Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~ET~OD, WELDING F~U~, AND APPARATUS ~OR EIECTRO-
. SLA~ WELDING
The present invention relates to the art Qf ~elding
and more particularly to a method for electroslag welding
of li~ht metals and alloys with a de~sit~ less than that
of the slag, to a weldin~ flux based on alkali and alkali-
earth metal halides, and to apparatus for accomplishing
said method.
The i~vention may be employed i~ welding ~luminium,
magnesium, titanium, their alloys, and other light metals;
it is particularly useful for welding aluminium busbars
in the nonferrous metallurgy 9 chemical and electrical in-
dustries, and in other fields of engi~eeringD
There is known a method for electroslag welding of
metals (~lektroshlakova;ia svarka (~lectroslag welding)
~d. by B.Ye. Paton. Moscow-Kiev, '~ilashgiz" Publishersg 1959,
pp. 90-1493, which includes establishing a slag bath,~us-
ing an electrode and edges being weld-aoined7 and filling
the gap between the edges with molten metal.
It is known that in the course of electroslag weld-
ing of light metals and alloys with the use of prior art
fluxes~ the content of gases in the weld metal rises with
the thickness of the workpieces being weld-joined.
~ or example, a flux has been proposed (USSR Invent-
or's Certificate No. 626,913) intended for electroslag
welding of light metals and alloys and containing alkali
and alkali-earth metal halides, the ~lux composition be-
.~
~52~
ing as follows (in wt %~:calcium ~luoride O . . . . . . . . 13-17
strontium ~luoride . . I . . . . . . 1~-17
magnesium fluoride . . . . . . . . . 10-14
lithium fLuoride . . a ~ o 16-20
potassium fluoride (concentrated
aqueous solution) . O . . . . . . . ~6-44
A weld produced with the use o~ the flu~ in the co-
urse o~ weldin~ 9 without resorting to known techniques ~or
reducing the gas content in the weld metal, is porous and
has an increased content of gases, which drastically im-
pair5 the mechanical properties o~ ~elded joints Further-
more, the flux is highly hygroscopic (because its comp~-
sition includes a concentrated aqueous solution of potas-
sium fluoride), which in the course of electroslag weld-
ing may give rise to weld pool splashouts upsetting the
stabili ~ o~ the process~
The above-men-tioned electroslag welding method con-
templates the use o~ apparatus consisting of a bottom plate,
mouldin~ shoes, run-on plates, and a ~elding electrode.
The use o~ such methods, flu~, and a~paratus results
in welds featurin~ an increased content of gas and calls
for additional ~rocessing operations to upgIade the weld.
quality in ~elding critical structures~
A ~ull degassing o~ the weld me-tal in the above me-
thod can be attained with inhibiting the weld metal cry-
stallization process by performing an additional operation
of a preliminary, accompanying, and subsequ`ent heating of
.
,
the weld metal, which is attainable only by the use of a com--
plex additional equipment.
Moreover 5 the method calls ~or introduction in the
course of welding into the weld metal of additio~al che-
mical elements which bind the gas-formin~ components for
preventing the formation of gas bubbles and ~or a~ addi-
tional protection of the welding zone by inert gasesD
The application of said method, flu~, and apparatus
involving the additional processing steps greatly increas-
es the labour consumptio~ and the cost o~ the welding pro-
cess~
There has also been proposed a method for vertical
welding of aluminium (US Pat. No. 3,585,343) 9 w~ich includes
establishing a slag bath o~ the ~ollowing compositio~ (in
%):
potassium chloride . . . . . . . . . 45
sodium chloride . . ~ 27
s~dîum cryolite (~NaF.AlF~ . . . . 22
( lithium chloride . . . . . . . . . 6,
followed by ~using the electrode and the edges being weld
joined and ~illing the gap betwee~ the edges with metal.
The above ~lux allows a stable electroslag welding
process to be conducted, adequately deoxidizes an oxide
~ilm on the workpieces being weid-joined, but ~ails to en-
sure sound welds unless the above-mentioned weld metal de-
gassing techniques are resorted to~
The method contemplates the use o~ an apparatus com-
prising a metal mould, graphite moulding shoes, current con-
tact members, and a solid-section electrode with a guide
bushing which provides ~or its rotation in the slag bath;
the current contact members are disposed outside the weld
pool.
Degassing thé weld in the course of vJelding proceeds
owing to the use of the graphite moulding shoes which re-
duce the heat removal from the weld pool as well as to the
electrode rotation in the slag bath~
Because of a h~gh rate of the weld metal crystalli-
zation as well as o~ that the elec-trode rotation exerts
1 a mechanical ef~ect on the slag bath alone in the course
of welding, this prior art method is incapable of fully
degassing the weld metal~
The electroslag welding method with the use of the
above-described flux and apparatus necessitates a complex
follow-up equipment to ensure stabilit~ o~ the ~rocess thro-
u~h controlling the electrode disposition in the weld pool~
which complicates the process, raises its cost, and still
Yails to ~ully remove gases from the weld metal be~ore
its crystallization because of a lo~ melting point o~ the
flux.
The principal object of the present invention is to
provide a method, a welding flux~ and an apparatus for
electroslag welding of lig~ht metals and alLoys~ which en-
sure a stable v~elding process and minimize the gas content
in the weld metalO
An object of the invention, following from the pre-
ceding one, is to provide a weldin~ f.lux whose quantitative
and qualitative composition raises the heat capacity of the
--5--
slag bath and thereby ensures the degassing of the liquid
metal of the weld.
A further object of the invention is to widen the
production possibilities of the method.
Still further object of the invention is to cut
down the labour consumption of the welding process.
Yet further object of the inven-tion is to raise
the productive capacity of the welding process.
An object of the invention is also to cut down
the cost of production of weld joints.
Still another object of the invention is to provide
an apparatus for electroslag welding, which ensures remo~-
al of gases from the weld pool in the course of welding
and self-regulation of the electrode fusion rate.
In accordance with a particular embodiment of the
invention, there is provided a flux for the method of
electroslag welding of light metals having the following
composition (in wt.%):
barium fluoride . . . . . 60.0 to 90.0
calcium fluoride . . . . . 5.0 to 15.0
lithium fluoride . . . . . 1.0 to 5.0
sodium fluoride . . . . . 1.0 to 10.0
potassium fluoride . . . . . 1~0 to 15Ø
This allows a weld joint with a sound weld metal
to be obtained.
The slag bath heat capacity may be raised by increas-
ing the bath volume. This slows down the rate of weld me-
35~8
tal cooling in the course o~ welding.To raise the.slag bath he~t ca~acity a flu~ of the
following composition (in %) is used:
barium fluoride . ~ . . . . . . 60.0 to 90.0
calcium ~luoride ~ . . . . . . . 5.0 to 15.0
lithium ~luoride . . . . . . . . 1~0 to 5~0
sodium fluoride . 0 . . . . ~ 0 to lOoO
potassium fluoride . . ~ . . . . 1.0 to 15,0
- I~corporation of barium fluoride in the above-speci-
fied amounts into the proposed flu~ increases the flux
density above that of the metal being ~elded~ and there-
by facilitates separation of molten metal from slag in the
course of electroslag welding as well as provides the sta-
bility of the process.
Reducing the barium fluoride content in the propos-
ed flu~ below the specified lower limit leads to a poor
separation o~ molten metal ~rom slag in the process and
impairs the stability of the latter, whereas e~ceeding the
s~ecified upper limit reduces the activit~ o~ the flu~ and
eventuallg results in weld de~ectsO
Incorporation of calcium fluoride in the above-spe-
cified amounts into the composition of the proposed flux
augments the activit~ of the latter and also, throu~h re-
ducing the sur~ace tension at the slag-metal interface, pro-
motes the merging of i~dividual liquid metal drops into
one metal pool in the course of electroslag welding. Reduc-
ing or increasing the calcium fluoride content in the pro-
posed flux composition beyon~ the above-specified range
s~
degrades the activity of the flu~.
Lithium, sodi~um, and potassium fluorides contained
in the above-sPecified amounts in the composition of the
proposed flux as well enhance its activit~.
The above-specified percentages of the flux compo-
nents raise the flu~ melting point above -that of the metal
being welded, which results in inhibiting the crystalliza-
tion o~ the molten metal in the gap between the edges be~
ing weld-joined and hence in a higher degree of degassing
the metal and in producing a sound wèld. ~he above advant-
ages of -the proposed flux allow the qualit~ and operational
dependability of welded joints to be greatly enhanced~
Increasing the heat ca~acity of the slag bath and
holding the weld metal in a liquid state till its degass-
ing in accordance with the proposed method are attained
with the use of an apparatus which includes a metal mould
with a bottom plate 7 moulding shoes, a current contact
member, and a welding electrode, in which apparatus the
welding electrode is installed through an aperture in the
bottom plate centre and a lo~-resis-tance current contact
member is installed in the electrode fusion zoneO
Such an arrangement provides for a stability of the
v~elding process owing to a self-regulation of the v~elding
electrode ~usion rate, since ~vhen the electrode end gets
fused down below the top plane of the current contact mem-
ber, the arc spot shifts from the electrode to the current
lead member, thereby slo~ving do~n the electrode fusion rateO
The current contact member installed in the electrode
-8-
~usion zone may be made of either a solid material whose
melting point exceeds the working temperature of welding
or a liquid material whose boiling point e~ceeds the work-
ing temperature of welding.
When thus selected, the current lead member material
is not destructed i~ welding.
When a liquid material is chosen for the current con-
tact member; the material is selected so that its density
exceeds that of the slag bath and so that it neither mixes
with ~or dissolves in the liquid electrode metalO
( Such a selection of the material precludes contamina
tion of the weld metal with the CurreQt contact member ma-
terial in the course of welding.
Preferable is such a modification of the electroslag
welding apparatus wherein the electrode has internal pass-
ages disposed along and across the electrode, ~illed with
a gas-conducting material, and communicating with a simi-
lar passage in the metal mould bottom plate.
The provision of such passages permits removal of gas-
es from the weld pool ln the course of welding, while fill-
ing the passages with a gas-conductin~ material prevents
the weld pool from .~lowing out o~ the gap bet~een the edges
being ~eld-.ioined~
The inven-tion will now be explained in greater de-
tail with reference -to the accompanying drawings~ in which~
~ ig. 1 illustrates the process of electroslag welding
of light metals and alloys according to the invention, with
a solid c~rrent COQtact member;
~ ig. 2 illu~trates the same as ~ig. 1, but with a li-
quid current contact member;
Fig. 3 illustrates the F~ocess of holding the liquid
weld metal on a high-temperature hearth, after switGhin~
off the welding current; and
~ ig. 4 shows the obtained weld after crystallizatio~
~ ne invention is explained by way of specific ~xa-
mples thereof~
E~ample 1
~ lectroslag welding of workpieces vas carried out
in an apparatus which was prepared for weldin~ b~ the ~ol-
lowing procedure.
50~100-mm section9 500 m~ long aluminium sDecimens
2 to be welded together were placed on a metal mould 1
(Fig. 1) so that the gap between the edges to be weld-join-
ed was of 60 mm; the specimens were insula-ted from the me-
tal mould.
Graphite run-on plates 3 were installed on the spe-
cimens 2. The gap between the edges to be weld-joined was
closed at the sides by moulding shoes 4 insulated ~rom the
specimens 2 to be welded.
An aluminium welding electrode 6, of 20x40 mm in secti-
on, was inserted through an aperture in the centre of a
bottom plate 5 into the gap between the edges to be weld-
joined.
The aperture wherethrough the we~ding electrode 6
had been inserted was sealed v~ith an asbesto~ cord 7. Ne~t,
a ~raphite current lead member 8 was installed around the
5~
--10--
welding electrode 6 and seal 7 on the bottom plate 5 in-
side the metal mould 1~
The bottom plate 5 and the electrode 6 were provid-
ed with internal passages 11, 129 13 for gases to escape
from the weld pool in the course o~ ~eldi~g, the passages
being filled with a mixture of a finely divided metallic
material and a coarse-grained flux 14 to prevent the weld
pool ~ro~ flowing out through the passages.
~ roceeding ~rom tne consideration that the melti~g
point of the flux 14 ~or producing the bath must e~ceed
that of the metal being welded (660C~9 the following flux
composition was selected (in wt.%):
barium fluoride . 4 ~ 60.0
calcium fluoride . ~ . . . . . . l~oO
lithium ~luoride . . . . . ~ . . 5.0
sodium ~luoride . ~ . . .lOsO
potassium fluoride . . . . . . . . 10.0
~ he density o~ the ~lux was o~ 3~1 g/cm3, and the
melting point, of 900C.
The ~lux 14 so selected was filled into the gaP bet-
ween the specimens 2 to be welded so that the top part o~
the welding electrode 6 was le~t exposed ~or 10 mm.
The run-on plates 3 and the welding electrode 6 were
connected bg current feeding cables 15 to a welding trans-
former 16.
Ne~t, a ~lux melted beforehand was poured over the
flux 14 filled in the gap bet~een the edges -to be weld-
-joined.
~ he apparatus to accomplish the method ~or electro-
slag welding of workpieces was thus prepared ~or operatiorl.
The welding conditions were as follows:
power source no-load voltage Url 1 = 38 Ys
welding current Iw = 405 k~-
Upon completion of the weldirlg circuit, the edges
being weld-joined of the specimens 2 a~d the welding elect-
rode 6 ~used; giving rise to a metal pool 17, while the
flux melted and formed a slag bath 18; the metal pool 17
was protected ~rom the atmospheric effects by an inert gas,
argon.
In the course of welding, the weldi~g electrode 6
fused down and filled the gap between the edges being
weld-joined with metal until the ~used end of the welding
electrode 6 had come to a positio~ below -the top face of
the current lead member 8.
Such being the case, the fusion of the welding elect-
rode 6 slowed down due to shifting of the arc spot from the
electrode end to the -top face of the current contact memb-
er 8; this in turn caused the electrode end to rise above
the top face of the current contact member 8, i.e. a self-
regulatiorl of the rate of fusion o~ the elec-trode 6 in the
course o~ welding took place.
The gases evolved in the course of welding from the
~eld pool escaped via the passages 11, 12, 1~ of the weld-
ing electrode 6 and the bot-tom plate 5~
hfber the gaP ~et-veen the ed~es being weld~joined
o~ the sPecimens 2 got ~illed with the molten metal 17,
-12_
t~e welding curre~t was switch2d off.
~ he slag bath 18 cr~stallized to ~orm a high-tem-
perature hearth 19 with a temperature of 900C.
r~he temperature o e the hearth 19 and o~ the liquid
metal 17 lowered from 900C to the crystallization tempe-
rature o~ the metal 2 being we~ded, i.e. to 660C, in 1~5
min~ Over this time, the metal pool 17 remained liquid,
which promoted the maxinum removal of gases from the ~eld
metal. The weld metal de~assing took 1.2 min ~the metal
pool degassing time was determined e~perimentally before
the welding)~
After the li~uid metal had crysta~lized, a welded
joint with a sound weld metal was obtained.
The weld metal strength ~as o~ 90-92% of that o~ the
metal being welded, which e~ceeds similar characteristics
for the prior art method.
The metallographic anal~sis demonstrated that the
weld metal was free of pores~
The solid-material current contact member 8 may be
substituted by a liquid-material current contact member 20
(Fig. 2). The welding process in the latter case i5 the
same as in the above Example.
E~amples 29 3, 4, and 5 were similar in the proce-
dure to Rxample l; the parameters ~or the ~xample~ are
given in the Table below.
Electroslag welding in E~amples 2 and 3 yielded
welded joints with a sound weld metal havin~ a strength
of 90.0 and 75.0 %, res~ectively, of that O:e the metal be-
in~ ~elded.
~ 5~
,
-13-
~able
Mate- ~lect ~lux composition (in wt.%)
ample being rode BaF2 CaF2 LiF ~aF K~
No. weld- rial
ed
____________________________________________________ _____
2 Titanium Titanium 90O0 5.0 2.0 2.0 1~0
~ ~iagnesium ~agnesium 7500 lOoO 7~0 2~0 lOoO
4 Aluminium Aluminium 50.0 20.0 ~- 5.0 20.0
5 Aluminium Aluminium 95.0 2.0 1~5 1.0 005
(
~ he metallographic analysis showed the weld metal
to be free ~rom pores.
In ~xample 4, the weld metal contained crystallized
slag iaclusions, which resulted ~rom a small dif~erence
between the densities of the slag and the metal being weld-
ed~
I~ E~ample 5, points of a poor ~usion of the weld
metal with the edges bei~g weld-joined were observed, which
stemmed ~rom an inadequate activit;y o~ the ~lux~
The Examples given above allow a conclusion to be
drawn that electroslag welding in accordance with the pro-
posed method with the use o~ the proposed flux composition
and apparatus yields a sound weld metal featurin~ high me-
chanical properties.
The E~amples given above do not restrict the range
of metals being welded 9 since the method of the invention
~ith the use of the ~lux and apparatus of the invention
.. .
will yield sound welded joints in welding metals whose
densit~ is less than that o~ the weldin~ ~lux.
