JUNE 2016 / WELDING JOURNAL 23 been developed to provide more sensitivity within the braking system and are particularly useful for improved feeding of aluminum wire. Liners and Wire Guides. It is very important that liners, as well as inlet and outlet guides (which are typically made from metallic material when used for a steel welding system), be made from a nonmetallic material such as TeflonTM or nylon to prevent abrasion and shaving of the aluminum wire during the feeding operation. Drive Rolls. Only drive rolls that have been specifically designed for feeding aluminum should be used. These will have U-type contours with edges that are chamfered and not sharp. Do not use V-shaped groove or knurled drive rolls, which are sometimes used for steel, for feeding aluminum. Drive rolls for feeding aluminum should be smooth, aligned, and provide the correct drive roll pressure. Drive rolls that have sharp edges can shave the soft aluminum wire. These shavings can collect within the feeding system and cause burnbacks from blockages within the liner. Excessive drive roll pressure and/or drive roll misalignment can deform the aluminum wire and increase friction drag through the liner and contact tip, which can also cause burnbacks. Contact Tips. The contact tip inner diameter and quality are of great importance. You should only use contact tips that are made specifically for aluminum wire welding, with smooth internal bores and no sharp burrs on the inlet and outlet ends of the tips, which can easily shave the softer aluminum alloys. Contact tip bore diameter should be approximately 10 to 15% larger than the electrode diameter. Quality of Aluminum Filler Metal. The quality of the aluminum filler metal that is used for GMAW can influence the feedability characteristics. Surface smoothness, wire diameter control, and final treatment of the wire during the spooling operation can assist or detract from the ability to easily deliver the wire through the feeding system. The consistent quality characteristics of the aluminum welding wire should be considered to minimize feedability problems. Selecting the Type of Feeding System. In aluminum wire feeding, there are four recognized feeding systems: push feeders, pull feeders, pushpull feeders, and spool-on-gun feeding systems. The choice of the most suitable feeding system for each application is based on the type of welding (light or heavy duty), electrode size and alloy (large or small diameter/ hard or soft filler metal), the need for a long, flexible conduit, and the importance of minimizing electrode cost (larger diameter wire is generally lower priced than smaller diameter). The demands of welding applications vary extensively, and the cost of each feeding Fig. 1 — Considerations for improved aluminum feedability. For info, go to aws.org/adindex
Welding Journal | June 2016
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