Tweco SLICE - Manual (Page 2)

2
FUNDAMENTALS OF THE
PROCESS
Process Description
The SLICE Exothermic Cutting
process uses an exothermic chemical
reaction that burns, melts, or
vaporizes most materials. The
reaction begins with an electrical arc
or alternate energy source that
causes a steel cutting rod to burn.
Oxygen flows through the center of
the rod.
Because of the rod's design, the
burning makes excess heat ("exo -
thermic"). This heat cuts the
workpiece. Once started, the burn will
continue as long as oxygen flows
through the rod. The heat created
melts the material being cut. The
velocity of oxygen through the rod
blows the molten material away,
creating the kerf or cut line.
This arc ignition process led to
invention of the "oxy-arc" torch and
design of equipment for underwater
construction and salvage.
The electrical arc that starts the burn
can be from a welding power source
that delivers at least 100 amps, a 12-
volt lead acid or similar low
impedance battery. The cutting
process can run without power, using
the heat of the reaction only, or with
power, cutting with an electrical arc
from a welding power source
providing more heat.
History
The exothermic cutting rod is a small
"oxygen lance." It is a prime example
of the combustion triangle, one side
being fuel (the steel lance), the
second the oxygen source (pure
oxygen being forced through the
lance), and the third the heat of
combustion (some external source of
heat). However, when the lance
pierces a slag puddle, the puddle
becomes the source of heat until the
lance is withdrawn, at which time
burning stops.
In 1888, a published paper described
passing oxygen through a steel tube
and heating the tube to a bright red.
Heat resulted. In 1901, Ernst Henner
filed a German patent on an early
oxygen lance made of two concentric
tubes. In 1902, documentation
shows that the oxygen lance replaced
oil and gas torches for opening
furnace taps in steel blast furnaces.
The oxygen lance has since been
used to cut rocks and concrete
structures. An example of this use is
cutting up reinforced concrete
structures such as bunker
emplacements and tank traps built in
Europe during World War II.
An ideal way to start the lance,
workers found, was to use a welding
power source on conductive material
to strike an arc and start the burn. In
construction this process worked well,
even in mud and water.
Around 1940, the burning bar or
exothermic lance was first marketed
as a cutting tool. A flexible version
made of an insulated cable was
introduced around 1960. Not until the
early 1980's were smaller burning
bars designed for hand-torch use,
above and below water. A one-piece
unit now allows for adequate rod
surface exposure to an oxygen
supply for exothermic cutting. Arcair
Company, a world leader in metal
removal and cutting, sells this
exothermic cutting equipment under
the trade name SLICE.