What is Arc Welding
In the arc welding the arc is initiated by touching the electrode and work piece. then gap is maintain between electrode and work piece. In gap, the free electrons and electrons holes will be formed in gas. when we touch the electrode and work piece the current that flow is called short circuit current. when electrode and work piece are at gap the current flow is called open circuit current.
- Amount of voltage required to generate the arc under no load condition is called open circuit voltage.The current required during arc generation is called short circuit current.
- Amount of time during which the transformer shall use for welding under normal loading condition is called duty cycle.
Principal of Arc:
Arc is generated when two conductors are touched and then they are separated by small distance.An arc is sustained by electric discharge through ionized gas column,called plasma.The electrons from the cathode strike at anode and produce the heat.
- The potential difference between the electrodes should be sufficient to allow them to move across the air gap.
TYPES OF ARC WELDING
- Submerged arc welding(SAW)
- Tungsten arc welding (TIG)
- Stud arc welding
- Inert gas shielded arc welding
- Plasma arc welding
- Gas metal arc welding (GMAW)
SUBMERGED ARC WELDING:
It is automatic faster welding process used for welding of plates of thickness as high 75 mm in a single pass. Very high current of the order of 300 to 4000 amp used in this process.
Welded zone is completely covered by granulated flux. which is delivered from an flux feed tube ahead of the welding electrode. Arc is obtained between the work piece and electrode and not visible from outside. A part of flux and metal melts to form slag.flux prevents spattering of molten metal and prevents welding joint from oxidation.The backing plate is used to avoid the loss molten metal this process is limited to flat welding although welds can be made on slight slope or circumferential joints also. It is used for low carbon steel, alloy steel. but sometime non ferrous metal also welded.submerge arc welding may done either by AC or DC. DC give bead shape, better penetration high welding speed and ac starting is easier. AC minimize arc blow.
Advantages of SAW
- Weld spatter is eliminate, high welding speeds are possible.
- Entire welding takes place beneath flux without spark,smoke and flux.
Limitation of SAW
- It is not favorable for thin plates.
- It can not weld cast iron because of high heat input.
- Slag continuously remove after its melts.
Tungsten Inert Gas Welding:
Tungsten inert gas welding or gas tungsten arc welding (GTAW) is inert gas shielded arc welding using non consumable electrode. A.C can be used for GTAW. A tungsten inert gas set up consist of a welding torch at the center of which a tungsten electrode is situated. The inert gas is supplied to the welding zone through the annular path surrounding the tungsten electrode.
The stud which may be small part or a threaded rod serves as one of the electrodes while being joined to another component which is usually a flat plates. in order to prevent oxidation and retain molten metal in weld zone a disposable ceramic ring is placed around the joint.
Inert gas shielded arc welding:
In inert gas shielded arc welding processes, a high pressure inert gas flowing around the electrode while welding would physically displace all the atmospheric gases around the weld metal to fully protect it.The shielded gases used are argon,helium, CO2. Argon, helium are completed inert and they provided a complete inert atmosphere around the puddle.
- Argon and helium is use with both AC and DC power supply but CO2 is use with DC power supply only.
Plasma Arc Welding:
Plasma is the state of the matter when part of the gas is ionized making it a conductor of electric current. it is state of matter present in between electrode and arc.Plasma arc is very similar to TIG. it uses the same electrode and same type of gas as used in TIG. the difference is only in the construction of torch.
- The arc temperature in the plasma arc welding is of the order of 11000 deg Celsius .
Gas metal arc welding(GMAW):
In GMAW the consumable electrodes are used.the TIG can be used only for thin metal and MIG can be use for thick metal because filler material is required for the welding of thick materials.In GMAW the consumable electrode is in the form of wire reel with is fed at constant rate.welding rod is connected to the gas supply cylinder which provides the necessary inert gas.
Filler Wire Designation:
ER XX S-X
- ER-Electrode rod
- XX-Minimum tensile strength of the deposited weld metal in 1000 psi.
- S-Solid Wire.
- X-Chemical composition
you can also read:http://mechmaintenance.com/welding-definition-types-welding-joint/
ARC BLOW :
- The AC arc is stable in nature but DC arc is not stable.
- The deflection of the arc by means of the magnetic fields set up due to flow of the welding current is called arc blow.
- All electrical conductors are surrounded by magnetic flux lines around them.
- Magnetic flux lines move easily in metal but not in air.When the electrode moves forward,flux line move with the electrode but when the weld comes to the edge of the plate then the flux line moves out of the base metal which is not possible.this causes high magnetic pull on the arc.