Announcement

Collapse
No announcement yet.

CopyCad & Zinc failure - electrolyte problems?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • CopyCad & Zinc failure - electrolyte problems?

    Hello everyone:

    I'm new to this plating game, and while I've been having success with other Caswell kits (anodizing and powder coating), this one has me completely frustrated. I'm already a month behind in my attempts to zinc plate, and need to get on with my project. This post is going to be long, and somewhat complicated. I've tried to organize it to make sense, but that's not one of my strong points. I hope you can bear with me.

    I got Caswells smallest CopyCad & Zinc kit. Everything is set up exactly to Caswells instruction from the Plating Manual. Part prep and cleaning is not an issue. I've tried more than a dozen tests, and have eliminated that as a cause.

    Problem: Plating is substandard due to too little voltage & too much current.

    Specifics:

    1) using Caswell kit supplied 1.7v, 300mA power brick.
    2) test piece is 2" x 3" piece of 18ga. mild steel sheet (12 sq.-in. total, supposedly exact dimensions for Caswell power brick).
    3) measured voltage is 0.4v, measured current is 800+ mA. (specs call for 1.5v, 300mA @ 25mA/in.)
    4) the part plates, but very little evidence of gas "fizzing", and plate is dark, uneven, and discolored w/streaks & patches.

    I reported this to Caswell via PRS, and they suspected bad electrolyte, so the sent me a new bottle. That's GREAT customer support, thanks Caswell!

    However, even with the new electrolyte, I get nearly the same results: measured voltage is 0.5v, measured current is 740 mA.

    I'm back in contact with Caswell about it, and hope to get it figured out, but meanwhile, I've been trying different things, and have spent a lot of time on the net investigating it. Unfortunately, I've not found anything specific addressing my issues, but have learned a lot about electroplating in general, and some technical info about zinc plating (a lot of it seems to be proprietary).

    Things I've tried:

    In messing about with it, I found that by lifting the part out of the electrolyte, voltage would increase. At about 0.7-0.8v., the part would clearly begin to "fizz" as expected (moderately). At this point, there's only about 2-3 sq.-in. still immersed in the electrolyte, and current is down to @ 600mA. The part plates much better this way, giving a fairly even finish w/out the discoloration. But, the current density is WAY UP with respect to specification, and parts coverage is equivalent to about a single 1/4" bolt at a time!

    Pulling the part out so that only the tip of one corner is immersed (@ 1/4"), would produce @ 1.1v, but the part is fizzing away furiously! Obviously not correct.

    Suspecting a defective power supply, I bench tested it with various resistive loads. It is consistent with its specification: with no load it measures 4.85v, 1 ohm load produced 0.72v = 0.72A, 5.2 ohms gave 1.7v = .33A, 15 ohm gave 2.6v @ .17A. It's clearly operating up to spec.

    So I tried beefier supplies:

    1) a 7.5v, 600mA brick: voltage was still drawn down to <= 0.4 v. The brick died at @ 5 minutes, I suspect the rectifier diode let go due to excessive current.

    2) a 12v 12 AH gel-cell battery: voltage drawn down to <= 0.4v.

    3) same battery w/in-line precision current limiter set to 350mA (an LM117 circuit). Voltage was down to 0.2-0.225 v.

    4) a CC/CV lab supply set to 300 mA. voltage came in @ 0.2v. Increasing current limit allowed voltage to rise, but once again, by the time it was up to 1.2 v, it was drawing 1.2 A!

    After these tests, a few thing became obvious to me:

    1) V = IR, and there's STILL not a damn thing I can do about it (I have know this for years, but that doesn't stop me from trying to get around it on occasion)!

    2) resistance (or conductivity) of the electrolyte is non-linear WRT immersed surface area. That really complicates troubleshooting by simple math.

    3) the electrolyte has COMPLETE control over plating bath resistance, and the only way to bring voltage & current to spec is to reduce electrolyte conductivity.

    With this in mind I began searching the net for more info. Here's what I've found:

    Regarding electrolytes:

    1) there are 3 zinc plating chemical processes: Cyanide zinc, Alkaline non-cyanide zinc, and Acid zinc. Acid zinc uses either potassium chloride or ammonium chloride as the primary bath ingredient, some w/ zinc chloride as an added metallic element, and all w/proprietary ingredients known as "carriers" and "wetting agents".

    It appears the Caswell kit is of the Acid zinc variety, since the MSDS lists it as 15%/85% (by weight) zinc chloride/ammonium chloride.

    Ammonium chloride is said to be more forgiving, providing a buffering action, producing acceptable plating over a wider current density range. I presume that's why Caswell chose it for us DIYers. Potassium chloride requires the addition of Boric acid to provide the buffering.

    2) the chloride content of the electrolyte bath determines it's conductivity. Chloride ions provide the electrical conduit to transport zinc atoms from anode to cathode. More chloride = more conductive, and vice-versa (up to a point).

    I more or less confirmed this by test. I set up a bucket of plain tap water. It produced 2.6v @ 150mA. Clearly not conductive enough.

    3) industry standards vary, but generally call for between 20-40 grams/liter of zinc chloride, and 120-200 grams/liter of ammonium chloride.

    Caswells electrolyte falls right in this range percentage wise, but there's nothing that says how much chloride (by weight) is actually present, so I can't compare the mixed bath w/industry standards.

    4) pH: in general industry calls for 4.5-5.5. My electrolyte is sitting at 5.5. Adjustment usually calls for small additions of hydrochloric acid (decrease) or ammonium hydroxide (increase).

    Regarding power supplies:

    1) industry standards vary here too, and there are 2 mechanical processes used: barrel plating (used for loose items, like nuts, bolts, washers etc.), and rack plating (items that can be fixed in position).

    2) the voltage and current density specs are different for these 2 processes: barrel plating specs generally fall in the range of 6-15 ASF (Amps/sq.-ft., = 40-100mA/sq.-in.) at 6-8v. Rack plating in generally calls for 20-40 ASF (140-275mA/sq.-in.) at 3 v.

    Caswells kit would SEEM to be a rack system (items fixed hanging in a bucket) but their V-I specs split the 2 processes, with voltage conforming more to rack plating standards, and current being more in line w/ barrel plating. However, both are slightly lower than respective industry standards. And the results I'm geting are WAY out of line.

    In closing:

    I've come to my own conclusions, which I hope someone can verify or correct, and get some input as to what I might do to rectify this problem.

    1) my electrolyte is WAY too conductive. No amount of external electrical correction is going to fix this or provide a workaround.

    IMHO, the "robber" and "rheostat" techniques are not applicable in this case. Neither can provide a boost in voltage, only a reduction in loop current, or a further reduction in anode-cathode voltage.

    2) one way to reduce electrolyte conductivity would be to dilute it with more distilled water until electrical parameters fall into line. However, this would consequently dilute the ammonium and zinc content, and I don't know how ultimately important their contribution is to the final result (since the ammonium acts as a buffer, too little might cause its own problems). At $33/gallon for electrolyte, I'm loath to experiment w/out some confirmation.

    3) does pH affect conductivity? I have found no information about this.

    4) are there any chemical additives that could be used to reduce conductivity (ie, reduce chlorides) without adversely affecting ammonium and zinc content?

    5) It's clear in my tests, that until voltage hits 0.7-0.8v., there is no appreciable "fizzing" of the part, so from this observation, and industry specs, it would seem that voltage is more critical than current density (40-300mA/in. is a wide window). Is this correct?

    6) What is a usable range of current densities for the Caswell kit, assuming I can get voltage to fall in line? (Caswell says 1-3 v, but only specifies the absolute current of 25mA/in)

    7) Does anyone have actual measured voltages and currents for their successful Caswell kits?

    Thanks for any help you can give!
    Seans Zinc Plating page

  • #2
    First, let me say I have never tried Caswell's zinc kit.
    (just never got around to buying it)
    I have been acid copper and nickel plating for a longggg time and have been using Caswell's "CopyChrome" for about (2) years.

    That being said (and perhaps none of this applies), but here goes:

    1. Anode to cathode (part) distance:
    It is important to keep the parts at least 3" away (or further) from the anode to prevent burning and excessive current draw. Get too close and they will "fizz" and burn.

    2. Agitation:
    This is key. I use a combination of coarse (large) air bubbles and a device that rotates the parts in the solution.
    I was having extreme issues with copper plating ("sandy" looking parts, burnt areas, extreme build-up) until I started using LARGE (1'4" dia.) air bubbles to agitate the solution (even though I was using the automatic part rotator). Forget about using those airstones....they just don't work too well.
    Now the copper comes out a super smooth pink color (as before it looked like copper colored sand granules).
    A note here: exactly the same set-up as before when I was having trouble with the only addition of the coarse air bubbles.

    3. "Fizzing" action on part(s):
    If I see any "fizzing" action the part is ruined!
    The coarse air bubbles keeps the tiny hydrogen bubbles off of the surface and allows fresh solution to come in contact with the part. Additionally, too much current or anode too close to part will cause the part to "fizz".

    4. CC/CV lab power supplies:
    I have one. 0-18V @10 amp.
    Believe it or not, I set the voltage to the recommended setting (or slightly lower) and let the part draw what it wants. I have hardly ever set the current limiter adjustment and all my parts come out fantastic. I keep an eye on the digital amp meter as copper will tend do draw more current then nickel/CopyChrome.

    Nickel: 2.25V
    Copper: 1.5 to 2V
    CopyChrome: 4.5V

    Now, from what I am reading in your post, I belive it can be rectified by #1 thru #3.
    #4 may be due to the fact that my parts are always 3" or more from the anodes.
    Give it another try and let me know.

    See some of my plating at:
    http://users.adelphia.net/%7Epatpawz/geo/plating.htm

    George W.

    Comment


    • #3
      George, thanks for the tips!

      And great looking chrome parts! I will have to do some chrome myself, but that’s further down the road on this project.

      On to my issue, regarding your points:

      1. Anode-cathode separation: the part being plated is 4.5” from each anode. (9” dia. bucket, part placed in the middle). This is per Caswells instructions, range 3-9”, and using Caswells supplied bucket (also see my “discoveries” further down).

      2. Agitation: I’m using a submersible, magnetic rotor pump. It’s rated at 2.5 gpm. In my 1.5 gal bath, it produces a lot of agitation (possibly too much). It’s clearly keeping the part, and anodes, bubble-free.

      3) Fizzing: If I see NO fizzing, I get a very poor plate. W/slight fizzing (barely noticeable), I get a so-so plate. W/some fizzing, I get a decent plate, but still not satisfied w/overall appearance. There is some unevenness of texture & reflectivity. W/strong fizzing, the part burns.

      All these states of “fizzing” are directly proportional to current & voltage.

      4) CC/CV power supply: perhaps these things are too “smart” for this application.

      If I set it for 1.5v CV, and let current do what it will, then current comes in way too high, @ 2-2.5 amps for 12 sq-in piece = @200mA/sq-in. The part burns. If I crank current control to begin limiting, voltage drops accordingly.

      If I set it for 300mA CC, and let voltage do what it will, then it comes in way too low, @ 0.2-0.25v. The part plates poorly.

      Both of these parameters are entirely consistent w/ohms law, V=IR. Given a fixed resistance (the electrolyte is actually variable, but still w/in a limited range), if you increase voltage, then current MUST increase. Conversely, if you decrease current, voltage MUST decrease too.

      And that’s the problem. There is NO way to get BOTH voltage and current to meet Caswells specification, EXCEPT by changing the resistance in the electrolyte.

      In further experimenting I’ve done since my original post, based upon tips and comments provided by users on other forums, I’ve made a few discoveries that are useful. The tips I received from other forums were to IGNORE voltage, and just set the current density as needed. To a man, they all said use 100mA/sq-in minimum, and this is in keeping w/info I have found at commercial & industrial plating system suppliers.

      1. Anode-cathode separation: during one test, I accidentally knocked one anode out of position ( it moved closer to the cathode), and noticed a corresponding voltage drop. So I fiddled w/the positioning, and found that by moving both anodes to one side of the tank, and the cathode to the other (@ 8” separation). I gained @ 35% in voltage! So I ran the next few tests in this configuration (increase was 0.4 -> 0.55v in one test, 1.0 -> 1.4v in another test), rotating the part every few minutes to get full coverage. The results were better, but still not optimal IMO. I’m trying to find a long/skinny rectangular tank to further experiment with.

      2. Electrolyte resistance: In 9 separate tests at different current densities, I noted that electrolyte resistance (as calculated from measured V & I), was inversely proportional to voltage and current. (resistance was higher for lower voltage/current & vice-versa).

      see tables & pictures at: <http://www.hogheaven.com/hobby/plati...c/cctest1.html>

      I had noted this non-linearity before, but had not quantified it until these tests. I have also noted that electrolyte resistance varies w/total immersed area, for any given current density. I have not yet quantified that data. Hope to do so one day.

      With this variability in electrolyte resistance, it makes it very difficult to “calculate” needed VI using only V=IR. I am looking for, but have not yet found, a simple explanation of this relationship. I have found a few sites with higher math equations, but they involve derivatives and integrals and such which are beyond my simple mind.

      3. current density: I tested following the other tips I received, and ran tests at current densities from 25-125 mA/sq-in. (results at the above link). I didn’t quite “ignore” voltage, but simply let it come in at whatever it wanted to be, and recorded that data. I got the best results at 75mA/sq-in., but since this also produced a higher voltage, it’s impossible to say which is the controlling factor.

      4. zinc brightener: the first 5 pieces I ran in electrolyte w/o brightener (90% of my needs are for un-brightened parts). While the higher current density pieces did plate better than prior tests, I still didn’t quite like the way they looked, and wanted to see the results w/brightener. So I ran 4 more pieces w/brightener added.

      Surprise! Voltage at EVERY current density was UP! I had not anticipated this, but it does point out that electrolyte conductivity CAN be manipulated chemically. So I still have some hope of finding the magic concoction that will allow me to do so.

      5. electrolyte temperature: I should have anticipated this, but simply forgot about it while planning more tests. In all my prior testing, ambient air temps were at 90-95º, and electrolyte solution usually 80-85º. Well for the last week it has been cold & rainy here, w/overnight temp @55º, and daytime @ 65º. The first test I ran I notice higher voltage than before, and realized that temp was different. Measured bath temp was 65º! So I have decided to keep the electrolyte as cool as possible from now on.

      With all these “discoveries”, I am able to plate much better now, but still not convinced that it’s the best it can be, particularly the brightened parts.

      Unfortunately, without any technical rebuttal or other explanation so far, I still have to conclude that either:

      a. Caswells specified electrical operating parameters are way off base, or

      b. the supplied electrolyte is completely out of balance to allow achieving these parameters

      Coming from an electronics background, I still have to believe that BOTH voltage and current play an important role (I can’t just ignore voltage), and they must be within their specified operating ranges to get the best results.

      So, I will continue to experiment and see what happens.

      Sean
      Seans Zinc Plating page

      Comment


      • #4
        Sean, looks like you really have done a lot of research and testing.
        Wish I had the zinc kit so I might be able to assist you.

        Concerning the current: I realize that one should adhere to the recommended current settings per square inch and for the most part when I just set the voltage to the specified amount the current draw on the parts is just about where it should be.

        Maybe I have just been real lucky.
        Like I said the only problem I ever had was with the acid copper.
        Every once in a while I might get a little burning on a part edge, however, I have learned by experience how to hang the part, anode placement or using cheater wires to prevent it.

        I just don't have a clue what is going on with your zinc, since you appear to be doing everything correctly.

        I understand what you are saying about the conductivity of the solutions and only being able to control that by chemical make up or alteration.

        My CopyChrome solution is not very "conductive" so that is why I have to run it at 4.5 to 5.0 volts.
        Like you said, the zinc solution may very well be very conductive and perhaps placing the part as far away from the anode may (at this point) be the only viable alternative until you do some more testing.

        Try Caswell's PRS site again, maybe they can help.

        On a side note, I always run my solutions at room temp (in FL that is about 95 degrees in the garage during our ( month summer) and in the winter temps (55 degrees or so) the only difference I see is a "slower to plate" issue, so sometimes I put the heater in to raise the temp to about 80 degrees.

        Good luck, and keep trying!

        George W.
        Orlando, FL

        Comment


        • #5
          Seanc, have you solved your problem yet? I'm all set to give it a try as well and wondered what you found out.

          Comment


          • #6
            Re: CopyCad & Zinc failure - electrolyte problems?

            Dead link below is fixed

            Originally posted by seanc View Post
            George, thanks for the tips!

            see tables pictures at: http://www.nulltime.com/hobby/plating/zinc/cctest1.html

            I had noted this non-linearity before, but had not quantified it until these tests. I have also noted that electrolyte resistance varies w/total immersed area, for any given current density. I have not yet quantified that data. Hope to do so one day.

            Sean

            Comment

            Working...
            X