FLUX CORED ARC WELDING TWI Training Examination Services

FLUX CORED ARC WELDING TWI Training & Examination Services EWF/IIW Diploma Course Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology

Flux cored arc welding FCAW methods With gas shielding “Outershield” Without gas shielding “Innershield” (114) With active gas shielding (136) Copyright © 2005, TWI Ltd With metal powder “Metal core” With inert gas shielding (137) World Centre for Materials Joining Technology

“Outershield” process Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology

“Innershield” process Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology

Structure of the cored wires Functions of metallic sheath: • provide form stability to the wire • serves as current transfer during welding Copyright © 2005, TWI Ltd Function of the filling powder: • stabilise the arc • add alloy elements • produce gaseous shield • produce slag • add iron powder World Centre for Materials Joining Technology

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 Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology

Types of cored wire Seamless 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 Copyright © 2005, TWI Ltd Butt joint cored wire Overlapping cored wire • 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 World Centre for Materials Joining Technology

Cored wire manufacturing process Forming rollers Draw die Thin sheet metal Closing rollers Flux input Strip reel Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology

FCAW wire designation Wire designation acc. BS EN 758: Diffusible hydrogen content (optional) Shielding gas Light alloy additions Tensile properties Standard number EN 758 - T 46 3 1 Ni B M 4 H 5 Tubular cored electrode Impact properties Type of electrode core Welding position (optional) Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology

FCAW wire designation Wire designation acc. AWS A-5. 20: 27 J 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 H 8 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 Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology

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 Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology

FCAW - differences from MIG/MAG 350 Amps self shielded welding gun Close wound stainless steel spring wire liner (inside welding gun cable) 24 V insulated switch lead Handle Conductor tube Trigger Thread protector Welding gun cable Hand shield Contact tip Courtesy of Lincoln Electric Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology

FCAW - differences from MIG/MAG Self shielded electrode nozzle Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology

Travel Angle 75° Copyright © 2005, TWI Ltd 90° 75° World Centre for Materials Joining Technology

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 Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology

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 Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology

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 Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology

FCAW advantages Deposition rate for carbon steel welding Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology

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) Copyright © 2005, TWI Ltd World Centre for Materials Joining Technology