In a previous post, I outlined the DIY electroplating I was doing using old nickel coins (basically putting a touch of old Mr Van Riebeeck on all of my nuts and bolts!). Despite the encouraging results I was getting, I needed to wait for after the Covid-19 lock-down (well, the full version, anyway) so I could source some decent plating material.
I recently obtained some old zinc sacrificial anodes, so decided to give them a go. I upgraded my workshop setup to include better cleaning (alkaline degreaser, deionised water), a larger bath, and some yellow and blue passivate for sealing the end product, and making it more corrosion resistant. Initial results were pretty much all over the place, and only through detailed logging of all parameters, settings and results did I manage to pick up problem areas, and ways to address them. Through this process, I managed to converge on a "recipe" that produced consistent and satisfying results.
The biggest impact, I found, we determining the correct plating current. Too much current, and the item "burned". Too little, and it didn't coat properly. The best results were obtained by applying the following rule of thumb: (i) Calculate the approximate surface area of all parts being plated (I know that sounds more like an Advanced Programme Mathematics course than a DIY chemistry practical, but you can easily work out a value per bolt, per nut, per rod, etc, and just apply multiples of them for each batch). (ii) If the area calculation above is in square centimetres, convert to square inches (because all the good electroplaters descended from Mr Van Riebeeck, apparently, and they obviously used an Imperial system!) by dividing by 6.45. (iii) Multiply the plating area by 125mA (anywhere between 100mA and 150mA per square inch is workable), and that will give you the current required through your plating solution to give a plating thickness of approximately 20 microns (a decent value), in one hour. Shorter than 1 hour will produce a thinner plating thickness, and longer will mean a thicker plating (kind of intuitive, really, even to us non-AP Maths students...). The trick is not to try and make it plate quicker by increasing the current, as that can result in burning...!
Once plating with zinc is complete, the parts need to be rinsed with deionised water, and then dipped very briefly in either yellow (which is "sexy", has better corrosion resistance, but it a bugger to get to stick!) or blue (which works like a dream, looks fantastic, but isn't as durable), or dip briefly into blue before going into yellow (which marginally improves the "stickability" of the yellow passivate, but is rather confusing and has a dubious and unknown impact on the overall durability of the part in question...). Then, an air-dry for 24 hours produces parts that look brand new, which is a remarkable feat given that they started off all rusty and gunky, and were destined for the bin!
Based on the success of this exercise, I have decided not to purchase a single new nut or bolt (or any component, really) if the old one can be refurbished and made to look as good as these ones. Sure, it is much more work, but for me this is the crux of such a project - making the old one look good and work as new, without replacing each component with a new one. After all, if they gonna call it a "nut-and-bolt-restoration", you may as well restore each nut and bolt, not so!?