METAL IDENTIFICATION

Many methods are used to identify a piece of metal. Identification is necessary when selecting a metal for use in fabrication or in determining its weldability. Some common methods used for field identification are surface appearance, spark test, chip test, and the use of a magnet.

SURFACE APPEARANCE

Sometimes it is possible to identify metals by their surface appearance. Table 1-3 indicates the surface colors of some of the more common metals. Referring to the table, you can see that the outside appearance of a metal helps to identify and classify metal. Newly fractured or freshly filed surfaces offer additional clues.

A surface examination does not always provide enough information for identification but should give us enough information to place the metal into a class. The color of the metal and the distinctive marks left from manufacturing help in determining the identity of the metal. Cast iron and malleable iron usually show evidence of the sand mold. Low-carbon steel often shows forging marks, and high-carbon steel shows either forging or rolling marks. Feeling the surface may provide another clue. Stainless steel is slightly rough in the unfinished state, and the surfaces of wrought iron, copper, brass, bronze, nickel, and Monel are smooth. Lead also is smooth but has a velvety appearance.

When the surface appearance of a metal does not give enough information to allow positive identification, other identification tests become necessary. Some of these tests are complicated and require equipment we do not usually have; however, other tests are fairly simple and reliable when done by a skilled person. Three of these tests areas follows: the spark test, the chip test, and the magnetic tests.

Figure 1-2.-Terms used in spark testing.

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