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Fcaw and saw welding process


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Fcaw and saw welding process

  1. 1. FCAW & SAW WELDING By- Jitendra Bhatia Date:- 2 Dec 2015
  2. 2.  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 welding AC welding DC welding
  3. 3.  Ac welding polarity are not fixed…  Due to polarity changes we can not use for all types of welding
  4. 4.  Fixed polarity  With the help of fixed polarity. We can handle according to use thick or thin welding.
  5. 5. WHAT IS CONCEPT BEHIND POLARITY If work piece is connect with positive terminal and electrode are connected with negative terminal then this type of polarity..called “straight polarity”
  6. 6. 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”
  7. 7. 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.
  8. 8. 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.
  9. 9. 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
  10. 10. 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
  11. 11. 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
  12. 12. 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
  13. 13.  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.
  14. 14. 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
  15. 15. CONSTANT CURRENT OUTPUT SLOPE Some jobs require steep volt-ampere curve Other jobs use less steep volt-ampere curve
  16. 16. CONSTANT VOLTAGE WELDING 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.
  18. 18. 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
  19. 19. 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
  20. 20. 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
  21. 21. 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
  22. 22. 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
  24. 24. 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
  25. 25. 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)
  26. 26. 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
  27. 27. FCAW ELECTRODE CLASSIFICATION E71 T – 1M Electrode Minimum UTS 70,000 psi Position Flux Cored /Tubular Electrode Type Gas, Usability and Performance Flux-Cored Arc Welding American Welding Society Specification AWS A5.20 and AWS A5.29.
  28. 28.  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
  29. 29.  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
  30. 30. • 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.
  31. 31.  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
  32. 32. 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
  33. 33. 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
  34. 34. 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
  37. 37. • 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.
  38. 38. • 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
  39. 39. 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
  40. 40. 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
  41. 41. 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  porosity  Restricted to the flat position for grooves - flat and horizontal for fillets  Slag removal required  Flux handling equipment Submerged Arc Welding
  42. 42. 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