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Thermit welding process

1 Inch SkV Weld - This is the typical process used to join two rails together and has been in use for decades.

1.5 Inch SkV-M Weld - This is a newer process that provides slightly wider gap and more Thermit®. This equates to a longer solidification period, which helps reduce the potential for internal inclusions. It is a more forgiving process for the welder, making it easier to install a sound weld.

2.75 Inch SoW-L Weld -This process is generally used to replace a defective Thermit® or Flashbutt weld.

Full Head Repair Weld - This is a process that is used after a defect is identified in the head of the rail via an ultrasonic detection car. The rail does not need to be cut all the way through. One of the most important advantages of this process is that the stress-free temperature (longitudinal stress) within the rail is not disturbed. The defect is removed from the head by grinding, and a Thermit® weld is installed to fill the removed area. This unique process is a dramatically significant savings to railroads in labor and material.

Head Alloyed Weld - This process is designed for all rails with a running surface hardness of 390 HB. The welding process allows the rail web and base to remain ductile. It uses standard Thermit® molds with the same tooling as traditional Thermit® welding. Head alloying is achieved by use of a patented diverting plug, which improves wear resistance of the weld on the running surface of the rail.

Major Steps in the Thermit® Welding Process

Rail end preparation

Setting the weld gap

Universal clamp application

Applying and luting the molds

Placing Thermit® portion into the crucible

Preheating the rail ends

Ignition and pouring of Thermit® steel


Shearing of excess head metal

Rough grinding

Final grinding


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