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Re: torque conv./ inner tubes
On Tue, 14 Jan 1997, Tesla List wrote:
> >> Subject: Re: torque conv./ inner tubes
>
> Subscriber: music-at-triumf.ca Tue Jan 14 22:12:03 1997
> Date: Tue, 14 Jan 1997 10:00:15 PST
> From: "Fred W. Bach, TRIUMF Operations" <music-at-triumf.ca>
> To: tesla-at-pupman-dot-com
> Cc: music-at-triumf.ca, wesb-at-spectra-dot-net
> Subject: Re: torque conv./ inner tubes
>
> >Message-ID: <199701140525.WAA20805-at-poodle.pupman-dot-com>
> >Date: Mon, 13 Jan 1997 22:25:36 -0700
> >From: Tesla List <tesla-at-poodle.pupman-dot-com>
>
> >Subscriber: wesb-at-spectra-dot-net Mon Jan 13 22:07:31 1997
> >Date: Mon, 13 Jan 1997 14:42:13 -0500 (EST)
> >From: Wes A Brzozowski <wesb-at-spectra-dot-net>
> >To: tesla-at-pupman-dot-com
> >Subject: Re: torque conv./ inner tubes
> >
> >
> >
> >On Sat, 11 Jan 1997, Tesla List wrote:
> >
> >> Subscriber: music-at-triumf.ca Sat Jan 11 20:44:07 1997
> >> Date: Sat, 11 Jan 1997 17:48:14 PST
> >> From: "Fred W. Bach, TRIUMF Operations" <music-at-triumf.ca>
> >> To: tesla-at-pupman-dot-com
> >> Cc: music-at-triumf.ca
> >> Subject: Re: torque conv./ inner tubes
> >>
> >> As do I. Plating is a very good idea. Starting out small is an
> >> excellent idea. One thing that we should remember is that plating
> >> any object with pure smooth DC will likely result in uneven
> >> thicknesses depending on the distance from the plating point or
> >> plating surface to the opposite electrode. Unless you saturate the
> >> solution electrically then the points closest to the other
> >> electrode will plate thicker.
> >
> >Fred, are you sure about this?
>
> Yes. Poor surface resistance uniformity and high surface
> resistance is a recipe for poor plating. Far-away places may not
> get plated, as you say. One wants to insulate (or electrically
> shadow) any areas which are plating too heavily. Once the surface
> to be plated has a low resistance, then other factors take over such
> as the column resistance of the plating solution, and the electric
> field shape in the solution!
I can agree with all of this completely; it's all pretty standard stuff,
but may be of use to the folks interested in learning the intricacies of
plating. As far as my question is concerned though, that partial line was
cut from the following paragraph and really has nothing to do with the
answer you gave. Let's read that snippet back into the paragraph where it
belongs, and move on...
> >Commercial plating has used DC since
> >plating's been done, and none of the standard plating texts (at least
> >those in my personal library)
> >mention anything about using pulses.
>
>
> Pure ***filtered**** DC? I really don't think so. Too expensive.
> They use simple rectified AC, don't they?
Now Fred...
You've added a word to what I said, then emphasized it and answered the
new statement, rather than what I said. This is very disappointing.
Okay, now I'm off the soapbox; sorry to get up on it in the first place.
To answer your question, it's useful to check the literature.
Now, commercial plating certainly can use DC, but not filtered (that's your
word, not mine). If you check out the waveform obtained from rectifying
3-phase power, you'll see what I mean. DC is quite useful for some plating
baths, where there's a limit on the current density to produce a plate with
particular characteristics. Since a plating house makes more money if they
can bump up the throughput of their process, DC may be preferred, so that
time isn't lost during that percentage of the time when the "simple rectified
AC" is down near zero.
But all of this is digression and tangents from my original statement; that
being that your statement about using pulses to compensate for uneven
current density does not seem to be used in practice, and I've not seen
any references to it in the literature. (That doesn't mean that it hasn't
been studied; I'd be surprised if it hadn't, but I was and still am
curious about any data that may exist and wether you know of any. This
still really hasn't been answered.)
> > Getting an even plate is a classic
> >problem, but there's no mention I've seen of solving it with pulses. It's
> >odd, because it would be such a simple fix, if it were workable. Might
> >you have any references to share?
>
>
> Sure.
>
> First, if you talk to enough old geezers in the lead-acid business,
> it's folklore that storage batteries live longer when charged with
> noisy DC rather than quiet DC. Also, they charge better in an
> environment with a **slight** mechanical vibration which keeps
> hydrogen bubbles small. Too much vibration knocks stuff off the
> plates.
[Lots of interesting battery discussion snipped; I hated to do so, but
this note's getting **big**]
Fred, this is an interesting explanation, and I thank you for sharing it,
but by asking for references in a discussion on plating, I really meant
plating references. What we have here is an interesting speculation on your
part, and who knows -- it may even have some merit when tried in plating.
But it appears that we presently have no references on its usefulness in
plating. Since this was originally a suggestion to some folks who wanted to
plate a toroidal shape, I really think they deserve to have it pointed out
that this is presently speculative stuff. A lot of people on the list are
glad to experiment; others are interested in knowing what's known to work.
I think the distinction should be made, and I hope someone tries to work
out your ideas. Could end up with something interesting.
> >> So, either very good dimensions of the plating tank are needed
> >> (i.e., to plate a toroid the plating tank should be exactly
> >> toroidal as well, with the graphite-coated inner tube suspended
> >
> >Actually, any convenient shape is acceptable for a plating tank; what you
> >need be concerned about is the shape of the anode,
>
> Of course I was thinking of lining the tank with the anode material
> if necessary, somewhat of a standard practice, or at least it
> should be! You see, that way you need the MINIMUM VOLUME of
> plating solution! Sorry, I thought that was an obvious technique
> which I neglected to explain. Oh there are so many things we may
> have come across in our private experience that we just *assume*
> others will also have done. Again, my apologies for that
> unclarity.
Quite true. Just for future reference though, if you talk to people with
plating experience, it's most likely they won't assume that you're using
a specialized tank for plating. That requires specialized tooling with
a poorer potential for reuse. For hobby stuff, particularly if you don't
have to completely cover the work peice with plate, it could be useful.
Frankly though, once you can plate up cheap toroids, you'll want to try
different sizes and shapes, and a tank that conforms closely to one shape
or size will be not too useful for another. Also, there's precious little
room to make adjustments, should they be needed; you end up making another
plating tank.
As far as what "standard practice" "should be", this depends a lot on the
particular problem you need to solve. It appears that this is workable
for the kinds of problems you've solved, and that's great. But there are
a whole universe of problems out there in which it would be much more
trouble and more costly than it's worth. Sure, different sized plating tanks
are used for different problems, to to optimize the cost per peice produced,
but we often need lots of room to tweak and tinker.
Of course, if you have some ideas of how to produce a toroidal-shaped
tank, and a toroidal copper anode, why not just put the copper anode on
the outside of the tank and use that for the toroid! We can drop the
plating altogether. (That's not a smart a** answer; it just occurred to
me that it might be doable if there are some ideas out there.)
> > which should really
> >not be the plating tank, as the tank's integrity would slowly be eaten
> >away, resulting in a disastrous break-through at an unexpected moment.
> >The standard fix is often to use multiple anodes, with different spacing
> >to the work piece, to get a more uniform current density at the work piece
> >surface. Also, the further the anode(s) is (are) from the work piece, the
> >more uniform the current density becomes at the surface.
>
> Sure, if you've got lots of solution and a huge tank to start with!
If ya wanna play, ya gotta pay. There are tricks to minimize the amount
of solution even with a standard plating tank. Polyethylene bottles, filled
with water, and weighted down with rocks, can be placed in areas where
the current flow would not be disturbed. As far as needing a "huge" tank,
I guess you'll have to define huge. It's typical to require some distance
between the anode and cathode; that, and multiple anodes are needed to get
an even plate for a large variety of shapes.
> >> inside the plating chamber it would be like a doughnut within a
> >> doughnut), or else deliver the plating current in high-peak-current
> >> low-average short duration pulses which saturate the
> >> current-carrying capacity of the plating solution. This "saturation
> >> effect" will make for a more even plating of copper all around. I
> >> am not sure of the frequency of the pulses, I would imagine that
> >> anything between 10 Hz and 1KHz would work. 60Hz sounds likely.
> >> One drawback with this pulsing technique is that the resistance of
> >> the graphite will be a big problem to high-current pulses at the
> >> beginning of the plating job. So it would be best to start the
> >> plating job with smooth DC until you get a thin copper plating all
> >
> >Actually, they may want to start with a large resistance in series. The
> >resistance should be much larger than the resistance of the toroid with its
> >graphite-loaded binder. (Per my previous note on this subject, a loose
> >graphite coating will work very poorly. It may be fine to demonstrate
> >that plating can happen on a small object, but it will yield poor results
> >if you want to produce a usable plate.)
>
> I agree that a loose graphite will be a poor plating surface,
> mainly because of its high and unpredictable results, especially
> over a large surface. I recently read where the plates in a
> storage battery perform better and charge quickly when the material
> is deposited on a certain kind of polyester mesh rather than a
> metal grid.
>
> Experimenting with plating small objects first was an excellent
> idea that someone suggested.
Doing smaller, pilot jobs is standard procedure when developing any process,
at least if the process allows smaller jobs. This may not be as obvious to
the hobbyist who's interested in seeing results, but it tends to get you to
good results the fastest. Using the plated plastic process I described in an
earlier post, I've made up many dozens of parts, using variations in solvent
mixes, variations in the conductive coat components, variations in current
density, and variations in anode distance. Sometimes you produce something
interesting, sometimes you get crap. Sometimes the results are repeatable,
and sometimes a very minor and uncontrolled variation is all you need to
throw everything out of whack. You have to look for those spots where "the
curve" is relatively flat, and so where minor variations don't have a
major effect. The plating part has been very extensively studied over
the past century, but a lot of the other parts, and merging the plating
steps with the others, is what makes it interesting...
> I have not done any LARGE plating jobs like an inflated inner tube.
> Mostly just small plates and circuit boards and the like. Some
> with electroplating gold as well for a groundplane for RF circuits
> and microwave transistors. This is why I was very interested in the
> results (since I had not tried anything that big.)
Aha! Well, this explains much, then. I can see how those items could allow
one conformal tank to be reused over many jobs. That sounds like a prudent
solution to the problem. I think that once a coiler finds out what can be
done with plating, though, he'll want to experiment with lots and lots
of size & shape variations. (We do with everything else!)
> > The large resistance will swamp
> >out the varying resistance of the graphite coat as it gets further and
> >further from the point where the wire is attached. If this isn't done,
> >the current density will start out highest at the point where the wire
> >attaches. (It will anyway, of course, but the variation will be reduced.)
> >This will be the first spot to get any significant copper. After
> >it gets the copper, that small spot will have such a small resistance
> >compared to the rest of the toroid that almost all the current will flow to
> >that spot, and it will be the only spot to get any significant plate.
>
> Sure, but you can prevent this problem by applying an insulating
> paint over the connection to prevent this initial buildup. Another
> trick is a guard electrode.
Well, there's one little problem there. All that will do is prevent plating
from building up over the point of the connection. The point I was making was
that the resistance between the connection point and various points on
the toroid will vary enormously the further you get from the connection
point. This will upset the current density in the worst possible way, and
the problem will snowball as the a few square inches around the
connection point pick up some significant copper and then hog almost all the
current. The point of the resistor is to keep the current through the
conductive coat so low that there's almost no voltage drop between one
end of the toroid and the other. That's never a problem when there's a layer
of copper, but when there's only graphite, the problem's significant. When
there's basically no voltage drop across the workpiece,the current
density is much more even, and you can start out with a fairly even starting
layer of copper. If you get spotty copper over a graphite-loaded coating,
it'll be very difficult to correct. (I've used nitric acid to "clean up"
some early mistakes to prevent having to make up new work peices too
quickly, but this produces some very toxic gas, and I'm not at all happy
to do it. I'd be very hesitant to do this with a toroid-sized peice.)
The guard electrode idea is useful in sone situations, but in a situation
like this one, if there is a way to solve the problem with special electrode
placing, the tank size required would likely be quite impressive!
> >While this description may not be particularly descriptive of what they're
> >likely to see while plating a toroid, it's perfectly applicable to describe
> >why the portions of the toroid closer to the anode will receive a heavier
> >plate than those portions farther away. The closer a point on the cathode
> >is to the anode, the higher the current density will be at that point on
> >the cathode, and the heavier the plate will be.
>
>
> Yes. That is why I was suggesting a formed chamber (with lining or
> thick enough walls of course) or else as my second suggestion said,
> one must be prepared to move the other electrode(s) [ I didn't use
> the plural - sorry ] around, experimenting with the thickness of
> plating at each position on your object being plated.
Sure. But rather than moving your anodes around, multiple anodes can do
the same without having to touch anything. With acid copper, or worse,
cyanide coppper, the less you move things, the less you'll want to splash.
The use of different sized anodes, and at different distances from the
cathode, you can do a lot of current shaping.
Anyway, there's a lot of good discussion here. I do hope we haven't
discouraged the others from contributing, though. This topic's quieted
down lately (except for us :-). But I'd be interested in hearing of
others' experiences in the area, as well as more details of the methods
you used in your work.
Wes B.