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SAW Sub Merged Arc Welding (121)
This process is an automatic process and used both constant
current/voltage power sources. The
arc is normally formed as the point of wire comes into contact
with the work piece.
The flux blanket helps to protect the arc from the atmosphere
and decomposes with heat of the arc
to form a gaseous protective shield.
Adding alloy elements and de-oxidants that are contained in the
flux compounds. The flux
produces a slag to protect the weld from cooling.
Once the switch on, the following actions takes place
a the flux is delivered and forming a layer beneath the torch
head
b the wire begins to feed and strike the arc
c the contactor closes and delivers current to the contact
tip
d the tractor begins to move !if mechanical
- Amperage can range from "##-$###
- %eep penetration- %eep dilution into the base metal.
- &estricted position, because of the nature of granular
flux.
- 'sed to weld ( "# mm thickness
A common application of this process is )piral *elding of
+ipe.
&un on/off Tabs
&un on tabs - 'sed to settle the welding arc for its reuired
conditions prior to the actual welding
seam, and maintained by &un Off tabs in the other end.
oth are removed after the weld seam has been completed.
+ower
)ource
-
Work piece
Flux Hopper
WireFeed
Unit
Torch HeadAssembly
GranularFlux
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Basic Equipment requirements:
" Transformer/&ectifier
$ +ower and power return cable
A torch head assembly
0 A granulated flux of the correct type/specification and mesh
si1e
2 A flux delivery and recovery system ! 3lux hopper4 5lectrode
wire to correct specification and diameter
6 7orrect safety clothing
Arc blow is a ma8or problem, as magnetic field strength is
proportional to the current. y using
of tandem wire mechanism can avoid arc blow.
i.e., leading wire in %7 ve and trailing wire in A7.
Variable Parameters
" *3)
$ 9oltage Travel )peed
0 5lectrode )tick out
2 3lux %epth
mp!rtant nspecti!n P!ints
". *elding 5uipment
$. *elding head assembly
. flux delivery : recovery mechanism
0. 7urrent and polarity
2. Other variable parameters
a backing strips
b compound preparation
c narrow gap preparation
4. )afety checks
"#pical mper$ecti!ns
". +orosity
$. 7enterline cracks. ;ack of fusion
0. )hrinkage cavities < high depth/width ratio
Ad%antages &isad%antages
" ;ow weld metal cost " &estricted in position welding
$ =igh productivity !O/3 $ =igh probability of arc-blow
5asily mechani1ed &elatively =igh 5uipment cost
0 ;ow level of o1one production 0 %ifficult to penetration
control
2 >o visible arc 2 +rone to shrinkage cavities
