The arc heats the used wires, because of the thermal
conductivity of metals, in three different zones. Figure 12
clearly shows the three different arc heated zones of the
wires.
The first zone is the intersection surface of the wires,
which is directly exposed to the arc ignition or re-ignition.
Owing to the induced heat, this area consists of fully liquefied
metal. The depth of this zone depends on the
magnitude of the induced heat and the melting point of
the materials involved. The presence of solidified droplets
at the wire surface is evidence of liquefied metal (Fig. 12a,
b). The holes in Fig. 12(d) are a sign of escaped bubbles
caused by boiling metal. The thermal conductivity of the
metals causes a heat transfer to the boundary layers.
These layers reach a temperature which is high enough to
generate a doughy metal area. The solidified metal sheets
are evidence for the presence of easily deformable doughy
metal (Fig. 12e). The temperature of the wires at deeper
layers (at the doughy area bordering layers) is decreased.
Nevertheless, the temperature is still high enough to
enable a permanent deformation at the wire tips. This is
due to the acting aerodynamic forces (Fig. 12f).