Zinc plating help

N

nigpig

Low Mileage
I have a ZnCl2 based kit and am having difficulty getting an even spread of plate on a motorcyle centre stand spring. The spring is 3 inches long and 3/4 inch in diameter. It has a hook on each end.

After cleaning, degreasing and pickling I have proceeded to suspend the spring in the solution by running a copper wire down the centre of the spring. The problem is that each of the hoods either end get too much current and get a very rough coating. Then the plating stops where the hook bends into the spring coil, with no plating but a grey colour on the main coils of the spring. If a place one of the Zinc anodes right next to the coils that local area gets some plating.

I calculated my area as 7.3 inches plus the inside of the spring. I am running at about 1 amp and works out at 1.4 volts at 75F temperature.
I'm wondering if my solution does not contain enough Zinc Chloride and if this would give this result of too much current at the ends and none in the middle of the spring.

Just done some research online and found this.
http://journals.tubitak.gov.tr/chem/issues/kim-02-26-5/kim-26-5-11-0108-10.pdf

Im using only 50g/litre of Ammonium Chloride and I should be nearer 200 g/litre.
My ZnCl2 is about right at 50g/litre.
pH is about 4.
Going to try more Ammonium Chloride and see if this was the problem.
 
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I'm not a chemist and my experience is far less...

than yours... but when I had a problem I did these things.

1. Reverse the current and DE-ZINC the part.
2. Re-clean the part in acid. I used Sulfuric Pool Acid... its hard to find any more...
3. Re-buff the part insuring all areas are as clean and EVENLY polished so that the zinc should adhere uniformly. This has gotta be a challenge with springs!
4. Then re-zinc the part and using "SemiChrome" or a similar product, polish and buff the part to the sheen you want.

Lastly... if I were you... I would simply purchase a spring already coated to a sheen or shine that is similar... or contrasts nicely with what you are doing.
 
Thank you Black Dog.
I did manage to plate the spring quite well. When I washed it I used water from the previous pickle wash. Part of the spring went black.

It is becoming something of a chelenge that I need to complete so will try some more. I will take your advice and reverse polarity and try some more and perhaps lower the current as the ends of the spring are still showing over current accumulations. Not sure about the back oxide though.
 
Well... the part turning BLACK is something...

I have not experienced.

As I said, I don't have much experience outside of what I told you... but I have coated many different parts on things that were 100 years old and several different metals.

My kit came from the Eastwood Company (http://www.eastwood.com/eastwood-s-tin-zinc-electroplating-system.html) and came with a 6 volt lantern battery about 15 years ago. Cost was around $49 bucks back then as well.

I see that the kit now comes with two "D" cell batteries... Hmmmm! BTW... when my 6 volt lantern battery went flat, I tried using 1 "D" cell and it seemed to work just as well! Given that... and what you were saying also... the amount of current may not be the big issue here.

Some things I polished, and still other things I left a flat silver color... but all things needed to be cleaned well and polished as smooth as I could get them before plating, especially if I wanted a "chrome-like" finish.

Again... I experienced uneven plating and told you what worked for me... but have no idea why a metal would turn black.

Hope you find the problem easily... and do send fotos!
 
Suggest you post a pic of your setup.

uneven plating can be helped by water circulation (a fish tank recirculator) and/or aeration (bubbler or compressor rig).

plating at .18 amps per in^2 you should be at 1.4 amps, voltage doesn't matter (within reason)... you just need enough potential to push the electrons. Amperage is what is doing the work.

what about your zinc bars?

What is a zinc cl plating? I'm only familiar with 2 types of zinc plating.. hot dip (galvanizing) and electro-plating with bars of zinc through an electrolyte bath.

what is the PH or freshness of your solution?
 
I will take some pictures if this occurs again. I have started to prep the spring for the next go so cant go back.

The solution is one from Gatros Plating here in the UK. I have Zinc strip as the anodes and a pH of about 4. ZnCl 250 g in 4.5 litres of distilled water. Ammonium Chloride 750g. Zyolite 290 brightner 250ml. Zyolite maintenance 3ml.

I'm working to get 0.1 A per inch^2.

I think it may be down to a cleaning issue. It could be that the poorly plated/unplated area of the spring went black on contact with my contaminated washing solution as there was a cell set up between the plated parts and and the unplated parts of the spring. Just guessing.
 
I've gotten black stuff on parts while working around my zinc rig for a couple of reasons:
- dirt / grease particles(it is black to start but becomes more noticable during plating)
- poor electrical connection between hangar and part causing a black type of soot, this seems to wipe off with a 3m pad
- contact with a strong acid (as in Hcl).
- contamination by the plastic insulation of my copper (electric wire) hangar.

not all the same "black" mind you, but basically any contamination seems to result in black junk of some sort.

the zinc bars themselves can get quite black, but that doesn't appear to effect the plating.

Can't help with electrolyte chemistry much because I don't care (not negligant, just buy the solution from a vendor and it works). If in doubt you could get a fresh electrolyte solution :)

I suggest turning up your amperage, you can safely run .20 per in^2 or higher. Lately I just rough guess it, put the part in without the agitator running and look for the stream of bubbles and adjust it isn't plating too aggressively, then turn pump / air on and go for it. The pH of your electrolyte solution may be causing zinc corrosion quicker than your plating is resisting the force... that's purely a guess though. I have never had parts come out bad from a little over current.
 
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I have tried for the seventh time.
The ends are blackened from what looks like burning. But they have little ball like formations of Zinc.

After removing from the electolite I gave the spring a wash in fresh water.
After handling with (nitrile gloves) they started to go black.

20140513_163513.jpg

blistering.jpg
 
WOW... almost looks like RUST or some other...

form of corrosion... like the electrolyte is eating it up.

I wonder if it is the QUALITY of the metal.

If this is the only part doing this... I'd toss it and look for another from your local hardware store or McMaster-Carr.
 
Maybe

I have never zinc plated anything just as a precursor.

The spring is tightly wound. With all the coils touching won't that effectively increase the resistance, or with the metal quality have areas of lower/higher resistance?
 
By "very strong" Muratic Acid... is this...

the typical pool acid concentrate you find by the gallon at pool supply stores... or it is something else.

As I said earlier, I once used Sulfuric (pool) acid that came in gallon jugs from the markets! Can't find that anymore... and haven't really looked for it at pool supply stores either. I would assume the Muratic acid is just as good? Have you ever compared them?

Thanks...
 
I use Kleen Strip from Home Depot called "safer" muriatic acid at 100% strength. It is very aggressive at rust and zinc / chromate removal and lasts a long time (I've never worn it out really). I filter it through paper shop towels and keep it going. That is hydrochloric acid
http://www.homedepot.com/p/Klean-Strip-1-gal-Green-Safer-Muriatic-Acid-GKGM75006/202690263

every part is different, some are greasy, some are rusty, some I want to bead blast others I dont.. my usual process is ultrasonic bath in water based cleaner (simple green or something) until all the grease is off. If it isn't I may wire brush or hand brush parts. I then hand-spray / clean parts in my sink. Next step is to bulk dip parts in hydrochloric acid to remove previous zinc coatings and rust, I let them site a while. After that I remove them, rinse them, then put them in the dip tank holders (14ga thhn housing wire striped bare at contact points). I then degrease the assembly with a final spray of simple green and without touching put it back in the muriatic acid tank. This final dip removes the flash rust but is quicker because the heavy stuff is off. After that it's dipped in rinse tank and into plating.

Things must be thoroughly degreased and thoroughly derusted and you can go back and forth as many times as you wish until that goal is achieved.

I just picked up some phosphoric acid that I want to try, but it is much weaker and turns rust parts black, which is IMO not ideal for zinc (but better for painted).

Muriatic acid is not to be used as the final step to remove corrosion on painted parts because the cl ions will lead to further corrosion, but the zinc plating process this is not an issue.

I forgot to mention, I have had previous issues using non-copper wire (like SS safety wire). Although it worked, there was more fizzing and some discoloration.

in OP issue.. maybe the parts are too close to the anodes? are you using copper wire? are you using too high a voltage? (try 3 volts)
 
Thank you for all your posts as these are very helpful seeing what others are doing. I took some advice from the company that supplied the kit in the UK. This was to 1. better clean parts and 2. add more brightner. Something called Zylite 260 solution.
3. reduce the current and 4. place anodes at 90 degrees from the spring body when held horizontal in the bath.

I tried a smaller spring and got quite a good plating. I have not had time to redo this larger spring, but I am more hopeful of a better result.
I have been using an ultra sonic clean with just water. Then Caustic solution to remove grease followed by strong acid dip for three hours to remove plating and corrosion. Followed by more ultra sound dip to remove black oxide, then a final acid dip, rinse and then plate. I might try some dish washing liquid with the ultra sound clean, next time.
 
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