Analysis of high contact resistance in silver impregnated graphite (SIG) contacts
- 75 Downloads
Silver impregnated graphite (SIG) contacts are used in high safety applications of railway signaling, traffic signaling, and numerous other applications due to high silver content that eliminates the risk of welding in the presence of graphite. High contact resistance (>200 mΩ) was observed in SIG contacts in a railway signaling operation after a few thousand operations of the relay. The high contact resistance was discovered to be a result of loose dust/foreign particles residing between the two contacts. Silver had been preferentially removed from the contacting surfaces during switching operations by an abrading effect of the dust/foreign particles, leaving only graphite on the contact area. Wear was accentuated by the presence of porosity and low hardness of the contacts, leading to improper interaction between the mating surfaces.
KeywordsSIG contact materials contact resistance failure analysis contamination
Unable to display preview. Download preview PDF.
- 1.Anon.: IRS-S67-85,Indian Railways Standard Specification for Silver Impregnated Graphite Contacts for Railway Signaling Relays, Department of Railways, New Delhi, India, Jan 2001, pp. 1–20.Google Scholar
- 2.A. Keil: Ruhender:4. Seminar Kontakt-verhalten und Schalten, (in German), 1977.Google Scholar
- 3.G. Weik and K. Herz:Beitrage zur elektronemikrosko-pischen Direktabbildung von Oberflachen, Verlag R. A. Remy, (in German), 1983,16, pp. 193–8.Google Scholar
- 4.C.L. Meyer:4. Seminar Kontakt-verhalten und Schalten, (in German), 1977.Google Scholar
- 5.L. Horn and A. Merl:7. Internationale Tagung uber elektrische Kontakte, Paris, 1974, pp. 73–9.Google Scholar
- 6.H. Ulbricht:Feinwerktechnik und Mebtechnik, (in German), 1980,1, pp. 21–7.Google Scholar