FIELD OF THE INVENTION
The invention relates generally to submerged arc welding, and in particular to a
process of narrow gap submerged arc welding for boiler drum suspension rod
butt joint.
BACKGROUND OF THE INVENTION
Submerged Arc Welding (SAW) involves formation of an arc between a
continuously fed bare wire electrode and the work piece. The process uses a flux
to protect the molten pool and form the slag, and to add alloying elements to the
weld pool. Flux is used as shielding. Prior to welding, a flux is covered on the arc
zone in the work piece surface. The arc moves along the joint line and as it does
so, unused flux is recycled via a hopper. Remaining fused slag layers can be
easily removed after welding. As the arc is completely covered by the flux, the
weld area is also not visible during welding. The welding is spatter free and there
is no need for fume extraction.
As the operator cannot view the weld-pool, greater reliance requires to be placed
on setting of welding parameters.
Narrow gap SAW is a process variant, which utilizes two or three bead per layer
deposition technique.
Narrow gap arc welding is particularly suitable for welding of thick-section
material.
Narrow gap submerged arc welding (SAW) uses different techniques for
example, tandem or multi-wire technique. However the known techniques used
for narrow gap welding involve either high cost or operational criticality or both.
In SAW for narrow gap welding, the following features of the welding heads are
needed, which is costly and need precision handling:
a) Massive frame for rigidity, current transfer and heat dissipation.
b) Controlled torch angle drives for programmable precision torch
placement and smooth transitions from pass to pass.
c) Controlled X and Z slides for precise, smooth height and cross-seam
(tracking) control.
d) Redundant, off-set wire straightening to ensure wire is straight for
consistent and accurate placement.
US patent No 4,442,334 dt April 10 1984, discloses a device for feeding the
welding wire for submerged arc welding for narrow gap joint.
Indian Patent No. 216941 Date: Dt.28-Mar-2008, entitled "An improved torch
assembly for narrow gap welding using single and tandem wire techniques in
submerged arc welding", describes an improved torch assembly for feeding the
welding wire for narrow gap submerged arc welding process.
In conventional SAW process the heat energy is distributed in such a way that
only 20-25% of the heat energy is used for melting the filler wire and the rest is
utilized in melting the flux, super heating the molten weld pool and melting the
parent plate. In this high dilution process twice as much plate are being melted
as wire, which is undesirable.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a process for narrow
gap submerged arc welding for drum suspension rod butt joint.
Another object of the invention is to propose a process for narrow gap
submerged arc welding for drum suspension rod butt joint, which eliminates
generation of excess arc energy leading to deformation of micro-structure,
shrinkage and distortion of the main plate.
Yet another object of the present invention is to a process for narrow gap
submerged arc welding for drum suspension rod butt joint, which reduces
number of passes, increases productivity at least by 50% and achieve improved
mechanical properties.
A further object of the present invention is to a process for narrow gap
submerged arc welding for drum suspension rod butt joint, which enables
savings of upto 70% in weld metal requirement compared to conventional
processes.
SUMMARY OF THE INVENTION
According to the invention, the submerged arc process for narrow gap welding
employs substantially parallel-sided edge preparation. The included angle for
joint is maintained in the range of 2-4 deg. The width of the joint at the root is
selected within 18~25 mm depending upon the thickness of the material welded.
Thus, this process enables savings of upto 70% in weld metal requirement.
The narrow-gap submerged arc welding process of the invention adapts a
narrow torch interfaced with a known wire feeder having means for controlling
the wire feed rate. The wire in the contact nozzles are arranged perpendicular to
the welding direction.
In the invented process, a low heat input energy is utilized in the arc cavity. The
low heat input energy is used efficiently for melting the wire.
A low heat energy inputted in a narrow gap, increases transfer efficiency. This
results in a highest usable melting rate for a given arc energy and prior art
disadvantages namely, unwanted heat causing heavy penetration, unfavorable
micro structure formation, high shrinkage and distortion of the main plate, are
eliminated.
This invented process increases productivity rate by 50% and better mechanical
properties are achieved over conventional submerged arc welding process.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING:
Fig. l: shows a schematic of narrow gap submerged arc welding technique for
butt welding of drum suspension rod fabrication.
The invention now will be described in detail in an exemplary embodiment as
depicted in the accompanying drawings. There can however be other
embodiments of the same invention, all of which are deemed covered by this
description.
DETAILED DESCRIPTION OF THE INVENTION
Figure-1 shows a wire feeding device with a control means, and a narrow gap
torch, attached to a conventional submerged arc welding machine. In the
present invention, the main wire is fed through a feeder assembly (2) with an
improved narrow gap torch (3). The wire is fed using the single feeder with a
narrow gap nozzle (4). Narrow gap nozzle (4) draws power from a single power
source (5). A single weld pool is created in which the required weld chemistry is
obtained from the use of one wire. Common arc pool gives the required
microstructure of the weld metal and the weld joint attains the required
hardness.
Not limiting the scope of the invention, the present invention can be applied for
welding in narrow grooves having different width. The process, by a narrow gap
torch, can be used for welding of drum suspension rod butt joints of different
sizes. This process can be in a mechanized mode.
This will result in savings in consumables cost, cycle time reduction and higher
productivity with savings of weld materials.
WE CLAIM
1. A process of narrow gap submerged arc welding with an improved narrow
gap torch for boiler drum suspension rod butt joint, comprising the steps
of-
- preparing substantially parallel-sided edges for welding;
- maintaining an included angle for the joint in the range of 2-4°, the width
of the joint at the root being in the range of 18~25 mm;
- feeding one wire with said narrow gap nozzle;
- interfacing the narrow gap torch in a conventional submerged arc welding
machine,
- inputting low heat energy into the narrow groove, wherein the process
enables savings of up to 70% in weld metal requirement.
2. A process of narrow gap submerged arc welding as claimed in claim 1,
wherein a welding torch enabled to input low heat energy into narrow gap
for drum suspension rod butt joint, is adapted.
3. A process of narrow gap submerged arc welding as claimed in claim 1 or
2, wherein the narrow gap nozzles are arranged perpendicular to the
welding direction.
4. A process of narrow gap submerged arc welding as claimed in claim 1,
wherein a single wire with two pass or three passes per layer technique
welding is performed to avoid distortion.
An apparatus for narrow gap submerged arc welding process as claimed
in claims 1 to 4, comprising:
a main wire-feeder assembly (2)
a narrow gap nozzle (3),
a boiler drum suspension rod (4) and
a single power source (5)
An apparatus for the narrow gap submerged arc welding as claimed in
claim 5, wherein the wire fed into the weld is of similar combination.
An apparatus for the narrow gap submerged arc welding as claimed in
claim 5, wherein both the wire feeder (2) and the narrow gap nozzle
draws power from a single power source (5).

This invention relates to a process of narrow gap submerged arc welding with an
improved narrow gap torch for boiler drum suspension rod butt joint, comprising
the steps of -preparing substantially parallel-sided edges for welding; maintaining
an included angle for the joint in the range of 2-4°, the width of the joint at the
root being in the range of 18~25 mm; feeding one wire with said narrow gap
nozzle; interfacing the narrow gap torch in a conventional submerged arc
welding machine, inputting low heat energy into the narrow groove, wherein the
process enables savings of up to 70% in weld metal requirement.