METAL PROPERTIES, CHAR, USES, AND CODES - OD1643 - LESSON 1/TASK 2
6.
Torch Test
a.
General.
Various metals can be identified by using an
oxyacetylene torch and observing how fast the metal melts, the
appearance of the puddle of molten metal and slag, and by the color
changes that occur during heating of the metal.
The following
paragraphs serve to describe the effects of the torch test on various
metals.
b.
Gray Cast Iron. A heavy tough film forms on the surface as it
melts. The puddle is quiet and very fluid. When the torch flame is
raised, the depression in the surface of the puddle disappears
instantly.
The molten puddle solidifies slowly and gives off no
sparks.
c.
Malleable Iron.
The molten metal boils under the torch flame
and, when the flame is withdrawn, the surface will be full of blow-
holes.
The melted part will cool very hard and brittle; it is, in
fact, white cast iron or chilled iron produced by the melting and
comparatively rapid cooling.
The outer steel-like shell will give
off sparks under the torch, while the center portion will not.
d.
Low-carbon Steels. The steel gives off sparks when melted and,
when the flame is removed, solidifies almost instantly.
e.
High-carbon Steels.
The molten metal is brighter than molten
low-carbon steel and the melted surface has a cellular appearance.
f.
Steel Forgings. Steel forgings spark when melted. The greater
the carbon content, the greater the number and brilliance of the
sparks.
g.
Alloy Steels.
Steels containing a considerable quantity of
chromium display a greenish-colored slag on the weld or puddle when
cold.
In general, the effects of the torch test depend on the
composition of the alloy steel and must be determined by trial and
experience.
h.
Cast
Steels.
The
steel
sparks
when
melted
and
solidifies
quickly.
i.
Aluminum. Aluminum does not show red before melting. It holds
its shape until almost molten and then collapses suddenly.
A heavy
coating of white oxide forms instantly on the molten surface.
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