7 The tremendous
heat evolved by the passage of the electric current through the welding zone melts
the end of the wire and the adjacent edges
of the workpieces, creating a puddle of molten metal. This puddle is in a
highly liquid state, and is turbulent. For these reasons,
any slag or gas bubbles are quickly swept to the surface.
The submerged are welding flux completely shields the welding zone from contact
with the atmosphere. A small amount of the
flux fuses. This fused portion serves several functions: it completely
blankets the top surface of the weld, preventing atmospheric
gases from contaminating the metal, it dissolves
and thus eliminates impurities that separate themselves from the molten steel
and float to its surface, and it also can
be the vehicle for adding certain alloying elements. The combination of all these
factors results in a sound, clean, homogeneous weld.
As the welding zone moves further down the seam, the
fused submerged arc welding flux cools and hardens
into a brittle, glass-like material which protects the weld until cool, then usually
detaches itself completely from the weld.
Since properly made submerged arc welds are made without
arc flash sparks, protective equipment against harmful
radiations is not needed. There is no spatter to be removed. Basic
Principles -Theory of Welding Wire Feed Control The
high welding speeds and high deposition rate which are characteristic of
submerged arc welding require automatic
control of the motor that feeds the welding wire into the weld. No hand welder
could smoothly deposit welding wire at
speeds comparable to those of a submerged arc welding machine. Nor
could he maintain the same precise control of welding
conditions. The automatic control and power
supply system used in submerged arc welding operates to maintain a
constant voltage and current.
