How, When, and Why to change the Tungsten electrode in your Weld Head

Why replace a tungsten electrode?

Even though orbital welding is a very consistent process in and of itself, the frequency for replacing a tungsten electrode will likewise vary widely. Wall thickness, tube diameter and material, weld recipe values, quality of the inert gas shield, and many other parameters can all play a role in the service life of the electrode.   A tungsten may fail in a single weld, or run 700+ cycles.

One example of what can happen when an electrode goes bad is the ‘roll back’. The weld may start normally, but part way through the arc does not follow the seam between the two pieces, and the edges do not join, but appear to roll back from each other.

With the price of a new tungsten so low, typically only a few dollars, and the cost of a bad weld potentially ruining expensive components and meaning lost production, it only makes sense to be proactive in replacing the electrode.

When to replace a tungsten electrode?

How can you tell if a tungsten is going bad? There are several indications that an electrode is at the end of its life.

  1. Visually inspect the electrode prior to use. Discoloration can range from a hazy grey color to a black carbon appearance. Check to see if the profile on the ground tip has become deformed or shortened.
  2. Check the arc gap. Correct values will vary depending on the specific application, but are critical for consistent high quality welds. If this gap has changed since set-up, the electrode may be the culprit.
  3. Check a coupon. Cut open a sample of the appropriate size. Does the weld bead wander or is the internal seam straight, evenly sized, and the correct width for the wall thickness?
  4. Listen to the sound of the arc start, during the weld, and the down slope. Does the weld begin with a sharp ‘snap’?  If it sounds more like a hiss, odds are good that the electrode has gone bad. Does the weld end with a smooth gradual down slope sound, or does it sound gravelly or rough?

Any of the previous observations can indicate a bad tungsten, or at least one on the way out.

How to replace the electrode:

  1. Switch the power supply from WELD to TEST. This prevents a non-intention weld attempt.
  2. With the clamps open, turn the rotor until the tungsten set-screw can be accessed. Loosen the tungsten set-screw. On the AMI 9-750 this requires the use of a 0.050” Allen wrench.  (NOTE:  If the head has been in use, the rotor will be hot!)
  3. Discard the old electrode and select the correct replacement for your application. This will vary depending on weld head, tube diameter and wall thickness, and other factors.
  4. Clamp a short piece of tubing of the correct diameter on the side of the head away from the tungsten set-screw.
  5. Placing a feeler gauge of the desired arc gap on the top surface of the tubing, slide the new tungsten through the hole in the rotor, and rest the electrode tip on the feeler gauge.
  6. Making sure that the tungsten is pressing firmly on the feeler gauge; tighten the set-screw, locking the electrode in place. Make sure the set-screw is tight. Should the electrode slip and contact the work piece during a weld, the components will be damaged and the weld will have to be redone.
  7. Remove the feeler gauge and piece of tubing, and return the rotor to the home position.
  8. Test your new tungsten with a weld coupon.

Changing the tungsten is a quick, easy, and inexpensive way to prevent a worn out electrode from causing expensive production waste, AND helps reduce QA/QC issues.   Finally, if you’re renting orbital welding equipment, be sure to ask how they check the condition of the tungsten.  This will be a good indication of how thorough the company is in their rental fleet’s refurbishment process.

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