Note: Descriptions are shown in the official language in which they were submitted.
~7466
: Improvement.s in and relating to explosive claddi.n~
This invention relates to explosi.ve claddi.ng of
structura]. metal members by a corrosion resistant
metal layer and is particularly, although n~t
exclusively, applicable to strip cladding across
~egions of fusion welded joints between two or more
clad plates.
There is an increasing use of corrosion resistant
clad plate in the construction of vesse].s and
structures for use in corrosive environments such as
those cxperienced in chemi.cal prant. The plate
employed is usually steel, clad with a relatively
thin layer of corrosion resistant metal such as, for
example, titani.um, and since it is not normally
possible to fusion weld this layer to the base metal
it is usually formed by explosive welding. The
technique of forming this material is well known in
the art.
When lar~e vessels are to be constructed it is
often necessary to join two or more such clad plates
together and this presents difficulties since it is
not possible to fusion weld the complete clad plates.
Thus to fabricate butt joints between titanium clad
steel plates it is necessary to machine off the
titanium cladding for a small distance so that fusion
welding of the steel plates may then be effected
without interference from the titanium cladding layer.
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It is then necessary to repair the ga~ in the titanium
cladding to restbre the corrosion resistant ]ayer. ~ne
known method is describe~d in a Paper entitled
"Explosion Clads" by A H Holtzman - Proceedings oi'
Seminar o~ NATO Advanced Study Institute on High
-~ Energy Rate Working of Metals - Oslo 1964, page 51~.
- This metho~ involves the use of a silver,titanium or
copper insert which is laid within the gap a~d then
bridged by an overlaid strip of titanium which is
fusion welded to the titanium cladding along each side
of the joint region. 'rhe insert acts as a fiLler
` material to prevent fatigue failure of the titanium
strip and attendant welding. Similar techniques are
employed for joining clad plate made in other such
metallurgically incompatible combinations such as
tantalum/steel and zirconium/steel.
This so]ution is expensive due to the"cost of the
insert employed and the high degree of welding skill
required to perform the joint.
It has also been pro~osed in United Kingdom
, Patent Specification No. 986,435 to explosively
weld a corrosion resistant layer across a fusion
welded zone in clad metal plate by assembling over the
fusion weldecl zone a strip of cladding metal and an
overlying layer of explosive material and detonating
the explosive along one edge. For best results the
cladding strip was disposed at an angle to the clad
; metal base plate but the assembly is difficult to
, assemble accurately and the resultant weld is not
uniform over the fusion welded zone.
The object of this invention is to provide a less
expensive,convenient method of surface cladding joints
between clad metal plates which produces a high
integrity weld.
In accordance with the present invention a method
of applying a surface layer across a surface layer or
joint between cladding layers on a clad metal plate
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or plates comprises forming a sllal.low chamfer along
each opposi.ng cladding layer edge and positioning
over the said chamfers a corrosion resi.stant metal
flyer-plate having a shallow generally V-shaped
configuration, o~tionally applying a ~uffer layer of
transmitting medium placed on the outside surface of
the flyer--p].ate, further superimposing an explosive
layer upon the flyer-plate or buffer layers and
detonating the explosive layer so as to explosively
weld the flyer-plate material at least to the
cladding layers.
The optimum angles of the chamfers and the
flyer-plate legs relative to the clad base plate
for optimum welding may be calculated by known
methods described, for example, in the following
papers:-
Papers by H K Wylie, P E G Williams and ~ Cross].andentitled "An Experi.mental Investigation of
Explosive Welding Parameters" - Proceedings of the
first Syrnposium on the use of Explosive Energy in
Manufacturing Metallic Materials of New Properties,
Marianske Lazne, 1970, published hy the Institute of
Industrial Chemistry,Pardulice, Czechoslovaki.a and
"Further Experimental Investigation of Explosive
Welding Parameters" - Proceedings of the Third
International Conference of the Center for High Energy
Forming, Denver 1971.
Paper by R H Wittman - Proceedings of the Second
Symposium on Explosives Working of Metals at
Marianske Lazne, 1973, Pages 153-167.
Paper entitled "Some Aspects of Exp].osive Welding
in Different Geometries" by M D Chadwick - Proceedings
of The Welding Insti.tu-te Select Conference on
Explosive Welding, Hove 1968.
In some cases i.-t is advantageous to form a
groove in the base metal layer o~ the clad plate
centrally between the chamfered edges of the cladding
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layers, in order to facilitate positioning of the
flyer-plate. The groove may conveniently be formed
simultaneously wlth the chamfers of t!1e cladding
layers and effectively extends the chamfer surfaces.
The invention is preferably applicable to the
joint region of clad metal plates where two base
metal pla.tes have been fusion welded together.
The flyer-plate may advantageously have integral
extensions which become detached by the explosion,
whereby high quality welds up to the flyer-plate
edge are achieved. The extensions are conveniently
defined by longitudinal grooves formed at the
commencement of the extensions or by bending the
extended flyer-plate along a line at the commencemellt
of the extension in a direc-tion outwardly from the
base plate.
In a further modification each leg of the flyer-
plate is provided with a pair of ang].ed portions to
provide for a partial weld to occur to the base or
target as well as the cladding portions.
The flyer-plate may be spaced apart from the base
or target plate in order to modify the explo~ive
weld between the flyer-plate and the base pl~te.
Preferably a plastic explosive, such as Metabel,
(Registered Trade Mark) having a high detonation
velocity is employed in the form of a flexible sheet.
Other features of the invention will become
apparent from the description which follows of three
specific embodiments.
The invention will now be described, by way of
example only, with reference to the accompanying
drawings in which
Figure 1 shows a diagrammatic cross-section of
one embodiment in accordance with the invention;
Figure 2 shows schematically the resultant
explosive weld achieved with the arrangement shown
in Figure l;
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Fi,gure 3 shows a d-iagrammatis cross-section of
an al~ernative embodiment in accordarlce with the
invention.
Figure ~ shows schematically the resultan-t
explosive weld acllieved with the arrangement show
in Fj.gure 3.
Figure 5 shows a diagrammatic cross-section of
a further embodiment in accordance with the in~ention.
Figure 5A is a modification of the embodiment
of Figure 5.
Figure 6 shows schernatically the resultant
explosive weld ac~hieved with the arrangement shown
in Figures 5 and 5A.
' In the drawings like elements are designated by
the same numeral.
In the embodiments shown in Figures 1-6 the
invention is applied to the fusion butt weld region
joining two flat steel base plates 1 and lA. The
cla,dding layers 2, 2A are machined back for a short
dis-tance from the weld region to prevent interference
with the fusion we]ding process and shallow chamfers
at an angle ~ are machined on the exposed ends of the
cladding layers 2, 2A adjacent to the subsequently
formed fusion weld ~one 6.
As shown in Figure 1 a rectangular flyer-plate 3
of cladding material compatible with the cladding
layers 2, 2A is bent to a shallow generally 'V'
configuration such that each side subtends an angle
~ and is closely positioned as shown. The sides may
meet at an angle or on a radius along the apex. The
angles ~ and ~ are determined on the basis of
calculation of the required collision angle which
provides the suitable set-up angle ~-R required for
explosive welding to take place. The flyer 3 will
also be curved in side profile along the weld when
the weld is curved or circumferential.
The flyer-plate 3 is covered with a buffer layer 4
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comprislng a transmittlng medium sucil as rubber and a
l~yer of explosive medium 5 whlch is preferably a high
detonation velocity explosive such as ~etabel.
In order t.o avoid distortion of -~he base plates l
and lA it may be necessary to place the base plates
on a matching anvil such as a heavy metal plate which
resists the detonation of the explosive.
The explosive medium 5 is detonated in the
direction of the ~usion weld seam, i..e. perpenclicu'ar
to the section of the plate shown in Figure 1. The
velocity of the flyer-plate 5 at impact is determi.ned
by the e~plosive loading and detonation velocit:y of
layer 5; the collision angle and collision point
velocity are determined by the velocity of the flyer-
plate 3 and also by the angle ~-~ and may be
calculated fiom a know].edge of the prior art.
The form of the resultant weld after dressing,
i.e. removing excess material, is as shown in Figure 2.
No weld occurs centrally, although in certain
conditi.ons some welding may take place between the
flyer 3 and the base 1, lA at some distance
from the centre, but weldi.ng occurs along the sloping
portions of the cladding, thereby effectively
maintaining the continuity of the cladding across
the joint regi.on.
The arrangement described above with reference
to Figures 1 and 2 is suitable when the weld zone
width is small. However, when the weld zone is wider
the embodiment illustrated in Figures 3 and 4 may be
employed.
Thus as shown in Figure 3 the extent of welding
may be increased by forming an additional inclined
portion 3B havi.ng an inclination of angle ~ to the
target or base layers, 1, lA so that inclined
portion 3A form an angle ~ with the base 1, lA and
the portion 3B form a resultant angle ~-~ with the
chamfers on the clad layers 2, 2A. The resultant
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weld after dressing is shown schematically in
Figure 4 and it w,ll be seen that welding of the
flyer occurs right across the joint surface except
for a narrow centrai region, due to the normal
impact and the low stand-off.
In the arrangement shown in Figure 5 the edges
of the cladcllng layers 2, and 2A and the portion of
the base 1 and lA adjacent to the weld 6 are
machined at a chamfer angle a thereby forming a
groove 7 above the weld 6, the angle ~ being the
~ppropriately choser. welding angle. The f1yer~ 3,
with its sides including an angle 180-2~ is
positioned with its apex in register in the groove 7.
On detonation of the explosive layer 5 the
flyer is welded to the upper surface of the cladding
layer 2, 2A as shown in Figure 6.
In the modified assembly of Figure 5A the
flyer plate 3 advantageously has integral
extensions 3C which can be coplanar with the flyer
plate or bent upwards as shown. In addition the
flyer plate 3 has longitudin~l grooves 8 at the
commencement of the extensions.
The buffer layer 4 and the explosive layer 5
covers all the area of flyer plate 3 and extensions 3C.
The buffer layer 4 may also be locally thickened in
the area immediately over the weld 6 for increased
protection of the flyer plate in the region of the
weld.
On detonation of the explosive layer 5 the
extensions 3C become detached and the flyer is
welded to the upper surface of the cladding layer 2,
2A, as shown in Figure 6, the extension promoting
welds of high quality up to the flyer plate edge.
The invention described above has the following
advantages:-
The flyer or cladding plate 3 may be pre-formed
with the buffer layer 4 and explosive charge layer 5
74~6
prior to welding and simple end jigs may be employed
to maintain the required set-up geometry prior to
detonation of the explosive layer.
Welding may be performed on curved seams by
using shaped (curved) flyers, provided that the
correct relative angles are maintained. ~ow~ver,
final closure of a full circumferential weld may
not be achieved because of pressure do~bling and
overlap effects and therefore final closure of a
small region only may require the more complex
fusion welding technique to be employed.
The method in accordance with the invention is
applicable to seams lying in any direction or
or.ientation, e.g. vertical, horizontal, overhead
or downhand.
~ xplosives whose detonation velocity fall
within a wide range are suitable~ However, plastic
explosives, such as Metabel which has a high detonation
velocity, are preferred mainly on the grounds that
they are readi.ly moulded to shape and will stay in
position without further packag~ng being required.
It shou]d also be no-ted that an explosively
welded seam can readily be inspected by ultrasonic
techniques which are not applicable to fusion welded
seams.
