View source for Spark testing

{{Short description|Method to classify ferrous materials}}
{{distinguish|Streak test (mineralogy)}}
{{For|spark testing explosives|Safety testing of explosives}}

[[File:SparkTestToolSteel.jpg|thumb|right|Spark testing of [[tool steel]]]]
[[File:SparkTestMildSteel.jpg|thumb|right|Spark testing of [[mild steel]]]]
'''Spark testing''' is a method of determining the general [[steel grades|classification]] of [[ferrous]] materials. It normally entails taking a piece of metal, usually scrap, and applying it to a [[grinding wheel]] in order to observe the sparks emitted.<ref name="geary">{{harvnb|Geary|1999|p=63}}.</ref> 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]] must be used.<ref name="davis"/>  The spark comparison method also damages the material being tested, at least slightly.

Spark testing most often is used in [[tool room]]s, [[machine shop]]s, [[heat treating]] shops, and [[foundry|foundries]].<ref name="em"/>

==Process==
A [[bench grinder]] is usually used to create the sparks, but sometimes this is not convenient, so a portable [[grinding machine|grinder]] is used. In either case, the grinding wheel must have adequate surface velocity, at least 23&nbsp;m/s (4500&nbsp;[[surface feet per minute]] (sfpm)), but should be between 38 and 58&nbsp;m/s (7500–11,500&nbsp;sfpm). The wheel should be coarse and hard, therefore [[aluminium oxide]] or [[Silicon carbide|carborundum]] 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.<ref name="geary"/><ref name="davis">{{harvnb|Davis|ASM International|1994|pp=126–127}}.</ref>

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 [[grinding dresser|dressed]] frequently to remove metallic build-up.<ref name="geary"/><ref name="davis"/>

===Compressed air method===
Another less common method for creating sparks is heating up the sample to [[red heat]] 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.<ref>{{harvnb|Saunders|1908|pp=4808–4810}}.</ref>

===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]], [[Mass spectrometry|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.<ref name="davis"/>

==Spark characteristics==
[[File:Spark testing 1.png|thumb|400px|{{colbegin}}(A) High-carbon steel<br />(B) Manganese steel<br />(C) Tungsten steel<br />(D) Molybdenum steel{{colend}}]]
[[File:Spark testing 2.png|thumb|400px|{{colbegin}}(A) Wrought iron<br />(B) Mild steel<br />(C) Steel with 0.5 to 0.85% carbon<br />(D) High-carbon tool steel<br />(E) High-speed steel<br />(F) Manganese steel<br />(G) [[Mushet steel]]<br />(H) Special magnet steel{{colend}}]]

;Wrought iron: [[Wrought iron]] sparks flow out in straight lines. The tails of the sparks widen out near the end, similar to a [[leaf]].<ref name="geary"/><ref name="lee">{{harvnb|Lee|1996|p=22}}.</ref>
;Mild steel: [[Mild steel]] 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.<ref name="geary"/><ref name="lee"/>
;Medium-carbon steel: This steel has more forking than mild steel and a wide variety of spark lengths, with more near the grinding wheel.<ref name="lee"/>
;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.<ref name="lee"/>
;Manganese steel: [[Manganese]] steel has medium length sparks that fork twice before ending.<ref name="lee"/>
;High-speed steel: [[High-speed steel]] has a faint red spark that sparks at the tip.<ref name="lee"/>
;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.<ref name="davis"/>
;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.<ref name="davis"/>
;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.<ref name="davis"/>
;Cast iron: [[Cast iron]] has very short sparks that begin at the grinding wheel.<ref name="geary"/>
;Nickel and cobalt high-temperature alloys: These sparks are thin and very short, they are dark-red in color, and do not fork.<ref name="davis"/>
;Cemented carbide: [[Cemented carbide]] has sparks under 3 inches, which are dark-red in color and do not fork.<ref>{{Citation | last = Woodson | first = C. W. | title = Spark Streams Identify Metals | journal = [[Popular Mechanics]] | volume = 112 | issue = 3 | pages = 192–193 |date=September 1959 | url = https://books.google.com/books?id=jt8DAAAAMBAJ&pg=PA192 |issn=0032-4558 | postscript =.}}</ref> 
;Titanium: Although [[titanium]] 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.<ref>{{cite web|url=http://www.popsci.com/diy/article/2007-12/titanium-or-plain-ol-steel |title=Titanium, or Plain Ol Steel? |access-date=2011-02-21}}</ref>

==History==
In 1909,<ref>Max Bermann first reported the spark testing method at the fifth [[International Association for Testing Materials]] conference, which was held in [[Copenhagen]], as reported by ''The Engineering Magazine''. Based on knowing the conference was held in Copenhagen, the year can be found from:
*{{Citation | title = Copenhagen Congress on the Testing of Materials of Construction | journal = Nature | volume = 81 | issue = 2082 | pages = 377–378 | date = 1909-10-23 | doi = 10.1038/081377a0 | bibcode = 1909Natur..81..377. | postscript =.| doi-access = free }}
*{{Citation | last1 = François | first1 = D. | last2 = Pineau | first2 = André | title = From Charpy to Present Impact Testing | publisher = Elsevier | page = 7 | year = 2002 | url = https://books.google.com/books?id=Tg23LBRz4cMC | isbn = 978-0-08-043970-9}}</ref> Max Bermann, an engineer in [[Budapest]], 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.<ref name="em">{{harvnb|The Engineering Magazine|1910|pp=262–265}}.</ref><ref>{{harvnb|Oberg|Jones|1918|pp=88–92}}.</ref>

Tschorn <ref name = "tschorn">{{harvnb|Tschorn|1963}}.</ref> 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 <ref name="dulski">{{harvnb|Dulski|1996|p=57}}.</ref>

As of the late 1980s, the industrial use of spark testing is not as common as it used to be.<ref>{{harvnb|Drozda|Wick|Benedict|Veilleux|1987|p=7{{hyphen}}18}}.<!-- Not a range --></ref> In the early 21st century the availability of portable [[X-ray fluorescence]] equipment largely superseded it in laboratory practice.

== See also ==
* [[Flame test]]
* [[Emission spectrum]]

==References==
{{Reflist}}

===Bibliography===
*{{Citation | last1 = Davis | first1 = Joseph R | last2 = ASM International | author2-link = ASM International (society) | title = Stainless steels | publisher = ASM International | year = 1994 | edition = 2nd, Illustrated | url = https://books.google.com/books?id=OrlG98AHdoAC | isbn = 978-0-87170-503-7}}.
*{{Citation | last = Dulski| first = Thomas R. | title = A manual for the chemical analysis of metals | publisher = ASTM International | year = 1996 | isbn = 978-0-80312-066-2}}.
*{{Citation | last = Gladwin | first = W.M. | title = Spark Testing | publisher = United Steel Co., Sheffield, UK }}.
*{{Citation | last1 = Drozda | first1 = Tom | last2 = Wick | first2 = Charles | last3 = Benedict | first3 = John T. | last4 = Veilleux | first4 = Raymond F. | last5 = Bakerjian | first5 = Ramon  | title = Tool and manufacturing engineers handbook: Quality Control and Assembly | publisher = [[Society of Manufacturing Engineers]] | year = 1987 | volume = 4 | url = https://books.google.com/books?id=5I1wNgGvuxsC | isbn = 0-87263-135-4}}.
*{{Citation | title = The Engineering Magazine | publisher = Engineering Magazine Co. | year = 1910 | volume = XXXVIII | url = https://books.google.com/books?id=7BHOAAAAMAAJ |ref={{sfnref|The Engineering Magazine|1910}}}}.
*{{Citation | last = Geary | first = Don | title = Welding | publisher = McGraw-Hill Professional | year = 1999 | url = https://books.google.com/books?id=6gPEaTnuOEgC | isbn = 978-0-07-134245-2}}.
*{{Citation | last = Lee | first = Leonard | title = The Complete Guide to Sharpening | publisher = Taunton Press | year = 1996 | url = https://books.google.com/books?id=CtkWaJw5iXkC | isbn = 978-1-56158-125-2}}.
*{{Citation | last1 = Oberg | first1 = Erik | last2 = Jones | first2 = Franklin Day | title = Iron and Steel | publisher = The Industrial Press | year = 1918 | edition = 1st | url = https://books.google.com/books?id=F8QxAAAAMAAJ}}.
*{{Citation | last = Saunders | first = William Lawrence | title = Compressed Air Magazine | publisher = Compressed Air Magazine Company | year = 1908 | volume = XIII | url = https://books.google.com/books?id=-BDOAAAAMAAJ}}.
*{{Citation | last = Tschorn | first = Gerhart  | title = Spark Atlas of Steels: Cast-Iron, Pig-Iron, Ferro-Alloys and Metals, New York | publisher = The MacMillan Company | year = 1963}}.

==External links==
*[http://machinetoolrecyclers.com/spark-test.html Spark test pictures of various materials]

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[[Category:Ferrous alloys]]
[[Category:Metalworking]]