in accordance with the method of our Pat. No. 3,461,523 and a component of the apparatus employed in carrying out that method;

FIG. 2 is a view similar to FIG. 1 showing the multilaminated tube produced by the improved method of th instant application; and

FIG. 3 is a fragmentary enlarged sectional view of the encircled region shown in FIG. 2.

Referring now to the drawing and first, particularly, to FIG. 1 thereof, there is shown a multilaminated threelayer tube produced by the method of our aforementioned patent. The tube of FIG. 1 is made up of an inner hollow tube 1 of niobium, for example, such as the anode of a thermionic tube, which is coated with a layer 3 of aluminum oxide by a conventional plasma spray method, for example. After the desired thickness of the insulating layer has been achieved, it is externally worked by polishing so that a close union is afforded to a tube 2, also for example of niobium, that is thereafter fitted thereon. The tube 2 initially has a slightly larger diameter than the previously coated inner anode tube but is heated at progressive locations alon the length thereof by a highfrequency induction coil 4 to a temperature at which the tube 2 attains a substantially plastic state, andtensile stress is applied in the direction of the arrow P simultaneously for deforming the respective plastic portion of the tube 2 and tightly fitting the tube onto the previously formed two-

layer tube

1, 3. Continued relative displacement of the

tube assembly

1, 3, 2 and the heating coil 4 in the axial directions thereof causes the tube 2 to e completely shrunk onto the insulation-coated inner tube 1. This assembly, which is especially suitable for thermionic converters employed Within nuclear reactors, must be operable uninterruptedly for at least two years during which it is cooled by liquid sodium to a temperature of about 700 C. The inner surface of the multilaminated tube assembly forms one wall of the converter gap wherein cesium having a vapor pressure of about 4 torr is contained. The temperature differential between the inner and outer wall thereof should not exceed 1 C. for a heat flow of 1 watt per square centimeter.

With the multilaminated tube produced according to the method of our aforementioned patent, the temperature differential across the inner and outer walls was found to be from 3 to 4.5 C., however. Accurate tests disclosed that this rather poor thermal conductivity was due to insufficient thermal contact between the metal and the A1 0 layer resulting from the following causes. When a layer 3 of A1 0 was applied to the hollow metal tube 1 it was necessary to completely melt the A1 0 particles, requiring for example the expenditure of 12 kw. heat energy. This was possible, however, only if nitrogen were employed as working gas. This gas formed a nitride layer on the niobium tube 1 which became decomposed when cooled, causing a decrease in thermal contact between 3 the niobium tube 1 and the A1 layer 3 due to the formation of a fine, i.e. narrow, gap or space between the adjacent surfaces thereof. This phenomenon was found to be preventable according to our invention by applying a layer 52, according to one example of our invention, of an alloy Nlgo'crgo, having a melting point of 1440 C., to the niobium tube 1 before spraying the insulating layer 3 thereon. In accordancewith another feature of the invention and in order to achieve adequate Wetting of the niobium tube 1 with this alloy, a thin coating of copper is first applied to the niobium tube 1 by a spray technique or galvanically. When the insulating layer 3 was subsequently applied by plasma spraying, the copper coating 51 melted momentarily and wetted the surface of the niobium tube 1 as well as the opposing surface of the NiCr layer 52. The Ni-Cr layer 52 was not attacked by the nitrogen working gas and was partly melted by the application of the ceramic A1 0 layer so as to provide thereby a relatively good contact with the A1 0 particles.

In a similar manner, the thermal connection or bond between the insulating layer 3 and the outer niobium tube 2 is produced. The nickel-chrome alloy is again initially sprayed onto the insulating layer 3 to form a layer 61 thereon, and a thin copper layer 62 is again applied to the nickel-chrome layer 61. Thereafter, the outer niobium tube 2 is sweated onto the thus-formed mutilaminated

tubular assembly

1, 51, 52, 3, 61, 62 in the manner disclosed in our Pat. No. 3,461,523. The outer copper layer 62 accordingly melts and, upon cooling, in effect solders the nickel-chrome layer 61 to the outer niobium tube 2.

It is possible to produce multilaminated or compound tubes by the improved method invention of the instant application practically of any desired length wherein, for example, the spacing between the tubes 1 and 2 can be extremely small, such as for example of the order of magnitude of from 0.2 to 0.3 mm. The thickness of the A1 0 insulating layer is then about 0.15 to 0.2 mm.

Collector tubes produced by the method of the instant application exhibit a temperature differential of from 0.7 to 1 C. with respect to unity of the heat flow density and consequently meet the aforementioned requirement.

The aforedescribed example taken from the technology of thermionic converters indicates quite clearly the great demands with respect to insulation stability and thermal conductivity that can be satisfied by the method of the invention in this application. It is of course quite obvious that the method of this invention is applicable as well to other technological arts.

We claim:

1. In a method of producing a multilaminated tube having at least one electrically insulating lamination by spraying a layer of insulating material on an elongated metallic member, moving the insulation-coated metallic member and a hollow metallic tube, having an inner diameter greater than the outer diameter of the insulationcoated member, axially relative to one another so as to locate the metallic tube around the insulation-coated member, heating the metallic tube in zones progressively along the length thereof to a temperature at which the material of the tube is in plastic state, and simultaneously applying tensile stress to the metallic tube in the longitudinal direction thereof, so as to deform the plastic material in the heated Zones whereby the metallic tube is shrink-fitted onto the insulation-coated metallic member, the improvement which comprises applying both to the elongated metallic member, before spraying the latter with the layer of insulating material, and to the layer of insulating material thereafter, at least one layer, respec tively, of metal having a lower melting point than that of the insulating layer and relatively good wetting characteristics with respect to the metal material in engagement 1 metal layer applied to the metallic member being resistant to attack by the working gas.

3. Method according to claim 2 which comprises initially applying to the elongated metallic member a coating of metal having good wetting characteristics relative to the material of the elongated metallic member.

4. Method according to claim 3 wherein the metal layer applied to the insulating layer is resistant to attack by the working gas.

5. Method according to claim 4, which comprises ap plying to the metal layer initially applied to the insulating layer a coating of metal having good wetting characteristics relative to the material of the metallic tube.

6. Method according to claim 5 wherein the working gas is nitrogen, the elongated metallic member and the metallic tube are formed of niobium, the metal coatings having good wetting characteristics are formed of copper, the metal layers resistant to attack by the nitrogen are formed of a niobium-chromium alloy, and the insulating material is a ceramic selected from the group consisting of A1 0 ZrO and BeO.

References Cited UNITED STATES PATENTS 2,609,595 9/ 1952 Rossheim.

2,781,308 2/1957 Creutz et al.

3,009,484 11/1961 Dollens.

3,010,355 11/1961 Cutforth.

3,279,028 10/1966 Hall et al 310-4 X 3,318,340 5/1967 Torti 138-140 3,368,084 2/1968 Hall 310-4 3,461,523 8/1969 Peehs et a1 29-25.l3

CHARLIE T. MOON, Primary Examiner U.S. Cl. X.R.

Patent No. 3,532,476 Dated October 1-970 Inventor(s) Martin Peehs and Heinz SchBrner It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading, page 1, column 1 the German priority number should read --P 18 00 307.1--

SIGNED mu QEALEF Atteat:

Edward M. Fletcher, Ir. WIMIAM E. SGHUYLER, JR. L Ane ti Offi commissioner of Patents