FIELD OF INVENTION
The present invention relates to a device for one sided root pass welding in
grooved joints using a copper backing for root bead formation.
BACKGROUND OF THE INVENTION
One of the most common types of welding found in industry, especially for
industrial fabrication, is the open butt joint weld. Such type of weld is most often
a multipass weld since more than one pass is generally required to fill the joint,
but the first or "root" pass is by far the most difficult to perform and only
experienced certified welders are able to perform good quality root pass welds
having adequate penetration. Precise centering of the welding torch in the joint
and critical control of the welding parameters, i.e. heat and mass balance, are
required to maintain an adequate penetration of the weld pool. The welders
having inadequate skill produce root pass welds with lack of fusion faults or
burn-through defects particularly for the initial/starting portion of the joint.
Tolerances for weld penetration are particularly stringent since stress raising
defects at root dramatically reduce the fatigue life of the joint. In open butt joint,

the weld pool undergoes in a mechanical equilibrium that changes much more
rapidly than temperature and is affected by many other factors, e.g. gap,
alignment, root face, etc. Thus, mechanization/automation of this type of
welding needs proper root pass welding to achieve near uniform weld
penetration.
Welding from one side is employed where access to the second side is difficult or
not possible i.e. in the welding of small diameter pipes. One sided welding of
plates is normally resorted to in an attempt to avoid overhead welding or where
job positioning or plate turning is not possible. Where plates could be turned to
other side, double side welding is easily done, however at increased overall
welding time owing to back chipping and sealing run.
Conventional one sided welding techniques use either metallic copper or ceramic
materials to support the molten pool and give a uniform under bead shape. The
specialized backing materials are quite expensive and not available indigenously.
The use of copper backing for longer joints is very difficult since slight mismatch
affects the proper fit-up of backing. Further, the fixing of long copper backing for
longitudinal welding of small diameter pipes will be very difficult. The improper
fixing of copper backing for long joints will lead to lack of fusion, improper bead
shape and excess penetration weld defects employing Shielded metal arc welding
(SMAW), Gas Tungsten arc welding (GTAW) and Gas metal arc welding (GMAW)

in manual, semiautomatic or mechanized mode of application. It can also lead to
leakage of molten slag/flux in case of mechanized Submerged arc welding
(SAW).
The new machines developed by few foreign companies to weld pipes initially
either from inside or outside followed by welding from other side in
mechanized/automatic mode are very expensive and require elaborate
preparation for the welding of these joints.
US-patent US05676857 relates to a new system for welding sections of pipe
together to form a long, continuous pipeline. A welding bug is mounted on a
guide track which goes around the circumference of the pipe. The welding bug is
provided with a wire feeder, a motor to drive the wire feeder, and driving motor
for driving the bug around the track. One may vary the speed of the bug and the
wire feeder while the bug is continuously driven around the track. The welding
head on the welding bug is powered by a surface-tension-transfer power source.
The initial or root pass is made external of the pipe. However, this is method is
applicable for welding circumferential joints only.
US-patent US05981906: The description of equipment is similar to previous
patent except that in one embodiment there is a dual welding wire feeder for
driving two welding wires simultaneously at the same speed.

US-patent US5030812 (EP 0402648, KR 920006416B, CA 2018701) relates to a
method for one-side root pass welding of a pipe joint comprises the steps of for
forming a ring groove having a V-shaped bottom portion thereof at end faces of
both pipes whose joint is circumferentially welded, attaching a backing material
to a butt portion of the pipes from an internal side of the pipes, running an
automatic welding machine along a guide rail mounted on an outer surface of
the pipes in the circumferential direction thereof, controlling a position of a
welding torch along a seam by means of an arc sensor, and welding root pass
form the outer side of the pipes with a predetermined welding current and at a
welding speed in a high-speed rotating arc welding of the pipes at a
predetermined rotational speed and with a predetermined diameter of rotation.
The limitation of equipment is similar to as given for the previous patent.
US-patent US4733051 (CA 1276245) is concerned with a method and apparatus
for controlling weld pool penetration during root pass welding in open butt joints.
A visual sensor is positioned ahead of the welding torch and in alignment with
the joint for frontly viewing the weld pool. The weld pool image is then
processed through a computer including image processor operatively coupled to
controller, the image processor analyzing the weld pool contour line to derive
there from weld pool penetration depth with a predetermined value, to thereby
provide an information signal representative of weld pool penetration error which

is fed to the controller, the controller issuing control signals in response to the
information signal for controlling welding parameters such as to provide a root
pass weld having a predetermined penetration. This is a very advanced method
and can be advantageously employed for critical applications involving root pass
welding in open butt joints to control the weld penetration.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a device for one
sided root pass welding of grooved joints using a copper backing which
overcomes the limitations of prior art.
Another object of the present invention is to propose a device for one sided root
pass welding of grooved joints using a copper backing which is a simple
apparatus and other settings for root bead formation during root pass welding in
butt joints.
Still another object of the present invention is to propose a device for one sided
root pass welding of grooved joints using a copper backing which enables root
pass welding in manual, semiautomatic or fully mechanized/automated mode.

Yet another object of the present invention is to propose a device for one sided
root pass welding of grooved joints using a copper backing which performs root
pass welding of joints with moveable copper backing and which is more
productive.
A further object of the present invention is to propose a device for one sided root
pass welding of grooved joints using a copper backing which with a suitable joint
preparation and fit-up for root pass welding.
A still further object of the present invention is to propose a device for one sided
root pass welding of grooved joints using a copper backing which ensures
optimum parameters and technique for root pass welding of proper fusion of
edges at the root.
SUMMARY OF THE INVENTION
In welding of grooved joints, the significance of root pass welding is well known.
To produce satisfactory root pass weld, proper settings w.r.t. joint preparation
involving adequate lip thickness, joint included angle, root gap, joint fit-up,
proper selection of welding technique, welding arc parameters etc. are required
to achieve defect free root pass weld. Particularly mechanized/automatic welding
requires adequate attention to achieve good quality root pass welds.

Accordingly, there is provided a device for one sided root pass welding of
longitudinal groove joints using a copper backing in plate formed pipes and
plates.
In a new concept developed by the inventors, a short length of copper backing is
used to support the molten pool and it is moved at the corresponding speed of
welding arc. Optimum welding parameters are selected such that weld pool is
always present to maintain arc over the molten metal to avoid direct arcing on
the copper backing as normally done in the case of forehand welding technique.
The objective of this small copper backing is to minimize the effect of
misalignment of plates by reducing the bearing area of the backing. This concept
has been experimented successfully to achieve good quality root beads in
mechanized CO2 welding.
The proposed method provides the application of a specially developed device
moveable along with a grooved copper backing for root bead formation. The
device can be used in manual, semiautomatic or fully mechanized/automated
mode.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1 - shows schematic sketch of the device according to the invention.

Fig.2 - shows a schematic representation of the edge preparation of the butt
joint in welding of plates and pipe along with grooved copper backing.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Figure-1 shows a moveable device with a water cooled grooved copper backing
developed to carry out one sided root pass welding to facilitate root bead
formation in grooved joints of plates and plate formed pipe. It consists of main
supporting assembly component (7) which also works as water carrier assembly.
The front support assembly (8) containing flat rollers (3) and spring loaded front
guide wheel assembly (5) are attached to the main supporting assembly
component (7). The front support assembly can be adjusted depending upon the
curvature of the pipes to provide required stability through flat rollers to the
device during travel of the device. The front guide wheel (5) is supported by a
spring loaded machined rod assembly (6) to provide the flexible guidance and
stability to the device during welding operation. The rear guide wheel and
support assembly (4) is also attached to this main supporting assembly
component (7). Water cooled copper backing (9) is aligned below the grooved
joint (refer Fig.1). The length of copper backing is 100 mm approximately. It is
supported by spring loaded rods housed in assemblies (11 & 12) and are
mounted on supporting link (10) which is attached to the main support assembly

component (7). The copper backing water inlet & outlet nipples (13 & 14) are
connected to the water carrier assembly through high temperature flexible
hoses. The inlet & outlet nipples (15 & 16) of water carrier assembly are
connected to the main water connecting points.
Figure-2 shows a typical edge preparation for one sided root pass welding in
grooved joints. The plate/pipe ends to be joined are assembled to form a V-
grooved butt joint. The included angle (a) of the joint can be varied between
5½-11° and root gap (Y) is maintained in the range of 7±1 mm to facilitate
insertion of flat machined rod through joint gap. The gap (X) may vary
depending upon the pipe thickness and included angle of the V-groove. Similarly,
the maximum thickness of the joint may vary to a specified limit and accordingly
the length of guide rod (6) can be varied to suit the thickness of the pipe/plate.
The water cooled copper backing (9) is aligned below the grooved joint to
support the molten pool during welding to facilitate root bead formation. In the
case of pipe welding, a curvature in the face of copper backing should be
provided to suit the internal diameter of the pipe for matching. The groove depth
is generally kept between 1.5 to 2 mm and width of the groove in copper
backing can be kept equal to the joint gap plus 1.5 to 2 mm on both sides of the
edges. The lip thickness of the joint can be kept in the range of 1.0 to 2 mm
depending upon the welding process and parameters selected for the welding.

The device has the self -guiding facility in the joint groove and can be moved
with the hand gently to provide incremental movements to facilitate root welding
by manual SWAW, GTAW or semiautomatic GMAW/FCAW. In the case of
mechanized welding, device can be attached to the moving head mounted on
the carriage through a suitable link plate or providing a continuous movement by
connecting the device to metallic link of wire rope to trolley actuated by
motorized drive system. The rear guide wheel can be detached in the case of
mechanized welding. The start-on and run-off plates with required included
angle and having a sufficient length should be provided for starting and ending
the weld in the grooved joints. It is important to ensure that the restart points
are ground properly to ensure proper melting of the starting bead and to avoid
poor bead shape and lack of fusion defects.

WE CLAIM
1. A device for one sided root pass welding in groove joints using a copper
backing comprises:
- a main supporting assembly (7) which also works as water carrier;
- a front support assembly (8) containing a flat rollers (3);
- a spring loaded front guide wheel assembly (5) are being attached to
main supporting assembly (7);
- the front guide assembly is supported by a spring loaded machined rod
(6) to provide the flexible guidance and stability to the device during
welding operation;
- a rear guide wheel and support assembly (4) being attached to main
supporting assembly components (7);
- a water cooled copper backing (9) is aligned below the groove joint;
- a supporting means by spring loaded rods housed in assemblies (11 & 12)
and are mounted on supporting link (10) which is attached to main
support assembly (7);
- a copper backing water inlet and outlet nipples (13 & 14) are connected
to the water carrier assembly through flexible hoses;
- an inlet and outlet nipples (15 &16) of water carrier assembly are
connected to the main water connecting points;

- a provision for attaching a moving head mounted on the carriage through
a suitable link plate or providing a continuous movement by connecting
the device to metallic link of wire rope to trolley actuated by motorized
device/mechanized system.
2. The method for one sided root pass welding in grooved joint using a
copper backing comprising the steps of:
- preparation of edge of both sided of copper plate/pipe in the form of V-
notch;
- the angle of V-notch of joint are varied between 5½-11o;
- the root gap (Y) is maintained in the range of 6 to 8 mm;
- the grove depth in the copper backing is kept between 1 to 3 mm;
- the lip thickness of joint are kept 1.0 to 2.0 mm;
- aligning the water cooled copper backing below the grooved joint to
support the molten pool during welding to facilitate the root bead
formation;
- welding starts after proper preparation of the copper plate/pipe from one
end.
3. The device as claimed in claim l,wherein the device has the self-guiding
facility in the joint groove and can be moved with hand gently to provide

incremental movements to facilitate root welding by manual SMAW, GTAW
or semiautomatic GMAW/FCAW.
4. The method as claimed in claim 2 wherein the length of copper backing is
around 100 mm.

In welding of grooved joints, the significance of root pass welding is well known.
To produce satisfactory root pass weld, proper settings w.r.t. joint preparation
involving adequate lip thickness, joint included angle, root gap, joint fit-up,
proper selection of welding technique, welding arc parameters etc. are required
to achieve defect free root pass weld. Particularly mechanized/automatic welding
requires adequate attention to achieve good quality root pass welds.
Accordingly, there is provided a device for one sided root pass welding of
longitudinal groove joints using a copper backing in plate formed pipes and
plates.
In a new concept developed by the inventors, a short length of copper backing is
used to support the molten pool and it is moved at the corresponding speed of
welding arc. Optimum welding parameters are selected such that weld pool is
always present to maintain arc over the molten metal to avoid direct arcing on
the copper backing as normally done in the case of forehand welding technique.
The objective of this small copper backing is to minimize the effect of
misalignment of plates by reducing the bearing area of the backing. This concept
has been experimented successfully to achieve good quality root beads in
mechanized CO2 welding.
The proposed method provides the application of a specially developed device
moveable along with a grooved copper backing for root bead formation. The
device can be used in manual, semiautomatic or fully mechanized/automated
mode.