Page 116 - CITS - Welder - Trade Theory

WELDER - CITS

3 Function of flux
1 Arc stabilizing substances: These are carbonates known as chalk and marble. These are used for the
stabilisation of the arc.
2 Deoxidizers: These substances prevent porosity and make the welds stronger. The deoxidising substances
are iron oxide, lamitite, magnetite.
3 Slag forming substances: These substances melt and float over the molten metal and protect the hot
deposited weld metal from the atmospheric oxygen and nitrogen. Also due to the slag covering, the weld
metal is prevented from fast cooling. The slag forming substances are clay, limestone.
4 Fluxing/cleaning substances: These substances remove oxides from the edges to be welded and
controls the fluidity of the molten metal. The cleaning substances are lime stone, chlorides, fluorides.
5 Gas forming substances: These substances form gases which aid the transfer of metal. They also shield
the welding arc and weld pool. The substances are: wood flour dextrin and cellulose.
6 Binding and plasticizing substances: These sub- stances help the applied coating to grip firmly around
the core wire of the electrode.
These are: sodium and potassium silicates.
Purpose or function of flux coating: During welding, with the heat of the arc, the electrode coating melts and
performs the following functions.
a It stabilizes the arc.
b It forms a gaseous shield around the arc which protects the molten weld pool from atmospheric contamination.
c It compensates the losses of certain elements which are burnt out during welding.
d It retards the rate of cooling of the deposited metal by covering with slags and improves its mechanical
properties.
e It helps to give good appearance to the weld and controls penetration.
f It makes the welding in all positions easy.
g Both AC and DC can be used for the welding.
h Removes oxide, scale etc. and cleans the surfaces to be welded.
i It increases metal deposition rate by melting the additional iron powder available in the flux coating.
4 Types of flux Coating

a Cellulosic (Pipe welding electrode e.g. E6010)
b Rutile (General purpose electrode e.g. E6013)
c Iron powder (e.g. E7018)
d Basic coated (Low hydrogen electrode e.g. E7018)
5 Method of flux coating:
a Dipping
b Extrusion
Dipping method: The core wire is dipped in a container carrying flux paste. The coating obtained on the core
wire is not uniform resulting in non-uniform melting; hence this method is not popular.

Extrusion method: A straightened wire is fed into an extrusion press where the coating is applied under pressure.
The coating thus obtained on the core wire is uniform and concentric, resulting in uniform melting of the electrode.
This method is used by all the electrode manufacturers.
Coating factor (Fig 6): The ratio of the coating diameter to the core wire diameter is called the coating factor -
Coating diameter
= Coating wire diameter
It is 1.25 to 1.3 for light coated

1.4 to 1.5 for medium coated

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CITS : CG & M - Welder - Lesson 27 - 30 CITS : CG & M - Welder - Lesson 27 - 30