Electroslag welding

Electroslag welding (ESW) is a highly productive, single pass welding process for thick (greater than 25mm up to about 300mm) 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 reaches the tip of the electrode it extinguishes the arc. The wire is then continually 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. This process uses a direct current (DC) voltage usually ranging from about 600A and 40-50V, higher currents are needed for thicker materials. Due to the fact that the arc is extinguished, this is not an arc process.

History

The process was patented by Robert K Hopkins in the United States in February 1940 (patent 2191481) and developed and refined at the Paton Institute, Kiev, USSR during the 1940s. The Paton method was released to the west at the Bruxelles Trade Fair of 1950. [cite book |last=Pires |first=J Roberto |authorlink= |coauthors=Loureiro, Altino; Bolmsjö, Gunnar |title=Welding Robots: Technology, System Issues and Application |year=2005 |publisher=Springer |location= New York|isbn=1852339535|pages= p11 ] The first widespread use in the U.S. was in 1959, by General Motors Electromotive Division, Chicago, for the fabrication of engine blocks. In 1968 Hobart Brothers of Troy, Ohio, released a range of machines to for use in the shipbuilding, bridge construction and large structural fabrication industries. However the Federal Highway Administration (FHA) 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. [cite web
last = Lindberg
first = H. A.
authorlink =
coauthors =
title = Notice: Electro-Slag Welding
work =
publisher = Federal Highway Administration
date = February 1977
url = http://www.fhwa.dot.gov/legsregs/directives/notices/n5040-23.htm
format =
doi =
accessdate = 2008-04-21] The FHA commissioned research from universities and industry and Narrow Gap Improved Electro Slag Welding (NGI-ESW) was developed as a replacement. The FHA moratorium was rescinded in 2000. [cite web
last = Densmore
first = David
authorlink =
coauthors =
title = Narrow-Gap Electroslag Welding for Bridges
work = Bridge Technology
publisher = Federal Highway Administration
date = 2000
url = http://www.fhwa.dot.gov/BRIDGE/esw.htm
format =
doi =
accessdate =2008-04-21]

Benefits

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.

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. The maximum workpiece thickness that has ever been successfully welded was a 0.91 m (36 in) piece that required the simultaneous use of six electrodes to complete.

References

*Cary, Howard B. and Scott C. Helzer (2005). "Modern Welding Technology". Upper Saddle River, New Jersey: Pearson Education. ISBN 0-13-113029-3.
* Serope Kalpakjan and Steven R. Schmid. "Manufacturing Engineering and Technology". Fifth Edition. Upper Saddle River, New Jersey. ISBN 0-13-148965-8
* [http://www.welding-advisers.com/PRACTICAL_WELDING_LETTER-PracticalWeldingLetterNo07_C.html] . Feb 29, 2004.
* [http://www.twi.co.uk/j32k/protected/band_3/ksokg001.html] . Written by Owen Gorton. Copyright © 2001, TWI Ltd