On Dec 12, 1:15*pm, Tim Wescott wrote:
On Tue, 11 Dec 2012 22:06:24 -0800, Searcher7 wrote:
I'm working on a project that is a mechanical switch of sorts, and it
entails running electrical signals through Phosphor-Bronze contacts.

Now since *all* alloys will oxidize to an extent, I was wondering if I
were to wipe the phosphor-Bronze contacts with the same
material(Phosphor-Bronze), would that be serve to keep the alloy's
surface clean? (The wiping action will be part of the mechanics of the
switch).

Wow. *No one who actually knows is answering. *Here's my two bits, but
take them with a large grain of salt, 'cause I'm no expert.

I know that "wiping action" is an advertised feature on many switches.

There is probably some minimum normal force that you want to achieve to
make sure that the oxide is wiped off, and probably some minimum wiping
distance to boot. *I absolutely couldn't tell you what the necessary
forces and/or distances are, but I'll bet you that there's standards out
there, and probably huge amounts of tribal knowledge at the various
switch manufacturers.

None of that will be a problem, since I can adjust the wiping force
and number of times.

If you can get a good thick silver plating on your contacts then your
required forces will go way down -- silver is a pretty good conductor,
and silver oxide is both mechanically weak and (I understand) not a bad
conductor in its own right.

Electroplating silver onto Phosphor-Bronze would require redesigning
and and result in an increase in complexity and cost of the project.
The idea is to stick with a material that I wouldn't need to plate. If
it is conductive enough, then wiping would take care of the oxidation.
(The switch of course will be used under "normal" environmental
conditions).

Silver does however have the best conductivity of all metals, but not
the *spring* of Phosphor-Bronze. Copper also has more electrical
conductivity than Phosphor-Bronze, but not it's corrosion resistance.
Gold has excellent electrical conductivity, but is not as wear
resistant.

Finding a switch that has about the same ratings as what you need, taking
it apart, and copying it's actions and forces may not be a bad way to
go. *You won't be able to duplicate their metallurgy, but you can't have
everything.

Nope. This is a switch that doesn't exist in any form yet and will
incorporate unorthodox connections. (One particular version will allow
switching between a dozen 40 pin connections). The wiping will
actually be in the mechanical action of switching from one connection
to the next.

You might try asking this question on sci.electronics.design, since you
don't seem to be getting much info here.

I actually tried a similar question at Sci.Electronics.Basics two or
three years ago, only to have to deal with personal attacks by a group
led by a "John Fields" because I wouldn't give them *detailed* plans
of what I was working on. Specifics that had nothing at all to do with
the question concerning wiping material.

I'd think that lot of the same trolls who hang out at
Sci.Electronics.Basics also frequent Sci.Electronics.Design.

Thanks.

Darren Harris
Staten Island, New York.