METAL PROPERTIES, CHAR, USES, AND CODES - OD1643 - LESSON 1/TASK 2
until they are learned.
These tests are described in the following
paragraphs.
2.
Tests Used to Identify Metals
a.
General. Simple tests can be conducted in the shop to identify
the different metals.
Since the ability to judge can be developed
only through personal experience, practice these tests with known
metals until you are familiar with the reactions of each metal to
each type of test.
The tests are described in the following
subparagraphs.
b.
Appearance/Chemical Analysis.
Appearance/chemical analysis, as
the name implies, is based on the general appearance of the metal,
which includes such general features as the color and texture of
machined and unmachined surfaces. It is obvious that the appearance
portion of this type test is not an extremely accurate method;
however, the experienced metalworker can make a reasonably good
determination
based
on
experience
and
the
above
mentioned
characteristics. The chemical analysis procedure referred to in the
following paragraphs is confined to the analysis used to distinguish
between aluminum and magnesium, and between steel and aluminum or
lead.
c.
Fracture.
The fracture of many metals may be used for
identification through the appearance of the fracture and study of
metal chips.
This test is made by simply notching a specimen and
then breaking it.
Although no measurable indications of the
properties of a metal are obtained from this test, many metals can,
through experience, be quickly identified by examining the surface of
the break, or by studying the chips produced with a hammer and
chisel. The fracture test is probably the oldest of the methods used
in the inspection and testing of metals.
d.
Sparks. When the exact type of material is unknown, a spark test
may be used to determine its identity.
The test is conducted by a
study of the sparks formed when the material is held against a high-
speed grinding wheel.
A grinding wheel may be used on the various
types of iron and steel because they produce sparks which vary in
length, shape, and color when held lightly against a grinding wheel.
When any form of iron or steel is held against a grinding wheel, small
particles, heated to a red or yellow heat, are released from the metal
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