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Welding history

Classification of welding

Effect of welding speed

Welding defects

Types of welding joints

Welding position

Welding electrodes

Types of welding flame

Welding flux

Welding techniques

Welding symbol

Welding edge preparation

Advantages of welding joints

Thermal properties of metal

Welding safety

Types of welds

Brazing

Soldering

Plasma welding

Plasma welding

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 electrode.

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 torch.

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.

Plasma_Arc_Welding_Image

Advantage of plasma welding :


# It has excellent type weld quality.

# Arc is stabilized.

# It needs very simple type’s fixture.

# Root welding does not required.

# Penetration is uniformed.

# It produces radio-graphic quality welding.


Application of plasma welding


# Nuclear submarine pipe welding.

# Cryogenic and aerospace component welding.

# Nickel and high nickel alloy welding.

# Melting the high melting point temperature metals.

# Titanium plate welding up to 8 mm thickness.

# Welding the stainless tubes up to 1/4” thickness.

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Plasma weld principle