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Thread: Zinc Plating
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7th Dec 2018, 11:35 PM #16Member: Blue and white apron brigade
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Well I finally got all the bits and pieces I needed for a crack at basic Zn Chloride plating (ie no brightener).
I got the chemicals and Zn rod all from ebay for ~$90.
The chemicals were mixed according to a technical paper I found online.
Because I was unsure how pure the chemicals needed to be I purchased either food grade or analytical grade chemicals but there is enough Potassium Chloride and Boric acid to make about ~12L of plating solution.
The most expensive things were the Zn Rod ($28, but have since discovered a cheaper source of Zn rod here in Oz) and the Zinc Chloride (ZnCl2) salt (also $28, and only enough to make 4L of plating solution). However, using cheap Zn rod and HCl it will be easy to make bulk lower cost ZnCl2 salt in the future.
Provided all this works the overall cost of bulk plating solution should be <$5/L
I just made up 1.5L of plating solution to perform some trials on a small scale.
Here is the setup - I could probably move the anode and cathode closer together.
I was surprised at how syrupy the solution was.
IMG_3450.jpg
Here's the first try 30 minutes of plating at ~1.5A in comparison to a similar unplaced bolt.
As you can see it's patch probably because I was not super careful during the initial prep.
It looks a bit friable but it seems to have adhered pretty well.
IMG_3453.jpg
While I'd like to eventually get more of a bright finish I'm not worried about brightness at this stage - just want to see if I can get the Zn to plate out.
A couple of natural brightening agents that I might give a go are corn syrup and glucose syrup although I also read that these eventually develop a bacterial growth and start to stick.
I have also found some references to natural cyano brightening agents on line, two of which are sugar cane juice and cassava root!
My understanding is that sugar can juice is a seasonal product and cannot find any around here in WA.
I have a lead on some cassava root so will try to track it down.
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8th Dec 2018, 12:24 AM #17.
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Bob,
I'm looking at the amount of zinc deposited on the suspension wire and wondering if a shorter plating time might result in a finer, less furry finish? Does a nut still fit the thread?
Bob.
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8th Dec 2018, 06:37 AM #18Senior Member
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Bob,
Well done sourcing the chemicals. The Jane Kits solution works out at $10 to $13 per litre, and you've got your's together for half that.
It looks to me like you've used way too much plating current. The furry finish, zinc colour, and sometimes a burnt appearance is what happens when the current is too high. I've plated multiple small parts and bolts in one session and never gone above 0.5 A.
The Jane Kits handbook advises about 1 amp per 160 sq cm of surface area. I'm guessing those bolts are about 1/2 inch x 3 inch, so about 30 sq cm. That would indicate about 0.2 A plating current.
I generally plate for 45 min to 1 hour.
Graham.
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8th Dec 2018, 08:43 AM #19Member: Blue and white apron brigade
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Thanks Bob and Graham. I agree with your suggestions and try them today.
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8th Dec 2018, 09:32 AM #20Most Valued Member
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Do you have a constant-current power supply Bob?
Chris
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8th Dec 2018, 09:43 AM #21Member: Blue and white apron brigade
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Yes I have several.
Yeah i noticed that and then thought, why is so much Zn plating out onto the support wire compared to the bolt? My guess is that the contact between the wire and the bolt is not too good and in fact when I had a look at the contact point there is a sort of a burn point with very little plating on it.
IMG_3454.jpg
I will set up a better connection point, use a lower current and better prepare the surface.
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8th Dec 2018, 10:26 AM #22Senior Member
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It's unlikely that the bolt was making a bad contact, otherwise you wouldn't have been able to get 1.5 A into the electrolyte, you'd need the surface area of the bolt to get that much current through the circuit, unless you had a stupidly high voltage pushing the current. Did you notice what the voltage was?
The black mark on the bolt is consistent with the current being too high - the burning that is talked about.
Graham.
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8th Dec 2018, 11:06 AM #23Member: Blue and white apron brigade
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6V.
Interestingly the current is 1.5A just using the SS wire dunked into the solution even without the bolt being attached!
I am starting to doubt the current reading provided by the ammeter on the PS and will connect an independent ammeter to see what is going on
The black mark on the bolt is consistent with the current being too high - the burning that is talked about.
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8th Dec 2018, 01:17 PM #24Member: Blue and white apron brigade
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I decided to try a remove some of the Zn plating using a medium/fine Scotchbrite wheel and found after a 1 minute of application in the same spot there did not appear to be any change although it a lot shinier. Then I quickly shined up the whole bolt - even the ridges of the thread still look good.
This suggests the Zn plating is well and truly bonded onto the the underlying steel.
The result (top bolt compared to original below) also IMHO looks pretty good - this took a minute to do.
IMG_3457.jpg
The PS I'm using at ATM does not start providing juice unless it's delivering 0.6A but I'm giving that a whirl while I dig out the other PS which I know goes right down to 0V an 0A.
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8th Dec 2018, 04:33 PM #25Senior Member
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I think that 6V is your problem, you're driving way too much current through the circuit with such a high voltage. For a handful of bolts and small parts I plate at about 1 V and 0.5A. But what might complicate any direct comparison is the relative conductivity of different plating solutions.
Graham.
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8th Dec 2018, 07:55 PM #26Member: Blue and white apron brigade
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OK some comparisons.
The 6V 1.5A bolt is the same one I did yesterday and is included here for comparison.
This one has been polished with a Scotchbrite wheel - the other 2 are as they come out of the bath
Lower current (ie 0.5A) definitely produces a thinner smoother layer but does not seem to cover the entire surface in the 45 minutes.
If anything the 6V 0.6A seems to produce better coverage that the 1V 0.5A.
Higher V doesn't seem to have affected the middle one.
COmp1.jpg
45 minutes at 1V 0.5A added to both the middle and right hand bolts from above - improved coverage but still a few gaps.
COmp2.jpg
I'm starting to think my surface prep is maybe not good enough.
I start with a wire wheel to remove any rust/scale and give it a bit of a polish, then Isoropyl Alcohol for 10 minutes in an Ultrasonic bath followed by Sodium carbonate for 10 minutes in an Ultrasonic bath.
The US bath is pretty powerful (120W) and it warms the liquid in the bath but wondering is this surface might need some sort of light acid etch?
These are high tensile bolts so maybe that's part of the prob.
I might try some mild steel next.
BTW the plating solution seems to have change from a syrup to a much thinner solution?
Also I should definitely try using two Zn electrodes.
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8th Dec 2018, 10:23 PM #27Most Valued Member
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Bob,
I can't understand how you are getting 0.6A at 6V and then 0.5A at 1V. Ohm's Law says they can't both be right, unless you are changing some other variable (e.g. surface area, conductivity, bath temp, wire-bolt resistance). My guess is your wire to bolt connections had differing resistances for each test piece.Chris
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8th Dec 2018, 11:19 PM #28Member: Blue and white apron brigade
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Good point - should've picked that up.
In fact I was assuming the "6V" @ 0.6A for that PS as it has no V meter (just ~6V stamped on it!) but when I actually measure it it was 1.1V @ 0.6A.
So at the 1.5A setting it was outputting about 3V.
The 0.5A @1V plating was done with a different PS with V and I measured with decent meters.
This nominally makes the resistance of the setup with the electrodes spaced as far apart as possible ~2Ω
I've also measured the resistances of the electrode connections and they are 0.1Ω which is the limit of the meter.
This thus means there is no difference in the plating conditions between the middle and rightmost bolts in the above pics.
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9th Dec 2018, 08:19 AM #29Most Valued Member
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9th Dec 2018, 08:52 AM #30Member: Blue and white apron brigade
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