3 Reviewers The authors and publisher wish to thank the following teaching professionals for their valuable input into the development of the Gas Tungsten Arc Welding Handbook: Cletus B. Geurts Parkland College Champaign, IL Art Karbowski Western Technical College La Crosse, WI Lisa M. Legohn Los Angeles Trade Technical College Los Angeles, CA Branden Otto Iowa Central Community College Fort Dodge, IA New to This Edition The seventh edition of Gas Tungsten Arc Welding Handbook has been carefully revised to provide readers with a superior learning resource. The changes made for this edition address the latest trends in the welding fi eld, advancements in equipment and technology, and updated standards. The following is a summary of the most signifi cant changes by chapter: • Chapter 1, Gas Tungsten Arc Welding History and Safety: Information regarding safety data sheets, explosion hazards, and fi re extinguishers has been updated and reorganized. • Chapter 3, Auxiliary Equipment and Systems: Information about Tri-Mix electrodes has been added. Color-code information for tungsten electrodes has been updated. • Chapter 4, GTAW Shielding Gases and Filler Metals: Information about Dewer fl asks, microbulk systems, and shielding gas safety has been updated and clarifi ed. • Chapter 6, Tooling: Information regarding backing bars, backing rings, and purge blocks has been reorganized, expanded, and clarifi ed. The section on seam trackers has been moved to improve the logical fl ow of the text. • Chapter 9, Manual Welding of Aluminum: Information about the use of Tri-Mix electrodes for the welding of aluminum alloys has been added. • Chapter 11, Manual Welding of Magnesium: The use of DCEP and DCEN for welding magnesium have been de-emphasized in this edition to refl ect their infrequent usage. In addition to the changes listed here, numerous small changes were made to each chapter of the seventh edition of the Gas Tungsten Arc Welding Handbook to improve the readability, organization, and technical accuracy of the text.