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PARAMETERS IN SUBMRGED ARC WELDING

Apr 04, 2018

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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