FIELD OF INVENTION ;
The invention relates to a process of submerged are welding with forward and
backward feeding of cold wire addition for butt joint welding applications.
BACKGROUND OF THE INVENTION :
Submerged arc welding with cold wire addition is a technique applied for joining
thick section materials. This technique enables a considerable reduction to the
amount of weld metal required for a given joint. Forward and backward feeding
of cold wire in submerged arc-welding uses a joint gap width in a range of 25 to
45 mm depending upon the thickness of the material to be welded.
In order to improve the productivity in thick section material welding, several
techniques are employed, for example, tandem or multi wire technique, metal
powder addition, long stick out welding etc. One of the important techniques is
the use of forward and backward feeding of cold wires in the joint grooves.
Conventional welding process makes use of a typical joint edge preparation,
wherein the angle for the joint is selected in the range of 30 to 75 deg, as shown
in figure 1. The width of the joint at the root is maintained at about 30 mm
depending upon the thickness of the material welded. This technique results in
saving of up to 60% in cycle time and productivity.
United States Patent 7166818 discloses an electric arc welding apparatus
comprising at least a first consumable electrode and a second consumable
electrode movable in unison along a welding path between the edges of two
adjacent, mutually grounded plates, a first power supply for passing a first
welding current at a first low frequency between the first electrode and the two
plates, a second power supply for passing a second welding current at a second
low frequency between the second electrode and the two plates, where each of
the power supplies includes a three phase voltage input operated at line
frequency, a rectifier to convert the input voltage to a DC voltage link and a high
frequency switching type inverter converting the DC voltage link to a high
frequency AC current, an output rectifier circuit to provide a positive voltage
terminal and a negative voltage terminal, and an output switching network
operated at a given low frequency for directing a pulsating welding current at the
given low frequency from the two terminals across one of the electrodes and the
plates, and a circuit for independently adjusting the given low frequency so the
value of the first low frequency of the first power supply is different from the
second low frequency of the second power supply.
US patent 4,572,936 describes a submerged arc multiple wire welding system in
which only one or two of the welding wires used are over or microalloyed wires.
The other wires are commercially available unalloyed or low-alloyed solid wires.
The process produces a weld metal, which has unexpectedly high toughness
values, and can be performed more economically. This multiple wire welding
system is used in single or multiple-pass welding operations.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose a submerged arc
welding process with forward and backward feeding of cold wire addition for butt
joint welding application.
Another object of the present invention is to propose a submerged arc welding
process with forward and backward feeding of cold wire addition for butt joint
welding application, which is enabled to hardface dissimilar fillers to create a
common weld pool with required chemistry, the code of highest quality welds,
with which considerable manufacturing economics.
A further object of the present invention is to propose a submerged arc welding
process with forward and backward feeding of cold wire addition for butt joint
welding application, which reduces the cycle time and effects substantial savings.
SUMMARY OF THE INVENTION
According to the inventive technique of forward and backward feeding of cold
wire addition in submerged arc welding process essentially is characterized by
the use of two additional wire feeders with a welding torch. No power source is
interfaced with the additional wire feeder. The control system for controlling the
wire feed rate is interfaced with the existing feeder. Along with the main wires,
the cold wire is fed simultaneously on either sides a different feed rate or same
feed rate. The wires in the contact nozzles are tangentially disclosed along the
welding direction. In conventional SAW process the heat energy is distributed in
such way that only 20-25% is used for melting the filler wire, the rest being
utilized in melting the flux, super heating the molten weld pool and melting the
parent plate. The SAW process is a high dilution process with twice as much
plates are being melted as wire. This forward and backward feeding of cold wire
addition in submerged arc welding process is one of the advanced technique
which makes use of the excess energy available in the arc cavity for addition of
filler material in the form of wire. With addition of cold wire, the excess heat
energy is used efficiently for melting the wire. The addition of "cold wire" in the
arc stream can increase the deposition rate. Thus, the addition of cold wire
increases transfer efficiency comparatively with other method. Thus this forward
and backward feeding cold wire addition technique results in 60% increase in
deposition rate and better mechanical properties over conventional
single/Tandem submerged arc welding process.
The present invention is directed to a multiwire system in which a dissimilar wire
combination is fed using a different wire feeders with two nozzles drawing power
from a single power source with parameters of 425 A, 28 V and 0.5 m/min as
welding speed". Thus, a single weld pool is created in which the required weld
chemistry are obtained from the use of two wires of different chemistry. This
results in savings of consumables cost, cycle time reduction and high
productivity.
The invention is enabled to save the cycle time and production time of a single
component. This cold wire feeder system with forward and backward feeding of
cold wire addition technology using a welding torch technique can be extended
to the other butt-welding application using narrow gap submerged arc welding
process.
According to the invention, the wire combination is having flux which is
analytically neutral. The weld metal structure is produced with a high proposition
of acicular/martensetic structure, and the surface proportion thereof is 100
percent. Preferably, a single pass welding is performed to avoid buffering layer.
In order to enhance mechanical properties, a multi layer pass welding can be
done.
This invention allows welding to be carried out in grooves having a width of
different sizes. The cold wire feeders with forward and backward feeding cold
wire addition technology using welding torch can be used for welding of drum
butt joints, valves wedges and seat rings of different sizes. This technique can be
used for both manual as well as mechanized mode. This results savings in
consumables cost, cycle time reduction, energy saving and higher productivity.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Figure 1 shows a conventional weld design
Figure 2 is prospective view of forward and backward feeding of cold wire
addition technique using special torch for single submerged arc welding
technique for butt welding of drum shell
Figure 3 shows the arrangement of the main Dc wire and forward and backward
feeding of Cold wire addition in the butt joint.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention, a wire feeder with control means for forward and
backward feeding of cold wire addition, adapting a welding torch can be fitted to
conventional submerged arc welding machine. By this technique same/different
composition (1) of filler materials weld metal combination can be obtained
effectively. The construction of a main wire feeder (2) and the cold wire feeders
of forward and backward (3) assemblies are shown in figure 2. The
dissimilar/similar wire combination is fed using a three wire feeders with three
nozzles (4) drawing power from a single power source (6) with parameters of
500A, 28V and 0.5 m/min as welding speed. A single weld pool is created in
which the required weld chemistry can be obtained by the use of three wires of
different chemistry. In this technique, to attain the required hardness properties
as well as the required microstructure, the weld metal was created with new
technique of wire feeder in the single submerged arc welding by creating a
common arc pool (5). As shown in figure 3, in the arc cavity, the cold wire fillers
with different/same chemical composition of different alloy wires are fed
simultaneously in a three nozzle configuration, i.e. each one on either side along
with the main wire feeder which creates the common weld pool to give the
desired weld properties.
The invention relates to a process to improve the technology in submerged arc
welding wherein for feeding the wire from wire spools, only single power source
with control system is required for performing the welding process. For adding
two more wires as the same as that of the main wire with same or different
chemistry wire, require a separate wire feeder for performing forward and
backward feeding of cold wire addition technology in submerged arc welding
process.
It is possible to simultaneously feed multi wires with same or different chemistry
in three wire feeders at same feed rate or different feed rate for different current
rating. This new wire feeding with controller and special torch will enhance the
production rate in double when compared to the conventional submerged arc
welding process. A cold wire feeder with special is designed and interfaced with
the available DC wire feeder for coupling the additional wire feeder for feeding
the forward and backward feeding of cold wire in the arc cavity in submerged arc
welding process. With this new wire feeder the cold wire addition can be
provided in both direction of welding. This results in additional weld deposit with
same heat in-put energy available in the arc zone. Additional power source is not
required for this new design of wire feeder and special torch. This new wire
feeder and special torch is interfaced with the existing convention SAW machine
for drum test plate welding. The test results of radiographic test, Ultrasonic test
are found satisfactory as per IBR and ASME Sec IX.
WE CLAIM :
1. A process for submerged arc welding with forward and backward
feeding of cold wire addition for butt welding applications, comprising :
Electrically coupling a plurality of welding wires to a source of electrical
energy, feeding welding wires of different chemistry through at least
three wire feeders, wherein three nozzles of the wire feeders drawing
power from a single power source.
2. A process as claimed in claim 1 wherein, the similar/dissimilar wire
combination is fed using a three wire feeders with three nozzles for
creating a common weld pool with required chemistry and hardness.
3. A process as claimed in claim 1 wherein the similar/dissimilar wire
combination is fed through at least three wire feeders.
4. A process as claimed in claim 1 wherein, the similar/dissimilar wire
combination is fed using at least three wire feeders with three nozzles.
5. A process as claimed in claim 1 wherein, the similar/dissimilar wire
combination is fed using at least three wire feeders with three nozzles
drawing power from a single power source.
6. A process as claimed in claim 1 wherein, the similar/dissimilar wire
combination is fed using at least three wire feeders with three nozzles
creating a common weld pool.
A process according to claim 1 wherein said common weld pool
creating required chemistry to provide improved weld quality.
A process as claimed in claim 1 wherein said flux is analytically neutral.
A process as claimed in claim 1 wherein a weld metal structure is
produced with a high proportion of acicular/martensetic structure.
A process as claimed in claim 9, wherein the surface proportions of
acicular/martensetic is 100 percent.
A process as claimed in claim 1 wherein a single pass welding is
performed to avoid buffering layer of welding and machining.
A process as claimed in claim wherein a multi layer pass welding is
performed to enhance the mechanical properties.

The invention relates to a process to improve the technology in submerged arc
welding wherein for feeding the wire from wire spools, only single power source
with control system is required for performing the welding process. For adding
two more wires as the same as that of the main wire with same or different
chemistry wire, require a separate wire feeder for performing forward and
backward feeding of cold wire addition technology in submerged arc welding
process. It is possible to simultaneously feed multi wires with same or different
chemistry in three wire feeders at same feed rate or different feed rate for
different current rating. This new wire feeding with controller and special torch
will enhance the production rate in double when compared to the conventional
submerged arc welding process. A cold wire feeder with special is designed and
interfaced with the available DC wire feeder for coupling the additional wire
feeder for feeding the forward and backward feeding of cold wire in the arc
cavity in submerged arc welding process. With this new wire feeder the cold wire
addition can be provided in both direction of welding. This results in additional
weld deposit with same heat in-put energy available in the arc zone. Additional
power source is not required for this new design of wire feeder and special torch.
This new wire feeder and special torch is interfaced with the existing convention
SAW machine for drum test plate welding. The test results of radiographic test,
Ultrasonic test are found satisfactory as per IBR and ASME Sec IX.