US3141236A - Method of cladding - Google Patents

Description

y 21, 1964 B. B. DUNNE ETAL METHOD OF CLADDING 2 Sheets-Sheet 1 Filed June 1, 1960 .005 Climfg m m 7 mm? m MWZ 3B4, NVOm p w 50W 6?. {as

y 21, 1964 B. B. DUNNE ETAL METHOD OF CLADDING 2 Sheets-Sheet 2 Filed June 1. 1960 By PZ/F/PVB 7F/77Z WON/41D H KEZSfy S OMS andvbsm a oeals 3,141,236 NETHOD OF CLADDING Brian B. Dunne, San Diego, Perry E. Ritter, Encinitas,

and Ronald A. Kelsey, Del Mar, Califi, assignors to General Dynamics Corporation, New York, N.Y., a

corporation of Delaware Filed June 1, 1960, Ser. No. 33,133 3 Claims. (Cl. 29421) This invention relates to a method of cladding which is of particular value for applying coverings of metal or other similar materials to objects of irregular shape or of non-uniform cross section.

In the application of thin protective metallic sleeves or jackets, in certain cases, it is not possible to employ a rolling, swaging or extrusion process. This is particularly true in the case of an element of such character that it is either not feasible to use an extrusion process because of the nature of the product, or where the element is irregular in shape or has circumferential grooves or other indentations.

The object of this invention is to provide a convenient, economical and efficient method of applying a protective jacket or other relatively thin metal covering to an object made of a rigid material such as metal, for example, a fuel rod of irregular cross section such as may be used in nuclear reactor.

A further object of the invention is to provide a cladding method as an incident to which method there is evacuated from the interior of the sleeve any air or other gas which might be present in or about the object in such amounts as might interfere with the efficient prac tice of the method, or which might later interfere with the use of the finished product.

Other more specific objects and advantages of the invention will be disclosed as the description proceeds.

In general, it may be said that these objects and results are effected by detonating an explosive charge within liquid in which there has been immersed the rigid metal object around which has been placed a jacket of deformable material such as loosely fitting metal sleeve. When the explosive is detonated, the pressure created within the liquid adjacent the jacketed object will almost instantaneously cause the jacket to be forced into intimate engagement with the exterior of the rigid object. To avoid air pockets between the jacket and the metal object, the space between the metal object and the jacket is preferably evacuated prior to the detonation of the explosive.

The drawings which accompany this specification illustrate an embodiment of the invention which has successfully been employed in the cladding of nuclear reactor fuel rods, the exterior surfaces of which have exterior indentations, for example, in the present instance, circumferential grooves or recesses.

FIGURE 1 of the drawings represents a side view of a partial vertical section through a tank in which the fuel rod with its prospective shield has been assembled in a treatment tank before detonating the explosive;

FIGURE 2 is a plan view of the set-up shown in FIG- URE 1, partly in section, and taken through the line 2-2 of FIGURE 1; and

FIGURE 3 is a side elevation, partly in section, of the jacketed fuel rod after the cladding has been applied and the ends of the cladding sleeve have been scaled by insertion of the upper and lower heads.

Referring to the drawings, which disclose the invention as applied to the cladding of a nuclear reactor fuel rod, the fuel or meat of the rod is represented by the numeral 10 which, as shown in FIGURE 1, is provided with a series of circumferentially extending grooves 11. Except for the said grooves 11, the fuel rod 10 is in United States Patent "ice the form of a cylinder which may be two or more feet in length and one and one-half inches or more in diameter. The sleeve or jacket 12 which can be of aluminum or other appropriate metal, has a wall thickness of about .030 inch, and has an interior diameter about 0.003 inch greater than that of the rod 10 so that it will loosely fit the exterior of the rod 10 whereby said core rod 10 may be easily slipped into the sleeve 12, as shown in FIG- URE 1.

For the purpose of evacuating any gas, such as air, which may be contained within the grooves 11 or elsewhere in the assembled or jacketed rod, the ends of the sleeve 12 are sealed. This may be done by means of a pair of end plates or discs 13 and 14 made of lucite or other suitable material. Each of these end plates is made with an internal circumferentially extending groove 15, preferably rectangular in cross section, and fitted at its inner end with an O-ring 16 or similar gasket serving as a seal to prevent air or other gas from leaking back.

into the assembly after it has been evacuated. Such evacuation may be effected through a small pipe 17 in the upper lucite cover plate 13. It is not generally necessary to evacuate the assembly to a very low pressure. Evacuation to a level of the order of 1 mm. of mercury (absolute pressure) will ordinarily be sufiicient.

The evacuated assembly with the sealing caps 13 and 14 still in place is now placed in a tank of water large enough so as to avoid distortions in the inwardly directed pressure waves which are subsequently formed in the water. In the case of a rod one and one-half inches in diameter, the assembly should be completely surrounded by at least about twelve inches of water.

Before the sealed and evacuated assembly is lowered into the tank of water, a pair of thin discs 18 and 19 are secured to the outer surfaces of the plates 13 and 14. These serve to position the explosive charge which, in the present instance, comprises a plurality of, preferably three or more, vertically extending, generally parallel cords 20, 21 and 22, the upper ends of which are tied or otherwise brought together at the firing point 23. In the case of a rod one and one-half inches in diameter, and where three explosive cords are used, these cords may be located in a cylindrical zone and about one inch from the sleeve or jacket 12, the cords being equally spaced around the axis and positioned at an angle of as shown in FIGURE 2.

The explosive cords are formed of an explosive which preferably has a relatively high detonation velocity, for example, such as that which is marketed by The Du Pont Company under the name Primacord and contains PETN (pentaerithritoltetranitrate). In the present case, it may have an outside diameter of about onequarter inch and contain about thirty grains of PETN per foot. It has been found that when this explosive cord is detonated at the firing point 23, the explosion will be propagated simultaneously at the same rate through each of the three explosive cords, and since the three cords are symmetrically positioned around the axis of the rod and of equal length, the shock waves from the three cords will be at the same level and the combined shock wave will travel progressively downward from the disc 18 to the disc 19. This will produce a sudden hydraulic pressure, around the jacketed rod, of about three to four kilobars above the yield point of the aluminum sleeve 12, causing it to flow plastically.

In view of the fact that the shock wave will travel down the Primacord cords at an extremely high velocity (about 6000 meters per second) whereas the propagation velocity through water is only about 1500 meters per second, the pressure around the sleeve will be well distributed and concentrated around the circumference of the outside of the sleeve with the result that the sleeve contracted onto the object.

n) will be forced into close fitting intimate engagement with the rod As a result, the sleeve will be forced tightly into intimate contact with the rod 10 progressively threuLgrhout its entire length of two feet or more.

After the explosion has been effected, the assembly may be removed from the tank. To form the fuel element shown in FIGURE 3, seals, preferably of the same metal as the sleeve 12, aluminum in this case, are then applied and welded in place in the ends of the sleeve, as

jshown in FIGURE'3, Where 25 represents the seal at the upper end of the rod and 26 represents the seal at the lower end of the rod.

v In some instances, particularly when the object which is to be clad is of generally nniformpcross section, the air in the space between the object and the cladding may The expelleclby the progressive downward passage of the shock wave which will force the air between the rod and cladding to move downwardly as the cladding is In such a case, the prior evacuation of the air from the assembly will not be necessary.

' The method of cladding described above has been used to successfully clad objects of various shapes, including cruciform shaped rods, hexagonal rods, rods of rectangular cross section, rods provided with spiral grooves, rods provided with elongated fins, etc. It should be understood that the optimum number of explosive cords and the path of the cords relative to the object being clad will depend upon the specific shape of the object being clad. If the plurality of Primacord elements is such that they are adjacent, or nearly adjacent to one another,

they may be conveniently replaced by a thin sheet of 'or a sheet of the explosive material, one may use a single co-axial strand of the explosive material or a sheet of the explosive formed into a tubular shape.

Various of the features of the present invention believed to be new are set forth in theappended claims.

What is claimed is:

1. A method of applying a tight-fitting layer of metal to a rigid elongated core, which comprises inserting the core in a loose fitting jacket of malleable metal, evacuating the space defined between the core and the jacket, immersing the jacketed core in a liquid, providing a plurality of elongated bodies of an explosive substance which,are spaced from and which extend generally parallel to the jacketed core and which are positioned in generally equi-spaced relationship around the jacketed core, and simultaneously detonating said elongated bodies of explosive substance from the same ends to thereby provide a generally uniform shock wave in the liquid which extends around the jacketed core and which travels progressively along the length of the jacketed core to progressively contract the jacket into generally intimate contact with the core; L p n v 2. A method of applying a tight-fitting layer of metal to a rigid elongated rod, which comprises inserting the rod in a loose jacket of malleable metal, placing the jacketed rod in a tank of liquid, providing at least three explosive cords which are spaced from and which extend generally parallel to the jacketed rod and which are positioned in generally equi-spaced relationship around the jacketed rod, and simultaneously detonating said explosive cords from the same ends to thereby. provide a generally uniform shock wave in the liquid which extends around the jacketed rod and which travels progressively along the length of the jacketed rod to progressively contract the jacket into generally intimate contact with the rod while simultaneously exuding air from the space between the jacket and the rod.

3. A method of applying a tight-fitting layer of metal to a rigid elongated rod, which comprises inserting the vrod in a loose fitting jacket of malleable metal, evacuating the space defined between the rod and the jacket, placing the jacketed rod in a tank of liquid, providing at least three explosive cords which extend from a cornmon detonating point and which are spaced from and extend generally parallel to the jacketed rod and which are positioned in generally equi-spaced relationship around the jacketed rod, said explosiveco'rds extending along the entire length of the rod, and simultaneously detonating said explosive cords from said common detonating point to thereby provide a uniform shock wave in the liquid which extends, around the jacketed rod andrwhich travels progressively along the length of the jacketed rod to progressively contract the jacket into generally intimate contact with the rod.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Explosives Form Space Age Shapes, Steel, Aug. 25, 1958, pages 82-86.

Explosive Forming, American Machinist, June 15, 1959, vol. 103, No. 12, pages 127-138.

Claims (1)

1. A METHOD OF APPLYING A TIGHT-FITTING LAYER OF METAL TO A RIGID ELONGATED CORE, WHICH COMPRISES INSERTING THE CORE IN A LOOSE FITTING JACKET OF MALLEABLE METAL, EVACUATING THE SPACE DEFINED BETWEEN THE CORE AND THE JACKET, IMMERSING THE JACKETED CORE IN A LIQUID, PROVIDING A PLURALITY OF ELONGATED BODIES OF AN EXPLOSIVE SUBSTANCE WHICH ARE SPACED FROM AND WHICH EXTEND GENERALLY PARALLEL TO THE JACKETED CORE AND WHICH ARE POSITIONED IN GENERALLY EQUI-SPACED RELATIONSHIP AROUND THE JACKETED CORE, AND SIMU-SPACED RELATIONSHIP AROUND THE JACKETED CORE, AND SIMULTANEOUSLY DETONATING SAID ELONGATED BODIES OF EXPLOSIVE SUBSTANCE FROM THE SAME ENDS TO THEREBY PROVIDE A GENERALLY UNIFORM SHOCK WAVE IN THE LIQUID WHICH EXTENDS AROUND THE JACKETED CORE AND WHICH TRAVELS PROGRESSIVELY ALONG THE LENGTH OF THE JACKETED CORE TO PROGRESSIVELY CONTRACT THE JACKET INTO GENERALLY INTIMATE CONTACT WITH THE CORE.

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