Witches brew for pro chemical removal of zinc plating

[AshimotoK0]

If you want to strip zinc the pro way chemically, use this (all available cheapish of eBay). It's a lot gentler on the base metal  and is a natural degreaser, that's why I don't use Hydrochloric acid (brick cleaner). I got this formula from a place I used to work who supplied zinc plated parts to the coal mines. This was the only method of stripping allowed, within a very tight specification of supply,  as it does not denature the properties of the base metal.  I particularly  recommend this method for stripping critical components such as spokes.

 
To make up 1 litre of stripping solution (use de-ionised/distilled water) :-

100 grammes ---  Sodium Hydroxide  (Source:- Poundshops, B &Q, Wilkinsons, ect)

90 grammes --- EDTA---- (EthyleneDiamineTetraAcetic acid)  Source eBay

4 grammes ----  Triethanolamine   ..........Source:-  eBay

Immersion is at 70 degrees C +/- 5 degrees for about 20 minutes (basically until the bubbling stops).

Slow cookers are mega cheap (Lidl, Aldi, loft  ) and will not overheat the solution on max. setting so make a good cheap form of heating the solution.

After stripping, rinse in tap water and then  plunge the parts into boiling water, remove and then dab away  excess water with paper towels and the heat in the parts  will full dry them  in seconds. If you do this properly they won't badly flash rust afterwards

At the platers, specify if you need passivate finish either gold chromate or bluish tinge clear (example of gold chromate are CB750 regulator cover, spoke nipples). Some parts are olive drab passivate but not so much on Hondas.  Sometimes you get black passivate. Examples of black passivate  are the  'D' spacer washers on 500/4 & 750/4 top yokes and the earthing covers on USA 500/4 rear indicator brackets. However, the bluish tinge passivate is used for most parts.

If you want a really nice silky smooth  finish after stripping then dry bead blast with 0/50 grade glass beads or tumble small parts in a vibratory tumbler.  The plater will love you for this and the results back will be superb and probably cheaper to plate, as the main cost is prepping them before plating IMHO.

Home plating is fine for the few odd parts or bits you don't want to let out of your sight because of their rarity. I have  done it myself  and had decent results but unlike chroming, BZP should be very cheap and I don't bother doing my own plating any more. Quite often, you can get a complete bikes worth of BZP parts done for what it would cost you for the DIY chemicals.

Older Hondas like the CB72 and CB450K0 I suspect didn't use BZP . It was a zinc plating process which,  I suspect,  used cyanide (like cadmium plating) and you will be hard pushed to get that done these days. It was a lot duller but much more corrosion resistant IMHO than 'acid' BZP.

At the time of writing this post.

EDTA

http://www.ebay.co.uk/itm/EDTA-disodium-salt-dihydrate-1kg-6381-92-6-/292107165917?hash=item4402f1a0dd:g:V7sAAOSwhQhYx672


Trietholamine

http://www.ebay.co.uk/itm/Triethanolamine-TEA-99-Liquid-125g-RM100TRIE-/142303469073?hash=item2121f29e11:g:-iEAAOSwWxNYvXzd


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[Johnwebley]

thank you ,

 I really enjoy your tech posts

[JamesH]

Superb. Thanks for taking the time to share this Ash.

[K2-K6]

Very good and useful writeup Ash, thanks for posting.

I hope you don't mind me adding something about safety as others may not be as familiar as you in handling things like this.

Eyes are particularly vulnerable to things like caustic solutions, so ideally some good goggles are reasonable precaution. I've used things like this from the link below as they are double lensed so less likely to steam and have shielded vents to avoid splashes getting past.

http://www.protecdirect.co.uk/Personal-Protective-Equipment-PPE-/Safety-Glasses-and-Goggles/Safety-Goggles/Ventura-SG740PC-Polycarbonate-Clear-Lens-Goggle~p~SG740PC

Good for use with metal grinding wheels as well.

Also, if you use rubber chemy gloves then make turnups of the wrist end as it stops chemicals running down onto your arms if you lift your hands upward with wet gloves

Added by Ash   Yes you are dead right, my missus is always telling me I am too blasé when it comes to H&S with chemicals and electricity, so thanks for adding the spot on advice.

[RGP750]

Thanks Ash and K2-K6, great and useful as usual.
Didn't know about the double lenses, always a problem i have, ordered some.

[AshimotoK0]

Update on this.  I was prepping some parts for zinc plating at the weekend  and thought I would try the stripper in my heated ultrasonic bath and it worked really well, so recommended if you have one but it must be heated (I guess mine was at about 65 degrees C).  I put the parts into a container and covered with the stripping solution and  then put into my US bath with the heated tap water in it.

When I take the parts out I rinse them really well in cold water then put them after draining into a plastic bucket then pour boiling water on them. After a few seconds, I then drain through a sieve and spread out on loads of kitchen roll, then after drying for a few seconds  but still really hot, I  tip them off the damp kitchen rolll onto a flat surface. Doing this, the water totally flashes off and they don't then flash rust.

A few peopl have asked me why not use hydrochloric acid? The chemist guy I worked in the 1980'/90's with, recommended my witches brew  because it is much gentler on the steel base material. I also got his from one of the pro-plating forums. Also hydrochloric acid is bad news in your shed garage as the fumes from it will promote rusting of everything around it.



"2004
A. We use HCl to strip zinc from steel. You can use sodium hydroxide too. Why use power when it's unnecessary?

Steve Clark
- Belfast, Maine, U.S.A.

2004
A. Acid stripping is bad news for hard bolts. Hydrogen embrittlement is a very strong possibility. Bake (soon) after strip if you do. Caustic is slower than acid, but it also has a lot smaller risk or attacking the steel. Electrolytic will speed up the operation, but costs more-- a tradeoff.

James Watts
- Navarre, Florida"

[Oggie400F]

Great Info Ash
Thanks. 👍

[kettle738]

Really interesting stuff, thanks Ash..... I used to have a local plater (chrome and Zinc) who had a rotating drum for zinc plating small parts....they didn't need to be wired and they self 'burnished' as they tumbled.....the results were superb.... and quick.  This was a bloke who would recreate linishing marks in the chrome on Jap rims....every other plater I've ever met only wants to do the bathroom tap finish.

Sadly.....he closed down and the only remaining local plater which is a far larger outfit does everything by hand, each part including spoke nipples, tiny nuts etc is wired, it must take forever, I can't understand why a business would continue to use such an archaic method for small parts.....I always prep them, so I'll try your method for my next batch.   

[Nurse Julie]

99% of our zinc Plating is done in a tumbler that holds 50kg. We usually have 25-35 kg done at a time. Very rarely we may have certain parts that are wired for whatever reason, usually due to them being fragile parts.

[SteveD CB500K0]

Can you explain the different chrome finishes Mick?

Assumed “bathroom tap” was what you got.


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[AshimotoK0]

Mick ... I know what you mean about the chrome being too blingy (like you get on bathroom taps etc.)... .. I recently had a NOS one-piece CB250K0 exhaust rechromed (downpipe was corroded in storage) and the chromer asked me if I want 'show'  or 'Honda original' style finish. I opted for 'Honda finish' and the chroming is great ..... it just looks like another NOS exhaust I have.