Re: [CAD_CAM_EDM_DRO] EDM Fluid

> 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.

As you warm up water the concentration of contaminates in it increases. The
molecule resonates (rings if you want) so that there is a tiny, tiny, tiny
fraction of ionisation at elevated temperatures. But in reality you could
contaminate it more by just sneezing on the water.

> 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.

Theoretically, and practically, you can turn metal into metal ions without
any other chemicals, if you throw electrons at the metal hard enough. This
is _precisely_ how a mass spectrometer works. The metal is vapourised and
then high energy electrons are thrown at the metal atoms as they pass by,
these knock electrons out of the atom's shell, poor guy. But in an EDM
machine any ions that are made are just going to find another metal ion and
pair up. So I'd go with this, it probably is almost all metallic molecules,
not ions. Since the metal will be in < micron size particulates though it'll
have a similar effect anyway.

> >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.

Why would they have one of each? Some wizardry must be at work because
reacting them with acids would produce salts which will quite easily
dissolve in polar solvents like water. This would just make the water
conductive again. Hydroxides dissolve okay as well. Maybe some sort of weird
base??? I've not read much about iron bases but iron chlorides dissolve
quite nicely in water (I think). Or perhaps the beads catch and hold the
product. Metallic ions are unstable and are looking to get back to a stable
state. That means the minute one ion drifts next to another few they all
suck onto each other and form a metal particle. Atoms are roughly 1.0 x
10^-10m across, so a few of them is still too fine for a filter to remove.

> 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.

The acids and bases themselves will supply the components needed to conduct
a current. For instance, HCL gives H+ and Cl- in water, H2SO4 gives 2H+ and
OSO3-, NaOH gives Na+ and OH- etc. I assume the reagents are locked in the
beads somehow and capture their product. The same is done with the enzymes
used to brake down apple mush to make apple juice. The reaction occurs
inside the beads and the enzymes remains there.

> 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.

Yep, they just swap the metal attached so that it doesn't stick to your
pipes or react with your shower gel to muck scum.

> >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?

Ions will be produced but they just reform as the solid metal as soon as
they hook up, party down and share electrons. Remember, they don't like
being ions, they'd rather be metal. Even if the spark blasted some H20 into
H202 or OH- and H+ it'd just decay back into the original state in
millionths of a second.

John