The Arc Blow Problem
Arc Blow is a problem that exists with most electric welding
processes. It is caused by the preferential magnetic fields developed near
the arc. These are most
often caused by the arc current ground path or in the fixture holding the part to be welded. The
fields interact with the self induced field around the electrode. When
employing DC
power the external field will be preferentially in one direction. This
builds a stronger field on one side of the arc than the other causing it to move
in the direction of the weakened field. The worse situation is when this
movement causes the arc to blow backwards and become unstable. This can
generate gross porosity in the deposit. See the picture below:

The above sheet metal weld was made at 200 ipm travel
speed with the submerged arc welding
process and shows classic arc blow porosity at the finish end of the weld. It
is common to have the visual effects of arc blow occur at the end of the plate to be
welded. The magnetic field force line concentrate at the plate end as
the arc approaches causing what is often referred to as "back blow" porosity.
Details of how this problem can be solved in submerged arc
welding are discussed in a technical paper on multi-wire multi-power welding.
A recent major porosity problem on an ID weld in a spiral pipe mill was solved
with a unique approach. Details are covered in the paper. If you are
interested in purchasing this technical paper
Contact Us.
AC power can not only solve many arc blow problems but also can be
shown to produce more penetration that DC under certain conditions. In
fact in two wire systems there are demonstrated benefits of AC-AC versus the
more commonly used DC-AC. These details are covered in the
technical paper. Want to see an overview of
what is included? Click here.