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It is also common to use longer contact tip to 
workplace distances with flux cored arc welding 
than with solid wire MIG welding and this also 
has the effect of increasing the resistive heating 
on the wire further accentuating the drop in 
welding current. Research has also shown that 
increasing this distance can lead to an increase 
in the ingress of nitrogen and hydrogen into 
the weld pool, which can affect the quality of 
the weld.
Flux cored arc welding has a lower efficiency 
than solid wire MIG welding because part of the 
wire fill contains slag forming agents. Although 
the efficiency varies differs by wire type and 
manufacturer it is typically between 75–85%.
Flux cored arc welding does, however, have 
the same drawback as solid wire MIG in terms 
of gas disruption by wind, and screening is 
always necessary for site work. It also incurs 
the extra cost of shielding gas, but this is often 
outweighed by gains in productivity.

Self-shielded Operation

There are also self-shielded consumables 
designed to operate without an additional gas 
shield. In this type of product, arc shielding is 
provided by gases generated by decomposition 
of some constituents within the flux fill. These 
types of wire are referred to as ‘self-shielded’.
If no external gas shield is required, then the 
flux fill must provide sufficient gas to protect 
the molten pool and to provide de-oxidisers 
and nitride formers to cope with atmospheric 
contamination. This leaves less scope to 
address performance, arc stabilisation, and 
process tolerance, so these tend to suffer when 
compared with gas shielded types.
Wire efficiencies are also lower, at about 65%, in 
this mode of operation than with gas-shielded 
wires. However, the wires do have a distinct 
advantage when it comes to site work in terms 
of wind tolerance, as there is no external gas 
shield to be disrupted.

Extended self shielded flux cored wire nozzle

When using self-shielded wires, external gas 
supply is not required and, therefore, the gas 
shroud is not necessary. However, an extension 
nozzle is often used to support and direct the 
long electrode extensions that are needed to 
obtain high deposition rates.

2.3   Introduction to Metal Cored 

Arc Welding (MCAW)

How it Works

Metal-cored arc welding (MCAW) uses the heat 
generated by a DC electric arc to fuse metal 
in the joint area, the arc being struck between 
a continuously fed consumable filler wire and 
the workpiece, melting both the filler wire and 
the workpiece in the immediate vicinity. The 
entire arc area is covered by a shielding gas, 
which protects the molten weld pool from the 
atmosphere.
As MCAW is a variant of the MIG welding 
process there are many common features 
between the two processes, but there are also 
several fundamental differences.
As with MIG, direct current power sources 
with constant voltage output characteristics 
are normally employed to supply the welding 
current. With metal-cored wires the terminal 
the filler wire is connected to depends on 
the specific product being used, some wires 
designed to run on electrode positive, others 
preferring electrode negative, and some which 

Summary of Contents for 180P

Page 1: ...180P O P E R AT I N G M A N U A L...

Page 2: ...omission which may become apparent after the document has been issued Neither BOC nor any of its agents has independently verified the accuracy of the information contained in this document The infor...

Page 3: ...elding MCAW 8 2 4 Fundamentals of MIG FCAW and MCAW 12 3 0 General Welding Information 14 3 1 Recommended Welding Parameters 14 4 0 Correct ApplicationTechniques 15 5 0 Troubleshooting and Fault Findi...

Page 4: ...es Be alert to this at all times Keep your head out of the fumes rising from the arc Fumes from the welding of some metals could have an adverse effect on your health Don t breathe them in If you are...

Page 5: ...ian and operator and will void your warranty Only qualified personnel approved by BOC should perform repairs Always disconnect mains power before investigating equipment malfunctions Parts that are br...

Page 6: ...l of manual welding The process is also suitable for mechanised set ups and its use in this respect is increasing MIG welding can be carried out using solid wire flux cored or a copper coated solid wi...

Page 7: ...ed to as gas shielded Using an auxiliary gas shield enables the wire designer to concentrate on the performance characteristics process tolerance positional capabilities and mechanical properties of t...

Page 8: ...ves less scope to address performance arc stabilisation and process tolerance so these tend to suffer when compared with gas shielded types Wire efficiencies are also lower at about 65 in this mode of...

Page 9: ...tes the shielding gas evenly around a shroud which then allows the gas to flow over the weld area The position of the contact tip relative to the gas shroud may be adjusted to limit the minimum electr...

Page 10: ...with these types of wire GlobularTransfer Metal transfer is controlled by slow ejection resulting in large irregularly shaped globs falling into the weld pool under the action of gravity Carbon dioxid...

Page 11: ...o the weld In spray transfer as the current density increases an arc is formed at the end of the filler wire producing a stream of small metal droplets In solid wire MIG this transfer mode occurs at h...

Page 12: ...roperties or level of residual hydrogen in the weldmetal Solid MIG wires are all considered to be of the low Hydrogen type consumables The following table gives a general overview of the selection of...

Page 13: ...al rule all solid and metal cored wires are welded on electrode positive Work return lead fitted to the negative connector Some grades of self shielded flux cored wires i e E71T 11 E71T GS etc needs t...

Page 14: ...14 16 16 17 16 18 16 18 23 25 Wire feed speed m min 3 5 5 0 4 0 7 0 4 0 7 0 4 0 7 0 7 5 9 0 Gas rate flow L min 15 15 15 15 15 Travel speed mm min 350 500 350 500 320 500 280 450 800 1000 Stainshield...

Page 15: ...rcement Flux cored welding with cored wires takes place normally with the drag technique when there is slag in your drag The welding gun is tilted at an angle of 10 away from the direction of welding...

Page 16: ...the melt off rate of the wire that will have an influence on the weldbead profile Short Normal Long Normal Long Short Normal Long Influence of the change in electrical stickout length on the weldbead...

Page 17: ...deformation Incorrect feed roll size incorrect tension adjustment misalignment Inlet outlet guides Wire shaving or snarling Incorrect wire guide sizes misalignment Universal adaptor Wire restriction...

Page 18: ...workpiece No nozzle insulator fitted Regulator flowmeter Component Fault symptom Cause Inlet stem No gas flow gas leaks at regulator body or cylinder valve Blocked inlet stem leaking inlet stem to bo...

Page 19: ...tput voltage adjustment V 14 26 Duty Cycle 60 Power Factor 0 73 Efficiency 80 Type of wirefeeder machine Compact Wire speed m min 2 15 Post flow s 1 Maximum spool size mm 200 Wire diameter mm 0 6 0 8...

Page 20: ...that the wire feed speed is not excessive Adjust the pressure adjusting knob to ensure 4 that the wire is fed evenly Over tightening the adjusting knob will cause undue strain on the wire feed motor S...

Page 21: ...achine and its consumables 8 1 Power Source Check electrical connections of unit at least twice a year Clean oxidised connections and tighten Inner parts of machine should be cleaned with a vacuum cle...

Page 22: ...o daily allowances or accommodation and travelling costs Note Under the terms of warranty welding guns and their consumables feed drive rollers and feeder guide tubes are not covered Direct or indirec...

Page 23: ...inder Never use oxygen for venting containers 10 0Recommended Safety Guidelines Diagram and safety explanation Electrical safety alert Welding electrode causing electric shock Fumes and gases coming f...

Page 24: ...believed to be correct at the time of printing Whilst proper care has been taken in the preparation no liability for injury or damage resulting from its improper use can be accepted BOC Limited 970 98...

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