6
However, as the arc voltage is raised
to excessive levels, undercutting may again appear. This is particularly
true in spray arc welding. When the
arc becomes very long, it also becomes too wide. This results in an
increased amount of base material being
melted. However, the heat transfer of a long arc is relatively poor,
so actually the arc
is supplying no more total heat to the weld zone. The outermost areas are very
quickly cooled
and again proper wetting is prevented. The arc length should be kept short, not
only to avoid undercutting
but to increase penetration and weld soundness. Excessive
welding currents can also cause undercutting. The arc force, arc heat and penetration
are so great that
the base plate under the arc is actually ”blown” away. Again, the outermost
areas of the base material
are melted but solidify quickly. Puddle turbulence and surface tension prevent
the puddle from wetting
properly. It is always advisable to remain within the current ranges specified
for each wire size.
