In grinding, it is highly important to know properties of different materials. For this purpose, various standard and non-standard methods are used (Kreibig and Vollmer 46). The report at hand is going to sum up the key assumptions concerning the shape, color, and brightness of sparks produced in grinding, which can serve as a practical guide for identifying the type and condition of the material being ground.
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First and foremost, it is important to note that this spark testing procedure allows differentiating between materials rather accurately. The method is not only efficient but also fast, easy, and cost-saving since it does not require any special equipment (a sample of the material and an abrasive wheel are enough). That is why mastering the procedure can considerably facilitate the work process.
When a piece of material contacts with an abrasive wheel, glowing particles of metal that are given off follow a certain carrier line (trajectory), which is visible against a dark background. Besides the length of the stream, one should also pay attention to the form, brightness, and color of sparks (Fleming 65). It is quite challenging to differentiate between steels having the same carbon content (with different alloying elements); however, using this method, it can be done by analyzing how the alloying element accelerates or slows sparks and makes the line darker or brighter (Dalke et al. 167). For instance, nickel is identified by blocks of white light, which shine brightly; molybdenum releases orange sparks with spearheads; silicon gives off a white flash of light after an abrupt end of the carrier line. Other spark patterns include the following ones:
- Cemented carbide releases sparks that are tiny in size (about 3 inches) and never fork. The color is typically dark-red.
- Monel forms sparks that are similar to those released by nickel. They are typically rather small, wavy, and have almost no sparklers. Their color is orange.
- Gray cast iron also produces rather small (<25 inches) sparks, following a repetitive pattern. The color is red with a straw-colored outer sphere.
- Stainless steel releases much longer sparks (about 50 inches) with a moderate volume. Sparklers are scarce. Sparks are straw-colored close to the wheel and white at the end of the line.
- Wrought-iron gives the longest stream of all the enumerated materials (>65 inches), having a large volume. However, there are also very few sparklers. Sparks are forked (widening out close to the end) and straw-colored. The carrier line’s end is bright red (Black and Kohser 85).
However, the spark test allows identifying not only the type of the material but also its condition. For instance, if sparks become purple or dark blue, this implies that there is a leak free lining. If there appears a leak, sparks become light blue or white. Dampness typically increases brightness of sparks. If there is any foreign matter present, the color and shape of sparks will be irregular (Li et al. 815).
Thus, it can be concluded that spark test is a highly effective and quick method of determining the type of the material and assessing its properties. Yet, it is important to bear in mind that a number of conditions have to be observed to obtain accurate results. An abrasive wheel must be properly positioned and particular pressure is needed to not to increase the temperature (which gives appearance of higher brightness). Only those sparks that cross the line of vision should be watched (Aurich and Effgen 588). Another problematic issue is that certain materials have very similar spark patterns. This implies that, despite its demonstrative character, the test is not universal and should be complemented by other procedures.
Aurich, Jan, and Christian Effgen. CIRP Encyclopedia of Production Engineering. Springer, 2014.
Black, J. Temple, and Ronald A. Kohser. DeGarmo’s Materials and Processes in Manufacturing. John Wiley & Sons, 2017.
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Dalke, Tyler et al. “Material Determination Using Spark Observation.” Global Journal of Engineering Education, vol. 15, no. 3, 2013, pp. 165-170.
Fleming, Roland W. “Visual Perception of Materials and Their Properties.” Vision Research, vol. 94, no. 2, 2014, pp. 62-75.
Kreibig, Uwe, and Michael Vollmer. Optical Properties of Metal Clusters. Springer Science & Business Media, 2013.
Li, Beizhi, et al. “Study on High-Speed Grinding Mechanisms for Quality and Process Efficiency.” The International Journal of Advanced Manufacturing Technology, vol. 70, no. 5, 2014, pp. 813-819.