3.5 Copper and copper alloys
Cleanliness is important when welding copper, and
all dirt, grease, and other contaminants must be
removed before welding. Copper alloys containing
aluminium will form a surface oxide film and this
must also be removed before welding. Preheat will
be required for unalloyed copper but some copper
alloys can be TIG welded without preheat except
on thick sections.
Standard DC TIG welding equipment is suitable
for most copper and copper alloys, but aluminium
bronze is normally TIG welded using AC current to
break down the tenacious oxide film on the surface.
Pure argon, helium, or argon-helium mixtures
are standard shielding gases for DC TIG welding
copper and copper alloys. Alushield Heavy is ideal
for TIG welding copper and some copper alloys,
particularly in thicker sections. Pure argon is the
shielding gas used for AC TIG welding.
TIG consumables are solid filler rods based on pure
copper and several copper alloy compositions,
including aluminium bronzes, silicon bronzes, and
cupro-nickels. It is normal to try to use a filler
material with a similar composition to that of the
parent material but this is not always possible, and
sometimes not desirable.
Porosity is the main welding problem encountered
when TIG welding unalloyed copper and some
copper alloys are prone to solidification cracking
and porosity. Certain alloys are difficult to weld
(brass will lose zinc if welding is attempted), and
those containing lead are virtually unweldable.
Plate
thickness
(mm)
Joint
type
Root
gap
(mm)
Layers
Tungsten
size
(mm)
Consum-
able size
(mm)
Current
(A)
Welding
speed
(cm/min)
Gasflow
(l/min)
1.5
Square butt
1.0
1
1.6
2.0
120
0.29
7
3
Square butt
2.0
1
3.2
3.0
185
0.25
8
5
Square butt
3.0
2
4.0
4.0
270
0.15
8
3.4 Stainless steel
Is a high quality process ideally suited for welding
of stainless steels, particularly thin sheet up to
about 5 mm thick where weld integrity and good
surface finish are critical. The process has a high
degree of controllability resulting in clean, smooth,
high quality welds with good penetration and
strength with very low defect rates.
Standard TIG equipment is suitable and stainless
steels are TIG welded using DCEN polarity.
A thoriated tungsten electrode is normally used but
health concerns have promoted use of ceriated or
lanthanated instead. The filler rod used depends on
the type of stainless being welded but, in general,
is matching for austenitic grades, enriched in nickel
for duplex grades, and may be matching or an
austenitic type for ferritic and martensitic grades.
Shielding gas is conventionally pure argon, but
other gases are available to provide specific
properties and these include argon-hydrogen,
argon-helium mixtures, argon-helium-hydrogen,
and argon-nitrogen mixtures.
When welding pipes an inert gas purge is required
inside the pipe to prevent oxidation on the
underside of the weld. Gas purging may also be
used to protect the root side of butt welds in plate
or sheet materials too.
BOC Smootharc TIG 185 Operating Manual
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BOC Smootharc TIG 185 Operating Manual