Welding
process and welding engineering came into its own in early 19’s. It was at the
time of World War II that welding processes got a new face. Today welding has
turned to vital field where lots of career opportunities in it. Welding process
or technology had gone through different phases and evolved from a trade to
science. Traditional methods got modified during this period of time. In the
last 10-15 years plasma gouging became a viable solution. In 1940s the gouging
was done using carbon arc with help of welding machine and a carbon electrode
to melt metal. The metal part of surface is melted or removed and a gouge or
groove is fumed on it. Many types of gouging like oxyfuel gouging, air carbon
arc gouging mechanical gouging exist in this field.
In plasma
air gouging smooth and clean grove is obtained. The main advantage that this
method provides is that, it is smoke free and also quiet operation. A correct
knowledge about the working of this technology and scope of being merged with
application based solution is necessary for growth of implementation of the
technology.
Defining the
gouge is basic of plasma gouging. For each operation gouge varies according to
the application. A gouge which is ideal for one operation may not be ideal for
another application. Quality of gouge is another parameter in plasma gouge.
Factors that makes a gouge perfect is, whether the operation the operator
removed correct amount of material from the surface and also it should be in
correct controlled manner. Shape in some case plays vital role in other case
may not be crucial.
The removal
of part can be categorized into two ways, positive feature removal and negative
feature removal. The positive feature removal refers to the removal of those
part above the surface i.e. it will be in space and will not be covered by
other material. The negative feature removal refers to removal of part
surrounded by other material. Seized bolt removal which is also called nut
removal, casting sprue removal, protruding surface features removal such as
fillet weld comes under the positive surface feature removal. The excavation of
weld defect, spot weld removal and back gouging comes under negative feature
removal.
In negative
feature removal, the gouge profile is more important. It is crucial than the
rate at which one can remove material. Few assumptions are done regarding gouge
profile like relation between width and depth of gouge i.e. width of gouge
should be greater than its depth and profile should be maximum symmetrical.
The ionized
gas which are electricity conductive is super-heated to obtain plasma. The
velocity and energy density is increased by constricting its cross section
area. Supersonic speeds are achieved. These parameters are varied to obtain
different bore design. When the area become more constricted velocity increases
and its cutting capabilities are also increased. These factors are combined to
produce partial melting and effective subsequent clearing of slag.
The system
amperage and angle of torch are other features that influence plasma gouging.
The gouge depth is proportional with amperage. The depth of gouge is increased
as amperage increases. The angle of torch influence the gouge shape. A primary
angle is given to make basic gouge shape then another, a second angle is given
to increase the width of gouge. This process is called offset angle gouging.
When angle is zero it is straight line gouging. As angle increases gouge get wider.
As angle approach 90 profile become asymmetric shape. WQC NDT Institute
provides welding inspection courses in Kochi.
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