Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to an arc welding
process and apparatus for preventing the occurrence of pits and
blowholes which are often times generated when steel plates
coated with, for example, anti-rust paint are butted together
in a T-shape for horizontal fillet welding, thus obtaining an
improved weld bead appearance.
In shipbuilding and bridge construction, a large
portion of the weld ~oints are fillet welds, so that an auto-
mated fillet welding technique will improve upon the efficiency
of the overall welding operation.
DESCRIPTIO~ OF THE PRIOR ART
Gas shielded arc welding, submerged arc welding and
other welding techniques are all capable of bein automatically
carried out. However, when fillet welding steel plates coated,
for example, with anti-rust paint, the gas generated by the
decomposition of the anti rust pai~t causes pits and blowholes
in the plates, thus requiring additional labor for repairs
which decreases the efficiency of the operation.
Furthermore, during such horizontal fillet welding
the generated arc is customarily not made coincident with the
line of intersection between the horizontal steel plate and
the vertical steel plate~ but is instead directed at the top
surface of the horizontal plate,
To enable the prior art to be described with the aid
of the drawings, these will now be listed.
Figure 1 is an end elevational view illustrating a
horizontal fillet welding technique in accordance with the
prior art. ~ ;
Figure 2 is an enlarged sectional view of Figure 1
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illustrating a weld bead and an undercut typlcally caused by
conventional ~elding techniques.
Figure 3 is a schematic side view of a welding
apparatus according to an embodiment oE the present invention,
shown in relation to the prependicularly related plates of
Figure 1.
Figure 4 is an enlarged view of the welding section of
~ig. 3.
Figure 5 is an enlarged plan view of a welding wire
feed roll taken substantially along line 5-5 of Fig. 3.
In the prior art as shown in Fig. 1, wherein a vertical
steel plate 1 is disposed in perpendicular fashion to a horizontal
steel plate 2 and the fillet welding operation is carried out
with the use of a power supply nozzle 3 supporting a welding wire
or electrode 4. The center of the generated arc is normally
off center from the line of intersection of the plates by a
distance x of approximately 2mm from the vertical plate. The
reason for this is that when the arc is directed toward such
line of intersection, an undercut 5 of the weld bead 6 results
in vertical steel plate 1, typically as shown in Pig. 2.
Moreover, it has been found that the above-mentioned
deviation of the arc center by the distance x likewise causes
the anti-rust paint of the horizontal steel plate to decompose
at the butt section of the vartical steel plate and the horizontal
plate, whereby the decomposed gas is contained within the weld
bead, which itself develops pits and blowholes.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to
avoid the above-mentioned drawbacks. An improved welding zone
is effected by the invention by regularly and alternately feeding
during a single pass two welding wires so as to provide an arc
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welding procesa-for horizontal fillet welded ~oints whereln the
generation of blowholes ls avolded in the horizontal fillet
welding zone.
Another object o~ the present invention is to provide
a horizontal fillet welding apparatus which carries out the
above-mentioned arc welding method effectively.
More specifically, the inventlon consists of a method
for horizontal fillet welding of a vertlcally oriented steel
plate to a horizontally oriented steel plate which have been
butted together in a T-shape, the welding being conducted along
the line of intersection therebetween in a single pass, the
method comprising directing a pair of spaced-apart welding wires
in the general direction of said line of intersection, each of
said wires having a predetermined diameter, said wires being
disposed such that one is directed towards the vertically
oriented steel plate and the second is directed toward the
borizontally oriented steel plate and such that the centerline
therebetween lntersects with the line of intersection between
said piates; and alternately feeding during the single pass
said wires at predetermined time intervals towards said plates;
and when feeding said wires, feeding said wire directed towards
said vertically oriented plate at a rate equal to or less than
the rate of feeding of said wire directed towards said
horizontally oriented plate.
The invention also consists of an apparatus for
horizontal fillet welding together a vertical steel plate and
a horizontal steel plate butted together in a T-shape and
having a line of intersection, comprising a pair of welding
wires, means for alternately feeding said wires at different
rates of feed, a power nozzle through which said wires are fed,
said power supply nozzle being directed toward said line of
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intersection and so disposed that one of said wires is fed to
said vertical plate and the other of said wires is alternately
fed to said horizontal plate, a welding power sDurce connected
to said nozzle and to one of said plates for passing an electric
current alternately through said wires for the fillet welding
of said plates 7 and means for moving said nozzle along said
line of intersection.
Other features of the invention will become more
apparent from the following detailed description of an embodiment
thereof when taken in conjunction with the accompanying drawings.
DESCRIPTION OF THE PREFERRED EMBODIME~T
The apparatus according to the present invention will
be described with reference to Figs. 3 to 5, Figs. 1 and 2
illustrating the prior art as described above.
Welding electrodes in the form of wires 7 and 8 are
unwound from welding wire feed rolls 9 having axes disposed
parallel to one another so that the unfed wires 7 and 8 are
likewise disposed in parallel. The wires are extended to the
intended weld zone of plates 1 and 2 through a power supply
nozzle 10, and a wire feed roll 12 driven by a motor 11 is
provided between power supply nozzle 10 and feed rolls 9 for
carrying out the unwinding operation. The outer peripheral
surface of wire feed roll 12 is disposed in contacting engagement
with a smooth surface of a pressure roll 13 as shown in Fig. 5
Parallel welding wires 7 and 8, which are spaced
apart a distance of less than about 2mm~ are so disposed that
the centerline (dotted line in Fig. 4) between them substantially
intersects with the line of intersection between vertical steel
plate 1 and horizontal steel plate 2, with the end tips of the
power supply nozzle 10 being spaced from such line of inter-
section by about 15 to 25mm (See Fig. 4).
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A drive unit 20 ls provided for moving feed rolls 9,
nozzle 10, motor 11 and hence feed roll 12 parallel to and along
the llne of ln~ersection defined between vertlcal steel plate 1
and horizontal steel plate 2. Such a unlt ls designed to move
nozzle 10 at a constant speed along the aforedescribed line of
intersectlon.
Pressure roll 13 ls mounted for free rotation about
its axis and is rotated solely by the rotation of wire feed
roll 12 in rolling contact therewith.
Parallel grooves 15 and 16 are disposed in theoouter
peripheral surface of wire feed roll 12, which roll is normally -~
rotated at 30 to 80 rpm. Each parallel groove 15, 16 comprises
a narrow guide groove 17 having a cross-sect~onal dimension
substantially equal to the dlameter of the welding wire, and a
guide groove 18 wider in cross~section than groove 17 as shown
in Fig. 5. The narrow and wider guide grooves of groove 15 are
disposed oppositely of the wider and narrow guide grooves of
groove 16, respectively, so that the narrow and wider guide
grooves are positioned alternately, as shown. At least one
narrow guide groove 17 and one wider guide groove 18, having
their centerlines coincident, open into one another for each
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parallel groove 15 and 16, although more than one narrow
and one wider groove for each parallel groove may be
provided without departing from the invention.
The width of -the narrow guide groove 17 in each of
the grooves 15 and 16 is determined by each diameter of
welding wires 7 and 8 to be fed, and the length of each
guide groove 17 is determined by each feed time desired
for welding wires 7 and 8.
Welding wires 7 and 8 are fed by their length cor-
responding to the length of narrow guide groove 17 by
the frictional force generated between narrow guide
groove 17 and pressure roll 13, but -they are not fed in
wide guide groove 18 because no frictional force is gen-
erated therein.
The positive side of a welding power unit 19 with a
DC constant voltage characteristic is connected to
power supply nozzle 10, and the negative side is connect-
ed to horizontal plate 2, as in the normal manner.
As mentioned above, the welding operation carried
out with the present apparatus is performed alternately
by igniting one welding wire during it feeding condition
forimelting same by the arc in the customary manner, and
extinguishing the other welding wire which is in the stop-
ped condition for feeding.
The method which is carried out by using such appara-
tus will be described with reference to Fig. 4.
As shown in Fig. 4, two welding wires 7 and 8 are
alternately fed from the solid power supply nozzle 10 to
the line of intersection between vertical steel plate 1
and horizontal s-teel plate 2, although this is not the
simple
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alternate feed of two welding wires, bu-t is improved
further in the feed conditions -thereof.
In the present invention, the respective welding
wires for the vertical and horizontal steel plates are
of different diameters so as to render the welding cur-
rents thereby produced different, and/or they are fed
at different intervals. In such case, the welding
wire for the vertical steel plate is of a smaller dia-
meter (therefore, the narrow guide groove is accordingly
more narrow), to lower the welding current, and/or -the
feed time of the welding wire for the vertical steel
plate is made shorter (-therefore, the narrow guidegroove is
shorter in length), to obtain a favorable weld bead.
Shown below is a comparison between the embodiment
of the present invention and the prlor art. ~ -
The 12mm thick sample steel pla-tes shown in the
following Table l coated with a 20,~ thick wash primer,
and -they were butted together in a T-shape;as shown in
Figs. 3 and 4 to be used as the test pieces for welding.
Table l: Chemical composition of sample steel plate~
_ _C Si Mn P S _
0.15 0.02 0.4 7! 0.021 0.020
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For welding, the submerged arc welding and the car-
bon dioxide gas arc welding techniques were employed, and
the chemical composition of the flux for submerged arc
welding are respectively shown in Table 2 and Table 3.
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Table 2: Chemical composition of welding wires
C Si Mn Ti
C2 gas are welding 0.08 0.73 1.42 0.17
S merged arc welding 0.12 0.01 1.43
Table 3: Chemical composition of flux for submerged
arc welding
SiO2 CaO MgO CaF2MnO 2 3TiO2
40 20 20 6 6 4 4
'
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The carbon dioxide gas as shielding gas is for
welding, and the flow rate is 25 / min.
Seven types of driving wire feed rolls (outer dia-
meter 32mm) were prepared as shown in Table 4. The A of
Table 4 shows the wire feed roll used as the prior art,
and the remainder is for the welding apparatus with the
feed roll according to the present invention.
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Table ~: Wire feed rolls
No. Number of Diameter of welding welding wire feed
grooves wire used (mm) ~ time ratio
in the For For For For
roll horizontal ver-tical horizontal vertical
_ plate plateplate plate
A 1 1.6 - 1 0
B 2 1.6 1.6 1 1/
C 2 1.6 1.~ 2
D 2 1.6 1.6 3
E 2 1.6 1.2 2
F 2 1.6 1.2 2
G 2 1.6 1.2 3
_ .
The speed of the feed rolls was set to 50 rpm.
Table 5 shows the welding conditions and results
for and by the horizontal fillet welding of the above- -
mentioned welding test pieces.
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Table 5; Embodiment (welding conditions and results~
Test Welding Wire Wire diameter Wire feed time Welding current
No. method feed used (mm) ratio (amp) **
* roil For For For For For -r4For
(table hori- ver- hori- ver- hori- ver-
4) zontal 6ical zontal tical zontal tical
plate plate plate plate plate plate
l. SAW A 1.6 ~ 1 0 300
2 C02 A 1.6 - 1 0 1~ _
3 " B 1.61.6 1 1 " 300
4 " f;C 1.61.6 2 1 " "
11 D 1.61.6 3 l " "
6 ~' E 1.61~6 l 1 " 170
7 " F 1.61.2 2 l " "
S ~ G 1.6102 3 t l~
9 SAW F 1.61.2 2 1 " " ~-~
~ G 1~6l.2 3
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W,elding Results Remark
Bead _ _ _ _ s ~:~
Appearance Pits Blowholes _ _ _
N=rmal_Generated Generated _ Prior Art
NormalGenerated Generated
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Und~rcut N~t Not , Weld_ Method
caused Qenerated Qenerated!~, ing by the
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wire present
Normal ~ .-~ alter- inven-
nate tion
Good _ " .. " - feed : ~:
~ormal ll ll ~: :
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Good . - "- . ll
Good ll _ ~ ~ : :
Good . . ~ : .
Good . ll . ~ '.
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* C02: Carbon d~ox~de gas arc welding
SAW: Submerged arc welding
** Arc voltage: 30V for 300 amp
26V for 170 amp
*** Welding speed: 70cm.min.
As can be seen from the above Table, according to the
prior processes in which the steel plate coated with a wash primer
is used, the pits are observed on the surface of the weld heads.
According to the method of the present invention on the other
hand, no pits are observed on the weld bead surface, though
some blowholes are generated.
It was also found that with the wire feed conditions
of the present invention, to obtain good bead appearance free
from the generation of an undercut, it was necessary to make
the wire diameter for the ve~tical steel plate side smaller
than that for the horizontal steel plate side and/or to make
the wire feed time for the vertical steel plate side smaller
than that for the horiæontal steel plate side.
Thus, in the horizontal fillet welding of the steel
plate coated with an anti-rust paint, the prior art renders the
welding difficult to automate because of the generatlon of
blowholes. However, according to the present invention generation
of blowholes is avoided, and while one welding wire is ignited,
the other welding wire which is extinguished is positioned apart
from the welding zone 90 that it is unnecessary to insulate these -
two welding wires from each other. Therefore, the horizontal
fillet welding technique is capable of being automated in
accordance with the invention.
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Furthermore, the method according to the present
invention can be used as a preceding head with the conven-
tional method used as a following head to produce the same
effect, and it can be applied not only to steel plates but
to other steel materials as well.
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