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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!


>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?


> 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.

   Also we have experience with controlling electric trains (there is
   a useful analogy), some personal experience, common sense, applied
   physics, and a good thread with another person with the same
   experience on the ELECTRIC_VEHICLES mailing list when we discussed
   this very topic, more or less, but in regards to batteries.  I
   believe I have enough of the archived articles to repost or send.

   If you think about it, in a given column of plating solution
   between the object to be plated and the other electrode there are
   so many ions with a certain mobility (there's where current pulse
   duration and plating pulse frequency come into play).  The ability
   of that column to conduct current is a function *of* the current. 
   The max plating rate should be a function of the ion mobility and
   concentration.  The resistance at max current would be more of a
   function of the availability of ions to be plated rather than the
   actual length of the column.  So, bringing the current up briefly
   to the point where the plating rate maxes out will produce a high
   resistance right at the plating point by ion depletion, and force
   the current to seek another path around that column.


>>    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.


> 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!

>
>>    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.

   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.)



> 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.

  [ snip ]

>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.


>>    the spiky filament, and so the plating on the spiky filament grows
>>    faster than the surrounding area.  You can modify or ward-off this
>>    annoying effect with with external magnetic fields to stir up the
>>    ions in the solution, or by just by using a low-duty-cycle pulsed
>>    DC source for the plating current.  Instantaneously forcing the
>>    solution between the electrode and the end of the spike into
>>    saturation forces the current to move out and flow to other more
>>    far-away places on the plating surface.
>> 
>>    Does anyone else have any plating experience in this area?  I know
>>    the effects but I don't know the currents or duty cycles used with
>>    the different strengths of CuSO4 solution.  I suppose I could
>
>Nah. No need to calculate it when we have libraries. The literature's
>filled with data on this often-solved problem. While not directed at you,
>there's an unusual tendency on this list to forget that a lot of the
>problems we seek to solve have already been heavily researched, or at least,
>many problems similar enough to be very useful. There's mountains of data
>out there, just waiting to fascinate us...

   Indeed.  Looking it up with the Library in another building about 2
   kilometers away from me down in the UBC library is my problem. 
   The only other easy thing to do is an Altavista web search which
   can sometimes bring up some surprisingly good stuff.

   [ GREAT plating info snipped ]


   Wes,

   Thanks for the great plating information!  My plating experience
   is on small things in the laboratory.  My closest experience with
   a BIG commercial copper-plating installation was when I was quite
   young I went with my Dad to visit the copper-plating baths at some
   big industrial outfit.  I think it was in Montana, maybe Idaho. 
   The plates were about 2 foot square (maybe a little bigger) and
   there were banks and banks of them all sitting in a big bath about
   20 foot square.  The wires to carry the plating current to each
   bank were  over an inch thick, and rather heavily insulated. I
   recall the solution was copper sulphate with acid.  It sure smelled
   like acid.  Once you've smelled sulphuric acid on copper you never 
   forget the smell (I was already familiar with it as a child).
   
 Fred W. Bach ,    Operations Group        | Internet: music-at-triumf.ca
 TRIUMF (TRI-University Meson Facility)    | Voice:  604-222-1047 loc 6327/7333
 4004 WESBROOK MALL, UBC CAMPUS            | FAX:    604-222-1074
 University of British Columbia, Vancouver, B.C., CANADA   V6T 2A3
 "Accuracy is important. Details can mean the difference between life & death."
 These are my opinions, which should ONLY make you read, think, and question.
 They do NOT necessarily reflect the views of my employer or fellow workers.