METAL PROPERTIES, CHAR, USES, AND CODES - OD1643 - LESSON 1/TASK 2
stream are a function of the metal specimen rather than of grinding
Use a portable grinder to spark test heavy pieces of
Make sure that the full length of the spark stream can be
seen to permit adequate inspection.
Specific Metals. Refer to figures 4 and 5 (on pages 31 and 32)
during the discussion of the specific metals in the following
(1) Wrought Iron.
Wrought iron represents nearly pure iron with
very few spurts.
(2) Low-carbon Machine Steel.
Low-carbon machine steel yields a
few plain forked spurts. As the carbon content is increased in plain
steel, the explosions increase and assume more intricate patterns.
(3) Carbon Tool Steel.
In carbon tool steel the initial
explosions called "bursts", produced by its carbon content, are so
profuse that the stream becomes very bushy.
Particles from the
initial bursts dart out and produce secondary explosions called
"spurts" which in turn produce a fine branching network of light.
(4) Gray, White, and Malleable Cast Irons.
The difference among
these three cast irons is not apparent at first glance. Streaks near
the wheel are red and spurts from all three are similar to those from
carbon tool steel. However, the length of the stream from each will
Gray cast iron produces a small volume of dull, red sparks
that form a straight line close to the grinding wheel. These sparks
break up into many fine repeated spurts which change to a straw
White cast iron shows many fine noncurving streaks close to
When malleable cast iron is ground, the outer bright
layer gives off bright sparks like steel.
As the interior of the
malleable cast iron is reached, the sparks quickly change to a dull
red color near the wheel. These sparks from the interior section are
very much like those of gray cast iron; however, they are somewhat
longer and are present in a larger volume.
(5) High-speed Steel.
High-speed steel is not easily mistaken
when inspected by the spark method.
The dull color near the wheel
and its long spark stream are very apparent.