TIG for welding titanium tube(II)

　　Last week,we mainly talked about cleanness and fit-up in welding titanium tube.Today,Baoji Xilitong will present the importance of shielding gas coverage and filler metal selection in TIG for welding titanium tube.

　　The Importance of Shielding Gas Coverage

　　Pure argon is recommended for welding titanium because of its high purity and low moisture content. A 75/25 mixture of argon/helium may be used to improve stability and increase penetration only when specified.

　　The American Welding Society (AWS) recommends measuring welding gas purity to make sure it meets the standards set for each application. Typical specifications suggest that shielding gas be at least 99.995 percent pure with no more than 20 parts per million (PPM) of oxygen and a dew point greater than -76 degrees F. Other applications require a 99.999 percent pure flow of argon.

　　Outfitting your welding torch with a trailing shield is critical—otherwise the risk of oxygen contamination rises, and with it the potential for cracking. Some welders fabricate their own trailing shields, although many styles are available for purchase. Trailing shields conform to the shape of the tube and follow the GTAW torch around the pipe. The shields provide an extra protection of argon over the weld after the torch and its argon flow have passed. Setting the torch and trailing shield gas flow at 20 cubic feet per hour (CFH) provides the best coverage.

　　Purging, a process that eliminates the oxygen contained within the pipe, also is required when welding titanium tubing. This process can be completed with any kind of purge dam: water-soluble dams, rubber gaskets, specialty tape, or inflatable bladders. Argon flows into the dammed area to replace the oxygen contained within the tubing. Allow the argon to flow long enough to replace the oxygen 10 times over to ensure the purest welding environment.

　　Always use a clean, nonporous plastic hose to transport the shielding gas to the torch, trailing shield, and purge. Do not use rubber hose; rubber is porous and absorbs oxygen that could contaminate the weld.

　　Filler Metal Selection

　　Use a filler metal when welding titanium tubing thicker than 0.010 in..Typically, you should match the filler metal to the grade of titanium being welded—it should be an exact match. Some applications allow exceptions, such as a filler metal with a lower yield strength than the base metal to improve ductility. Any variation, however, should be carefully tested and investigated to make sure it meets process demands and specifications.

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