Spark Testing
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Spark testing is a method of determining the general
classification Classification is the activity of assigning objects to some pre-existing classes or categories. This is distinct from the task of establishing the classes themselves (for example through cluster analysis). Examples include diagnostic tests, identif ...
of
ferrous In chemistry, iron(II) refers to the chemical element, element iron in its +2 oxidation number, oxidation state. The adjective ''ferrous'' or the prefix ''ferro-'' is often used to specify such compounds, as in ''ferrous chloride'' for iron(II ...
materials. It normally entails taking a piece of metal, usually scrap, and applying it to a
grinding wheel Grinding wheels are wheels that contain abrasive compounds for grinding and abrasive machining operations. Such wheels are also used in grinding machines. The wheels are generally made with composite material. This consists of coarse-parti ...
in order to observe the sparks emitted.. These sparks can be compared to a chart or to sparks from a known test sample to determine the classification. Spark testing also can be used to sort ferrous materials, establishing the difference from one another by noting whether the spark is the same or different. Spark testing is used because it is quick, easy, and inexpensive. Moreover, test samples do not have to be prepared in any way, so, often, a piece of scrap is used. The main disadvantage to spark testing is its inability to identify a material positively; if positive identification is required,
chemical analysis Analytical chemistry studies and uses instruments and methods to separate, identify, and quantify matter. In practice, separation, identification or quantification may constitute the entire analysis or be combined with another method. Separa ...
must be used. The spark comparison method also damages the material being tested, at least slightly. Spark testing most often is used in
tool room Tool and die makers are highly skilled crafters working in the manufacturing industries. Tool and die makers work primarily in toolroom environments—sometimes literally in one room but more often in an environment with flexible, semipermeable ...
s,
machine shop A machine shop or engineering workshop is a room, building, or company where machining, a form of subtractive manufacturing, is done. In a machine shop, machinists use machine tools and cutting tool (machining), cutting tools to make parts, usua ...
s,
heat treating Heat treating (or heat treatment) is a group of industrial, thermal and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are al ...
shops, and
foundries A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal into a mold, and removing the mold material after the metal has solidified as it cools. The most common metals pr ...
.


Process

A
bench grinder A bench grinder is a benchtop type of grinding machine used to drive abrasive wheels. A pedestal grinder is a similar or larger version of grinder that is mounted on a pedestal, which may be bolted to the floor or may sit on rubber feet. Thes ...
is usually used to create the sparks, but sometimes this is not convenient, so a portable
grinder Grinder may refer to: Machinery *Various types of grinding machine, used in a machining operation to refine the surface of materials *Food grinders **Blade grinder, includes food processors, blenders, electric coffee and spice grinders, etc. **Co ...
is used. In either case, the grinding wheel must have adequate surface velocity, at least 23 m/s (4500 
surface feet per minute Surface feet per minute (SFPM or SFM) is the combination of a physical quantity (''surface speed'') and an imperial and American customary unit (''feet per minute'' or ''FPM''). It is defined as the number of linear feet that a location on a ro ...
(sfpm)), but should be between 38 and 58 m/s (7500–11,500 sfpm). The wheel should be coarse and hard, therefore
aluminium oxide Aluminium oxide (or aluminium(III) oxide) is a chemical compound of aluminium and oxygen with the chemical formula . It is the most commonly occurring of several Aluminium oxide (compounds), aluminium oxides, and specifically identified as alum ...
or
carborundum Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A wide bandgap semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder ...
often are employed. The test area should be in an area where there is no bright light shining directly into the observer's eyes. Moreover, the grinding wheel and surrounding area should be dark so that the sparks can be observed clearly. The test sample is then touched lightly to the grinding wheel to produce the sparks.. The important spark characteristics are color, volume, nature of the spark, and length. Note that the length is dependent on the amount of pressure applied to the grinding wheel, so this can be a poor comparison tool if the pressure is not exactly the same for the samples. Also, the grinding wheel must be dressed frequently to remove metallic build-up.


Compressed air method

Another less common method for creating sparks is heating up the sample to
red heat '' Red heat'' is a practice of using colours to determine the temperature of metal Red Heat may also refer to: * ''Red Heat'' (1985 film), a 1985 film starring Linda Blair * ''Red Heat'' (1988 film), a 1988 film starring Arnold Schwarzenegger a ...
and then applying compressed air to the sample. The compressed air supplies enough oxygen to ignite the sample and give off sparks. This method is more accurate than using a grinder because it will always give off sparks of the same length for the same sample. The compressed air applies in essence the same "pressure" each time. This makes observations of the spark length a much more reliable characteristic for comparison.


Automated spark testing

Automated spark testing has been developed to remove the reliance upon operator skill and experience, thereby increasing reliability. The system relies upon
spectroscopy Spectroscopy is the field of study that measures and interprets electromagnetic spectra. In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Spectro ...
, spectrometry, and other methods to "observe" the spark pattern. It has been found that this system can determine the difference between two materials that give off sparks that are indistinguishable to the human eye.


Spark characteristics

;Wrought iron:
Wrought iron Wrought iron is an iron alloy with a very low carbon content (less than 0.05%) in contrast to that of cast iron (2.1% to 4.5%), or 0.25 for low carbon "mild" steel. Wrought iron is manufactured by heating and melting high carbon cast iron in an ...
sparks flow out in straight lines. The tails of the sparks widen out near the end, similar to a
leaf A leaf (: leaves) is a principal appendage of the plant stem, stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leav ...
.. ;Mild steel:
Mild steel Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, cobalt ...
sparks are similar to wrought iron's, except they will have tiny forks and their lengths will vary more. The sparks will be white in color. ;Medium-carbon steel: This steel has more forking than mild steel and a wide variety of spark lengths, with more near the grinding wheel. ;High-carbon steel: High-carbon steel has a bushy spark pattern (much forking) that starts at the grinding wheel. The sparks are not as bright as the medium-carbon steel ones. ;Manganese steel:
Manganese Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...
steel has medium length sparks that fork twice before ending. ;High-speed steel:
High-speed steel High-speed steel (HSS or HS) is a subset of tool steels, commonly used as cutting tool material. Compared to high- carbon steel tools, high-speed steels can withstand higher temperatures without losing their temper (hardness), allowing use of ...
has a faint red spark that sparks at the tip. ;300-series stainless steel: These sparks are not so dense as the carbon steel sparks, do not fork, and are orange to straw in color. ;310-series stainless steel: These sparks are much shorter and thinner than the 300-series sparks. They are red to orange in color and do not fork. ;400-series stainless steel: 400-series sparks are similar to 300-series sparks, but are slightly longer and have forks at the ends of the sparks. ;Cast iron:
Cast iron Cast iron is a class of iron–carbon alloys with a carbon content of more than 2% and silicon content around 1–3%. Its usefulness derives from its relatively low melting temperature. The alloying elements determine the form in which its car ...
has very short sparks that begin at the grinding wheel. ;Nickel and cobalt high-temperature alloys: These sparks are thin and very short, they are dark-red in color, and do not fork. ;Cemented carbide:
Cemented carbide Cemented carbides are a class of hard materials used extensively for cutting tool material, cutting tools, as well as in other industrial applications. It consists of fine particles of carbide cemented into a composite material, composite by a ...
has sparks under 3 inches, which are dark-red in color and do not fork. ;Titanium: Although
titanium Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...
is a non-ferrous metal, it gives off a great deal of sparks. These sparks are easily distinguishable from ferrous metals, as they are a very brilliant, blinding, white color.


History

In 1909, Max Bermann, an engineer in
Budapest Budapest is the Capital city, capital and List of cities and towns of Hungary, most populous city of Hungary. It is the List of cities in the European Union by population within city limits, tenth-largest city in the European Union by popul ...
, was the first to discover that spark testing can be used reliably to classify ferrous material. He originally claimed to be able to distinguish different types of ferrous materials based on percent carbon and principal alloying elements. Moreover, he claimed to achieve an accuracy of 0.01% carbon content.. Tschorn . produced an exhaustive treatment of spark testing. His book, Spark Atlas of Steels, along with Spark Testing by Gladwin represent the two most comprehensive texts on the subject . As of the late 1980s, the industrial use of spark testing is not as common as it used to be.. In the early 21st century the availability of portable
X-ray fluorescence X-ray fluorescence (XRF) is the emission of characteristic "secondary" (or fluorescent) X-rays from a material that has been excited by being bombarded with high-energy X-rays or gamma rays. The phenomenon is widely used for elemental analysis ...
equipment largely superseded it in laboratory practice.


See also

*
Flame test A flame test is relatively quick test for the presence of some elements in a sample. The technique is archaic and of questionable reliability, but once was a component of qualitative inorganic analysis. The phenomenon is related to pyrotechnics ...
*
Emission spectrum The emission spectrum of a chemical element or chemical compound is the Spectrum (physical sciences), spectrum of frequencies of electromagnetic radiation emitted due to electrons making a atomic electron transition, transition from a high energ ...


References


Bibliography

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External links


Spark test pictures of various materials
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