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TWI Training & Examination Services EWF/IIW Diploma Course

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Presentation on theme: "TWI Training & Examination Services EWF/IIW Diploma Course"— Presentation transcript:

1 TWI Training & Examination Services EWF/IIW Diploma Course
FLUX CORED ARC WELDING TWI Training & Examination Services EWF/IIW Diploma Course

2 Flux cored arc welding FCAW methods With gas shielding - “Outershield”
Without gas shielding - “Innershield” (114) With metal powder - “Metal core” With active gas shielding (136) With inert gas shielding (137)

3 “Outershield” process

4 “Innershield” process

5 Structure of the cored wires
Functions of metallic sheath: Function of the filling powder: provide form stability to the wire serves as current transfer during welding stabilise the arc add alloy elements produce gaseous shield produce slag add iron powder

6 Core elements and their function
Aluminium - deoxidize & denitrify Calcium - provide shielding & form slag Carbon - increase hardness & strength Manganese - deoxidize & increase strength Molybdenum - increase hardness & strength Nickel - improve hardness, strength, toughness & corrosion resistance Potassium - stabilize the arc & form slag Silicon - deoxidize & form slag Sodium - stabilize arc & form slag Titanium - deoxidize, denitrify & form slag

7 Overlapping cored wire
Types of cored wire Seamless cored wire Butt joint cored wire Overlapping cored wire not sensitive to moisture pick-up can be copper coated  better current transfer thick sheath  good form stability  2 roll drive feeding possible difficult to manufacture good resistance to moisture pick-up can be copper coated thick sheath difficult to seal the sheath sensitive to moisture pick-up cannot be copper coated thin sheath easy to manufacture

8 Cored wire manufacturing process
Strip reel Thin sheet metal Flux input Draw die Closing rollers Forming rollers

9 FCAW wire designation EN 758 - T 46 3 1Ni B M 4 H5 EN 758 T 46 3 1Ni B
Wire designation acc. BS EN 758: Diffusible hydrogen content (optional) Shielding gas Light alloy additions Tensile properties Standard number EN T Ni B M 4 H5 EN 758 T 46 3 1Ni B M 4 H5 Tubular cored electrode Impact properties Type of electrode core Welding position (optional)

10 FCAW wire designation E 71 T-6 M J H8 E 7 1 T -6 M J H8
Wire designation acc. AWS A-5.20: 27J at -40°C requirement (optional) Electrode usability (polarity, shielding and KV); can range from 1 to 14 Welding position (0 - F/H only; 1- all positions) Designates an electrode E 71 T-6 M J H8 E 7 1 T -6 M J H8 Minimum UTS of weld metal (ksi x 10) Flux cored electrode Shielding gas for classification Diffusible hydrogen content (optional); can be 4, 8 or 16

11 FCAW - differences from MIG/MAG
usually operates in DCEP but some “Innershield” wires operates in DCEN power sources need to be more powerful due to the higher currents doesn't work in deep transfer mode require knurled feed rolls “Innershield” wires use a different type of welding gun

12 FCAW - differences from MIG/MAG
350 Amps self shielded welding gun Courtesy of Lincoln Electric Close wound stainless steel spring wire liner (inside welding gun cable) 24V insulated switch lead Handle Conductor tube Welding gun cable Trigger Thread protector Hand shield Contact tip

13 FCAW - differences from MIG/MAG
Self shielded electrode nozzle

14 Travel Angle 75° 90°

15 Backhand (“drag”) technique
Advantages preferred method for flat or horizontal position slower progression of the weld deeper penetration weld stays hot longer  easy to remove dissolved gasses Disadvantages produce a higher weld profile difficult to follow the weld joint can lead to burn-through on thin sheet plates

16 Forehand (“push”) technique
Advantages preferred method for vertical up or overhead position arc is directed towards the unwelded joint  preheat effect easy to follow the weld joint and control the penetration Disadvantages produce a low weld profile, with coarser ripples fast weld progression  shallower depth of penetration the amount of spatter can increase

17 FCAW advantages less sensitive to lack of fusion
requires smaller included angle compared to MMA high productivity all positional smooth bead surface, less danger of undercut basic types produce excellent toughness properties good control of the weld pool in positional welding especially with rutile wires seamless wires have no torsional strain  twist free ease of varying the alloying constituents no need for shielding gas

18 FCAW advantages Deposition rate for carbon steel welding

19 FCAW disadvantages limited to steels and Ni-base alloys
slag covering must be removed FCAW wire is more expensive on a weight basis than solid wires (exception: some high alloy steels) for gas shielded process, the gaseous shield may be affected by winds and drafts more smoke and fumes are generated compared with MIG/MAG in case of Innershield wires, it might be necessary to break the wire for restart (due to the high amount of insulating slag formed at the tip of the wire)

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