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SAW FUNDAMENTALS
Principles of operation
Principles of operation
Principles of operation
Factors that determine whether to use SAW
•chemical composition and mechanical
properties required for the weld deposit
•thickness of base metal to be welded
•joint accessibility
•position in which the weld is to be made
•frequency or volume of welding to be
performed
Principles of operation
SAW methods
•semiautomatic - for relatively small
diameter electrodes and moderate travel
speed
•mechanised - the majority of applications
•automatic - for mass production (e.g.
pipes)
Principles of operation
SAW methods features
Semiautomatic
Mechanised
Automatic
Starts and
maintains
the arc
Machine
Machine
Machine
Feed the
electrode
Machine
Machine
Machine
Control
heat input
Person
Machine
Machine
Provide
Person
travel speed
Machine
Machine
Principles of operation
SAW methods features
Semiautomatic
Guides the
arc along
the joint
Mechanised
Automatic
Person
Person
Machine
Manipulates
welding
Person
head to
direct the
arc
Person
Machine
Person
Does not
correct!
Corrects arc Person
to overcome
deviations
Advantages/disadvantages
Advantages of SAW
•high current density  high deposition rates (up to 10 times
those for MMA)  high productivity
•deep penetration  small welding grooves
•fast travel speed  less distortions
•deslagging is easy
•uniform bead appearance with good surface finish  good
fatigue properties
•can be easily performed mechanised  high duty cycle and
low skill level required
•provide consistent quality when performed
automatic/mechanised  assure radiographically sound welds
•arc is not visible
•little smoke/fumes are developed
Advantages/disadvantages
Disadvantages of SAW
•limited mainly to flat/horizontal position
•limited to carbon, low alloy, creep resisting and stainless
steels; also nickel alloys
•due to the high heat input, impact strength of weld
metal/HAZ may be low; also high dilution
•slag must be cleared away after welding  danger of slag
inclusions
•need flux storage, handling and recirculation control
•difficult to apply on-site due to complicated equipment
•high capital costs
•weld line must be regular (straight or circumferential
seams only) with accurate fit-up
SAW equipment
Power sources can be:
•transformers for AC
•transformer-rectifiers for DC
Static characteristic can be:
•flat (CV) - most of the power sources
•drooping (CC)
SAW equipment
Flat (CV) power sources:
•most commonly used supplies for SAW
•can be used for both semiautomatic and
automatic welding
•self-regulating arc  simple wire feed speed
control
•wire feed speed controls the current and power
supply controls the voltage
•applications for DC are limited to 1000A due to
severe arc blow (also thin wires!)
SAW equipment
Drooping (CC) power sources:
•can be used for both semiautomatic and
automatic welding
•not self-regulating arc  must be used with a
voltage-sensing variable wire feed speed control
•more expensive due to more complex wire feed
speed control
•arc voltage depends upon wire feed speed whilst
the power source controls the current
•cannot be used for high-speed welding of thin
steel
SAW equipment
Welding heads
Wire reel
Flux recovery
system
Slides
Flux
hopper
Wire feed
motor
Feed roll
assembly
Torch
assembly
Tracking
system
Contact tip
Courtesy of ESAB AB
SAW equipment
Welding heads can be mounted on a:
Courtesy of ESAB AB
Tractor type carriage
Courtesy of ESAB AB
Column/beam carriage
SAW equipment
Tractor type carriage
•provides travel along straight
or gently curved joints
•can ride on tracks set up
along the joint (with grooved
wheels) or on the workpiece
itself
•can use guide wheels as
tracking device
Courtesy of ESAB AB
•due to their portability, are
used in field welding or where
the piece cannot be moved
Courtesy of ESAB AB
SAW equipment
Pilot lamp
Guide wheel
bogie
Radius from
1500mm
Inside welding
from 1150 mm
Simultaneous
welding
Guide rail with
magnets
Support-roller
for fillet weld
Idling-rollers
SAW equipment
Column/beam carriage
•provides linear travel only
•are capable of linear
motion in 3 axes
•because workpiece must
be brought to the weld
station, they are use
mostly in the workshop
Courtesy of ESAB AB
SAW equipment
Ancillary equipment
•tilting-rotating positioners bring the area to be
welded on irregular parts into flat position
Courtesy of ESAB AB
Courtesy of ESAB AB
SAW equipment
Ancillary equipment
•roller beads rotate cylindrical parts under the
weld head
Courtesy of ESAB AB
Courtesy of ESAB AB
SAW filler material
Welding wires
•supplied on coils, reels or drums
•random or line winding
Courtesy of Lincoln Electric
coil (approx.
25 kg)
Courtesy of Lincoln Electric
reel (approx.
300 kg)
Courtesy of ESAB AB
drum (approx.
450 kg)
SAW filler material
Welding wires can be used to weld:
•carbon steels
•low alloy steels
•creep resisting steels
•stainless steels
•nickel-base alloys
•special alloys for surfacing applications
Welding wires can be:
•solid wires
•metal-cored wires
SAW filler material
Welding wires:
•carbon and low alloy wires are copper coated
•stainless steel wires are not coated
Courtesy of Lincoln Electric
Courtesy of Lincoln Electric
•wires must be kept clean and free from oil and dust
SAW filler material
Copper coating functions:
•to assure a good electric contact between wire
and contact tip
•to assure a smooth feed of the wire through
the guide tube, feed rolls and contact tip
(decrease contact tube wear)
•to provide protection against corrosion
SAW filler material
Welding fluxes:
•are granular mineral compounds mixed according
to various formulations
•shield the molten weld pool from the atmosphere
•clean the molten weld pool
•can modify the chemical composition of the weld
metal
•prevents rapid escape of heat from welding zone
•influence the shape of the weld bead (wetting
action)
•can be fused, agglomerated or mixed
•must be kept warm and dry to avoid porosity
SAW filler material
Fused welding fluxes
Components
are dry mixed
Product is
crushed and
screened for
size
Components
are melted in
an electric
furnace
Shooting the
melt through a
stream of water
Pouring melt
onto large chill
blocks
Charge is
cooled by:
SAW filler material
Fused fluxes advantages:
•good chemical homogeneity
•easy removal of fines without affecting flux
composition
•normally not hygroscopic  easy storage and
handling
•readily recycled without significant change in
particle size or composition
Fused fluxes disadvantages:
•difficult to add deoxidizers and ferro-alloys (due
to segregation or extremely high loss)
•high temperatures needed to melt ingredients
limit the range of flux compositions
SAW filler material
Agglomerated welding fluxes
Components
are powdered
and dry mixed
Pellets are broken
up and screened
for size
Components
are bonded
Pellets are
baked
The wet
mix is
pelletized
SAW filler material
Agglomerated fluxes advantages:
•easy addition of deoxidizers and alloying
elements
•usable with thicker layer of flux when welding
•colour identification
Agglomerated fluxes disadvantages:
•tendency to absorb moisture
•possible gas evolution from the molten slag
leading to porosity
•possible change in flux composition due to
segregation or removal of fine mesh particles
SAW filler material
Mixed fluxes - two or more fused or bonded fluxes
are mixed in any ratio necessary to yield the
desired results
Mixed fluxes advantages:
•several commercial fluxes may be mixed for
highly critical or proprietary welding operations
Mixed fluxes disadvantages:
•segregation of the combined fluxes during
shipment, storage and handling
•segregation occurring in the feeding and
recovery systems during welding
•inconsistency in the combined flux from mix to
mix
SAW filler material
From the chemical point of view, fluxes can be
(see BS EN 760):
Acid
Neutral
(contain acid
oxides like SiO2,
Al2O3, TiO2, ZrO2)
Basic
(contain basic
oxides like FeO,
MnO, NiO, CaO)
High
basic
Welding characteristics (more stable arc,
improved weld appearance, easier slag
removal, higher welding speeds)
Weld metal mechanical properties (YS, KV,
UTS), amount in Mn and Si, melt temperature
SAW filler material
Welding flux:
•can be supplied in bags/pails (approx. 25 kg) or
bulk bags (approx. 1200 kg)
Courtesy of Lincoln Electric
Courtesy of Lincoln Electric
Courtesy of Lincoln Electric
•handling and stacking requires care
•if flux is too fine it will pack and not feed properly
 cannot be recycled indefinitely
SAW filler material
Wire/flux combination designation acc. BS EN 756:
Type of welding flux
Tensile properties
Standard number
EN 756 - S 46 3 AB S2
Wire electrode and/or
wire/flux combination
Impact properties
Chemical composition of
wire electrode