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WHAT IS PLASMA?
Plasma is commonly described as the fourth state of matter (i.e. solid, liquid, gas then plasma).
If you increase gas to an extremely high temperature you get the fourth
state plasma, the energy begins to break apart the gas molecules and
the atoms begin to split. Normal atoms are made up of protons and
neutrons in the nucleus surrounded by a cloud of electrons. In plasma,
the electrons separate from the nucleus. Once the energy of heat
releases the electrons from the atom, the electrons begin to move
around quickly. The electrons are negatively charged and they leave
behind their positively charged nuclei. These positively charged nuclei
are known as ions. When the fast-moving electrons collide with other
electrons and ions, they release vast amounts of energy. This energy is
what gives plasma its unique status and unbelievable cutting power.
Plasma is a gas which has been heated to an extremely high temperature and ionized so that it
becomes electrically conductive. An example of naturally occurring plasma is lightning.
The plasma arc cutting, gouging and welding processes uses plasma to transfer an electrical arc to the
work piece, the electrically conductive gas will transfer the energy from the plasma power source
through a plasma torch to the material being cut.
The plasma arc cutting process basics can be seen in the
illustration. The basic principle is that the arc is formed
between the electrode and the work piece by forcing the
plasma gas and the electrical arc through a small orifice
within the copper tip. This will increase the speed and
temperature of the plasma exiting the tip. The temperature
of the plasma is in excess of 15000°C and the speed can
approach that of sound. This plasma gas flow in conjunction
with the high temperature enables a deeply penetrating
plasma jet to cut through the work piece material and at
the same time molten material is blown away from the cut.
The process differs from the oxy-fuel process in that the
plasma process works by using the high temperature arc to melt the metal to be cut. With the oxy-
fuel process, the oxygen oxidises the metal to be cut and the heat from the exothermic reaction melts
the metal. So, unlike the oxy-fuel process, the plasma process can be used to cut metals including
those which form protective refractory oxides such as aluminium, stainless steel, non-ferrous alloys
and cast iron.
The output current (amps) of the power supply will determine the cutting thickness and speed
capabilities of the plasma machine.
While the primary goal of plasma arc cutting is the separation of metal, plasma arc gouging is used
to remove metals to a controlled depth and width.
Plasma machines consist of a power supply, an arc starting circuit, a plasma torch and a compressed
air supply.
Direct current (DC) straight polarity is used for plasma cutting with the electrode being - negative
and the tip/work piece being + positive.
