FIELD OF THE INVENTION
The invention relates to an improved torch for welding in narrow groove joints
using Gas Metal Arc Welding process (GMAW).
BACKGROUND OF THE INVENTION
In order to improve the productivity in thick section material welding, several
techniques are employed. One of the important techniques of interest is the use
of narrower joint grooves. The conventional welding makes use of typical joint
edge preparation indicated in Fig.1. As compared to this, the narrow gap welding
employs near parallel sided edge preparation. The included angle of joint will be
in the range of 1-2 degree as shown in Fig.2. The principal welding processes
normally employed for narrow gap welding are Submerged arc welding (SAW),
Gas Metal arc welding (GMAW), Gas Tungsten arc welding (GTAW) and
Electrogas Welding (EGW). In some countries, narrow gap Submerged arc
welding is preferred because of the easy availability of equipment and the
familiarization with SAW for thick section welding. In some other countries,
narrow gap gas metal arc welding is used to greater extent due to the overall
cleanliness, better quality welding associated with this process and lesser gap
compared to SAW.
The width of the joint at the root is required to be maintained at 10-12 mm
depending upon the thickness of the material and the technique employed with
GMAW process. Accordingly the thickness of the GMAW torch plays an important
role in decreasing the gap of joint at the root i.e. lesser the thickness of torch, it
will better reduce the gap of joint leading to less volume of weld metal.

Narrow gap - Gas metal arc welding (NG-GMAW) differs from the conventional
GMAW process in two ways, for example, in providing a wire feeding mechanism
to ensure reliable sidewall fusion and the capacity of the torch to provide
adequate gas shielding to the arc zone. In all advanced narrow gap GMAW
equipments, the welding torch is placed inside the joint to be welded. There are
many variations in this type. However, one technique, which is most widely
used, is related to bending of the wire in sinusoidal waveform to oscillate the arc
across the joint gap to achieve an adequate sidewall fusion. The other
requirement is to ensure quality weld joints devoid of defects like porous beads,
lack of fusion, lack of penetration, blow holes etc. in weld zone.
Patent WO 98/ 00265 relates in particular to a process titled "Process for Narrow

- Gap welding by the MAG arc welding process" in which the welding device is
conveyed in the welding groove, and consequently at least one fusion wire
electrode guided through a contact tube is delivered with inert gas to the
welding zone at a predetermined wire feed rate. The arc produced between the
wire electrode and the workpiece should be formed alternately with respect to
the two workpiece edges to ensure good welding seam quality, which used to be
achieved by which rotation adjusts at particular welding parameters.
Patent No. JP7116852 discloses a torch for narrow gap MIG welding and welding
method thereof capable of obtaining stable good quality weld zone without
generating welding defects of blowhole, incomplete penetration, etc., in weld
zone. The torch has a typical constitution wherein an oval shaped hole for the
shield gas injection ports for welding is provided for, improving spreading of
shield gas, further a hole of a contact tip of torch is made to oval, by always
setting a weaving direction of a welding wire in the fixed direction, high quality
weld zone is obtained etc., also, the welding wire is weaved in the fixed
direction.

Patent No.JP4158983 describes a torch for narrow gap welding to improve a gas
shielding effect by providing an outside shielding gas hole vertically on the
outside of a torch main body and providing a deflecting means to guide gas
outward on the opposite part of a tip exhaust nozzle thereof. A welding wire is
introduced from a wire introduction port of the torch main body and power is
supplied from a contact chip and an arc is generated at an interval with materials
to be welded to perform welding.
Patent No. EP01953410 discloses a torch for welding a narrow groove gap joint
wherein a welding torch is described comprising a tip with a through slot in
which a welding wire is inserted. Said slot has a end section which diverges from
the main axis A-A and is curved, such that the welding rod extends out of said
end section at a predetermined angle. The tip's axis of rotation is parallel to the
joint's axis of symmetry. The tip can also be translated by a suitable actuating
means so as to alter its distance from the walls of the joint
OBJECTS OF THE INVENTION
It is therefore an object the of invention to propose an improved torch for gas
metal arc welding in a narrow groove joints having means for feeding a waved
wire and thereby providing adequate gas shielding to perform narrow gap gas
metal arc welding (NG-GMAW) without any mechanical rotation of the wire or
wire guide and thus avoiding complicated machining operations and eliminating
disadvantages of prior art.
Another object of the invention is to propose an improved torch for gas metal
arc welding in a narrow groove joints which is capable to operate in grooves
having 10-12 mm, and joint thickness upto 250mm.

Still another object of the invention is to propose an improved torch for gas
metal arc welding in a narrow groove joints which is sleek and light-weighted
and having a simple construction.
A still further object of the invention is to propose an improved torch for gas
metal arc welding in a narrow groove joints which is easily mountable on a wire
feeding means.
A still another object of the invention is to propose an improved torch for gas
metal arc welding in a narrow groove joints which has sufficient rigidity and
stability in carrying out the welding operations.
An yet another object of the invention is to propose an improved torch for gas
metal arc welding in a narrow groove joints which is so configured to allow easy
wrapping of insulating tape over the affected area to avoid any stray arcing
during welding operation.
SUMMARY OF THE INVENTION
Accordingly, there is provided an improved torch for narrow gap - gas metal arc
welding comprising a central tubular member for feeding a wire; an water inlet
tube; a water outlet tube, a gas inlet tube, a first solid block to hold atleast one
contact tip, a plurality of outer flattened tubes for gas shielding and a second
solid block to hold the tubes.
BRIEF DESCRIPTION OF THE ACCOMAPNYING DRAWINGS
Fig-1 A schematic representation of edge preparation for conventional Gas Metal
Arc welding

Fig-2 schematically shows an edged preparation for Narrow Gap Gas Metal Arc welding
according to prior art.
Fig-3 shows schematic sketch of an improved torch for carrying out gas metal arc
welding (GMAW) in narrow groove joints according to the invention.
Fig-4 shows the torch with wire feeding from the spool
Fig-5 shows the bent wire in the torch according to the invention
Fig.6- shows conventional wire feeding
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Fig.1 shows a typical edge preparation employed for one side conventional gas metal
arc welding. The material to be joined is machined to have a J groove edge
preparation. When the two halves of the joints are assembled, it forms a groove with
an included angle of (D) equaling 20°. The bottom of the groove has a radius of 9 mm
(C) thus making a joint of 18 mm gap. The root thickness (B) can vary between 3-5 mm
depending upon the current level employed. The thickness of joint (A) can vary up to
150 to 250 mm. Generally, such edge preparation requires a backing plate being tack
welded on the reverse side to support the molten weld metal created by the welding
arc.
Fig-2 shows a typical edge preparation employed for one side Narrow gap gas metal arc
welding. The material to be joined is machined to have a J groove edge preparation.
When the two halves of the joints are assembled, it forms a groove with an included
angle (D) equaling 1 to 2°. The bottom of the groove has a radius of 6 mm (C) thus
making joint of 12 mm gap. The root thickness (B) can vary between 3-5 mm
depending upon the current level employed. The thickness of joint (A) can vary up to
150 to 250 mm.
As shown in Fig-3 the improved narrow gap torch is attached to a wire feeding means
(not shown) to facilitate smooth travel of a wire in a center of the torch through a
copper tube (1). Two flattened copper tubes (5) are attached to both sides of the
copper tube (1) to provide gas shielding over the welding area. The

central copper tube (1) is attached to a first solid block (7) of copper where a
contact tip is attached. The first solid block (7) is water cooled through an inlet
tube (2) and an outlet tube (3). All the copper tubes (1,2,3,5) are attached to a
second solid copper block (6) on the top. The second solid block (6) is drilled
suitably to house the copper tubes (1,2,3) including the connectors (4) to
provide water-cooling and gas shielding. The overall thickness of the torch is
kept within 7 mm. Apart from primary shielding near the arc, the arc zone
requires secondary shielding to avoid induction of air. It can be insulated easily
by high temperature insulation tape to avoid any arcing during the welding.

WE CLAIM
1. An improved torch for narrow gap gas metal arc welding comprising:
a central tubular copper tube (1) for feeding a wire;
a water inlet tube (2);
a water outlet tube (3);
a plurality of outer flattened copper tubes (5);
a first solid copper block (7) for holding at least one contact tip;
a second solid copper block (6) for holding all the copper tubes (1,2,3,5);
a plurality of connectors (4);
characterised in that,
the narrow gap torch is attached to a wire feeding means for facilitating smooth
travel of an wire in a center of the torch through the said central copper tube (1)
attached to the first solid block (7) when a plurality of said flattened copper
tubes (5) attached to both sides of the said copper tube disposed for gas
shielding over the welding area wherein suitably drilled second solid block houses
the copper tubes (1,2,3) and the connectors (4) for providing water cooling and
gas shielding for avoiding induction of air.
2. An improved torch as claimed in claim 1, wherein the inlet tube (2) and outlet
tube (3) are disposed for water cooling the first solid block (7).

3. An improved torch as claimed in claim 1 to 3, wherein the overall thickness of
the torch is maintained within 7 mm.

ABSTRACT

AN IMPROVED TORCH FOR NARROW GAP GAS METAL ARC WELDING
An improved torch for narrow gap gas metal arc welding consists of a central tubular
copper tube (1) for feeding an wire, a water inlet tube (2) and outlet tube (3) for water
cooling, a first solid copper block (7) for holding at least one contact tip and a second
solid copper block (6) for holding all the copper tubes (1,2,3 and 5) when a plurality of
outer flattened copper tubes (5) are attached to both sides of the copper tube (1) for
providing gas shielding over the welding area. The second solid block (6) houses the
copper tubes (1,2,3) including the connectors (4) for providing water cooling and gas
shielding for avoiding induction of air.