Re: gEDA-user: pcb anti-environment coating?

["Bob Paddock" <bob.paddock@xxxxxxxxx>]

   On Thu, Jan 1, 2009 at 5:07 PM, Dave McGuire
   <[1]mcguire@xxxxxxxxxxxxx> wrote:

   On Dec 31, 2008, at 8:39 PM, Bob Paddock wrote:
   > I'd put them in a sealed box, with a Gore-Tex Vent so that the
   > enclosure can 'breath' but not pass water.

       This is an interesting idea.  Can Gore-Tex be found in small
     squares for this type of application, or would one be stuck
     destroying an expensive jacket to get some?

   Salvation Army or Good Will would be a good place to look
   if you want to go the clothing route, but there is more to the story.
   The whole story goes like this:  Gore-Tex was invented ~1978,
   used in clothing as everyone knows, and didn't really
   find many other uses then.   Jump forward to 1982.  I was designing
   a hand held control to run some 50 Ton Coal Mining Equipment.
   The control was a sealed box with a membrane switch on the front.
   We very shortly ran into problems.  Taking it down into the Mine
   would cause a pressure reduction that would suck the switches in,
   activating the switches.  Having a stuck switch on a 50 Ton machine
   with
   sharp cutting bits is *bad*.  Very **bad**.  Also found that taking it
   up in a
   plane, as non-pressurized luggage, would deform the switch by
   causing it to balloon out to about four times what it should be.
   From flat to nice dome.  You then had worthless junk, it did not
   recover.
   I had recently read about the the propertis of Gore-Tex, tracked
   down one of the enginners in the factory and asked him if
   he thought it would make a good vent for such an application.
   He said he had no idea, but he would send me several different
   types of the stuff to try out.  Which he did.
   Putting cloth over a whole in mining equipment would last a few
   minutes,
   on on optimistic day.  So a colleague of mine, Don, came up with this
   labyrinth  sandwich to put the Gore-Tex between.
   Take two flat disks, we used thick fiberglass, each about 1/4" thick.
   Mill out a pocket in both disks, place them face to face, then drill a
   hole through
   both disks at one of the ends of the milled circle.  Now rotate a
   single disk 180 degrees.
   Put the Gore-Tex between the disks and epoxy.  If you try to stick
   your Sharp Pointy Coal Mining Implement into the hole you hit
   the fiberglass and not the Gore-Tex.  The assembly was then
   held in the box by a screw in the four corners.  Pressure problem
   was solved.
   Went back to the fellow at Gore-Tex to get more material,
   which he supplied.  Thought our idea was a good one and
   filed for the patent.  So he got it and Don and I didn't.
   Today you can buy Gore-Tex pressure relief vent off-the-shelf.
   Most a screw in type plug, but they come in all kinds of sizes.
   I'll try dig up some part numbers when I get to work.
   Search for these things on Google is useless as you get
   all of the clothing stuff you have no interest in.

   --
   [2]http://www.wearablesmartsensors.com/
   [3]http://www.softwaresafety.net/
   [4]http://www.designer-iii.com/
   [5]http://www.unusualresearch.com/

References

   1. mailto:mcguire@xxxxxxxxxxxxx
   2. http://www.wearablesmartsensors.com/
   3. http://www.softwaresafety.net/
   4. http://www.designer-iii.com/
   5. http://www.unusualresearch.com/


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