How should I sharp my tungsten electrode? What type of electrode should I buy? What is its real impact on the quality of my weld?
The preparation of a tungsten electrode is an extremely important variable in the final quality of the weld, and its analysis must start already in the choice of the type of electrode that will be used. With the great ease of finding different types of tungsten electrodes and the complexity of judging the best choice, it is common to use electrodes with random composition or even sharpening and preparation without prior analysis of the application requirements.
Found commercially with length between 150 mm and 175 mm, the tungsten electrode is required for the execution of some welding procedures such as TIG and Plasma Welding processes (PAW and PTA). In these processes, the electric arc is opened between the electrode and the part to be welded, keeping the electrode protected from atmospheric contamination by an inert gas, usually argon or helium.
Chemical Composition of Tungsten Electrode
The tungsten concentration in the electrodes may vary between 96% and 99.9%, depending on their application. This high content of tungsten is justified by the high melting point of this element, above 3500ºC. The balance of its composition, known as doping material, is determinant and can influence positively or negatively the following characteristics:
Easy arc opening;
Increased arc stability;
Increase in the current capacity to pass through the electrode;
Reduce risks of welding contamination;
Increase electrode life.
To facilitate the sale and use of electrodes, a convention is used between the colors of the tips and their composition. The metal oxides usually used are: zirconium, thorium, lanthanum, iridium and cerium. See below the main doping and their respective colors of the tip of the electrode:
+++ Good ++ Regular + Bad
Diameter of the Tungsten Electrode
Besides the composition, another factor that should be taken into consideration as soon as the electrode is purchased is its diameter. This factor is directly related to the current that will be used in the procedure, and the larger the diameter of the electrode, the greater the possible current to be used. On the other hand, electrodes with larger diameter can present greater difficulty of opening and stability of the electric arc. See below the diameter ratio of the electrode with the current level that can be used during welding:
Preparation of Tungsten Electrode
Now that we have decided the electrode to be purchased, the preparation/sharpening of this electrode must be carried out. If the preparation of the electrode is done incorrectly, all the benefits brought by the chemical composition may be affected, sometimes even being impossible to open the arc by the sharpening done. Even with the best equipment, if the electrode is not sharpened correctly, the welder will not be able to perform the procedure with efficiency and quality.
The sharpening of the electrode is directly associated with:
Easy arc opening;
Less deterioration of electrode tip;
Regularity and geometry of the weld;
Prevention against contamination.
There are several equipments that allow an automatic sharpening of electrodes. If the operator does so using a grinding wheel, he must perform it in the longitudinal and concentric sense (axial grinding). Many do this without worrying about the sharpening direction of the electrode, believing that the electrode is sharp and sharp is enough. But the scratches direction generated by the sharpening should be parallel to the length of the electrode. For this operation, diamond or borazon discs are recommended due to the high hardness of the tungsten.
What angle should I sharp the electrode?
The electrode sharpning format directly influences the shape of the electric arc and the plasma jet pressure on the part, contributing to the weld penetration, the life of the electrode, and even the welding speed. Another important detail in the preparation of the electrode is the truncation of its tip, often performed only because it is considered a good welding practice, without thinking about its real influence on the process. This operation aims to create a flat circumferential surface on the electrode tip, helping to reduce the penetration of the arc over the part and increasing the life of the electrode.
Avoiding electrode contamination
A factor that dramatically reduces the productivity of the TIG process is in the contamination of the electrode, forcing the operator to change through a new electrode or recondition the contaminated electrode, cleaning its surface and sharpening it again. In addition to wasted time with reconditioning, the use of the electrode in non-ideal conditions leads to poor quality welds and lack of penetration.
Contamination of the electrode can be minimized / avoided by:
Use of gas after arc closure (Gas After Flow);
Electrodes with composition and diameter suitable for application;
Good preparation of the tungsten electrode.
Now that you are updated, do not accept any electrode, always try to define your welding process in more detail to get the maximum efficiency of your equipment.
References: http://www.esab.com.br/br/pt/education/blog/como_identificar_eletrodo_corrente_correta_soldagem.cfm http://www.esab.com.br/br/pt/education/blog/como_identificar_eletrodo_corrente_correta_soldagem.cfm http://guias.oxigenio.com/guia-dos-eletrodos-de-tungstenio-no-processo-de-soldagem-tig http://www.mastertecabrasivos.com.br/page.php?not_id=105