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Thread: Zinc Plating

  1. #1
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    Default Zinc Plating

    Hi Guys,

    I couple of people have asked for more information on the set-up I use for zinc plating, so here's a description and some photos of how I do it.

    I started with this Jane Kits zinc plating kit: https://janekits.com.au/products/zinc-kit-4-ltrs/ I got it without the power supply as I have a variable current lab supply to hand, so the cost was only a couple of hundred dollars. I'm not endorsing Jane Kits, in fact the manual is tragic, and I had to do quite a bit of web research before I understood enough to proceed. There are other suppliers of DIY type plating kits in Australia. This is just the one I got.

    One very informative source of information on electroplating is Geoffrey Crocker's youtube channel. In fact, that's where I heard about the Jane Kits. I'm not a chemist, so I'm not going to attempt to describe what's going on with electroplating, I'll leave that to others such as Geoffrey. I'd also hope that BobL will chime in with more information.

    So far I've only plated steel, but IIRC I think I can do other metals as well with this kit. I'm building a sawmill and I wanted a way of protecting the steel parts that are not practical to paint. The kit has provided me with just the right solution. It's a fantastic capability to have added to my workshop, and well worth the couple of hundred dollars I've spent.

    Here's the set up. The kit did contain almost everything needed, including all chemicals, 2 zinc anodes, aluminium tubes and copper wire to dangle the parts off, a jumper lead to connect the two anodes, etc. All I needed to buy was de-mineralised water to mix the chemicals into, and suitable plastic tubs for the various pre-treatments, rinses, and the plating electrolyte solution. The power supply is hooked up positive to the zinc anodes, negative to the part to be plated.

    The 4 litres of electrolyte has been fine for small parts like spacers, bearing retaining rings and nuts and bolts, and some small brackets, but I'll be ordering another bag of the electrolyte powder to mix up to 10 more litres. The process has proved so successful that I'm now wanting to plate more and larger parts.

    IMG_0950.jpg

    IMG_0814.jpg

    IMG_0951.jpg


    The process is very simple. The parts are cleaned very thoroughly, dipped in a rust and scale remover (came in the kit), rinsed in de-mineralised water, dipped in degreaser (came in the kit), rinsed, then hung in the electrolyte solution for a calculated time and current based on surface area (the current info is buried in the manual). For most parts I've left them in for 45 minutes, and I've used between 0.5 A and 3 A of current depending on the size of the parts. Total time from finished and cleaned part to shiny plated part, is therefore about an hour, and you're then supposed to leave the parts to dry and harden for 24 hours before handling. I've not always followed this advice and have not had issues with the parts being handled after only a brief drying time.

    After plating I use a chromate passivation process that improves the appearance of the plating and apparently also the rust preventative properties. The pre-dip and two colours, bright blue and yellow, come in the kit. These add either a bright shiny finish, or that gold like passivated finish that comes on some nuts and bolts. Both significantly improve the appearance. Fun fact: passivation means passive, or inert, as in less likely to corrode.

    Here's some examples of what I've plated so far, all parts for the sawmill I'm building. The last photo here is of the first batch of parts I did. It looks like I didn't get some of these parts de-greased well enough because there are stains around the tapped holes where cutting oil must have been trapped. Actually, now that I think about it I had used Trefolex, which is difficult to clean off anything.

    As always with electroplating, the surface finish you get on the plated part is exactly what you had on the raw part. Every file mark, machining mark, scotchbrite finish etc. will print through to the final finish. I'm more than happy with the finish on these parts, they are all going on an outdoor machine so looks don't really matter. I just wanted the rust preventative properties of zinc plating. I have great sympathy for anyone wanting to do decorative plating though, getting a good surface finish on machined or cut steel parts would be a real challenge.

    IMG_0953.jpgIMG_0841.jpgIMG_0817.jpgIMG_0822.jpgIMG_0837.jpg

    I'm sure I've missed some important information, so feel free to ask questions.

    Graham.

  2. #2
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    Here's another example of a part that I've zinc plated. I purchased a second hand Honda GX610 V twin engine for the sawmill. It had been used for a generator and apparently out in the weather for a few years, and the steel exhaust manifold, muffler, and heat shield were badly rusted. The manifold and muffler are getting stripped and painted with high temperature paint, but I thought I'd see if I could plate the heat shield for a better appearance. It took a few days in the electrolysis bath, and lots of time on the wire brush wheel, but I got it down to clean, but pitted, shiny bare steel.

    The heat shield is quite large, and I only have the 4 litres of zinc electrolyte, so I made a tight fitting tank out of 160mm PVC pipe with an end cap glued on one end, and hung the shield vertically in the tube with one zinc anode half way down in the centre. I still couldn't get full emersion, but I thought I'd try plating it in two goes, turning it around half way to plate the end of the part that was sticking out of the electrolyte. I knew this would leave a mark, or maybe two, where the electrolyte level ran out, but the finish didn't worry me, I just wanted zinc on there for corrosion protection.

    It worked better than I thought. After a few heat cycles I think the whole surface will assume an even, dull plated look. You can see the pitting from the rust, but it's not intended to look new, just not rusty. I'm claiming success.

    Here's a before and after shot.

    Graham.

    IMG_0602.jpg

    IMG_0974.jpg

  3. #3
    BobL is offline Member: Blue and white apron brigade
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    Good work Graham.

    I'd like to know what the electrolyte is?
    The rest seems quite straight forward and surprisingly quick.
    I'd be interested in trying this to measure the thickness of the plating as a function of the variables.

    The one thing that concerns me is the use of chromate passivation.
    What sort of chromate is it and what concentration is it?
    I know Zinc chromate paints have been around for years but only recently have most chromates been identified as toxic and should be treated with the same respect as hexavalent Chromium oxide.
    Whatever the solution is the resulting Zinc chromate coating is high toxic and carcinogenic.

    From Wikipedia
    Recent studies have shown that not only is zinc chromate highly toxic, it is also a carcinogen.[17] Exposure to zinc chromate can cause tissue ulceration and cancer.[1][3] A study published in the British Journal of Industrial Medicine showed a significant correlation between the use of zinc chromate and lead chromate in factories and the number of cases in lung cancer experienced by the workers.[18] Because of its toxicity the use of zinc chromate has greatly diminished in recent years.
    This means any of the plated pieces should not be ground/cut/sanded drilled or heated by say a plasma cutter, oxy or welder.
    The OHS recommended level of chromate in air is 100 ug/m^3.
    For reference a drop of water contains 30,000 ug

    I would recommend any work with chromate solutions be done in a fume hood, or outside while wearing a chemical mask, gloves and full face PPE.
    Presumably you can reuse the chromate but otherwise safe disposal is an issue - not recommended it be poured down the drain.

  4. #4
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    Thank you for the informative and well illustrated description of the process Graham.

    I imagine many of us have had the occasional component or two that would benefit from a replating but have been hesitant to approach a commercial plater. You have shown an alternative.

    Bob.

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    Thanks for the report Graham. I'll be getting a kit, for sure, as I quite often needed to get bits done, but never bothered because it was a special trip to Adelaide.
    Now I'll be able to do it myself.
    Kryn
    To grow old is mandatory, growing up is optional.

  6. #6
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    Bob and Kryn,

    I had originally planned to get a batch of steel parts together and take them to an electroplaters, but here in Sydney the minimum charges were all around $150 to $200, so the kit at $200 (without power supply) was easily justified. The electrolyte is supposed to last "forever" so I'm already ahead cost wise. Plus, it's so good having the flexibility to just plate parts as I need to, and in small batches or individual.

    BobL. Thanks for you comments on safety.

    On the electrolyte, here's a clip from the Jane Kits website, https://janekits.com.au/product-cate...-plating-kits/
    "Jane Kits has taken advantage of the modern trend of the zinc chlorides plating bath. The zinc crystals supplied in your kit contents will be mixed to make up an all chlorides plating bath. This type of bath is user friendly, easy to control, and produces excellent results. The all chlorides electrolyte will plate successfully on to steel, brass, copper, and as an added bonus will plate on to cast iron. In the past there have been problems with some types of zinc electrolytes plating on to cast iron, as cast iron has graphite content in the metal. The chlorides bath runs at a PH value of between 4.5 and 5.0 which is mildly acidic.
    The zinc plating baths used in the past were cyanide baths or alkaline baths. These were not user friendly and presented problems to the operators by way of skin contact, splashes into the eyes, and the breathing in of fumes from the plating bath."

    On the Chromate solution: "Jane Kits offer two chromates in blue and yellow variations. They are referred to as Gold Bright and Blue Dip. These chromates are trivalent chromium chromates and therefore have an extremely lower toxicity to the traditional hexavalent chromium that was traditional used."

    I did some research on this, and it seems that the hexavalent chromium is the real nasty one, which is not what's used in this kit. From the Wikipedia page on Chromate conversion coating: "..... hexavalent chromium is toxic, thus, highly regulated,[3] so new, non-hexavalent chromium-based processes are becoming more readily available at a commercial level.[4] One alternative contains trivalent chromium." What do you reckon?


    BTW, I always use these chemicals next to an open roll-a-door, and I wear gloves and a mask.

    Graham.

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    A question for both Graham and Bob.

    What type of mask and filters are you using or recommend using? I have a Sundstrom mask but its forward facing single filter cartridge location prevents its use while wearing my full face shield, a BobL recommended Armadillo.

    Bob.

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    BobL is offline Member: Blue and white apron brigade
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    Thanks Graham, its good to hear its a trivalent Cr which is indeed safer, still good idea to wear gloves and a mask.
    Do you know what the electrolyte is?

    The cartridge or filter required is one for organic volatiles and inorganic acids. They usually have a charcoal or similar air scrubbing filter.
    eg
    https://www.rsea.com.au/ppe/respirat...vapours-044072
    or
    https://www.3m.com.au/3M/en_AU/compa...3696435&rt=rud

    Please note that over time small amounts of vapour will eventually condense out inside these masks and eventually some will make its way through the filter which is why the use by dates should be adhered when used in areas of high vapour concentration. Bob this is unlikely to be a problem for you as your total exposure while getting the work pieces in and out of the fume chamber will be quite low. However if you smell the vapour with the mask on then you will need a new cartridge.

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    Hi Bob,

    All I know about the electrolyte is what I quoted above from the Jane Kits website. They say it's an "all chlorides plating bath".

    Graham.

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    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Oldbikerider View Post
    Hi Bob,

    All I know about the electrolyte is what I quoted above from the Jane Kits website. They say it's an "all chlorides plating bath".

    Graham.
    Thanks.
    I've looked up a few DIY brews, there are quite a few of them, some using acetic acid.
    The closest to the "All chlorides" uses zinc chloride, potassium chloride, boric acid, HCl acid and a brightner and carrier with pH of around 5.
    With a pH of around 5 there can't be a lot of HCl in it.

  11. #11
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    Hi Bob,

    That's interesting. In this youtube video: https://www.youtube.com/watch?v=G-PtnwtOR24 Geoffrey Crocker shows nickel, copper, and zinc plating using only white vinegar (acetic acid) and salt. Two anodes of the metal to be plated are first put in the electrolyte and current passed through to put nickel, zinc or whatever is to be plated into the electrolyte.

    If this works, it would be a very cheap way to do plating. The only cost would be for vinegar and salt (and that can be disguised as "groceries"), and the metal anodes. I'm going to give this a try as a cheaper alternative to purchasing the electrolyte for a larger tub from Jane Kits.

    Do you have any comments on this ghetto technique? Can you explain how it works?

    Graham.

  12. #12
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Oldbikerider View Post
    Hi Bob,

    That's interesting. In this youtube video: https://www.youtube.com/watch?v=G-PtnwtOR24 Geoffrey Crocker shows nickel, copper, and zinc plating using only white vinegar (acetic acid) and salt. Two anodes of the metal to be plated are first put in the electrolyte and current passed through to put nickel, zinc or whatever is to be plated into the electrolyte.

    If this works, it would be a very cheap way to do plating. The only cost would be for vinegar and salt (and that can be disguised as "groceries"), and the metal anodes. I'm going to give this a try as a cheaper alternative to purchasing the electrolyte for a larger tub from Jane Kits.

    Do you have any comments on this ghetto technique? Can you explain how it works?
    Sure, this is as simple an explanation I can make it and applies to nearly all of the recipes I have seen.

    The Positive terminal (anode) of the power supply strips electrons from the Zinc atoms in the Anode and the solid Zn dissolves into the electrolyte as Zn+2 ions which are attracted to the Negatively charged workpieces where the power supply provide plenty of free electrons. When the Zn+2 grabs a couple of electrons this converts it back to metal on the workpiece surfaces.

    The ghetto technique (if it does indeed only use acetic acid and salt) will be slow to start plating the first time because it will take some time to dissolve/release/ionize enough Zn from the anodes to start plating. This is why most of the electrolyte recipes I see include a "Zinc something salt" (eg ZnCl2 or ZnSO4) in the brew. This preloads the electrolyte with Zn+2 ions and allows the plating to commence immediately. Once the ghetto method has run for a while the electrolyte should stay charged with Zn+2 provide the anodes are still in place ie have not dissolved away.

    Vinegar is a weak acid so it won't provide many extra ions to generate a strong enough current in the tank so some sort of salt (eg NaCl) is added to enable a higher current through the tank. There are lots of other salts that appear can be used eg Epsom (MgSO4) and KCl. The vinegar is there probably to act as a mild buffer to help control the pH (ie not let it get too acid or alkaline). If it gets too acidic the Zn anodes will completely dissolve into the electrolyte and break the circuit. If it gets too alkaline strange things may happen and the plating will be affected. Certain strongly alkaline electrolytes can using, for example Sodium Hydroxide (NaOH/caustic) can be used, but these are not nice or that safe.

    In the "zinc chloride (ZnCl2), potassium chloride (KCl), boric acid (H3BO3), HCl acid and a brightener and carrier with pH of around 5" brew, the ZnCl2 provides the preloaded Zn+2, the KCl is the salt, the HCl is probably used to initially balance the pH and then the Boric acid is probably the buffer to stabilise the pH.

    It's pretty easy to make some ZnCl2 by slowing adding Zn chips to some dilute HCl ( you can get this at Bunnings), keep adding the Zn chips until it stops bubbling (beware this process generates hydrogen which is explosive - do it outside the shed) when it is no longer bubbling the acid is spent and the solution will be relatively safe.

    I have ordered some Zn anodes from ebay have a couple of power supplies I can use, and figure I can scrounge the rest at least for a trial.
    I see folks using the Zn outer casings from dry cell batteries but they are pretty thin and I wonder about their purity. The other cheap source of Zn would be sacrificial anodes but I wonder how pure any of these are and how this will effect the plating. The stuff I ordered claims to be 99.95% pure and is specifically for electroplating.

    This is right up my alley as there are lots of variables to play with.

  13. #13
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    Thanks Bob, I think I actually understand what's going on now.

    The video I linked in post #11 talks about pre treating the electrolyte with the same anode material in both positive and negative. This makes sense now.

    On power supplies: I find it very useful to use mine in its adjustable constant current mode. This way I can stick exactly to the calculated current throughout the process. I just set it at the required current setting and it sorts out what voltage it needs to drive that current. The voltage that it needs depends on the resistance of the circuit, ie. electrolyte concentration and surface area of the part and of the anodes. My supply will output 30 volts and up to 3 amps. It usually sits at 2 to 3 V to get 1 A through the bath.

    Graham.

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    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Oldbikerider View Post
    Thanks Bob, I think I actually understand what's going on now.

    The video I linked in post #11 talks about pre treating the electrolyte with the same anode material in both positive and negative. This makes sense now.
    Yep thats the pre loading I spoke about in my post.

    On power supplies: I find it very useful to use mine in its adjustable constant current mode. This way I can stick exactly to the calculated current throughout the process. I just set it at the required current setting and it sorts out what voltage it needs to drive that current. The voltage that it needs depends on the resistance of the circuit, ie. electrolyte concentration and surface area of the part and of the anodes. My supply will output 30 volts and up to 3 amps. It usually sits at 2 to 3 V to get 1 A through the bath.
    Thanks - I have one that does up to 10A @ 6V which should do the job

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    Quote Originally Posted by BobL View Post
    Yep thats the pre loading I spoke about in my post.
    Got it. Thanks.

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