EDM Fluid

At 08:14 AM 6/9/02 -0700, you wrote:

>concentration of any ions other than H+ and OH-,

Actually, water itself has nearly no ions. The concentration of those two
is so low it's probably way less than 1 in 10^8 or so.

>continually producing a lot of metallic ions from the workpiece and the
>wire.

Really, it's producing lots of metallic fines but very few metallic ions.
In order to produce metallic ions in water, the metal has to react with
other chemicals, to which each metal atom loses an electron. In pure water,
there are no other chemicals.

>The ion burden is sufficiently important that commercial machines have a
>sensing system to continuously monitor the conductivity of the water, and a
>resin bed consisting of porous plastic beads impregnated with strong acids
>and strong bases to suck up the unwanted metallic ions.

Sensing the conductivity is a grand idea. But strong acids and bases, in an
aqueous medium, will neutralize each other, usually to produce a dissolved
salt and high conductivity. Also, plastic ion exchange resins do not need
those in order to remove ions, if any ions exist; in fact, in say water
purification systems, they are pre-impregnated with NaCl. That is
substituted for ions that harden water, leaving it soft but salty. And
conductive to precisely the same degree. If indeed ion exchange resins are
used in EDM and exchange ions, they would do exactly the same thing. Not to
say that water-based systems do or don't use resin beds, but if so for the
several reasons above they don't exchange.

>The creation and subsequent collapse of the ion channel between electrode
>and workpiece is what blasts a bit of metal away from the workpiece.

Not quite: the spark itself erodes the material. Ion channels do not
themselves 'collapse', they just go neutral when electric stress is removed.

>Since water is such an efficient solvent, many more ionic species will stay
>in solution with water,

That's true of water and ions, but there are few ions if any produced by
EDM in pure water. Or, where do they come from?