Copyright 2002 - 2007 IFORGEIRON, All rights reserved.
BP0020 Spark Testing
Compiled by Quenchcrack aka Bob Nichols © 2003
Click to enlarge the images.
Spark testing can be dangerous! Wear appropriate protective gear and observe all warning labels on grinding equipment!
This short paper is a summary of two papers on spark testing: The Art of Spark Testing, published by Wyckoff Steel in 1953, and Spark Testing...a quick way to identify steels, no author listed. If anyone recognizes the second paper, please post it so that proper credit may be given.
Spark testing was at one time the quickest way for a steel company to separate mixed steels. However, the success depended entirely on the skill of the tester and many steel companies had regular training classes for testers. Today, portable spectrometers do the job quicker, safer, and more accurately, and spark testing is rarely done except by hobbyists and Blacksmiths.
The following elements produce a visible color or effect in a stream of sparks: carbon, manganese, sulfur, silicon, phosphorus, nickel, chromium, molybdenum, tungsten, copper, aluminum, cobalt, titanium and vanadium. The relative amount of an element is determined by observing the frequency of its characteristics and the variation in the shade of color in the spark stream.
Elements seen by spark testing:
Like any grinding process, spark testing can be dangerous. Follow these rules to prevent harm to yourself and others.
1. Wear safety glasses with clear or slightly tinted lenses and side shields, or wear a full-face shield.
2. Watch where you direct the stream of sparks to prevent setting fire to anything in the shop.
3. If you use a fixed grinder, keep the work-piece below the center of the wheel.
4. Keep all guards on equipment in place.
If you use a portable grinder, use one with a no-load speed of 15,000 rpm, 9,000 rpm loaded. The grinding wheel should be coarse grained. Modern fiberglass reinforced wheels come in several grits, so check to see what is available. Note: when spark testing was widely practiced, the wheels used were all stone, no fiberglass. It is not known what effect the fiberglass might have on the characteristics of the spark stream.
The following terms will be used to describe the characteristics of the spark stream.
1. Spark Stream: the entire display of sparks thrown off the grinding wheel.
2. Length of spark stream: the distance from the wheel to the farthest visible spark.
3. Width of spark stream: the width of the angle at which sparks leave the wheel, generally described as narrow, medium or wide.
4. Carrier lines: the glowing path of an individual particle as it leaves the wheel.
5. Density: the relative number of carrier lines across the width of the stream.
6. Swellings: definite seed-like expansions along the carrier line.
7. Burst: the explosion of a particle along or near the end to its visible path.
8. Star (or sprigs): a more complex fork-type burst which shows lines radiating in a star-like pattern.
9. Spear-points (or heads): the final glow at the end of the carrier line.
Most elements contained in steel impart some distinguishable characteristics in the spark stream. It must be kept in mind that some elements interact with each other and therefore it becomes highly important that the operator know the patterns of various types of steel.
Elements and Effects:
Carbon bursts vary in intensity depending on the carbon content of the sample and can be detected by observing the change from a series of simple sprigs to a complex star having a sparkler effect.
When the carbon is low, sulfur is easy to see. As carbon increases, it is more difficult to see. Higher silicon content suppresses the sulfur burst. Sulfur bursts appear as an orange, seed shaped swelling on the carrier line.
Phosphorus is recognized as a reddish colored spear-point shape that is detacked from the end of the carrier line.
Silicon appears as an oblong-shaped white fleck of light on the carrier line, particularly on the first few inches of the spark stream.
Manganese is difficult to recognize in the spark stream and it may take a lot of practice to identify it. Manganese over 1% appears as fine bright lines that break at right angles to the carrier line.
Nickel imparts two characteristics, depending on the steels composition. Nickel appears as a white rectangular shaped block of light throughout the spark stream. When nickel and molybdenum are included in the steel, nickel takes on the appearance of a candle flame with a dull orange color
Molybdenum appears as small, detached spearheads at the end of the carrier lines, orange in color.
Vanadium is an orange color and bursts as a spear-point at the end of the carrier lines. They do not detach themselves and have a tendency to bend back under.
Spark Patterns for Common Steels
The following are drawings of spark patterns for some common steel grades. They are reproduced from drawings made about 50 years ago and are not as crisp as computer-generated graphics. However, they have been enlarged and digitally ï¿½cleaned upï¿½ so that the details are clearer. The patterns here are no substitute for collecting samples of known steel for comparison while grinding. They are only an aid in recognizing the patterns.
Click to enlarge
Fig. 1 AISI 1015 C = .14, Mn = .47
Fig. 2 AISI 1030 C = .32, Mn = .72
Fig. 3 AISI 1050 C = .48, Mn = .66
Fig. 4 AISI 1095 C = 1.01, Mn = .49
Fig. 5 AISI 1120 C = .19, Mn = .90, S = .113
Fig. 6 AISI 1350 C = .51, Mn = 1.1
Fig 7 AISI 2340 C = .42, Mn = .69, Ni = 3.47
Fig. 8 AISI 2312 C = .11, Mn = .39, Ni = 4.95
Fig. 9 AISI 4130 C = .32, Mn = .69, Cr = .75, Mo, = .22
Fig. 10 AISI 4615 C = .16, Mn = .55, Ni = 1.80, Mo = .25
Fig. 11 AISI 4640 C = .38, Mn = .59, Ni = 1.80, Mo = .28
Fig. 12 AISI 5150 C = .51, Mn = .66, Cr = 1.00
Fig. 13 AISI 6140 C = .38, Mn = .61, Cr = 1.0, V = .17
Fig. 14 AISI 9260 C = .57, Mn = .81, Si = 1.92
Fig. 15 AISI 12L14 C = .09, Mn = .95, P = .07, S = .35
Fig. 16 AISI 12L14+ Te C = .09, Mn = .94, P = .07, S = .35
C = Carbon
Mn = Manganese
Mo = Molybdenum
Cr = Chromium
Si = Silicon
Ni = Nickel
P = Phosphorus
S = Sulfur
Bob Nichols, PE, is the manager of metallurgy for the Lone Star Steel Co.