METAL PROPERTIES, CHAR, USES, AND CODES - OD1643 - LESSON 1/TASK 2
and thrown into the air. Through contact with the oxygen in the air,
the particles oxidize, or burn.
If an element such as carbon is
present in various quantities rapid burning occurs, resulting in the
bursting of the carbon particles.
Because of their varied carbon
content, the various forms of iron and steel produce sparks that vary
in length, shape, and color.
The grinding wheel should be of the
aluminum oxide type, hard enough to wear reasonably long, yet soft
enough to retain free cutting properties.
The peripheral speed
should be approximately 4000 feet per minute in order to produce
good, short bright sparks. The tests should be conducted in diffused
daylight against an ordinary background.
In all cases, it is
advisable to grind standard samples of metals of known composition so
that the sparks produced can be compared with those emitted by the
material under test.
e.
Torch.
The behavior of metal under a torch can be identified
with different metals by studying the melting rate, the appearance of
the molten metal, and slag and color changes during heating.
In
other words, with the oxyacetylene torch, one can identify a metal by
studying how fast it melts and by the color changes during heating.
3.
Appearance and Chemical Analysis of Various Metals
a.
General.
The following subparagraphs provide a list of the
general appearance of various ferrous and nonferrous metals.
The
chemical analysis portion is discussed only where applicable.
b.
Appearance of Ferrous Metals.
(1) Gray Cast Iron. When visually observing gray cast iron, the
unmachined surfaces are very dull gray in color and somewhat
roughened by the sand mold used in casting the part.
Unmachined
castings may have brighter areas where rough edges have been removed
by grinding.
(2) Malleable Cast Iron.
The surface of malleable iron is much
like gray cast iron; however, the dull gray color is somewhat lighter
and the surface is usually free from sand.
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