Page 96 - SSAB Welding Handbook Edition 2

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15.0 Magnetic arc blow Welding handbook

Workpiece connections Welding joints of larger plate thicknesses
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Proper placement of the workpiece connection can If arc blow is encountered due to large plate
diminish magnetic arc blow. This technique intro thicknesses in the joint, and the level of residual
duces a magnetic field in the opposite direction to magnetism is insignificant, then widening the joint
the one causing the arc blow. at the root section may be beneficial. One example
is to change the V-prepared joint to a U-prepared
The cause is that the current return from welding joint.
goes through the workpiece, which causes a magnetic
field in its path. This magnetic field supports an arc
deflection away from the workpiece connection, Demagnetizing equipment
according to fig. 15.8. The steel in the joint can be demagnetized from
residual magnetism. There are different types of
If back blow of the arc is encountered, it can be techniques and equipment available for this
counteracted by positioning the workpiece purpose. The appropriate solution is situation
connection away from the direction of welding. based.
If forward arc blow occurs, locate the workpiece
connection towards the direction of welding. The
use of more than one workpiece connection might
further improve this method. The effect from the
location of the workpiece connection is limited, so
this measure is normally done together with other
complimentary measures in order to avoid arc blow.

Current return

Arc
Workpiece connection Direction of
magnetic flux

Direction of arc blow

Fig. 15.8: The position of the workpiece connection supports an arc deflection in accordance to the figure.

96 This handbook contains general suggestions and information without any expressed or implied warranty of any kind. SSAB hereby expressly disclaims
all liability of any kind, including any damages, in connection with the use of the information and for their suitability for individual applications.
It is the responsibility of the user of this brochure to adapt the recommendations contained therein to the requirements of individual applications.