Copper
wire may also be used for this purpose, the spaces being filled with
melted spelter.
THERMIT WELDING
The process of welding which makes use of the great heat produced by oxygen
combining with aluminum is known as the Thermit process and was perfected
by Dr. Hans Goldschmidt. The process, which is controlled by the
Goldschmidt Thermit Company, makes use of a mixture of finely powdered
aluminum with an oxide of iron called by the trade name, Thermit.
The reaction is started with a special ignition powder, such as barium
superoxide and aluminum, and the oxygen from the iron oxide combining with
the aluminum, producing a mass of superheated steel at about 5000 degrees
Fahrenheit. After the reaction, which takes from. 30 seconds to a minute,
the molten metal is drawn from the crucible on to the surfaces to be
joined. Its extreme heat fuses the metal and a perfect joint is the result.
This process is suited for welding iron or steel parts of comparatively
large size.
_Preparation._--The parts to be joined are thoroughly cleaned on the
surfaces and for several inches back from the joint, after which they are
supported in place. The surfaces between which the metal will flow are
separated from 1/4 to 1 inch, depending on the size of the parts, but
cutting or drilling part of the metal away. After this separation is made
for allowing the entrance of new metal, the effects of contraction of the
molten steel are cared for by preheating adjacent parts or by forcing the
ends apart with wedges and jacks.
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