Flux Coating

Definition - What does Flux Coating mean?

A flux coating is a layer of a chemical which acts as a cleaning agent, a purifying agent or a flowing agent. The coating is used on electric welding rods and serves several functions. It protects the weld pool and solid metal from atmospheric contamination and helps in removing impurities from the weld pool. The impurities float on the surface of the pool and are easily removed after it cools down. These two functions contribute to the formation of a strong and durable welded joint.

Corrosionpedia explains Flux Coating

When a flux-coated electrode is heated up, part of the flux burns and forms a gaseous shield which keeps the oxygen away from the weld. This prevents the formation of a poor weld which occurs when iron burns in oxygen. Another part of the flux melts and mixes with the weld pool, the impurities of which float and are easily removed when the weld joint cools down.

The main functions of the coating are:

  • Forming a gaseous shield around the weld area
  • Removing impurities from the weld
  • Introducing deoxidizers into the reaction zone using the coating (to reduce oxidation of the base metal)
  • Formation of a solid coating on the weld as it cools
  • Additional alloying elements are introduced through the coating

A variety of flux coatings are available and each determines how the electrode acts. The environmental conditions, temperature and type of metal are the factors that determine the type of coating to be used.

Some specific advantages of flux include:

  • Electrodes with heavy flux coating produce high-quality welds because they have a deeper penetration.
  • The cellulose coating offers increased burn-off rate and imparts deep penetration.
  • The iron oxide coating produces great weld appearance.
  • Low-hydrogen coatings produce crack-resistant welds.

Flux coating on the electrodes ensures a weld with good mechanical properties, chemical composition and weld metal cleanliness.

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