Zinc plating coming out "whiteish"

[roger440]

Hi, ive only just found this place, and not a moment too soon!

Ive been doing some zinc plating, and to start with it seemed to go well but a little hit and miss at times.

More recently, the zinc plating seems to be coming out a matt whiteish finish.

If its rubbed hard or sanded with say some 1500 then it is nice and shiny so under the surface it seems ok.

On a couple of parts it flaked off and seemed to leave the parent metal in a gold/brassy color.

Any ideas? Or am i going to fast?

[woodjames]

Flaking off is simply due to poor surface prep - dirty or oxidized. Better cleaning and the appropriate pickel will take care of that. Without knowing what base metal you're using, can't really help you with the discoloration - but the correct surface prep will take care of that.

The matte finish can be brightened with the correct brighteners, but they're all proprietary solutions and developed for specific bath components. You may want to call Caswell and see if their brightener will work with your bath. If unsure, just buy and try - it's pretty cheap.

-Jimmy.

[roger440]

After much messing about, i think ive concluded that i was going to fast, ie too much current, and more critically, a lot of my parts have been rusty. The subsequent pitting does not lend itself to a good finish.

Plated 2 bolts (identical) one that had been rusty and one not at the same time. The pre rusty one looked rubbish. Just dull and flat. The other looked right.

I think i need to buy some sort of tumbler that i can put all the bits in with some walnut shells or similar which hopefully will smooth the finsh of the pitted parts a bit. anyone tried this?

[JHudgens]

The only real way to clean rusty parts for plating with zinc is to sandblast them. Even then, if the pits are deep, you need to follow up with a soak in phosphoric or muriatic acid, followed by sandblasting (again). Finally, a dip in Pickle #1 before plating with appropriate rinses.

For threaded fasteners, particularly those with fine threads, even sandblasting may not clean the threaded area on the first try. I usually sandblast the threads, then wire brush them with a fine wire brush (on an electric motor) and then re-sandblast. You must inspect the threads carefully to make sure you have them clean.

I get the best results with zinc by using a relative low current for plating and plating longer to increase the plating thickness. Chromate conversion solutions will not work if the plating thickness is too thin.

Jerry Hudgens

[JHudgens]

Postscript:

I bought a tumber and used it on several parts that were rusty. After letting it run on the parts (fasteners) for a couple of days, it somewhat polished the parts but did not remove the rust sufficent for plating. I don't think you will get consistent, satisfactory results using a tumbler for cleaning rusty parts.

Jerry Hudgens