Electroslag welding is a non-traditional welding process in which molten metal pool is created. This method is combination of both arc welding and resistance welding because at starting, heat is generated by establishes an arc between electrode and base metal (as in arc welding). This heat leads to melt flux and create a molten metal pool between the electrode and base metal. Now the current flow through this molten metal pool and heat is developed due to electric resistance (as in resistance welding). Due to this reason, this is called combination of arc welding and resistance welding.
Electrosalg welding is an uphill welding process. Uphill welding process is a process in which weld joints are made in vertical direction and the plates to be weld held vertically. This welding is done both in single pass and multipass. Before discussing its working we should learn about the principle of electroslag welding machine.
It works on common principle of heat generation due to arc and electric resistance. At the starting, arc is produce between welding electrode and base metal which tends to melt filler metal. This filler metal will fill the cavity at some extent. Now the current passes through this extended surface and heat generate due to electric resistance. This heat further tends to melt filler metal which is continuously fed from the roller. Filler wire is fed through the roller continuously. This wire fed through a tube witch direct its flow. This filler wire melts and fills the weld and made a strong joint.
As we know, electroslag welding is an uphill welding process so the plates to be weld held vertically at some distance. The weld metal or filler metal deposit between the cavities formed between the plates by melting electrodes using heat develop by flow of current. This filler metal forms metal pool which solidified into the weld cavity so a strong joint is created between the plates. Electroslag welding works as follow：
- First current is flow between welding electrode and base plate. This establishes an arc between electrode and base plate which heat the flux or filler wire. This heat leads to melt the filler metal and deposits into the weld cavity.
- Now the cooled copper shoe comes into action and start solidified this filler metal into weld cavity. This will made to avoid flowing out the weld metal.
- As the filler metal solidified into weld cavity, the current flow through it. It will generate heat due to electric resistance. This heat is further use to continuous melting down the filler metal into weld Cavity.
- The filler metal continuously provide through roller arrangement.
- During welding both the copper shoe and feed mechanism moving upward unlit the whole cavity is formed.
- This will create a strong joint in single pass. The single or multi-pass weld is used according to plate thickness.
It is used in heavy industries where plate thickness up to 80mm to be joint. This process is used to joint large casting and forging to produce very large and composite structure. Welding of thick walled large diameter pipes, pressure vessels, storage tanks and ships etc.
- Cooling rate is very low so there is no problem of cold cracking.
- There is no problem of slag inclusion or porosity in electroslag welding.
- The process is semi-automatic and faster.
- Heavier section can be welded in single pass.
- High productivity can be achieved.
- Low cost for joint preparation.
- Too high heat input to base.
- High temperature of welding needs cooling arrangement.
- Slow rate of cooling give columnar grain in weld.
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