Flux Cored Arc Welding (FCAW) Self-Shielded.
In cored arc welding the heat is obtained from an arc between a continuous flux cored wire and the work. The flux provides gas shielding for the arc and a slag covering of the weld deposit.
What is the self-shielded flux-cored arc welding process, and how did it develop from stick welding?
The self-shielded flux-cored arc welding process is a development of the shielded metal arc welding process.
The versatility and manoeuvrability of stick electrodes in manual welding stimulated efforts to mechanise the process, allowing a continuous wire electrode to be used. A continuous electrode would eliminate the welding time lost in changing electrodes and would eliminate the material lost in electrode stubs. The main problem with a continuous coated electrode is to find a suitable means of making electrical contact with the core wire and coiling it without cracking the brittle coating. The need for a continuous arc welding electrode led to the development of the self-shielding flux-cored wire, where the material needed for shielding is contained inside the core of a hollow wire.
How did the self-shielded flux-cored wire develop from stick welding electrodes?
The "inside-out" construction of the flux-cored wire solved both problems. Continuous electrical contact can be made with the wires at any distance from the arc, and they can be coiled and packaged on any of the standard spools used for filler wire. The outcome of these efforts was the development of the semiautomatic and full-automatic processes for welding with continuous flux-cored tubular "wires". Such wires contain in their cores the ingredients for fluxing and deoxidising molten metal and for generating shielding gases and vapours and slag coverings.
In essence, semiautomatic welding with flux-cored wires is equivalent to manual shielded metal-arc welding with an electrode several feet long instead of one of a few inches. By the press of the trigger to complete the welding circuit, the operator activates the mechanism that feeds the wire to the arc. He uses a welding gun instead of an electrode holder, but it is correspondingly light in weight and easy to use. The only difference is the weld metal of the electrode surrounding the shielding and fluxing chemicals, rather than being surrounded by them.
In the flux-core arc welding process, partial shielding is provided by vaporisation of ingredients of the flux, which form a protective gas covering of the weld pool. When molten weld metal is transferred across the arc, it may not be completely covered by molten flux since the metal surrounds the flux, as both are heated. This means that some oxidation and nitrogen pickup may occur before the metal enters the weld pool. However, as opposed to the gas-shielded flux-cored process, the self-shielded flux-cored process does not depend on gas shielding; it can operate satisfactorily outdoors where strong air currents are encountered.
The self-shielded flux-cored process is characterised by wire beyond the contact tip. Extensions from 6 mm to 30 mm are used depending upon the application. Welding equipment for Gas Metal
Arc Welding (GMAW) can, in most cases, also be used for Self Shielded Flux Cored Arc Welding with small modifications (wire feeder rolls should be knurled, insulation nozzle instead of gas nozzle, etc.). Note that flux-cored arc welding takes place with the welding torch connected to minus (-) polarity.
Wires for self-shielded flux-cored arc welding are available in standard sizes from 0.9mm in mild steel.