Ok so let’s look at it from a scientific perspective.
Zink plating is a rust inhibiter technic, zinc is more reactive than steel and will act like a sacrificial metal and will corrode before the steel does so. In order to inhibit the zinc to corrode to quickly the zinc can be passivated with a passivate like a chromate that bounds the outer electron layer on the zinc, thereby making the zinc less reactive and less prone to corrosion.
Therefor we zinc plate fasteners usually with a coating of zinc 5-25 microns thick and then dip it in a passivate that will end up less than 1 micron thick.
I order to get the zinc to stick to the metal the metal needs to be clean, free from rust och grease.
In most of the cases our fasteners are both greasy and rusty and we need to get them spanking clean before we plate them.
1. If greasy.
Soak in diesel for a day and shake the container from time to time, resorting to equal solves equal and thereby getting the diesel to dissolve grease. Then soak in a petrochemical degreaser for a while, rinse in scalding hot water. Then soak in a alkaline degreaser for a while, rinse in scalding hot water again.
Now your fasteners should be free of grease. They might still be rusty though.
2. If rusty.
Rust can be removed in many different ways,
• mechanically with a steel brush
• by blasting, wet or dry, with less ore more aggressive blasting media. Just make sure your method doesn’t remove too much goods from your fasteners as they will go out of dimension. Dry sand is very aggressive, plastic beds, walnut shells, Vapor blasting, soda and dry ice the least aggressive.
• reverse electrolysis is also a method, but it’s quite cumbersome hanging bolts and nuts in the bath and you will need to remove the black ferrite that will form on the fasteners from the reversed rust.
• Chemically with acid, my favorite method. The more aggressive acid the faster it will dissolve the rust, but be careful because an aggressive acid like HCL will also dissolve the iron in your fasteners if you leave it in for to long.
So now that your fasteners are clean and free of rust its time to set up your plating set.
I set up 7 different plastic tubs and always go through the complete cycle even if my fasteners has just been cleaned with any of the methods described above.
I hang my fasteners in copper wire and start dipping
1. Alkaline degreaser
Just to make sure that there is no grease, remember fingers might be fatty, dip in the degreaser and leave for a couple of minutes.
2. Distilled water
Then a dip in distilled water to get rid of the degreaser.
3. Acid
I use 30% HCL which is pretty aggressive, I looks at the fizzing and when the fasters look clean and the fizzing slows down its done. No need to remove all the zinc but you need a spakning clean surface to get the zinc to plate to.
You can use a less aggressive acid, it might just take a little bit longer.
White vinegar (acetic acid), Tile cleaner (phosphoric acid) at ca 30% can be good alternatives to HCL (hydrochloric acid).
4. Distilled water
Then a dip in water to get rid of the acid.
5. Plating solution
I preheat my plating solution by placing the plastic can where I store the solution in a bucket with scalding hot water in before filling up my plating tub.
The tub is also equipped with an aquarium heater set at 25⁰ C and an aquarium air pump that makes sure the solution is circulated.
Before dropping my zinc anodes into the bath I give the a good brush of and make sure the copper wires has a good connection.
Makes sure I connect the polarity right and then hang my fasteners for plating.
If the fasteners come out dull I rise the current a bit and try again and might add brightener.
As Nessism wrote, let the solution sit for a while every now and then and siphon of the plating solution in order to get rid of the muck that will fall to the bottom of the can when stored.
Some items are a bitch to plate, like inside insex sockets, inside swingarm pivot tubes and might require some moving around and makings sure the solution are able to flow through while plating. If consider that the zinc atoms shall leave the anodes and travel to your fastener through the solution, the atoms will need a clear line of travel in order to attach to the right spot on your goods.
Power source, a bike battery can be used as a power source with some kind of rheostat like a wolfram coil, but a good power supply with a amp meter is the best.
6. Distilled water
Now a last dip in water
7. Passivate
Dip and leave in the passivate for 3-4 minutes
8. Hang to dry
Do I need to say that even though the stuff used to day is not highly toxically, its not meant for human consumption, its pretty nasty stuff and shall be handled and stored accordingly. Passivate used to contain hexavalent chromium that is seriously bad for you, nowadays not so much, they have come up with new solutions but it should still be handled with outmost respect and 30% HCL will hurt you.
Like Nessism I restore carburetors and a lot of the parts on eighties jap bike carburetors are made of unobtanium, therefor are no longer available on the open market and replating is the only option.
Happy dipping!
/Anders
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