Note: Descriptions are shown in the official language in which they were submitted.
075938
This invention relates in general to the welding
of metal and more particularly to a process whereby metal
surfaces may be welded together using an explosive charge.
It is, in general, an object of this invention
to provide a method for forming gas-tight welds.
It is a further object of this invention to
provide a method for welding both similar and dissimilar
metals.
Still another object of this invention is to
provide a novel method for generating the heat and pressure
necessary to form a gas-tight weld between metals of a spec-
ified maximum degree of hardness.
In the drawings:
Figure 1 shows a typical apparatus set-up for
performing the process of this invention;
Figure 2 shows a process variation wherein the
two metal surfaces have been placed together preparatory to
forming the weld;
Figure 3 shows the appearance of the plates shown
in Figure 2 after a weld has been formed;
Figure 4 shows an alternative method for securing
the necessary gas volume between plates to be welded;
Figure 5 shows the appearance of plates which
have been welded according to the process variation of
which Figure 4 is illustrative;
Figure 6 shows still another process set-up
suitable for the formation of spot welds;
Figure 7 sh~ws the appearance of metal plates
which have been welded according to the technique to which
Figure 6 relates; and
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75938
Figure 8 shows the set-up utili2ed when it is
desired to weld two pipes of dissimilar diameter together.
Generally, it has been found that pieces of metal,
whether similar or dissimilar, may be welded together, pro-
vided that at least one of the metals being welded is of
lesser hardness than titanium, by a method which relies,
for the heat necessary to form the required molten surfaces,
upon the sudden compression of a specified quantity of gas
between the metal surfaces being welded. The compressive
effect is due to a sudden increase in hydraulic pressure
upon one of the metal elements and the necessary sudden
increase in pressure is, in turn, provided by the detonation
of a high explosive beneath the surface of a reservoir of
hydraulic fluid positioned adjacent the surface of one of -
the elements. More particularly, it has been found that if
care is exercised to maintain a critical mimimum quantity of
air and no more than a critical maximum quantity of air
between the two metal surfaces to be welded and if the weld
site is separated from an hydraulic fluid only by a diaphragm
(to prevent the hydraulic fluid from replacing the gas
between the metals) and, finally, if a high explosive is
detonated beneath the surface of the fluid, the explosive
being selected so that a certain critical ratio of gas
volume to pressure can be obtained, a gas-tight weld may be
effected in a very short time - in the order of one milli-
second.
The method may be used to weld similar or dis-
similar metals together, provided one of the metals used
has a lower melting point than titanium. For example, the
1075938
method of this invention has been successfully employed
in welding:
1. Stainless steel to stainless steel;
2. Nickel to nickel;
3. Zircalloy-2 to Zircalloy-2 (Zircalloy-2 is
a trade mark).
4. Stainless steel to carbon steels;
5. Nickel to stainless steel;
6. Aluminum alloys to each of the following:
a. Alumin~n alloys
b. stainless steels
c. carbon steels
d. titanium alloys
e. nickel alloys
f. molybdenum alloys
g. zircalloy-2
The method may also be used in what may be termed
a "cladding" operation whereby a thin metal liner may be
formed inside a pipe. A smooth weld is formed at the metal
interfaces. The procedure is the same as that used in welding
flat surfaces, the only difference being in the relative
thickness of one of the two metals involved. Cladding
entails a very thin layer of one metal bonded to a relatively
thicker layer of a second metal.
It is possible also to weld three layers of metal
simultaneously to form a sandwich. The use of a thin foil
as the internal layer is especially advantageous since such
material tends readily to melt, thus to insure a secure bond.
The gaseous layer separating the surfaces to be
welded may be a single gas or a mixture, as air. While
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1075938
there is nothing critical about the specific gas used, the
spacing or standoff of the metals is extremely important
since this determines the amount of gas to be compressed.
If too little gas is present on application of a given
pressure, insufficient heat will be generated properly to
soften the metal surfaces~ Alternatively, if too much gas
is present on application of a given pressure, some will
fail to be expressed as intended, but will be trapped be-
tween the surfaces, thus resulting in a pourous weld.
Thus, the ratio of gas volume to pressure must remain
within a given range. Lessened gas volumes will justify
somewhat lessened pressures while greater gas volumes will
require greater pressure and hence more powerful explosives.
Another critical feature which affects the deto-
nation velocities, pressures and quantities of gas required
-~ is the melting point of the metals used. Where a weld is
to be formed involving any metal or metal alloy having a
melting temperature of 600-900C such as aluminum, either
to itself or to another metal, the volume of gas between
the surfaces to be welded should be between 1 and 3 cc. per
linear foot of 1 inch width. Expressed differently, a
good working range is between about 0.08 cc. and 0.25 cc.
gas per sguare inch of surface to be welded. The pressure
! requirement for such metals, measured as the pressure pro-
duced by the effect of the explosive gases on water, is
between about 50,000 and 70,000 psi and the explosive used
should have a deto~ation velocity of between about 20,000
alld 30,000 feet per second.
Where both metals being welded having melting
temperatures in excess of 900C, e.g., steel to be welded
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either to itself or to another equally high melting metal,
the gas volumes required are approximately those stated
above. For example, for a line weld of 1/2 inch width,
0.5 to 1.5 cc. per linear foot are required. However,
greater pressures are necessary, pressures on the order of
80,000 to 120,000 psi being required with a detonation
velocity of 20,000 to 30,000 feet per second. Typical
welds of this type include nickel to nickel!alloy, nickel
alloy to stainless steel or stainless steel to stainless
steel.
As stated, when higher melting metals are welded,
gas volumes are used which are identical to those listed
for the lower melting metals but the grea,er pressures
generated in the latter process variation result in the
generation of the additional heat necessary to weld these
harder metals.
The quantities and pressures listed may be varied
somewhat, as indicated, since similar results can be obtained
by reducing the gas volumes and pressures as long as the pro-
portions of gas to pressure remain the same and do not droptoo low.
As indicated above, the explosives are immersed
; directly in the hydraulic fluid, conveniently water. Any
explosive is satisfactory which has a detonation rate equal
to or greater than the minimum rate required for the type
of metal used. For example, "Tetryl", "H-6", "Primacord",
"Trona" explosives "502" and "508", "PETN","RDX" and "TNT"
- have all been used successfully. ~The terms H-6, Primacord
and Trona are all trademarks).
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The thickness of the metals used is not particu-
larly critical unless the metal is of such thickness and
strength that the explosive force transmitted by the fluid
medium is incapable of forcing the metal surfaces to conform,
in which event the process obviously will not work satis-
factorily. Also, one must be cautious in attempting to weld
thick pieces of metal together (e.g. ends of rods) as the
force of the explosion may cause the metal to collapse.
Finally, if extremely thick pieces of metal are treated ac-
cording to the process of this invention, results may not
be entirely satisfactory as a "heat sink" may be formed,
i.e., the heat generated by the compression of gas between
the metal surfaces may be dissipated rapidly into the sub- -
stantial volumes of adjacent metal, thus precluding the
proper localization of the heating effect and the desired
softening of the metal surfaces at the interfaces.
Referring now to the drawings, wherein like
characters refer to like parts throughout, the process is
most conveniently carried out by simply placing a conven-
tional 2-1/2 gallon cardboard ice cream can 10 atop a steel
` block 12 and positioning therebetween the assembly 14 to
be welded. The ice cream can contains a suitable hydraulic
fluid 16, of density 0.8 to 1.2 grams per cc. An explosive
charge 18 is positioned a preselected distance from the
base of the can 10. The charge is electrically detonated
by means of wires 19 from a remote means, not illustrated.
A commercial blasting cap is used to detonate the explosive.
As shown ir the figures, the surfaces of the ele-
ments can be arranged in a number of manners. Referring
to Figure 2, there is shown a lower plate 20 having a second
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plate 22 positioned thereover, the second plate having
therein a linear semi-cylindrical depression 24. In
practice, the arrangement shown in Figure 2 will be found
to be exaggerated as the quantity of air required between
the plates is substantially less than that which would be
indicated in Figure 2, but the structure has been so shown
for clarity of illustration.
Upon detonation of the explosive, the raised
portion 24 collapses and, as shown in Figure 3, a weld
26 forms between the two plates in the area 26. On compres-
sion of raised area 24 due to hydraulic pressure, the air
within the space is compressed and rushes out at a great
velocity and the metal surfaces adjacent thereto melt and
fuse together.
The second process variation is depicted in
Figures 4 and 5 wherein two metal plates 40 and 42 are
shown adjacent one another. If surfaces to be welded have
been etched, a network of cavities is formed which pro-
vides many bonding surfaces and a better weld than might
otherwise be obtainable. The surfaces of the metal plates
shown in Figure 4 have been etched, as with sulfuric acid,
to an extent sufficient to insure the proper quantity of air
between the adjacent surfaces and in Figure 5 the welded
area has been formed by the mechanism described earlier.
Spot welds may be formed, as shown in Figures
6 and 7. Dimpled plate 60 is secured to plate 62 and the
raised portions 64 are collapsed and welds 66 formed by
the mechanism already described.
Pipes can also be welded in the manner in Figure
8. Here the split die 84 surrounds the larger pipe 85 and
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075938
the smaller pipe 86. Pipe 86 has an outside diameter less
tihan the in~ide diameter or pipe 85 and thus telescopes
thereinto. With the overlapping ends of the two pipes held
in the split die, the explosive ~38 is detonated and the two
pipes thus fuse together in the area corresponding to
groove 89. A seal 90 prevents the hydraulic fluid from
filling the air space between the pipes, and pipe 86 is
plugged at its lower end.
In the case of welding two pipes together, the
inside surface of the die can: (a) be smooth so that a
flat weld results; (b) have a circular ridge so that a
grooved weld results; or ~c) have a circular groove so
that a raised weld results.
In a typical preferred procedure, as when weld-
ing aluminum to aluminum, the weight of explosive which
produces the required 50,000 to 70,000 psi at the weld
~ site, when fired at the selected standoff, is calculated.
An explosive is then selected which has a detonation
velocity in the region of at least about 20,000 feet per
second, preferably 25,000 feet per second. The plates
are taped together in such a fashion that adequate air
remains between them. Any other means desired may be
used for holding the plates together but the use of tape
of some ~ind is a convenient procedure. An expandable con-
tainer, such as a 2-1/2 gallon cardboard ice cream can,
is filled with water and the charge is immersed at the
selected standoff. The explosion is then detonated.
In another typical procedure wherein steel
is welded to steel, the surfaces to be welded are etched
with chemicals (e.g. H2S0~ or H~03). In alternative pro-
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07ss3s
cedures, an abrasive compound is used either with or with-
out the chemical etching. The treated surfaces are placed
face-to-face on the foundation of the welding set-up. ~he
explosive is selected so that its detonation velocity is in
the region of at least 20,000 feet per second and prefer-
ably 25,000 feet per second, and the weight of explosive
which will produce 80,000 to 120,000 psi for the selected
standoff is calculated. Thereafter, the steps are identical
to those described with respectto the aluminum operation
above.
Examples are set forth below showing preferred
embodiments of this invention. These are for illustrative
purposes only and are not to be construed as imposing limi-
tations on the scope of the invention other than as set forth
in~the appended claims.
Example l - Sheet to Sheet Without Etch
Material: Aluminum alloy to aluminum alloy; mating surfaces
were roughed with emery to remove oxides.
Size: 2" x 2" x ".062 thick to 2" x 2" x ".062.
Location: One sheet on top of the other and both placed
flat on a steel foundation plate.
Air Between Sheets: From ".005 to ".015 average thickness.
Explosive Container: 9-l/2" x 9-l/2" cardboard container
holding water and 25 grams RDX high explosive (20,000 to
25,000 ft./sec. detonation rate~, located 1-3/4" above the
material to be welded and in the water.
Detonator: A No. 6 cap
.
Approximate Pressure at Weld Site: 50,000 to 70,000 psi.
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1C)75938
Example 2 - Sheet to Sheet Without Etch
Material: Nickel Alloy to stainless steel mating surfaces
were roughed with emery to remove oxide~.
Size: 3/41l X 2" x ".062 thick x 3/A 1l X 2" x".062 thick.
Location: Same as Example 1.
Air Between Sheets: Same as Example l.
Explosive Container: Same as Example l except that explosive
weight was 36 grams of RD~ and the explosive was located 1-1/4"
above the material to be welded.
Detonator: Same as Exampls l.
Appriximate Pressure at Weld Site: 80,000 to 120,000 psi.
The above examples for ".062 material have also
been applied to material from ".020 to "~125 thick without
changing the test conditions.
Example 3 - Sheet to Sheet with Etch
Material: Stainless steel to stainless steel (both Types
17-7)-
; Size: l/2" x 2-l/2" x ".015 to l/2" x 2-l/2" x ".062.
Location: Same as Example 1.
Etch Preparation: Nitric acid was used to etch the surfaces
of the material to be welded. The acid was dabbed onto the
surfaces and then the acid-treated surfaces were washed with
water to prevent further etching about 2 minutes after apply-
` ing the acid.
Explosive Container: Same as Example 1 except that the
explosive was located 1-l/2" above the material and the
explosive weight was 30 grams.
Detonator: Same as Example 1.
Approximate Pressure at Weld Site: lO0,000 psi.
~C)759;~8
Example 4 ~ Tube to Tube Without Etch
Mat : Aluminum tube to stainless steel tube.
Size: "1.66 O.D. x ".137 wall aluminum Type 3003 tube to
"1.898 O.D. x ".148 wall stainless steel Type 304 tube.
Location: The aluminum tube was inserted into the stainless
steel tube so that 3/4" of length was overlapped.
Air Between Tubes: The aluminum tubes O.D. was reduced for
this 3/4" to "1.588 O.D. leaving a ".oa7 thick air space
between the overlap.
Explosive Container: A steel die enclosed the walls of
both tubes. The inside of the tubes contained a 1-1/4"
diameter rubber insert enclosing a 21/2 grams of Tetryl
explosive which was centered relative to the tubes. The
remainder of the cavity was filled with water. The joint
was sealed with masking tape to prevent water seepage to
the welding area.
Detonator: No. 6 electric blasting cap.
, Approximate Pressure at Weld Site: 100,000 psi. All of the
above tests produced gas-tight welds.
As is e~ident, this process does not depend upon
heat being transmitted from the explosive directly to the
site of the weld. Rather, the only heat utilized in forming
the weld is that which is created as the gas between the
surfaces to be welded is compressed and expressed.
As can be seen from the foregoing, the "diaphragm"
referred to throughout this specification may consist of the
bottom of a cardboard carton, the seal 90 taken together with
the telescoped portion of inner pipe 86 shown in Figure 8
or any other means for maintaining the hydraulic fluid out
of direct contact with that portion of the plate assembly 14
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which serves as an air vent at the time the metal elements
are forced together.
Obviously, many modifications and variations of
this invention may be made without departing from the spirit
and scope thereof, and therefore only such limitations as
are indicated in the appended claims should be imposed.
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1075938
SUPPIEMENTARY DISCLOSURE
In the above application, it is stated - it
has been found that pieces of metal, whether similar or
dissimilar, may be welded together by a method which re-
lies, for the heat necessary to form the required molten
surfaces, upon the sudden compression of a specified
quantity of gas between the metal surfaces being welded,
provided _hat _ least one of the metals being welded is
of lesser hardness than titanium.
Further work has now shown that the statement
underlined above should read - provided that at least one
of the metals being welded is of lesser hardness than
molybdenum (m.p. 2620C). -
It is also stated in the above application that
the necessary sudden increase in pressure required to achieve
the sudden compression of a specified quantity of gas between
the metal surfaces being welded may be provided by the
detonation of a high explosive beneath the surface of a
reservoir of hydraulic fluid. It has now been found that
the hydraulic fluid may be eliminated provided that the
explosive used is selected so as to ensure pressures at
the weld site at least as great as those specified.
The further work conducted since the above appli-
cation was filed has shown that the method in accord with
this invention may be used to weld similar or dissimilar
metals together, provided one of the metals used has a
melting point lower than 2,700C, and that the explosives
used not be immersed in a hydraulic fluid although it is
preferable to do so.
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The method in accord with this invention has now
been successfully employed in welding molybdenum to molyb-
denum and in welding without a hydraulic medium.
Examples of these further embodiments of this
invention are as follows:
Example 5 - High Temperature Sheet to High Temperature Sheet
(~olybdenum or its alloys, or other metals and
their alloys, having melting points of 1800C to
2700C).
Material: Molybdenum (1/2% Titanium) to Molybdenum (1/2%
Titanium)
Size: 1" x 1" x 0.040" to 1" x 1" x 0.040".
Location: Same as Example 1.
Etch Preparation: Concentrated nitric acid was used to
etch the surfaces to be welded. The sheets were immersed
in the acid for 120 seconds (two minutes) and then washed
with water to remove any traces of acid.
Explosive Container: Same as Example 1 except that the
explosive was located one inch above the material, and the
explosive weight was 75 grams.
Detonator: Same as Example 1.
Approximate Pressure at Weld Site: 150,000 to 250,000 psi.
ExamPle 6 - Sheet to Sheet Without HYdraulic Medium and
With Etch
Material: 1020 steel to 1020 steel.
Size: 3" x 3" x 0.030" to 3" x 3" x0.030".
Location: Same as Example 1.
Explosive Container: Same as Example 1 except that the
explosive was on the bottom of the container. The water
on the side and above the explosive charge was used only to
dampen the noise from the explosion. The explosive weight
was 100 grams.
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Medium: A one-inch thickness of chipboard was placed
between the explosive and the top sheet of steel as
the medium to transmit the forces for welding~
Detonator: Same as Exam?le 1.
Approximate Pressure at ~eld Site: 150,000 to 300,000 psi.
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