The Physics of the Arc Essay

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ABSTRACT

Several researchers have devoted efforts on studying physics of arc and descriptive models are used to explain many arc welding related phenomena. However, due to the subject complexity, doubts still emerge about the mechanisms of some phenomena related to the arc. For instance, the description about electromagnetic interactions with the arc, which governs the arc trajectory and lead to plasma jet and arc blow formation, seems to be yet controversial. Thus, the present study aimed a better understanding of these phenomena. An e-mail survey was carried out to confirm discordant descriptions of the phenomena. Some points were raised about the actual physical explanation used in the current literature. Some experimental work with
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On the other hand, books and handouts about arc welding are written aiming to transfer new practices and theoretical knowledge to users. And they have to cite definition and characteristics of some fundamentals, such as plasma jet and arc blow formation. For instance, in the case of arc blow, classical pieces of literature such as AWS Welding Handbook [1] do not further explain this phenomenon beyond “the result of magnetic disturbances surrounding the arc”. The Lincoln’s Procedure Handbook of Arc Welding [2] limits to state that “the magnetic arc blow is caused by an unbalanced condition in the magnetic field surrounding the arc”. According to Lancaster [3], “arc blow may result from asymmetric current paths in the work-piece close to the arc or from the magnetization of the plate material”. In the case of plasma jet, Houldcroft and John [4] cite that “the flow of current in the arc results in a magnetic field, which involves the arc and tends to compress it, the so-called ‘pinch effect’. Due to the way the arc expands from the electrode to the work-piece, an axial component of the pinch effect happens and it causes the hot ionised gas in the arc to be set in motion from the electrode to the work. This is sometimes called plasma jet and it is responsible for the depression, which is formed in the surface of molten pools at high welding currents”. Lancaster [3], in turn, declares that plasma jet is an

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