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About Welding Process 49

The document discusses different types of electrode coatings used in welding processes. It describes four main types: (1) gas shielded electrodes that use organic materials in their coating to produce a protective gas shield during welding and allow for good penetration and positional welding; (2) rutile electrodes that contain titania which provides good arc stability and protection against contamination through a gaseous atmosphere and acidic slag; (3) basic or low-hydrogen electrodes that use calcium compounds or rare earth metals in their coating to control the slag and reduce hydrogen; and (4) cellulose electrodes that use cellulose in their coating to provide a stable arc and slag control.

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58 views1 page

About Welding Process 49

The document discusses different types of electrode coatings used in welding processes. It describes four main types: (1) gas shielded electrodes that use organic materials in their coating to produce a protective gas shield during welding and allow for good penetration and positional welding; (2) rutile electrodes that contain titania which provides good arc stability and protection against contamination through a gaseous atmosphere and acidic slag; (3) basic or low-hydrogen electrodes that use calcium compounds or rare earth metals in their coating to control the slag and reduce hydrogen; and (4) cellulose electrodes that use cellulose in their coating to provide a stable arc and slag control.

Uploaded by

Xerex
Copyright
© © All Rights Reserved
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Welding Processes 49

rise to the surface of the pool, freeze before the metal below freezes and thus aid in
the protection of the molten metal from reaction with the atmosphere. Deoxidizers
in the covering serve to reduce oxides that might have been present on the work or
inadventently formed by oxidation of the molten metal through imperfect shielding
or slagging. Oxides would tend to make the weld metal brittle. The most commonly
used deoxidizing agents are silicon, aluminium and manganese.
Arc stabilization is another important function of the electrode covering. With
AC current, which reverses its direction, there is tendency for the arc to “cut-off”
every time the current flow is reversed. This problem is solved in the AC electrode
by incorporating potassium compounds, such as potassium titanate in the covering.
Thus DC electrodes are not useable with AC currents, but AC electrodes can be
used with DC current.
The electrode covering is also used for adding filler metal ingradients to the
weld deposits. Thus iron powder is extensively used in electrode covering-adding
iron to the weld, in addition to the iron supplied by the core wire. A small percentage
of iron powder, in some E6010 electrodes, stabilizes and quiets the arc without
loss of penetration characteristics. Iron powder added in large amount increases
the deposition rate, increases the optimum current and, with thick covering,
facilitates the use of the drag technique in welding. The electrode covering can
also be a source of alloying metals, such as manganese, nickel, chromium, and
molybdenum. When mixed with iron from the steel wire core, an alloy weld is
created during the welding process.
There are four main types of electrode coatings on which all mild and low alloy
steel electrodes are based.
(a) Gas shielded (cellulosic) electrodes : These coatings developed originally
nearly 60 years ago contain over 30 per cent of organic material such as
alpha flock, wood flour or other cellulose. In the arc the coating breaks
down to give a voluminous gas shield of H2, CO and CO2 which give good
protection of the molten weld metal with consequent good weld metal
properties. These electrodes develop a strong plasma jet which gives
excellent penetration. Burning off rate of the electrode is low and the coating
constitution leads to only a small amount of thin friable slag being formed,
which makes the electrode very suitable for positional welding, including
vertical position. Direct current is necessary.
(b) Rutile electrodes : This coating contains 50 per cent titania (TiO2) as the minerals
rutile or ilmenite. This compound gives good arc stability and low operating
voltage so that it can readily be used with alternating current. Protection
against contamination is effected by a gaseous atmosphere containing
hydrogen, oxides of carbon nitrogen together with an acidic slag, whose
viscosity can be varied by minor mineral additions. The easily controllable
slag, low spatter, medium penetration and high depostion rate make this
electrode type ideal for general engineering. Weld appearance is also good
and uniform and mechanical properties are generally sound. However,
ductility is lower than that with other coatings.

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