Welding

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  • Topic: Welding, Gas tungsten arc welding, Stainless steel
  • Pages : 10 (724 words )
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  • Published : February 19, 2013
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TIG welding

T

ungsten inert gas (TIG)
welding is a high quality
low deposition rate
welding process. It uses an arc
struck between a nonconsumable tungsten electrode
and the work to fuse the base
material and thereby form a
welded joint.
The TIG welding process may
be used on thin sheet material
without the addition of a filler
metal (autogenous TIG welding).
Alternatively, when working on
thicker sheet or when joining
dissimilar materials, a separate
wire filler metal is added into the
arc region where it is melted and
directed by the welder into the
molten weld pool.
The weld pool, the hot
tungsten electrode and the
melting filler wire are protected
from atmosphere by a shield of
inert or slightly reducing gas.
Argon is often used although
productivity and quality benefits
can be gained by using mixtures
of argon and helium or argon and
hydrogen (see the table of
recommended GeminiTM gases
over the page).

Operation
TIG welding is suitable for
manual, mechanised and
automatic (orbital) operation.
In manual welding, the
operator points the tungsten
electrode in the direction of
welding and uses the arc to melt
the base material along the joint,

Double operator AC TIG welding of an aluminium vessel.

ahead of the molten weld pool.
The filler metal is generally
added at the leading edge of the
advancing weld pool.

Welding current
Both Direct Current (DC) and
Alternating Current (AC) may be
used when TIG welding, the
choice depending upon the type
of material to be welded.
DC (electrode negative) is
used for the following

materials:–
carbon steel
q copper
q stainless steels
q nickel alloys
q titanium
q zirconium.
AC is used for the following
materials:–
q aluminium and its alloys
q magnesium
q aluminium bronze.
q

Non-consumable
electrodes

Ozone reduction

Electrode diameter to current
dia. mm

maximum operating current (A)
thoriated DC

zirconiated AC

1.2

70

40

1.6

145

55

2.4

240

90

3.2

380

150

4.0

440

210

4.8

500

Research carried out by Air
Products’ European Technology
Group has shown that, when
welding stainless steels, the
AstecTM and HytecTM ranges
of GeminiTM gases produce
significantly lower levels of
harmful ozone than traditional
shielding gases.

275

GeminiTM gases for TIG
welding

Taken from British Standards BS3019: Part 1

Pure tungsten electrodes may be
used for TIG welding. Special
tungsten electrode materials with
controlled additions of metallic
oxides are, however, generally
preferred because they allow
easier arc starting and provide
enhanced arc stability.
Thoriated tungsten electrodes,
containing generally 2% thorium
oxide, are commonly used for DC
welding of steels. Zirconated
tungsten electrodes, containing
2% zirconium oxide, are recommended for the AC welding of
aluminium and its alloys.
The diameter of the non-consumable TIG electrode is chosen
to suit the welding current. Below
the minimum current, for a given
electrode, the arc becomes unstable and cannot be maintained. Above the maximum current, the
electrode may become overheated, erode quickly and even melt.

Autogenous TIG welding of stainless
steel.

Reduced ozone
180 Mean ozone parts per billion

breathing zone
proximate zone

160
140
120
100

Occupational exposure standard
8 hour TWA reference period

80
60
40
20
0
argon

AstecTM30

HytecTM2

ozone measurements for TIG welding 304 stainless steel

Argon may be used for all of the
commonly welded materials.
However, the AstecTM range of
gases gives enhanced welding
speeds and deeper penetration in
a range of applications when
compared to argon. The HytecTM
gas mixtures provide improved
weld profile, welding speed,
penetration and surface finish
when compared to argon for
the welding of austenitic
stainless steels, cupro-nickel
and nickel alloys.

Recommended...
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