FIELD OF INVENTION
The present invention generally relates to a gas shielded arc welding
processes as gas metal arc welding (GMAW) and gas tungsten arc welding
(GTAW) process. More particularly, the invention relates to a novel narrow
groove torch design used for gas shielded arc welding processes as gas metal
arc welding (GMAW) and gas tungsten arc welding (GTAW) process, to
accommodate narrow weld groove design having groove width less than 10mm
for thick wall section of thickness beyond 25mm.
BACKGROUND OF THE INVENTION
One of the major limitations of using narrow groove design for thick sections
in case of gas shielded arc welding processes as gas metal arc welding
(GMAW) and gas tungsten arc welding (GTAW) process is non- availability of
narrow torch nozzle. In this context, plethora of research has been carried out
in the past. However, for the existing groove torches used for narrow groove
gas shielded arc welding of thick walled butt-welded pipe, entering in a groove
less than 10mm groove width is not possible.
For Example, in the United States Patent numbered US4460659 and titled
“Narrow groove gas shielding and related method” is discussed a shielding
gas supply tube for delivering shielding gas to a welding arc at the bottom of a
narrow groove includes at least one substantially hollow, elongated planar
tube having a gas supply end and a gas discharge end; a pair of gas
passageways within the tube, isolated from each other, extending between the
supply end and the discharge end, and a pair of gas supply fittings at the
supply end communicating separately with the pair of gas passageways.
Further, in the United States Patent numbered US4298783 titled “Deep
narrow groove tungsten inert gas shielded welding process” is discussed a
method of applying a gas shielded tungsten arc welding process in a deep,

narrow groove joint wherein the shield gas is directed to the weld puddle
through an elongated gas nozzle which surrounds a substantial length of the
welding electrode and is sized to extend into the groove. The improvement
including incrementally increasing the width (20) of the nozzle to correspond
to increases in the width of the groove at preselected increases in the width of
the groove as the nozzle is withdrawn from the groove during successive weld
passes. The preselected elevations and nozzle widths are chosen so that the
desired gas shield area does not substantially exceed 1.25 times the nozzle
width.
Furthermore, the United States Patent numbered US4309590 and titled
“Narrow groove welding torch” discusses a narrow groove welding torch
having an internally insulated metallic housing and a rectangular cross
section with cooling ducts and shielding gas ducts disposed within the
housing.
Moreover, the European Patent Application numbered EP2929973 and titled
“Method for narrow-groove gas-shielded arc welding” discusses a method for
gas-shielded arc welding to join thick steel materials having a sheet thickness
of 22 mm or more by narrow-groove multilayer welding, a bottom portion
groove angle being 10° or less, and a bottom portion groove gap being 7-15
mm, includes using two passes or more for initial layer welding, distributing
the passes over both sides of the bottom portion groove gap, and controlling a
feed angle of a weld wire fed from a power supply tip of a welding torch end to
be 5-15° with respect to a perpendicular line so as to set a depth of fusion at a
bottom portion of the thick steel materials to be 1.5 mm or more. Even when
using low-cost groove formation by gas cutting, plasma cutting, or the like,
defects such as high-temperature cracks and lack of fusion can effectively be
prevented without treating the groove face.
Additionally, another United States Patent numbered US4495401 and titled
“Torch for gas-shield arc welding in deep narrow groove” discusses a torch for

gas-shielded arc welding in a deep narrow groove comprises a current contact
torch bit with an electrode and a nozzle for supplying the shielding gas to the
welding zone, which communicates with a gas-feeding tube and is provided
with at least one row of horizontally arranged holes. The nozzle is a closed
chamber made as a symmetrical wedge whose sharp edge faces the electrode
and is in one plane with the axis thereof. The side walls and bottom of the
chamber feature at least one additional row of holes whose axes lie in one
plane approximately perpendicular to the walls of the groove. The torch is
designed primarily for welding of very thick work pieces.
Thus, in view of the foregoing, the skilled person in the art would appreciate
that there remains a need to develop a new torch design configured to
accommodate the groove width of less than 10mm. There is a need for a
narrow and deep groove torch, designed in such a way so as to be used in
GMAW and GTAW process in welding of thick wall section of various ferrous
and non-ferrous materials.
OBJECTS OF THE INVENTION
An object of the invention is to overcome the aforementioned and other
drawbacks existing in prior art systems and methods.
It is therefore the object of the invention to develop a narrow torch nozzle to
accommodate narrow groove width having less than 10mm.
Still another object of the invention is to improve the weld bead through
analysis of fluid flow behavior.
Yet another object of the invention is to develop a narrow torch nozzle
configured to weld thick-walled butt-welded pipe of thickness beyond 25mm.
Still further object of the invention is to develop a narrow torch nozzle for
facilitating welding using single pass for each layer of welding.

These and other objects and advantages of the present invention will be
apparent to those skilled in the art after a consideration of the following
detailed description taken in conjunction with the accompanying drawings in
which a preferred form of the present invention is illustrated.
SUMMARY OF THE INVENTION:
The present application discloses a novel narrow groove torch for narrow
groove gas shielded are welding of thick walled butt-welded pipe. The narrow
groove torch comprises a narrowed groove nozzle made as a symmetrical
wedge having an extended narrowed taper-curve nozzle edge for feeding the
shielding gas to the weldment area through an electrode. Further, the
narrowed taper-curve nozzle edge is configured to enter the narrow and deep
groove of the thick-walled butt welded pipe secured to a chuck by one or more
clamping jaws for welding of one or more layers of the thick-walled butt
welded pipe.
The above and additional advantages of the present invention will become
apparent to those skilled in the art from a reading of the following detailed
description when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The drawings refer to embodiments of the invention in which:
Figure 1A illustrates the conventional torch design used in gas shielded
welding process.
Figure 1B illustrates the cutaway of conventional torch design used in gas
shielded welding process.
Figure 2 illustrates the welding machine with gas shielded conventional torch.

Figure 3 illustrates the novel narrow groove torch design used in gas shielded
welding process.
Figure 4 illustrates the welding machine with novel gas shielded narrow
groove torch.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Although the disclosure hereof is detailed and exact to enable those skilled in
the art to practice the invention, the physical embodiments herein disclosed
merely exemplify the invention which may be embodied in other specific
structure. While the preferred embodiment has been described, the details
may be changed without departing from the invention, which is defined by the
claims.
It will be apparent, however, to one of ordinary skill in the art that the present
invention may be practiced without specific details of the well known
components and techniques. In other instances, well known components or
methods have not been described in detail but rather in Figures in order to
avoid unnecessarily obscuring the present invention. Further specific numeric
references should not be interpreted as a literal sequential order. Thus, the
specific details set forth are merely exemplary. The specific details may be
varied from and still be contemplated to be within the scope of the present
invention. The features discussed in an embodiment may be implemented in
another embodiment.
Moreover, occasional references to the conventional torch for narrow groove
gas shielded arc welding of thick walled butt-welded pipe are made in order to
better distinguish the present inventive disclosure discussed later in greater
detail. Few of the ancillary details pertaining to the present invention are well-

known in the art, and therefore, are described herein only in the detail
required to fully disclose the present invention.
Improving upon the conventional techniques discussed at length above
(background), in the present disclosure the inventive design of the narrow
groove torch in Figs. 3-4 clearly makes the proposed narrow groove torch as
disclosed in the present application advantageous over the existing arts as
would also become clearer to the knowledgeable in the art with the particulars
of the aforesaid techniques being described below in greater detail.
Turning now to Figures, the conventional torch nozzle [1] design used in gas
shielded welding process is shown in Figure 1B. The cutaway of the
conventional torch nozzle is shown in Figure 1A. Inside the torch nozzle [1] a
contact tip [2] made of copper is firmly secured by thread means and
connected to the positive pole of the arc welding power source through an
insulated copper cable to transfer electric power to the fusible welding
electrode [3] and direct the electrode [3] to the weldment area. The shielding
gas diffuser [4] drives the gas evenly to the weldment area and protects the
weld. Shielding gases are essential for gas metal arc welding to guard the
weldment area from interference of other atmospheric gases such as nitrogen,
oxygen, which results in fusion defects, porosity and metal embrittlement
because of contact of nitrogen, oxygen with the electrode [3] or the welding
arc, or the molten welding pool.
Further, Figure 2 illustrates the welding machine with conventional gas
shielded torch. The welding machine consists of lathe chuck [5] rotated by an
electric motor. The steel pipes [6] to be joined together by welding are fixed to
the chuck by clamping jaws [7]. The entire set-up is mounted on a bed [8] to
provide rigid mechanical support. The butted steel pipes [6] are made to rotate
to enable uniform welding by the welding torch [9] comprising the
conventional nozzle [1] and welding electrode [3]. The welding electrode [3] is
fed continuously during the entire welding operation. Thus the V-type groove

[10] of the butted steel pipes [6] is welded together. Depending upon the wall
thickness of the pipe the number of welding layers is determined. For
instance, if two welding layers are required to complete the butt-welding
process, after layer one was welded, i.e. after one complete 360 degree
rotation by the chuck [5], the torch [9] lifts up to pre-set position to start a
new layer of welding. The height of the uplift of the torch [9] is defined the
wall thickness of the steel pipes [6] and the number of welding layers. The
conventional torch nozzle [1] will not be able enter in high wall thickness
pipes V- groove configuration as the V-groove [10] will be deep and narrow
and normally have a 6° to 8° inclined angle. The problem associated in
welding in deep groove configuration with conventional nozzle [1] is that the
first layer of welding will not fuse the two pipes butted together. As a result
there will be an un-welded ring inside the pipe, which will lead to poor
strength at the joint and may cause serious problem during flow of high
pressure fluids.
Furthermore, for use in narrow and deep groove configuration a special type
of narrow groove nozzle is designed as shown in Figure 3. The narrowed
groove nozzle [11] with a size (width) less than 10 mm is designed and used
for joining butted steel pipes [6] welding of high wall thicknesses using gas
shielded arc welding process. The narrowed groove nozzle [11] has a taper-
curve nozzle edge [12] as shown. The main drawback in design of such special
narrowed groove nozzle [11] is that the disturbance and inconsistency in
shielding gas flow to the weldment area. The shielding gas flow behavior is
controlled by analyzing the flow behavior in the nozzle. This special narrowed
groove nozzle [11] provides greater shielding gas flow even with smaller nozzle
volume as compared to conventional nozzle [1], which is sufficient for high
welding current applications.
Figure 4 shows the welding machine fitted with narrowed groove nozzle [11]
performing welding in a narrow and deep V-grooved [10] steel pipes [6] butted
together. This butt welding will have a good quality welding inside the pipe

and this will ensure the pipe joint is strong enough to handle high pressure
fluid flow through it. Even though the narrowed groove nozzle [11] will not
have any effect during third or fourth layers of welding to maintain continuity
of welding process, the same nozzle can be used for welding all layers of the
process. The length of the V-groove determines the angle of inclination and
size of the taper-curve nozzle edge [12] and can be standardized for a set of
pipes having similar range of wall thickness.
In an embodiment, a unique analytical model has been developed by using
fluid flow equations. This model helps to predict the flow behavior as laminar
or turbulence during welding. Due to narrow nozzle, in general the flow
behavior changed frequently during welding. By using this model, the realistic
fluid flow behavior has been derived. This type of model is first time used for
designing of narrow torch nozzle.
Analytical estimation of heat flow analysis in GMAW torch nozzle is discussed
below:
The purpose of heat flow study on torch nozzle in GMAW is to find out the
heat accumulation amounting to melting of contact tip does not occur.
Moreover, studies on heat flow analysis may provide wider opportunity to
design the different GMAW torch nozzle for welding of various plate
thicknesses and groove design as well as positional welding. For estimation of
total heat transfer on torch nozzle (QT), the following assumptions has been
considered conceptually is shown clearly in Fig. 5.
• The torch nozzle gains the heat from the welding arc (QRA) and contact
tip (QRC) through radiation. It is often found that, some of the heat loses
are also taken away from the torch nozzle due to radiation (QRN),
natural convective cooling by surrounding air (QCN) and forced
convective cooling by shielding gas (QCF). These phenomenon's are also

considered for total heat flow analysis of the torch nozzle. Thus, the
total heat transferred (QT) in the torch nozzle is estimated as follows.

• Initial temperature of the nozzle (TNozzie) is taken as 300° K.
• The temperature on the surface of the arc cavern (TM-C) generally lies in
the range of 5000 to 6000° K. In this study TArc considered as 6000° K.
• All incident heat radiations are assumed to reach the nozzle.
• The cross sectional area of the torch nozzle is circular.

Fig. 5: Schematic diagram showing stages of heat transfer and conceptual
consideration in GMAW torch nozzle.
Estimation of Radiation Heat Gain by Torch Nozzle Through Welding Arc
(QRA)
Heat generated at the surface of the arc cavern transferred by radiation (QRA)
to the surface of the torch nozzle was estimated as follows.


Here, o is Stefan-Boltzmann constant (5.67xl0~8 W/m2K4). The surface area of
the arc column (As, m2) has been calculated by using following relation. The
shape of the arc assumed as a frustum of cone as shown schematically in Fig.
6.

For AWS:5.18: E70S-6 filler wire of 1.2mm diameter under argon gas
shielding at a given gas flow rate and electrode extension of 151pm and 15mm
respectively, the arc root diameter (DR), projected arc diameter (Dp) and arc
length (La) under different GMAW parameters (Globular and Spray transfers
range) have been estimated by following empirical relation reported earlier.
DR{135A)= 9.02-0.166V
"-(4)
^(230^=7-51-0.1367
--CO
Dp(amA) = -im5 + uxar
"(6)
DpizaajQ = -7.705+1.297
"(7)
La(asa=-S.39 +0.536V
"(8)
"(9)
The length of lateral surface of the arc column (S) is estimated as follows.



Fig. 6: Schematic diagram of arc shape
The view factor (F) for QRA is estimated based on the geometric configuration
of filler wire and torch nozzle as shown in Fig. 7 and the expression is given
below.
R1
f =
{Rz + L2)
" "(11)
Where, R and L are axial distance and length from radiation source
respectively.

Fig. 7: Schematic diagram showing the geometric factors involved in
estimation of view factor for QRA
Estimation of Radiation Heat Gain by Torch Nozzle Through Contact Tip
(QRC)

The contact tip develops more heat than in comparison to the torch nozzle
because it is near to the welding arc in comparison to the torch nozzle. The
heat gained from the arc to contact tip by radiation (QAC) is also shown in Fig.
5. In addition, resistance heating of contact tip due to energy input from the
power source also plays the major role for enhancement of heat generation in
the contact tip. Because of more heat generation in the contact tip, it is often
found that in continuous operation in GMA welding, the contact tip failed
with respect to enlargement of hole diameter and melting frequently. Thus, it
is very much important to study the heat transfer mechanism in the contact
tip. The heat generated at the surface of the arc transferred by radiation to
the contact tip (QAC) and heat gained by resistance heating (QIP) was estimated
as follows.

Where, I and RH are the welding current and resistance heating of contact tip
respectively. The contact tip temperature (TCTip) is taken as 673º K. Thus, the
total heat developed (QTC) in the contact tip is estimated as follows.

In this case the view factor (FC) is estimated based on electrode stick out (LS)
and outer radius of contact tip (RC) as shown in Fig. 8 and expression is given
below.



Fig. 8: Schematic diagram showing the geometric factors involved in
estimation of view factor for QAC
The heat generated at the surface of the contact tip transferred by radiation
(QRC) to the surface of the torch nozzle was estimated as follows.

The surface area of the contact tip (AC, m2) has been calculated by using
following relation [refs]. The shape of the contact tip is assumed as hollow
cylinder as shown in Fig. 9.

Where, the RC and rC are the outer and inner radius of contact tip
respectively.

Fig. 9: Schematic diagram of contact tip shape

Radiation Heat Loss from the Torch Nozzle (QRN)
Radiation heat loss from the torch nozzle (QRN) has been estimated as follows.
In this case, the view factor (F) is not considered because it is assumed that
the all the radiated heat loss going to the atmosphere.

Here, ε is emissivity of argon plasma taken as 0.012, ANozzle is nozzle area
exposed to radiation by arc heating (m2). The ANozzle was estimated as follows:

Where, D and Ln are diameter and length of the nozzle respectively.
Natural Convention Heat Loss from the Nozzle (QCN)
The nozzle loosed some of the heat due to atmosphere by natural convection
(QCN). The QCN was estimated as follows.

Where, TAir is temperature of the atmosphere assumed as 300⁰ K. The
convective heat transfer coefficient h can be estimated as follows.

In case of natural convection, the Nusselt number (Nu) can be estimated as
follows.


The Rayleigh number (Ry) and Prandtl number (Pr) were estimated by
following expressions.

Where, g is acceleration due to gravity (9.8 m/s2), β and D are coefficient of
thermal expansion and diameter of the nozzle respectively. The α and ν
considered as 56.7 x10 -6 m2/s and 38.79 x10 -6 m2/s respectively.
Forced Convection Heat Loss from the Nozzle (QCF)
In addition to the natural convection heat loss in the nozzle by atmospheric
air, the nozzle also loosed some of the heat due to incoming shielding gas by
forced convection heat transfer (QCF). The QCF was estimated as follows.

Where, TGas is temperature of shielding gas and h is convective heat transfer
coefficient. The h can be estimated as follows.


Where, D is the diameter of the nozzle and K is thermal conductivity of copper
was taken as 401 J/s/m/K. In case of forced convection, the Nusselt number
(Nu) can be estimated as follows.

The Prandtl number (Pr) and Renolds number (Re) are estimated as follows.

Where, Cp, Kargon, ν and μ are specific heat capacity (kJ/kg K), thermal
conductivity (W/m K), kinematic (m2/s) and dynamic (Ns/m3) viscosity of
argon gas respectively.
The foregoing is considered as illustrative only of the principles of the
invention. Furthermore, since numerous modifications and changes will
readily occur to those skilled in the art, it is not desired to limit the invention
to the exact construction and operation shown and described. While the
preferred embodiment has been described, the details may be changed
without departing from the invention, which is defined by the claims.

We Claim:
1. A novel narrow groove torch for narrow groove gas shielded arc welding
of thick walled butt-welded pipe (6), the narrow groove torch
comprising:
a narrowed groove nozzle (11) made as a symmetrical wedge
having an extended narrowed taper-curve nozzle edge (12)
for feeding the shielding gas to the weldment area through
an electrode (3), said narrowed taper-curve nozzle edge (12)
further configured to enter the narrow and deep groove (10)
of the thick-walled butt welded pipe (6) secured to a chuck
(5) by one or more clamping jaws (7) for welding of one or
more layers of the thick-walled butt welded pipe (6).
2. The narrow groove torch as claimed in claim 1, wherein the taper-curve
nozzle edge (12) configured to enter the narrow and deep groove (10)
which has a width less than 10 mm.
3. The narrow groove torch as claimed in claim 1, wherein thickness of the
thick-walled butt welded pipe (6) is about and over 25 mm.
4. The narrow groove torch as claimed in claim 1, wherein the narrow and
deep groove (10) is configured as a V-groove inclined at an angle
between 6°-8°.
5. The narrow groove torch as claimed in claim 1, wherein the welding of
one or more layers of the thick-walled butt welded pipe (6) is based on
thickness of the thick-walled butt welded pipe (6).

6. The narrow groove torch as claimed in claim 1 and 3, wherein length of
the V-groove determines angle of inclination of the taper-curve nozzle
edge (12) and width of the taper-curve nozzle edge (12).
7. The narrow groove torch as claimed in claim 1, wherein the narrowed
groove nozzle (11) is further configured to remove disturbance and
inconsistency in the shielding gas flowing to the weldment area by
analyzing the shielding gas behaviour.