Electroslag welding, also known as ESW, is a single-pass welding technique that is designed for joining thicker materials. The process is often done in a vertical or near-vertical position. ESW is a semi-automatic process, making it faster and more efficient.
Additionally, the process utilizes filler metal and generates heat between two materials through an arc and electrical resistance, resulting in a high level of productivity.
Electroslag welding is mainly used for joining low-carbon steel plates and very thick sections. It is also used on structural steel if certain precautions are adhered to. Furthermore, they are used for large cross-section aluminum busbars.
The slag, in its name, helps protect the weld from oxidation and contamination from the atmosphere. It also maintains the molten weld pool joint as it cools, which is essential for out-of-position welding.
In this reading, we will delve into the definition of electroslag welding, its various applications, the parts and equipment involved, a diagram explaining its operation, and its working principles. We’ll also explore the advantages and disadvantages of electroslag welding.
Let’s begin!
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What is Electroslag Welding?
Electroslag welding is an arc welding process that generates heat using an electric current. The process utilizes a consumable electrode and coats the weld surface with molten slag. It is a highly productive, single-pass welding process for thick materials ranging from about 25mm to about 300mm. It is performed in a vertical or close to a vertical position.
ESW is a combination of both arc welding and resistance welding because, initially, the heat is generated when the electrode is stuck to the workpiece, leading to a melt flux and creating a molten pool on the joint surface. The current now flows between the pool and the heat, developed due to electric resistance.
Applications of Electroslag Welding
The applications of electroslag welding are vast and specialized. However, they are used for the following:
- It is used in heavy industries where plate thickness is up to 80 mm to be joined.
- This welding process welds thick-walled, large-diameter pipes.
- Welding of storage tanks is done by it.
- It is used to construct big and thick parts of ships.
- While it primarily joins mild and low-alloy steels, it also successfully joins high-alloy steels, titanium, and aluminum.
Electroslag Welding Tools and Equipment
The major parts of electroslag welding include filler metal, flux, retaining blocks, a wire feeder, a welding head, and a wide guide.
Electroslag welding involves the use of base metal and filler metals to join workpieces together. Filler metal melts at the weld joint, creating molten slag. Flux converts electrical energy into heat, providing heat for the weld.
A power source provides the electrical current. Retaining blocks hold workpieces in place, while a welding head controls the molten slag’s direction. A wire feeder feeds filler metal into the weld pool, while a wide guide tube protects the electrode from being consumed by the slag.
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Diagram of Electroslag Welding Machine
How Does Electroslag Welding
Electroslag welding (ESW) is a process that uses molten slag to melt filler metal and join workpieces. The slag moves along the joint’s cross section, shielding the weld pool. The process begins with an arc, which heats the granulated flux and forms the slag. As the slag becomes sufficient, the conductive slag extinguishes the arc, keeping the existing slag molten.
ESW has a high rate of deposition, allowing for welding thick sections in a single pass. However, it requires vertical performance and is only suitable for carbon steel and low-alloy steels. Materials must be at least 19 mm thick.
Electroslag welding is a process used for welding thick mild and low-alloy steels, primarily in vertical or near-vertical positions. It is arc-less and requires resistive heating of the molten slag bath to melt the wire and fuse the parent material.
To ensure uniform fusion, thick material requires multiple electrodes or oscillation across the joint. A typical speed for electroslag welding of 76 mm thick mild steel is 1 m/h at 550 A and 44 V. However, the process is virtually continuous, resulting in large grain size and poor mechanical properties.
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Advantages and Disadvantages of Electroslag Welding
Electroslag welding is a fast and efficient process that offers advantages such as high deposition rates, excellent penetration into thick materials, minimal preparation, and fewer defects.
However, it has drawbacks such as a coarse grain structure, which can lead to lower toughness, and its use in a vertical or near-vertical position may not be suitable for some applications. Additionally, the high temperatures associated with ESW may require additional cooling arrangements to ensure high-quality welds.
The initial setup costs for an electroslag welding station are typically higher than for other traditional processes. However, the benefits of ESW include avoiding cold cracking, being semi-automatic and faster, eliminating slag remaining, welding heavy parts, low cost for joint penetration, and low distortion.
Other disadvantages of ESW include a slow cooling rate, columnar grain, high heat applied to base metals, proper cooling needed for high-temperature applications, and only the vertical position being welded. Despite these drawbacks, electroslag welding remains an affordable and effective welding method.