Advanced Welding Processes: Technologies and Process Control

Filler materials for arc welding 55
porosity (referred to as ‘worm tracks’) if short electrode extensions are used,
particularly in the downhand position. Increasing the extension allows the
excess lubricant to be driven off and avoids the problem. Short electrode
extensions are also associated with higher weld metal hydrogen levels. For
manual operation, the minimum extension may be controlled by the relative
position of the gas shroud and contact tip as shown in Fig. 4.9. The equipment
required for flux-cored wire operation is basically the same as that required
for GMAW welding, although, for the less tolerant types of self-shielded
consumable, a voltage stabilized power source may be specified (the electronic
designs discussed in Chapter 3 will meet this requirement). For all fluxcored
wires, it is important to use specially designed feed rolls to avoid
crushing the wire in the feed system.
4.4.6 Applications of FCAW
The applications of flux-cored wires include the joining of thick-section
high-strength steels for critical applications as in high-speed mechanized
welding of lighter sections using metal-cored wire or the fabrication of highquality
stainless-steel process plant.
4.4.7 Limitations of flux-cored wires
The apparent limitations of flux-cored wire are:
∑ cost;
∑ fume;
∑ consistency of the consumable.
Contact tip
Gas nozzle
Minimum
extension
4.9 Limiting the minimum electrode extension by means of contact
tip to gas nozzle adjustment.