Tube Mill Welding
Tube mills produce pipe and tube by taking a continuous strip of material and continuously rollforming until the edges of the strip meet together at a weld station. At this point the welding process melts and fuses the edges of the tube together and the material exits the weld station as welded tube.
Stainless steel pipe and tube are often produced by arc welding with either the TIG or Plasma process. The benefits of TIG versus Plasma welding has long been debated and each tube mill manufacturer has their own opinion on the subject. Keyhole Plasma welding offer benefits for guaranteeing weld penetration and for thick wall tube manufacture. High frequency pulsed arc TIG welding has produced some benefits in speed and quality. Multi-cathode welding has long been used in Europe for increasing tube mill speed but is less common in the U.S..
The output of the tube mill depends on the arc welding speed and total time spent welding. Each time the mill shuts down and starts up again there is a certain amount of scrap produced. Thus the most important issues to the tube mill user are:
For Plasma weld process users the key electrode issues are material selection, electrode material quality, and pre-ground electrode cost. Using a different electrode material such as 1.5% Lanthanated Tungsten and ensuring premium quality electrode material can increase the arc life of the electrode by at least 15%.
Tube mill TIG welding places enormous importance on the Tungsten electrode material selection, material quality, electrode tip geometry, and tip surface condition. Improving the electrode material and changing to polished electrode finishes can increase electrode life by over 200%. Choosing the correct electrode tip angles and tip flat diameter can also improve arc stability and electrode life thereby improving weld quality and increasing the number of hours before electrode changover is required.
The quickest and easiest means to increase mill performance through improvements in the welding process is to upgrade the tungsten electrode material and tip geometry preparation method.
Pre-Ground electrodes are the obvious choice for tube mill applications and are surprisingly economical. Pre-ground electrodes remove the variability of operator grinding from the weld process. Pre-Ground electrodes improve weld quality, increase electrode life and offer extreme tip dimensional tolerances and surface finishes to ensure the consistency of output that tube mills require.
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