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2.3.2 Contacts

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    2764
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    Contacts, meaning mechanical contacts here, are a major part of most electronic products. Even if there is no mechanical switch anymore, you still have the contact between the plug and the outlet, and/or the contact springs for the batteries.

    Contacts include the following items:

    • Switches, plugs, relays, connections to removable parts (batteries, light bulbs, ...), pantographs (the thing on top of a locomotive), "brushes" (for motors), and so on.
    • Contacts are also the components or materials that often cause trouble. Contacts or switches are often the first components to break, and thus a nuisance to consumers like you and me.

    There are many specific requirements for contact materials:

    • Small contact resistance (it is never zero).
    • No sticking or welding under load.
    • No abrasion under load.
    • No intermixing of materials.
    • No wearing and tearing.
    • Suitable mechanical properties, e.g. good elasticity (forever) for switches.

    There are specific materials and group of materials generally favored for contacts:

    • C (graphite in many forms) for pantographs and whenever you want to draw a big current.
    • CuAgAu.
    • RuRhPdOsIrPt.
    • MoW.
    • ....
    • An example of Ag-based contact materials can be found in the link.
    • For contact applications we find expensive materials, because in many applications only small quantities are needed and the inertness of noble metals is what counts.