[NewCandle] Contact Potential and Charge

[Frederick Sparber]

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http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/28/29491/01337047.pdf?arnumber=1337047
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*Contact charging between metals revisited
*Castle, G.S.P.; Inculet, I.I.; Sines, G.S.; Schein, L.B.
Industry Applications, IEEE Transactions on
Volume 40, Issue 5, Sept.-Oct. 2004 Page(s): 1226 - 1230
Digital Object Identifier   10.1109/TIA.2004.834038
*"Summary:* The theory of contact charging between metals was established in
1951 by Harper and confirmed experimentally in 1975 by Lowell who measured
the net charge after separation of pure metals in contact and related it to
the contact potential difference and capacitance of the surfaces using a
specialized measurement technique. It is generally assumed that these
contact charges can be ignored for metals used in common industrial
processes because of charge backflow on separation. A series of experiments
carried out on commonly used industrial materials shows that net charge does
exist on spherical metal balls rolling out of a metal tube into a Faraday
pail. The experiments were carried out using three different tube materials
(copper, brass, aluminum), five different ball materials (copper, brass,
aluminum, steel, and stainless steel), for ball diameters ranging from 0.24to
1.27 cm. The surfaces of the materials were only rinsed with water and
dried. Analysis of the results shows general agreement with the Harper
theory and confirms the presence of net charge on metals separated in this
simulated industrial operation, i.e., moving metal parts off a conducting
conveyor. This process is analyzed from the point of view of possible
discharge hazards and the reasons why this phenomenon is not more widely
observed in industrial processes are discussed."
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*Copper Clad Steel BBs:*

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http://images.google.com/imgres?imgurl=http://www.pyramydair.com/blog/images/daisy-precision-bb-web.jpg&imgrefurl=http://www.pyramydair.com/blog/2006/10/who-makes-best-bbs.html&h=286&w=281&sz=12&hl=en&start=2&um=1&tbnid=8gCUAoy1AjnrjM:&tbnh=115&tbnw=113&prev=/images%3Fq%3Ddaisy%2Bbbs%26svnum%3D10%26um%3D1%26hl%3Den%26sa%3DN
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*" How BBs are made
*A BB starts out as a piece of steel wire that is chopped into rough chunks
quite a bit larger than BB size. Those chunks are fed to two steel plates
that have a long spiral tapering groove. One plate turns while the other
remains stationary, which rolls the rough chunk into a sphere. From there,
it goes on to grinding, where it is reduced in size to the desired caliber.
Next, it gets a flash plating of some anti-oxidant, such as copper or zinc.
Then, it's sorted by centrifugal force in a long spiral slide. The good BBs
go on to packaging and the rejects become scrap. *I saw this process in the
Crosman plant, where they produce 10 million BBs every workday."*
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