©
COPYRIGHT 1999 THE ESAB GROUP, INC. LESSON
I, PART B
1.8 ELECTRICITY
FOR WELDING 1.8.1
Principles
of Electricity
- Arc welding is a method of joining metals accom-
plished by applying sufficient electrical
pressure to an electrode to maintain a current path (arc)
between the electrode and the work piece. In this process, electrical energy
is changed into
heat energy, bringing the metals to a molten state; whereby they are joined.
The electrode (conductor) is either
melted and added to the base metal or remains in its solid
state. All arc welding utilizes the transfer of electrical energy to heat
energy, and to understand
this principle, a basic knowledge of electricity and welding power sources
is necessary.
1.8.1.1 The
three basis principles of static electricity are as follows:
1. There are two kinds
of electrical charges in existence - negative and positive.
2. Unlike charges
attract and like charges repel. 3. Charges
can be transferred from one place to another. 1.8.1.2
Science has established that all matter
is made up of atoms and each atom contains
fundamental particles. One of these particles is the electron, which has
the ability to
move from one place to another. The electron is classified as a negative
electrical charge.
Another particle, about 1800 times as heavy as the electron, is the proton
and under normal
conditions the proton will remain stationary. 1.8.1.3
Material is said to be in an electrically
uncharged state when its atoms contain an equal
number of positive charges (protons) and negative charges (electrons). This
balance is upset
when pressure forces the electrons to move from atom to atom. This pressure,
sometimes referred to as electromotive
force, is commonly known as voltage. It should be noted
that voltage that does not move through a conductor, but without voltage, there
would be no current
flow. For our purposes, it is easiest to think of voltage as the electrical
pressure that forces the electrons
to move. 1.8.1.4
Since we know that like charges repel
and unlike charges attract, the tendency is for
the electrons to move from a position of over-supply (negative charge) to an atom
that lacks electrons
(positive charge). This tendency becomes reality when a suitable path is
provided for the movement of the electrons.
The transfer of electrons from a negative to a positive
charge throughout the length of a conductor constitutes an electrical current.
The rate
that current flows through a conductor is measured in amperes and the word ampere
is often used synonymously with the
term current. To give an idea of the quantities of
electrons that flow through a circuit,
it has been theoretically established that one ampere equals
6.3 quintillion (6,300,000,000,000,000,000) electrons flowing past a fixed point
in a conductor
every second.
