Tungsten Inert Gas (TIG) also referred as Gas Tungsten Arc Welding (GTAW) uses a non-consumable tungsten electrode to generate an arc welding process between the electrode and the parent material. This arc creates a molten pool that will join 2 metallic workpieces together (examples of thin sections of tube to tube welding, tube to fitting, tube to tubesheet…). Depending on the thickness of the workpiece, a cold of hot filler wire is added to the weld area and oscillates into the welding pool (examples of thick sections of tube to tube joining, tube to fitting, tube to tubesheet, narrow grove pipe joining…). The success of TIG welding depends on a number of factors like using the correct type and size of the electrode, one of which is the correct electrode preparation.
Types of electrodes
Tungsten is a highly refractory metal with a melting point of 3,410 °C. It withstands the heat of the electric arc and keeps its hardness even if it becomes red hot. In the past, thoriated tungsten electrodes have been widely used for TIG welding, but as thorium is a low-level radioactive element, special grinding equipment is required to ensure a safe disposal of the grinding particles. Today, different alloyed tungsten electrodes are preferred, e.g. Ceriated or Lanthanated types, which are free of any radioactivity. In addition, their performance is comparable to that of thoriated tungsten electrodes. This results in a colour coding (displayed at the electrodes ends), identified according to ISO Standard 26848 (shown in the table below).
To maintain a constant and compact form of welding arc, tungsten electrodes which will be used for mechanised or automatic welding should be prepared with a tapered end. The diameter of the electrode, the grinding angle "A" and the diameter "M" of the flattened tip depend on the weld current intensity. The grinding angle "A" should have a value between 18° and 30°, the flattened tip diameter should be prepared between 0.1 mm and 0.5 mm. Higher weld current intensities request a larger grinding angle and greater flattened tip diameter.
The length of the electrode must be calculated and cut dependant on the type of welding head, the OD of the tubes to be welded and the specified arc length. In many cases it is difficult to prepare the electrodes with the necessary precision on site even by using an electrode grinder. The purchase of ready-to-use electrodes on the market is often considered to be an efficient and economic solution.
Influence of the cone on the shape of the arc, thus the melting bath, thus the penetration (at fixed electrode-to-work distance, without stroke)
The electrode geometry has a direct influence on the height of the arc and thus on the geometry of the weld pool. For the same application, the electrodes must have a constant geometry (with AVC).
The tungsten electrodes should always be changed preventively, so a considerable amount of welding problems and defects (arc instabilities, ignition difficulties) can be avoided. Delicate applications sometimes require the electrode to be changed after each weld.
The Electrode grinder
To get the precise end preparation and sufficient repeat accuracy which is necessary to maintain a stable arc and a consistent level of weld penetration, a special electrode grinder should be used.
The design of the grinder must ensure that the grind marks on the tapered part run in correct alignment with the grain structure of the electrode: lengthwise. This guaranties better ignition and improved arc stability.
1- The higher the current values, the larger the diameter and flatness will be.
2- Sharpening grooves parallel to the axis of the electrode = better priming and better holding of the electrode over time (avoids deposits on the electrode = dendrite).
Our answer: Polysoude's tungsten electrode preparation tool
UG1 Electrode Sharpner and grinder
The high-performance UG1 electrode sharpener allows precise sharpening, blending and cutting to eliminate ill-defined or unstable arcs.
It also considerably improves electrode life and promotes better ignition of tungsten electrodes.
- Sharpening capacity: Ø: 1-4 mm
- Electric motorisation: 720W - 220V
- Numerous accessories available