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NG-ESW :

Narrow Gap ElectroSlag Welding

Narrow Gap Electroslag welding (NG-ESW) is a highly productive, single pass welding process for thick (greater than 20 mm (3/4”) up to about 600 mm (24”). The plates are in a vertical position. The gap between them  is 20 mm (3/4").  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 is about 25 mm thick, reaching the tip of the electrode, 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 (normally is water cooled) that was put into place before starting is used to keep the weld between the plates that are being welded. Electroslag welding is used to join low carbon steel plates and/or sections that are very thick. It can also be used on bridge or structural steel.

This process uses a direct current (DC) voltage or AC square wave, usually ranging from about 600A for single wire to 1600A for multiple wires and 30-40V.

One electrode is commonly used to make welds on materials with a thickness of 20 to 30mm (3/4” to 1.5” ), and thicker pieces generally require more electrodes. The maximum workpiece thickness that has ever been successfully welded was a 0.91m (36 in) piece that required the simultaneous use of six electrodes to complete

Because the arc is extinguished, this is not an arc process.

Benefits of the process includes :

• High metal deposition rates— the range is typically between 15 and 30 kg/h (30 and 60 lb/h) depend of the electrode and guide tube configuration.

• No sophisticated welding knowledge is required. All process is computerized.

• Reduced preparation time. Joint preparation and materials handling are minimized while filler metal utilization is high.

• The process is very 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.