Piet van der Horst

Piet van der Horst

In 1970 Piet made welding his trade en since then he never stopped learning about that trade. By now he is well past his retirement age, but not welding is still not an option for him. It is not just work, it is a passion.

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Gases for welding processes

Inert and active gases

Classification according to the standard In NEN-EN-ISO 14175 standard, gases are divided into main and subgroups. In this article we discuss four main groups of

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TIG welding – Temperatures

During TIG welding, various temperatures arise in and around the tungsten electrode. These temperatures depend on the gas used and also on the type of tungsten electrode used. The different dopes (combination of alloying elements) have their own influence on the conductivity of the tungsten electrode and thus also on the temperature. The better the conductivity, the lower the temperature of the tungsten electrode during welding. Of course, the height of the set welding current also influences the temperature of the tungsten electrode. At a low current the tungsten electrode will become less hot than at a high welding current.

The temperatures below are measured in an argon arc, at a welding current of 150 amperes and with a 2.4 mm tungsten electrode with a top angle of 60 degrees. The addition of hydrogen or helium will increase the temperatures even further.

A tungsten electrode with 2% thorium reaches a temperature of about 3325 degrees Celsius during welding. This comes close to the melting temperature of the tungsten, 3410 degrees Celsius. (Note! The electrodes with 2% thorium are strongly discouraged for use.  In some countries they are even prohibited.)

A three component tungsten electrode with zirconium and yttrium (purple) reaches only 2350 degrees Celsius under similar conditions. The resistance in this tungsten electrode will be less, which makes it easier for the electrons to move. At this lower temperature, the service life of the tungsten electrode tip of the purple tungsten electrode compared to the thorium-containing tungsten electrode will be considerably longer. The efficiency in the arc will also be higher because less energy will remain in the tungsten electrode.

The temperature of the blue tungsten electrode (WLa 20) is higher than that of the purple tungsten electrode during welding with equal parameters. The temperature of the gold (WLa 15) is a lot higher and the grey (WCe 20) is higher than the gold. None of these three reaches the temperature of the tungsten electrode with thorium (WTh 20).

In the arc plasma, near the tip of the tungsten electrode, the temperature is about 18,000 degrees Celsius. The electron that escapes from the tungsten electrode still has maximum energy and speed here, more than 2000 km/sec. These high temperatures are caused by collisions between the electrons and the gas ions.

At the surface of the material to be welded, the arc plasma still has a temperature of about 10,000 degrees Celsius. The reason for this is that on its way to the material the electron rapidly loses its speed and thus its energy and therefore produces less heat during the collisions with the gas ions. This temperature becomes even lower when the tungsten electrode is welded with an incorrect top angle. For example, if the tungsten electrode tip is too pointed, the path the electron has to travel to the workpiece is longer* and it will lose even more energy. The temperature at the workpiece can then drop to about 8,000 degrees Celsius.

*Remember: an electron always leaves the material at an angle of 90 degrees. This makes the journey longer at a pointed top angle.

 

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