What is Electroslag Welding?
Definition: Electroslag Welding (also known as ESW welding) is a welding process which is generally used for joining thick metals (25 mm to 300 mm thick) by using a molten slag that melts the filler metal and the surface of workpieces.
In Electroslag Welding Process, the heat is generated by electric current which passes from electrode to the workpiece through the molten slag present between the workpieces.
I know you might not have understood this. So let me explain this in detail with the working principle of electroslag welding.
Electroslag welding process (How it works?)
The Electroslag Welding diagram is shown in the above image.
Hence, the electroslag welding is suitable for such metal pieces which have more thickness (ranging from 25 mm to 300 mm).
How electroslag welding works?
As shown in the diagram above, first of all the workpieces are set in the proper positions with 15 to 30 mm distance apart from each other.
The starting plate is attached at the base of the workpieces (see image).
The main purpose of placing the starting plate is to build up a proper depth of conductive slag before the molten pool comes in contact with the workpiece. This process is somewhat similar to the Submerged arc welding process.
The electric current is then allowed to pass from the electrode to the metal plates which are to be welded.
The current passes through this molten slag which produces heat due to resistance heating in the slag.
This heat is enough to melt the surface of the workpieces.
The filler material (i.e electrode) also melts in the molten slag and so the liquid weld pool is formed between the two metal plates (see above image).
This molten metal formed from the melting of electrode is collected under the slag bath.
More electrodes can be fed to get more molten metal.
The copper mold or copper shoes are provided to hold the molten metal between the metal plates, so that the molten metal will not spill out of the pool.
The molten metal forms a strong joint with the surface of the metal plates and these molten metal solidifies gradually.
During the solidification process, a small portion of slag (5% to 7%) is also consumed in the weld.
The copper shoe travels in a vertically upward direction as the metal solidifies at the bottom.
The copper shoe is also provided with a cooling water supply which helps in solidification of the molten metal.
In the beginning of the Electroslag Welding Process, the arc is formed between the electrode wire and the steel backing plate.
Further the melting of electrode wire occurs on its own due to the heat generated by resistance to the current flow through the molten slag.
What type of workpiece can be welded using electroslag welding?
Electroslag welding is generally used for welding butt joints or square grooved plates.
In order to get the good quality welds, the minimum plate thickness should be 1 inch to 1.5 inch.
Difference between Electroslag and Electrogas Welding
Electroslag Welding and Electrogas Welding are quite similar to each other and they have the same working principle. But Electrogas Welding has some additional features of Submerged Arc welding.
In Electrogas Welding Process, the electric wire is either bare or flux coated and this electrode wire is protected from the outer atmosphere by using inert gas.
In electrogas welding process, the mixture of argon and carbon dioxide is used as a shielding gas.
Here also the copper shoe is used to prevent the molten metal from spilling out of the pool.
The main difference between Electroslag and Electrogas Welding is that in electrogas welding, an inert gas is used to protect the weld from atmospheric contamination. Also there is a continuous arc that heats the weld pool.
Advantages of electroslag welding
The advantages of electroslag welding are mentioned below.
- The thick workpieces having thickness up to 400 mm can be welded easily without edge preparation (more number of electrodes are used to speed up the process).
- If proper care is taken during the ESW process, then defect free welds can be achieved.
- ESW welding process is highly productive and it can be used for manufacturing machine beds, drums, etc.
Electroslag welding: Image by Duk via wikimedia commons