• Post category:weld tech

Flux in welding operation


Flux is used to protect the molten metal from all types of atmospheric contamination.

In Gas welding, the metal is heated in air, oxygen from the air combines with the metal to form oxides that result in poor quality, low strength welds or, in some cases, welding may be impossible. To avoid this difficulty, a flux is employed during welding.

Flux Used in various metals

The flux is always fusible, but non-metallically and chemically reacts with the oxide and forms slag that floats and covers over the molten puddle of the metal, thus keeping atmospheric oxygen and other harmful gases out. Helps in
Flux ards are available as power, pests, and liquids and can be used either by applying directly to the base metal surface or by immersing the hot end of the filler rod in it.

Flux is used in gas welding of cast iron, stainless steel, and most non-ferrous metals, in addition to lead, zinc and some precious metals.  

  Shielding Gasses


Flux in cast iron

In cast iron, flux is required. Flux fusible increases the fluidity of iron-silicate slag, as well as being helpful in removing slag.
Usually made of flux, borates or boric acid, soda ash and other compounds such as sodium chloride, etc., for gray iron rods.
See Cast Iron

Flux in stainless steel

To ensure better control of molten metal and to make a sound weld fluxes are required. Flux should also be applied inside the prevent oxidation. It may include compounds such as borax, boric acid, fluorspar, etc.

Flux in Aluminium 

In the welding of aluminum welding, flux is necessary due to the formation of oxide film on the metal which will prevent the sound welds.
When flux is used the oxide breaks down and turns them into a fusible slag. Fusible slag weld lighter than base metal floats on the puddle surface. It can be applied to the base metal by brush and immersed in the flux past before welding and applied to the filler rod end. The composition of flux in aluminum and alloys is lithium sodium and potassium in insect or powder form. It may contain potassium chloride, lithium chloride, etc.

Flux in Nickel 

For welding of nickel, the flux is not required but if welding its alloys like Inconel and Monel flux is needed.
 Flux content for Inconel Ca(OH)2, Boric anhydride B2O3
Flux content for Monel


Flux in Copper

For welding of Copper, the flux is not required but if welding its alloys flux is needed. The flux for copper alloys may contain Borax, Boric acid, Phosphate, Magnesium silicate, and Lime, etc.

Flux in Magnesium

For welding of Magnesium flux is necessary and should be applied to all edges of the base metal to be welded and filler metal .the flux may contain Sodium chloride, Potassium fluoride, Magnesium chloride, Barium chloride, etc.

Filler metal Melting Point °CFlux Required 
Copper Coated Mild Steel1490NO
High Carbon Steel1350YES
Nickel Steel1450YES
Wear-Resisting Alloy Steel1320NO
Pipe Welding Electrodes1450NO
Stainless Steel1440YES
Super-Silicon Cast iron1147YES
Copper Silver alloy1068YES
Nickel bronze910YES
Aluminum alloys with 5% copper640YES
Aluminum alloys with 5%silicon635YES