Re: [CAD_CAM_EDM_DRO] EDM Fluid

At 08:52 AM 6/10/02 -0700, you wrote:

>A half remembered blurb by Agie or Charmilles(I can't remember which)
>seemed, to me, to state that the spark vapourizes or melts the substrate,
>but it is the gas bubble collapse at the end of the cycle that actually
>blasts the molten bit free, and that the molten remnant that is left behind
>forms the recast layer.

That's OK with me, point was ionization channels don't do that themselves.
They're nothing more than a linear path of ions in medium, existing for an
instant before the current flows. The spark itself makes a pathway that's
vapor, not vacuum. It does condense back to liquid water, but that is not
the same as cavitation, which produces a vacuum having ability to displace
metal on its own. Cavitation collapse is instantaneous and focused.
Condensation takes a bit more time. As for what does displace metal under
spark, I don't think you need anything but a bit of vaporised metal blowing
up from impact point.

>The ionization of some of the metal is not too far fetched when you consider
>the energies involved, and of course, the presence of water should hold them
>stable in the ionized state.

Apparently not, someone else commented on this too. Water as we all know is
an excellent medium for mobilizing ions, allowing them to come together.

>I was always operating under the belief that ionization was not exclusively
>a consequence of solution but could also be achieved by high energies, such
>as those used to create plasmas (ion clouds??)

Quite true.

>The deionizing resin bed, from my understanding, substitutes H+ for metal
>ions and OH- for non-metal ions.

I saw ref to that on one of the sites someone posted. First, he talks about
filtration and then he talks about two resins, one each for releasing H+
and OH- ions in exchange for metal ions. I'm still wondering where all the
ions are coming from, and also why home softeners don't use similar resins.
Must be expense.

>I do know that the conductivity sensors in the water system operate a valve
>that directs water into the resin bed when the conductivity rises above the
>threshold set by the valve and sensor.

I think we're dealing largely with filtration systems here. It does make
sense to use a medium that has surface charge state though as most
colloidial sized materials have such a charge and that would respond to
charged filter medium. If the resins work by capturing a charged particle
and release only one ion in exchange, it sounds like quite a bargain.

>To drag this whole discussion back to the practical; I contend that the
>practical problems in using water as the dielectric in a home brew system
>are not trivial, and center around keeping the dielectric sufficiently
>non-conductive to maintain reasonable properties.

That sounds quite reasonable.

>With our rather crude home made electronics for control of all the other
>things that need to happen for the system to work well, it seems to me, that
>ignoring this aspect of the process invites poor results.

I agree.

>Distilling the water in the family teakettle and then using it in the belief
>that it has been optimized for use and will stay that way long enough to do
>useful amounts of work doesn't strike me as the best way.

I use oil but I'd buy distilled water instead of trying to make it.

>Don't forget, as Mark Fraser pointed out...you will consume a fair bit of
>expensive wire to make your cut.

Quite true, but so far all I've had to do is minor sinking and contouring
with solid trodes. BTW, by using a trode that rotates and is grooved, one
need not feed the work zone with pressurized fluid.

Regards, Hoyt


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