METAL PROPERTIES, CHAR, USES, AND CODES - OD1643 - LESSON 1/TASK 2
a chisel curl up, except manganese steel which can not be cut with a
chisel.
i.
Aluminum.
Aluminum
castings
show
a
bright
crystalline
structure. A fracture in rolled aluminum sections shows a smooth and
bright surface.
j.
Aluminum Bronze.
The fractured surface of aluminum bronze is
smooth.
k.
Brasses and Bronzes.
The fractured surface ranges from smooth
to crystalline, depending on the composition of the metal and on
whether it has been cast, forged, or rolled.
l.
Copper.
Copper presents a smooth surface with no crystalline
appearance.
m.
Lead.
Lead has a
smooth
gray-white
surface
when
polished,
oxidizing to a dull gray.
n.
Magnesium.
The fractured surface is rough and finely granular.
o.
Monel Metal.
The fractured surface is crystalline.
Its color
is similar to that of nickel.
p.
White Metal Die Castings.
The fracture is white and somewhat
granular.
5.
Spark Test
a.
General.
When the exact type of metal is not known, a spark
test may be used to determine its identity.
This identity is
revealed by a study of the sparks formed in the stream emitted into
the air when the material is held against a high-speed grinding wheel
(bench, pedestal, or portable hand grinder).
Examples of the spark
streams formed by different metals are provided in figures 4 and 5 on
the following pages.
Spark testing is a rapid economical method of
separating and classifying types of irons and steels and some
nonferrous metals.
b.
Degree of Sp ark S tream Glow. The d egree of glow observ ed
in the formation of sparks in the spark stream is a function
o f t h e g r i n d i n g r e s i s t a n c e a n d o t h e r co n d i t i o n s w h i c h a f f e c t
the
initial
temperature
of
the
metal
chip
and
the
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