Blowing effect: (Un) Desired disturbance in direct current welding

Welding with luminous flux is usually done with direct current. It favors the build-up of a uniform arc and in most cases leads to the desired results. However, welding with direct current (mostly) has an unpleasant side effect.

Definition of blowing effect

Turbulence can occur at the tip of the electrode, introducing undesired gases into the weld pool. This can result in oxidation, burn-in or pores, which reduce the quality of the welded connection. In this context, the welder speaks of the blowing effect. The blowing effect is a phenomenon that only occurs when welding with an arc. For stud welding, the blowing effect is a challenge, especially for studs with larger diameters from approx. 14 mm. Stronger studs have longer welding times, which favors the blowing effect.

Creation of the blowing effect

This phenomenon is caused by the electromagnetic fields that inevitably form around current-carrying conductors. The electrode is under the same high voltage as the base material on which the component is welded. These magnetic fields interact with each other and create turbulence. These eddies can “flush” air and welding gas into the weld pool and thus degrade the welding quality. After setting, the welder sees that the stud is welded more strongly on one side than on the opposite side. In most cases this is an undesirable result. In addition, the welder notices a restless course and heavy spatter when setting the stud with an arc.

Avoiding the blowing effect

In order to avoid this phenomenon when joining with an electric arc, a high level of expertise is required. The specific cause of this disorder can be varied. It must always be decided on site which measure should be used to avoid the blowing effect. Typical countermeasures to avoid such turbulence in the magnetic fields are:

  • Relocating the connection terminal on the workpiece
  • Manufacture of welding templates from non-ferrous material
  • Setting of leveling compounds for edge welds
  • Hold up the welding cable

Special case of predetermined breaking points

There are also cases when this phenomenon is deliberately used. For example, predetermined breaking points can be created, which make it easier to remove the welding stud at a later point in time. With the correct parameters and the right technique, the blowing effect can be intentionally induced.

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Written by

Markus Neuse

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welding

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