METAL PROPERTIES, CHAR, USES, AND CODES - OD1643 - LESSON 1/TASK 2
Small amounts of molybdenum in steel can be
recognized by the detached arrowhead in a stream that otherwise looks
much like that of wrought iron.
This is the easiest metal of all to recognize
because of the dull red color it imparts to the spark stream,
especially near the grinding wheel.
(7) Cast Iron. Cast iron sparks are of medium length; the carrier
lines are dull red near the grinding wheel and they end in bright
curved spear points coming out of very fine carbon bursts.
(8) High-Speed Steel with Tungsten.
The spark streams are very
simple in appearance and are composed of a few long, dull-red,
carrier lines having no carbon bursts at all.
(9) High-Speed Steel with Molybdenum.
For this type steel, the
spark stream is shorter and denser than for high-speed steel with
The sparks are definitely orange or straw in color with
small amounts of red near the grinding wheel. The carrier lines end
in spear points preceded by at least occasional carbon bursts.
Factors Affecting the Spark Stream.
The streams emitted by
high-speed steels are affected considerably by a number of factors.
The following subparagraphs provide a listing of these factors.
(1) Grinding conditions and the condition of the steel itself.
(2) Whether the steel is annealed or hardened.
(3) Whether a small wheel on a portable grinder, as opposed to a
large wheel on a bench grinder, is used.
(4) Grinding pressure, specimen size, and the shape of the region
(5) The best way to avoid pitfalls is to perform the spark test by
direct comparison with a standard of known composition. Only in this
manner can the maximum benefits of spark testing be obtained.