Welding electrodes.pdf

Welding electrode: Types, functions
Welding electrode
A welding electrode is a piece of wire or rod, which can be of metal or alloy
and has a flux with or without flux and carries an electric current to obtain
sufficient heat for welding. At one end it is fastened to a holder and an arc
is installed at the other.
Welding electrode an
introduction
Electrodes are the most
part of welding work.
Welding without electrodes
is impossible in most
welding processes, mainly
divided into two parts,
based on the electrode work function.
Types of welding electrode
Depending on the function, electrodes can be classified as follows:
NonConsumable Electrode
Consumable electrode
NonConsumables(refractory) Welding electrodes
1. These electrodes do not fuse at the time of welding and only act as electrical
conductors that generate arcs to obtain sufficient heat, called none
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consumable electrodes, and they are made up of high melting point metals
Such as tungsten ( melting point 6150 ° F), carbon (melting point 6700).
These electrodes do not melt while welding and a separate filler wire is
required with these electrodes to fill the joint. However, due to the evaporation
and oxidation of the electrode during welding, the length of the electrode
decreases with the passage of time.
No consumable electrode may be classified as follows:
a Carbon or Graphite electrodes
b Tungsten Electrodes
Nonconsumable electrodes often have coppercoated carbon or graphite
electrodes. The copper coating increases the electrode’s electrical
conductivity or current conduction capacity.
Carbon electrode and graphite electrode
Carbon Electrode is less expensive than graphite electrodes. The resistive
capacitance inside the carbon electrode is higher as compared to the graphite
electrode, as a result, this current stream takes comparatively less, short life due
to soft material while the graphite electrode is more expensive, carrying current
more because of less electrical resistance. Its material is hard and brittle thus
the carbon electrode has longer life compared to the carbon electrode.
Tungsten Electrodes
The next electrode in the series of nonconsumable electrodes is tungsten which
can be basically classified as follows:
Pure tungsten,
Zirconiated tungsten, (0.3 to0.5%)
Thoriated tungsten (1 2%).
In pure tungsten the alloy increases, resistance to contamination, arc stability,
and electrode life. In addition, arc initiation is easy, the electrode tip remains
cold (compared to pure tungsten electrodes), electrode consumption is low, and
current carrying capacity gains. Compared to carbon electrodes, tungsten
electrodes are much more expensive and alloy tungsten electrodes are still more
COStlier. Tungsten/alloy tungsten electrodes from 0.5 mm to 6 mm directors are
commonly available for welding purposes

Consumable (Metallic) Welding Electrodes

These type of
welding electrodes
have a low melting
point, and act as
electrical conductors
that generate arcs to
obtain sufficient
heat, melts the
metal, and fills the
joint, are called
consumable welding
electrodes,
Consumable
electrodes can be
classified as follow:
a Bare electrode
b Flux covered
electrode
a Bare Electrodes:
This type of electrode requires additional shielding to protect the metal from
atmospheric contamination of the molten weld pool which may be in the form of
gas or flux.
b Flux covered electrode

This type of electrode does not require any additional
shielding to protect the metal from atmospheric
contamination. These are themselves coated with
fluxes that would completely cover the weld pool as
slag at the time of welding. And are subsequently
removed after cooling.
Electrodes and material data with the full description you can download here…..

Download
Flux Covered Electrodes
Electrode
coating
ingredients
The
covering/coating
on the core wire
consists of
several materials
that provide a
variety of
properties to the
electrode.
These ingredients
and their
functions are as
follows:

Slag forming
ingredients
Slag forming ingredients produce a lightweight slag which forms a layer on the
molten metal and protects the weld pool from atmospheric contamination.
silicates of sodium, potassium, magnesium, aluminum, iron oxide, china clay,
mica, etc., are responsible for the slag forming process.
Gas Shielding ingredients,
The gas shielding ingredients produce a protective gas shield around the
electrode tip arc and the weld pool.
Cellulose, wood flour, starch, calcium carbonate, etc., are used as gas shielding
ingredients.
Deoxidizing elements
Deoxidizing elements refine the molten metal, for this ability, ferromanganese,
and ferrosilicon, are used.
Purpose of using ingredients in electrodes
Proper coated ingredients produce weld metals resistant to cold and hot
cracking and improve metal deposition rate.
The coating protects the welding operator from electric shock and radiation.
Alloying elements such as iron alloys of manganese, molybdenum, etc. may be
added to provide suitable properties and strengths to the weld metal and to
make up for the loss of certain elements, which vaporize during welding.
Coating/covering Improves, weld penetration and surface finish, it limits
spatter, produces a quiet welding arc, and easily removable slag.
Sizing of welding electrodes
Wires of different chemical compositions and sizes are obtained from electrode
manufacturing companies. manufacturing companies, chemically cleaned, cut
into different lengths, and straightened in the electrodemaking plant. Generally,
electrodes come in sizes 300, 350, 450, etc.
Flux application on the Welding Electrodes

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The flux coating is applied on the core wire by two methods, which are as
follows:
Dipping method
Several core wires cut to the desired length are clamped vertically into a fixture
and immersed in a bath of molten flux. When a suitable thickness of flux is glued
to the core wire, the fixture is raised up and the flux is allowed to dry.
Extrusion method
The extrusion method is much faster than the dipping method and is widely used
these days.
In this method, the coating material is mixed in the desired quantity, and the
resultant mass is brought to a thick, viscous, hardpaste. The paste is shaped
like a cylinder that is poured into the extrusion press.
The thick paste of core wire and flux are simultaneously passed through a die
under pressure, thus enclosing the flux coating on the core wire. The thickness
of the coating depends on the opening of the die and can be varied.
As a next step the flux from the gripping end of the electrode is removed by an
electrically rotating wire brush; After which the electrodes are fed into an oven
where they are dried and baked to remove excess moisture.

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