PLASMA CUTTER
PlasmaCutting is a very interesting field of physical sciences
that will always intrigue anyone who has the attraction to the dynamics of
science.
Before going into a deep interrogation of plasma cutting, it is vital that we
first understand what plasma is.
I am pretty
convinced that you are well vast with the three states of matter which are
solid, liquid and gas. For water which is a very common element to us, ice,
water and steam are its subsequent states of matter dependent on how much
energy is applied or reduced from or on them.
When more energy is introduced to ice, its kinetic
energy rises and water is then formed as a result of the ice melting. As we
continue adding energy in the form of heat to the water, vapor is formed. This
then leads to the vapor decomposing to hydrogen and oxygen in form of steam.
By adding more and more energy to the steam, the
oxygen and hydrogen gas making it upbecome ionized, a process that makes them
electronically conductive. The end product then is an electrically conductive
gas that is at the same time ionized named as plasma.
Plasma cutting
Most metals have been known to possess very tough
surfaces that have been known to provide a kind of impenetrable cocoons. However
after the discovery of plasma, electronically conductive metals like brass, aluminum etc, can be cut using
plasma gas. The gas is used to transfer
energy from an electrical power source to the material being cut by the use of
a plasma torch.
Components of a basic plasma cutting system
·
Power supply
·
Arc starting circuit
·
A torch
The above mentioned basic components provide very
important aspects in the system. First, they allow for proper control of the
plasma cutting system, they also provide a good ionization capability for the
gas and also provide electrical power which is the key propelling energy
sustaining the cutting process.
Power supply
Plasma
Cutting is supplied by a constant Direct Current power
supply system. The voltage that passes through the system is of a range of 240
to 400 volts. The speed of the cutting process is determined by the output
current of the power supply while the same output amperage also determines the
cut thickness.
The sole purpose of the power supply is to provide
the appropriate amount of energy to maintain and keep the system working
immediately after ionization process.
Arc starting circuit
This is a generator system that runs at very high
frequency producing an Alternating Current voltage that ranges between 5000
volts to 10000volts at a frequency of approximately 2 megahertz.
High intensity arc inside the torch is created by
this high voltage, the torch then causes an ionizing effect to the gas hence
creating the plasma.
The Torch
This is now the holder of the nozzle to be consumed
and also the electrode. Besides these, it also provides cooling effect which
can be in the form of water or gas to the parts exposed to friction: nozzle and
the electrode, while at the same time ensuring that the plasma jet is well
maintained.
Series of operating a plasma cutter
Interconnecting leads and cables connect to the
torch after sourcing power from the power supply. The leads and the cables ensure that there is
convenient gas flow while alsoassuring that current flows at remarkably high
frequency towards the torch so that the process starts well and is also
maintained.
When an ON signal is sent to the power supply, gas
and current flow to the torch start simultaneously as they become activated.
The metal to be cut should then be connected
directly to the positive while the nozzle is connected to the negative in the
power supply that must also consist of a resistor and a relay.The gas then
should flow through the nozzle exits.
After it is established that the gas flow has
stabilized, the activation of high frequency circuit is initiated. This causes
the high frequency to breakdown amid the nozzle and inside the torch in a way
that the gas must go past this arc before being let out by the nozzle. The
energy transfer causes an ionization effect to the gas hence becoming able to
conduct electricity. The gas then creates a current path between the nozzle and
electrode hence resulting to plasma that
goes out through the nozzle.
If the nozzle is close enough to the metal, the
pilot arc will attach to the work piece.
The ionization of the gas is then continued to be maintained by the
drive from the main Direct Current arc.
Owing to the high temperature of the plasma, the
metal melts while at the same time the fast flowing gas blows away the molten
material. Perhaps at this time, the cutting process is started.
Convectional plasma cutting and how to vary the process.
The nitrogen or air used provides a cooling effect
and also produces the plasma. The rating of plasma systems are usually under
100Amps, this is for cutting material below 5/8 inches thick.
Cutting using two gases
When two types of gases are used, one is usually for
the plasma while the other is a guard gas. The guard gas shields the cut area
from the atmosphere henceforward producing a cleaner cut edge.
More gas combinations when used, they
produceexcellent quality cut off the work piece material.
Water shielded cutting
Here water is substituted for the shield gas. The
water provides a cooling effect that goes along with better quality of cuts on
stainless steel.
Water injection plasma cutting
A single gas is used here for plasma utilizing water
radically or spin injected directly in to the arc. This increases constriction
resulting to improved density and temperature of the arc. This type of process
is strictly for mechanized applications.
Precision plasma cutting
Precision plasma cutting produces excellentcuttings
especially on less thick materials which are 0.5 inches or even less but at
gentler speeds. This latest discovery in cooperates the super constriction of
the arc that in turn increases the density of energy.
Less fast speeds are needed to allow the device cut
more accurately. Precision plasma
cutting is also strictly for the mechanized applications only.
