2.Welding history

The ruins left from ancient times, illustratrate the fact that in those days, humans joined metal parts together using the physics theories that establish the basis of today’s modern welding processes .analysis of discovered tools shows that they used to overlap the heated edges of them and join them together by hammer strokes.
The most important physics theories forming the sub-structure of current century’s welding processes have been discovered in the latest of 19th century, gradually finding their usage in industry. In 1887 a Russian scientist “Bernados” invented a way to locally melt pieces of metal between the piece and an electrode, using an electric arc. He set two metal pieces in a specific distance to each other making a notch, and using the above phenomenon plus the motion of the graphite electrode across the notch, and simultaneously entering a metal bar into the electric arc, he made a molten bath that later after freezing, filled the notch and caused the unity of the pieces.
Later in 1891, another Russian scientist (Slavjanov) invented the melt able electrode method in which, instead of graphite electrode, he used a metal one that fulfilled the role of filler metal too.
In this method, the molten electrode exposed to air in the distance between electrode tip and the notch of two – piece that resulted to oxidation of molten metal thus causing problems in the weld. Moreover, the electric arc was unstable which caused nonuniformaly in the weld metal.
To eliminate these problems, a Swedish craftsman “Oscar Kjellberg” invented shielded metal electrode. The shield was made of a mixture of various mineral materials producing slag and gas to protect the molten metal bath against the destructive effects of atmosphere. Furthermore, the electrode cover could stable the arc and uniform the weld.

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