FIELD OF INVENTION
The invention relates to an apparatus for and a method of joining heavy wall
thickness plates and pipes employing Tandem Gas Metal Arc Welding [Tandem
GMAW] procedure preceded by a narrow gap joint configuration. The invention
further relates to an improved Narrow Gap Welding Torch suitable for Tandem
GMAW process.
BACKGROUND OF THE INVENTION
The Gas Metal Arc Welding is an arc welding process wherein coalescence is
produced by heating with an electric arc between a consumable electrode wire
and the based metal, or the work. In this process, the consumable electrode is in
the form of a wire which may have a diameter generally between 0.8 mm to 2.0
mm. The wire is continuously fed from a wire reel by means of a wire feeder
through a welding torch which further guides a supplied shielding gas to the
work area in order to prevent oxidation of the hot metal being formed during the
welding. The shielding gas provides an ionized gas electrical characteristics for
the welding arc. It is necessary that the wire be directed to the exact spot at
which the welding is desired. The GMAW process gives a deposition rate up to
6.0 kg/hours, and a welding speed up to 800 mm/min.
Tandem GMAW Is a high performance GMAW process which has been developed
to increase the metal deposition rate and welding speed beyond what is possible
with a single wire GMAW process. In the Tandem GMAW process, at least two
consumable electrode wires are fed through a single torch but both are
electrically isolated and powered by two individual power sources. The two
electric arcs generated from the two wires act to create a common weld-pool,.
This particular feature provides a superior weld-pool dynamics over the single
wire GMAW and other known techniques. The Tandem GMAW process provides
much higher deposition rate than the single wire GMAW process. The higher
deposition rate can be advantageously converted into a higher welding speed or
a higher cross section of the weld seam depending on the requirement.
A Narrow Gap Welding on the other hand, warrants deposition of filler weld
metal within a narrow groove formed between two thick metal plates which are
to be welded. In practice the plate thickness may be 50 mm or more and when
positioned for welding, the gap between the two plates is maintained between 8
to 10 mm. Several Narrow Gap Welding techniques have been developed
employing a single wire GMAW process to achieve a higher productivity.
However, lack of side-wall fusion has been the prime concern among other, in all
these known techniques. Some of the major disadvantages of the single wire
GMAW process are the extremely narrow gap, the necessity of directing the filler
wire to the bottom of the gap in order to lay welding beads progressively one
over the other form alternate sides to develop a herringbone pattern of weld
beads between the two plates; and the extremely high temperature and violent
environment of the welding arc. Accordingly, the Single wire GMAW based
Narrow Gap Welding techniques have not gained wide acceptance or commercial
success except in a few isolated applications.
The two parallel arcs operating in the Tandem GMAW process seems to be a
major solution to the problems residing in the single wire GMAW Narrow Gap
welding. If the two arcs are properly directed to both the side walls, the problem
on the lack of side wall fusion Is moot. This eliminates the major problem that
was plaguing the Narrow Gap Welding with single wire GMAW process. Since
both the side walls are fused simultaneously, each layer is completed In one go.
The higher deposition rate and higher welding speed of the Tandem GMAW
further increase the productivity multifold as compared to the single wire GMAW
based Narrow Gap techniques. The narrow gap joint preparation compared to
the V-groove joint preparation greatly reduces the volume of weld-metal per
joint.
However applying Tandem GMAW for Narrow Gap joint requires a special torch
which should be enabled to work inside the Narrow Groove at higher
temperature, withstanding the two electric arcs operating side by side, electrical
isolation of the two currents flowing through the torch body to the two wires,
electrical and thermal insulation of the torch body from the job i.e., the narrow
groove joint itself.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method of joining heavy
wall thickness plates and pipes employing Tandem Gas Metal Arc Welding
[Tandem GMAW] procedure preceded by a narrow gap joint configuration, which
eliminates the disadvantages of the prior art.
Another object of the invention Is to propose a method of joining heavy wall
thickness plates and pipes employing Tandem Gas Metal Arc Welding [Tandem
GMAW] procedure preceded by a narrow gap joint configuration, which enhances
the welding productivity multifold.
A Still another object of the invention is to propose an apparatus for joining
plates, pipes with higher wall thickness of 40 mm and above, by adapting
Tandem GMAW process preceded by narrow gap joint configuration.
A further object of the invention is to propose an apparatus for joining plates,
pipes with higher wall thickness of 40 mm and above by adapting Tandem
GMAW process preceded by narrow gap joint configuration which improves the
weld quality.
A still further object of the invention is to propose an apparatus for joining
plates, pipes with higher wall thickness of 40 mm and above by adapting
Tandem GMAW process preceded by narrow gap joint preparation, which
includes an innovated narrow-gap welding torch.
SUMMARY OF THE INVENTION
Accordingly, there is provided an integrated apparatus adaptable to Narrow Gap
welding employing Tandem GMAW process for joining heavy wall thickness
plates and pipes. An improved welding torch is developed for implementing the
high performance Tandem GMAW process for welding of Narrow Gap Joints. The
torch body is provided with means for water circulation for keeping the torch
cool during welding. The torch body is further enabled to separately guide the
two consumable electrode wires which create two electric arcs and deposited as
weld metal filing the narrow groove during the process of welding. The Torch
body consists of two separate channels for carrying the current to the respective
wires which are electrically isolated from each other. Both the channels of the
torch body is capable to carry and supply the shielding gases in the front, and
rear side of the weld-pool for protecting the weld-pool from atmospheric
contamination. The torch body is coated with an insulating material to prevent
any electrical arcing with the job during welding. The two contact tips of the
torch are suitably oriented so as to focus the arc on the wall to ensure 100%
side wall fusion. A thin plate type configuration has been adopted for the torch
so as to keep the joint gap small and efficient. The Narrow Gap Welding with
Tandem GMAW process is adaptable for all position welding of plates and pipes
with thickness of 40 mm and above.
According to the invention, the joint gap is reduced to 8 or 10 mm to achieve
higher productivity by reducing the volume of weld metal. The Narrow Gap
Tandem GMAW torch is supplied with two wires for producing two arcs thereby
achieving tandem welding.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 (Schematic) - shows an embodiment of the apparatus according to the
invention.
Figure 2 - shows an improved Narrow Gap welding torch to be used with
Tandem GMAW process according to the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Referring now to the drawings. Wherein like reference numerals designated
identical or corresponding parts throughout the several views.
Figure 1 shows the schematic of an apparatus for Narrow Gap Welding with
Tandem GMA Welding process. In this apparatus, a Narrow Gap Tandem GMAW
torch is adapted. The torch body having two channels (1,2) electrically separated
by an insulator (3). Each channel of the torch body has a provision for receiving
the current (positive polarity) from two separate power source (4,5) and the
current received is transmitted to the respective consumable electrode wires.
The wire is wound individually in two spools (8,9) and fed by two wire feeders
(6,7) into the respective channels (1,2) of the narrow gap torch. The negative
terminal of both the power sources (4,5) are connected to a job (10). A shielding
gas required for protecting the weld pool is supplied from two individual gas
cylinders (11,12) through the respective wire feeders (6,7) into the respective
receptacle (1,2) in the narrow gap Tandem GMAW torch.
As shown in figure -2, the channels (1,2) of the welding torch has provision for
water cooling inlet (13,14), water cooling outlet (15,16) for restricting the torch
body from overheating. Each channel has provision for (18,19) shielding gas
supply and wire feeding. The torch body can be mounted using a frame (17)
provided for that purpose.
The narrow gap tandem GMAW system as a whole and the torch in particular can
be used for welding of heavy thickness plates and pipes in downhand, horizontal,
vertical and overhead positions.
8
WE CLAIM
1. An apparatus for joining heavy wall thickness plates and pipes employing
Tandem gas metal arc welding (TANDEM GMAW) procedure preceded by
a narrow gap joint configuration, the apparatus comprising:
- at least two wire spools (8,9) having consumable electrode wires wound
thereon;
- at least two wire feeders (6,7) receiving the respective wires from the two
spools (8,9) and feeding to a narrow gap Tandem GMA Welding torch;
- at least two separate power sources (4,5) supplying positive-polarity
current to the respective electrode wires, the negative terminals of the
power source (4,5) being connected to the weldable job (10);
- at least two separate sources (11,12) for supply of shielding gas through
the respective wire-feeders (6,7) into the respective channels (1,2) of the
torch;
characterized in that the narrow gap Tandem GMAW torch comprises a
body having two separate channels (1,2) electrically separated by an
insulator (3), the channels (1,2) each having water cooling Inlet (13,14)
and water cooling outlet (15,16) including a provision for (18,19) receiving
of from the wire feeders (6,7) and electrode wires from the respective
wire feeders (6,7) and in that the channels (1,2) are enabled to receive
positive-polarity current through the respective electrode wires.
2. The apparatus as claimed in claim 1, wherein the narrow gap tandem
GMAW torch is mountable on a frame (17) during the welding operation.
3. An apparatus for joining heavy wall thickness plates and pipes employing
Tandem gas metal arc welding (TANDEM GMAW) procedure preceded by
a narrow gap joint configuration as substantially described and illustrated
herein with reference to the accompanying drawings.

An apparatus for joining heavy wall thickness plates and pipes employing
Tandem gas metal arc welding (TANDEM GMAW) procedure preceded by a
narrow gap joint configuration, the apparatus comprising at least two wire spools
(8,9) having consumable electrode wires wound thereon; at least two wire
feeders (6,7) receiving the respective wires from the two spools (8,9) and
feeding to a narrow gap Tandem GMA Welding torch; at least two separate
power sources (4,5) supplying positive-polarity current to the respective
electrode wires, the negative terminals of the power source (4,5) being
connected to the weldable job (10); at least two separate sources (11,12) for
supply of shielding gas through the respective wire-feeders (6,7) into the
respective channels (1,2) of the torch; the narrow gap Tandem GMAW torch
comprises a body having two separate channels (1,2) electrically separated by an
insulator (3), the channels (1,2) each having water cooling inlet (13,14) and
water cooling outlet (15,16) including a provision for (18,19) receiving of from
the wire feeders (6,7) and electrode wires from the respective wire feeders (6,7)
and in that the channels (1,2) are enabled to receive positive-polarity current
through the respective electrode wires.