Identification of Sparks

Metal Properties, Characteristics, Uses, And Codes
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a standard for learning to identify the various types of sparks and

for comparison with metals of unknown composition.

When a spark

stream is studied carefully, it becomes apparent that it consists of

a large number of sparks of various lengths which look alike except

for size. A spark is understood to mean not only the main shaft or

carrier line, but also any burst and other details which may develop

from it. The details of a spark stream can often be seen better by

reducing the grinding pressure so there are fewer overlapping sparks.

The effects of alloying elements in the spark stream are important

because of their influence on the stream.

These effects are

discussed in the following subparagraphs.

(1) Wrought Iron with Carbon.

The spark stream of an alloy

containing about 0.08 percent carbon consists of long, moderately

bright carrier lines each of which thickens strongly at the end and

is followed by a fairly dull arrowhead separated by a small gap from

the rest of the spark. The sparks range in length all the way from 1

or 2 inches up to roughly 25 inches.

(2) Manganese.

Manganese affects the spark stream in much the

same way as carbon and steel containing 1 or 2 percent of manganese

may be confused with carbon steel. When the manganese content rises

to 10 or 12 percent, the spark stream retains its brilliance and the

length of the stream drops to about 20 inches, as compared with 30

inches for carbon steels.

(3) Nickel.

The distinguishing feature of the spark is a short

sharply outlined dash appearing near the end of the carrier just

before the fork.

(4) Chromium.

In steels that contain 1 or 2 percent chromium

there will be nothing to indicate its presence. But, an 18 percent

chromium content produces a spark much like wrought iron, except that

it is only half as long.