1 Introduction to Tungsten Guidebook
This specification is intended to assist welders in selecting and preparing one of the most important and frequently overlooked welding process variables: the electrode. Welders can spend thousands of dollars on welding equipment, but if they do not select and prepare their electrodes with this less expensive process component properly, then their welding results can be poor, inconsistent, or problematic. This guide will help eliminate this variable as a concern in your welding and make it an asset.
This information applies only to the selection and preparation of electrodes for Gas Tungsten Arc Welding (GTAW), also known as Tungsten Inert Gas (TIG) welding and Plasma Arc Welding (PAW). The different types of GTAW and PAW welding that this applies to includes but is not limited to Orbital Tube and Pipe Welding, Automatic/Mechanized TIG Welding, “Micro-TIG,” Automatic/Mechanized Plasma Welding, “Micro-Plasma,” and Manual Arc Welding. The section of this booklet that describes the proper electrode grinding techniques is dedicated almost entirely to direct current welding, since electrodes for alternating current welding are usually balled and not ground.
GTAW is used in many industries, including Aerospace, Semiconductor, Biotechnology/Pharmaceutical, Tube Producers, Contractors, Automotive, Fitting and Valve Manufacturers, Industrial, Nuclear, and Speciality Gases.
Table 1: Applications for Correctly Ground, Cut and Prepared Tungsten Welding Electrodes For TIG Welding Applications
|Orbital TIG/ Tube
|To produce the high quality orbital fusion welds required of today’s high tech industries, tungsten electrode shape is an important variable that must be kept consistent. Most orbital manufacturers require a precise tungsten length.|
|Orbital TIG/ Pipe
|Orbital pipe welding application using TIG is primarily limited to the nuclear, pharmaceutical, and chemical processing industries. These industries, along with a few not mentioned, require X-ray perfect orbital pipe welds in the 125 amp – 300 amp current range.
A consistently prepared electrode is required for consistent current flow and arc voltage characteristics. Most orbital pipe welders use 3/32 or 1/8 diameter electrodes. They also must be cut-to-length, however, not as precise as the orbital tube welder.
|Mechanized Tig Welding encompasses a wide spectrum of applications such as precision bellows welding using .040 diameter tungsten electrode at 1.0 ampere up to high speed tube mills welding with a .250 diameter tungsten electrode using current as high as 600 amperes. A precise yet consistent electrode will have a dramatic effect in weld results and tungsten electrode life. Cutting the tungsten electrode is usually required if the electrode is grossly contaminated.|
|Arc starting and arc stability from a consistently prepared tungsten electrode will be beneficial to the manual welder. Most hand welding ‘FIG torches require a 7.0″ long electrode be cut in half to fit the manual welding torch. This can be accomplished best with the diamond cutting mechanism described in this booklet.|
|The plasma arc welding process requires a very precisely shaped, tungsten electrode. The tip of the tungsten must be kept concentric to the diameter to place it in the correct position entered in the plasma torch. This is a critical parameter adjustment in plasma arc welding. Most plasma welding torches also require a cut-to-length tungsten electrode.|
The technical details of TIG and PLASMA arc welding are that an electric arc is transferred from a tungsten electrode to a work piece. Typically, to initiate the arc, high voltage is used to break down and ionize the shielding gas between the electrode and the work piece. Current is then transferred from the electrode to the work to create an electric arc. The tungsten electrode serves as the terminal for the electric arc and fuses together either with or without filler material. Although there are different methods of arc initiation, high voltage arc starting is the standard used in this guidebook.
There are several variables to consider in a welding procedure. Tungsten electrode geometry affects the arc shape (thereby affecting the weld bead size and shape), the weld penetration, and point longevity of the electrode. Proper electrode grinding procedures and equipment should be used in order to ensure that electrodes are dimensionally correct. Finally, different tungsten materials posses different characteristics in arc start ability, electrode life, and contamination resistance. This makes the selection of the proper material for your application an important variable in welding performance. The proper preparation of electrodes in each of these areas will provide the benefits of consistent welding with optimum performance.