What is Welding Flux?
Welding flux is a combination of silicate and carbonate material which is used in the welding process to form a shielding layer which prevents the contamination of atmospheric gases with the weld.
The flux is present in the outer coating of the welding electrodes.
This flux has less density than the metal to be welded. So during the welding process, the flux melts and it floats above the weld.
In this way, the welding flux protects the weld from the contamination of atmospheric gases.
Functions of flux in welding process
The functions of flux coating on electrodes are mentioned below.
- During the welding process, the flux melts and forms a shielding layer around the arc. This shielding layer prevents the reaction of atmospheric gases with the weld.
- The welding flux helps to deoxidize and refine the weld metal.
- It also helps in reducing the weld spatter.
- The welding flux generates the gases which displace the nitrogen and oxygen of the atmosphere. This way the flux also provides the gaseous shield around the arc as well as molten weld puddle.
- The slag is produced on the weld metal (see the first image) which further protects the finished welded part from the atmosphere.
- Weld flux helps to control the weld bead profile and hence a smooth weld surface is obtained.
- The purpose of the flux coating on an electrode is to insulate the electrode so that it can operate at higher current without getting overheated.
- Vertical and overhead welding is also possible by controlling the viscosity of the slag (using different types of coating materials).
- The flux coating also increases the weld deposition rates if iron power or ferro alloys are added.
- The weld flux coating controls the arc voltage as well as current intensity.
Flux coating material of welding electrode
The flux coating materials of welding electrodes are listed below.
- Flux agents: Silica, CaO (from like stone).
- Slag formers: Titania, Titanate, Rutile, Asbestos, Silica flour, Alumina, Feldspar, Iron powder, etc.
- Arc stabilizers: Potassium silicate, Zirconium carbonate, Titania, potassium oxalate, Potash.
- Gas forming materials: Limestone, cellulose, wood flour.
- Binding agents: Dextrin, sodium silicate, potassium silicate, asbestos, etc.
- Deoxidizers and alloying materials: Ferrosilicon, Ferrotitanium, Ferrochromium, Ferromanganese, Ferromolybdenum, etc.
- Slipping agents: Glycerin, Kaolin clay, talc, bentonite clay, mica.
Types of flux coating on electrodes
There are different types of flux coatings on electrodes depending upon the welding power source, material to be welded, etc.
6 types of flux coatings used on electrodes are mentioned below.
- Cellulose type
- Rutile type
- Acid type
- Acid rutile type
- Oxidizing type
- Basic type
For more information on the types of flux coatings, visit the main article: Guide on coated Electrode and its types
SMAW process: Image by U.S. Army, Public domain, via Wikimedia Commons