Plasma is the ionized state of gas atoms. When an ionized gas passes through the
electric current, it becomes mixture of ions, electron and highly excited atoms.
Thus the energy of plasma and the temperature is dependent on the amount of the electrical
power employed. A tremendous amount of temperature is obtained from plasma torch
is about 500000F.
The plasma welding is one type of arc welding process by which single body is produced
by heat is obtained from plasma between the work piece and tungsten or tungsten alloy
There are two types of inert gas is employed for plasma welding process, one formed
the plasma and other is shielding the plasma.
Principle of plasma welding
A non-consumable cathode electrode as a tungsten and water cooled copper as anode
is used in this welding process. The initial arc is ignited with the high frequency
arc. A pilot circuit is used to produce initial ionization for the plasma jet. The
torch body water cooling must be provided for sufficient cooling otherwise premature
overheating is occurred. The arc is compacted with the help of a small diameter nozzle.
Which is squeezes the arc, increases the pressure, temperature and heat intensity,
thus the arc is obtained stability.
There are two types of plasma arc torch is used, 1.Transferred arc torch, 2. Non-transferred
In the non transfer arc process the arc is produced between the tungsten electrode
(-) and water cooled nozzle (+). Plasma is produced as a flame. The arc is totally
independent of the work piece and it does not help to completion of electrical circuit.
In the transferred arc process is also an arc is produced between the work piece
(+) and electrode (-). In this
process the produced arc is transferred electrode to work piece. It has extraordinary
power of plasma arc, which posses high jet velocity and high plasma density. By this
facility, it is used to cut and weld the metals. Which metals we can not cut by means
oxy-acetylene process, there plasma arc can do very effectively due to its high arc
travel speed. A pilot arc is established in between the electrode and nozzle for
initial ignition. As the pilot arc touches the job, then immediately the main current
start to flow between the work and electrode. Thus the arc is produced.