DIY Zinc (Cad-lookalike) Plating

A couple of people asked about home based plating, so here is a little demo w/ pics. I decided to try this just because its interesting and I like to do things myself rather than pay a professional.

All the stuff Im using is available from http://www.caswellplating.com/
Im using the 3 gallon copy cad (zinc) kit and I also bought one of their power supplies (you need a PS capable of a constant current, not a constant voltage, for reason i will explain later). I wont go into the background on plating, but its high school physics...you can read the basics here http://en.wikipedia.org/wiki/Electroplating

You can also put together your own kit for much cheaper if you want to experiment with the electrolytic solution etc. I just wanted to try some plating without experimenting a great deal, so i bought a kit.

First off, heres the set up. 5 or so 5 gallon buckets, each containing:
1. distilled water
2. Plating solution
3. 5% HCL
4. Degreaser
5. Blue chromate solution (pic is of the blue chromate...the yellow looks same, but, errr, yellow/orange.
6. Yellow chromate solution

Ill explain what they each do in a bit.
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Here are the other bits of kit you need:
1. constant current power supply
2. pure copper wire to hang things
3. zinc anode
4. copper tube for hanging/conducting
5. temp gauge/water heaters
6. tank pump for agitating the cad solution while plating.

The cad solution needs to be at approx 110F for plating, the chromates at approx 80, and the degreaser at 140. One of my tank heaters broke, so i didnt bother heating the degreaser. Also, the ambient temp was 95 anyways, so i didnt really need to switch on the chromate heaters.
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Well...just like anything else to do with metal refinishing, the key is in the preparation. The smoother/shinier the raw metal, the smoother/shinier the plate will be. But before I start plating I usually get everything else set up/switched on. I check levels of various baths, and add distilled water if necessary. I went ahead and switched on the cad heater, even though at close to 100F outside, it probably wasn't necessary. I plop the zinc anode in and start the aerator running.

Can anybody see the mistake in the pic?

Anybody?

Yep...wired wrong. I got the negative lead on the zinc anode and the positive on the piece (copper pipe). I didnt realize until a little later when the plating was, well, not happening. I guess i got distracted by trying to juggle the camera etc.
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As i mentioned, most of the work is in the metal prep. The metal HAS to be clean as a whistle...just like if you were going to paint it. Sand blasting/bead blasting is the best prep. If you want super shiny parts, you have to wire wheel the steal too. I have two cabinet blasters, one set up with 50 grit, the other with 300 grit. For fine finishes, the 300 grit is excellent (it feels like flour) and cuts surprisingly fast.

Anyways, I took two nasty pieces from the Healey 100-6 Im restoring, and bead blasted them.

Sorry about the cruddy pics, Im using an old digital camera from about 10 years ago...its doesnt do macro/close up very well, so the pics are blurry sometimes. The parts have a fine satin finish to them.

Note: This plating only puts 1 or 2 thousands of zinc on in 20-30 mins. Any imperfections in the metal will be readily evident in the finished parts

Also, you can only do steel and pot metal. You can do aluminum, but you have to follow and special procedure with different baths because aluminum will oxidize IMMEDIATELY on contact with air (cant see w naked eye) and prevent plating.
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OK, so parts are blasted (and you have to wear gloves, even a trace of body oil on the metal will ruin the plating0 and wire up...now you just hang them in the degreaser for 5 mins. After 5 mins in there, you give them a swish in the H2O, then its a 3 second dip in the HCL to remove any final trace contaminants, then another swish in the water, then its into the cad bath.

So, how much power? And why constant current? Its pretty simple, you have to calculate 0.14a per square inch. I measured approx 18 square inches of surface area on those two parts...I know, sounds a lot and doesnt look a lot, but you have to account for both sides of the pieces AND the edges etc. With this power supply I can do up to 5 amps, so up to 35 square inches. Doing nuts and bolts is a nightmare because of the copper wiring.

Constant current? Easy. As the part is plated, the resistance increases, thus the voltage must vary (increase) to keep the amps constant and keep the plating going. Many people use a battery charger and lights bulbs to vary the amperage, but the power supply is way easier.
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OK, so now you just go do something else while the magic happens.

Remember my incorrect wiring? well after 2 mins, I pulled the parts out (you can just pull em out with no ill effects) and noticed....nothing. Hmmm.

Oops...quick check of the wires...FAIL. Wired things up properly and dumped the parts back in. Now, what I SHOULD have done is cleaned the anode as it was now contaminated from running the system backwards. I didnt, as as you will see, the final plate didnt come out quite as shiny as it should. Oh well....just doing it to show you guys.

I dumped the pieces back in for 20 mins....and voila. PLated parts. As I said, you get about 0.001 for every 20 mins. You can leave in as long as you like. The parts look kinda like raw steal, but pay attention to the copper wire...see how it has a nice zinc plate too?
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The final step is chromating. You can leave the zinc plate raw, but it doesnt hold up so well. The chromating process makes the plate last longer. You can read about it here: http://en.wikipedia.org/wiki/Chromate_conversion_coating

All you do is dip the piece in the chromate bath you want for the finish you want. I only have a blue and yellow bath...you can get black and drab olive too, but you are all most familiar with the blue and yellow.

The blue chromate finish isnt really blue at all...its actually clear. You do get a faint iridescent kind look, kind of like oil on water, but for the most part, it looks like raw metal. The yellow chromate of course gives you that "grade 8 bolt" look and finish, with the same irredescance. My camera did a crap job of showing the finish....but you get the idea. I generally leave the pieces to dry overnight, then they are ready for use!
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Here are some parts I did a few weeks ago, pics taken with a modern digital that can handle macro shots!
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I plated a 6" long piece of 1" angle iron, used typical prep methods, and plated for 30 mins (so 0.0015 plate thickness). I threw it outside next to my stand pipe on the grass about 3 months ago now....out in the open air, no shelter, just sitting in the grass. Still looks as good as when I plated it. Im just going to leave it there for a few years and see how well it holds up. Kinda like my own salt spray test, but no salt, and using Nebraska summer and winter instead!

Marcus

 

Costs: the 3 gallon kit is 200 bucks, and the power supply is 179. The only other thing u need to source is distilled water, hcl and copper wire, all a few dollars from the hardware store

You could get by using an old school battery charger ( no load protection) and maybe source a big rheostat for a few bux then youd have a power supply you could adjust. If i wwere buying again, id get a 10 amp so i coukd do pieces that filled my bucket.

Chromium: i have no idea...the chat lists on caswell are very active, but its easiest to call and ask the man himself, the guy that owns it frequently respon to tech questions online etc.

I have been tempted to try tge chroming too, but usually the pieces i want to do are bigger...bumpers etc.

 

Zinc plating introduces hydrogen embrittlement. You can relieve hydrogen embrittlement by baking the parts for a few hours at about 200 degrees C.

Note...check with an expert, that bit of wisdom is remembered by me from metalwork class at a sub par high school in the UK over 25 years ago...now where did i put my keys?

Experts?

M

P.s. U will find zinc plating is relatively cheap...i dont have numbers handy, but i recall maybe $10 a pound for nuts and bolts with maybe a 5 or 10 ib minimum. Frankly, if i was worried about cost, id continue to use the plating shop in omaha! Its more about the skill/learning. Now, CHROME plating is a different world...way more prep needed, nastier chemicals, etc etc, so yes, chrome plating does get expensive...and it also cause the same hydrogen embrittlement.