FCAW & SAW WELDINGBy- Jitendra BhatiaDate:- 2 Dec 2015

Arc welding is of two types

Why? DC welding are used for all types of welding{thick or thin material}

Why AC welding machines are not .

Arc weldin

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AC weldin

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DC weldin

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Ac welding polarity are not fixed…

Due to polarity changes we can not use for all types of welding

Fixed polarity

With the help of fixed polarity. We can handle according to use thick or thin welding.

WHAT IS CONCEPT BEHIND POLARITYIf work piece is connect with positive terminal and electrode are

connected with negative terminal then this type of polarity..called “straight polarity”

REVERSE POLARITY If work piece are connected with negative terminal and electrode

are connected with positive terminal then this type of welding we called “Reverse welding”

HOW CAN WORK POLARITY When we flow current in electrode and work piece, then due to flow of

current a magnetic field is obtained between electrode and work piece.

MAGNETIC FIELD Then those magnetic field are set up b/w work

piece and electrode .then due to magnetic field are some deflect in magnetic field direction.

These concept are use in forward and reverse welding.

When electrode are move in magnetic field direction .then we called forward welding. Due to this welding we weld very thick material.

When we move electrode in reverse dirction of magnetic field.then these type of welding we called revrse welding .due to this welding we can weld thin type of material.

WELDING POWER SOURCES Each type of power source has fundamental electrical differences

that best suit particular processes Welding machine

Must meet changing arc load and environmental conditions instantly

Must deliver exact amount of electric current precisely at right time to welding arc

Available in wide variety of types and sizes

WELDING POWER SOURCES Also known as power supplies and welding machines Two classifications

Output slope constant current constant voltage

Power source type Transformer – Will deliver only AC Transformer-rectifier – Either AC or DC Motor Alternator – AC and DC if equipped with rectifier Motor Generator – Only DC

TYPE OF OUTPUT SLOPE Two basic types

Constant current Referred to as variable voltage power sources

Constant voltage Referred to as constant potential power sources

OUTPUT SLOPE Relationship between output voltage and output current (amperage)

of machine as current increased or decreased Also called volt-ampere characteristic or curve

Largely determines how much welding current will change for given change in load voltage Permits welding machine to control welding heat and maintain

stable arc Indicates type and amount of electric current designed to produce Each arc welding process has characteristic output slope

SMAW and GTAW require steep output slope from constant current welding machine

GMAW and FCAW require relatively flat output slope from constant voltage power source

Submerged arc welding adaptable to either slop

Constant current Power Sources Has a static volt-ampere curve that tends to produce a

relatively constant load current If arc length varies because of external influences which result

is slight change in arc voltage the welding current remains substantially constant

Each current setting yields separate volt-ampere curve No-load or Open Circuit voltage of constant current arc

welding power sources is considerably higher than the arc voltage.

When used in a semi automated or automated application where constant arc length is required, an arc voltage sensing wire feeder can be used to maintain constant arc length.

CONSTANT CURRENT WELDING MACHINES

Used for shielded metal arc welding and gas tungsten arc welding Current remains fairly constant regardless of changes in arc

length Called drooping voltage, variable voltage, or droppers because

of the substantial downward (negative slope) of the curves Load voltage decreases as welding current increases

Constant current welding machines Steep output slope Available in both d.c. and a.c. welding current

Steeper the slope, the smaller current change Enables welder to control welding current in specific range by

changing length of arc

CONSTANT CURRENT OUTPUT SLOPE

Some jobs require steep volt-ampere curve

Other jobs use less steep volt-ampere curve

CONSTANT VOLTAGEWELDING MACHINES

A Constant voltage arc welding power sources is a power source which has means for adjusting the load voltage and which has a static volt ampere curve that tends to produce a relatively constant load voltage.

TYPICAL OUTPUT SLOPES

OPEN CIRCUIT VOLTAGE/ARC VOLTAGE/LOAD VOLTAGE

OCV is the voltage at the output terminals of a welding power source when it is energized, but current is not being drawn.

OCV is one of design factors influencing the performance of all welding power sources

Voltage generated by welding machine when no welding being done Machine running idle

Arc voltage Voltage generated between electrode and work during welding

Load voltage Voltage at output terminals of welding machine when arc is

going Combination of arc voltage plus voltage drop in welding circuit

OPEN CIRCUIT AND ARC VOLTAGE Open circuit voltage runs between 50-100 volts

Drops to arc voltage when arc struck Arc voltages

Range: 36 volts (long arc) to 18 volts (short arc) Determined by arc length held by welder and type of electrode

used Arc lengthened, arc voltage increases and current decreases

OPEN CIRCUIT AND ARC VOLTAGE Open circuit voltage on constant current machines higher than on

most constant voltage machines Arc voltage depends on physical arc length at point of welding and

controlled by welder Shielded metal arc welding Gas Tungsten arc welding

Arc voltage much lower than open circuit voltage

FOUR TYPES OF POWER SOURCE Engine-driven generators

Powered by gas or diesel combustion engine Can be found with a.c. or d.c. electric motor

No longer being manufactured and rarely found Transformer-rectifiers

Use basic electrical transformer to step down a.c. line power voltage to a.c. welding voltage

Welding voltage then passed through rectifier to convert a.c. output to d.c. welding current

May be either d.c. or a.c.-d.c. machines

FOUR TYPES OF POWER SOURCE A.C. transformers

Used to step down a.c. line power voltage to a.c. welding voltage Inverters

Increases frequency of incoming primary power Constant current, constant voltage, or both Produce a.c. or d.c. welding current

FLUX CORED ARC WELDING (FCAW)

FCAW Process uses an arc between continuous filler wire and weld pool. Process is used with shielding from a flux contained within the

tubular electrode, with or without shielding from an externally supplied gas, and without the application of pressure.

Flux cored electrode is a composite tubular filler metal electrode consisting of metal sheath and a core of various powdered materials.

The feature that distinguishes the FCAW process from other arc welding processes is the enclosure of fluxing ingredients within a continuously fed electrode.

Normally a semiautomatic process

FCAW FCAW process is similar as MIG The electrodes, or filler wire, used in FCAW is completely different

then MIG welding. The main difference is that the electrodes have a hollow centre filled with flux.

Flux Cored Arc Welding Electrodes Types and Designations Flux core arc welding electrodes come in two types: 1. Self-Shielding – Molten Metal is protected through the

decomposition and vaporization of flux core by the heat of the arc. 2. Gas-Shielding – Makes use of a protective gas flow in addition

of the flux core action Shielding Gas usually Co2 or Mixture of Argon and Co2 (Here we

are using 80% Argon + 20%Co2)

FCAW Function of Flux same as SMAW Flux Coating

To Provide Shielding gas through chemical decomposition Act As di-oxidisers which will help to purify and produce a sound

weld metal. To Form a slag and this will float on the molten weld metal and

protect it from atmosphere during solidification. Act as Arc Stabilizers Add alloying elements

FCAW ELECTRODE CLASSIFICATION

E71 T – 1MElectrode

Minimum UTS70,000 psi

PositionFlux Cored /TubularElectrode

Type Gas, Usabilityand Performance

Flux-Cored Arc Welding

American Welding Society SpecificationAWS A5.20 and AWS A5.29.

Flux Cored Arc Welding (FCAW):- Current- DC Polarity – DCEP Current Range 142-185 Amps Voltage Range 20-22V Electrode wire speed range – 140-155 mm/min Size of filler metals – 1.2 mm dia Preheat temp – 121 degree C

E - Stands for electrode. 7 – Identifies the minimum tensile strength of the weld per square

inch, and in this case, you need to add four zeros (70,000). What this means is the filler metal has a minimum of 70,000 pounds of tensile per square inch of weld.

1 – Identifies what position the electrode is designed to weld in. There are only two designations and they are zero and one. Zero means the electrode can only weld in the flat and horizontal positions. One means it can weld in any position.

T – Stands for Tubular and this will be how you know it is a flux cored electrode. If this were a MIG electrode, it would have an “S”, which stands for Solid.

1 – Identifies the type of flux that is inside of the electrode. M stands for Low Maganese

• Fluxes:- Flux gives alloys to bead material Bead becomes stronger than even parent material Provide heat treatment to the bead Protect the bead from attack of atmosphere gases Better arc stabilization Control the arc weld pool viscosity.

Material Used for electrode coatings:- Rutile Calcium carbonate or limestone Fluorspar or fluorite Solka floc Felspar Ball clay Iron powder Ferromanganese Mica Sodium alginate

Deoxidizing Elements :- Alumina, Graphite Slag Formation Component :- Iron oxide, Silicon oxide Arc Stabilizers:- Sodium oxide, magnesium oxide, calcium oxide,

titanium oxide Weld Strength :- Chromium, Tungsten, Nickel, Cobalt, Vanadium

APPLICATIONS Use to weld carbon and low alloy steels Stainless steels Cast irons It is also used for arc spot welding of lap joints in the sheet and plate, as

well as for cladding and handcrafting.

Flux-Cored Arc Welding

ADVANTAGES High deposition rates Deeper penetration than SMAW High-quality Less pre-cleaning than GMAW Slag covering helps with larger out-

of-position welds Self-shielded FCAW is draft tolerant. Using small diameter electrode

wires, welding can be done in all positions

Some flux-cored wires do not need an external supply of shielding gas, which simplifies the equipment

The electrode wire is fed continuously so there is very little time spent on changing electrodes.

Flux-Cored Arc Welding

LIMITATIONS Slag must be removed More smoke and fumes than

GMAW and SAW Spatter FCAW wire is more expensive Equipment is more expensive and

complex than for SMAW

Flux-Cored Arc Welding

SUBMERGED ARC WELDING

SUBMERGED ARC WELDING

• Submerged Arc Welding :- SAW produces coalescence of metals by heating them with an arc

between a bare metal electrode and the work. The arc and molten metal are submerged in a blanket of granular fusible

flux on the work. In SAW, the arc is covered by a flux. Flux main roles are :-

The stability of arc Mechanical and chemical properties of the final weld deposit Quality of the weld.

• Submerged Arc Welding :- The submerged arc welding process is similar to the gas metal arc

welding process except the arc is struck under a blanket of granular flux, hence the name submerged arc welding.

Continuous bare wires in the form of coils and dry granular fluxes are used in the combination as consumables for SAW

The Flux protects the arc, the molten filler metal and hot base metal from oxygen, nitrogen and water vapor in air.

The Flux Sprinkles on the work piece ahead of the welding wire and the electrode ploughs through the flux making the weld.

Arc being Submerged, there are no heat losses from arc through radiation. This makes the process highly thermal efficient (nearly 90% of the heat generated in arc is utilized).

Current- DC Polarity – DCEP Voltage- Constant Current Range – 390-530 Amps Travel Speed– 295-405 mm/min Electrode – F7A2-EL8

SAW FLUX / FILLER METAL COMPOSITIONS

F7A2-EL8 F indicates a submerged arc welding flux 7 indicates the tensile strength ( in increments of 10000 psi) A indicates condition of heat treatment ( A for as welded and

P for post weld heat treatment) 2 indicates the temperature in -20°F at which the impact

strength of the weld metal meets or exceeds 20 ft-lbs EL8 – Wire E – For Electrode L – Indicates for Low Manganese 8 Stands for .08% C

ADVANTAGES High deposition rates Consistent weld quality attributable

mechanized application of process. High weld metal recovery due to absence

of spatter losses High thermal efficiency Reduced welder fatigue due to absence of

irritating arc radiation No arc flash or glare Minimal smoke and fumes Flux and wire added separately - extra

dimension of control Easily automated Joints can be prepared with narrow

grooves Can be used to weld carbon steels, low

alloy steels, stainless steels, chromium-molybdenum steels, nickel base alloys

Submerged Arc Welding

LIMITATIONS High current associated with the

process limit the application to thickness greater than 3/16”.

Flux obstructs view of joint during welding

Flux is subject to contamination Þ porosity

Restricted to the flat position for grooves - flat and horizontal for fillets

Slag removal required Flux handling equipment

Submerged Arc Welding

APPLICATIONS Pressure Vessel Fabrication Ship and barge building railroad car fabrication Pipe manufacturing Fabrication of structural members where long welds are required. SAW is not suitable for all metals and alloys.

It is widely used on carbon Steels, Low alloy structural steels, and stainless steels, high carbon Steels and nic

Flux-Cored Arc Welding

Thank u