PARAMETERS IN SUBMRGED ARC WELDING
Transcript of PARAMETERS IN SUBMRGED ARC WELDING
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INFLUENCE OF DIFFERENTPARAMETERS IN SUBMRGEDARC
WELDING
BY sri ram vikas.k
(11102263)
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SUBMERGED ARC WELDING
Submerged arc welding (SAW) is a welding processwherein coalescence is produced by heating with an
electric arc between a bare metal electrode and the job.
The arc, end of the electrode and molten pool remain
completely hidden and are invisible being submergedunder a blanket of granular material (flux)
The continuously fed bare metal electrode melts and
acts are filler rod.
No pressure is applied for welding process
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Schematic illustration of the submerged-arc welding processand equipment.
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Advantages
High deposition rates . High operating factors in mechanized applications. Deep weld penetration. Sound welds are readily made (with good process design and control). High speed welding of thin sheet steels up to 5 m/min (16 ft/min) is
possible.
Minimal welding fume or arc light is emitted. Practically no edge preparation is necessary. The process is suitable for both indoor and outdoor works. Distortion is much less. Welds produced are sound, uniform, ductile, corrosion resistant and
have good impact value.
Single pass welds can be made in thick plates with normal equipment. The arc is always covered under a blanket of flux, thus there is no
chance of spatter of weld. 50% to 90% of the flux is recoverable
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Operating Variables
Control of the operating variables in submerged arc welding is essential if high
production rates and the welds of good quality are to be obtained. The
following are the important variables:
(i) Welding amperage
(ii) Welding voltage(iii) Welding speed
(iv) Electrode size
(v) Electrode work angle
(vi) Electrode stick-out
(vii) Depth of flux
(viii) Flux basicity index
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Welding amperage
Welding current is the most influential parameterbecause it affects bead shape, controls the rate at which
electrode is melted and therefore also controls the
deposition rate, heat affected zone, the depth of
penetration, and the amount of base metal melted.
Penetration and reinforcement increase with theincrease in welding current. If the current is too high at a
given welding speed, the depth of fusion or penetration
will also be too high so that the resulting weld may tend
to melt through the metal being joined. High current alsoleads to waste of electrodes in the form of excessive
reinforcement and produces digging arc and undercut.
This over welding increases weld shrinkage and causes
greater distortion.
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Penetration and reinforcement increase with theincrease in welding current. If the current is too high at a
given welding speed, the depth of fusion or penetration
will also be too high so that the resulting weld may tend
to melt through the metal being joined. High current alsoleads to waste of electrodes in the form of excessive
reinforcement and produces digging arc and undercut.
This over welding increases weld shrinkage and causes
greater distortion.
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Effect of current on flux consumption
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Welding voltage
The arc voltage controls the arc length, flux consumptionand weld metal properties.
Increase in arc voltage increases the arc length which
results in wider bead width .
As increasing the arc voltage increases the arc length somore heat is available to melt the metal and flux due to
which more alloying elements enter the weld metal.
Thus arc voltage affects the weld metal composition.
Flux consumption is also increased as more flux ismelted.
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Effect of voltage on flux consumption
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Welding speed
Welding speed is the linear rate at which an arc ismoved along the weld joint. With any combination of
welding voltage and welding current, the effect of
changing the welding speed confirms to a general
pattern. If the welding speed is increased, power or heatinput per unit length of weld is decreased and less filler
metal is applied per unit length of the weld, resulting in
less weld reinforcement.
Thus, the weld bead becomes smaller.
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Effect of welding speed on flux consumption
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Flux basicity index
Flux basicity index also influences the penetration
In general higher penetration is obtained with the use of
low basicity index fluxes due to high viscosity which
enhances the tendency of heat concentration in the
narrow zone.
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Effect of basicity index on flux consumption
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General types of fluxes
Fused Fluxes
Bonded Fluxes
Agglomerated fluxes
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neutral flux
As with any flux, a neutral flux does affect the welddeposit chemistry. The levels of alloying elements added
to the weld are generally consistent across even
significant changes in voltage. Therefore, the deposit
chemistry will not match the wire chemistry. Neutral fluxes can be used in multiple pass applications
of unlimited plate thickness without the concern for alloy
buildup, as with active fluxes. Neutral fluxes are
generally not designed to handle rust and mill scaletolerance, and therefore should be used on clean plate.
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Advantages of Neutral Fluxes:
Unlimited number of weld passes
Unlimited plate thickness allowed
Weld deposit chemistry not sensitive to changes in
voltage/flux consumed
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Active fluxes
Active fluxes are those fluxes that add manganese and silicon to theweld deposit in proportion to the arc voltage.
As voltage increases, the amount of flux consumed during the
welding process also increases, which leads to more Mn and Si
added to the weldment. The addition of Mn and Si make active
fluxes well suited to welding over rust, mill scale and light oil. They also provide excellent welder appeal.
However, due to the alloying tendency of active fluxes, they can add
excessive amounts of Mn and Si, which can lead to weld
embrittlement and/or cracking.
As a result, active fluxes are recommended only for use below 36
volts and for single or multiple pass welds up to 1-inch thickness
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Advantages of Active Fluxes:
Good for use over rust , even light rust
Excellent slag peeling characteristics
High speed capability
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Alloy fluxes
Alloy fluxes create an alloyed weld metal, whencombined with unalloyed wires.
alloyed fluxes used for cladding applications. These
fluxes add C and Cr as well as Si and Mn to the weldmetal. The alloying of elements is related to the arc
voltage, since this has an influence on the amount of flux
being melted and taking part in the chemical reaction.
In order to create a specific weld metal composition, thearc voltage must be carefully controlled.
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Conclusion
Flux consumption influences the economic aspects of
welding and chemical composition of the weld metal. Flux
consumption depends upon the welding parameters such
as welding current, arc voltage, welding speed and type offlux. Flux consumption increases with the increase in arc
voltage and decrease in current. The electrode extension
has no significant effect on flux consumption Agglomerated
fluxes have low flux consumption as compared to fusedfluxes.
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References :
[1] Nadkarni,S.V. (1988): Modern Arc Welding Technology , New Delhi, India:IBH Publication.
[2] Parmar, R.S. (1997): Welding Processes and Technology, Khanna
Publishing Company, New Delhi.
[3] Parametric Effect on Mechanical Properties in Submerged arc welding
process - A review Ravinder Pal Singh et al. / International Journal of
Engineering Science and Technology (IJEST)
[4] Effect of SAW Parameters on Weld Element Transfer in SS316 Karun,
Sandeep Jindal, R.D. Gupta Current Trends in Engineering Research Vol.1,
No.1 (Dec. 2011)
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Suggestions
Any
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THANK U