Surface Oxidation: Wiping

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).
Thanks.
Darren Harris Staten Island, New York.
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On Tue, 11 Dec 2012 22:06:24 -0800, Searcher7 wrote:

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.
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.
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.
You might try asking this question on sci.electronics.design, since you don't seem to be getting much info here.
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Or no one actually knows. The question is like "How long will this bearing last" without giving the load, speed, misalignment, temperature, contamination, etc.
In this case the main electrical conditions that matter are the voltage and current the switch makes and breaks and how much resistance increase is too much. Mechanically the contact force and opening speed affect the life. I've seen contact lifetime ratings range from 10 to 10 million cycles, and occasionally seen and heard the number be 1.
Wiping makes the resistance stay low longer and the contacts wear away faster.
jsw
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How do you figure?

None of that matters. I have control over the contact thickness, number of wipes between connections, length of wipes between connections, pressure of wipes between connections, and "Break" and "Make" will only occur when there is no current, so there will be no arcing.
I was just concerned about using a different material/metal to wipe the Phosphor-Bronze contacts. If I can just use the same material then problem solved.
Thanks.
Darren Harris Staten Island, New York.
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wrote:

-How do you figure?
Long experience building prototypes, switching signals from microVolts to 40KV, from picoAmps to 1000 Amps, both AC (locomotives) and DC (48V telephone batteries), and a few RF diode switches. Much of it was custom test equipment that didn't permit sloppy design.
I trained for but never practiced teletype repair. They use a voltage high enough to blast through minor contact oxidation: http://ed-thelen.org/Teletype-28/index.html http://www.navy-radio.com/manuals-ttycorp.htm
Whatever you are thinking of, if you haven't seen it done you either didn't look hard enough or it had been tried and discarded by 1930, or disappeared into crypto machines: http://en.wikipedia.org/wiki/Enigma_rotor_details
These switch hundreds of contacts manually: http://www.digikey.com/product-highlights/us/en/itt-cannon-dl-series/1174 If your alignment tolerances are good enough they can be used on the inaccessible rear of plug-in modules.
jsw
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t
None of that will be a problem, since I can adjust the wiping force and number of times.

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.

e
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.

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.
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On Thu, 13 Dec 2012 11:17:12 -0800, Searcher7 wrote:

There are certainly switches that are made of phosphor bronze.
There are no "normal" environmental conditions -- only the environmental conditions that people of limited imagination assume is normal.

Yes, I think we all understand that. What we didn't know until this moment, though, is that you had considered silver plating and decided against it for cost reasons.
Because, you see, we can't read your mind.

If you can't replicate _just the forces and actions_ of an existing switch at the contacts, then you're in a different universe from me, and no advise that I can give you will help. In fact, no amount of advise that you get from any of the regulars here will help, because as far as I know they're all in the same universe as I am, too.
Perhaps this is why you thought that the help you got on s.e.b was all from trolls? Getting sound engineering advice from the wrong universe can do that.
Here in this universe, how you _connect_ to a switch is largely independent of how the _switch's contacts come together_, and with what forces. This applies in particular if your switch is currently just a connection diagram, and has not been reduced to practice in a way that involves any means of making the contacts come together, with or without any forces.

John Fields is pretty astute, and engineers learn early not to answer general questions with specifics. "How much paint does it take to paint a door?" should be immediately replied to with "How big is the door, and what sort of paint?", because any specific answer is only going to be correct if the questioner and respondent both share all the same assumptions.
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So that you will understand what I meant, the switches will not have to operate in space, under the ocean's surface, immersed in harsh chemicals or substances, or temperatures below or above what humans consider comfortable.

You still don't know that. Because it's not true. I decided against *any* plating of whatever materials I settled on for reasons involving complexity. Even cost was secondary. But way address it if it had nothing to do with my original question?

I'm not sure what you meant by "replicate _just the forces and actions_ of an existing switch at the contacts". Or if you were referring to general principles or copying exactly. But either way this has all been addressed in my design and has nothing to do with the wiping material question.
I set the parameters for the shape, number, and arrangement of Phosphor-Bronze contacts, as well as the allotted space needed and supplied by the encasement because it had to be done in order for the switch to accomplish was is needed.

I don't know what this universe stuff is about, but personal attacks are of a different order. I couldn't tell if there was a genuine failure to understand my simple question or just immaturity at work.
I asked if Phosphor-Bronze was an acceptable wiping material for Phosphor-Bronze because I wasn't sure if there would be any problems with using a different metal as the wiping material even though contact during wiping is brief.

I'm not sure what that meant, or what exactly you are addressing. But since this is my design, as I mentioned I have control and the option to change all important variables like "contact thickness, number of wipes between connections, length of wipes between connections, pressure of wipes between connections..."

I have no idea how "astute" John is. I only know that like several others on that group, his maturity level needs work.
And if I asked if it was reasonable to make a door knob out of metal, then I shouldn't expect to be berated because I didn't include information on the size of the door or what kind of paint I'd be using on it.
Darren Harris Staten Island, New York.
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Searcher7 wrote:

Will it be in a vacuum? If not, you have a lot of arcing & surface oxidation that will degrade the contacts. Real switches use some type of contact lube to keep oxygen away from the contacts. Also, you never want any silicon based lube on switch contacts. The phone companies learned that the hard way.

It means that you have to obey the same laws of physics as everyone else.

Wiping requires force. It sounds like it won't do you any good.

Remember mechanical TV tuners? The cheap ones depended only on 'wiping action' and very thin plating. As soon as the plating wore through they were unrepairable. Contact resistance is important to proper switch design, in all cases.

You should talk. John has designed and built custom electronics for decades. OTOH, he doesn't like to waste time on people who ask questions and ignore the answers.

If you asked that on an electronics group you would deserve to be treated like a troll. You asked a question and gave no information. Engineers want to know what you really need, not what you think you want. Your doorknob statement proves that. Even doorknobs aren't 'one size fits all'.
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03:47:08 -0500 typed in rec.crafts.metalworking the following:

    What, other than "don't" was the lesson? -- pyotr Go not to the Net for answers, for it will tell you Yes and no. And you are a bloody fool, only an ignorant cretin would even ask the question, forty two, 47, the second door, and how many blonde lawyers does it take to change a lightbulb.
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03:47:08 -0500 typed in rec.crafts.metalworking the following:

    Oh shoot, that's easy. "A cup" - you may have to thin it a bit to cover the whole door, but a cup will paint it.     For a more precise answer: If you are going to paint just one side, then half as much as to paint both sides. Conversely, twice as much to paint both sides as you'd need for one side.     For more precision, you can mark out a scale representation on the wall of the door, paint it, and the scale up the quantity needed.     Of course, all this presupposes that the inquirer wants to apply paint to the entire door, and not just put some paint on the door.
    It is like determining how long is a piece of string: Hold by both ends, flip it up in the air, guess how high up the mid-point is, and then double it.
    (Similar as to hear how Frislanders weigh pigs.]
tschus pyotr -- pyotr Go not to the Net for answers, for it will tell you Yes and no. And you are a bloody fool, only an ignorant cretin would even ask the question, forty two, 47, the second door, and how many blonde lawyers does it take to change a lightbulb.
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On Fri, 14 Dec 2012 14:22:26 -0800, pyotr filipivich wrote:

Alternately, "a bucket". Just be sure to size the bucket differently if it's the front door of a doll house, or the door to the hanger where you keep your 747.
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typed in rec.crafts.metalworking the following:

    True that. -- pyotr Go not to the Net for answers, for it will tell you Yes and no. And you are a bloody fool, only an ignorant cretin would even ask the question, forty two, 47, the second door, and how many blonde lawyers does it take to change a lightbulb.
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snipped-for-privacy@mindspring.com says...

Then there's the VAB, where each door is roughly an acre in area.

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wrote:

Harsh chemicals include ammonia from cleaners and sulphur from eggs. Silicones can cause some strange problems when they break down in electric arcs too.
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I know that I am jumping in late, but unless you tell us what voltages and currents you will be connecting, you won't really get any useful solutions. Do you know what a "dry circuit" is?
Pete Stanaitis ----------------

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d
s.

I've concluded that I wouldn't get any useful solutions here anyway since it was implied that I posted this in the wrong group.
But since you asked, when the circuits are closed and power applied the voltages can be +3.3, +5, +7, +9, +12, and -5v, not to mention data lines.
However I have no idea why it would make a difference, because as I mentioned there would be no current during "make" or "break" of the connections.
And yes, I know what a dry circuit is. Why do you ask?
Thanks.
Darren Harris Staten Island, New York.
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-However I have no idea why it would make a difference, because as I -mentioned there would be no current during "make" or "break" of the -connections. -Darren Harris
Even after we told you the reason.
BTW, if the ground connection fails or is made after the others, the +3.3 supply line (for example) could disastrously become the return for the +12V.
http://en.wikipedia.org/wiki/Hot_swapping
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Darren Harris Staten Island, New York.
http://www.technology.niagarac.on.ca/staff/mcsele/TelephoneSwitch.html http://www.moog.com/products/slip-rings/
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That's the approach Ford took with their relays they use for low- voltage and current switching in their cars. Took one apart and it had a pretty elegant method for wiping the contacts. Relay lived in the rear of the van and was exposed to salt spray vapor a lot of the time. Not sure of the material, the contacts themselves consisted of wire welded onto the springs, when in contact, they made an "X" with each other rather than being parallel and wiped each other the length of the contacts. It all worked until the non-conformal-coated circuit board got eaten up.
Stan
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