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Thread: Zinc Plating
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9th Dec 2018, 01:43 PM #31Member: Blue and white apron brigade
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I took the two unpolished bolts with the patchy plating in the photos above and polished them with a Scotchbrite wheel and replated them for another 45min @ 0.5A each and the result seems to be pretty good. Perhaps what was causing the patchiness was removed by teh wheel?
The two re-plated bolts I'm referring to are the two in the middle and LHS in the photo below, these are shown as they came out of the tank.
The other one the RHS is the one plated @1.5A.
IMG_3466.jpg
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9th Dec 2018, 03:26 PM #32Senior Member
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Bob, the patchiness and furry finish is what happens if the current is too high. I get that sometimes, if it's bad I strip off the zinc with hydrochloric acid and start again using a lower current and/or moving the electrodes further away or to a different position relative to the part. When you get used to it, if you momentarily lift the part out of the solution early in the process you can see the furriness starting to happen and make changes to correct it.
I just plated this spacer, it's 50 mm long. I did it together with another smaller spacer at 0.4 A for 60 min. The total surface area would be about double that of your bolts. Even at that current there is some furriness on the surface (actually, on the side that was facing upwards in the tank if that's significant), but this part will go outdoors and a good thickness of zinc is more important than appearance, so I drove it pretty hard. If I wanted to be sure of a high surface appearance I would have dropped the current to 0.2 or 0.3 A. There was no post plating treatment apart from a dip in the blue chromate solution, then a good drying in the sun.
IMG_1406.jpg
Graham.
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9th Dec 2018, 10:59 PM #33Member: Blue and white apron brigade
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Thanks for the info Graham.
Reviewing my surface prep I figured I wasn't including a descaling step so I decided to use a 10 min dunk in 4% citric acid.
Here are two bits of mild steel sanded back to bare metal with a 80 then a 120 grit belt.
The longer one then has the 10 minute dunk in the CA (there is no visible change to the surface shine/sheen).
Then both have 10 minutes in IPA in the ultrasonicator, then 10 mins in Na2CO3 in the ultrasonicator, then rinsed clean with demineralised water.
Then both have 45 minutes, @0.5 and 0.4V in the plating solution.
Descaling.jpg
I'm going to try a bit longer in the CA tomorrow as I know even though it produces bubbles it only dissolving 0.002% of the metal per hour.
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21st Dec 2018, 05:45 PM #34Member: Blue and white apron brigade
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Just a followup to say I found a cheaper source of Zn rods to use as electroplating electrodes and as source for the ZnCl2 preloading of the electroplating solution.
The first pair of Zn electrodes I purchased on ebay worked out to 25c/g, whereas the recent electrodes I purchase from Cathodic anodes in QLD as cathodic anodes worked out to 3.8c/g. Both include delivery.
I didn't try shopping around too hard so you can probably find them even cheaper.
The unit cost of the plating solution thus drops to <$5/L and even lower if you need to use larger volumes and purchase 5 or more kg amounts of boric and KCl.
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