Linde BOC RAPTOR 160 MIG Operating Manual page 21

Metal-cored wires transfer metal in dip mode at
low currents just like solid MIG/MAG wires. This
transfer mode is used for all positional work with
these types of wire.
Globular Transfer
Metal transfer is controlled by slow ejection
resulting in large, irregularly-shaped 'globs'
falling into the weld pool under the action of
gravity. Carbon dioxide gas drops are dispersed
haphazardly. With argon-based gases, the
drops are not as large and are transferred in a
more axial direction. There is a lot of spatter,
especially in carbon dioxide, resulting in greater
wire consumption, poor penetration and poor
appearance. Globular transfer occurs between the
dip and spray ranges. This mode of transfer is not
recommended for normal welding applications
and may be corrected when encountered by
either decreasing the arc voltage or increasing the
amperage. Globular transfer can take place with
any electrode diameter.
Basic flux-cored wires tend to operate in a globular
mode or in a globular-spray transfer mode where
larger than normal spray droplets are propelled
across the arc, but they never achieve a true spray
transfer mode. This transfer mode is sometimes
referred to as non-axial globular transfer.
Self-shielded flux-cored wires operate in a
predominantly globular transfer mode although
at high currents the wire often 'explodes' across
the arc.
Spray Transfer
In spray transfer, metal is projected by an
electromagnetic force from the wire tip in the
form of a continuous stream of discrete droplets
approximately the same size as the wire diameter.
High deposition rates are possible and weld
appearance and reliability are good. Most metals
can be welded, but the technique is limited
generally to plate thicknesses greater than 6mm.
Spray transfer, due to the tendency of the large
weld pool to spill over, cannot normally be used
for positional welding. The main exception is
aluminium and its alloys where, primarily because
of its low density and high thermal conductivity,
spray transfer in position can be carried out.
The current flows continuously because of the high
voltage maintaining a long arc and short-circuiting
cannot take place. It occurs best with argon-based
gases.
In solid wire MIG/MAG, as the current is increased,
dip transfer passes into spray transfer via a
transitional globular transfer mode. With metal-
cored wires there is virtually a direct transition
from dip transfer to spray transfer as the current is
increased.
For metal cored wire spray transfer occurs as the
current density increases and an arc is formed at
the end of the filler wire, producing a stream of
small metal droplets. Often the outside sheath of
the wire will melt first and the powder in the centre
flows as a stream of smaller droplet into the weld
pool. This effect seems to give much better transfer
of alloying elements into the weld.
In spray transfer, as the current density increases,
an arc is formed at the end of the filler wire,
producing a stream of small metal droplets. In
solid wire MIG/MAG this transfer mode occurs at
higher currents. Flux-cored wires do not achieve a
completely true spray transfer mode but a transfer
mode that is almost true spray may occur at higher
currents and can occur at relatively low currents
depending on the composition of the flux.
Rutile flux-cored wires will operate in this almost-
spray transfer mode, at all practicable current
levels. They are also able to operate in this mode
for positional welding too. Basic flux-cored and
self-shielded flux-cored wires do not operate in
anything approaching true spray transfer mode.
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