Full Answer
What is electrogas-welding?
Open in a New Window. Electrogas-welding (EGW) is a high productivity process derived and adapted from the older Electroslag Welding, (ESW). The original purpose of developing EGW was of adapting the ESW process for welding thinner plates.
What is electro slag welding?
Electroslag welding is a single pass welding process, hence it is very convenient to weld thick materials. It was in the year 1940 when the first patented electro slag welding process was published in the name of Robert K Hopkins.
What is the difference between arc welding and electrogas-welding?
For basic information on the physics of electric arc for welding, see our new page on Arc Welding . Electrogas-welding is similar to the Gas Metal Arc Welding (GMAW) process, except that the progression of the weld is up, towards the top.
What is electroslag welding (ESW)?
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.
What is the difference between electroslag and Electrogas welding?
Electrogas welding is very similar in principle to electroslag welding in that it is used for welding thick section material in a single pass and in the vertical position. The main difference being that the heat for welding is generated by an arc which is formed between a flux-cored electrode and the molten weld pool.
What is electroslag welding used for?
Electroslag welding is used mainly to join low carbon steel plates and/or sections that are very thick. It can also be used on structural steel if certain precautions are observed, and for large cross-section aluminium busbars.
What is the difference between Egw and ESW?
A major difference between ESW and EGW is that the former relies on slag conduction to carry the welding current and the latter uses arc conduction.
What are the advantages of electroslag welding?
Advantages and Disadvantages: 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.
Is electroslag welding an arc welding?
What Is Electroslag Welding? The Electroslag Welding process can be explained as a combination of Arc welding and Resistance welding. This is because an arc is created at the very beginning of the process and then the weld is produced by the resistance offered by the Flux used.
What is the heating element in electroslag welding?
Updated Thursday, 8th March 2018. Heat is generated by an electric current, via flux covered electrode wire, which passes through conductive liquid slag sitting in the weld gap. Melted material from the workpiece amalgamates with molten flux, to form the weld joint.
Which increases the porosity on the Weld?
As little as 1% air entrainment in the shielding gas will cause distributed porosity and greater than 1.5% results in gross surface breaking pores. Leaks in the gas line, too high a gas flow rate, draughts and excessive turbulence in the weld pool are frequent causes of porosity.
What is the principle of electro gas welding?
Electro Gas Welding Process In electro gas welding (EGW), the heat produced by the electric arc is used to melt the electrode and the workpiece and allow to flow into the cavity between the parts being welded. The molted metal solidifies from the bottom up and thus joining the parts.
What is saw welding process?
Submerged-arc welding (SAW) is a common arc welding process that involves the formation of an arc between a continuously fed electrode and the workpiece. A blanket of powdered flux generates a protective gas shield and a slag (and may also be used to add alloying elements to the weld pool) which protects the weld zone.
What is reverse polarity in welding?
“Straight” and “reverse” polarity are common terms for “electrode-negative” and “electrode-positive” polarity. Welding currents with electrode-positive (reverse) polarity result in deeper penetration, while electrode-negative (straight) polarity has the benefit of faster melt-off and faster deposition rate.
How hot is slag from welding?
We all know welding includes hot hot heat, but how hot is the welding arc, really? On average, a welding arc is between 6500 and 10,000˙F.
Which is the oldest form of welding?
The oldest known examples of welding are small golden boxes that date back to the Bronze age over 2,000 years ago. Archaeologists have found jewelry, dining utensils, and weapons from this time period. In 3000 B.C., Egyptians used charcoal to pressure-weld swords, and in 1500 B.C., iron smelting became more common.
What do they use to weld railroad tracks?
Thermite welding is widely used to weld railway rails.
What is atomic hydrogen arc welding?
Atomic hydrogen welding (AHW) is an arc welding process that uses an arc between two tungsten electrodes in a shielding atmosphere of hydrogen. The process was invented by Irving Langmuir in the course of his studies of atomic hydrogen.
What is electroslag welding?
The electroslag process has been developed to weld seams of thick section or joints in a single pass, thus eliminating the need for multiple passes and preparation of bevel, V, U, or J groves and edge preparation.
Why do welders use electrodes?
Several electrodes are used for long welds so that the heat is more uniformity spread. Water cooled shoe or dam-plate fastened to the sides of the workpiece prevents the pool of melted metal from escaping.
What is the temperature of a slag bath?
The interior temperature of the slag bath for steel is about 1925°C and the surface temperature is approximately 1650°C.
What is the gas used in electrogas welding?
In electrogas welding process, the mixture of argon and carbon dioxide is used as a shielding gas.
What welding process is not suitable for thick metal plates?
You can see that the metal plates are thick in size. So for such thick workpieces, the welding process like stick welding, MIG welding, TIG welding, etc are not suitable.
How is heat generated in welding?
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 .
Why do you put a starting plate on a welding plate?
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.
Why does electrode wire melt?
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.
Why does current pass through molten slag?
The current passes through this molten slag which produces heat due to resistance heating in the slag.
How thick can a welding piece be?
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).
How fast can electroslag weld?
Benefits of the process include its high metal deposition rates—it can lay metal at a rate between 15 and 20 kg per hour (35 and 45 lb/h) per electrode—and its ability to weld thick materials. Many welding processes require more than one pass for welding thick workpieces, but often a single pass is sufficient for electroslag welding. The process is also very efficient, since joint preparation and materials handling are minimized while filler metal utilization is high. The process is also safe and clean, with no arc flash and low weld splatter or distortion. Electroslag welding easily lends itself to mechanization, thus reducing the requirement for skilled manual welders.
Why is electroslag welding banned?
However the Federal Highway Administration (FHWA) monitored the new process and found that electroslag welding, because of the very large amounts of confined heat used, produced a coarse-grained and brittle weld and in 1977 banned the use of the process for many applications.
What is a slag welding?
Electroslag welding (ESW) is a highly productive, single pass welding process for thick (greater than 25 mm up to about 300 mm) materials in a vertical or close to vertical position. (ESW) is similar to electrogas welding, but the main difference is the arc starts in a different location. An electric arc is initially struck by wire that is fed into the desired weld location and then flux is added. Additional flux is added until the molten slag, reaching the tip of the electrode, extinguishes the arc. The wire is then continuously fed through a consumable guide tube (can oscillate if desired) into the surfaces of the metal workpieces and the filler metal are then melted using the electrical resistance of the molten slag to cause coalescence. The wire and tube then move up along the workpiece while a copper retaining shoe that was put into place before starting (can be water-cooled if desired) is used to keep the weld between the plates that are being welded. Electroslag welding is used mainly to join low carbon steel plates and/or sections that are very thick. It can also be used on structural steel if certain precautions are observed, and for large cross-section aluminium busbars. This process uses a direct current (DC) voltage usually ranging from about 600 A and 40-50 V, higher currents are needed for thicker materials. Because the arc is extinguished, this is not an arc process.
What is the thickness of an electrode used for welding?
One electrode is commonly used to make welds on materials with a thickness of 25 to 75 mm (1 to 3 in), and thicker pieces generally require more electrodes.
Which buildings were welded in California?
Two of the tallest buildings in California were welded, using the electroslag welding process - The Bank of America building in San Francisco, and the twin tower Security Pacific buildings in Los Angeles.
Why Is Electroslag Welding Used?
Electroslag welding is a single pass welding process, hence it is very convenient to weld thick materials.
How does slag welding work?
Electroslag welding works on the principle of joining two metals with heat generation between them due to arc and electric resistance. The arc is first created by applying a potential difference between the base and the electrode. This arc melts the filler and fills the cavity. Then the filler is melted due to the resistance offered by the slag. Now the electrode wire and filler melt to form a fillet weld in the vertical direction between the workpieces.
What is the most important filler material used in electro slag welding?
Flux may be said to be the most important filler material used in electro slag welding. Flux is added in the form of powder and then is melted because of the arc produced.
Why does a weld crack when cold?
cold cracking is a phenomenon because of which cracks are developed on the welds due to sudden cooling of the welded areas. In the case of electro slag welding, the welds do not cool suddenly, preventing then cold cracking on the welded areas.
When was electro welding invented?
It was in the year 1940 when the first patented electro slag welding process was published in the name of Robert K Hopkins. It was 1959 until electro slag welding was used effectively by General Motors Electromotive for the fabrication of engine frames.
Why was welding banned?
Though this process was banned for several applications due to the excessive heat produced during the process forms the Brittle and coarse-grained weld.
Is electro welding complex?
The construction of electro slag welding is not very complex.
What is electrogas welding?
Electrogas welding is a mechanized welding process. The nature of the melting and solidification during welding results in a high-quality weld deposit. Little or no angular distortion of the base metal occurs with single-pass welds. For these reasons, major applications of electrogas welding have historically been in tank fabrication and shipbuilding.
What is a square groove welding?
Typically, in electrogas welding, a square-groove or single-V-groove joint is specified and positioned with the axis or length of the weld vertical. No repositioning of the joint occurs once welding has started; welding continues to completion so that the weld is made in one pass.
How does a weld tab work?
The consumable electrode (either solid or flux cored) is fed downward into the joint root opening, which is a cavity formed by the base metals to be welded and the backing shoes. A starting weld tab (sump) is required to seal the bottom of the weld joint to allow the process to stabilize and to support the molten weld metal until it reaches the workpiece. An arc is initiated between the electrode, consumable guide tube (when one is used), and starting weld tab. The heat generated by the arc melts the continuously fed electrode and groove faces. Melted filler metal and base metal collect in a pool beneath the arc and solidify to form the weld. As the weld metal fills the joint, the weld pool rises, progressing in the uphill direction.
How thick is a weld?
Thicknesses of 13 mm (1⁄2 in.) to 38 mm (1 1⁄2 in.) are typically welded with electrogas welding. When thicker sections are welded, the electrode may be oscillated horizontally through the joint for uniform distribution of the heat and weld metal. If moving shoes are used, one or both shoes may move upward as the cavity fills. Although the weld travel is vertical, the weld metal is actually deposited in the flat position at the bottom of the cavity.
What happens if a weld is not completed in one continuous pass?
4. If the weld is not completed in one continuous pass, the resulting restarts usually require that a repair be made. Additionally, the reworking of problem welds is difficult.
Is electrogas welding cheaper than welding?
For thicker materials, electrogas welding is often less expensive than the more conventional joining methods, such as submerged arc and flux cored arc welding. Even in some applications involving thinner base materials, electrogas welding may result in cost savings because of its efficiency and simple requirements for joint preparation.
What is electrogas welding?
Electrogas-welding is similar to the Gas Metal Arc Welding (GMAW) process, except that the progression of the weld is up, towards the top.
What are the applications of electrogas welding?
Typical applications of Electrogas-welding represent a whole collection of different manufactured structures, including storage tanks, pressure vessels, nuclear components, ship subassemblies, bridges, oil drilling platforms, power generating equipment, heavy presses, rolling mills, and other constructions where the advantages of the process determine its economy.
What are the advantages of ESW and EGW welding?
Although there is a range of thicknesses where both ESW and EGW could be used, the advantages for Electrogas-welding are lower heat input, more refined microstructure and improved Heat Affected Zone (HAZ) properties. Moreover the EGW process can be more easily (than ESW) restarted if interrupted for any cause.
Why are flux cored wires special?
However these flux cored wires are of a special type, containing fewer slag building ingredients (than regular FCAW filler wires) because excessive slag buildup on the molten metal surface can affect arc stability and cause slag entrapment.
What is EGW welding?
Electrogas-welding (EGW) is a high productivity process derived and adapted from the older Electroslag Welding, (ESW).
How thick is a plate for welding?
For Electrogas-welding, the reported thickness range of plates is between 13 and 38 mm (0.5 and 1.5 in.). Thicker plates, up to about 75 mm (3 in.) can be welded usually with two or more electrodes dipping into the weld pool, possibly with an oscillation movement being imparted to the welding head, to distribute more uniformly heat and filler material.
How fast is a weld?
The range of welding speeds is therefore quite large, between 38 to 200 mm/min (1.5 to 8 in./min).