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LORCH
15
Welding basics
15.1
Stick
elect
rode welding
<---
- - - -
Coated
stick
electrodes
are used
for
the
widely-used
manual
metal
arc
welding
process
(stick
electrode
weld-
ing).
The coating of the
electrode
melts
off
during
the
welding
process together
with
the
core
wire.
The coating
generates
the
shielding
gas.
Additionally the
burning-
off
coating compensates
alloy
elements. which are
de-
stroyed
in
the
molten
pool. A slag layer forms on
top
of
the
welding
seam.
which covers and
protects the
cooling
welding
seam against the air.
The
coatings of the
electrodes
differ
according
to thick-
ness
and
type, i.e. chemical
composition.
This
results in
different welding
properties
and
consequently different
applications
for the
e'
l
ectrodes. Types
and
nomenclature
are
defined
in DIN EN 499
(formerly
1913).
- ' - - -
Stick electrode
Base
metal
15.2
TIG welding
The
TIG
welding
process is a universally-applicable
pro-
cess
which
creates
high
quality
joints.
The electrode of
the TIG
process
consists
of
non-melting
tungsten,
the
shielding gas is
an
inert gas.
In
English
usage
we speak
ofTIG
welding
("Tungsten"
=
Wolfram).
Inert gas
is chemically
neutral
and does
not
react
with
the
weld
metal.
Inert gases are, e.g.
argon,
helium
and
their mixtures.
Usually pure
argon (99.9%) is
used.
The
welding gas
must
be
dry.
DIN
32
526
defines the
differ-
ent
types
of shielding
gas.
TIG
welding
process bas ics
A non-melting
tungsten
electrode
is clamped
with a
col-
let
into
a gas or water-cooled torch
.
The
arc
burns
be-
tween the
tungsten
electrode
and
the workpiece
in
an
inert shielding gas
atmosphere.
Thus
the tungsten
elec-
trode
acts
as
an
arc
carrier.
The arc
melts the
workpiece
point
by
point and
forms
the
weld
pool.
The
shielding
gas
escapes through
the
gas
nozzle.
This
gas protects
the
tungsten
electrode,
the
arc
and
the
molten
pool
against
the
surrounding
air.
This
prevents
undesired
oxidation.
Consequently,
poor welding
results
may
occur
due
to
trouble with
the shielding gas
supply.
In
case
additional
filler
material is
required.
filler
~1\re
is
supplied either
manually,
as in
gas
name
welding,
or
-18
-
Welding basics
automatically
by
means
of
a
cold
wire
feeder.
The filler
wire
must be
equally
or
more
highly
alloyed
than
the
base material. Flange
and
corner welds
can
be
crea ted
easily
without filler
wire.
Shielding
gas
Basically,
both DC and
AC
may
be used
for
TIG
welding.
The current mode
and
polarity
depend
on
the
material
to
be
welded.
Non or
low-alloyed
steel,
high-alloyed
steel and
copper,
as well
as
titanium
and tantalum
are welded
with
DC.
The electrode
is
connected
at
the
minus
pole
because
of
the
stronger
current
loading.
When
welding aluminium
and
nnagnesium
as
well
as
their
alloys,
AC must
be
used in
order
to
tear
up the
high-
melting and
tough
oxide skin
which forms
on the
molten
pool or
which
is
present on
the
base
metal. If
the
oxide
skin
is
missing.
e.g.
there
has been
welding
on
the
same
part for
a
longer time,
the
arc
can
be
unstable
or break
up from
time
to
time.
Shape
of
t he electrode
tip
Tungsten electrodes
always
have
to be
ground
length-
wise
because
crosswise
grinding
marks
cause
an
un-
steady
arc.
10.13
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