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Zinc plating

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Murf:
Thanks for the replies,
I believe Derby plating has ceased trading, they are just open to finish off orders they have but not taking any new work on.  Yet another one los.

DDG plating are only about 5 miles from me and they do hexavalent zinc plating which is supposed to be more corrosive resistant and less toxic and polluting than trivalent plating. I have phoned them and they will do small batches for restoring work. However they will not clean the parts, you have to clean them yourself. They told me that the parts go in the plating tank exactly as you bring them in, if they have rust or grease on them then they won’t come out very well.
  I have had a go at cleaning and degreasing some of the bolts I have and have given them a session in my ultrasonic cleaner, they have come out very clean but have a sort of brown rainbow colour to them. I suspect this is a reaction between the cleaning fluid and the remaining zinc plating.


I have no idea if they are ok or not to be replayed so plan to take some to DDG and see if I can get to ask someone there.  I am also worried about flash rusting on any parts I do clean before they get replated. 
I will keep you informed.

exvalvesetdabbler:
A soak in white spirit to shift most of the grease then oven Pride is your friend if there is stubborn grease. Warm it up to speed things up.  If there is any deep pitting with rust in them they won't plate and you'll be left with black spots in the finish.  Either electrolytic clean or a long soak in warm citric acid solution so that the pits are showing metal.

Once past this stage they need to be kept dry to prevent further rusting because any residual plate will be gone.

The platers will degrease and pickle as part of the process but mostly to  clean off polishing compounds and cutting fluids from manufacturer of new components. Any black gunge might not be removed, also they don't want their baths crapping up.

I doubt they are still using hexavalent chrome as that has been banned through some end of  life vehicle directive. They will probably be using a  trivalent yellow passivate that gives a similar appearance to the old hexavalent finish.  If you need a clear passivate on some stuff best to bag them separately to those needing yellow.

Regards
Dave

Oddjob:
Wasn’t hexavalent chrome the stuff in the Erin Brockovich film?

kent400:
 I started re-plating parts a few years ago when the local plater ceased trading. A bit of a learning curve and research but now I get good results. Although most parts I'm re-plating are unseen.

The procedure place the parts in vinegar if rusty, that dissolves the rust and will also remove zinc plating. That can take a few days, then into brick acid and rinse. Dry off with heat gun. Some flash rust can appear.

Now ready to plate after a dip in caustic soda, a rinse and a dip in brick cleaner followed by a rinse. Now in the plating tank, It takes a bit of trial and error to set the amps correctly. Probably takes about half an hour on the larger bases and a bit less on smaller ones. Out of the tank, a rinse, into the passivate followed by a rinse. A drying cabinet would be ideal as despite a final rinse the passivate does sometimes leave slight stains.

 

 

exvalvesetdabbler:
Those Speedo bases look shiny enough for me.

What bath chemistry and brighteners are you using? Alkaline zincate or acid chloride?

Not sure about using vinegar though, makes me cough and gag if I spend too long sniffing that.  One reason I started using citric acid for stripping. Works quickly enough if you warm it up to 'cup of tea' temperature.  Also citrate will chelate iron so more efficient than acetate for getting residual  rust out of any pitting.(Same mode of action as evapourust)

I'm currently using boric acid to contro/bufferl the ph around the cathode, again less smelly than vinegar. 

I'm just setting up to do all the metalwork on a set of carbs.

Getting hold of chemicals needed for making your own brighteners is impossible in the nanny state that we live in.

Regards
Dave

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