plasma arc welding,principle,plasma transferred arc welding and non transferred types,applications,advantages and disadvantages.
PLASMA ARC WELDING:
Conventional methods are not suitable for machining metals such as cast alloy, wasp alloy, carbides having promising applications in various industries also machining these materials in conventional methods causing increased machining cost. So, these types of materials in special welding methods are preferred. It will increase the productivity, number of rejected components are reduced and achieving the close tolerance.
Principle:
Plasma is high temperature ionized gas. It is a mixture of neutral atoms, positively charged atoms and free elements. When this high temperature plasma is passed through the orifice, the proportion of the ionized gas increases and plasma arc welding is formed.
Working:
When the high heat content plasma gas is forced through the torch, orifice is surrounded by negative tungsten electrode in the form of j et. The plasma cutting force imposes a swirl on the opening gas flow. The are is initiated in the beginning by supplying electrical energy between nozzle and tungsten electrode. This will release high energy and heat. This heat is normally in between 10,000°C to , 30,000°C. This high amount of heat energy is used to weld the metal. Their types are
1. Transfer type, and
2. Non-transferred type.
1. Transferred type:
In transferred type, the tungsten electrode is connected to the negative terminal and the work piece is connected to the positive terminal. An electric arc is maintained between the electrode and the work piece heats a co-axial flowing gas and maintains it in a plasma state. It is difficult to initiate the are first between the work piece and the electrode. For that, the pilot arc is struck between the nozzle and the electrode.
2. Non-transferred type:
In this type, power is directly connected with the electrode and the torch of nozzle. The electrode carries the same current. Thus, the ionizing is at high velocity gas that is strewing towards the work piece. The main advantage of this type is that the spot moves inside the wall and heat the incoming gas and outer layer remains cool. This type plasma has low thermal efficiency.
The base metals welded by plasma arc welding are:
1. Stainless steels
2. Titanium alloys
3. Carbon and low alloy steels
4. Aluminium alloys
5.copper alloys
The types of joint which are made by plasma arc welding are:
1. Filler welds
2. T-Welds
3. Grooves [Single groove (or) ‘V’ groove]
4. Square groove.
Applications:
1. It is used in aerospace applications.
2. It is used for melting high melting point metals.
3. It is used for welding titanium plates.
4. It is used in welding nickel alloys.
5. It is used for tube mill applications.
Advantages:
l. Penetration is uniform.
2. Arc stability is good.
3. Fully penetrated keyholes can be obtained.
4. High accuracy weld can be produced.
5 .High speed weld can be obtained.
Disadvantages:
1. Huge noise occurs during welding.
2. Chances of electric hazards may occur during welding.
3. It is limited to high thickness applications.
4. Ultra violet radiations can affect human body.
5. Gas consumption is high.
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