This hood may be made from metal, although some
material that does not conduct electricity is to be preferred. The work is
watched through pieces of glass formed with one sheet, which is either blue
or green, placed over another which is red. Screens of glass are sometimes
used without the head protector. Some protection for the eyes is absolutely
necessary because of the intense white light.
It is seldom necessary to preheat the work as with the gas processes,
because the heat is localized at the point of welding and the action is so
rapid that the expansion is not so great. The necessity of preheating,
however, depends entirely on the material, form and size of the work being
handled. The same advice applies to arc welding as to the gas flame method
but in a lesser degree. Filling rods are used in the same way as with any
other flame process.
It is the purpose of this explanation to state the fundamental principles
of the application of the electric arc to welding metals, and by applying
the principles the following questions will be answered:
What metals can be welded by the electric arc?
What difficulties are to be encountered in applying the electric arc to
welding?
What is the strength of the weld in comparison with the original piece?
What is the function of the arc welding machine itself?
What is the comparative application of the electric arc and the
oxy-acetylene method and others of a similar nature?
The answers to these questions will make it possible to understand the
application of this process to any work.
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